August
1999 QUESTION 3 Total Marks: 20 Marks |
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questions
SUGGESTED SOLUTIONS |
| (a) | Name and briefly explain any three services provided by telecommunications service providers. | [6] |
| Digital
leased line support speeds from 2600bps to 140Mbps. specially suitable for private data
networks other relevant explanations also acceptable Analog leased line similar to digital leased line but a modem is required. Cheaper option as compared to digital leased line but speeds lower than of digital leased lines. Other relevant explanations also accepted. Domestic and international telephone services user requires a modem in order to transmit data. Other services named such as ISDN or packet switched services are also acceptable.
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| (b) | Typically a bridge connects LANs of similar architecture. Can a bridge connect networks of different architecture? Explain your answer. | [4] |
| Yes. It is
possible to connect LANs for different MAC sublayers using a bridge provided that these
network have the same 802.2 logical link control format. This however requires a higher
level of protocol conversion.
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| (c) | Give three reasons for breaking up a LAN into smaller interconnected LANs. Provide explanations for your reasons. | [6] |
| Reducing
Load: if LAN is divided into segments where most traffic does not have to leave segment,
then overall congestion is reduced. Security: data passing between two machines on one segment is not accessible to machines on other segments. Reliability: if one segment fails, the others may continue operating.
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| (d) | At which OSI layer(s) does the router operate? What types of issues are handled by the router? | [4] |
| Network
layer. Different addressing schemes: routers used 2 level addresses namely the address of the network and the address of the node within that network. Different packet sizes: different sub-networks have restrictions on packet sizes they can handle. Therefore the router has to deal with segmentation and reassembly.
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