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Protocols and Layering

Learn about OSI network layer model, internet protocols, and layering concepts in computer networking. This guide covers physical, data link, network, transport layers, protocols, and more.

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Protocols and Layering

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  1. Protocols and Layering • OSI Network Layer Model • Define the ‘internet’ and the ‘Internet’

  2. OSI Network Layer Model Application Presentation Application Transport Session Transport Network Data Transport Datalink Physical

  3. Physical Layer • Physical Layer: covers the physical interface and defines the rules by which bits are transferred.

  4. Datalink Layer • The data link layer provides reliable (or unreliable) transit of data across a physical network link. • Different data link layer specifications define different network and protocol characteristics, including ?? • WAN examples ?? • High level Data Link Control HDLC • The point-to-point protocol PPP • For a LAN, IEEE has defined layered architecture: • Logical Link Layer (LLC) : higher level protocol logic- retransmissions, segmentation • Machine Access Control (MAC): abstracts the PHY layer.

  5. 802.2/802.3 Frame Format MAC Dest Address (6) MAC Source Address (6) CRC (4) Length (2) DSAP SSAP cntl code type (1) (1) (1) (3) (2) Data ( 46-1500) Preamble (7) Type indicates the type of protocol contained in the data …. This is how the LLC layer forwards received frames to the correct next layer (example - ARP or IP ) Payload : ARP frame, IP packet Maximum Transmission Unit (MTU) defined by the physical medium and the link layer

  6. Network Layer • The network layer provides routing and related functions that enable multiple data links to be combined into an • internetwork. • This is accomplished by the logical addressing (as opposed to the physical addressing) of devices. • The network layer supports both connection-oriented and connectionless service from higher-layer protocols. • Network-layer protocols typically are routing protocols

  7. Transport Layer • The transport layer implements reliable (or unreliable) internetwork data transport services that are transparent to upper layers. • Transport-layer functions could include • Error detection – with checksums or CRCs. • Error recovery (reliable transfer) (TCP only) • Acknowledgements • Timeouts • Retransmissions • Stream or datagram service – maps to TCP and UDP resp. • Oriented towards window+ACK OR rate-based • Flow control (TCP only) • Window flow control • End-to-end network congestion control (TCP only) • Reacts to implicit signals of network congestion (packet loss events) or explicit signals of network congestion (Explicit Congestion Notification)

  8. Protocols • A Protocol defines the rules and conventions that govern how computers exchange information over a network medium. • Examples: • Application protocols • Transport protocols • Network protocols • LAN/WAN protocols • Physical protocols HTTP, telnet,... TCP,UDP IP, ICMP, RIP IEEE 802.2, PPP Ethernet

  9. Introduction • Internetworking: a collection of individual networks connected by intermediate networking devices that function as a single large network. • An internet approach hides lower layer details from the user via network-level interconnection methods. The Internet is an implementation of a network based on the internet approach. The term TCP/IP refers to the large number of protocols and standards that have been developed by the IETF (the Internet’s standards organization) The IETF issues Request For Comments - that represent the protocols and standards that have been reviewed, refined, and agreed upon by the majority in attendance at voting meetings.

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