Managing Computer and Communication Networks

Managing Computer and Communication Networks

Part1

Dr. Hamid Reza Naji

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• Information Access

• Sharing of Resources

• Facilitate Communications

Motivation for Networks

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• Transmission hardware• Special-purpose hardware devices

– interconnect transmission media– control transmission– run software protocol

• Software Protocol– encodes/decodes and formats data– detects and corrects problems

What A Network Includes

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• Provides communication that is– Reliable– Fair– Efficient– From one application to another

• Automatically detects and corrects– Data corruption– Data loss– Duplication– Out-of-order delivery

• Automatically finds optimal path from source to destination

What A Network Does

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Point-to-point - Individual connections between pairs of machines.

Broadcast Networks - Single channel with multiple machines connected to it.

Packets - Messages - the "chunk" of data transmitted from one machine to the

next.

Addressing - One to one: Packet contains specific target address. Broadcasting: All machines on the network receive and process the

packet. Multicasting: A subset of machines receive and process the packet.

Issues we’ll be dealing with

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view messaging in terms of the transmission distance

100 meter Building -- Local area network 10 kilometer City -- Metropolitan area network 1K kilometer Country -- Wide area network 10K kilometer Continents -- Internet

transmission distance

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• Dedicated– fixed bandwidth– route fixed at setup– idle capacity wasted– network state

Circuit Switching

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• Best Effort– end-to-end control– multiplexing technique– re-route capability– congestion problems

Packet Switching

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LANs are:Privately owned. Can be up to several kilometers long;Run at speeds of 10, 100, or more Mbps.Low delay. High reliability.Requires collision arbitration.

Ethernet:IEEE 802.3.Bus based broadcast network with decentralized control at 10 or 100 Mbps.

Token Ring:IEEE 802.5Ring based broadcast network with token arbitration at 4 or 16 Mbps.

Network Hardware

LOCAL AREA NETWORKS

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MANS are:Larger version of LAN ("city" wide).Public or private / data or voice.Broadcast Can be distinguished from LANs based on wiring mechanism.

Network Hardware

METROPOLITAN AREA NETWORKS

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WANS are: Networks spanning large distances.

Hosts or End Systems - Machines running user applications.

(Communication) Subnet -Connections between hosts - transmission lines + switches.A "locality" understanding each other's addresses.

Circuits/Channels/Trunks -Transmission lines move the bits.

Network Hardware

WIDE AREA NETWORKS

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Router - Generic term for switching computers.

Point-to-point/Store-and-forward/Packet-switched -Moving through a series of routers, packets are received at a

router, stored there, then forwarded to the next router.

Network Hardware

WIDE AREA NETWORKS

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WirelineString, Copper (Twisted Pair, Coax), Optical Fiber

WirelessSound, Light, Infrared, RF, Microwave

• Used where computer is mobile or far away from wires.• Only few Mbps / higher error rates / interference.

Network Hardware

Media

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• Layers - The concept that network software is organized

functionally into levels. A level on one host talks to the same level on another host (its peer).

• Protocol - The protocol is the convention or standard that a layer

uses to talk to the other layer. An agreement or standard on the conversation.

PROTOCOL HIERARCHIES

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• Physical Medium - Underneath the layers is the wire or fiber or whatever.

• Interface - Defines the services that one layer offers another

(either up or down.)

Important that each layer perform specific actions.

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• Network architecture -

A set of layers and protocols. It contains details on what happens in the layer and what the layer says to its peer.

• Protocol stack -

A list of protocols used by a system, one protocol per layer.


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• Both Directions Simultaneous• Simplex No No• Half duplex Yes No• Full duplex Yes Yes

• o Number of logical channels per connection• o Error control. • o Flow control.• o Breaking up messages into a smaller chunks (and • reassembly.)• o Multiplexing messages on same connection.• o Routing - how to get from one host to another.

DESIGN ISSUES FOR THE LAYERS

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DESIGN ISSUES FOR THE LAYERS

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• Purpose of each layer is to provide services to the layer above it.

• Entities / Peer entities -• Active element in each layer (processor / IO chip). • Peer entity = layer N entity <--> layer N entity.• Layer N entity provides service for layer N + 1.

• Service providers and users -• Layer N is a provider for user N + 1.

• SAPs (Service Access Points) -• Entry points in N that layer N + 1 can access.• Has an address that uniquely identifies it.

INTERFACES AND SERVICES

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• IDUs (Interface Data Unit) -• The information from N + 1 provided at the SAP.• Made up of SDU + control information.

• SDUs (Service Data Unit) -• The portion of the IDU that will be passed up to the peer entity.

• PDUs (Protocol Data Unit) -• The SDU may be broken up into PDUs, that being the chunk

size

for further transmission.


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• Connection oriented service -

Like the phone system. The system establishes a connection, uses it, and closes it. Acts like a tube. Data comes out the other end in the same order as it goes in.

» Connection Setup» Data Transfer» Connection Termination

CONNECTION-ORIENTED SERVICES

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• Connectionless service -

Like the post office. Each message has the entire address on it. Each message may follow a different route to its destination. Ordering is not important

CONNECTIONLESS SERVICES

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• Quality of service -• Will the message arrive?? • A reliable connection-oriented service guarantees success.• Message sequence - message boundaries and order are maintained.• Byte streams - messages are broken up or combined; flow is bytes. • Can pair mechanism with upper-layer requirements (matching).

