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Just curious.

My ISP (and also Telco) recently upgraded us to their NGN (IP-based) network.

In the past, in order to authenticate with the IPDSLAM, we use PPPoE to provide the login credentials that our ISP gave us. The DSL rate/speed is determined by this account. We actually have two subscription to the same ISP (one in our house, another in our shop), and when we close down our shop for the day, we use the faster shop subscription in our home line by logging in with the shop credentials.

Now, instead of asking us for our credentials via PPPoE, the modem the ISP provided automatically authenticates with the IPDSLAM. We are now using ENET ENCAP on ITU G.992.5(ADSL2PLUS).

So I'm curious, how does our ISP know what speed to give us? Are they using the MAC address of the device? Or is the speed embedded in the device (highly unlikely because it will be harder to upgrade subscribers)? Or can they use TR-069 to assign us our speed? (I telnet'd to the device and TR069 is turned on).

Thanks!

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closed as not constructive by Nifle, Mokubai, Dave M, Tog, 8088 Jan 17 '13 at 3:49

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1 Answer

Your DSL line speed is not decided by the PPPoE account you use. By the time you begin to establish your PPPoE session, the DSL line has already come up at a particular speed. In order to change the line speed at that point, the PPPoE endpoint (which is generally NOT the same piece of network gear as the DSLAM) or RADIUS server (which is definitely NOT the same piece of network gear as the DSLAM) would have to automatically automatically locate the correct port on the correct DSLAM and reconfigure it for the new speed, whereupon the port would go down and come back up at the new speed.

Your DSL line speed is decided solely by the DSLAM. The line will come up at the best available speed based on the quality of the line. The available speeds on the DSLAM port might go up to the maximum rate supported by the DSL technology, or they might be constrained by the provider to a speed you have purchased.

What might be happening is that the flow of IP packets is rate-limited or traffic-shaped. That could be done on the PPPoE endpoint (usually L2TP LAC) or on the L2TP LNS, or even elsewhere. The presence or absence of rate limiting or traffic shaping and the configured rate could be based on which PPP account you use.

If there is no more PPP session in the new setup, the only reasonable place for the ISP to limit the rate of your traffic is on the IPDSLAM, and it's probably configured directly on your DSL port. Without a PPP session, there is no way for you to use the "trick" you used to use of getting higher speeds at home by using the shop's PPP account.

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Thanks! How does my ISP know which DSL PORT to use for my connection? I guess I'm trying to understand how my ISP "identifies" our connection? (Is it using the MAC of the modem?) –  Ian Aug 20 '12 at 12:39
    
The DSLAM is physically at the other end of the wire that goes to your premises. It certainly knows what port you're on! –  Celada Aug 20 '12 at 13:31
    
Oh. Never could have guessed that you're talking about the actual physical port. Thanks. –  Ian Aug 20 '12 at 14:23
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