Packet Softswitches – The Next Generation


Overview & Discussion on Softswitches (carrier grade packet switching), the next generation of telephone switching systems in the Public Switched Telephone Network.

Overview & Background

The Internet and the technologies that are used with the Internet changed the idea of how communications are handled. Traditional telephone company technologies were direct point-to-point systems where dedicated “trunks” (toll circuit routes) were used. Once a trunk was allocated, the trunk stayed up for the entire connection. If a trunk was not being used, it sat idle – underutilizing limited resources.

The Internet (TCP/IP and Ethernet in particular) uses a completely different paradigm (methodology). In the TCP/IP world, all systems share a common connection. Each system (usually a computer) was connected to this common system and shared “bandwidth” with other people. Resources were not allocated for just one user, but all users can share resources.

Another advantage of using TCP/IP technology is the switching “matrix” is also different and more efficient. Instead of using a dedicated switching matrix – with a limited amount of circuits in a traditional telephone switch, TCP/IP routers (traffic handlers) could be used. This increases the amount of switching “lines” and can do it more efficiently than traditional switching systems since all the switching is done on a “virtual” scale in software rather than in hardware.

Telephone systems have been slowly adopting the “IP” (Internet Protocol) technology over the last 8 to 10 years. Early experiments proved that voice can be converted to digital “packets” and sent over the Internet. The packets would be collected and converted back to analog voice. The quality of the calls was not great but it showed that it could be done. The major problem was something called “packet loss” which is common with TCP/IP connections.

By the early 2000s, the IP telephony (or “VoIP” – Voice over Internet Protocol) technology had improved. Using “classes” of service, reliable connections could be obtained and packet loss reduced to minimum levels. Business systems started using VoIP technology in their PBX (Private Branch Exchange) switches. The telephones themselves were almost like small computers that had their own analog/digital conversion systems and TCP/IP networking technology all the same system. The phone could “piggy-back” on their existing computer network system. Hence having voice AND data traffic over the same wires!

Telephone companies – both local and toll – are also handling data traffic at alarming rates. For example, AT&T is handling 5 to 10 times more data traffic than it handles for traditional voice traffic. To handle both efficiently – it would be cost effective to have switching systems that handle data switching on a high volume scale – that can serve both the voice market AND the data market at the same time.

The result is a new market for a new kind of telephone switch known as the “softswitch” that can route both traditional “circuit-switched” and more modern “packet-switched” telephone calls utilizing software VoIP packet-switching technologies rather than hardware time-division multiplexed technologies

Softswitches in the Public Switched Telephone Network

Starting at the turn of the 21st century, there was a huge push to move from the traditional digital telephone switch (called Time Domain Multiplex or TDM) in the network to go to carrier-grade softswitches. There were a number of vendors, big and small who were making softswitches. Then basically overnight, most of the market had vanished. As of 2021 there are very few carrier grade softswitch vendors left in the industry.

In the early 2000s, companies such as Lucent (now Nokia) and Nortel (out of business) were making softswitches. Lucent was making the Lucent SoftSwitch (LSS) which was based off the then-current #5ESS TDM based switch. It was designed to be fully compatible and work in conjunction with the #5ESS. This turned out to be a very short lived product, and I don’t recall this being used in the public switched telephone network (PSTN).

Nortel was working on the Communications Server (CS) family of softswitches, also starting around the year 2000. Nortel was making a huge push for them to replace TDM switches, including their own DMS line of TDM switches (DMS-10, DMS-100, etc.). Several independent companies were starting to replace their DMS based switches. Sprint Local (now part of CenturyLink/Lumen Technologies) had started down the path of installing the Nortel Communications Server 2000 switches in various places nationwide starting in the fall of 2003. This included cities such as Las Vegas, NV.

Other traditional switch manufacturers were making softswitches as well. Siemens of Germany had started making the SURPASS line of softswtiches. The SURPASS hiQ 8000 Softswitch provides the switching matrix while the SURPASS hiG 1200 Media Gateway interfaces traditional digital time-division multiplex switches to VoIP technology. Like the Lucent switches above, I’m not sure how many of these actually made it to the PSTN.

Finally, smaller manufacturers of softswitches got into the game. This included a now defunct company called CopperCom. For example, local telephone providers in Iowa in 2005 and 2006 replaced their older Vidar and Mitel switching systems with CopperCom Converged Switching eXchange (CSX) softswitching systems.

The following are pictures of a then new installation (November 2005) of a CopperCom softswitch which replaced on old Vidar switch in Linn Grove, Iowa. Notice the use of Sun Sunfire computers below the CopperCom softswitch.

CopperCom CSX Softswitch in Linn Grove, Iowa

In the early 2020s, there are a handful of companies that are left that are making softswitches for the PSTN. Metaswitch and Ribbon Communications (formerly Genband) are two such companies. Ribbon primarily makes them for the former Bell companies, while Metaswitch makes them for the independents.

Ribbon Communications is one of few remaining companies that are still making carrier grade softswitches. Ribbon purchased Genband, who had originally purchased the intellectual property of the Nortel softswitch line when they went bankrupt. Towards the end of the 2010s, AT&T local (mostly the old BellSouth and SBC areas) were finally replacing their very long in the tooth #1AESS switches.

By the time the were replacing these very old switches, the TDM switches that replaced the majority of these switches in the 1980s and 1990s were no longer being made. The WECO/Lucent #5ESS line, the Nortel DMS-100 line and the Siemens EWSD line were no longer being made as of the mid 2000s. So the #1AESS actually outlived the entire TDM production line! The last 50 or so #1AESS switches were replaced with Genband (now Ribbon) softswitches – either the G5 Line Access Gateway or the G6 Universal Gateway or both together. The last #1AESS in the PSTN was in the Lincoln wirecenter of the Odessa, TX ratecenter – and was replaced with one of these G5/G6 switches in June 2017.

The Ribbon/Genband G5 Line Access Gateway Softswitch


Finally, Metaswitch continues to make carrier grade softswitches, primarily used in the independent (non former Bell) market. Many small independent “mom and pop” type of phone companies as some larger independents (Windstream, for example) have converted over from TDM switching (such as the Nortel line of DMS switches) to Metaswitches. Starting in 2005, they introduced their VP2510 and VP3510 universal gateway switches. As of 2021 they are producing the VP6010 integrated softswitch and the MG6010 and MG6050 Media Gateways.

Metaswitch VP2510 (Produced 2004-2012) and still in use


Metaswitch VP6010

Metaswitch MG6050

More Details

Wikipedia article on softswitches
A Wikipedia article that gives a good background and description of softswitches.

What is a VOIP Softswitch

Modern Telephone Switching Systems Index

Overview & Background of Modern (Electronic & Digital Switching) Systems
Automatic Electric Modern Switching Systems
Northern Telecom (Nortel) Modern Switching Systems
TRW-Vidar Switching Systems
Other Modern Switching Systems of Note
Western Electric/Lucent Technologies
Packet Switching/Softswitches

Telephone Switching Systems of North America

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