Computer Networks
Tutorial #14
- What is the conceptual difference between Telstra
Big Pond and
Telstra On Ramp?
- In the lecture, it was noted that the Optus
Spinnaker service was a "wholesale"
Internet Service Provider, as was (for example)
Big Pond Direct and
connect.com.au.
What does this mean, and what is the alternative?
- Two aspects of 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?
A local ISDN data call has a flagfall cost (day rate) of 20 cents (which
includes the first 180 seconds of the call) plus 0.05 cents per
second after 180 seconds has elapsed. Under what conditions do
you think it would be reasonable to configure a local-call ISDN-based system to use
"dial on demand" and/or "bandwidth on demand"?
- 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[1]
for one B channel. How does this compare to using dial-up ISDN over a year? (NB:
NDD3 call costs are 12 cents flagfall plus 0.43483 cents/sec (8am-6pm Mon-Fri),
0.31339 cents/sec (6pm-10pm Mon-Thurs) and 0.18853 cents/sec (other times).
- A Bendigo business wants to build a computer network connecting its
Bendigo branch office with its Melbourne HQ. Explain briefly the
economics of directly connecting the two sites with a "leased-line" service
compared to using the Internet. What is the "downside" of using the
Internet? Use information from Question 3 and
Question 4 to support your argument. NB: this
leads us into a more advanced topic, that of extranets, or
Virtual Private Networks (VPNs). We should get to talk about these
later in the semester.
- 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?
- How is it possible for a frame relay service to drop frames? How can a
user recover if this happens?
- Why would a frame relay customer choose a CIR of zero bps?
[1] 1998 prices. These figures are no longer available
on Telstra's Web Pages.
[Previous Tutorial]
[Tutorial Index]
[Next Tutorial]
[Suggested Solutions]
Phil Scott