CPSC 463 Networks and Distributed

Processing

Willis F. Marti

Course Overview

Syllabus/policy {handout}

Schedule {handout}

Comments on Term Project

Course Objectives

Opinions and Facts

Class Admin

• Test taking

• Attendance & Job Searches

• Sympathy

Project

Purpose

Task Network Design

Approach {customer/boss/professor}

Teams {preferred size is 4 or 5}

Course Objectives

• Science

• Engineering

• Attitude

• Understand what a network is, especially in the context of distributed systems

• Learn a good model for investigating networks

• Learn some network programming

• Identify (some) real world components

• How networks are built

• Understand there’s more than one correct solution

• Understand “the map is not the territory”.

Why Study Networks

• When computers were rare, we studied all the new facets of computers: operating systems, languages, ... As computers became common, we added the fields that have become computer engineering. Now that computers are ubitquitous, we add the study of how best for them to communicate: networking.

• A network is part of a distributed system. Part of computer science (and computer engineering) is learning how to build all the components.

• What is a network? Surprisingly, few people will give you a definition that always fits.

• How will we study networks? There are several methods...

Is this a Distributed System?

Computing(CPU)

MassStorage

UserInterface

Just insert a network?

Distributed System (!)This represents our definition of a distributed system,

focusing on delivery of services to end users. We will explore this more after we understand more about networks.

Network

Servers (Storage, Compute)

Services

User InterfacesUsers

Network Definition

"A network is a collection of media, devices and protocols used to facilitate the exchange of informationbetween computing devices in a manner relativelytransparent to the end user."

Contrast:The Telephone Company (TELCO) & networks.:{network as a collection of media without regard to applications}

Still Defining a Network

• An ordered collection

• of media, devices and protocols

• used to facilitate the exchange of information

• between computing devices

• in a manner relatively transparent

• to the end user."

Another Definition

• LAN vs WAN vs MAN vs CAN ...

Geography

Another Definition, cont.

• LAN - Local Area Network

• WAN - Wide Area Network

• MAN - Metropolitan Area Network

• CAN - A metal container

LAN vs MAN vs WAN

• Historical Def’n {physical proximity}

• Advance of Technology changes definitions

• Modern DefinitionsTotal Travel Time

Data Transmission Time

Total Travel Time

Data Transmission Time

<= .01 to .05

LAN -- Key Points

• Historically, LANs meant fast speed.– Fast speeds meant short(er) distances.

– Therefore LANs became defined by local {short} distances

• the REAL key points– Travel time about 1 to 5% of total time

– LANs ‘tend’ to use broadcast protocols; WANs ‘tend’ to be point-to-point

Studying Networking

• by protocols & programs ...

• by technology ...

• by components ...

• Layered Models of a System!

“The key to understanding networks is the idea

of layered architectures.”

Layered Architectures-Principles-

Clearly Defined Interfaces Separation of Functions Peer to Peer Protocols Provide Services Up, Request Services Down

PHYSICAL

NETWORK

TRANSPORT

Message

PktsPackets

10010111001 {Bits}

{Signal}

10010111001 {Bits}

PktsPackets

Message

Layering

Packet Formats

Framing

Link Header

Network Header

Transport Header

Session Header (?)

Presentation “Header”

Application “Header”

Stream

Packets

Protocols and Services

<some function>This:or

this...or

this...?

Protocols and Services-a better model

Which Architecture to Study?

• TCP/IP {Internet suite}

• SNA

• Novell

• IEEE

• OSI Reference Model

Network Models

Standards & Committees ANSI IEEE {most important for LANs} EIA ISO {does more than just data standards} ITU-T {international PTT oriented. Formerly CCITT} etc

Standards & Users {cost, flexibility}

Purpose of the Open Systems Interconnection Model{remember, it's just a model}

Using Models for Understanding

Models are created by extracting key features, functions and information from a specific domain of interest so that the model contains essential attributes for understanding. Road maps are models. We extract positions of towns and cities and the roads that connect them. We ignore most terrain or reduce it to color. Road maps are good for planning trips by car but relatively useless for determining where to drill for oil. A key part of building a good model is ensuring that all features of interest are included, but only those. When using a model (network or otherwise), remember the limitation: "The map is not the territory."

IEEE 802 Protocols

• .1 - Management– .1d - Bridge Spanning Tree

• .2 - Link Layer

• .3 - CSMA/CD [Ethernet]

• .4 - Token Bus

• .5 - Token Ring

• .6 - DQDB

• .7 - MAN

(Partial) TCP/IP Stack

DIX Ethernet or ...

ICMPIP

TCP UDP

DNSTELNET

Why the OSI Reference Model?

• OSI RM is not the ISO protocol(s)

• Not tied to any specific protocol suite

• ‘Clean’ start

• Completeness

Example: OSI & the Internet

Application

Presentation

Session

Transport

Network

Data/Link

Physical

DIX Ethernet

IEEE 802.3

The OSI Model

Application

Presentation

Session

Transport

Network

Data/Link

Physical 1

7{remember, enveloping at each layer}

OSI Reference Model

Application

Presentation

Session

Transport

Network

Data/Link

Physical

Application

Presentation

Session

Transport

Network

Data/Link

Physical

{Each layer communicates with its peer by using the services of thelayer just below, and provides services to the layer above. Only thephysical layer has an actual connection}

OSI Model, cont

Application

Presentation

Session

Transport

Network

Data/Link

Physical

Application

Presentation

Session

Transport

Network

Data/Link

Physical

{there can be multiple, separate entities at each layer}

Repeater

Bridge

Router

Gateway

Physical Layer

• Converts Bits -> Signals & sends signals across the media• Recovers Bits from incoming Signal

Key Aspects of Physical layer specifications:

• Signaling Method• Connectors• Media• Voltages/Power Levels

Media Considered -- Optical Fiber, Broadband Coax, baseband coax, UTP

Media not Considered -- Radio/Microwave/Satellite

Data/Link Layer

• Gets bits from A to B along a (logically) single physical link• Provides addressing and error detection.• OSI model talks about error recovery -- not usually implemented in LANs, and only in some point-to-point networks (X.25 best example)

• Why no error recovery? In the case of an error in the packet, where did itcome from and where was it really addressed to...

Data/Link Layer

• Gets bits from A to B along a (logically) single physical link• Provides addressing and error detection.• OSI model talks about error recovery -- not usually implemented in LANs, and only in some point-to-point networks (X.25 best example)

• Why no error recovery? In the case of an error in the packet, where did itcome from and where was it really addressed to...

Network Layer

• End-to-end packets (each system on the network has a network address

each packet (is)(may be) treated separately

• This layer is supposed to hide all the messiness of differing link andphysical layer requirements from the upper layers

Transport Layer

• End-to-end messages

Usually provides reliable, sequenced byte stream to upper layers.Does error recovery.

• There are options for non-guaranteed transport

Session Layer

• Control layer

• Manages 'sessions'

Presentation Layer

• Provides information transform services

-> translation->encryption->compression

Application Layer

TCP/IP ISO

email SMTP X.400

file transfer FTP FTAM

remote terminal/access TELNET VTS

Basic Network Concepts

Circuit switching - {basic TELCO service. Guaranteed responsebecause resources are guaranteed. Inefficient for some applications}Virtual-circuit packet-switching - {divide the info into packets tomultiplex}Datagram packet-switching - {like the US Mail....}

Connectionless vs Connection-oriented{At the Link layer, do we do acknowledgements? At the network layer,doall the packets have to follow the same route?}

Multiplexing - {single media, multiple independent 'circuits'}{putting multiple 'sessions' on a single media}

Terminology

• SAP -- Service Access Point {see Fig 1-9}

• Connection Oriented

• Connectionless

• Datagram

• Primitives

Modulation

ASK - Amplitude Shift Keying {varying signal strength}

FSK - Frequency Shift Keying {varying signal frequency}

PSK - Phase Shift Keying {don't ask!}

{NB the above three methods are usually applied to signal carriers}

PCM/PWM - Pulse Code Modulation/ Pulse Width Modulation{good for fiber}

Others

"Modification of a transmitted signal to encode information (bits)"

Switching

• Circuit Switching– Guaranteed resource

– No size limit on information sent

• Packet Switching - Divides the information into packets; restricts sizes; also sharing of resources

– Virtual Circuit // Connect-oriented

– Datagram // Connection-less

Multiplexing

TDM - {time division multiplexing} {low overhead, inefficient}

FDM - {frequency division multiplexing}

STDM - { statistical time division multiplexing} {some overhead, more efficient, may FAIL}

Multiplexing Examples

BADCBADCBADCBAD

2400 2400

BACACBDCBDBABBD

Multiplexing w/ Packets

Like STDM, except NO "ROUND ROBIN"

Physical Layer Issues

• Theoretical Underpinning– or, Bandwidth 101

• Media Characteristics– Optical Fiber

– Coax

– Copper Wire (Twisted Pair)

– Wireless

• Other Useful Ideas

Signals

• Propagation - {how fast does the signal travel in that media, esp. compared to light?}

• Frequency - {number of oscillations per second of the electromagnetic field of the signal}

• Bandwidth - {the width/size, in Hz, of the signal -- usually defined by where most of the energy is}

• Data Rate - {the number of bits per second. Distinct from, but related to, frequency and bandwidth}

• Baud - {Changes per second in the signal. Limited by bandwidth.}

Freq/BW/DR

Frequency

{see Fig 2-1}

Maximum Data Rates

• Nyquist: – DataRate <= 2*BandWidth * log2 V

where ‘V’ is the number of values which are encoded into

the signal. In the On/Off, 0/1 world, V = 2. Your highspeed

modem has V = 16.

• Shannon:– The real world is noisy, so Nyquist was an optimist.

• Marti:– Complexity costs money and adds fragility.

So be choosy.

DR ~ 2 * BW {Max by Theory}

DR ~ 1/2 * BW {Practical}

<- In an On/Off world (V = 2)

Physical Effects

Bandwidth Limits - {Signals consist of many (infinite) different sine waves, not all of which can be carried by the media}

Dispersion - {Particularly for multimode fiber, different parts of thesignal may move at different speeds, thus changing the shape ofthe signal at the receiver}

Jitter - {Imperfect clock synchronization along the transmission path}

Noise - {Unwanted, external energy that may corrupt the signal}

Framing & Synchronization

Synchronous - Sender and receiver somehow share a common clock.good for longer runs of data; more efficient but requires the clock signalsomehow be sent along with the data

Asynchronous - Sender and receiver use different clocks so data runshave to be shorter. Doesn't require the extra clock signal

Synchronous vs Asynchronous - Framing & clocksIsochronous vs Aperiodic - Characteristics of traffic {beware ofconfusion as each writer may mix terms}

{Here synchronization refers to the sender's and receiver's clocks}{Frames are packets added signal needed to transmit them on Physical Layer}

Specific Framing

Bit Stuffing - Used to ensure special framing and/or control characters are not sent in the data. A problem because the 'clock' isusually continuous but data may not be there, so we have to know whenthe line is idle and when a frame starts {frame delimiter}

Manchester Encoding - Example of combining clock with data toform a single signal -- no separate line is required. It does require twicethe bandwidth of the original signal

ManchesterEncoding

Ensures for each bit there is a clock transition. Data values (0 or 1)are encoded by positive or negative clock transitions in the middle ofthe bit time. Transitions are made at bit edges if needed so that thecorrect transition can be made in the middle of the bit.

• Optical Fiber {pg 87} Multimode Single Mode

• Coax {pg 84,85} Broadband Baseband

• Twisted Pair {pg 83} Shielded Unshielded

Cost and Performance

Media Types:

Coax Baseband Broadband

Fiber Multimode Single Mode

IncreasingBandwidth

IncreasingCost

But remember, cost includes --material--LABOR--electronics

Biggest part of installation cost

Distances

Media Types:

Coax Baseband Broadband

Fiber Multimode Single Mode

Typically 100m +/-

200m-500mup to 40km

depends on power budget;can be 100s of km*

* Most LANs use 2km between devices

Fiber Facts

CoreCladding

Protective Coating

Core Cladding50 125 Multimode (microns)62.5 125 " "8 to 10 n/a Singlemode

Fiber Facts, cont.

"photons"

Modes == Different paths thru core

Since the photons travel at the same speed, but for different distances,the energy is spread out, or dispersed, at the receiver

Fiber is specified as XX Mhz-km. So a specification of 800Mhz-kmmeans you could have a bandwidth of 400Mhz over a 2km distanceor 1.6Ghz over a 0.5km distance.

Dispersion has two components: modal and material

Traditional Baseband

Terminator

Transceiver

Transceiver Cable

CATV Systems

Headend

Amplifier

Splitter

NetworkInterfaceUnit

Translator

"Forward" Signal"Return" Signal

Twisted Pair

• Just copper wire where each two wires (“pairs”) have been twisted around each other in the cable. {Phone wire}

• Rejects common mode noise

• Minimizes antenna characteristics

• Shielded or Unshielded refers to a ground sheath around the whole cable.

