Signaling System No.1, Signaling System No.7, and PRI Signaling

Classified by signaling channel, signaling can be divided into:

    1. Channel Associated Signaling (CAS)

    2. Common Channel Signaling (CCS)

    Channel Associated Signaling (CAS):

    A signaling method in which signaling and voice are transmitted in the same voice channel. The channel associated signaling currently adopted in China is called the Chinese Signaling System No.1.

    Common Channel Signaling (CCS):

    A signaling method in which signaling for a group of voice channels is transmitted over a high-speed data link in a time-division manner. It is typically used between exchanges. The common channel signaling currently adopted in China is the Chinese Signaling System No.7.

    Chinese Signaling System No.1:

    It is a channel associated signaling. It is an inter-exchange trunk transmission method with 30/32 timeslots at 2048K. Timeslot 16 is used to transmit signaling for its voice channels. The register signaling is MFC (Multi-Frequency Compelled, i.e., two out of six frequencies are combined into a code group, yielding a total of 15 forward signaling types; two out of four frequencies are combined into a code group, yielding a total of 6 backward signaling types. Forward refers to transmission from the calling party to the called party, and backward refers to transmission from the called party to the calling party). The line signaling a, b, c, d is xx11. The difference between R2 signaling and Chinese Signaling System No.1 is that the register signaling of R2 signaling is DTMF (Dual-Tone Multi-Frequency), and the line signaling a, b, c, d is xx01.

    Signaling System No.7:

    SS7 is a common channel signaling. It transmits call control information and other service information through an independent signaling network. Since signaling and voice channels are separated, high-speed data links can be used to transmit signals, resulting in features such as fast transmission speed, short call setup time, and large signaling capacity. The standardization level of SS7 signaling is better than that of R2 signaling, but standardization compatibility issues still exist. For example, the domestic SS7 is called Chinese Signaling System No.7. In application, due to the need for destination address information, it is widely used for inter-exchange transmission. However, when used for subscriber-side access, due to the existence of destination address resource issues, its application is not as flexible or widespread as PRI signaling. Timeslot 0 is used as the frame synchronization information channel, timeslot 16 is used as the common signaling channel, and the remaining 30 timeslots are used as voice or data channels.

     PRI Signaling:

    Also known as ISDN (30B+D) signaling, DSS1 signaling, or PRA signaling.

    In North America and Japan, ISDN PRI provides 23B+D channels with a total rate of 1.544Mbps, where the D channel rate is 64kbps.

    In Europe, Australia, and other countries, ISDN PRI is 30B+D with a total rate of 2.048Mbps. In China, the 30B+D method is adopted.