INT21CN Computer Networks

Tutorial #15

1. What is a leased line? Why is this considered an outmoded term nowadays?

2. What is meant by the term peering in the context of Internet Network Providers? In the diagram in the lecture, which of the links constitute peering relationships and which are "provider-client" relationships? Describe a path (or route -- ie, a sequence of two or more links) through the given diagram over which packets would ordinarily be expected to flow. Now describe a route over which packets would not be expected to flow.

3. Two aspects of a generic ISDN service which have been 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 (for business use)in Australia has a flagfall cost (day rate) of 15 cents (which includes the first 5 minutes of the call) plus 4 cents per minute subsequently. 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"?

4. What is the attraction of a frame relay telecommunications service over an ISDN service at the same "port speed" (say, 64kbs)?

5. As mentioned in the lecture, Telstra in Australia separates costing for "Basic Carrier service" from that for "Internet Service" for full-time ("Always On") Internet access.
   1. What is meant by the term "Basic Carriage Service" (sometimes called a Telecommunications Service) and why does Telstra separate it from Internet service?

   2. It's possible to purchase (in some Australian capital cities) an "always on" Internet service from (eg) Optus@Home, a competitor of Telstra, which doesn't separate the Basic Carrier service from the Internet service in the same way as Telstra does. Why/how can they do this? Discuss. Extra questions: do these in your own time if interested: Optus@Home also doesn't have a data volume charging component -- there's a single, simple monthly access charge. This, on the surface, seems like a great idea, so what's the "downside"? Note: Optus@Home is also not terribly useful for business-style permanent Internet connection. Look up the Web page and explain why not?

6. Prac exercise: do this in you own time if interested! Imagine that you (as a graduate of this subject) have been asked to advise a small Australian business on establishing a permanent connection to the Internet. As part of your work, you decide to investigate the performance and price options available from Telstra, the dominant telecommunications (and Internet Service) provider in Australia. Start at Telstra's Bigpond Direct Web pages, and attempt to answer the following questions:
   1. Telstra splits Bigpond Direct (see also here) pricing into four components. What are they? You're excused if you can't immediately see what the fourth one is...!
   2. What are some of the options for the "Basic Carriage Service"?
   3. You should have discovered that one of the options for Basic Carriage Service is a dial-in modem link. Why is this a particularly attractive option?
   4. Some (all?) of Telstra's pricing options for Bigpond Direct have a data volume component. What does this mean, and which ones have this "feature"? What is the particular disadvantage of this pricing model in a business context? Does it have any advantages? Do any of the pricing options not have a volume component?
   5. VERY Hard question: Telstra's OnRamp XPress has some attraction as a Basic Carriage Service for a full-time Internet service. What would the minimum monthly cost for a business using this service for its Internet link, including the Bigpond Direct charges? Don't even try to incorporate the Back Channel Tariff stuff into your calculations! NB: I don't seriously expect you to do this -- I've tried and failed myself! However, if you're an Accounting Major you might find it fun to try.
   6. Research and extension question: What other issues will your client business have to have in place in order to establish a full-time "Internet Presence"?