What is a Protocol?

A Human Analogy

Excuse me...    
   
    Yes?
   
What time it is?    
   
    12:30pm
   
Excuse me...    
   
    Get lost!
   
????    

Network Protocols

Request for connection    
   
    Connection granted
   
Time request    
   
    Current time 12:30pm
   
Request for connection    
   
    Connection refused
   
Program closed    
A protocol defines the format and the order of messages exchanged between two or more communicating entities, as well as the action taken on the transmission and/or receipt of a message or other event.

End Systems, Clients and Servers

  • End systems - computers connected to the Internet.
  • Hosts -- same things.
  • Clients -- usually desktops and mobile PCs.
  • Servers -- more powerful machines hosting server programs.

    Connectionless and a Connection-Oriented Service

    Connection-oriented service:
  • reliable data transfer
  • flow control
  • congestion control

    Protocol Layers and Their Service Model

    A Human Analogy

    Lawyer   Lawyer
     
    Secretary   Secretary
     
    Mailmen   Mailmen
     
    Post Office   Post Office
     
    State Sorting Office   State Sorting Office
     Postal plain 

    Protocol Layering

    Reasons for having a layered conceptual model:

  • divides complex system into discrete and understandable subsets
  • standardizes layer interfaces for programmers, encouraging modular engineering
  • isolates upgrades to a layer from other layers in the stack
  • explains the general function of each layer

    Internet Protocol Stack. OSI Model.

    OSI (Open System Interconnection) Reference Model Layers
    Layer Unit Function
    Application Data Provides the interface and services that support user applications and provides general access to the network.
    Presentation Data The translator for the OSI model; responsible for the conversion of data into a generic format and the coding of data using various encryption methods.
    Session Data Establishes and maintains the communication link between communicating computers.
    Transport Segment Responsible for end-to-end data transmission, flow control, error checking, and recovery.
    Network Packet Provides the logical addressing system used to route data from one node to another.
    Data Link Frame Responsible for the framing of data packets and the data movement across the physical link between two nodes.
    Physical Bit Manages the process of sending and receiving bits over the physical network media (the wire and other physical devices).

    Internet Protocol Stack. Textbook Model.

    Layer Unit Function
    Application Message Provides the interface and services that support user applications and provides general access to the network. Responsible for the conversion of data into a generic format and the coding of data using various encryption methods.
    Transport Segment Responsible for end-to-end data transmission, flow control, error checking, and recovery.
    Network Datagram Provides the logical addressing system used to route data from one node to another.
    Data Link Frame Responsible for the framing of data packets and the data movement across the physical link between two nodes.
    Physical 1-PDU Manages the process of sending and receiving bits over the physical network media (the wire and other physical devices).

    Power Point Presentation from the book web-site.