Computer Networks
Tutorial #13
- What is the conceptual difference between a supplier of
telecommunications services and an Internet Service Provider (ISP)?
NB: In Australia, these differences are exemplified by Telstra's
BigPond service
(which is an ISP) and Telstra
On Ramp,
which is a telecommunications service.
- Some notable "wholesale" Australian Internet Service Providers
include C&W Optus
Spinnaker, Telstra BigPond
Direct and
connect.com.au.
What does mean to say these services are "wholesale", 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 Telstra local ISDN data call in Australia
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 Microlink
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 install a point-to-point link connecting its
Bendigo branch office with its Melbourne HQ. Explain briefly the
economics of directly connecting the two sites with a "leased-line"
service such as an ISDN SPC 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 may 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?
- Want a challenge? Try and figure out how much you'd pay for a Telstra
OnRamp
Xpress data service in a typical small business.
[1] 1998 prices. These figures are no longer
available on Telstra's
Web pages.
See Prac #13 for the practical exercises
accompanying this tutorial.
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Copyright © 2000 by
Philip Scott,
La Trobe University.