Tuesday, November 25, 2008
Tuesday, September 23, 2008
3. Remembering the discussion of deadlocks, if you were designing a networked system, how would you manage the treat of deadlocks in your network? Consider all of the following: prevention, detection, avoidance, and recovery.
· Deadlock Prevention:
Preventing deadlocks by constraining how requests for resources can be made in the system and how they are handled (system design).
The goal is to ensure that at least one of the necessary conditions for deadlock can never hold.
· Deadlock Avoidance:
The system dynamically considers every request and decides whether it is safe to grant it at this point,
The system requires additional apriori information regarding the overall potential use of each resource for each process.
Allows more concurrency.
Similar to the difference between a traffic light
and a police officer directing traffic.
1. Explain the cirumstances under which a token-ring netwrok is more effective than an Ethernet network.
-Stations on a token ring LAN are logically organized in a ring topology with data being transmitted sequentially from one ring station to the next with a control token circulating around the ring controlling access. This token passing mechanism is shared by ARCNET, token bus, and FDDI, and has theoretical advantages over the stochastic CSMA/CD of Ethernet.
Physically, a token ring network is wired as a star, with 'hubs' and arms out to each station and the loop going out-and-back through each.
When token ring LANs were first introduced, there were widely circulated claims that they were superior to Ethernet.[2] These claims did hold up when tested.[3]
With the development of switched Ethernet and faster variants of Ethernet, token ring architectures lagged badly behind Ethernet in both performance and reliability. The higher sales of Ethernet allowed economies of scale which drove down prices further, and added a compelling price advantage to its other advantages over token ring.
Token ring networks have since declined in usage and the standards activity has since come to a standstill as switched Ethernet has dominated the LAN/layer 2 networking market.
-Stations on a token ring LAN are logically organized in a ring topology with data being transmitted sequentially from one ring station to the next with a control token circulating around the ring controlling access. This token passing mechanism is shared by ARCNET, token bus, and FDDI, and has theoretical advantages over the stochastic CSMA/CD of Ethernet.
Physically, a token ring network is wired as a star, with 'hubs' and arms out to each station and the loop going out-and-back through each.
When token ring LANs were first introduced, there were widely circulated claims that they were superior to Ethernet.[2] These claims did hold up when tested.[3]
With the development of switched Ethernet and faster variants of Ethernet, token ring architectures lagged badly behind Ethernet in both performance and reliability. The higher sales of Ethernet allowed economies of scale which drove down prices further, and added a compelling price advantage to its other advantages over token ring.
Token ring networks have since declined in usage and the standards activity has since come to a standstill as switched Ethernet has dominated the LAN/layer 2 networking market.
Ethernet
Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium. The methods used show some similarities to radio systems, although there are fundamental differences, such as the fact that it is much easier to detect collisions in a cable broadcast system than a radio broadcast. The common cable providing the communication channel was likened to the ether and it was from this reference that the name "Ethernet" was derived.
A 1990s Ethernet network interface card. This is a combination card that supports both coaxial-based using a 10BASE2 (BNC connector, left) and twisted pair-based 10BASE-T, using a RJ45 (8P8C modular connector, right).
Despite the significant changes in Ethernet from a thick coaxial cable bus running at 10 Mbit/s to point-to-point links running at 1 Gbit/s and beyond, all generations of Ethernet (excluding early experimental versions) share the same frame formats (and hence the same interface for higher layers), and can be readily interconnected.
Friday, November 9, 2007
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