• Cat 3 vs Cat 4 vs Cat 5

Physical Design Ideas

Backbone

Distribution

Daisy Chain Home Run Bus

Riser Systems

Wireless Overview

• Radio– Mobile

– Cellular

• Microwave

• Satellite

• Infrared/Laser

TELCO Architecture

Trunks

TELCO Trunking

Older, Analog World: Frequency Multiplexing

Current World: Digitizing & Time Multiplexing

Integrated Services Digital Network

"Think of defining ISDN by looking at the two pairs of words"

BRI • 2B+D Basic Rate Interface B = 64kbps each D = 16kbp for TELCO signaling

PRI • 23B+D

BISDN: So fast it seems like broadband!

ISDN Nets

"User"

Definition points

Data/Link Layer Issues

• Protocol & Services

• Topology

• Error Detection & Recovery

Topology vs Geography

Logical Layout

"How devices talk toeach other" -or-"How devices heareach other"

Physical Layout

How the signal actually travels

Topologies

• Every node hears every other node's transmissiondirectly.

• Series of unidirectional point-to-point linkswithout "store & forward", usually with a bypassability.

• Switching functions all in central node

• Each node independently routes over (bi-directional) point-to-point links.

IEEE & OSI

LLC = Logical Link ControlMAC = Media Access ControlPHY = Physical

Link/Physical Layer Standards

• Ethernet– 10BASET, Fast Ethernet, Gigabit Ethernet

• Token Ring– 4/16MB

• FDDI

• ATM

Ethernet & IEEE 802.3

What the IEEE standard covers- Physical layer andinterface to the link layer. IEEE 802.2 is the Link layer standard.

History- DEC/Intel/Xerox came up with it, then submitted toIEEE for standardization. Some changes were made soEthernet is not identical to IEEE 802.3

Differences between Ethernet and 802.3

There are some electrical and connector differences; most equipment uses IEEE 802.3.There is difference in the header. DIX uses TYPE, 802.3uses LENGTH. SInce the frame is limited in size, the two coexist.Most people use the DIX format.

Ethernet

• Work started back in 1973 by Bob Metcalfe and David Boggs from Xerox Palo Alto Research Center (PARC).

–He studied the Aloha network and "fixed" the mathematics.

• Experimental Ethernet implemented in 1975.

• Cooperative effort between Digital, Intel, and Xerox produced Ethernet Version 1.0 in 1980. –This also became known as the Blue Book specification or DIX

standard. Ethernet V2.0 adopted in 1982.

• Ethernet was adopted with modifications by the standards committees IEEE 802.3 and ANSI 8802/3.

• Ethernet allows for only connectionless communication.

CSMA/CD

"Carrier Sense/Multiple Access with Collision Detection"

"Driving in Boston"

"Many stations; Listen before talking; listen while talking; if a collision,backoff and try again"

51.2 microseconds

Normal Ethernet Operation

Address mismatchpacket discarded

Address matchpacket processed

Send datato node D

Transmitted packet seenby all stations on the LAN

(broadcast medium)

Ethernet Collisions

Collision

Data transmission for A Data transmission for C

CSMA/CD - A Simple Definition

• A network station wishing to transmit will first check the cable plant to ensure that no other station is currently transmitting (CARRIER SENSE).

• The communications medium is one cable, therefore, it does allow multiple stations access to it with all being able to transmit and receive on the same cable (MULTIPLE ACCESS).

• Error detection is implemented throughout the use of a station "listening" while it is transmitting its data.

• Two or more stations transmitting causes a collision (COLLISION DETECTION)

• A jam signal is transmitted to network by the transmitting stations that detected the collision, to ensure that all stations know of the collision. All stations will "backoff" for a random time.

• Detection and retransmission is accomplished in microseconds.

Frame/Packet Format

Preamble SFD Dst Src Type Data/Pad FCS

Size 7 1 6 6 2 46-1500 4(octets)

In IEEE 802.3, the Type field is used as a Length field.

Addresses are generally (3) octets vendor code, (3) octets device number.

Ethernet Addressing

Each station recognizes three classes of addresses.• Own address• Broadcast address (all 1's)• Optionally, one or more multicast addresses

Major reason for broadcast is address discovery.Multicast addresses are used for specialized link layer functions.

Ethernet Cable Names

RG-8 RG-58 22 - 26 AWG 62.5/125 micron10BASE5 10BASE2 10BASET 10BASEF

IEEE 802.3 IEEE 802.3a IEEE 802.3i

Wire Type

IEEE Name

Standard Number

Other names

FiberUnshielded Twisted PairThin coaxialThick coaxial

Thick net Thin net UTP

Thick Coax Makeup

Jacket of PVC or Teflon

Thick braid for EMI

FoilThin braid for EMI

Thin foil bonded to insulation

Center conductor of tin plated solid copper conductor

Teflon is used forfire code regulations

Thick Coaxial Connection

Pierce clamp

Transceiver

Transceiver cable

Black marksevery 2.5 meters

to show transceiverplacement

500 meter maximum cable run

Transceivers• Transmitter/Receiver: AUI on one side, media on the other

• Used on all Ethernet networks and is the device that allows data to flow between the controller card and the network.

• Detects errors on the bus cable plant and reports them to the station's controller card.

• For thick coaxial cable, the transceiver is external to the controller card and attaches directly to the thick coaxial cable via a special cable known as the transceiver cable.

• External transceivers have a SQE function that enables the controller to determine the status of the transceiver.

• Usually has status indicators (LEDs) physically located on it to indicate the state of the transceiver (transmitting, receiving, collision, and power.)

Thin Coaxial Cable Makeup

Jacket made of PVC or Teflon

Polyethylene foam

Tinned copper wire

EMI braided shielding

Thin Coaxial Connection

T connector

Directconnection

to card

BNC connector at each cable end

Concatenation of network attachments

Thin Coaxial Connection (cont.)

Interface to computer bus

T connector for connection to cable plant

transceiver logicOn-board

BNC connector

AUI connector

02608C

UTP Makeup

• UTP was standardized by the IEEE 802.3 committee in October of 1990.

• Standardized by the EIA under TIA 568A.

• UTP for LANs is now classified as:

–Category 3 - used for LANs up to 10 Mbps.

• Cable is made up of 8 strands of 24 AWG wire.–Only 2 pair are used for single 10BASET connection.

Unshielded Twisted Pair

Unshielded twisted pairatleast two (2) twists per foot

RJ-45Connector

RJ-45connector

100m max cable run

8 pin 8 pin

Unshielded twisted pair cable

Straight through pins 1, 2, 3 and 6

Repeater unit required

Concentrator (Hub) Management• With the concentration of the wiring into a common point, network managers can manage the hub

with specialized software.

• Network management software resides not only in the concentrator but on an external workstation’s device (a PC, for example).

– The workstation can query the concentrator for information.

• Concentrators also allow the control of individual ports.

• This software allows managers to extract information from each card that is inserted in the repeater. You could query the hub for statistics such as:

– number of packets (bytes),

– number of collisions (single and multiple),

– number of framing errors,

– number of time the particular card de-inserted itself from the network,

– ability to turn on/off any repeater card in the hub, and

– all information is time and date stamped.

• With 10BASET, all information is provided on an individual-connection basis, giving a manager information right from the desktop.

Ethernet Repeaters• Extend the network by interconnecting multiple segments

– Extend the physical domain of the network

• Governed by the IEEE 802.3c working group standard.

– This governs the electrical specifications of a repeater.

– The physical configurations of a repeater varied from vendor to vendor.

• Some repeaters contain the intelligence to:

– detect collisions per cable plant (will not repeat collision fragments to other cable plants).

– de-insert themselves from a wiring concentrator (when there are excessive errors on the cable plant).

– submit network management information to a central controller.

• Repeaters have been transformed into wiring concentrators or hubs

• Repeaters can be used to interconnect different wiring types but not different access methods (i.e., not Token Ring to Ethernet).

IEEE802.3 Efficiency

"WARNING: Opinion"

% Utilization Status

0 - 10 Great!

10 - 40 OK

40 - 60 Performance Problems -- look at it

60+ RIP

SignalOn

"Utilization"

Token Ring - IEEE 802.5

What the IEEE standard covers

History

Differences between 802.5 and 802.3

"Physical layer standard (gives link layer format)"

Essentially an IBM standard 'given' to the industry"

"Guaranteed response PrioritiesControlled delays"

Token Ring History

• Presented by IBM in 1982 to IEEE 802 committee.

• First prototype developed in 1983 in Geneva, Switzerland.

• Cabling System was announced in 1984.

• Officially announced in 1985.

• Standardized by IEEE in 1985.

• Only one adopted by the IEEE 802.5 committee.

Token Ring Technology Summary• Access method by which network attachments gain access to the cable plant

by acquiring a special frame called the token. {Token is a special 24-bit pattern that continuously circulates the ring.}

• Token Ring is a broadcast medium. {To receive data, a destination station performs an address match.}

• The destination station merely copies the frame as it repeats it back to the ring.

• When the frame arrives back to the source station, it strips the frame from the ring and then releases the token (4 megabit operation only).

» The token is allowed to be released prior to frame reception on 16-megabit rings.

• Token Ring originally ran at 4 Mbps. Upgraded in 1989 to 16 Mbps• Maximum frame size for 4 Mbps is 4472.

– This is based only on the fact a station cannot hold the token longer than 10 milliseconds.

• Maximum frame size for 16 Mbps is 17,800.

TRN Features

Traffic usually (always in 802.5) unidirectional

RAR (802.5) vs RAT (FDDI) for Token Passing

Recovery from lost token

Priorities

Frame Structure

"data rate of 4 or 16Mbps"

"one frame on the net at a time..."

Controller Attachment to a MAU

The IBM 8228 MAU

Shielded or UTP cable Lobe cables

Cable Connectors

Token Ring controller

DB-9 connector

RJ-11 or RJ-45connector

Hermaphroditic or RJ-45connectors on MAU

Media filterfor UTP only

Media filtercan be on-board

Multiple MAU Connection

Ring inRing out MAU

Type 6 patch cables

MAU Operation

MAU top view

Relays

Lobe cables

All stations are active

Ring inRing out

MAU bus

Closed Closed Closed

MAU Operation (Inactive Station)

MAU top view

Relays

Lobe cables

Ring inRing out

MAU bus

Closed Closed Closed

Inactive station

Token Ring Cable Types• Type 1

– A shielded data grade cable with two solid wire twisted pairs.– Available in indoor and outdoor versions.

• Type 2– A Type 1 indoor cable with four solid twisted pairs of 24 AWG wire. – Contains four voice grade wires along with four data grade wires.

• Type 3 – Unused existing telephone wire or EIA category 3 wire (4 Mbps operation).– Category 4 is needed for 16 Mbps (speed of the Token Ring) operation. – Must use a special media filter.

• Type 5– 100/140 micron fiber cable used for fiber optic repeater links.

• Type 6– Often used for patch cables.

» Patch cables can be used for MAU-to-MAU connection or from a wall outlet to a network attachment.

Type 3 Media Filter

• Type 3 cable requires a device known as a media filter.

• Its purpose is to filter out any unwanted signals.

• It is a small rectangular device that is usually part of the UTP cable itself.

• It can be a separate device that attaches to the UTP cable at the end of the cable that attaches to the controller card.

• It can be used on 16- or 4-mb Token Rings.

• It is only used with Type 3 (UTP) cable.

802.5 Framing

• IEEE 802.5 uses special characters, but does not use bit stuffing!

“1” bit “0” bit

Manchester

Violations!

Token Ring Frames

1 byte 1 byte

Physical header Physical trailer

MAC or LLC Frame

Abort frame

SD AC FC DA SA Routing Information Fields

Data FCS ED FSIEEE802.2

no preset size

1 byte 1 byte 1 byte

Token frame

SD AC ED

Token Ring Frame Field Definitions

SD AC FC DA SA Routing Information Fields

Data FCS ED FS

SD - Starting Delimiter

AC - Access Control

FC - Frame Control

DA - Destination Address

SA - Source Address

FCS - Frame Control Sequence

ED - Ending Delimiter

FS - Frame Status

Legend

IEEE802.2

no preset size

1 byte 1 byte 1 byte 6 bytes 6 bytes <= 18 bytes

1 byte 1 byte 1 or 2 bytes

4 bytes 1 byte 1 byte

DSAP SSAP Control

The SD and the AC Fields

P P P T M R R RAC

Bit 0 Bit 7Field

SD J K 0 J K 0 0 0

PPP - priority bits

T - Token bit

M - Monitor bit

RRR - Reservation bits

The FC, ED, and FS Fields

Bit 0 Bit 7Field

F F r r Z Z Z Z

A C r r A C r r

A - Address recognized bits

C - Frame copied bits

ED J K 1 J K 1 I EI - Intermediate bit

E - Error bit

FF - indicates a MAC or LLC frame.

ZZZZ - indicates the type of MAC frame.

