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phyoptik

DSL and Speed

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I'm still quite new to the Testmy.net community, but this appears to be a question asked frequently, "Why is my DSL connection not as fast as advertised?"  Here's my answer...

DSL (Digital Subscriber Line) is an interesting technology which allows broadband internet via your telephone lines.  This technology occupies the upper frequency bands of the phone system (32Khz~1.1Mhz) and because this is not true digital, but a system that really runs via an analogue network, it is subject to interference from all kinds of sources (AM Radio anyone?) that this can cause odd results during speed tests, as well as when playing online multiplayer games.

This type of service is dependant on your distance from the telco central office (CO) and alot of people do not understand this, and spend alot of time getting angry and frustrated because their speed is not exactly what is posted on the ISP website.  A closer look shows us that any ISP uses an "Up To" phrase to communicate speeds, ie: up to 3Mbit.

In the case of a DSL provider, if you are more than 3200 meters (3.2KM) from a telco facility, your speeds will be reduced, and you may be placed on an interleaved profile (more on interleave further down)  This is all done to help keep the consistency of your service constant, and if we do change your speed profile to something higher, it will degrade the quality of service delivered to you, including slower speeds, frequent losses of communication (Synch) and even total loss of use!

The closer you are to a central office, the better your DSL connection will be, but these are not the only factors involved.  Obstacles to the signal are scattered around the telephone network, such as load coils, which can pretty much destroy a DSL signal.  In the case of a load coil, they are required to keep voice services running reliably, and no telco will remove them just so you can get DSL, as this would cause voice disruptions to everyone else on that loop!

If you are further than 3.2KM on the wire from the CO (not line of sight) then you will most likely be placed on an interleaved profile, which allows for better error checking and correction to be done, and therefore helping to maintain your speed, but there is a downside, you will never see ping times under 60ms.  For most applications this is perfectly fine, and you will never even know that you are on interleaved most of the time.  However, if you are a gamer, you will see in-game latency jump all over the place and probably not get the same kind of results as you would with a cable connection.

To determine what type of profile you are on, you can always call and ask one of the technical support agents for your ISP, but this does not always answer the question, as there are agents who really don't understand the difference, and don't understand what you're asking for.  If you encounter this, ask them to read you the profile name, most DSL isp's have specially formatted profile names to indicate whether it is interleaved or not. As I work for Bell Canada, on Sympatico if you are on an interleaved profile your profile name will begin with "al2" and "al1" for FAST channel.

Example: Interleaved: al2_d3008_3008_256_u800_800_256

        Fast: al1_d3008_3008_256_u800_800_256

        (These examples are Bell Sympatico profile names for a 3Mbit connection)

Typical Downstream Speeds

1Mbit = 1184Kbps

1.5Mbit = 1728Kbps

3Mbit = 3008Kbps

3.5Mbit = 3488Kbps

4Mbit = 4032Kbps

5Mbit = 5056Kbps

This is by no means a complete explaination, but due to the sheer number of questions that have been asked of myself and others, this is the beginning of a complete explaination DSL technology and your speed to the internet.

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nice info thanks :)

cable has its issues to....

especially when there are lots of users on the network.....

i have experience this a few times myself....

my advertized speeds are 5/512 and i normall run about 4800/490

but when theres lots of people on the network i have seens speeds as low as 1100/350

so it gets as bad..... or worse than dsl sometimes......

with my cable connection i normally have ping times of 33-133 ms in games......

with my old dsl connection i had 166 ping constantly.....

dsl seems to be much mroe consistant in the speeds..... so if you could get a fast dsl connection (3Mb or higher) i wold choose that over cable..... it has better ping times.... and speed consistancy.....

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Why does Bell Canada cap the 3.5 Mbps service at 3488 Kbps?

there are 2 possable reasons for that

1. becuase they figure that is close enough, no one will ever see the difference between that and 3584kbps. bellsouth does the same thing they cap there 1.5mb service at 1.4mb.

2. you are too far from the dslam that you cant reach max synk.

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3.5Mbit = 3488Kbps...the reasoning...ever tried setting a true 3.5Mbps profile on a lucent FSLAM line card? kills the card :)  I've killed a few slams by trying to modify higher...however, with the Alcatel DSLAM cards (HDSLAM, etc...) it is alot easier to modify, as these cards operate a little differently.

Lucent cards however, are here to stay, as they broadcast the signal a little farther, and allow for greater error correction.  And implimenting faster network types (FTTN for example) requires major error correction, which is why the new Optimax service from Bell is using primarily Lucent (OSLAM_GIGE) cards, as opposed to using Alcatel slams...it's basically a quality of service tradeoff, to run a DSL connection at 16Mbps (Optimax) you are bound to run yourself some errors on the copper between your house and the node on your street/neighbourhood. :)

And as for the argument, which is better, cable or dsl?  The real answer is, what are you doing on the internet?  Most cable networks are monitoring for P2P filesharing now, and throttle that customers bandwidth as such (usually to 56k speeds!) whereas DSL providers dont care, because DSL operates on a part of the telephone cable which is ONLY used by DSL, whereas cable internet comes down the same frequency pipe as digital cable, and digital home phone service alot of cable providers are offering, so having 50+ connections on a single file, downloading as fast as it can, can cause 'undesirable' operation of digital cable terminals, and digital home phone service :)

And thanks for the welcome, i've been coming to this site for quite sometime, but never really trudged my way into the forums until recently.  This site is used alot for testing real-world throughput for Bell customers, we probably send a few thousand hits to you guys, and they love it!

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