The SIGTRAN Working Group of
the IETF has specified the MTP2
User Adaptation Layer as its standard protocol to enable remote termination of SS7
links via an SCTP association. The M2UA protocol is the layer between SCTP and MTP3
that separates the physical SS7
termination from the actual signaling point within the network. M2UA serves several
purposes. The first purpose is to provide a mechanism for the transport of SS7 MTP2
user signaling (e.g., MTP3 messages) over IP using SCTP. The second purpose is to
allow remote placement of SS7 link terminations and back haul SS7 traffic to a centralized
point in the network.
With M2UA several signaling points can be consolidated into a centralized network
element. In turn, one can then co-locate points of SS7 presence closer to the element
to which they need to connect. This results in a substantial cost savings in terms
of backhauling SS7 dedicated circuits. M2UA deployments consist of 2 entities, the
client and the server. The server provides physical SS7 termination and communicates
with the client over an SCTP
association using IP. The client houses the MTP3 and thus is the point code addressable
element within the SS7 network. M2UA is appropriate in those situations where the
remote signaling point does not support
M2PA yet the benefits of signaling over IP are required. It is also appropriate
for consolidating point code usage and simplifying SS7 network provisioning overhead.
The following diagram is an example of how M2UA may be used in the network.
As shown, the physical SS7 termination is made in the switched circuit network (SCN),
and the signaling information is carried over an IP SCTP association back to the
centralized control point. There may be several instances of the SCN interconnect
shown. In each case, the centralized element has a signaling presence, i.e. its
point code is reachable. Although there are several termination points, there is
a single SS7 element represented.
M2UA allows Telecommunications Equipment Makers (TEMs) to optimize their network
topology and use IP to transport their SS7 messages instead of traditional 64K-based
links. It still allows interconnection with legacy SS7 equipment however. All remaining
elements from the classic SS7 network remain the same. From the outside, the fact
that signaling is carried over IP is not detectable. M2UA can be used in the event
where there are many points in the network where an element needs signaling connectivity
and the costs for deploying several smaller nodes or the cost of back hauling legacy
TDM links is prohibitive. It is also applicable in areas exhibiting point code exhaust
since a single MTP3 point code is used.
The signaling stack is depicted below:
Advantage Summary
- Remotely locates SS7 terminations from point of interconnection
- Enables network architecture with minimal point codes
- Reduces SS7 transport, overhead, collocation and maintenance costs
- Separates and centralizes service signaling components from transport
- Reduces network routing complexity
- Deploys remote points of presence in interconnecting networks
- Easily expands network reach (eg; wireless, ITU signaling-based networks)
- Increases operational flexibility and scalability