Bit Order Transmissionfor Token Ring

• Bit 0 is the first bit transmitted.

–Bit 0 is the left most bit of the byte.

»Unlike Ethernet, the bits in the bytes are not reversed as they are transmitted.

• Example:

–40-00-12 are the first three bytes of a MAC address.

»Translated to binary:

01000000-00000000-00010010

»As transmitted on a Token Ring:

01000000-00000000-00010010

»Compared to Ethernet transmission:

00000010-00000000-01001000

Token Passing Policies (Defn)

• Multiple Token– RAT (FDDI): free token is appended to tail of last packet

• Single Token– ?: Token is released upon receipt of leading edge of own

packet

• Single Packet– RAR (802.5):Token is released upon receipt of trailing

edge of own packet

Token Passing Policies (Usage)

• Multiple Token– Allows multiple packets on the segment at one time.

Good when packet length is less than ring latency

• Single Token– More efficient than RAR; when packet length is about the

same as ring latency

• Single Packet– Least efficient, but allows controlling station knowledge

of (un)successful transfer before the token is released (see pg. 224, 1st paragraph)

Token Passing Policies (Perf.)

• Multiple Token– Always the best performer, but more complex

• Single Token– Closer to RAR than RAT

• Single Packet– ‘Worst’ performance

KEY POINT: Ratio of ring latency to packet length, a, is real determiner of performance. For a << 1, RAR is OK.

Controller Operation - Phases 0 and 1• Five-phase initialization

– Phase 0 - Lobe test

» The controller transmits frames between the controller card and the cable attached between the controller card and the MAU.

» The controller tests to ensure that the lobe cable can successfully transmit and receive frames.

– Phase 1 - Monitor Check

» Station inserts into the ring (flips the relay in the MAU) and looks for special frames that are transmitted by the monitors.

» Sets a timer to wait for these frames.

» If the station does not receive any of the frames, the controller assumes:

• it is the first ring station on the network,

• there is not an Active Monitor present, or

• inserting into the ring disrupted the ring.• The controller may initiate the token claim process.

Controller Initialization - Phases 2, 3, and 4

• Phase 2 - Duplicate address check.

–Checks to ensure that it can successfully transmit and receive a frame and to detect other stations that might have the same MAC address.

»The controller transmits a frame to itself.

» If the frame returns with the address recognized bit set, it notifies one of the monitors and removes itself from the ring.

• Phase 3 - Participation in neighbor notification.

–The station transmits a special frame that will identify itself to its downstream neighbor.

–The station should receive a similar frame for its upstream neighbor.

• Phase 4 - Lan Network Manager Notification

–Notifies LAN Network Manager about its presence on the ring

Claim Token Process• A ring cannot operate without a token circulating on the ring.

– There is only one token per ring.

• The token-claiming process allows one station to insert the token onto the ring.

– This station will be elected as the AM.

» It will purge the ring (ability to transmit a frame to itself).

» After purging the ring, it will insert a new token on the ring.

• The Token-Claim process can be started when the AM

– detects a loss of signal,

– a timer expires and it has not yet received its AM frame back, or the AM

– cannot receive enough of its own Purge Ring MAC frames.

• It can be started when the SM

– detects loss of signal or

– detects expiration of its timer for receiving SM frames.

Details of the Claim Token Process• If there is no token on the ring, all activity will cease on the ring.

– The Active Monitor should be able to recover by purging the ring and issuing a new Token.

– If the Active Monitor cannot recover, the token-claim process will begin.

• Any station will insert its master clock, a 24-bit delay, and start to transmit Token-Claim frames.

– These frames are received by all stations on the ring.

– The station will follow these frames with idle (clock) signals.

– After transmitting the Token Claim frames, the station starts a timer.

» If it does not receive its frames or someone else’s claim frames, it will beacon the ring.

• Once the process is started other stations may participate.

– Stations bid for the right to become the AM.

– The station with the highest priority (MAC address) wins.

– That station becomes the AM.

» It will purge the ring and insert a new token.

Claim Token Process Example

Detected condition

Token Claimframes

Not participating

Repeat frame

Higher prioritythan C. Doesnot repeat C’s

A transmits its ownToken Claim frames

B has higherpriority than A

B transmits its ownToken Claim frames

Continuestransmitting

its own

Stops transmittingits own Claim frames

and repeats B’s

RepeatsB's Token

Claim frame

Stops transmitting its ownand repeats B’s claim frames

Token Ring Transmit Mode• A station that needs to transmit receives the SD of approaching frame. This

station quits transmitting idles (clock signals).

• Checks for priority.

– If the priority in the frame is greater than the station's priority, then

» the station sets reservation bits and awaits new token.

• If the priority in the frame is less than or equal to the station’s priority then

– the station changes the T bit in the AC field from a 0 to a 1,

– appends its information to the rest of the frame and transmits the frame.

– If the end of its transmission is reached and it has not received its current transmission back, the station

» transmits idle characters and awaits current transmission.

• When the station receives its frame back it will strip the frame and release the token.

• The station enters normal repeat mode.

Token Ring Copy Mode• The destination Token Ring controller recognizes its address in the

destination field of a received frame and copies the frame into its buffer.

• If at any time an error is detected, the copy phase ends and the controller sets the A and E bits and repeats the frame back to the ring.

• If no errors are found, the destination sets the A and C bits and repeats the frame back to the ring.

• The destination station enters Normal Repeat mode.

• The frame travels on the ring until it reaches the originator and that station strips the frame off of the ring and submits the token to the ring.

Normal Repeat Mode• A station in normal repeat mode checks current

frames and token for signalling errors.

– If any errors are found the station sets the E bit and repeats the frame back to the ring.

• A station in this mode also checks every frame for its address. –A duplicate address could be found.

– If a duplicate address is found, the station will transmit a soft error MAC frame to one of the monitors.

The Active Monitor (AM)• Functional address is C00000000001.

• It must be present in order for the ring to function properly.

• The AM is the kingpin of the ring.

• The AM:

– tracks lost tokens and ensures that only one token exists on a single ring.

– monitors frames and priority tokens that circulate the ring more than once.

– initiates neighbor notification,

– provides a latency buffer to recover the clock signal and so that at least 24 bits (the size of the token) can be transmitted on the ring, and

– supplies the master clocking .

Token Recovery

• Monitor Station– 1 station becomes responsible for monitoring the token

for token loss or token busy

• Time Outs– Token time out (‘Beaconing’)

– No monitor (Claim frames (highest addr wins)

Options for Token Ring• For 16 megabit rings, early token release allows a ring station to release the

token before receiving its original frame back.

– It is based on the ring length

» A station will not release the token when it is still transmitting its frame and it has started to receive its frame back.

– Allows greater use of Token Ring bandwidth.

• Token Ring operates at 4 and 16 Mbps.

– 4 and 16 Mbps controllers are not allowed on the same ring.

» Ring will beacon when this condition occurs.

– To have 4 and 16 Mbps ring interoperate, you must use a data forwarding device such as a bridge or a router.

• IBM is currently experimental with a new Token Ring controller which allow it to operate between 52 - 100 Mbps.

Data Link Layer

Uses 'bit pipe' Physical Layer to send packets

Packet Formats - Generic: Framing (Layer 1), Addresses andcontrol information (layer 2), and data (info from layer 3 and up)

Point-to-Point vs Broadcast - Key idea is that not allpacket formats are alike. One needs to look at particluar technologiesto see what is needed.

Data Link Services

• Unacknowledged Connectionless Service– Most LANs

– Upper layers handle error recovery

• Acknowledged Connectionless Service– Odd duck. Example?

• Connection-oriented Service– Reliable Delivery ...

Link Protocols

Used to provide reliability. Basic idea can be used at any layer

GoBack N

Windowing & Flow Control

Don't need to know details at this time, but know general operationand that they provide assured delivery.

Performance

• Overhead vs Frame Length

• Error rate (bit error vs block error)

• Physical Layer– distance

– propagation delay

Error Control

Error Detection - Methods: Parity, Checksum, CRC --generically Frame Check Sequences

Error Correction - The basic idea is to add redundant informationso that the receiver can deocde the message even if some (specified)number of bits are damaged (e.g., Hamming codes)

Error Recovery includes error correction but also includes actions takento get a message retransmitted

Connection Oriented Services

• Two modes of operation:

– Operational

– Non-operational

• Operational mode incorporates three functions:

– Link establishment.

» A source station sends a frame to a destination station requesting a connection.

» The destination station may accept or reject the connection request.

– Information transfer.

» Allows information to be transferred after a connection is set up and the required handshaking has taken place.

» Reliable information is transferred between the two stations.

– Link termination.

» Either side of the connection may terminate the connection at any time.

IEEE & OSI {again}

LLC = Logical Link ControlMAC = Media Access ControlPHY = Physical

IEEE 802.2 Fields

Destinationaddress

Source address

Lengthfield

IEEE 802.2 field CRC

DSAPaddress

SSAPaddress

Control Information

1 byte 1 byte 1 or 2 bytes

Length of the Information fieldis access method dependent

I/G D D D D D D D D C/R S S S S S S S

SAP Types

• E0 - Novell NetWare

• F0 - NetBIOS

• 06 - TCP/IP

• 42 - Spanning Tree BPDU

• FF - Global SAP

• F4 - IBM Network Management

• 7F - ISO 802.2

• 00 - NULL LSAP

• F8, FC - Remote Program Load

• 04, 05, 08, 0C - SNA

• AA - SNAP

• 80 - XNS

• FE - OSI

SubNetwork Access Protocol (SNAP)• Most common implementation of LLC1 is from a subsection of the IEEE 802.2

standard known as SNAP.

• At the time of IEEE 802.2’s introduction, most network protocols were designed to use the Ethernet packet format.

• SNAP allows for the migration of the standard network protocols to the IEEE 802.2 format.

• Supported by TCP/IP, NetWare, OSI, AppleTalk, and many other protocols.

• The second purpose for the SNAP protocol is to allow those protocols that do not support the IEEE 802 standard to be able to traverse IEEE 802 LANs.

• SNAP uses a reserved SAP: AA (for both the DSAP and SSAP).

– It uses the unnumbered frame format: control field equal to 03.

– Actual SNAP header consumes 5 bytes:

» Three bytes for the Organizationally Unique Identifier (OUI) field, and

» Two bytes for an Ethernet Type field.

Protocol Discriminator

OUIType field

3 bytes 2 bytes

Length field DSAP SSAP Control SNAP

header Data Pad CRC-32Sourceaddress

Destinationaddress

AA AA 03

Protocol discriminator

00-00-00 08-00

Verification

• Finite State Machines

• Estelle & Other Languages

• Petri Nets

• Blind Faith (or, code it in C...)

Naming Conventions{and Confusion}

Segment

Bridge

Repeater

Router

Link Layer Subnet

Link Layer NetworkNetwork Layer Subnet

Network Layer Network

Naming Conventions {cont}

Application

Presentation

Session

Transport

Network

Data/Link

Physical

Application

Presentation

Session

Transport

Network

Data/Link

PhysicalRepeater

Bridge

Router

Intro to ATM

• Asynchronous Transfer Mode

• Text References– Sect 2.6

– Sect 3.6.3

– Sect 5.6

– Sect 6.5

ATM Background

• Outgrowth of TELCO transition to integrated services

• Only “real” >100Mbit standard

• Offers multiservice (voice video data) potential

• Switched architecture familiar to TELCOs, not to high speed data networks

What is ATM?

PLPhysical

Data/Link

Network

Transport

Session

Presentation

Application Note: Tanenbaum considersthis more a network layertechnology.

ATM - A layered standard

AAL - ATM Adaptation Layer • Assembles and disassembles broadband servicesinto a stream of cells • Each cell has a header that contains routing information

ATM - Asynchronous Transfer Mode • Switches the cells around the network based on the routing information in the header

Physical Layer • Provides the physical transportation of cells across the network

(Note: CCITT reference model, p. 63)

ATM - A Switched Architecture

• Cells (small, fixed length packets) are switched in a connection-oriented manner but not using circuits like today’s voice.

Switch Switch

Edge Device

What is ATM Switching?

• Why small cells?– (32+64)/2=48 + 5 header bytes

– Mixed Traffic

• Packet (random)vs Circuit (TDM) Switching

• Q.2931– SVC, PVC

Physical Layer Options

• SONET (US)/ SDH (Europe)• SMDS• DQDB

• Speeds from DS3 on up! (45Mbs to Gbps)• OC-3c => 155.52Mbps => 149.76Mbps ^ optical carrier ^ 3rd level in heirarchy ^ full duplex (two strands of fiber)• Also OC-12c (622Mbps), OC-48c (2048Mbps)

[Look at the interesting way to frame cells]

ATM Adaptation Layer(AAL)

• Classes of Service: 1, 2, 3/4, 5 1: circuit emulation 2: variable bit rate service 3/4: connection oriented data service 5: connectionless data service

• SAR - Segmentation and Reassembly

• Convergence Sublayer the miscellaneous category

ATM Cell

• ATM cells are constant size packets of 53 bytes size. -- 48 bytes payload, 5 bytes header/overhead.

