Have you considered converting your physical SS7 links to SIGTRAN? This article will give you a short introduction to the topic so you can knowledgeably consider your options.
SS7 links can be kind of a pain. They’re critically important to the network, but they are usually expensive, and you’ve got to carefully transport these two individual circuits across your network from the interconnection point to your signaling / media gateway.
So it’s not surprising that people are looking for alternatives. While we may one day end up with an entirely SIP-based network, in the interim we can use SIGTRAN to transport these SS7 links over the IP network. It may not be a revolutionary change, but it should save money and make your transport network a little simpler.
What is SIGTRAN?
SIGTRAN (from Signaling Transport) is a family of protocols for transporting telecoms signaling messages over IP. It actually includes ISDN signaling too, but for today’s purposes we’re going to focus on SS7. My goal in this article is to provide as little information as possible – but still cover the most important things you might need to know.
Different types of SIGTRAN
For SS7 you might hear four different protocols mentioned. I’ll try to summarize them here.
- SCTP (Stream Control Transmission Protocol) is the transport layer protocol (like TCP) that provides reliable connections on the IP network. Everything else is built on top of it.
- M2UA – in a Metaswitch network, this is the protocol used by the CFS to send MTP3 messages to a media gateway, from where they can be sent over a TDM link. So in this model there’s still a physical TDM SS7 link, which is connected to a media gateway that’s being controlled remotely.
- M2PA – this basically mimics the behavior of a TDM SS7 link but over IP. So it’s operates at the data link layer – mimicking a copper circuit, except the link is a peer-to-peer IP connection to a specific IP address and port.
- M3UA – this operates at a higher layer in the network, so instead of worrying about links, it just transports (e.g) the ISUP messages to the destination application with a certain point code.
That was too complicated…
Sorry, you’re right. I’ll leave the above text in place for reference, but let’s see if we can make this much simpler.
- You already use M2UA anytime you have a CFS / signaling gateway controlling a media gateway.
- If you have an existing SS7 network and you want to convert to SIGTRAN, then I would highly recommend using M2PA. This allows you to build a new IP-link alongside your physical link, and reuse all your existing signaling route logic with this new SIGTRAN M2PA link.
- If you were building a brand new SS7 application (installing a new network element with a new point code) then probably M3UA would be simpler. But we almost never encounter situations like that.
So you’re saying we should use M2PA?
If you’re an expert on SIGTRAN, then I’m sure there are situations where another choice makes sense. However, if you’re a typical ILEC or CLEC with existing physical A-links and you want to connect to your STPs over SIGTRAN – we recommend M2PA as the simplest path forward.
Does my equipment support SIGTRAN?
Metaswitch introduced support for M2PA in V7.1.01. I don’t know of any system on an older release than that, so Metaswitch users almost certainly have M2PA available.
If you’re not using a Metaswitch switch, then you may not have SIGTRAN support, or you may only have some protocols available. You’ll need to check with your vendor’s documentation.
If you don’t have SIGTRAN available natively then one option would be to install an affordable third-party device (e.g. a TelcoBridges Tmedia) which could terminate your physical link and then convert to SIGTRAN.
If you’re considering a move to SIGTRAN and would like some help, please contact us and we can discuss your situation and how we can help.