Evalution of SS7

When telephone networks and network switching hierarchies were first engineered, their creators gave little thought about future technological advancements. Early telephone systems were based on transferring analog voice signals using analog equipment over analog transmission media. As a result , early telephone systems were not well suited for modern day digital services, such as data, digitalized video transmission. There fore, when digital services were first offered in the early 1960s, the telephone networks were ill prepared to handle them, and need for an intelligent all-digital networks rapidly became evident.

The ITU commissioned the Comitee Consultatif International Telephonique et Telegraphique to study the possibility of developing an intelligent all-digital telecommunications networks. In the mid -1960s, the ITU - TS developed a digital signaling standard known as Signaling system N0.6(SS6) that modernized the telephone industry. Signaling refers to the exchange of information between call components required to provide and maintain service SS6, based on a proprietary , high-speed data communications networks, evolved into signaling system.no.7(SS7) , which is now the telephone industry standard for most of the people in the world. High-speed packet data and out-of-data signaling characterize SS7. Out -of-band signaling is signaling that does not take place over the same path as the conversation.

The protocol used with SS7 uses a message structure, similar to x.25 and other message based protocol , to request services from other networks. The message propagate from one network to another in small bundles of data called packets that are independent of the subscriber voice or data signals they pertain to. In the early 1960s, the ITU - TS developed common channel signaling known as common channel interoffice signaling system no. 6 (SS6). The basic concept of the common channel signaling is to use a facility for transferring control and signaling information between telephone offices.

SS7 in an architecture for performing out-of-band signaling in support of common telephone system functions of the ,such as call establishing , billing , call routing , and information exchanging functions of the PSTN .SS7 identifiers functions and enables protocols performed by a telephone signaling networks . The major advantages of SS7 include better monitoring maintenance , and network administration. The major disadvantages is its complex coding .

Because SS7 evolved from SS6 there are many similarities between the two systems. SS7 uses variable - length signal units with a maximum length, therefore making it more versatile and flexible than SS6. In addition, SS7 uses 56-kbps data links which provide a much faster and efficient signaling network. In the future, data rates of 1.544 Mbps nationally and 2.048 mbps internationally are expected. The solution involved adding a second number to every 800 number that is used by the switching equipment to actually route a call through the voice network.

The second number is placed in a common, centralized database accessible to all central offices. When an 800 number is called, switching equipment uses a data link to access the database and retrieve the actual routing number. This process is of course , transparent to the user. Once the routing number is known , the switching equipment can route the call using standard signaling methods.

Today , SS7 is being used throughout the Bell Operating Companies telephone network and most of the independent telephone companies. This itself makes SS7 the worlds largest data communications networks, as it links wireline telephone companies, cellular telephone companies , and long-distance telephone companies together with a common signaling system. Because SS7 has the ability to transfer all types of digital information, it support most of the new telephone features and applications and is used with ATM, ISDN, and cellular telephone.