Muni fiber: L1 or L2?

Wed Feb 6 21:06:16 UTC 2013

On 13-02-06 10:16, Eric Wieling wrote:
> Can anyone out there in NANOGland confirm how ILECs currently backhaul their DSL customers from the DSLAM to the ILECs IP network?

In Bell Canada Territory, wholesale traffic between DSLAM and BAS/BRAS
travels normally.

The BAS establishes the PPPoE session with end user. When the PAP/CHAp
authentication requests arrive, the BAS sees that it has a realm that
belongs to ISP-X and declares that all packets in that PPPoE session
should be forwarded to ISP-x from now on.

The BAS establises an L2TP tunnel to and IP address that belongs to
ISP-X.  This tunnel travels through Bell Canada's aggregation network to
a router near the ISP's own facilities. There, the L2TP continues on a
GigE link to the ISP's incumbent facing router.

ISP gets PPPoE packets encapsulated in L2TP. It is responsible for
responding to the authentication request, and if positive, providing IP
address/dns/router/etc via IPCP.

Note that incumbents have been telling the CRTC for years that gigE was
the latest and greatest and couldn't do better. Some ISPs require a
large number of gigE links to handle the load. The CRTC last year
mandated incumbenst learn about the less old 10gigE technology and
provide it to ISPs who need it.  Bell Canada has yet to comply. But some
cable incumbents have complied.

In this scenario, there is an ISP of record for the DSL last mile. That
ISP gets billed for the monthly fees for the DSL last mile. (roughly
$20). However, the end user can establish a PPPoE session with another
ISP if he has valid credentials with that other ISP.

When a user formally switches ISP, Bell Canada only needs to change the
ISP of record attached to the phone line so the old ISP is no longer
billed for it and the new ISP is.  The user can start using the new ISP
as soon as his credentials with the new ISP are setup.

Bell canada also offers a non PPPoE service (it calls HSA). However, it
is priced to dissuade use. This trafic is in a PVC between the modem and
the ISP and not switched by a BAS.  I believe Bell uses VLANs to funnel
traffic into the link leading to the ISP.  (not sure if L2TP is involved).