adam's notes

TCP-IP

The Transmission Control Protocol/Internet Protocol (TCP/IP) suite is used to perform logical addressing and data forwarding functions on most networks.

A protocol is a set of rules that allows networked hosts to communicate data in a structured format.

  • Often, several protocols used are designed to work together as a protocol suite
  • Most networks have converged on the use of the Transmission Control Protocol/Internet Protocol (TCP/IP) suite
    • function of each protocol can be better understood by dividing network functions into layers
    • Protocols operating at lower layers are said to encapsulate data from higher protocols
    • Each protocol adds its own header fields to data it is transporting from an upper layer protocol

Layers

  • the TCP/IP suite uses a model with four distinct layers

  • Link layer is responsible for putting frames onto the physical network
  • does not contain TCP/IP protocols as such
  • at this layer, different local networking products and media can be used
    • Ethernet or Wi-Fi.
  • WAN interfaces, such as DSL and cable modems, also work at the Link layer
  • Communications on this layer take place only on a local network segment and not between different networks
  • On an Ethernet or Wi-Fi segment, data at the link layer is packaged in a unit called a frame
  • node interfaces are identified by a MAC address

Internet Layer

The Internet Protocol (IP) provides packet addressing and routing within a network of networks.

  • device that communicates on IP network is generically referred to as an end system host
  • For data to be sent from one IP network to another, it must be forwarded by an intermediate system (a router)
  • provides best effort delivery that is unreliable and connectionless
    • packet might be lost, delivered out of sequence, duplicated, or delayed
  • deals with addressing

Transport Layer

  • Transport layer determines how each host manages multiple connections for different application layer protocols at the same time
  • implemented by one of two protocols:
    • Transmission Control Protocol (TCP)
      • guarantees connection-oriented forwarding of packets
      • can identify and recover from lost or out-of-order packets
        • mitigates the inherent unreliability of IP
      • used by most TCP/IP application protocols, as failing to receive a packet or processing it incorrectly can cause serious data errors
    • User Datagram Protocol (UDP)
      • provides unreliable, connectionless forwarding
      • faster than TCP
      • comes with less of a transmission overhead
        • does not need to send extra information to establish reliable connections
      • used in time-sensitive applications where a few missing or out of order packets can be tolerated
        • E.g., speech or video
        • manifests as a glitch in video or audio, instead of crashing the application

Application Layer

  • contains protocols that perform some high-level function
  • numerous application protocols in the TCP/IP suite
    • used to configure and manage network hosts and to operate services
    • each application protocol uses a TCP or UDP port to allow a client to connect to a server

Info

  • TCP/IP was originally developed by the US Department of Defense
    • but is now an open standard to which anyone may contribute
  • Developments are implemented through the Internet Engineering Task Force (IETF), which is split into working groups
  • Standards are published as Request For Comments (RFCs)
  • The official repository for RFCs is at rfc-editor.org

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