tailieunhanh - Signaling System No.7 Protocol Architecture And Sevices part 4

Common Channel Signaling (CCS) CCS refers to the situation in which the signaling capacity is provided in a common pool, with the capacity being used as and when necessary | Common Channel Signaling CCS CCS refers to the situation in which the signaling capacity is provided in a common pool with the capacity being used as and when necessary. The signaling channel can usually carry signaling information for thousands of traffic circuits. In North America signaling can be placed on its own T1 carrier even though it only takes up one timeslot. This means that two physical networks speech and signaling can have different routings. Please refer to Chapter 5 for a description of carriers and timeslots. Alternatively the signaling might exist on a carrier with other user traffic depending on the network operator. Outside of North America the signaling is placed in its own timeslot on an E1 that is logically rather than physically separated . The other timeslots on E1 are for user traffic apart from TS0 which is used for synchronization. E1 systems tend to use the TS16 timeslot for signaling some core network equipment ignores TS16 expecting it to be used for signaling traffic because it has historically been the timeslot for digital CAS signaling. The only CCS systems that have been implemented to date are Signaling Systems No. 6 and No. 7 SS6 and SS7 . The ITU for the international network originally standardized SS6 but they saw limited deployment. AT T nationalized SS6 for the North American network and called it Common Channel Interoffice Signaling CCIS No. 6. SS6 saw a limited deployment after the mid-1970s because it had far less bandwidth and a much smaller packet size than SS7. In addition its evolutionary potential was severely limited because it was not a layered protocol architecture. CCS systems are packet-based transferring over 200 bytes in a single SS7 packet as opposed to a few bits allocated to act as indicators in digital CAS. The signaling information is transferred by means of messages which is a block of information that is divided into fields that define a certain parameter or further sub-field. The signaling system s .