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Old 08-29-2004, 02:19 PM
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Default Alternatives to ADSL

Alternatives to ADSL



Most experts share the view that ADSL is very securely fitted into a niche market. Quite possibly, a market where very few other technologies (with the exception of local wireless local area network (LAN) initiatives are present) can compete.



On the whole, the main contenders to ADSL are: modem links, ISDN connectivity, private circuits (leased lines), and satellite links.



Modem links are notoriously slow, with a maximum speed of 56kbit – quite possibly and realistically unachievable due to the number of variables (line length and attenuation, quality of line, etc). Generally, most organisations find that even with the newest 56k protocols, their speed is generally in the region of 40-50kbit, with only the newer of telephone lines, closer to the exchanges receiving the thicker end of the 4x-kbit range.



ISDN (Integrated Services Digital Network) products, specifically ISDN 2e or BT Highway in the UK, are moderately faster than modem, guaranteeing 64kbit (single channel) or 128kbit (bonded, dual channel) connections, with split-second connections, as opposed to 10-30 seconds of handshaking time that a modem would take. As with modem links, each “call” (a.k.a. Internet connection) costs the same as an ordinary call would, double for a connection at 128kbit. Add on top of this, most ISP’s reluctance to prevent dual-channel connections, in favour of more expensive packages, and ISDN on a “per minute” basis is still very expensive, pro-rata. Although flat-rate packages on freephone or special numbers (such as BT Surftime call packages) can reduce the cost of extended connections, these add to the overall monthly tariff significantly.



Leased lines, or private circuits, or even Kilostream/Megastream connections as they are technically known, are very popular with larger SME’s, and other organisations. Offering speeds of 2.4Kbit to 1024Mbit at Kilostream levels, and 2.04Mbit to 155Mbit at Megastream levels [6], they are generally scalable to need, symmetric allowing full-speed connections in either direction, complete with 1:1 contention (guaranteeing the full speed of the link), and also come with very enticing service-level agreements (SLA’s), a must for any serious organisation, dependant on the link for mission-critical operations. However, these favourable extras come at a large cost – up to tens or even hundreds of thousands of pounds tariff per year, and a 4-5 figure sum for the installation alone. Only big players need apply.









Finally, satellite connections are amongst the few wireless link options, which have wide support in the UK and the rest of Europe. Traditionally, satellite services have only been used for downstream links, due to the technical difficulty of transmitting without incurring large equipment (and satellite bandwidth) costs. Besides further adding to the cost of the link by requiring a means of uploading data to make requests, the latency of the link is also a major factor, often adding 1-2 seconds of lag onto the link, making it unpractical for “real-time” traffic requirements, including live video, audio, and even online gaming. Add to this, the habit of satellite ISPs to introduce download limits or even “time slices” (where you are given a few minutes each day, at high-speed, to download a day’s worth of selections), and this makes satellite a very inflexible Internet tool. British Telecom are currently using two-way satellite links, pushed into the market and aimed at organisations and companies out in the sticks, where conventional high-speed Internet connections are unavailable.


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Gareth Roberts
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