Skinny Client Control Protocol (SCCP)

Skinny Client Control Protocol (SCCP) is a proprietary protocol line side protocol that was originally created by Selsius. Cisco acquired Selsius in 1998 for 145 million in cash and stock. The newly acquired Selsius Call Manager platform used a standard Intel based PC architecture and all connections to time-division multiplexing (TDM) resources were accomplished using PCI expansion cards. The platform had analog cards (trunk or station) and gateway interfaces (T1 or E1) that all used a protocol called the Skinny Gateway Control Protocol (SGCP). SCCP was the line-side protocol using TCP port 2000 that was responsible for the communications between the Call Manager and the IP Phones (12SP+ and 30VIP at the time). As of this writing, SCCP registrations in Call Manager prefix the Cisco IP Phone MAC address with SEP (Selsius Ethernet Phone). All Selsius PCI expansion cards are EoS (end of sale) and EoL (end of life), but are mentioned for the sake of understanding the history of SCCP used in gateways, and how the SGCP protocol capabilities were merged into SCCP. Skinny Gateway Control Protocol was the protocol used to communicate between Call Manager and the gateway interfaces using TCP port 2001 for T1 and E1 digital gateway interfaces (SDA = Selsius Digital Access) and TCP port 2002 for analog gateway interfaces (SAA = Selsius Analog Access). TCP port 2001 and 2002 are still used in Auto QoS policies generated in routers and switches to ensure all voice signaling protocols receive a bandwidth guarantee over the network. SGCP is no longer used today, but SCCP is the only protocol supported by the VG248 gateway platform. The VG248 is a voice gateway with two female RJ-21 (amphenole) connectors. Each RJ-21 interface connects 24 FXS (Foreign Exchange Station) ports that connect analog devices with two-wire tip and ring connections. Punching down the RJ-21 connector cable to 110 blocks will surely test your patience. Fortunately, Cisco partners re-sell 110-blocks with RJ-21 connectors that match the pin out on the VG248. The VG224 is an EoS gateway platform that offers 24 FXS analog gateway interfaces. The VG224 supports the MGCP and H.323 protocols, but must use SCCP to support the entire supplementary service feature set. Supplementary services are voice feature such as: call hold, call park, conferencing, call transfer, etc. SCCP is very similar to MGCP in that there is minimal configuration that occurs on the Cisco IOS gateway platform. Most of the SCCP controlled gateway configuration is performed on the Call Manager platform. Cisco Unified Communications Manager (CUCM) version 4.2 and Cisco Unified Communications Manager Express (CUCME) version 3.2.2 introduced SCCP support of FXS gateway interfaces. Use the Cisco Feature Navigator available at to find the IOS version and feature set that supports SCCP Controlled Analog (FXS) Ports with Supplementary features in IOS Gateway for the IOS based gateway hardware in question. SCCP controlled FXS voice ports support many supplementary service features not supported by H.323, SIP, or MGCP gateway interfaces. A link to a detailed SCCP Controlled Analog (FXS) Ports with Supplementary features in IOS Gateway configuration has been provided for your reference. SCCP is also leveraged as the protocol in which CUCM communicates to DSP (digital signal processor) resources in gateways to provide hardware based conferencing and transcoding functionality. A link to an example of this configuration has been provided. The next blog post will examine the call survivability features of various gateway protocols. Feel free to post comments or ask questions about anything discussed in this blog. What gateway protocol do you use? Why did you select that gateway protocol and what advantage does it bring? Global Knowledge’s GWGK, CVOICE, CIPT, and IPTX classes offer more detailed information regarding gateway interfaces. Cisco Press Books CIPT1 GWGK SCCP Controlled Analog (FXS) Ports with Supplementary Features in Cisco IOS Gateways VG248 Enhanced Transcoding and Conferencing for IOS Voice Gateways in a CallMananger Network using DSP Resources Configuration Example

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