SIP on FTTH systems

Mikael Abrahamsson swmike at
Thu Feb 6 14:56:15 UTC 2014

On Thu, 6 Feb 2014, Mark Tinka wrote:

> On Thursday, February 06, 2014 04:17:42 PM Mikael
> Abrahamsson wrote:
>> You don't need a BNG. You need an L3 switch as the first
>> hop the customer is talking to.
> Fine for FTTB, but not for FTTH where you're serving tens-
> to-hundreds-of-thousands of customers.


> If your FTTH deployments are low scale (measure of low or large scale 
> depends on each operator's point of view), the case for doing without 
> subscriber management technologies can be made.

Why is it different?

> I'm curious; in these deployments, what kind of customer scale are you 
> talking about? When someone says FTTH, I'm thinking thousands and 
> thousands of customers, in which case not having a scalable susbcriber 
> management system as well as not having a scalable customer termination 
> topology could be difficult. Unless I misunderstand...

Yes, this is for hundreds of thousands of customers. Why do you need 
customer management? You document where a certain fiber goes to (what 
port), and then this port goes to a certain customer. That is the only 
customer management you need.

So you provision your L3 switch with a protocol based 0x86dd vlan per 
port, put a static /64 L3 subinterface into this vlan, then you have a 
built in DHCPv6(-PD) server in the same switch that hands out a static /56 
on this vlan, plus hands out DNS-resolver etc. No dynamics, just static. 
You provision ACLs to only allow the /56, /64 and LL in on the L3 
interface. You set ND cache max size to 20-50 entries per L3 subinterface 
to protect the 1024-2048 entries or whatever the L3 switch can handle. For 
IPv4 you need to do all the L2/L3-inspection magic in a common vlan.

This is now a standalone unit and you don't need any central system to 
stay up and running in order to move IPv6 packets, and you support both 
directly attached computer or a residential gateway that wants PD.

I did this type of DSL deplayment early 2000nds with an L3 switch and an 
ethernet DSLAM as media converter. This was obviously IPv4 only, but 
worked very well. At the same time the guys with central DHCP systems had 
a lot of country wide outages when the DHCP system went belly-up.

I only a few years later learnt what an LNS was when I talked to someone 
else who did more of a "follow-the-whitepaper" deployment of DSL.

> Modern Metro-E switches that support full IP/MPLS in the Access have a 
> lot of good IPv4 and IPv6 features, including DHCP_IA and DHCP_IA_PD, 
> but again, these are more FTTB- than FTTH-focused, if you're talking 
> about scale.

I would never want to have MPLS that far out into the network.

Mikael Abrahamsson    email: swmike at

More information about the NANOG mailing list