(8 bits wide)VPI

VPI VCI

Type Res CLP

VPI - Virtual Path IDVCI - Virtual Channel IDType - Payload type (internal)Res - reservedCLP- Cell loss priorityHEC- Header Error Control

VCI/VPI Operation

• A Virtual Channel exists between two switching points

VCI = a VCI = b

• A Virtual Path contains 'bundles' of VCs

ATM Switch Architecture

• Crossbar

• Banyan

• TDM busses

• Buffering– Input

– Output

– Both?

ATM Protocols

• UNI, NNI

• Services

• “LAN” Stuff

ATM Services

• CBR

• VBR (RT, NRT)

• UBR

• ABR

ATM Quality of Service

• QoS: A contract

• Traffic Descriptors

• Cell Rate Options (pg 462)

• Traffic Shaping

• Traffic Policing

ATM Congestion Control

• Admission Policy

• Reservation System

• Rate Based Control

• Other

ATM Flow Control

• The leaky bucket algorithm

• CLP in ATM header

• Frame Relay comparisons

Routing

•IISP (Interim Inter-switch Signaling Protocol)

•PNNI (Private Network-Network Interface)

•Phase 1•Phase 2

• Interim– Allowed multi-vendor interoperability before

completion of NNI

• Signaling

• Routing via manually configured NSAP prefixes

• Topology abstraction

• Peer group(group of nodes)– One switch elected Peer Group Leader

– All nodes in group have identical view of group

• Hierarchy of logical groups– Up to 105 levels of hierarchy

PNNI Routing

B2B1A23

NSAP Domain

View from A117 at A11

Sequence of Events

• A117 -> B25• Forward to switch (A11)

– Switch knows topology of A1 group

– B reachable by A2 - A2 reachable by either A12 or A13

• DTL (Designated Transit List)– [A12][A2][B]– [A22][A23][B]– [B2]

ATM “LAN” Stuff

• LAN == Link Layer Domain

• ELANs & VLANs

• LANE & MPOA– LECS, LES, BUS

LANE v1

• LAN Emulation

• No QoS (Quality of Service) Support

• Uses AAL5 signaling optimized for data transport

entire cell payload available for user data

• LEC - LAN Emulation Client

• LAN Emulation Service LECS - LAN Emulation Configuration Server LES - LAN Emulation Server BUS - Broadcast and Unknown Server

• STP (Spanning Tree Protocol) supported

LEC - LAN Emulation Client

• Software process on any ATM-connected LAN switch, router, PC, or workstation

• Layer 2 process

• Prior knowledge of certain parameters LEC’s ATM address LAN type to be emulated maximum data frame size any route descriptors (for SR bridging) whether it is willing to proxy (respond to LE-ARP) LAN name - SNMPv2 display string

LECS - LAN Emulation Configuration Server

• One per administrative domain

• Gives identity of ELAN (Emulated LAN)

• Returns ATM address of LES, type of LAN emulated, and maximum PDU size of ELAN

• Controls which physical LANs are combined to form VLANs (Virtual LAN)

• LECS address known via ILMI or its well-known NSAP address

LES- LAN Emulation Server

• Adds LEC’s to ELAN

• Assigns LECID to joining LEC

• Table of address information of LEC MAC address proxy for MAC address Token Ring route descriptors

• LECs can communicate directly with each other only when they are connected to the same LES

• Multiple LESs on the same physical ATM LAN

• Answers LE-ARP requests from LECs

BUS- Broadcast and Unknown Server

• During address resolution LEC forwards all frames to the BUS floods frames to all LECs after address resolved flush protocol used to guarantee order of cells

• All multicast and broadcast traffic sent through BUS

• Traffic limited to 10 frames/second

• Intelligent BUS resolve destinations CLS- connectionless server

LANE Setup

Connections

• All SVC (switched virtual circuits)

• SVCs required: LECs and LECS LES and LECS Control Direct - LECs and LES pt-mpt Control Distribute - LES to LECs Multicast Send - LECs and BUS pt-mpt Multicast Forward - BUS to LECs Data Direct - LEC and LEC

• PVC (permanent virtual circuit) possible to connect LEC and LECS

Virtual Channel ConnectionsVirtual Channel Connections

LANE Client (LEC) LANE Client

LANE Server (LES)

LANE Configuration Server (LECS)

ATM Host

LAN Switch

Configuration Direct VCC

Control Direct VCC

Control Distribute VCC

LAN Switch

ATM Host

LANE Client (LEC) LANE Client

Multicast Forward VCC

Data Direct VCC

Multicast Send VCC

Broadcast and Unknown Server (BUS)

• Next Hop Resolution Protocol

• Grew out of ATMARP

• Only IP

• Allows shortcut routes (pt-pt) direct VCCs across ATM network

• Address resolution across multiple IP networks

• If network unknown, request forwarded to other NHSs (Next-hop Server) NHS with knowledge will forward response to source router

• Router must have ability to bypass default route

• Resource Reservation Protocol

• Provides QoS (Quality of Service) guarantees

• Operates in simplex each direction has separate reservation maps well to ATM (two individual VCCs)

• Built on IP, but no data transport built-in

• Only if resources available and does not conflict with policy

• Flowspec (bandwidth and delay) and filterspec (type of packets) transmitted downstream hop by hop

• Multiprotocol over ATM

• EDFG (Edge Device Functional Groups) existing LAN segments via LAN switches

• AHFG (ATM-attached Host Functional Groups) ATM-connected host

• Layer 3

• Only supports IP for now

• Uses LANE for Layer 2 forwarding within a single Layer 3 subnet

• Adaptation of NHRP to provide connectivity between hosts in different subnets

MPOA Operation

Competing Technologies

• “Fast Ethernet”– 100BASE-TX, 100BASE-FX,100BASE-T4, 100BASE-VG

• FDDI, FDDI- II

• HPPI

• Gigabit Ethernet (IEEE 802.3z)

ATM Issues

• SONET/SDH duplication of services

• ATM overhead

• ATM granularity and bandwidth management

• ATM & connectionless service

• End point synchronization

• Flow Control !!! (bandwidth allocation, correlated traffic)

• ATM Forum

“Internetworking”

• Bridges– Transparent bridges

– Source Routing - Transparent Bridges

• Routers (Network Layer)

• Brouters

Why Bridges

• Isolation of Physical Layer Effects

• Bandwidth Multiplication

• Security or Traffic Isolation

Segmenting Traffic

Workstations

File server

Terminals

Terminal server

LAN traffic

Bridge

Transparent Bridges• Interconnect multiple cable segments to allow

for extension of a network.

• Can be used to interconnect different access methods (Ethernet to Token Ring) and different physical layers.

• Operate at the data link layer.

• They are protocol transparent.

–They are designed to operate regardless of the upper-layer protocol.

–They operate on the source and destination address in the MAC header.

T-L-F Bridges

• Bridges only forward traffic destined for other cable segments.

• They operate transparently to any stations that are active on the network.

• Packet formats and software drivers on the workstations remain the same.

• Bridges do not have to be programmed with the addresses of all the devices on the network.

Learning, Filtering, and Forwarding

Terminals

Node A Node B

Node C

Node D

Cable segment 2

Cable segment 1

Node E

Forwarding table

Node C, D and F are on this cable segment through port 2.

Nodes A, B, and E are on thiscable segment though port 1.

Port 2

Port 1

Node F

Bridge

Filtering - An Example

A 1B 1

C 2 D 2

Node A Node B

Node C Node D

Fowarding Table

Filtered

Cable segment 1

Cable segment 2

Port ID 1

Port ID 2

Packet transmitted

Forwarding - An Example

Node A Node B

Node C Node D

Forwarded

Cable segment 1

Cable segment 2

Forwarding tableA 1B 1

C 2 D 2

Port ID 1

Port ID 2

Forwarding Beyond One Bridge

Node A

Node D

Node B

Node C

Cable segment Z

Cable segment Y

Cable segment X

Cable segment V

Bridge table

Bridge 3

Bridge 2

Bridge 1

Loops• Complexity of bridging arises when two or more

bridges interconnect the same two cable segments.

• This is called providing redundancy or providing a loop.

• There are problems with this type of design including:

–duplicate packets,

–broadcast packets, and

–unknown destination packets.

Duplicate Packets

Node A Node B

Node C Node D

Single packet transmitted

Two packets received

Cable segment 1

Cable segment 2

Bridge 2Bridge 1

Broadcasts

Node A Node B

Node C Node D

Broadcast packet transmitted

Cable segment 1

Cable segment 2

Packet received andtransmitted back by

second bridge

Bridge 2Bridge 1

Unknown Destination Address

Node A Node B

Node C Node D

Destination Z packet transmitted

Cable segment 1

Cable segment 2

Packet received andtransmitted back by

second bridge

Bridge 2Bridge 1

Spanning Tree Algorithm

• Bridged networks must allow for redundancy. Only one path should be enabled to any destination on the network.

• STA is a protocol unto itself. Don’t confuse it with the transparent bridge protocol. IEEE 802.1d

• In an active STA topology certain bridges are allowed to forward packets.

–Other bridges will participate in the STA but do not forward packets.

–These are backup bridges that dynamically become available.

• Bridges that do not forward packets are placed in blocking mode.

–These bridges still participate in the spanning tree protocol.

Source Routing Bridges• Developed as a bridge protocol for Token Ring LANs.

• Source routing gained popularity due to IBM’s support of it.

– It is easy to install a source route network.

– It is not easy to grow a source route network into a large network.

• Invented due to technical limitations of the source route chip set.. Early source route chip sets could not be set for promiscuous mode.

• Source routing was also invented to allow two non-routing protocols to be placed on a LAN: NetBIOS and SNA.

• Source Routing does not build forwarding tables based on MAC addresses.

• Most of the intelligence for this algorithm is found in the network stations.

• Each frame carries complete route information with it.

Source Routing Features

• Source routing requires split intelligence to be carried in the node and the bridge.

• All frames contain routing information, which does produce more overhead.

• Uses STA to configure which bridges will forward single route broadcast frames.

• All paths are active which legally allows loops to be designed.

• Provided a routing solution for those protocols that could not be routed (NetBIOS).

• Easy to follow ring/MAC address for troubleshooting.

Source Routing Features (cont.)

• Source Routing originated as an alternative to transparent bridging

• Originally, Token Ring could not be placed in promiscuous mode ( requirement for transparent bridging) and therefore an alternative model was created

• Allowed for SNA and NetBIOS traffic an attempt to enjoy the benefits of routing

–As a data link layer implementation.

Source Routing Overview

• Each separate ring is assigned a unique ring number, assigned on the source route bridge port and not on the ring station.

• Each bridge is assigned a bridge number. There is a single number for the whole bridge, no matter how many ports it has.

• End stations try to find destination ring stations by broadcasting special discovery frames.

• A frame will contain source route information based on one bit in the source address.

• A source route frame may not cross more than seven bridges.

–At the eighth bridge, the frame is discarded.

Source Routing Example

Ring 4 Ring 3

Node 1 Node 2

Find a station on

the local ring

Find a station off

Bridge 5

Bridge 6

Bridge 7

Routing Information Field

Starting Delimiter

AccessControl

Frame Control

Destination Address

Source Address

OptionalRouting

Information Field

Destination ServiceAccess Protocol

(DSAP)

Source ServiceAccess Protocol

(SSAP)

Rest of TokenRing frame

RoutingControl

RouteDesignator

RouteDesignator . . . . . .

B B B L L L L L D F F F r r r r Ring number Bridgenumber

12 bits 4 bits1 - F

bridge IDs

2 bytes Up to 8 RD fields

Routing Information Indicator (RII)

1 - 4095

The Route Designator

Ring B Ring A

Routing Control

TokenFrame Header

Token FrameTrailer

RoutingInformation

Routing Control

TokenFrame Header

Token FrameTrailer

RoutingInformation

00B1 00A0

RD1 RD2RCRC

Discoveryframe

Bridge 1

Source Route Frame Types• Four types of Source Route frames:

–Single Route Explorer (SRE)

»Also known as Spanning Tree Explorers (STE)

•So named by the IEEE 802.5 working group

–All Routes Explorer (ARE)

–Specifically Routed Frame (SRF)

–Single Route Explorer with a specific route return.

