Computer Networks

Tutorial #12

1. The semi permanent Internet link between bendigo and Bundoora runs at 252 Kbps. Why such a funny number?

2. Two aspects of the ISDN service which are emphasised by the marketing people are "dial on demand" routing, and "bandwidth on demand" data transfer. What do you think these terms refer to? Given that a NDD3 data call costs (day rate. NDD3 is 50km to 165 km) $0.39 for 1 minute, $0.91 for three minutes, $1.69 for six minutes, $2.73 for 10 minutes, $5.34 for 20 minutes and $7.95 for 30 minutes, what do you extimate to be the fixed overhead cost of each call?

3. What would be the total cost (including installation and annual charges) of a 64Kbps semi-permanent link between Bendigo and Castlemaine, given that the SPC cost alone is $5940 per annum (26 to 50 km). Extra information required for this question is in the previous tutorial.

4. A Bendigo business is investigating an ISDN SPC connection to its head office in Melbourne. The SPC charge for this distance is $9720 per annum for one B channel. How does this compare to using dial-up ISDN (see Q.2) over a year?

5. Explain how a frame relay service at a port speed of 64 kbps differs from an ISDN semi permanent link at the same speed. In particular, why would you expect the frame relay service to be cheaper?

6. How is it possible for a frame relay service to drop frames? How can a user recover if this happens?

7. Why would anyone choose a CIR of zero bps?

8. (Hard thinking question) One of the weaknesses of SLIP is that it doesn't have any provision for negotiating an IP address when it is used to connect to an ISP. However, dynamic IP addresses can still be used with SLIP due to a hack. What do you suppose this hack is?