SIP on FTTH systems
mark.tinka at seacom.mu
Thu Feb 6 08:01:14 UTC 2014
On Thursday, February 06, 2014 09:19:59 AM Måns Nilsson
> 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
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.
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