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For those of you who are not aware of the basic's of what is required to get from Telus servers to your house here is brief over view of the chain of events that have to happen in order for your service to work properly. I want to give a big thank you to twixt See Profile for taking the time to write this all out...We're all very greatful for it...

There are five (5), repeat FIVE, different places things can happen that screw up your data transfer rate. Your system only works properly when ALL FIVE things are working right. ANY ONE of the five things screw up, and data transfer rate goes into the toilet.

1. People are complaining about DNS latency. This is ONE of the five things that can go wrong. Currently, both Telus and Shaw's DNS response times are mediocre to poor, depending upon load (which means the response times get worse at the very times of day that everyone's complaining about). Poor DNS response-time means that when you click on a URL that is not cached in your router (or you are brainless enough to be running without a router), you will have to wait the required length of time for Telus or Shaw's DNS server to deign to reply to your request and resolve the URL into the required IP address.

This is completely out of your control. The retrieval-efficiency of DNS requests are a function of the DNS server and have nothing to do with anything at your end of the connection. You can MITIGATE poor DNS response from your ISP by using a router with its own DNS-caching capability. However, you will STILL be limited by the response time of the external DNS whenever you access something that is not already in the router's internal cache. This is normal and correct operation - handle it.

2. The second place things can go wrong is between you and your port at Telus. This can include problems with your ethernet card in your machine, the ethernet cable between your machine and your router, your router itself, the cable between your router and your ADSL modem, the power supplies for either your router or your ADSL modem, the wiring from your ADSL modem to the wall jack, the ADSL signal-splitter, the wiring from your wall jack to the demarc in your building, the wiring from the demarc to wherever your port is located, the port itself, or the wiring from the port into the internal Telus backbone.

You have control over this up to the demarc point - which sometimes includes the ADSL splitter. You have NO control over anything past the demarc point. Now, if your problem is time-of-day related, you can reliably assume that everything between your router and your port is OK - except for one issue. ADSL modems are sensitive to the NUMBER OF ADJACENT PAIRS IN THE TRUNK CABLE THAT ARE ALSO CARRYING ADSL TRAFFIC.

What the above means, is that if Telus has oversubscribed your trunk cable (has too many customers with ADSL on the set of cables going from your place to your ADSL port), then there will be interference between your set of telephone wires carrying your ADSL signal and the signal on the telephone wires of the person next to you in the cable bundle. When this happens, BOTH your ADSL modem and the other ADSL modem slow down until the bit-error-rate decays to an acceptable level. This is completely automatic - you have NO control over this. Now, extend this over multiple connections. As the load on the system imposed by users increases (time-of-day) the amount of interference increases. ALL the modems then start to throttle - quite correctly - so that everyone gets at least as much of the pie as they can get without robbing their neighbour.

Another thing - the higher the maximum ADSL transfer rate, the LOWER the number of ADSL pairs that are allowed in a cable bundle because the higher-frequency-signals used to achieve the higher ADSL transfer rate spread further from your pair than the lower-frequency-signals used for a lower ADSL transfer rate.

So, the result of the above is that if Telus offers high-speed ADSL to everyone - and a cable that has been working fine with an ADSL-pair-density originally set for 1.5Mb/s is suddenly faced with a lot of those people upgrading to 3MB or 6Mb/s, guess what happens? The higher interference caused by the higher-transfer-rate signals causes EVERYONE to slow down, because there are more EXISTING ADSL pairs in that cable than the enhanced or extreme-speed-service can support. And it only gets worse for every customer Telus upgrades from standard to enhanced or extreme service.

Now, please note that this trunk-cable-interference occurs on the Telus side of the demarc. You have NO control over this - trunk-cable ADSL density is a function of decisions made by Telus sales. IMO, from the results being shown, both enhanced and extreme service is massively oversubscribed - and a whole bunch of enhanced and extreme users should be downgraded back to 1.5Mb/s to allow the system to recover stability at that rate.

3. Once your signal passes out of your port, it goes onto the Telus INTERNAL backbone. This is a fiber-optic network that links all ADSL-capable exchanges and stingers that Telus operates. A problem with any of the routers on this internal network will also cause slowdowns - and again a router can work properly under low-load conditions and then gradually slow down as load-levels go up, so again we have another situation where time-of-day shows up as a factor.

4. Once the signal is on the Telus Internal backbone, traffic to "the outside world" is routed into the internal end of Telus' Western Canada Internet point-of-presence.

This router (or system of routers) must be able to reliably carry the TOTAL in-and-out-the-door traffic for ALL of BC and Alberta. Again, loading issues here can cause time-of-day-related slowdowns, just as in item 3.

5. A high-speed fiber-optic link carries the traffic from the internal point-of-presence router system to the external point-of-presence router system. The external point-of-presence routers (which live in the US) link Telus with the main US-based Internet Trunk Carriers.

The arrangement of the external connection is a function of the agreements Telus has made with the US-based carriers as to the amount of load Telus imposes on their network and the cost of that load. Router programming for this end of the connection is NOT trivial - there is a LOT of cross-connect-requirements that have to be met without screwing up things on the internet backbone itself. (Read: $$$$$)

Also, this is the place where egos and pissing contests between ISPs cause massive slowdowns when access to trunks are throttled or cut because people can't get along.

Conclusion:

WHICH of the above items causes your particular problem can vary. In some places, the problem is item 1. In some places, the problem is item 2. Grief with item 3 will usually cause a problem with an entire exchange-area and is usually fixed quite promptly. Grief with items 4 or 5 will cause the entire Western Canada region to be unable to gain access outside the internal Telus network and again is fixed with very high priority.

Note: If Telus has some sort of redundancy and/or load-sharing mechanism in place, Grief with Items 3, 4 and 5 will only cause slowdown, rather than stoppage. But this then masks the issue - so again you have difficulty in determining exactly what is causing the problem.

Finally:

There are a VERY SMALL number of situations where changing an ADSL modem to another brand - or changing a port to a different network stream on the Telus internal network - will cause an improvement in the minimum-data-transfer-rate the user will experience.

However, in the vast majority of cases, the only way the user is going to see minimum-data-transfer-rates which do not dip to less than 80% of their maximum-data-transfer-rates is if Telus loads their existing infrastructure according to proper ADSL design principles for their WORST CASE (all extreme-users) condition.

This means AVOIDING OVERSUBSCRIBING - and telling people on existing oversubscribed networks that their best option may be to downgrade to a slower maximum-data-rate so their minimum-data-rate stays higher.

twixt See Profile

by joshb See Profile
last modified: 2007-10-01 23:04:24