CONNECTION-ORIENTED / CONNECTIONLESS SERVICES:

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• Datagram Service – Like junk mail. It's not worth the cost to determine if it

actually arrived. Needs a high probability of arrival, but 100% not required. Connectionless, no acknowledgment.

• Acknowledged datagram service - As above, but improved reliability via acknowledgment.

• Request-reply service -Acknowledgment is in the form of a reply.


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• Primitives are:• The operations available to an entity. Possibilities

include:• Request -- An entity want some work done.• Indication -- An entity is told about an event.• Response -- An entity wants to respond to

an event.• Confirm -- Response to earlier request has come back.

SERVICE PRIMATIVES

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• Example of Connectionless Protocol:

• Data-request |--------->| Data-indication• Data-indication |<---------| Data-request

• Example of Connection-oriented Protocol: (needs connection establishment)

• Connect-request |--------->| Connect-indication• Connect-confirm |<---------|

• Data-request |--------->| Data-indication• Data-indication |<---------| Data-request

• Disconnect-request |--------->| Disconnect-indication• Disconnect-confirm |<---------|

SERVICE PRIMATIVES

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• THE RELATIONSHIP OF SERVICES TO PROTOCOLS:

• Services are primitives that a layer provides for the layer above it.

• Protocols are rules governing the meaning of frames/packets/messages exchanged with the peer entity.

SERVICE PRIMATIVES

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Layering

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Reference Models

Headers, Data, and Trailers

Encapsulation

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THE OSI REFERENCE MODEL

OSI == Open Systems Interconnection

Developed by ISO == International Standards Organization

Principles used to develop OSI Layering:1. Need a layer for each different level of operation.2. Each layer performs a well defined function.3. Each layer has a standard.4. Layer boundaries should minimize data flow across

those boundaries.5. The right number of layers - don't put too many functions

together, but not too many layers either.

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• Physical Layer -

• Purpose -- Transmits raw bits across a medium.

• Electrical -- Concerns are voltage, timing, duplexing, connectors, etc.


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• Data Link Layer -

• Framing -- Breaks apart messages into frames. Reassembles frames into messages. • Error handling -- solves damaged, lost, and duplicate frames.• Flow control -- keeps a fast transmitter from flooding a slow receiver.• Gaining Access -- if many hosts have usage of the medium, how is access

arbitrated.


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• Network Layer -

• Routing -- What path is followed by packets from source to destination. Can be based on a static table, when the connection is created, or dynamic when each packet is sent.

• Congestion -- Controls the number packets in the subnet.

• Accounting -- Counts packets/bytes for billing purposes.

• Heterogeneity -- Interfacing so one type of network can talk to another.


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• Transport Layer -

• Reliability -- Ensures that packets arrive at their destination. Reassembles out of order messages.

• Hides network -- Allows details of the network to be hidden from higher level layers.

• Service Decisions -- What type of service to provide; error-free point to point, datagram, etc.

• Mapping -- Determines which messages belong to which connections.

• Naming -- "Send to node xyz" must be translated into an internal address and route.

• Flow control -- keeps a fast transmitter from flooding a slow receiver.


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• Session Layer –

• Sessions -- Provides services that guarantee a particular message. For instance, a login session could be logged.

• Synchronization-- Provide way to subdivide a long mechanism for reliability.


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• Presentation Layer -

Prettiness

-- Syntax and semantics of information transmitted.

--Understands the nature of the data being

transmitted.

--Converts ASCII / EBCDIC.


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• Application Layer -

• Interfacing -- Terminal type translation.

• File transfer -- Programs able to understand directory structures and naming conventions and map them onto various systems.


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Data Transmission in the OSI Model -

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THE TCP/IP REFERENCE MODEL

Used in the Internet. Common mechanism that is surpassing the OSI Model.

Internet Layer - The IP (Internet Protocol) does delivery and congestion control.

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• Transport Layer - Allows peer entities to communicate.

• TCP -- Transmission Control Protocol provides a reliable connection oriented protocol that delivers a byte stream from one node to another. Guarantees delivery and provides flow control.

• UDP -- User Datagram Protocol provides an unreliable connection-less protocol for applications that provide their own.

• Application Layer - Terminal -- Telnet File transfer -- FTP The Web -- HTTP

THE TCP/IP REFERENCE MODEL

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LAYERS

Transport Network

OSI ConnectionlessConnection-Oriented Connection-Oriented

TCP Connectionless Connectionless Connection-Oriented

COMPARISON OF REFERENCE MODELS

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• NOVELL NETWARE: Heavily used in PC world.

• Proprietary protocol stack Network layer -- IPX - unreliable connectionless Transport layer -- NCP (Network Core Protocol)

- connection oriented• Naming and Addressing --• SAP (Service Advertising Protocol) - Servers

advertise their address to router machines. Clients, when booted, ask for location of nearest server.

Example Networks

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Example Networks

THE INTERNET:• Growing exponentially.• All nodes run TCP/IP. Means that all nodes have an

IP address by which they can be contacted.• Services provided include:

o e-mail o news o remote login

o file transfer o the web

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ISO (International Standards Organization)

ANSI (American National Standards Institute)

NIST (National Institute of Standards and Technology)

IEEE (Institute of Electrical and Electronics Engineering)

IAB (Internet Architecture Board)

Standards

Managing Computer and Communication Networks

Documents

Transcript of Managing Computer and Communication Networks