Computer Networks

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A History Lesson of Networking

• 1969 – ARPANET, first packet switched network consist of UCLA, Stanford, UC Santa Barbara and Utah University

• 1971 – first email program• 1974 – TCP/IP• 1980’s – Local Area Networks (LANs)• 1984 – OSI Layer• 1990’s – WWW / Internetworking

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Why Networking?

Efficiency and Productivity Reliability Distributed Systems

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What Applications?

Client/Server Business Applications Electronic Messaging Information Retrieval

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Network Classification by Area

Wide Area Network Metropolitan Area Network Local Area Network Personal Area Network Ad Hoc Network

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Protocols

Driving Force: need for different proprietary networking system to communicate

Protocol: set of rules for acceptable behaviour (how communication should take place in)

Specifically: the set of rules used by communicating parties for that

communication to be successful Suite of protocols cover all required behaviour Mostly implemented in Software Complexity demands that protocols are ‘layered’

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Advantages of Layering Protocols

Dividing complex network operation into more manageable layers

Defining the standard interface for the “plug-and-play” multi-vendor integration

Facilitate Modular Engineering Simplifies Teaching and Learning

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ISO/OSI Reference Model

ISO in 1984Open Systems Interconnect (OSI)A design guideline for network layeringAbstract layers provide different servicesDefines 7 layers of serviceEach layer provides service to adjacent layersEach layer communicates with same layer in remote

machine…

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OSI Reference Model

Physical Layer

Link Layer

Network Layer

Transport Layer

Session Layer

Presentation Layer

Application Layer

Physical Layer

Link Layer

Network Layer

Transport Layer

Session Layer

Presentation Layer

Application Layer

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Layer 1 - Physical

Physical Layer:Move bits between devicesSpecifies voltage, wire speed, and pin out cablesPasses data up to data link layer (and receives

from data link layer)

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Layer 2 – Data Link

Data Link Layer:Performs framing of bits, flow and error control but

not correctionResponsible for transmission of frames across the

physical linkProvide access to media using MAC addressPasses data between physical and network layers

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The Institute of Electrical and Electronics Engineers (IEEE) has subdivided the data link layer into two sublayers: Logical

Link Control (LLC) and Media Access Control (MAC).

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The Logical Link Control (LLC) 802.2 sublayer is responsible for identifying Network Layer protocols and then encapsulating them. An LLC header tell the Data Link Layer what to do with the packet if a frame is coming. Also provide flow control and sequencing of control bits

The Media Access Control (MAC) sublayer of the data link layer manages protocol access (logical topologies) to the physical network medium. The IEEE MAC specification defines MAC addresses, which enable multiple devices to uniquely identify one another at the data link layer. IEEE 802.3 dan 802.5

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Layer 3 - Network Network Layer:

Passes data between data link and transport layers

Responsible for routing data across a network, from source to destination using network-wide addressing

Pass data between (separate) subnetworks Hides network topology from higher layers

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Layer 4 - Transport

Transport Layer:Passes data between network and session layersProvides reliable end-to-end delivery of data,

including flow and error control of packetsFragmentation of large messagesQuality of Service (QoS), usually with layer 3Last of the pure network layers

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Layer 5 - Session

Session Layer:Passes data between presentation and transport

layersResponsible for managing network sessions

(series of related data streams)Provides synchronization and scheduling

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Layer 6 - Presentation

Presentation Layer:Passes data between application and session

layersProvides translation services for data to ensure

applications are using compatible formatsE.g. converting from ASCII to EBCDIC text

representations

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Layer 7 - Application

Application Layer:Passes data to presentation layer (and receives

from presentation layer)… to and from the user!Communicates with remote applicationsDetermines the user capability within the network

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Data Encapsulation

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Data Encapsulation

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OSI Layer vs. TCP/IP Layer

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IP

TCP UDP

FTP – File Transfer ProtocolHTTP – Hypertext Transfer ProtocolWAP – Wireless Application ProtocolSMTP – Simple Mail Transfer Protocol

e.g. IEEE 802.x1-2

4

5-7

3

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Some Protocols in TCP/IP Suite

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Quiz

ProtocolsWhat are they?Why do we layer protocols?

ISO/OSI – 7 layer reference modelHow does the OSI abstract services?How does data pass between layers

(local/remote)?How does Internet stack relate to OSI?