SIP on FTTH systems

Mark Tinka mark.tinka at seacom.mu
Thu Feb 6 08:01:14 UTC 2014


On Thursday, February 06, 2014 09:19:59 AM Måns Nilsson 
wrote:

> Or, one could make sure everything has a globally unique
> IP address and is using reasonably secured
> communications. The downside is that one then can't
> defend the existence  of those empire-building
> middleboxes. It is not the telco way, so is of course
> unthinkable. Like anything beyond WAP was on cell phones
> a decade ago.

There are, typically, three topology models for modern FTTH 
(wireline, really) networks that a service provider could 
deploy:

	1. SVLAN N:1 model
	2. CVLAN 1:1 model
	3. Hybrid of both

The SVLAN (N:1) model is simple; just have a single VLAN for 
each service (VLAN 10 for Internet/Unicast, VLAN 20 for 
VoIP, VLAN 30 for IPTv/Multicast). This is simple and easy 
to scale, but if one is using relatively "dumb" AN's (like 
GPON's or MSAN's), it can be difficult to control how much 
bandwidth customers need, and how they can roam between 
services in the home (given CPE ties services to ports).

The CVLAN (1:1) model is good for identifying services and 
bandwidth requirements on a per-customer basis. The main 
problem with this model is that Multicast traffic gets 
treated like Unicast, because each customer has a unique 
VLAN for themselves, and as such, the upstream PE router 
ends up having to replicate the same linear video stream as 
many times as there are customers down the line.

The Hybrid model, where CVLAN's are used for all Unicast 
traffic (Internet, VoIP and VoD, typically), and a single 
SVLAN is used for all customers to handle Multicast traffic 
(so-called MVLAN). The challenge here is if you're the type 
of operator that likes to have a consistent set of address 
per VLAN, it can become a little tricky if your VoIP service 
is a walled-garden running on private IP space, given it 
shares the same VLAN as Internet and VoD which would 
normally run on public IP space.

The N:1 SVLAN model is quite simple and scalable for 
wholesale FTTH services. 

There is product from some vendors, now, that is built with 
FTTH in mind. 1U, dense switches (Active-E) that support 
(reasonably) proper QoS and bandwidth management controls on 
customer- and core-facing ports, at Layer 2. So that offers 
you a lot more capability at the AN, and you can manage 
bandwidth as close to the customer as possible, unlike 
typical GPON deployments which may not have these features, 
leaving you to apply bandwidth policy at the PE router - 
much too far up the line.

These new products can also support split horizons across 
bridge domains (which GPON's and DSLAM's do today), meaning 
that customers can use the same SVLAN's, but can only 
communicate via the upstream router (Layer 3), eliminating 
risk associated with Layer 2 visibility between customers 
connected to the same bridge domain.

Cheers,

Mark.
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