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SGCP Simple Gateway Control Protocol Christian Huitema [email protected] SOLIANT Internet Systems May 1998 Page 1 State of the art, trunking GW SS7 relay => non standard, delays H.323 => transparency, delays TGW => real time, software ? STP SS7 GW SS7 GW IP Network CO Internet Systems relay ? TGW TGW <- H.323 -> SOLIANT STP May 1998 Page 2 C O SGCP: trunking gateway SS7 STP SGCP endpoint SS7 trunk group Call Agent TGW-1 TGW-2 CO TGW-3 Phys-R3W/15 @ tgw-1.example.net SOLIANT Internet Systems May 1998 Page 3 SGCP architecture (TGW) The call agent implements the SS7/ISUP standards. It uses SGCP to “remote control” the gateways. SS7/ISUP STP Call agent SS7/ISUP STP SGCP/UDP IP Network CO TGW TGW RTP SOLIANT Internet Systems May 1998 Page 4 CO SGCP: connection set-up SDP: Session Description Protocol (RFC 2327) Call agent 1- CreateConnection GW1 SDP data (E1) 2- CreateConnection (SDP, E1) GW2 SDP data (E2) 3- ModifyConnection (SDP, E2) GW1 ACK E1 GW1 GW2 RTP SOLIANT Internet Systems May 1998 Page 5 E2 SGCP: connection removal 1- DeleteConnection GW1 ACK Call agent E1 SOLIANT Internet Systems 2- DeleteConnection GW2 ACK GW1 GW2 RTP May 1998 Page 6 E2 State of the art, residential GW GW What protocol ? • H.323 ? (v1, v2, …) • SIP ? SOLIANT Internet Systems May 1998 Page 7 SGCP architecture (RGW) The intelligence is centralized in a call agent, not in the trunking gateway (TGW) or in the residential gateway (RGW) SS7/ISUP STP Call agent SGCP/UDP IP Network CO TGW RGW RTP SOLIANT Internet Systems May 1998 Page 8 SGCP: event notification 1- NotificationRequest (ring, off hook?) GW1 ACK 2- Notify (off hook!) Call Agent ACK Call agent E1 GW1 SOLIANT Internet Systems May 1998 Page 9 Incoming Call (from PSTN) Call Agent SCP STP SS7 Gateway IP Network CO SOLIANT Internet Systems GT1 GT2 May 1998 Page 10 SGCP architecture (H.323) The call agent implements multiple protocols, such as SS7 or H.323, uses SGCP to control the gateways SS7/ISUP Call agent H.323 STP SGCP/UDP RTP IP Network CO SOLIANT Internet Systems TGW RGW May 1998 Page 11 SGCP architecture (SIP) The call agent can easily implement multiple protocols. Relaying to SIP is easy, because SGCP incorporates the SDP protocol. SS7/ISUP Call agent SIP STP SGCP/UDP RTP IP Network CO SOLIANT Internet Systems TGW RGW May 1998 Page 12 SGCP architecture (NAS) The call agent receives a call to 1-800-INTERNET. It uses SGCP to parametrize the gateway. Call agent SS7/ISUP Radius STP SGCP/UDP IP Network CO SOLIANT Internet Systems TGW May 1998 Page 13 server SGCP Pros and Cons SOLIANT Internet Systems May 1998 Page 14 SGCP Pros SOLIANT Internet Systems SGCP is based on a Centralized Call Intelligence Architecture Centralized call intelligence can still rely on distributed systems to achieve high performance and reliability at an affordable price. May 1998 Page 15 SGCP Pros (Centralized Call Intelligence Architecture) SOLIANT Internet Systems Simple and stateless endpoints more reliable than complex and stateful. Call Agents with call intelligence and complexity under physical control by service provider. Large number of endpoints not a major OA&M concern. Services available strictly a function of Call Agents: - Different endpoint vendors not a concern - Different endpoint software version and vendor not a concern. May 1998 Page 16 SGCP Pros (Centralized Call Intelligence Architecture) SOLIANT Internet Systems A must for reliable billing. Feature change and software updates only needed on limited number of tightly controlled and centralized Call Agents. Total cost of ownership under control. Higher reliability and better service. May 1998 Page 17 SGCP Pros UDP based instead of TCP: - Support for failover - Scalable - Real-time SOLIANT Internet Systems No connection setup delay Avoid TCP retransmission strategy Small set of simple transactions: - Low CPU and memory requirement for endpoint No need for expensive and resource-hungry parsers. May 1998 Page 18 SGCP Pros SOLIANT Internet Systems Truly Interoperable endpoints can be developed cheaply. Simple to use and program Powerful enough to support/enable current: - Basic telephony services. - Enhanced telephony services, e.g. call waiting, call transfer, conferencing, etc. Flexible enough to support future IP telephony services. May 1998 Page 19 SGCP Cons SOLIANT Internet Systems Centralized Call Intelligence is critical to system - if Call Agents are unavailable, service will be unavailable (but servers can be made highly robust, SGCP supports failover). Requires low-delay and low-loss network for optimal performance (but so does VoIP in general). SGCP is not yet widely deployed. No self-announcement, self-provisioning (could be added, probably outside of SGCP -SGCP uses DNS names, appliance may well use DHCP). May 1998 Page 20 SGCP Industry Support SOLIANT Internet Systems May 1998 Page 21 Standardization SOLIANT Internet Systems SGCP is a completely open protocol. Bellcore will provide a reference implementation. SGCP Web site: http://sgcp.bellcore.com/ SGCP spec. publicly available at: http://www.ietf.org/internetdrafts/draft-huitema-sgcp-v100.txt SGCP reflector - subscription [email protected] May 1998 Page 22 Standards Bodies et. al. SOLIANT Internet Systems CableLabs First presentation of SGCP - May 13, 1998 IETF Submitted as Internet Draft - May 15, 1998 ETSI TIPHON Submitted for Helsinki meeting - May 26, 1998 IMTC VoIP Forum SGCP to be presented in mid-July May 1998 Page 23 Industry Support SOLIANT Internet Systems SGCP actively supported and currently being implemented by Cisco Systems and Bellcore. Currently working with a cable TV company on an end-to-end SGCP based Voice over IP solution. Several Voice over IP vendors have admitted privately to be working with “something like SGCP” Initial feedback from the industry has been mostly positive. Many VoIP vendors already subscribe to the SGCP reflector to ensure an open and comprehensive protocol. May 1998 Page 24