Contention Evalution Factors-8 ccategories
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This document discusses the characteristics and functioning of contention-based computer networks. Contention networks rely on stations listening to the transmission medium before transmitting to avoid collisions. They work best under light-to-medium traffic loads and are limited by network length and propagation delays. Refinements like CSMA, CSMA/CD, and CSMA/CA were developed to improve efficiency by detecting and avoiding collisions. Contention networks provide easy expansion and resilience to station failures. However, they have high overhead and access delays that increase significantly under heavy traffic loads.
Contention Evalution Factors-8 ccategories
- 2. • Smooth functioning of a contention-based network is dependent upon high availability of the transmission media and a low collisions rate.
- 3. The network is characterised by the following : • Message length • Traffic volume • Network length constraints • Performance • Overhead • Access Delay • Station Failures • Expansion
- 4. Message length : Messages are divided into short packets in order to reduce the amount of data that must be rebroadcast after collisions.Normally, the original message is also fairly short.
- 5. Traffic volume : Contention protocols are designed for networks with low traffic volume,that is one with few time. Low traffic volume implies a limited number of attached workstations.
- 6. Network length constraints : The longer the network,the greater the chance of collision. Contention networks are limited by the time needed for a signal to travel the length of the transmission media and have an acknowledgement returned (that is propagation delay).
- 7. Performance : Contention networks are most effective under light to medium load. Performance under those conditions is excellent. Under heavy load, a contention networks tends to be unstable,with service rapidly degrading.
- 8. Overhead : Contention networks have high overhead because of collisions and the need to acknowledge the successful receipt of messages.
- 9. Access Delay : Delay on the network is generally moderate to long depending on traffic. Delay under heavy load can be significantly higher than load alone would seem to dictate.
- 10. Station Failures : Because operation of the network is not dependent on the presence or absence of any one workstation,failure of workstation inconveniences only its users. Rarely does failure of a single station disrupt service on the whole network.
- 11. Expansion : Addition of new workstations is relatively easy because to be included in the network,the workstation simply must recognise its own unique address. Expansion may be achieved with minimal disruption of the network.
- 12. • Refinements on contention procedures are used by many of the current microcomputer local networks. • These refinements are : Carrier Sense Multiple Access(CSMA) Carrier Sense Multiple Access with Collision Detection(CSMA/CD) Carrier Sense Multiple Access with Collision Avoidance(CSMA/CA)
- 13. • STEP 1 : Station A Listening Station B Quiet
- 14. • STEP 2 : Station A Sending Station B Listening Message A
- 15. • Each will be discussed in separate sections. • For all practical purposes, charcteristics of these refinements are identical to the charcteristics of simple contention.
- 16. References • Information Technology Today By S. Jaiswal • https://en.wikipedia.org/wiki/Workstati on