SIP (Session Initiation Protocol) and SCCP (Skinny Call Control Protocol) are both session control protocols in IP based communication networks. SIP is used for establishing, modifying, and terminating IP based communication sessions with one or more participants whereas SCCP is a Cisco proprietary protocol which is used for communication between Cisco Call Manager and Cisco VOIP phones. Cisco devices mainly support both these protocols but run SCCP natively. SCCP also stands for Signaling Connection Control Part, which is a protocol in the application layer of Signaling System 7 protocol stack.
SIP
SIP is a session control protocol which resides in the application layer and can perform multimedia session establishment, modification and tear down in real time communications over IP based networks. SIP was originally developed by the Internet Engineering Task Force (IETF) together with many leaders in the industry.
In managing sessions, SIP can invite participants to sessions that already exist such as multicast conferences. Media of the already existing session can be added or removed in real time. SIP also support for the implementation of ISDN and Intelligent Network telephony subscriber services, with transparently supporting name mapping and redirection services, which also contribute to enable the personal mobility. This is defined as the ability of end users to originate and receive calls while being able to be located by the network as they move across different switching areas, fully accessing subscribed telecommunication services on any terminal in any location.
Generally SIP devices communicate with each other using SIP servers which provide an infrastructure for routing, registration, and authentication and authorization services. SIP cannot exist alone in a communications system. So it is rather used as a component with other IETF protocols in order to build a complete multimedia architecture. These consist of various protocols like RSTP (Real Time Streaming Protocol), MEGACO (Media Gateway Control Protocol), SDP (Session Distribution Protocol), etc. SIP supports both IPv4 and IPv6; thus, it is very popular among many users.
SCCP
SCCP, which is commonly referred to as ” Skinny, ” was originally developed by the SELSIUS Corporation, and currently, a Cisco proprietary terminal control protocol used for call establishment, modification, and tear-down in VOIP (Voice over IP) environments. It is a lightweight protocol used for session control signaling with Cisco Call Manager. The Call Manager or Soft Switch controls the call setup processing initiated over most other common protocols such as H.323, SIP, ISDN, MGCP while the endpoints stream media directly between one another.
SCCP use the TCP port 2000 as the signaling path and use UDP as its media path. In a SCCP supported network where the endpoints are VOIP phone sets or devices with VOIP capability, run a program called the Skinny Client which minimizes the cost and complexity of VOIP end points.
In a VOIP call, first the phone registers its IP, type, and name in the CCM (Cisco Call Manager). Then the CCM request from the device to provide a list of supported voice and video codecs. It stores this data in the cache and translates them to the H.323 capabilities. The “Keep Alive” messages are exchanged periodically between the CCM and the phone as negotiated during the registration. SCCP also send alarms via CCM when there are errors such as network errors. Generally SCCP contains one or more messages for a packet made up of 4 byte fields.
Because of the extreme simplicity of the SCCP, now it has become highly interested among many other third party vendors.
SIP and SCCP
- SIP is an open source protocol, which can be used in any device, whereas SCCP is a Cisco proprietary protocol, which can be used only in Cisco products.
- SCCP supported phone is better than a SIP supported phone, because in a SCCP phone, in hands free mode, when start dialing, the phone automatically goes off hook, whereas, in the case of a SIP phone, it is required to press the speaker button manually in order to dial a new call, or pick up the phone before dialing.
- When compare the features offered by SIP phones against the SCCP phones, latter has more features supported.
- SCCP (Skinny Client Control Protocol) registrations are different from SIP since SCCP do not register using username and password, instead registering by the MAC address and provisioning device(s).
- Both protocols support multicast conference calls.
- SCCP is a very light weight protocol having very simplified message structure, whereas SIP has got a range of different messages with each having lot of additional data.
- Both protocols use UDP as the transport medium for their media path, because it is very good for real time traffic like VOIP traffic.