SS7oTDM vs sigtran for roaming links

from a SCCP and upper layer perspective, the use of TDM or Sigtran is exactly the same. It transports MTP3 packets across. The interface to the lower layer is different in the case of M3UA and MTP3 but the functionality is the same. If you use M2PA then you have a "traditional" MTP3 layer.

M2PA does simulate a E1 or T1 connection over IP by encapsulating the MTP2 packets into SCTP packets.

M3UA simulates the internal interface between the SCCP layer (or any other Layer4 layer such as ISUP) and the MTP3 layer.

In todays world, I would recommend the use of Sigtran versus TDM because it gives you more flexibility and redundancy on the network level. IP can be easily routed across the world. Using E1's or T1's takes time to order and set up and are usually much more expensive. IP can give you 10GBps of speed if you want, using TDM you are limited to 16 channels of 64kbps in a E1 or T1 (unless you use some of the less often used high speed link options such as ATM or channel bundling). On IP you can have many many links to different carriers on one ethernet port. On TDM you have one port to one signaling peer.

What to choose largely depends on what your connection partner offers but the whole world moves to Sigtran. But if you need to connect to older equipment, you might simply not have the option. But in this case you can use a signaling gateway which makes your TDM accessible over Sigtran.

In my setups I have usually done this with CiscoITP which is a standard cisco router (2651xm, 7206vxr...) with an E1 card and special software (12.4SW). Unfortunately Cisco is no longer selling it. But that box basically is a full STP with TDM and Sigtran M2PA and M3UA links.

M2PA and M3UA serve different purposes. The processing power needed for them is similar. I've implemented them both. M2PA is STP to STP (peer to peer) while M3UA is STP to User. But at the end both can be used to transport MTP3 packets across.