Token Ring to Ethernet Conversion

SD AC FC DA SA RIF DSAP SSAP CTRL OUI Type Info FCS ED FS

DA SA Type Info FCSPreamble

Copy andbit reverse

CopyDiscard

Token Ring frame

Ethernet frame

SNAP header

Ethernet to Token Ring Conversion

DA SA Type Info FCSPreamble

SD AC FC DA SA RIF DSAP SSAP CTRL OUI Type Info FCS ED FS

Copy andbit reverse

Insert

Ethernet frame

Token Ring frame SNAP header

Token Ring to IEEE 802.3 Conversion

Copy andbit reverse Token Ring frame

CutInsert Copy

IEEE 802.3 frame

DA SA Info FCSPreamble SFD Length DSAP SSAPCTRL PAD

SD AC FC DA SA RIF DSAP SSAP CTRL Info FCSED FS

IEEE 802.3 to Token Ring Conversion

Copy andbit reverse

Token Ring frame

CutInsert Copy

IEEE 802.3 frame

SD AC FC DA SA RIF DSAP SSAP CTRL Info FCSED FS

DA SA Info FCSPreamble SFD Length DSAP SSAPCTRL PAD

Network Layer Functions

• Key Layer in Internet Architecture

• End-to-end Packets

• Adapt to lower layers

1 12 2

Network Layer

• Design Goals– ‘Independent’ of layer 1 & 2 implementations

– Hide layer 1 & 2 details from upper layers

• Architecture– Connection oriented

– Connectionless

– (where should reliability be done?)

• Services– Routing (Path selection)

– Adaptation to different lower layers

Routing Algorithms

• Goals– Optimality

– Fairness

– Stablility

– Robustness

– Correctness

– Simplicity

• Adaptive vs Static

• Congestion Control

Adaptive Routing

• Centralized

• Isolated

• Distributed

Distributed Routing

• Metric - Vector Algorithms– sometimes called shortest path

– Bellman-Ford most famous

– Knowledge of immediate neighbors

– Result is “first step” in path to ultimate destination

• Link State Algorithms– OSPF {Open Shortest Path First}

– Knowledge of network layer map (connectivity)

Congestion Control

RESEARCH ISSUE!

• Resource Reservation

• Packet Discarding

• Flow Control

Routers - Directly Attached Networks

Node A

Node D

Network 1

Network 100

CSend packetto router Z

Packet is given to the router

Find network 100

Router forwards packetto network station D

Step 1

Step 2

Step 3

Step 4

Router Z

Routers - Non-Directly Attached Networks

• If the destination network is not directly attached to the router, the router will forward the packet to another router in the forwarding path of the destination network.

• Router-to-router communication is directly MAC addressed.

• Will all routers in the path perform the same decisions as the previous router?

• The last router in the path to the destination will forward the packet directly to the destination.

• Important to note that the data link MAC headers will constantly change while the packet is being forwarded.

– Very little information in the network header will change.

» The network layer header in the packet will contain the originator’s full address and final destination address of the packet.

» The full address of a network station is the combination of the network ID and its MAC address.

• This uniquely identifies any station on the internet.

Multiprotocol Routers• LANs currently operate with many different types of protocols.

–Apple Computers can use AppleTalk.

–UNIX workstations use TCP/IP.

–Client/Server applications could use Novell NetWare.

• To require one router for each protocol on the LAN is not efficient.

• Multiprotocol routers were invented to handle this.

–Arrived around 1986.

–Routes not only based on the network IDs but are able to pass the packet to the correct protocol processor by examining the Type of packet.

Multiprotocol Routers - A Block Diagram

Bridge Router

Route onnetwork IDs

Forward on MAC address

Incoming packet Bridged or routed packet

Combine both into one

Can packet be routedbased on protocol type?

Bridge packet if not

Routing Diagram

Network 1

Network 2

Network 3

Network 4

MAC addresses Router Z

Router Y

Router X

Routing Information Protocol (RIP)

• Known as a routing table update protocol

• Developed by Xerox and gained widespread acceptance by the proliferation of TCP/IP’s implementation of it in UNIX.

• Other protocols (AppleTalk, NetWare) adopted RIP as their standard routing update protocol.

• Known as a distance vector protocol.

– Vector is an adjacent router and the distance is how far away (hops) the

network is.

– One hop is considered one router traversed.

• Devised for relatively stable, small-to-medium size networks (less than 16 routers in diameter) .

Calculating the Cost

Network 1

Network 2

Network 3

Network 4

Network Hops

Transmittedroutingtable

Internal routingtable

Router A

Router B

Router C

IP Routing

• Making Decisions

• Gathering Information

• ICMP

Routing Table

Network Mask Router Hops Age Port ID 3 255 C 1 30 1 4 255 C 1 30 2 2 255 B 2 15 2 1 255 B 3 45 2

Example: TCP/IP

• Not the only way to do things ...

• But well tested in the field

• Brief History

• TCP/IP vs ISO protocols

References TCP/IP

• Overall -- Douglas Comer– Internetworking with TCP/IP, Vol I, 3d ed.

– Internetworking with TCP/IP, Vol II

– Internetworking with TCP/IP, Vol III (Sockets)

– Internetworking with TCP/IP, Vol III (TLI)

• Unix Programming -- W. Richard Stevens– Unix Network Programming

– Advanced Unix Network Programming

• Stevens & Wright– TCP/IP Illustrated Vol I

– TCP/IP Illustrated Vol II

– TCP/IP Illustrated Vol III

TCP/IP Stack

DIX Ethernet or ...

ICMPIP

TCP UDP

DNSTELNET

Notes on TCP/IP Suite

• TCP/IP preceded the OSI Reference Model

• Layers 1 & 2 are not part of the standard

• Functions above the Transport Layer are consolidated

Brief Definitions

• ARP -- Address Resolution Protocol

• IP -- Internet Protocol

• ICMP -- Internet Control Message Protocol

• UDP -- User Datagram Protocol

• TCP -- Transmission Control Protocol

• DNS -- Domain Name System

• FTP -- File Transfer Protocol

• TELNET -- remote terminal

Other TCP/IP Protocols

• Routing Protocols -- RIP, OSPF, EGP, GGP

• BOOTP - Bootstrap Protocol

• RARP - Reverse ARP

• TFTP - Trivial FTP

• HTTP - Hyper Text Transfer Protocol

• SMTP - Simple Mail Transfer Protocol

• SNMP - Simple Network Management Protocol

Layer Protocols

DNSQuery DNS

SYN/ACK

ACKCaller Callee

{TCP Establishment}

ARPRequest ARP

IP Functionality

• Presents single, virtual network to user

• Connectionless Delivery

• Packet Routing

• Interface to Lower Layers

IP Addresses

• “Dotted Decimal”

32 bit (4 byte) address, written by taking each byte as an unsigned number

• Address Classes [first octet]

– A - <net> < > <host> < > 1-126

– B - <net> < > <host> < > 128-191

– C -< > <net> < > <host> 192-223

– D - special subset of C 224-239 multicast

– E - reserved 240-254

• Netmask – a 32 bit value which, when ANDed with an address, selects

only the network part

Netmask Usage

“Do a bitwise AND then compare for equality of results”

<src addr> & netmask =?= <dst addr> & netmask

if comparison is equal, then both src & dst are on same (sub)net.

Same netmask

Netmask Examples

S= 128.194.100.10M= 255.255.255.0result 128.194.100.0

D= 128.194.200.10M= 255.255.255.0result 128.194.200.0

Not Equal

S= 128.194.12.10M= 255.255.255.0result 128.194.12.0

S= 67.194.18.10M= 255.255.240.0result 67.194.16.0

D= 128.194.12.110M= 255.255.255.0result 128.194.12.0

D= 67.194.10.10M= 255.255.240.0result 67.194. 0.0

Special Address Conventions

• This host

• Host on this net

• Limited broadcast

• Directed broadcast

• Loopback

all 0’s

127 anything (usually 1)

hostall 0’s

all 1’s

IP Header0 16 31

VERS HLEN SERVICE TYPE TOTAL LENGTH

FLAGS FRAGMENT OFFSETIDENTIFICATION

TIME TO LIVE PROTOCOL HEADER CHECKSUM

SOURCE IP ADDRESS

DESTINATION IP ADDRESS

IP OPTIONS (IF ANY) PADDING

IP Packet Handling (rcv)

receiving

Transport Layer (TCP or UDP)

Sockets

Link {DIX Type or 802.3 DSAP}

Physical

IP Packet Handling (xmit)

sending Local or Non-Local ?

Search RoutingTable

Found! Missing!

ICMP Error

Send locally...

Bridges or Routers

Address & Netmask1: 131.122.24.12 255.255.255.02: 131.122.31.253 255.255.255.03: 131.121.18.12 255.255.240.04: 131.121.24.18 255.255.240.05: 131.121.31.254 255.255.240.0

• ping– ECHO Request/Reply

• traceroutetraceroute to falcon.ece.utexas.edu (128.83.196.10),

30 hops max, 40 byte packets

1 exit_133 (128.194.133.254) 2 ms 2 ms 2 ms

2 exit_128 (128.194.128.254) 2 ms 3 ms 2 ms

3 FDDI-T3.TAMU.EDU (128.194.1.13) 3 ms 3 ms 3 ms

4 FDDI-WAN.TAMU.EDU (165.91.128.17) 5 ms 4 ms 6 ms

5 sprint-gw-h1-0.the.net (129.117.16.161) 20 ms 5 ms 5 ms

6 ut8-h1-0.the.net (129.117.16.241) 8 ms 9 ms 21 ms

7 129.117.20.12 (129.117.20.12) 7 ms 11 ms 7 ms

8 ens.gw.utexas.edu (128.83.7.132) 16 ms 23 ms 21 ms

9 ece-e0.gw.utexas.edu (128.83.249.251) 12 ms 9 ms 9 ms

10 * * *

Project

• Purpose

• Options– Network Design

– Software (?)

• Approach {customer/boss/professor}

• Teams {prefered size is 3}

Project Phases

1. Enthusiasm

2. Disillusionment

3. Panic

4. Search for the Guilty

5. Punishment of the Innocent

6. Praise and Honors for the Non-participants

"almost a joke, but too often true!"

Project Schedules

EndStart*

* A miracle occurs

"don't let yourself plan like this"

Network Design

• An iterative, interactive process"you have to ask questions, & you'll never get it all in onemeeting with the customer"

• More than just selecting the media"remember you're designing a system -- make sure you look atsomething for all 7 layers of the OSI model"

• More than one right answer"don't be dogmatic. stay open to other soltuions than the one youfeel is technically best."

Network Design,cont

• What does the customer want to do?• What does the customer want to use?

{tentative design time}

• What are the customer's desires (biases)?

• Check for completeness...

• Check for integration...

• Implementation Plan

Time"Do them in order. Each step is important"

Functions

"the 2 main reasons for a network are connectivity and resource sharing"

Electronic Mail

File Sharing • Transfer • Virtual disk/files

Resource Sharing • Printers/plotters etc • Modems • CPU • Disk

Connectivity • Remote login

Software Management

Resources

"Remember to be precise!"

Systems Qty Mfg Version Software

Geography Distances Constructions Standards

Tentative Design

• Meant to bring out Key features ...

• ... and Decision points ...

with the Customer.

• Provide your “best” solution, and be ready with alternatives.

– Features vs “Costs”

• CYA, or “say it with memos”

User Input

"listen.

understand that you are the expert, responsible for making sure both sides understand each other.

But there are many different solutions to any networking problem."

Completeness

Integration

"Have you covered all the functions needed?"

"Does it all work together?"

Implementation"Make sure it can be built."

Sequence of actions

(1) Identify key points in schedule

(2) Provide alternative plans for problems

• Plan • Build • Test • Turn over

Project “Hints”

• READ the lecture slides– Ask the user closed end questions

– Don’t try to ask too much at one session

– No preconceived scenarios

• Remember Inventory (equip., s/w, space)

• Tentative Design– Informal

– High Level

– Drawings are “Good Things”

More Hints

• Look in catalogs

• Report Format;– Problem statement: don;t just repeat what I said

– Solution HIghlights

» Alternatives considered

» Word Description (logical, physical)

• Bill of Materials– Specific Items (model, brand)

– Costs aren;t very important

Transport Layer

• Services– Reliable Delivery

– or Not!

• Protocols– Internet: TCP, UDP

– ISO: TP0 thru TP4

Transport Services

Framing

Link Header

Network Header

Transport Header

Session Header (?)

Presentation “Header”

Application “Header”

Provider

{see page 481}

Delivery Services

• First layer that can really provide reliability

• Reliability means sequencing, error recovery, acknowledgements

• Not every application needs (wants) reliability

Quality of Service

• New idea from the voice, video folk

• Not (yet) part of Internet protocols– RSVP in process

• Unclear which layer guarantees QoS

Generic Transport Service Primitives

• Listen– notify Transport layer a call is expected

• Connect– establish Transport layer connection

• Send (or Write)

• Receive (or Read)– Both could be connectionless

• Disconnect (or Close)

Berkeley Sockets

• ‘Sockets’ are one of the 2 major Unix network programming application programming interfaces.

• The other is the System V Transport Layer Interface (TLI).

• Sockets are biased towards Unix and C.

• Good references are Doug Comer’s Vol III– both of them!

