Assigment # 1

1.)Explain the cirumstances under which a token-ring netwrok is more effective than an Ethernet network.

In a Token Ring network, each computer is constantly in direct contact with the next node in the ring but a Token Ring network cannot communicate within itself if any one of the rings is broken.
The token ring network architecture was developed by IBM and later standardized as the IEEE 802.5 standard and is the second most widely-used protocol on local area networks after Ethernet.

Token ring is more effective under high sustained load, and each slot may be used to carry a message, providing highthroughput.

2.) Although security issues were not mentioned in this chapter, every network owner must consider them. Knowing that open networks all data to pass to every node, describe the posssible security concerns of open network achitectures. include the implicatiions of passing logon procedures, user IDs, and passwords openly on the network.

Active networks are an exciting development in networking services in which the infrastructure provides customizable network services to packets. These custom network services can be deployed by the user inside the packets themselves. Furthermore, the custom network services require that the infrastructure performs much more sophisticated operations on packets than the traditional forwarding. Consequently, there are heightened concerns from users and network operators about security. We discuss security requirements and issues in active networks with respect to authentication and authorization in a node. We describe our prototype implementation of a solution to those issues. We go on to describe a security architecture derived from our experience and relate our prototype to the architecture.

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.
Prevention => A common scheme for preventing deadlock in networks is the virtual channel method of Dally and Seitz [DS87]. Due to the nature of this scheme, an otherwise completely uniform network will have non-uniformities introduced into it. The variations introduce several effects, ranging from limitations on overall network performance to differences in observed network characteristics from node to node and from message to message.

Detection and Recovery => Deadlock detection and recovery-based routing protocols in wormhole networks have gained attraction because they do not restrict routing adaptability unlike deadlock avoidance-based protocols. Network performance largely relies on the accuracy of deadlock detection. The lower the number of packets presumed as deadlocked by a protocol, the better the network performs, since the network rarely enters into deadlock state in reality and those packets presumed as deadlocked are usually killed or recovered according to a recovery procedure, causing extra overhead to the network. This paper proposes a deadlock detection protocol based on the turn model. It declares only one packet per simple cycle of blocked packets as deadlocked in most cases, thus considerably reducing the number of false deadlock detections over previous protocols. This results in less number of unnecessary recoveries to resolve deadlock. This achievement is made with lower hardware complexity than a most sophisticated previous protocol. The simulation study shows that our protocol outperforms previous protocols in the number of deadlock detections.

Avoidance => A feasible solution to cope with such unpredictable situations is to introduce an automated manufacturing system characterized by high flexibility, autonomy and cooperation. Much research has been done on negotiation-based scheduling and control under the distributed control architecture due to its operational flexibility and scalability. Despite many advantages, the probability of the system stalling at a deadlock state is high. Specifically, it is difficult to detect impending part flow deadlocks within the system. A system request network model is defined here to analyse various deadlock situations. Request cycles are then identified by a virtual part flow control mechanism. No request cycle in the system request network represents 'no system deadlock'. For any request cycle, a deadlock analysis is performed. If any request cycle exists that represents either a part flow deadlock or an impending part flow deadlock, then the system will be deadlocked. The proposed model can analyse all types of impending part flow deadlocks. Furthermore, it is more efficient through the reduction of search space, is applicable to various configurations and is less restrictive in dynamic shop floor control.

4.) Assuming you had sufficient funds to upgrade only one component for a system with which you are familiar, explain which component you would choose to upgrade to improve overall performance, and why?

Computer workstations are now an indispensable component of every office. Faculty, staff, and administrators use their workstations in every aspect of their duties. Since computers on campus are connected in a network, it is essential that each workstation represent current technology and be able to run the essential applications that define the University's business environment. It is also essential that each departmental file server be upgraded on a regular basis so that the network can function effectively. This plan describes an orderly approach to upgrading or replacing all computer workstations and large file servers on a regular basis, and it enables budget authorities to project the costs of such upgrades. This proposal does not affect computers used for special instrumentation purposes in University research laboratories.