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As the first ISP to launch IPStream MAX into the channel, Griffin Internet probably has more experience than most with the product.

There is a lot of confusion around how MAX works and where it is most effective. Common statements you may read and hear are;

1. MAX has a faster upstream than previous IPStream products.

FACT Absolutely correct. Upstream speeds on MAX can get up to 832 kbit/s, over three times faster than previously available. ADSL was originally designed for web browsing where most of the data transmitted is keystrokes and the real work is done downloading images from the WWW. Applications like voice however need the same bandwidth in both directions (unless you’re having a conversation our MD!) and this is where faster upstream speeds are valuable.

2. MAX is rate adaptive and constantly changes speed making it no good for carrying voice.

MYTH Griffin has many partners currently installing MAX products specifically for VOIP. The rate adaptive nature of MAX makes it more stable in the long run. Rather than dropping out when line quality deteriorates, the broadband carrier adapts by reducing the line speed. In the first 10 days of its life a MAX line is looking for its MSR (Maximum Stable Rate) which can make it seem unstable, particularly with some routers than were not designed for rate adaptive ADSL. We have found that 1-3% of local loops are unsuitable for MAX because of the quality of the copper. This is often, but not exclusively, because they are in rural areas far from the local exchange.

3. Most people can only get around 4Mbit/s downstream and so upstream speeds are only half of those advertised.

MYTH Across the Griffin base, the average downstream speed available on MAX is around 5.5Mbit/s, but at these levels most customers still enjoy maximum upstream speeds. This is because upstream and downstream speeds do not deteriorate at the same rate although both are affected by distance from the exchange (see below).

4. The nature of MAX is such that whilst speeds of up to 8Mbit/s are advertised most customers are often lucky to actually download data at anywhere close to that speed.

FACT But this is nothing to do with the rate adaptive nature of MAX. BTW’s SLA stipulates downstream throughputs of 400K and 800k (MAX and MAX Premium) across all of their exchanges but only some of the better business ISP’s will guarantee these speeds through their own networks. Most ISPs mix residential and business traffic and sell to home users at such low prices that they have to oversubscribe their network capacity. Ask your ISP what end-to-end throughput speeds they guarantee.

In next month’s edition find out the truth about QoS, the effect on MoS and what you really need to think about when using broadband to carry voice.

Published in Comms Business, January 2007, page 16.