Unix File I/O

• Unix treats a file as a ‘stream of bytes’

• API calls: open, creat, read, write, lseek, close

• All operate on file descriptors

• File descriptors are int’s, but represent a more complex structure

Socket I/O

• Transport layer also provides ‘stream of bytes’ type service to the upper layers

• API calls:– socket: Initialize data structure

– bind: set addresses

– listen: specify a queue

– accept: wait for connection

– connect: initiate a connection

– read, write, recv, send: transfer data

– close, shutdown: terminate connection

– recvfrom, sendto: datagrams

Overview -- connection

Server

Client

socket() bind() listen() accept() read()

connect()socket() bind() write()

server blocks

Optional(!!)

Overview -- connectionless

Server

Client

socket() bind() recvfrom() sendto()

sendto()socket() bind() recvfrom()

server blocks

Socket Paradigm

• Setup is ‘client/server’ because someone has to start the conversation

• BUT, communication is bidirectional (either end can read or write)

• Sockets (in Unix) are multiprotocol:– TCP/IP, UNIX, XNS {address families}

Server Types

• Iterative– Receive request, process it, go to next on queue

– Best in connection-less environment

• Concurrent– Receive request, fork process, reset socket

– Best when extended interaction is needed

Socket ‘Details’

• If you don’t want to block on a read, look at the select system call.

• You’ll need the following includes:– #include <sys/types.h>

– #include <sys/socket.h>

• Program examples are available on net.

Managing Connections

• Addressing

• Identifying duplicate TPDUs

• Three-way handshakes

• Flow control

• Crash recovery (largely ignored)

• Reliable, sequenced stream of bytes

• Virtual circuit

• Buffered transfer

• Unstructured

• Full Duplex

TCP - How it Works

• Positive Acknowledgements w/ Retransmission

• Sliding Windows

• Pages 531, 532 give the programmer’s state machine info

TCP Features

• A protocol, not a package

• Ports (Well Known Ports)

• Out of Band, or URGENT, data

• Timeouts– RTT Estimation (Karn’s Algorithm) (pg 541)

• Congestion– Slow-Start Methodolgy

• Limitations

TCP Header0 16 31244 10

HLEN RESERVED CODE BITS

PADDINGOPTIONS (IF ANY)

CHECKSUM URGENT POINTER

WINDOW

ACKNOWLEDGEMENT NUMBER

SEQUENCE NUMBER

SOURCE PORT DESTINATION PORT

TCP Connection Management

• Three Way Handshake– SYN, SYN/ACK, ACK

• May be viewed as two Simplex connections

• Window management– Advertising Zero Window Size

– Nagle’s algorithm

– Silly Window Syndrome

0 16 31

SOURCE PORT DESTINATION PORT

MESSAGE LENGTH CHECKSUM

• Your basic datagram

• No acknowledgements, no reliability

• Why use it?

Transport Layer Performance

• Timeout Values

• Inadvertent Synchronized Loads

• Latency (Bandwidth-delay product)

• MTU, MSS values

• Router impact

Performance Hints

• CPU normally is the bottleneck– most time is spent in protocol stacks, not on the wire

• Per-packet overhead means big packets are much more efficient…

• But delays to create big packets impact interactive applications

• Easy to increase bandwidth, impossible (?) to reduce propagation delay

Performance Challenges

• Gigabit networks

• Satellites

Packet Tracing -- Putting it all together

• Packet tracing: the actions of observing packets as they appear on the media and deriving the activities occuring on hosts; or, knowing the top-level commands issued and predicting the packets that will appear on the media.

Motivations for Packet Tracing

• Understanding network protocols

• Debugging your network

• Debugging applications that work over the network

Layer Protocols

DNSQuery DNS

SYN/ACK

ACKCaller Callee

{TCP Establishment}

ARPRequest ARP

Examples - 1

• Assumptions:Host A, IP Address 128.194.1.2

Host B, IP Address 128.194.1.3

netmask 255.255.255.0

ARP caches and bridge tables are empty

All hosts know DNS Server is 128.194.1.3

Trace command “DNS Query” initiated on Host A

Answer - 1

Seg DAE SAE “type” SAIP DAIP

1 FF EA ARP Req 1.2 1.3

1 EA EB ARP Reply 1.3 1.2

1 EB EA DNS Q 1.2 1.3

1 EA EB DNS R 1.3 1.2

Examples - 2

Host C, IP Address 128.194.1.4

netmask 255.255.255.0

Trace command “DNS Query” initiated on Host AB

Answer - 2

1 EB EA DNS Q 1.2 1.3

1 EA EB DNS R 1.3 1.2

Examples - 3

netmask 255.255.255.0

Trace command “telnet 128.194.1.3” initiated on Host A

Answer - 3

1 EB EA TCP SYN 1.2 1.3

1 EA EB SYN/ACK 1.3 1.2

1 EB EA TCP ACK 1.2 1.3

Examples - 4

netmask 255.255.255.0

Trace command “telnet B” initiated on Host A

Answer - 4

1 EB EA DNS Q 1.2 1.3

1 EA EB DNS R 1.3 1.2

1 EB EA TCP SYN 1.2 1.3

1 EA EB SYN/ACK 1.3 1.2

1 EB EA TCP ACK 1.2 1.3

Examples - 5

Host X, IP Address 128.194.1.254 on segment 1

Host X, IP Address 128.194.2.254 on segment 2

netmask 255.255.255.0

Trace command “telnet 128.194.2.2” initiated on Host A

Examples - 5 cont.

Routing table on A:

Net Mask Router

0.0.0.0 0.0.0.0 128.194.1.254

Routing table on B:

Net Mask Router

0.0.0.0 0.0.0.0 128.194.2.254

Routing table on X:

Net Mask Router

Answer - 5

1 EA EX1 ARP Reply 1.254 1.1

1 EX1 EA TCP SYN 1.1 2.2

2 FF EX2 ARP Req 2.254 2.2

2 EX2 EB ARP Reply 2.2 2.254

2 EB EX2 TCP SYN 1.1 2.2

2 EX2 EB SYN/ACK 2.2 1.1

1 EA EX1 SYN/ACK 2.2 1.1

1 EX1 EA TCP ACK 1.1 2.2

2 EB EX2 TCP ACK 1.1 2.2

Problem A -1

Use the data and diagram to show the packets resulting from the command "telnet B" being

executed on host C. Assumptions: The diagram consists of 8 numbered ethernet segments,

5 bridges (unlabeled rectangles), two routers (X, Y) and hosts A, B, C. ARP caches are

empty. Tables on bridges are empty. Routing entries are as shown below. Host A is the

DNS nameserver and its IP address is known to all machines.

Netmask for 128.194 is 255.255.255.0.

A- 128.194.15.1, ethernet e1

B- 128.194.99.2, ethernet e2

C- 128.194.12.3, ethernet e3

X- seg 7:128.194.15.100, ethernet e5

seg 3:128.194.12.100, ethernet e6

Y- seg 8:128.194.99.101, ethernet e7

seg 4:128.194.12.101, ethernet e8

Problem A - 2

Problem A - 3

Host Network Netmask Router

A: 0.0.0.0 0.0.0.0128.194.15.100

B: 128.194.12.0 255.255.255.0128.194.99.101

128.194.15.0 255.255.255.0128.194.99.101

C: 128.194.15.0 255.255.255.0128.194.12.100

0.0.0.0 0.0.0.0128.194.12.101

X: 128.194.99.0 255.255.255.0128.194.12.101

0.0.0.0 0.0.0.0128.194.12.101

Y: 128.194.15.0 255.255.255.0128.194.12.100

0.0.0.0 0.0.0.0128.194.12.100

Decode Example - 1

33 cfl02 -> h-207-200-71-52.netscape.com TCP D=80 S=1977 Syn Seq=1011631 Len=0 Win=0

0: 0000 ef03 efb0 00a0 2435 5343 0800 4500 ........$5SC..E.

16: 002c 6f03 0000 3c06 f2c2 80c2 8547 cfc8 .,o...<......G..

32: 4734 07b9 0050 000f 6faf 0000 0000 6002 G4...P..o.....`.

48: 0000 036d 0000 0204 05a0 0000 ...m........

Decode Example - 2

36 h-207-200-71-52.netscape.com -> cfl02 TCP D=1977 S=80 Syn Ack=1011632 Seq=1144453529 Len=0 Win=49152

0: 00a0 2435 5343 0000 ef03 efb0 0800 4500 ..$5SC........E.

16: 002c 914c 4000 3206 9a79 cfc8 4734 80c2 .,.L@.2..y..G4..

32: 8547 0050 07b9 4436 f999 000f 6fb0 6012 .G.P..D6ù...o.`.

48: c000 0577 0000 0204 05b4 15f8 ...w.......ø

Decode Example - 3

37 cfl02 -> h-207-200-71-52.netscape.com TCP D=80 S=1977 Ack=1144453530 Seq=1011632 Len=0 Win=2880

0: 0000 ef03 efb0 00a0 2435 5343 0800 4500 ........$5SC..E.

16: 0028 6f04 0000 3c06 f2c5 80c2 8547 cfc8 .(o...<......G..

32: 4734 07b9 0050 000f 6fb0 4436 f99a 5010 G4...P..o.D6ù.P.

48: 0b40 d1f4 0000 0204 05a0 0000 .@..........

Decode Example - 4 56 cfl02 -> h-207-200-71-52.netscape.com TCP D=80 S=1977 Ack=1144453530 Seq=1011632 Len=374 Win=2880

0: 0000 ef03 efb0 00a0 2435 5343 0800 4500 ........$5SC..E.

16: 019e 6f08 0000 3c06 f14b 80c2 8547 cfc8 ..o...<..K...G..

32: 4734 07b9 0050 000f 6fb0 4436 f99a 5018 G4...P..o.D6..P.

48: 0b40 a905 0000 4745 5420 2f65 7363 6170 .@....GET /escap

64: 6573 2f73 6561 7263 682f 696d 6167 6573 es/search/images

80: 2f68 6f72 697a 6f6e 7461 6c62 6172 2e67 /horizontalbar.g

96: 6966 2048 5454 502f 312e 300d 0a49 662d if HTTP/1.0..If-

112: 4d6f 6469 6669 6564 2d53 696e 6365 3a20 Modified-Since:

128: 5765 646e 6573 6461 792c 2031 362d 4170 Wednesday, 16-Ap

144: 722d 3937 2030 303a 3430 3a31 3620 474d r-97 00:40:16 GM

160: 543b 206c 656e 6774 683d 3534 0d0a 5265 T; length=54..Re

176: 6665 7265 723a 2068 7474 703a 2f2f 686f ferer: http://ho

192: 6d65 2e6e 6574 7363 6170 652e 636f 6d2f me.netscape.com/

208: 6573 6361 7065 732f 7365 6172 6368 2f6e escapes/search/n

224: 7473 7263 6872 6e64 2d31 2e68 746d 6c0d tsrchrnd-1.html.

240: 0a43 6f6e 6e65 6374 696f 6e3a 204b 6565 .Connection: Kee

256: 702d 416c 6976 650d 0a55 7365 722d 4167 p-Alive..User-Ag

272: 656e 743a 204d 6f7a 696c 6c61 2f32 2e30 ent: Mozilla/2.0

288: 2028 5769 6e31 363b 2049 290d 0a48 6f73 (Win16; I)..Hos

304: 743a 2068 6f6d 652e 6e65 7473 6361 7065 t: home.netscape

320: 2e63 6f6d 0d0a 4163 6365 7074 3a20 696d .com..Accept: im

336: 6167 652f 6769 662c 2069 6d61 6765 2f78 age/gif, image/x

352: 2d78 6269 746d 6170 2c20 696d 6167 652f -xbitmap, image/

368: 6a70 6567 2c20 696d 6167 652f 706a 7065 jpeg, image/pjpe

384: 670d 0a43 6f6f 6b69 653a 204e 4554 5343 g..Cookie: NETSC

400: 4150 455f 4944 3d31 3030 3065 3031 302c APE_ID=1000e010,

416: 3132 3336 3139 6130 0d0a 0d0a 123619a0....

Decode Example - 5

58 h-207-200-71-52.netscape.com -> cfl02 TCP D=1977 S=80 Ack=1012006 Seq=1144453530 Len=280 Win=49152

0: 00a0 2435 5343 0000 ef03 efb0 0800 4500 ..$5SC........E.

16: 0140 92eb 4000 3206 97c6 cfc8 4734 80c2 .@..@.2.....G4..

32: 8547 0050 07b9 4436 f99a 000f 7126 5018 .G.P..D6ù...q&P.

