Signaling Gateways: STP vs. SEP

The SEGway™ Signaling Gateway can be configured as an STP (Signal Transfer Point) or as a Signaling End Point (SEP). However, understanding how each configuration can be applied can be confusing. The following is a description that may be useful in distinguishing each capability.

Three important components of an SS7/IP converged network are the SSP (service switching point), the STP and the SEP. Equipped with SS7 software, the SSP is a telephone switch, or "end node," that sends signaling messages to other SSPs or STPs to set up, manage and release voice circuits required to complete a call. The STP is a signal packet switch (or router) that receives and routes incoming signaling messages on to their destinations. SEP is a generic term referring to an SS7 end node with similar functionality as the SSP in an IP telephony network.

A traditional voice switch (SSP) provides call control, trunk switching and signaling in a single (large) entity. These same functions in the IP telephony environment are provided by separate (distributed) entities: a softswitch or media gateway controller, a media gateway and a signaling gateway. The virtual switch created by combining these functions in the IP environment becomes a SEP. Both SSPs and SEPs are connected to STPs via "A" links. Both are also single point codes in the SS7 network.

SEP and STP configurations perform unique network functions. When the signaling gateway is configured as an STP, it can provide routing and concentrating capabilities and may also provide global title translation (GTT) and SS7 traffic concentration. Generally speaking, when signaling gateways are used as STPs in a converged network, they connect to other STPs in the PSTN (via "B" or "D” links) and offer the flexibility of routing to a number of different PSTN locations(e.g. an 800, LIDB, or local number portability database). If routing to IP based applications (e.g. databases or softswitches) is required and the customer needs unique SS7 network addresses (point codes), STP functionality is also needed.

The following diagram illustrates an STP configuration with the SEGway Signaling Gateway routing SS7 messages through various applications appearing as unique signaling points in the PSTN network or in the IP network. For example, the SCP in the PSTN could provide 1-800 service. The SCPs in the IP network could provide different applications (e.g. Internet call waiting, prepaid card, or HLR capability). More importantly, these databases have separate point codes in the SS7 network and therefore require STP routing functionality to access.

Figure 1 - SEGway Signaling Gateway Configured as an STP

In SEP mode, (illustrated below), the SEGway Signaling Gateway acts as an end node, terminating SS7 links. In this mode, the signaling gateway is not used for routing. The virtual switch composed of media gateway(s), media gateway controller (softswitch), and signaling gateway is represented by a single point code in the SS7 network.

Figure 2 - SEGway Signaling Gateway Configured as an SEP (End Node)