Chap 8 Suppl Logical

8/7/2019 Chap 8 Suppl Logical

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A Logical Explanation

The Business/IT Highway:

How Does IT Work?


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Objectives

Analyze the layered models

Review common protocols

Logical addressing

Understand the encapsulation process

Reliability issues How does my data get to its destination?


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Part 1 Overview of theOSI Model


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Benefits ofOSI Model

Reduce complexity

Standardize interfaces

Facilitate modular engineering

Ensure interoperable technologies

Accelerate evolution

Simplify teaching and learning


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What isOSI Model ?

Open System Interconnection (OSI) model is a set of

protocols that define and standardize the datacommunications process

The OSI model is set by the International Standards

Organization (ISO)

The OSI model has the support of most major

computer and network vendors

OSI model divides the process into seven groups,

called layers which are fitted with protocol standards


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OSI Layers


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TheOSI Model

Physical Layer (L1 or Layer 1) Connections and connector types

Cables

Wireless

Fiber

Signaling standards

Voltages, attenuation, noise, etc


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OSI Layers


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OSI Layers

Data Link Layer (L2 or Layer 2)

Physical addressing MAC Framing

Network topology

Error detection

Access to media

Sub-Layers MAC and LLC

Ethernet

LAN Switches are L2 devices


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OSI Layers

Data Link LayerProtocols

SLIP Serial Line Internet Protocol PPP Point to Point Protocol

HDLC High Level data link control


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OSI Layers

Provides connectivity and path selection between two host

Provides Logical address

No error correction, best effort delivery.


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OSI Layers

Network Layer (L3 or Layer 3)

Logical addressing IP address Packets

Connection-less, best effort

Best path selection

Routers are Layer 3 devices


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OSI Layers


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OSI Layers

Transport Layer (L4 or Layer 4)

Segmentation of Data Error correction

Reliability

End-to-end communication

Windowing

TCP and UDP


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OSI Layers


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OSI Layers

Session Layer

Two way alternate vs. two way simultaneous Synchronization between applications

Some protocols: NFS & SQL

This layer is part of the TCP/IP models Application layer


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OSI Layers


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OSI Layers


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OSI Layers

Application Layer (L7 or Layer 7)

Closest to the user This is NOT the application you interact with

This is the underlying protocol of the application

HTML for web browsers

SMTP and POP3 for email

This layer is part of the TCP/IP models Application layer


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Peer-to-Peer Communication


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Compare:OSI and TCP/IP models


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PART 2 The Details

Lets look at these layers a bit closer but lets

turn it around.


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Layer 7 Application Layer

Identifying and establishing the availability of

intended communication partners Synchronizing cooperating applications

Establishing agreement on procedures for

error recovery

Controlling data integrity


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Layer 7 Application Layer

Common Application layer protocols

HTTP Telnet

FTP

SNMP

DNS FTP and TFTP

SMTP


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DNS

The Domain Name System (DNS) is a systemused for translating names into IP addresses.

There are more than 200 top-level domainson the Internet

Uses port 53

.us United States.uk United Kingdom

.edu educational sites

.com commercial sites

.gov government sites.org non-profit sites

.net network service


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FTP and TFTP

FTP is a reliable, connection-oriented

service that uses TCP to transfer filesbetween systems that support FTP. Uses ports 20 and 21

TFTP is a connectionless service that uses

User DatagramP

rotocol (UDP

). TFTP is designed to be small and easy to

implement.

Use port 69


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HTTP

Hypertext TransferProtocol

Uses port 80


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SMTP

E-mail servers communicate with each otherusing the Simple Mail Transport Protocol(SMTP) to send and receive mail (POP3).

Uses port 25, 110


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SNMP

The Simple Network Management Protocol (SNMP) is anapplication layer protocol that facilitates the exchange of

management information between network devices.


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Telnet

Telnet client software provides the ability to log

in to a remote Internet host that is running aTelnet server application and then to executecommands from the command line.


