** Article reproduced from NECAssociate News August 2002 Issue.

To Handle Exploding Signaling Demands, Move SS7 to IP

With bandwidth less scarce than it once was, the networking world should now focus on the ongoing explosion in signaling obligations with a view to both reducing the number of SS7 links needed and conserving scarce STP link ports. SS7 signaling traffic can now be reliably shifted onto lower-cost IP-based networks and concentrated onto fewer, highly utilized signaling links using intelligent new SS7 transport and routing products such as SS7 link replacement devices or IP-STPs.

Burgeoning SS7 applications - including call display, caller ID, wireless roaming and short messaging service - are contributing to incredible growth in SS7 signaling needs. New SS7 technologies provide cost-effective options for offloading out-of-band signaling to more efficient and lower-cost IP networks while retaining the high reliability required in traditional SS7 networks. They can also free up STP connection ports by concentrating traffic onto fewer SS7 links.

Offloading SS7 to IP
Signaling traffic for voice telephony is transported, routed and housed in the SS7 network on dedicated circuits and facilities generally owned by ILECs, inter-exchange and wireless carriers. Often, SS7 links that originate and terminate at the edge of the PSTN transport signaling messages over dedicated 56kbs circuits with relatively low SS7 traffic utilization. Using SS7 network link replacement devices, wireline and wireless operators can offload long-haul signaling traffic now carried over redundant SS7 links, to much less expensive IP networks. These can be used separately to reduce long haul link costs, or can be integrated with IP-STPs to provide a more sophisticated and cost effective alternative to SS7 network configurations.

IP-STPs have general STP functionality that can be used to route SS7 traffic. They can look at a message, for instance, and determine it was destined for a database application, such as an HLR, an SCP or an SMS server. Routing directly to these large databases rather than an STP offers significant advantages to a carrier in terms of reducing costs and simplifying network configurations. It may also provide an opportunity to handle less critical SS7 messages (such as SMS text messages) through alternative network transport arrangements.

Figure 1: Transporting SS7 over IP in a Wireless Network

Network management and provisioning becomes much more complex as more SS7 links are added. Reliably offloading SS7 signaling to IP, however, can reduce network complexity and serve as a bridge for carriers planning eventual migration to all-IP based networks but currently committed to amortizing existing circuit-based infrastructure. It can help absorb demand for SS7 links and cut the swelling cost of provisioning new links.

SS7 over IP can Save Money
The typical service provider leasing SS7 circuits is probably paying about a dollar-a-mile, per-link, per-month for SS7 links, which could swell to $10-per-mile for international coverage. Using SS7 link replacement devices at the network edge to reliably run SS7 traffic over IP can virtually eliminate these long haul costs. Saving money on STP ports is the second part of this equation.

Because current network STPs are designed to handle a finite number of SS7 links, STP exhaust is the curse of the network planner. Carriers always look to efficiently add STP ports, but the last thing they want is to add a new multi-million dollar STP. For carriers leasing SS7 facilitates, small but powerful IP-STPs that "front-end" existing STPs can reduce incumbent STP port and core network access charges by as much as 80 percent.

Reliable and Secure Transport
These new devices use the new Stream Control Transmission Protocol (SCTP), an industry standard designed to provide SS7 transport reliability comparable to that in traditional TDM networks. SCTP insures message acknowledgement and retransmission schemes and supports multi-homing and multi-streaming capabilities that let connections simultaneously transfer signaling messages to independent networks quickly and efficiently. This routes more reliably than standard TCP over IP and supports multiple network-interface controllers so that end points can pick the most reliable IP-network route for transmission.

SCTP also works with IP SEC, a protocol designed to securely encrypt messages used over IP networks. Devices that support SCTP with IP SEC offer carriers a reliable and secure means of transporting SS7 over IP.

Conclusion
SS7 message transport is far outstripping the growth in voice traffic, particularly with the popularity of new wireless applications. Most carriers, meantime, are planning for IP while preserving legacy equipment. An efficient and reliable transition technology can save link-leasing costs for providers, conserve STP capacity for carriers, and provide a practical signaling platform for architects of next- generation all-IP networks.

No self-respecting carrier with a huge investment in SS7 - the most reliable piece of their networking architecture - is going to risk moving into such new territory unless they feel confident of the reliability of signaling transport in IP land. But with new, highly reliable technology standards for routing SS7 over IP, a credible economic and management-simplicity case can be made for it.