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Protocols and Layering

Protocols and Layering. OSI Network Layer Model Define the ‘internet’ and the ‘Internet’. OSI Network Layer Model. Application. Presentation. Application Transport. Session. Transport. Network. Data Transport. Datalink. Physical. Physical Layer.

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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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