Network-based Call Signaling, based on the Media Gateway Control Protocol (MGCP), is the VOIP signaling protocol adobted by the CableLab as a standard for PacketCable embbed clients, which is a network element that provides:

• Two or more traditional analog (RJ11) access lines to a voice-over-IP (VoIP) network.
• Optionally, one or more video lines to a VoIP network

MGCP is a call signaling protocol for use in a centralized call control architecture, and assumes relatively simple client devices. The call signaling protocol is one layer of the overall PacketCable suite of specifications and relies upon companion protocol specifications to provide complete end-to-end PacketCable functionality.

NCSprovides a PacketCable profile of an application programming interface (MGCI), and a corresponding protocol (MGCP) for controlling voice-over-IP (VoIP) embedded clients from external call control elements.MGCI functions provide for connection control, endpoint control, auditing, and status reporting.They eachuse the same system model and the same naming conventions.

Thr NCS profile of MGCP has been modified from the MGCP 1.0in the following ways:

• The NCS protocol only aims at supporting PacketCable-embedded clients. Functionality present in the MGCP 1.0 protocol, whichwas superfluous to NCS, has been removed.
• The NCS protocol contains extensions and modifications to MGCP. However, the MGCP architecture, and all of the MGCP constructs relevantto embedded clients, are preserved in NCS.
• The NCS protocol contains minor simplifications from MGCP 1.0

The relations between MGCP/NCS and other VOIP standards such as H.323 and SIP are displayed as follows:

NCS: Network-Based Call Signaling Protocol

Protocol Structure

NCS uses the same protocol format as the MGCP, which is a text-based protocol. The transactions are composed of a command and a mandatory response. There are eight types of commands:

• MGC -> MG: CreateConnection: Creates a connection between two endpoints; uses SDP to define the receive capabilities of the participating endpoints.
• MGC -> MG: ModifyConnection: Modifies the properties of a connection; has nearly the same parameters as the CreateConnection command.
• MGC <-> MG: DeleteConnection: Terminates a connection and collects statistics on the execution of the connection.
• MGC -> MG: NotificationRequest: Requests the media gateway to send notifications on the occurrence of specified events in an endpoint.
• MGC <- MG: Notify: Informs the media gateway controller when observed events occur.
• MGC -> MG: AuditEndpoint: Determines the status of an endpoint.
• MGC -> MG: AuditConnection: Retrieves the parameters related to a connection.
• MGC <- MG: RestartInProgress: Signals that an endpoint or group of endpoints is taken in or out of service.

Related protocols: MGCP, RTP, RTSP, SIP, H.323, Megaco, H.248

Sponsor Source: NCS is a CableLab defined standard based on MGCP.

Reference:
http://www.packetcable.com/downloads/specs/PKT-SP-NCS1.5-I01-050128.pdf: Network Based Signaling Protocol
http://www.javvin.com/protocol/rfc3435.pdf: Media Gateway Control Protocol (MGCP) Version 1.0.