/mcpStandard Feature Scenarios This section provides details with respect to overall flow and handling of standard SIP features on the Unified CM line-side interface. This includes, but is not limited to, the following features: Registration Unified Communications Manager supports standard RFC3261 registration from any compliant SIP phone. Because Unified CM is a B2BUA, however, it must be able to uniquely identify the registering device to match that device with a configuration entry in the database. Furthermore, Unified CM must be able to identify the originating device (and line) for all other SIP requests that it receives (INVITE, REFER, SUBSCRIBE, and so on) to authorize, filter, and route the message. Because standard SIP does not provide a consistent and unambiguous mechanism for identifying the originating device, for standard registration, Unified CM relies on the HTTP digest user ID to identify the sending device. Knowledge of the sending device and line allows Unified CM to apply various routing, authorization, and filtering logic to incoming registrations, subscriptions, and invites. The system supports TCP and UDP transports for Standard registration, but not TLS. Source Device ID for RFC3261-Compliant Phones Unified Communications Manager must uniquely identify the device sending the REGISTER message to apply authentication, routing, and filtering. The Contact IP address is not suitable because it can change dynamically if DHCP is used. Instead, Unified CM uses the HTTP digest user ID. Each device that is configured in Unified CM requires a unique digest user ID. When the device sends the REGISTER, Unified CM will immediately respond with a 401 challenge to get the Authentication header. The system uses the user ID from the authentication header to find the configuration entry in the database. If the third-party phone is not configured with the correct user ID, or the user ID is not associated with the device in the Unified CM database, Unified CM responds with a 404 Not Found. MultiLine Registration Multiple lines can register with Unified CM if each line has a unique directory number. The directory number must appear in the To and From header of the REGISTER, and it must be numeric. REGISTER Refresh (Keepalive) Unified Communications Manager uses REGISTER refreshes as keepalive messages to ensure the phone is still alive and connected. When the phone first registers with Unified CM, the 200 OK response will include an Expires header with the configured keepalive interval. The phone must send a REGISTER refresh within this interval with the same Call ID, Contact IP address, and Contact port number. If Unified CM fails to receive a keepalive message within the configured interval (default 120 seconds), it will unregister the phone internally, so no calls can originate from or terminate to the phone. Device Binding After the device has been identified by the digest user ID, the system creates a binding within Unified Communications Manager between that device ID and the transport address. This binding gets created because Unified CM must identify the sending device for all subsequent requests from the phone (INVITE, REFER, SUBSCRIBE, and so on), and these requests do not contain the device ID. However, these requests do contain SIP Line Messaging Guide (Standard Edition) for Cisco Unified Communications Manager 26 SIP Standard Line Interface Standard Feature Scenarios