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Layer 6 Presentation Layer

Responsible for

Data format - ASCII, jpeg, mp3, etc. Compression

Encryption


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Layer 5 Session Layer

Establish, maintain and terminate sessions

between applications. Dialog control - the session layer decides whether

to use two-way simultaneous communication or

two-way alternate communication.

Dialog separation - orderly initiate, terminate, andmanage transactions


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Layer 4 Transport Layer

Segments data

Adds a logical identifier (port number) Provides for reliability by ensuring segments

delivered are acknowledged

Provides for retransmission of segments no

acknowledged Reassembles segments at destination

Provides for congestion avoidance andcontrol


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Primary Transport LayerProtocols

TCP Connection oriented

Reliable

UDP

Connection-less

Unreliable

Best effort like IP


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Both TCP and UDP use port (socket) numbers to passinformation to the upper layers.

Port numbers identify specific

Application layerprotocols.

Numbers below 1024 are considered well-knownports numbers.

Numbers above 1024 are dynamically assignedports numbers.

Registered port numbers are those registered forvendor-specific applications. Most of these areabove 1024.

Well known ports: 80 = HTTP, 23 = telnet


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Layer 3 Network Layer

Layer 3 is responsible for:

Logical addressing (IP and others) Routing

Path selection

Packet switching

Encapsulation of Segments intoPA

CKETS


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Internet Protocol

IP is a connectionless, best-effort protocol Unreliable

It relies on TCP for reliability

It provides the ability for a logical address

Network (and subnetwork) Node

A mask is used to distinguish between net & node


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What is an IP address?

Logical address Two parts: network id and host id

32 bit address

Written in dotted decimal notation

4 sets of 8 bits written as decimal numbers192.168.1.1

205.200.3.24

10.3.5.254


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Private and reserved IP addresses

Some addresses are reserved for specialpurposes.

Some identify the Network ID and some Identify the

broadcast address for the entire network.

Some are considered Private and do not traverse the

internet


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Private and reserved IP addresses (cont.)

Some are for multicasting 224.0.0.0 through 239.255.255.255

Some are for testing purposes

127.0.0.0

Some are link-local

169.254.0.0 Some are reserved for no good reason

240.0.0.0 255.255.255.255


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IP version 6

Do I need to know this? Be aware of it. An IPv6 address is a 128 bit address

Written in hexadecimal notation2001:1234:0000:fb5d:0000:0000:0abc:def0/64

Can be shortened to:2001:1234:0:fb5d::abc:def0/64


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Ah.the IPPACKET


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The Router


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The Router a network layer device

Used to connect different logical networks Determines best path (routing protocols)

Switches packets (routed protocols) from

incoming interface to outgoing interfaces


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The router is responsible for determining bets path


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Layer 2 Data Link

LLC Logical Link Control

LLC is specified in IEEE 802.2 It is the upper sub-layer of layer 2.

It provides a logical service to the Network layer

It is independent of topology

It is independent of technology


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Layer 2 Data Link

MAC Media Access Control

This is the lower sub-layer of Layer 2 Topology dependent

Media dependent

Technology dependent

Physical addressing (naming) Encapsulating Packets into FRAMES


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Layer 2 Data Link

The LAN switch a layer 2 device*


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L3 vs. L2

Comparing layer 3 and layer 2 devices


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Layer 1

Layer 1 (We spoke in detail about layer one in the Lets Get Physical workshop)

Bits and signaling Cabling

Connectors and connection standards

Electricity


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Putting it together

Each layer accepts whatever is passed into it

from the upper layer. It then encapsulates that information.

Each layers encapsulation has a name, this

is called a Protocol Data Unit orPDU.


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Putting it together

Data flow example


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Summary

We use layers to simplify learning andunderstanding of data flow

Data is encapsulated into packets thenframes before being transmitted as bits

Routing protocols are used to determine thebest path to a destination

TCP/IP is the protocol suite of the internet IP is connectionless and unreliable

TCP provides connection-oriented service andreliability

Chap 8 Suppl Logical

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