Protocol Architecture and Design: Understanding Layers and Communication in Networking, Slides of Data Communication Systems and Computer Networks

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Chapter 2

Protocols and Architecture

Need For Protocol Architecture

• E.g. File transfer
  • Source must activate comms. Path or inform network of destination
  • Source must check destination is prepared to receive
  • File transfer application on source must check destination file management system will accept and store file for his user
  • May need file format translation
• Task broken into subtasks
• Implemented separately in layers in stack
• Functions needed in both systems
• Peer layers communicate Docsity.com

Protocol Architecture

• Task of communication broken up into modules
• For example file transfer could use three modules - File transfer application - Communication service module - Network access module

Simplified File Transfer Architecture

Network Access Layer

• Exchange of data between the computer and the network
• Sending computer provides address of destination
• May invoke levels of service
• Dependent on type of network used (LAN, packet switched etc.)

Transport Layer

• Reliable data exchange
• Independent of network being used
• Independent of application

Protocol Architectures and Networks

Addressing Requirements

• Two levels of addressing required
• Each computer needs unique network address
• Each application on a (multi-tasking) computer needs a unique address within the computer - The service access point or SAP - The port on TCP/IP stacks

Protocol Data Units (PDU)

• At each layer, protocols are used to communicate
• Control information is added to user data at each layer
• Transport layer may fragment user data
• Each fragment has a transport header added
  • Destination SAP
  • Sequence number
  • Error detection code
• This gives a transport protocol data unit

Protocol Data Units

Operation of a Protocol

Architecture

Standardized Protocol

Architectures

• Required for devices to communicate
• Vendors have more marketable products
• Customers can insist on standards based equipment
• Two standards:
  • OSI Reference model
    • Never lived up to early promises
  • TCP/IP protocol suite
    • Most widely used
• Also: IBM Systems Network Architecture (SNA)Docsity.com

OSI - The Model

• A layer model
• Each layer performs a subset of the required communication functions
• Each layer relies on the next lower layer to perform more primitive functions
• Each layer provides services to the next higher layer
• Changes in one layer should not require changes in other layers

OSI Layers