tutorial sheet 3 convergence and voice over ip

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					Tutorial Sheet 3: Convergence and Voice over IP 1. List the five main benefits and five main disadvantages of convergence on a single network technology for data and voice traffic. Benefits: Cost savings: – Single network, more rapid payback on new hardware; lower network charges from new supplier (?); free inter-site calls and toll bypass; externally managed service (usually) – staff cost avoidance; increased reliability and availability (?). 2. What is meant by “payback period”? Explain how the concept of a payback period relates to the choice of installation of a new communications technology. Payback period is the length of time taken to recover the initial investment on a project through the savings (cost avoidance) it permits the user. Initial investment includes both hardware/software costs and the costs of installation, service charges on borrowed money for the investment, training, change disruption, and facilities alterations necessitated by the new equipment. We only take up an approach if the payback period on the project is less than our required time. For example, a PC installation project that had a payback period of more than five years is unlikely ever to be approved by management (the kit is obsolete before it has paid for itself), whereas one with a six-month payback period is likely to be very attractive. After payback has occurred, later cost avoidances are effectively profit increases! (Hence the attraction). Interested to hear any experiences amongst the tutorial groups as to the use of payback period in project justification, particularly if it regards communications technology projects. 3. Given the existence of convergence as an option (perhaps even a goal) for large companies, the development of broadband fixed wireless access, the development of radio LAN technology and microcellullar radio data carriage (IEEE802.11b and Bluetooth), and the viability of ATM as a carrier for convergent traffic, comment on the likely take up rates for 3 rd generation GSM. What particular niches does it fill that are not covered by existing technology options? In addition, comment on the likely future prospects for the major telcos. (Hint: Think about the things you want from communications, particularly those items which are not supported well, or at all, by the technologies we have already studied. Think about radio LAN/wireless as having a maximum range of 20m from the antennae). In truth, much of the added value of 3GSM is in competitive market areas. The short range, high data rate service is unlikely to displace 802.11b and Bluetooth. The real added benefits come in the macrocellullar arena, and are fully dependent on the

development of real added value services for the mobile client (location based services, “on the go” computing, etc.) Given the initial investment, it is difficult to see how a short-term return can be made from the licences. Longer term prospects look equally bleak. Given the emergence of competitive, price sensitive regional carriers, and competition in the telco’s targeted future business areas, the huge debt burdens incurred in acquisition of 3GSM licences look to be a major burden. The “cash cow” period for 3GSM will be vastly shorter than that of the (enduring) cable carrier services. The telcos need something good to happen in short order – but probably can’t see anything on the horizon. In effect, they are probably deploying 3GSM in the hope, rather than the certainty, of recovering their initial outlay. 4. IP is fundamentally a connectionless network protocol, based on a datagram service. Discuss its suitability as a voice transmission protocol. IP is fundamentally unsuitable for voice traffic. The development of VOIP is an attempt to bolt on extras to the protocol to enable voice traffic over existing infrastructure. It is likely to work, but only by changing the whole nature of IP/UDP. If it can be done such that existing infrastructure can cope, then VOIP will be a massive success. The debate is still wide open – the creator of IP has publicly stated that he does not think it will ever be a complete success. Note also the effects of header size on efficiencies of transmission (from lecture slides). 5. Comment on the effects of compression in voice transmission. Does this change the effects on quality of service, and hence the value, of lost data packets in a connectionless service? The argument has always been that the ear is insensitive to the odd bit error on reconversion into analogue data. However, with compression, a single bit error corrupts the whole data of a packet (decompression will be incorrect). The ear is not insensitive to the loss of 20ms of data – this is likely to feature as unpleasant noise or drop outs. Given the propensity of IP to dump packets as congestion increases, voice traffic under heavy data conditions will have problems with perceived user quality. 6. There are a large number of layered standards involved in the concept of multimedia traffic (and voice) carriage over IP. Consider the effects of such complexity on the design of network equipment, and why communications companies are willing to adopt so much complexity to offer a VOIP service. The vast amount of money involved (think about telephony, and the sheer cost of maintaining BT/ Deutschpost/ PTT infrastructures) is such as to render the attempt worthwhile. If successful, a whole world of charging opportunities open up to ISPs and network suppliers. The “goose that laid the golden egg” syndrome comes to mind. (First find a suitable goose – unfortunately it probably doesn’t lay golden eggs, so

transfer it to a country with gold deposits, sit it in a cage, build a major gold mine under the cage, establish a smelting shop and foundry to cast the eggs, and (hey presto!) you have golden eggs under the goose. Spot the logical flaw in this process).