The paper “ Application of Polling Models to Computer Networks” is an affecting variant of assignment on information technology. Polling can be used in routers where the router (controlling device) repeatedly checks the state of the external device (low-level hardware) its forwarding packets to whether it’ s ready by reading the memory addresses through the use of memory-mapped I/O. Polling can also be used with busy-wait polling where when the receiving device is ready, the router then forwards packets to it otherwise the router performs other tasks. Polling in networks has its own advantage in that it is efficient in applications where the inbound data is a lot as in the case of a router receiving more traffic than it is able to forward.
The disadvantage of polling in networks is that the network becomes unpredictable and undependable causing polling to occur at all times. Secondly, in case the rate of polling is low trouble with latency might happen. Lastly, polling can lead to wastage of CPU cycles if no data is present when polling (Takagi, H. 1991, 193). Answer #1(b)In a Token Bus Network, every device has knowledge of its succeeding devices network address.
The devices are interconnected to the mainframe by a copper coaxial cable (communication bus) where the Token Bus protocol creates a token that manages a device's access to the communication bus. Any device that has the token packet is granted permission to transmit data. When done transmitting or when the transmission time specified by the network expires, the device sends the token packet to the successor device in the logical ring. This ensures that no two devices are transmitting at the same time and also gives each device time to transmit (Park, H.
Ahn, S., and Kwon, W. 1993, 412). In Token Bus networks as the transmission speed increases, the network efficiency drops. This is because the communication medium, a coaxial cable has a low transfer rate of 10 Mbps which leads to a reduced data transfer rate thus requiring more time for transmission compared to the Ethernet cable with a transfer speed of 100Mbps. Answer #1(c) (i) The nodes employ technology for media access control in order to be able to transmit simultaneously on the same bus.
The bus has only one channel for receiving and sending signals. However, it does not support receiving and sending signals at the same time. Therefore, if two nodes try to simultaneously send data collision happens since the shared media is half-duplex. Increased collision results in a network of low quality. A bus topology is considered a broadcast network because when one node transmits a signal, the signal travels in both directions of the bus to every node in the topology. The bus must, therefore, handle all the signals coming from the various nodes connected to it.
However, because only one signal can be sent or received at one time, it limits the data exchange rates by decreasing the available bandwidth. Answer #1(c) (ii)Switches help in reducing collisions where they are employed to divide big collision domain to small collision domains causing every port in the switch operates in a different collision domain. The switch also forwards broadcast packets to every port of the switch where each switch floods all ports with the broadcast packet.
A bridge also assisting in reducing collision by dividing the one collision domain to many small collision domains, buffering and forwarding frames. However, devices connected to switches and bridges belong to one broadcast domain. A repeater addresses attenuation where upon receiving a signal it rebuilds it and sends it out. A repeater extends to broadcast and collision domains. Hubs extend collision and broadcasts where upon receiving a data packet at one port, the hub transmits that packet to its other ports. Devices connected to a hub belong to one broadcast and collision domain.
Thus, if two devices connected to the same network send data packets simultaneously, a collision occurs.
Baker, F., and Coltun, R., 1995. OSPF version 2 management information base (No. RFC 1850).
Malkin, G., 1994. Routing Information Protocol (RIP) Version 2 Carrying Additional Information. Request for Comments (RFC 1723).
Park, H.S., Ahn, S.C., and Kwon, W.H., 1993. Performance and parameter region for real-time use in the IEEE 802.4 token bus network. IEEE Transactions on Industrial Electronics, 40(4), pp.412-420
Takagi, H., 1991. Application of polling models to computer networks. Computer Networks and ISDN Systems, 22(3), pp.193-211.