I'm on 21CN ADSL2+ now, so as I understand it that means no more ATM between DSLAM / MSAN (now) and BRAS so ethernet and possibly VLANs in it? And what, L2TP over UDP over say IPv4 over ethernet over something optical - just guessing - from DSLAM / MSAN to 21CN BRAS ?
Is that right? It's not just the BRAS-to-ISP side that uses L2TP perhaps then?
I've never managed to find out too much about the MSAN to BRAS path. Burakkucat and I were talking about it a good while back and I collected a list of every mention I could find, every scrap of info about the protocol stack along that stretch.
These are the notes I put together back then :
Exchange backhaul protocols BT 21CN MSAN
* BT 21CN: SIN466 says Ethernet, no mention of ATM at all.
* BT 21CN: SAMKnows states Ethernet replaced ATM
https://www.samknows.com/broadband/exchanges/21cn_overviewBut perhaps SAMKnows doesn't know :-)
* BT 21CN So does this :
http://blog.farnz.org.uk/2010/02/on-pppoa-pppoe-atm-and-adsl.htmlQ: Is WBC 21CN? - If so, SIN 472 v2, sec 3.7 says “WBC uses ATM over DSL for the link between the end user and the MSAN but Ethernet between the MSAN and the BRAS.”
Q: Is 21CN TR-101 a description of BT 21CN ?
This page hints that it is, not v explicit -
https://support.zen.co.uk/kb/Knowledgebase/Zen-ADSL-Broadband-Products-Line-DataAlso, this post claims it is -
http://forums.thinkbroadband.com/zen/4075096od-tr101.html?fpart=all&vc=1* If that's so, TR-101 (2006) talks unambiguously about the total replacement of ATM with Ethernet, and hallelujah that spec has explicit protocol stacks! Yay!
* Weak support: 21CN - the following doc makes no mention of ATM for 21CN, only ethernet
http://www.edinburgh.bcs.org/events/2007-08/080109.pptVvery weak hint: VDSL2 :- Paper by Eriksson and Odenhammar: Ericsson Review no 1 (2006) - "VDSL2", p. 38 - “The elimination of ATM in the first mile means the access architecture can be simplified into an end-to-end Ethernet access architecture that uses virtual local area networks (VLAN) as the service-delivery mechanism across the entire access network.” - does this apply to 21CN?
-- TR-101 refs --
2006:
a. Sec 2 "migration process from an ATM based aggregation network to an Ethernet based aggregation network."
b. sec 2.3 (p 21);