SS7 - Signalling System #7

Signalling System #7 is a set of telephony signalling protocols which are used to setup the majority of the world's PSTN telephone calls.
It is also known as CCS7 (Common Channel SS7), or CCIS7 (Common Channel Interoffice Signalling).

More information about the history specific workings of SS7 can be found at wikipedia.org∞

Optical Networking and SS7

The rest of this article is my personal view, based on some discussions, articles that I have read and my understanding of how PSTN works.

"Why don't we use SS7 in optical networking" is something you might wonder when looking at the research in the provisioning of optical and hybrid networks. After all, there are a lot of similarities between optical networking and PSTN. Both are circuit-switched networks, and ideally we want to setup a circuit in an optical network at the last possible moment, i.e. when it is actually going to be used.
Another similarity is that SONET and SDH are used to transport both data in optical networks and voice traffic in PSTN.

However, there are also a lot of differences between PSTN and optical networking. Unlike in PSTN, (most) optical networks allow for any kind of transport protocol, using a broad range of different bandwidths. And while there are some standards for interfaces between different exchange points, the general attitude between exchange points is one of openness and hardware independence.

Another important difference is that in the public telephony network, there is a global addressing system (prefix + phone number). Optical Networks currently do not have any addressing system. Theoretically they could use AS numbers, IPv4 address, or IPv6 address, but this would require global adoption of alll the exchange points. However, this is probably not something that will happen any time soon.

Routing in PSTN∞ is also something which cannot be implemented in optical networks. The main reason this cannot be used is the lack of addressing. Another reason that this is not suitable is because PSTN routing is based on global topology information, and analysis of traffic data. The topology information is currently not available (although the adoption of NDL will hopefully change that). And traffic data is not available at all, and even if it would help you take intelligent decisions about routing in optical networks, I don't believe that traffic data of optical networks will ever become available.