Computing 205/406 & IT8

Tutorial #12

1. Calculate how much it would cost to transfer 1 Mbyte between Bendigo and Melbourne using the PSTN. Assume that you've got all of the hardware needed at each end of the link (ie 2 phone services, 2 modems), and that the only charge is the STD phone call. Assume also that the call is done at "Day" rate (is, during working hours), for which the charge is (was, last time I looked!) $3.50 cents for each 10 minutes from Bendigo to Melbourne. We'll further assume that there are no overheads (ie: we asume there are 8 bits per byte transferred, ignore the "real life" extras). Work your calculations for data rates of 2400Êbps, 14400 bps and 28800 bps. What if the connection was between Bendigo and Castlemaine ($1.50 per 10 minutes)? What about Bendigo to Perth ($5.12 per 10 minutes)?

2. An ISDN data call between Bendigo and Melbourne (rate: NDD3) costs (day rate) 14.0¢ flagfall and 0.50006¢ per second. Calculate again the cost to transfer 1 Mbyte between Bendigo and Melbourne, except this time using ISDN. Assume, as before, that all of the necessary phone services are already connected and paid for for the purposes of this question. Recalculate for Bendigo to Castlemaine (NDD2: 14¢ flagfall, 0.23535¢ per sec).

3. Attempt to calculate the minimum price for a data service whereby an office in Castlemaine sends a daily transaction record of approximately 100 Kbytes to a Bendigo head office at the end of each working day. Include the cost of all equipment and services (modems, installation, etc) You can realistically assume there are 250 working days in a year. You should consider PSTN and ISDN initially. Is using the Internet (using email to transfer the data) a viable alternative, given that a local call is required at each end, and that ISPs typically charge $5.00 per hour for dial-in access.

4. In the lecture, it was noted that dial-in routers used by ISPs usually are configured so that customer's systems appear to be conncted to the ISP's own LAN. How is this done?