48: c000 3e23 0000 4854 5450 2f31 2e31 2032 ..>#..HTTP/1.1 2

64: 3030 204f 4b0d 0a53 6572 7665 723a 204e 00 OK..Server: N

80: 6574 7363 6170 652d 456e 7465 7270 7269 etscape-Enterpri

96: 7365 2f33 2e30 0d0a 4461 7465 3a20 5375 se/3.0..Date: Su

112: 6e2c 2032 3420 4175 6720 3139 3937 2030 n, 24 Aug 1997 0

128: 383a 3135 3a33 3820 474d 540d 0a43 6f6e 8:15:38 GMT..Con

144: 7465 6e74 2d74 7970 653a 2069 6d61 6765 tent-type: image

160: 2f67 6966 0d0a 4c61 7374 2d6d 6f64 6966 /gif..Last-modif

176: 6965 643a 2054 7565 2c20 3135 2041 7072 ied: Tue, 15 Apr

192: 2031 3939 3720 3233 3a34 303a 3136 2047 1997 23:40:16 G

208: 4d54 0d0a 436f 6e74 656e 742d 6c65 6e67 MT..Content-leng

224: 7468 3a20 3534 0d0a 4163 6365 7074 2d72 th: 54..Accept-r

240: 616e 6765 733a 2062 7974 6573 0d0a 436f anges: bytes..Co

256: 6e6e 6563 7469 6f6e 3a20 6b65 6570 2d61 nnection: keep-a

272: 6c69 7665 0d0a 0d0a 4749 4638 3961 0b00 live....GIF89a..

288: 1400 9100 00ff ffff 6699 9900 0000 0000 ........f.......

304: 002c 0000 0000 0b00 1400 0002 0f8c 8f01 .,..............

320: cbed 0fa3 9cb4 da8b b3de 9c17 003b .............;

Decode Example - 6

0: 0000 ef03 efb0 00a0 2435 5343 0800 4500 ........$5SC..E.

16: 0028 6f09 0000 3c06 f2c0 80c2 8547 cfc8 .(o...<......G..

32: 4734 07b9 0050 000f 7126 4436 fab2 5010 G4...P..q&D6..P.

48: 0b40 cf66 0000 0204 05a0 0000 .@.f........

Decode Example - 7

60 h-207-200-71-52.netscape.com -> cfl02 TCP D=1977 S=80 Fin Ack=1012006 Seq=1144453810 Len=0 Win=49152

0: 00a0 2435 5343 0000 ef03 efb0 0800 4500 ..$5SC........E.

16: 0028 92ec 4000 3206 98dd cfc8 4734 80c2 .(..@.2.....G4..

32: 8547 0050 07b9 4436 fab2 000f 7126 5011 .G.P..D6ú...q&P.

48: c000 1aa5 0000 6915 9192 0000 ......i.....

Decode Example - 8

0: 0000 ef03 efb0 00a0 2435 5343 0800 4500 ........$5SC..E.

16: 0028 6f0a 0000 3c06 f2bf 80c2 8547 cfc8 .(o...<......G..

32: 4734 07b9 0050 000f 7126 4436 fab3 5010 G4...P..q&D6ú.P.

48: 0b40 cf65 0000 0204 05a0 0000 .@.e........

Top Three Layers

• Session Layer

• Presentation Layer

• Application Layer

Session Layer Design

• Marks the division between “upper layers and lower layers”

– lower layers:= end to end communications

– upper layers:= user-oriented services

• Invented by ISO

• Can support transport layer QoS

• Not explicitly used by TCP/IP

• “Generally connection-oriented”

Mission of the Session Layer

• Provides a way for the session users to establish connections, called sessions, and transfer data over the sessions in an orderly way.

• Examples: – remote logins

– file transfers

– Remote Procedure Calls

Session Layer & Transport Layer

• Usually a transport connection is required to establish a session

• Session Layer provides Control. It says what to do, not necessarily how to do it.

• Can provide redundancy and multiplexing of transport layer resources

• Administrative control point

Data Exchange• Same three phases as transport layer

– establishment

– use

– release

• In many cases the session layer simply passes the primitive requests to the transport layer.

• orderly (graceful) release vs. abrupt release– abrupt release is analogous to hanging up the phone

– orderly release uses a full handshake, (not provided in transport layer)

Dialog Management

• In principle, all OSI connections are full duplex

• Some upper layer software is structured to be half-duplex

• This is to simplify the software and has nothing to do with hardware limitations

• The session layer supports data token schemes to support half-duplex transmissions

Synchronization

• Transport layer provides error recovery only from communication errors

• Synchronization in the transport layer provides for returning the session entries back to the last known correct state.

• Example: Session established and large file transmitted; receiving end has no storage and directly prints the incoming data. The printer dies and data is lost.

• Session users could split the text into pages and insert a synchronization point between each page.

Activity Management

• Users split the message stream into activities

• delimiters are added in the session to separate activities

FirstFileSent

Start Stop

Second File SentSession

Remote Procedure Calls

• Based on the connectionless model

• Generally outside the OSI model

• Can be implemented in the application layer

• Multiple Flavors– {Sun} ONC RPC

– {OSF} DCE RPC

“RPC School of Thought”

• Clients sending messages are viewed as procedure calls with the reply being the return from the procedure

• Contrast this to the more “conventional” school which views I/O with primitives such as X-DATA.request and X-DATA.return as I/O and interrupts respectively.

RPC Invocation

Client Client Stub Network {Portmapper} Server Stub Server

RPC Semantics and Orphans

• Operations– exactly once

– at most once

– at least once

• Handling crashes:– 1. Hang forever, waiting for reply that never comes

– 2. Time out and raise an exception

– 3. Time out and retransmit

• Orphans– extermination

– expiration

– reincarnation (kill & restart)

– gentle reincarnation (selectively kill and restart)

Session Layer Conclusions

• Not used in ARPANET or USENET

• Some debate on including it in the ISO modelClosest Internet example of an OSI (not ISO) stack:

whatever

Presentation Layer

NetworkFormat

LocalFormat

InformationTransformation

“few standards, but a lot of ideas”

Presentation Functions

These are examples!

• Syntax (format) conversion

• Compression

• Encryption– Sub-issue: Does it belong here?

Presentation Layer, cont.

• Providing a way to specify complex data structures

• Managing the set of data structures required

• Converting data between internal and external form

Data Representation

• ASCII vs. EBCDIC

• two’s complement vs. one’s complement

• FFF0 hex is -15 1’s complement; -16 2’s complement

• byte order right left vs. left right

• Text File formats

Abstract Syntax Notation 1 (ASN.1)

• Data Structures

• Abstract Syntax

• Transfer Syntax

• International Standard 8825

• Notation used to encode, transfer and decode data structures across a wide range of applications

• Both connection-oriented and connectionless primitives

Data Compression

• Encoding a Finite Set of Equally Likely Symbols

– Finiteness of the set of symbols.

• Frequency Dependent Coding– The relative frequencies with which the symbols are

• Context Dependent Encoding– The context in which a symbol appears.

Compression

• Elimination of Redundancy– (increased susceptibility to error)

• Examples– Run Length Encoding

– Predictive Codes

– Huffman

– LZW

Frequency Dependent Coding

• In English, “E” occurs ~100 times more than the letter “Q”

• So give common symbols short codes and longer symbols longer codes.

• Theoretical minimum encoding often requires fractional bits, but close approximations available.

Huffman Coding

• 1. Write down all symbols and associated probability of each. Eventually a binary tree is built on these nodes, with the symbols representing terminal nodes.

• 2. Find the two smallest nodes and mark them. Add a new node with arcs to each of the nodes just marked. Set the probability of the new node to the sum of the probabilities of the two nodes connected to the new node.

• 3. Repeat until all symbols are marked except one. The probability of the unmarked node will always be 1.0.

• 4. The encoding for each symbol is found by tracing the path from the unmarked symbol to that symbol, recording the sequence of left and right branches taken. The code is the path, left = 0, right = 1.

Context Dependent Encoding

• Uses conditional probability instead of independent probability.

• What is P(u|q)?

• So determine the conditional probability for each possible predecessor and store in a table.

• For k symbols this requires k2 entries.

Network Security and Privacy

• Protecting data from being read by unauthorized persons.

• Preventing unauthorized persons from inserting and deleting messages.

• Verifying the sender of each message.

• Allowing electronic signatures on documents.

Cryptography

• Traditional Cryptography– Substitution Ciphers

– Codes

– Transposition Ciphers

• Data Encryption Standard

• Key Distribution

• Public Key Crytography– MIT Algorithm

• Authentication & Digital Signatures– Federal Standards

Cryptography Users

• Military

• Diplomatic

• Diarists

• Lovers

• Curmugdeons

Cyptography Terms

• Ciphertext or Cryptogram -- encrypted message

• Cryptanalysis -- breaking ciphers

• Cryptography -- devising ciphers

• Cryptology := Cryptanalysis and Cryptography

Encryption Model

Plaintext Plaintext

Key-1Key-2

Ciphertext

Passive Listener

Active Intruder

• If Key-1 is the same as Key-2, then it has to be a secret key process. They can differ, making it a Public Key Process.

• Big Problems: key distribution and key security

Fundamental Truths of Cryptology

• Potential intruders know the general encryption method.

• Message contents may be guessed.

• Cryptographic systems may be changed, but rarely are.

• Non-technical compromises always outnumber successful cryptanalysis.

Ciphers

• Substitution (preserve order, disquise)– Caesar code = “shift 4”

– Alphabet shifted by k letters --”enigma”

– Exhaustive search infeasible

– Words and phrases may be guessed

• Codes– Purple code, Japanese translated into Latin

– Navajo talkers

• Transposition Ciphers (reorder, do not disguise)

– Game is up when key length is guessed

– Once close, easy to guess

Data Encryption Standard

• Developed by IBM in 1977

• Implemented in hardware

• Widely used

• 128 bit key proposed, 56 bit key specifiedAny guesses why?

Public Key Encryption

• Applying the decryption key to an encrypted message must return the plaintext message.

• The decryption key can’t be guessed from an encyption key.

• The encryption key cannot be broken by a plaintext attack.

• Key Point: the decryption key must be privately held.

RSA Algorithm

• 1. Choose two large primes, p and q, each greater than 10100

• 2. Compute n = p * q and z = (p - 1) * (q - 1).

• 3. Choose a number relatively prime to z and call it d.

• 4. Find e such that e * d = 1 mod z.

Implementation of the MIT Algorithm

• To encrypt– divide plaintext P into k bits where k is the largest integer

for 2k < n.

– compute C = Pe(mod n)

• To decrypt– P = Cd

(mod n)

• Encryption requires e and n (public key)

• Decryption requires d and n (private key)

• If n can be factored, then this yields p an q, then z.

• Euclid’s Algorithm will derive e and d from z.

Digital Signatures

• A’s secret key must remain secret

• B has A’s public key and A has B’s public key

• B received a encypted message from A that he decypts with A’s public key

• B can later show that lacking A’s private key that he could not have produced the encrypted message

Politics of Cryptography

• Software as Munition

• “Clipper” Chip

• Digital Telephony Bill

• Digital Signature Standard

• Other Countries

• Current Legislation

Application Layer

• File Transfer, Access and Management– virtual file store

– file servers and requesting clients

• Electronic Mail– process to process traffic expected to dominate Internet

– actually email dominates the Internet

• Virtual Terminals– representing the abstract state of the real terminal

• Remote Job Execution– JTM: Job Transfer and Manipulation

ISO Applications

• FTAM ~ FTP File Transfer, Access & Manipulation

• VTS ~ TELNET Virtual Terminal Service

• JTM ~ ??? Job Transfer & Manipulation {maybe rsh, RPC?}

• MHS ~ SMTP Message Handling System (X.400)

ISO Terminology

SASE SASE

“applications”

[Specific|Common] Application Service Elements

“think of them as programming libraries or APIs”

ISO Service Elements(examples)

• Association Control Service Element (primitives)

• Commitment, Concurrency and Recovery– atomic actions

– two phase commit

File Servers

• 1. File Structure

• 2. File Attributes– e.g. identifier, size of storage, access control

• 3. File Operations– create, delete move

– OSI has defined virtual filestore operations

Replicated Files

• Why multiple file servers?– 1. To split the workload over multiple servers.

– 2. To allow file access to occur even if one file server is down

– 3. To increase reliability by having independent backups of each file

• Updates

• Voting

Electronic Mail

• Motis and X.400CCITT has aligned them for compatibilityMay replace SMTP

• The user agentuser interface

• Message transfer agentpost office

Virtual Terminals

• Scroll mode terminalsno local resources; dumb display and transmission

• Page mode terminals25 x 80 character displayscreen editing via termcap

• Form mode terminalslocal processing enabled

• Bitmapped terminals

like X stations

• Browsers!

