tailieunhanh - Signaling System No.7 Protocol Architecture And Sevices part 16

Signaling Link Initial Alignment The purpose of the signaling link alignment procedure is to establish SU timing and alignment so that the SPs on either side of the link know where SUs | Signaling Link Initial Alignment The purpose of the signaling link alignment procedure is to establish SU timing and alignment so that the SPs on either side of the link know where SUs begin and end. In doing so you must inherently test a link s quality before putting it into use. Example L-1 in Appendix L shows a trace file of two aligned SPs. The signaling link alignment procedure ensures that both ends have managed to correctly recognize flags in the data stream. Initial alignment is performed for both initial activation of the link power on to bring it to service and to restore a link following a failure. Alignment is based on the compelled exchange of status information and a proving period to ensure that SUs are framed correctly. MTP3 requests initial alignment which is performed by MTP2. Because MTP2 operates independently on each link the initial alignment procedure is performed on a single link without involving other links. There are two forms of alignment procedures the emergency procedure and the normal alignment procedure. The emergency procedure is used when the link being aligned is the only available link for any of the routes defined within the SSP. Otherwise the normal alignment procedure is used. Status Indications LSSUs are exchanged as part of the alignment procedure. There are six different status indications as shown earlier in Table 6-1. Only the first four indications are employed during the initial alignment procedure. The alignment procedure passes through a number of states during the initial alignment Idle Not Aligned Aligned Proving Aligned Ready In Service Idle When an SP is powered up the links are initially put in the idle state. The idle state is the first state entered in the alignment procedure it indicates that the procedure is suspended. If the procedure fails at any time it returns to the idle state. Timer T17 MTP3 prevents the rapid oscillation from in service to out of service. Timer T17 is started when the link begins the .