Data Communication. OSI-7Layer & TCP/IP

Post outline 

• Protocol Layering 

• OSI Model

• TCP/IP Protocol suite

Protocol Layering

  Layering can be converted to modularization. For example, two peoples communicate through the mail system. 

Ref: Data Communications and Networking 5th edition, Forouzan, p 33

  In this case, each layer just does their's job. Post service just transfer Encrypted mail. This layer doesn't need any other process. Protocol layering is almost same with this example.

  Most important things on this subtopic is 'All of layer communicate peer to peer (same layer to same layer)'.

OSI Model

  The OSI (

Open System Interconnection) model is a layered framework for the design of network systems that allows communication between all types of computer systems. It consists of seven separate but related layers,  each of which defines a part of the process of moving information across a network.

Seven layers of the OSI model
Ref: Data Communications and Networking 5th edition, Forouzan, p 44

  In the past, development for layer 1 and 2 is the main issue, but after that it changes main issue to higher layer development.

These figures are summarized of below the description.

Ref: Data Communications and Networking chapter 2 slide pdf

Ref: Data Communications and Networking chapter 2 slide pdf

Layers description

•   Physical layer

  The physical layer is responsible for movements of individual bits from one hop (node) to the next. + error check
  → make bit by bit connection between sender and receiver.

    Core responsibilities

1. Representation of bits → sending a data
2. Error control

• Data link layer

  The data link layer is responsible for moving frames from one hop (node) to the next.

    Core responsibilities

1. Hop-to-hop (node-to-node) delivery
2. Framing → divide a data to packet
          (layer 1&2: frame,  layer 3: datagram, layer4: packet) 
3. Physical addressing= MAC address
4. Flow control → control the speed of sending and receiving
5. Error control

• Network layer

  The network layer is responsible for the delivery of individual packets from the source host to the destination host.

    Core responsibilities

1. End-to-end (source-to-destination) delivery → find routing path
2. Logical addressing = IP address

• Transport layer

  The transport layer is responsible for the delivery of a message from one process to another.

    Core responsibilities

1. Process-to-process delivery ┓
2. Service-point addressing.    ┛find exact process → use port number 
3. Segmentation and reassembly → decode flexible length of data
4. Connection control → check connecter information then connect.
5. Error control → in the computer hardware, data transmission could occur an error

• Session layer

  The session layer is responsible for dialog control and synchronization.

    Core responsibilities

1. Dialog control → for example, when a telephone call synchronizes voice sending and receiving

• Presentation layer

  The presentation layer is responsible for translation, compression, and encryption.

Core responsibilities

1. Compression and encryption.

• Application layer

  The application layer is responsible for providing services to the user.

    Core responsibilities

1. Providing UI and other functions

TCP/IP Protocol suite

  TCP/IP(Transmission Control Protocol/Internet Protocol) is a protocol suite used in the Internet today. It is a hierarchical protocol made up of interactive modules, each of which provides a specific functionality. 

  The layer in the TCP/IP protocol suite do not exactly match those in the OSI model. The original TCP/IP protocol suite was defined as having four layers: host-to-network, internet, transport, and application. However, when TCP/IP is compared to OSI, we can say that the TCP/IP protocol suite is made of five layers: physical, data link, network, transport, and application. (Look a figure below)

Ref: Data Communications and Networking chapter 2 slide pdf

Difference with OSI-7layer 

1. The protocol is limited (Some of the functionalities of the session layer are available in some of the transport-layer protocols.)
2. It represented only 5 layers (Application layer  is not only one piece of software.)

Summary of address name and packet name

Ref: Data Communications and Networking chapter 2 slide pdf