Case Study: Internet

• File Transfer

• Electronic Mail

• Virtual Terminals

Getting Started

• RARP

• BOOTP

• TFTP

• DHCP

Domain Name System

• A heirarchial, distributed database

• A service primarily aimed at mapping names to IP addresses

• Partitioned for ease of administration

DNS Structure (partial)

edu comgov

utexas tamu ibm

cs austin

mac1 mac1solar

DNS -- How it Works

• DNS Servers in a logical tree

• DNS clients on every host

• Iterative Queries

• Recursive Queries

• Address Resolution Protocol {translate network layer address to physical address}

• Part of general resolution procedure:

name {e.g., neuron.cs.tamu.edu}

IP Address {e.g., 128.194.133.1}

Ethernet address {e.g., 08:00:20:08:58:78}

File Transfer Protocol

• FTP recognizes four file types:

• 1. Image– bit by bit transfer

• 2. ASCII

• 3. EBCDIC

• 4. Logical Byte files– binary files which use byte size other than 8 bits

Electronic Mail

• Pioneered by ARPANET

• RFC 822 (widely used)

• Simple Mail Transfer Protocol (SMTP)

• Supports only ASCII text

• name@domain addressing

Virtual Terminals - TELNET

• Designed for scroll mode terminals

• Hit a key , 8-bit bytes are sent

• 95 ASCII and 7 control characters legal

USENET--HOW TO AVOID GRADUATION

• Internet compatible (now)

• Variety of newsgroups

• Moderated newsgroups

• NNTP, Network News Transfer Protocol, allows selective downloading of messagesto multiple sites

The Web

• “the” killer application for the Internet

• Two components for popularity– http combines multiple access (gopher, ftp, etc) methods

– hypertext interface supports point-and-click interface

• Who will organize the information?– No one...

– Database experts

– Librarians (!)

Web Terminology

• Web Browsers– Netscape

– Mosaic

• Web Servers– http daemon

» httd.conf - main server config file

» srm.con - server resource config file

» access.conf - global access control file

• Home Page– Eg., www.cs.tamu.edu

• HTML– HyperText Markup Language

HTML Document

<HTML>

<HEAD>

<TITLE>Willis Marti’s Homepage</TITLE>

</HEAD>

<BODY>

<H1> Sample HTML Document</H1>

<EM> To demonstrate HTML </EM>

Web Future Directions

• HTML Enhancements

• Secure Transactions

• Uniform Naming

• Librarians & Brokers

• Information “push” or “pull”

Layer 7 Summary

• Service Element Model

• Not all Apps belong here...

• Common Network Services

What is a Distributed System?

Computing(CPU)

MassStorage

UserInterface

Just insert a network?

Distributed System

Network

Servers (Storage, Compute)

Services

User InterfacesUsers

D.S. Design Issues

• Transparency

• Flexibility

• Reliability

• Performance

• Scalability

More Design Issues

• Global Clocks?

• Causality

• Information Consistency

Distributed Control

• Master/Slave (Issue: Response Time)

– Polled

– Command -> <-Response

– Schedule under control of server

• Client/Server (Issue: Server Size)

– Interrupt, or Event, Driven

– Aperiodic Scheduling

• Peer-to-Peer (Issue: Coordination)

– No single critical node

– Hard to describe or predict

Distributed System:Why or Why not?

• Performance

• Economics

• Reliability

• Security

D. S. Architectures

• Cooperating Peers

• Client-Server

• Tiered Client-Server– Data Repository

– Compute Servers

– Client Stations

“Intranets”

• Definition– Using Internet protocols, especially Web tools, for

internal MIS

• Motivation– Information “push” vs “pull”

• Problems– User Capabilities

– Corporate Policy or Personal Opinion

Key Protocol Areas

• Directory Services

• RPCs

• Security/Authentication

• (Performance) Management

• Programming Models

References

• ISO RM-ODP – ITU-T X.901/ISO 10746-1/2/3/4

• Amjad Umar Distributed Computing: A Practical Synthesis– PTR Prentice-Hall, Englewood Cliffs, NJ, 1993

• Sape Mullender Distributed Systems, 2d ed.– Addison Wesley, 1993

Network ManagementDefinition

"...deploying and coordinating resources in order to plan, operate, administer, analyze, evaluate,design and expand communication networks tomeet service-level objectives at all times, at a reasonable cost, and with optimum capacity."

Network ManagementFunctional Areas

• Fault Management detect -- diagnose -- repair•Configuration/Name Mgmt a database problem...•Performance Mgmt measure and predict•Accounting Mgmt look at individual usage•Security Mgmt access control and encryption

Management Protocols

– Internet

• CMIP - Common Management Information Protocol

– ISO

• TMN - Telecommunications Management Network

– ITU-T

Management ProtocolsPhilosophy

– keep it simple! (cf the Internet toaster)

• CMIP - Common Management Information Protocol

– the bazaar: whatever you want

• TMN - Telecommunications Management Network

– actually a separate network specification

SNMP vs CMIP {round 1}

Requirements fromvarious vendors and user communities

SNMP CMIP

ISO Management Overview

FaultManagement

AccountingManagement

SecurityManagement

PerformanceManagement

ConfigurationManagement

System Management Functions

Object Mgmt Alarm Mgmt Event Report Mgmt Workload MonitoringState Mgmt Log Control Security Alarm Security ReportingMeasurement Summarization Bill Verification BillingResource Utilization Test Mgmt Relation Mgmt

CMISE ServicesInitialize Event Report Terminate Action Create AbortSet Get Delete Cancel Confirmed Event Report Confirmed Get

SNMP Architecture

• Keep the agent as simple as possible

• Support remote management operations to the fullest extent possible

• Plan for future additions & expansion

• Be independent of specific hosts or devices

• Operate at the Application level

Internet Management Model

NetworkManagement

Managed Entities

Proxy Agent

• Intersection of vendor/user requirements

• Few ‘verbs’:– get / get-next

– get-bulk {SNMPv2}

– set

– trap

• Polled, Master-Slave, Request-Response

SNMP Format

• <header><verb><value><variable>[<verb><value><variable>]

• ASN.1 subset to describe value format

• MIB-II{Management Information Base} to identify variables

• UDP as a Transport layer

• Now out! SNMPv2

The MIB

• Standard set of data for managing network devices

• Variable names are part of the ISO/CCITT object identifier namespace

• Provides globally unique identifiers

• Variables governed by Structure of Management Information (SMI) specification

Accessing MIB Data

• SNMP Communities

• SNMP Views

• SNMP Authentication

Abstract Syntax Notation 1 (ASN.1)

• Data Structures

• Abstract Syntax

• Transfer Syntax

• International Standard 8825

• Notation used to encode, transfer and decode data structures across a wide range of applications

• Both connection-oriented and connectionless primitives

Example SNMP PDU using ASN.1

SEQUENCE len=41 INTEGER len=1 vers=0

30 29 02 01 00

string len=6 p u b l i c

04 06 70 75 62 6C 69 63

getreq. len=28 INTEGER len=4 -------request ID----------------

A0 1c 02 04 05 AE 56 02

INTEGER len=1 status INTEGER len=1 error index

02 01 00 02 01 00

SEQ. len=14 SEQ len=12 objectid len=8

30 0E 30 0C 06 08

1.3 6 1 2 1 1 1 0

2B 06 01 02 01 01 01 00

null len=0

SNMP vs SNMPv2

• History in Brief

• More features (more complex)

• BIG increase in security– authentication and integrity

– access controls

– security and privacy

• Better access controls in Views

• Trap confirmations

• Knowledge of multiple managers

Enterprise Architecture

• SNMP is designed for simple, manager-to-agent communications

• CMIP is complex and bulky, but complete

• Most Enterprise networks can’t be managed directly from a single place

Enterprise Management

LocalNetworks

SNMPManagers

CMIPManagers Separate

Organization

Management Tools

• Packet Analyzer

• Media Analyzers (TDR, OTDR, BER Tester)

• RMON devices

• Hosts (?)

Software Tools

• Hosted on PCs

• Hosted on Unix Workstations

• Commercial Packages

Decent Books

• Network Management Standards 2d ed– Uyless Black

• The Simple Book, 2d ed– Marshall T. Rose

• Communication Networks Management, 2d ed– Kornel Terplan

• Internetworking with TCP/IP, Vol I, 3d ed– Douglas E. Comer

Defining Network Security

Security is prevention of unwanted information transfer

• What are the components?– ...Physical Security

– …Operational Security

– …Human Factors

– …Protocols

Areas for Protection

• Privacy

• Data Integrity

• Authentication/Access Control

• Denial of Service

Regulations and Standards

• Computer Crime Laws

• Encryption

• Government as “Big Brother”

Security

Threat, Value and Cost Tradeoffs

• Identify the Threats

• Set a Value on Information

• Add up the Costs (to secure)

Cost < Value * Threat

Threats

• Hackers/Crackers (“Joyriders”)

• Criminals (Thieves)

• Rogue Programs (Viruses, Worms)

• Internal Personnel

• System Failures

Network Threats

• IP Address spoofing attacks

• TCP SYN Flood attacks

• Random port scanning of internal systems

• Snooping of network traffic

• SMTP Buffer overrun attacks

Network Threats (cont.)

• SMTP backdoor command attacks

• Information leakage attacks via finger, echo, ping, and traceroute commands

• Attacks via download of Java and ActiveX scripts

• TCP Session Hijacking

• TCP Sequence Number Prediction Attacks

Threat, Value and Cost Tradeoffs

• Operations Security

• Host Security

• Firewalls

• Cryptography: Encryption/Authentication

• Monitoring/Audit Trails

Host Security

• Security versus Performance & Functionality

• Unix, Windows NT, MVS, etc

• PCs

• “Security Through Obscurity”

Host Security (cont)

• Programs

• Configuration

• Regression Testing

Network Security

• Traffic Control

• Not a replacement for Host-based mechanisms

• Firewalls and Monitoring, Encryption

• Choke Points & Performance

Access Control

• Host-based:– Passwords, etc.

– Directory Rights

– Access Control Lists

– Superusers

• Network-based:– Address Based

– Filters

– Encryption

– Path Selection

Network Security and Privacy

• Protecting data from being read by unauthorized persons.

• Preventing unauthorized persons from inserting and deleting messages.

• Verifying the sender of each message.

• Allowing electronic signatures on documents.

FIREWALLS

• Prevent against attacks

• Access Control

• Authentication

• Logging

• Notifications

Types of Firewalls

• Packet Filters– Network Layer

• Stateful Packet Filters– Network Level

• Circuit-Level Gateways– Session Level

• Application Gateways– Application Level

Presentation

Transport

Network

Session

Data Link

Physical

Application

Packet Level

• Sometimes part of router

• TAMU “Drawbridge”

Campus

RouterDrawbridge

Circuit Level

• Dedicated Host

• Socket Interfaces

Local FW

Application Level

• Needs a dedicated host

• Special Software most everywhere

telnet

Firewall

Firewall Installation Issues

Router

FTP Web Mail

INTERNET

Firewall Installation Issues

• DNS Problems

• Web Server

• FTP Server

• Mail Server

• Mobile Users

• Performance

Address Transparency

• Need to make some addresses visible to external hosts.

• Firewall lets external hosts connect as if firewall was not there.

• Firewall still performs authentication

Network Address Translation

FirewallInternet

Gateway

Network Address Translation

Data Link

Hardware

Data Link

Hardware

proxy ftp

Data Link

Hardware

gw control

Host A: Internal HostGateway HostHost B: External Host

DatagramA GW DatagramA B

IP Packet Handling

• Disables IP Packet Forwarding

• Cannot function as a insecure router

• eg. ping packets will not be passed

• Fail Safe rather than Fail Open

• Only access is through proxies

DNS Proxy Security

finance.xyz.com marketing.xyz.comsales.xyz.com

Eagle Gatewayeagle.xyz.com

INTERNET

External DNS Server

INTERNET

Virtual Private Tunnels

Hello!@@%* !@@%* !@@%*

Encapsulate

Authenticate

Encrypt

Decapsulate

Authenticate

Decrypt

Creates a “ Virtual Private Network “

VPN Secure Tunnels

• Two types of Tunnels supported– SwIPe and IPsec tunnels

• Encryption– DES, triple DES and RC2

• Secret key used for used for authenticatio and encryption

• Trusted hosts are allowed to use the tunnel on both ends

Designing DMZ’s

INTERNET

ScreeningRouter

CompanyIntranet

Firewall Design Project

Wide Area RouterDallas

Raptor RemoteHawk Console

INTERNET

Mail Server

San Jose

Raptor Eagle

File Server

InternetRouter

Monitoring

• Many tools exist for capturing network traffic.

• Other tools can analyze captured traffic for “bad” things.

• Few tools are real-time.

Summary

• Security must be comprehensive to be effective.

• Remember threat, value, cost when implementing a system.

• Security is achievable, but never 100%.

• Make your system fault tolerant.

Where Do the 7 layers “fit”?

Application

Presentation

Session

Transport

Network

Data/Link

Physical 1

Or, where isthe dividing linebetween hdw & s/w?

Implementing the Model

User Space Software

OS SpaceSoftware

Firmware

Hardware

Some More Definitions

• User Space Software - Code that executes as any program that a normal user could compile and run

• OS Space Software - Code that executes on the host CPU but in a mode or with special access that normal users can not use

• ‘Firmware’ - Code that executes on a processor (special or general purpose) that is different from the host CPU; may be in PROM or RAM downloaded from another source

• Hardware - Generally special purpose VLSI and analog/linear interface components

Assigning the 7 layers

• Performance

• vs

• Flexibility

CPSC 463 Networks and Distributed

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