Internet Drafts: draft-draft-taylor-ipdc-00.txt, draft-calhoun-diameter-07.txt

IP Device Control (IPDC) is a family of protocols, components of which can be used individually or together to perform connection control, media control, and signalling transports. It fulfills a need for one or more protocols to control gateway devices which sit at the boundary between the circuit- switched telephone network and the internet and terminate circuit- switched trunks. Examples of such devices include network access servers and voice-over-IP gateways. The need for a control protocol separate from call signalling arises when the service control logic needed to process calls lies partly or wholly outside the gateway devices. IPDC was build on the base structure provided by the DIAMETER protocol which was specifically written for authentication, authorization, and accounting applications.

The format of the header is shown in the following illustration:

Radius PCC
Packet Compatibility Code (PCC) field is used for RADIUS backward compatibility. In order to easily distinguish DIAMETER/IPDC messages from RADIUS a special value has been reserved and allows an implementation to support both protocols concurrently using the first octet in the header. The RADIUS PCC field must be set to 254, DIAMETER/IPDC message.

PKT Flags
Packet Flags are used to identify any options.

Version
Version number associated with the packet received. This field is set to 1 to indicate IPDC version 1.

Packet Length
Indicates the length of the message including the header fields.

Identifier
Aids in matching requests and replies.

Next Send
This field is present when the Window-Present bit is set in the header flags. The Next Send (Ns) is copied from the send sequence number state variable (Ss) at the time the message is transmitted.

Next Received
This field is present when the Window-Present bit is set in the header flags. Nr is copied from the receive sequence number state variable (Sr) and indicates the sequence number (Ns) +1 of the highest (modulo 2^16) in-sequence message received.

Attributes
IPDC Attributes carry the specific commands and parameters which must be exchanged between IPDC protocol endpoints to perform the tasks associated with Media Gateway control.