ADSL Speed and Performance Part 2 : Contention and Congestion
What is a contended service? What does it mean if you say my ADSL exchange is congested and what can I do about it?
What is Contention?
For the average end-user this is probably the least understood part of ADSL services and the one that causes constant frustration.
ADSL is not a guaranteed speed service because it operates on contended infrastructure.
Contention means service providers cater for less bandwidth than they would require if all of their customers were connected at full speed at the same time.
Customers often have a negative reaction to hearing this the first time, but consider this:
A guaranteed service would mean that your connection was capable of operating at 100% capacity 24.7 regardless of what else was happening on the network. To provide bandwidth on the DSLAMS to allow for this would make ADSL services extremely costly.
In turn, as your service provider, MWEB also uses contention on the IPC and international capacity that we purchase. If we purchased enough bandwidth to cater for everyone going at full speed 24/7 on our network we would end up having far too much idle network capacity, which means we'd be wasting a lot of money!
This is why we try to make it very clear to our customers that ADSL products are advertised as a best effort service with "up to" and not guaranteed speeds.
What is Congestion?
Congestion occurs when a contended link is over-utilized. In other words there isn't enough bandwidth to meet the requirements of the customers using that link. MWEB's network is built to offer a superior performance and cater for the high demands of streamed online video and gaming, so you don't have to worry about our network links becoming congested.
Unfortunately congestion often occurs on the uplinks from the Telkom exchange equipment to the Telkom network and is one of the major causes of poor broadband experience for our ADSL customers.
These congested links result in symptoms like intermittent high latency, packet loss (which means stop start and skipping on streaming audio and video and dying a lot without seeing why in your online games). You can also expect poor speed test results and slow downloads if you are connected to a congested exchange.