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ENGS 112 Lecture 3 Packet Switching Chapter 3, Walrand WWW links, eg

This lecture discusses the functions of packet networks and the OSI reference model, which helps understand network terminology and organization. It covers the different layers of the model, including the physical layer, data link layer, network layer, transport layer, session layer, presentation layer, and application layer.

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ENGS 112 Lecture 3 Packet Switching Chapter 3, Walrand WWW links, eg

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  1. ENGS 112 Lecture 3 Packet Switching Chapter 3, Walrand WWW links, eg

  2. OSI Reference Model Reference model...helps to discuss packet network functions. Many networks do not follow the protocol but it is useful to know for terminology and organizational purposes.

  3. Layer 1: Physical Layer • Unreliable communication of bits between two points. • Link = transmitter, receiver, medium • Synchronization header required to indicate transmission • Unreliable....errors are not detected or corrected in this layer • Characteristics – bps rates and bit error rates

  4. Layer 2: Data Link Layer • Supervises transmission of packets • Adds sequence numbers and some form of error detection • Requests retransmission at link level if appropriate • This layer used for link level retransmission • End-to-end error detection and retransmission done • at Layer 4 (network) for networks with low BER. • Characteristics • Sublayer 2a: Media Access Control (MAC) • - identify the destination hardware address • in a shared medium • Sublayer 2b: Logical Link Control • - error detection and retransmission for • shared media (Ethernet, wireless, etc)

  5. Layer 3: Network Layer • Routes packets between computers using link by link • routing as specified in a routing table. • Specifies packet formats, addressing schemes and • routing protocols

  6. Layer 4: Transport Layer • Delivers messages between “ports” or Transport • Service Access Points (TSAP’s) • email, web servers, file transfer are standard services • with fixed, allocated ports. • Need to know the port or check with a server to locate port • Connection or connectionless (connect or not) • Messages decomposed into packets, sequenced and given TTL • Ping, traceroute

  7. Layer 5: Session Layer • Supervises dialogs between computers Layer 6: Presentation Layer • Encryption, number conversion, etc Layer 7: Application Layer • Network services used by user applications • remote login, directory services

  8. Ethernet (IEEE 802.3) Multiple Access Control in a broadcast medium CSMA/CD Implications and operational requirements LAN interconnections Spanning tree algorithm for bridges

  9. OEE (Due Friday, April 14) Walrand page 93+ 1. 2. 3. 4. 12. 16. 20. 25. Walrand page 149+ 1. 5. 9. 11.

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