What Are Signaling System No. 1, Signaling System No. 7, and PRI Signaling?

Signaling can be classified by the signaling channel 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 CAS 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 single high-speed data link in a time-division multiplexed manner. It is typically used between exchanges. The CCS currently adopted in China is the Chinese Signaling System No. 7.

    Chinese Signaling System No. 1:

    It is a Channel Associated Signaling system. It is used for 30/32 timeslot 2048K inter-exchange trunk transmission. Timeslot 16 is used to carry signaling for its voice channels. The register signaling is MFC (Multi-Frequency Compelled, which uses combinations of two out of six frequencies to form a code group, providing a total of 15 forward signaling types, and combinations of two out of four frequencies to form a code group, providing 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 R2 signaling uses DTMF (Dual-Tone Multi-Frequency) for register signaling, and its line signaling a, b, c, d is xx01.

    Signaling System No. 7:

    SS7 is a Common Channel Signaling system. It transmits call control information and other service information through a dedicated signaling network. Since signaling and voice channels are separated, high-speed data links can be used to transmit signals, resulting in fast transmission speed, short call setup time, and large signaling capacity. SS7 signaling is better standardized than 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 point code information, it is widely used for inter-exchange transmission. However, when used for subscriber-side access, due to the existence of destination point code resource issues, it is not as flexible or widely used 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 for 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 1.544 Mbps, where the D channel rate is 64 kbps.

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