Techopedia Explains Signaling Gateway (SGW)
To put Voice over Internet Protocol (VoIP) communications into operation, the ability to inform an end point that another end point wants to communicate is essential (e.g., by making the recipient’s phone ring). This process is known as signaling.
However, the signaling technique used in public switched telephone network (PSTN) circuits is different from those used in VoIP circuits. Therefore, a gateway should be used to translate between the two in cases where there is no pure VoIP connection. This is, in fact, the signaling gateway that is effectively used in standard interworking signaling protocols such as Channel-Associated Signaling (CAS), Dual-Tone Multi-Frequency (DTMF), Integrated Services Digital Network (ISDN), R1, R2, C5 and C7.
An SGW can be used as a standalone network element or as an integrated part of some other network element. The SGW function can be incorporated within the larger operational domain of the signal transfer point (STP).
The key SGW functions that establish the connection between an SS7 network and a VoIP network are as follows:
- Transparency: The SGW must be transparent to both the SS7 network and the VoIP. It needs to appear as a signaling end point or a pass-through device for SS7 messages, supporting the correct protocols and application programming interfaces.
- Translation: The address translation between the SS7's addressing scheme (point codes) and the VoIP network (IP addresses) is carried out by the SGWs. Also, if the SGW functions as an STP for the SS7 network, it is essential to carry out global title translation functions, for example, telephone number to point codes.
- Trusted routing: The trademark of the SS7 network is the dependability of its message delivery. The SGW ensures that the reliability is carried throughout the IP network. The stability is guaranteed by the multi-homing functionality of the SCTP.
