SS7 limitations

SS7 is a signaling network (data traffic) protocol used to send and receive signaling messages between Signaling End Points over dedicated signaling links. Operators deploy SS7 services over a dedicated network of 56- or 64-kbps Time Division Multiplexed (TDM) lines, or use high-speed T1 (1.5 Mbps) or E1 (2.048 Mbps) lines. SS7 uses centralized databases and services, achieves reliable connections through network management, and is secure because of its isolation from end users through the dedicated network. SS7 signaling is mature, with standards and a rich feature set, and offers these advantages to both wireline and wireless services.

However, SS7 limitations in scalability, bandwidth, and network availability slow network growth and opportunities to participate in new IP services:

• Scalability is limited by 16-link linksets consisting of 64 kbps transport

  Up to 16 links may be grouped into one circuit, or linkset. Adjacent network elements, such as Signal Transfer Points (STPs) and Service Control Points (SCPs), may be connected by no more than one linkset. The protocol further recommends that links and linksets are configured to no more than 40% of their maximum capacity, so that the alternate path can carry the full load of messages during failover.

• Bandwidth
  A traditional SS7 message size is limited to about 272 octets. E1/T1 links allow the transmission of larger messages, but not without originating, routing, or end points supporting either large messages or message segmentation.

  Note:

  If an E5-ENET-B card running the IPSG application is used and the E5-ENET-B IPSG High Throughput feature is turned on, then the optimal SS7 message size is 120 octets or less. See Table 5-5 for optimal configurations.

  A bandwidth of 56 kbps or 64 kbps per link and dedicated links reduce flexibility and increase cost significantly when creating sufficient bandwidth for new service applications. In a TDM network, entire transmission segments must be reserved for each call, even if the TDM connection is idle.

TDM-based SS7 is continuing to evolve, but slowly. Instead, wireline and wireless operators are looking to IP solutions.