IP DSLAM and BRAS Architecture

Unanswered Question
Apr 11th, 2009

Hello to everyone.

One of our SP customers is planning to upgrade their traditional ATM DSLAM to IP DSLAM to enhance customer services and integrate video on ADSL.

They need to upgrade their BRAS actually based on ATM interfaces. They don't have that much to invest so they are willing to buy not more than an ASR1006 whit 10G Processor and 10 gigabit ports.

Let's go now to my question. The PPPoE sessions (from the new DSLAMs) will terminate to the BRAS (ASR1006). Once the user receive the IP address from the BRAS after authentication, video traffic from a local Video Server can reach the customer directly (not passing trough the BRAS) or still need to go back to the customer passing trough the ASR1006? What I'm afraid of are the performance and the number of subscribers.

The DSLAM, BRAS and video servers are all connected in LAN.

Thank you in advance.

I have this problem too.
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Giuseppe Larosa Fri, 04/17/2009 - 09:09

Hello Frank,

if the PPPoX sessions are terminated on BRAS all traffic has to go through it not only authentication setup so it (the BRAS) can be a bottleneck

Hope to help


fbartolino Sat, 04/18/2009 - 01:05

Ciao Giuseppe,

I did clarify al my doubts with the DSLAM and IP/TV solution vendors (not Cisco). I'm attaching a simple layout that my be helpful for whom will read this post in the future.

As you can see the video box (STB) will not receive the video in PPPoE tunnels. This will offload the B-RAS (Cisco). When the STB sends a multicast join, the DSLAM will intercept and forward it directly to the video server (local, directly connected to the switch).

The customer CPE will be configured to handle PPPoE for Internet (that terminates on the B-RAS) and bridge connection for video that terminates directly on the DSLAM.

This is all.

Thank you.


Giuseppe Larosa Sat, 04/18/2009 - 03:43

Hello Frank,

interesting solution:

there is a separate ATM pvc for the video box that used bridged RFC1483 IP/eth/AAL5snap so offloading is possible.

Kind of you to provide a feedack

Best Regards



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