4 Steps in the Evolution of Telecommunications Signaling

8 Aug

The technological evolution of signaling has been very important to telecom carriers and equipment vendors throughout the history of telecommunications. Signaling has been, and will continue to be, the foundation of telecommunications – providing customers the ability to communicate both locally and over long distances. Moreover, the evolution of telecommunications signaling has changed societal behavior globally – allowing subscribers to move throughout the entire world while still remaining in constant communications, both personally and professionally. Signaling evolution continues today in the mobile environment as it moves from SS7-based networks to LTE/EPC/Diameter networks.

Step 1. Dial Pulse Signaling

The first stage of signaling evolution was from the mesh network, characterized by an operator assisted call setup, to an automatic selection network. Subscribers then dialed the number of the party they wanted to talk to. This Dial Pulse signaling was between the subscriber and the central office and also between central offices.

Advantages of Dial Pulse Signaling:

  • Easy to implement

Disadvantages of Dial Pulse Signaling:

  • Extremely slow (serial signaling)
  • Limited amount of signaling data between switches (10 digits)
  • Signaling equipment required on every inter-switch trunk

Step 2. Channel Associated Signaling

The next stage of telecommunications signaling evolution was Channel Associated signaling. Channel Associated signaling is either a digital or tone-based methodology and is also known as “Per Trunk signaling.” This type of signaling allowed more information to be sent between central offices (up to 15 different signals).

Advantages of Channel Associated Signaling:

  • More data sent between offices
  • Faster than Dial Pulse

Disadvantages of Channel Associated Signaling:

  • Sent on same channel as voice, limiting available bandwidth
  • Little or no error checking on signaling
  • Signaling equipment required on every inter-switch trunk

Stages of Telecommunications Evolution

Stages of Telecommunications Evolution

Step 3. Signaling System # 7 (SS7)

SS7 is still the predominant signaling methodology within the telecommunications network. SS7 is an out of band signaling concept where all of the signaling is separated from the voice or data connections that it is facilitating. The deployment of SS7 required the building of an overlay-signaling network including the following network elements:

  • Signal Transfer Point (STP)
  • Service Switching Point (SSP)
  • Service Control Point (SCP)
  • Signaling Data Links

The SS7 network, and its associated protocol, is the most robust, feature rich and long lived in telecommunications history. However, this was not always the case. In the early stages of SS7, there were many network outages caused by the network, protocol, and the unfamiliarity with these new concepts. The industry came together as a whole – setting up test environments and test plans to solve the problems and make the SS7 network and protocol what it is today. Lessons Learned.

The SS7 Protocol is made up of multiple layers including:

  • Message Transfer Parts (MTP)
  • ISDN User Part (ISUP)
  • Transaction Capability Application Part (TCAP)

As the network evolved from SS7 through SIGTRAN to LTE/EPC/Diameter, the transport medium was defined to be IP with a transport protocol of Stream Control Transmission Protocol (SCTP). The call setup layer of SS7 (ISUP) is being replaced by Session Initiation Protocol and the transaction layer of SS7 is being replaced by Diameter. More Lessons Learned.

Step 4. LTE/EPC Diameter

The next step in the planning and design was to decide which transport protocol to use. Because the IETF designed the Diameter protocol to use the services of either TCP or SCTP on top of IP, network operators and equipment vendors had to choose between the two. The reliability and survivability required in the Evolved Packet Core (EPC) made this choice relatively easy. Because the network required real-time, guaranteed sequence delivery of messages, the only choice was SCTP. SCTP also provided the added benefit of multi-homing, thus adding to the reliability of the network.

The Diameter protocol was selected over Radius to replace the transaction layer due to the following deficiencies of Radius:

  • Reliability
  • Scalability
  • Security
  • Flexibility

Importance of Understanding Evolution

Some people have said that the only way I know the stages of telecommunications signaling is that I was there for each of the stages – maybe or maybe not. Some others want to know why it is important to have an understanding of these stages. It is my belief that most everything is evolutionary and if we have an understanding of the foundation, we can avoid the pitfalls encountered in previous stages. I have read and heard that an exception to this rule is Steve Jobs and Apple, with their revolutionary products; however, Apple has never been first to market with any product. They have only advanced existing capabilities.


Source: http://blog.pt.com/4-steps-in-the-evolution-of-telecommunications-signaling?utm_source=linkedin&utm_medium=social&utm_content=1125590


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