RFC 3661 MGCP Return Code Usage December 2003 1. Introduction This document provides implementation guidelines for the use of return codes in the Media Gateway Control Protocol MGCP 1.0 [1]. Return codes in [1] do not cover all possible specific situations that may ever occur in the gateway. That is not possible and not necessary. What is important is to ensure that the Call Agent that receives that return code behaves appropriately and consistently for the situation that occurred. The solution described in this document is to categorize return codes that gateways return based on the expected behavior for the Call Agents that receive them. Categorizing errors helps both Call Agent and gateway developers: it helps gateway developers choose an appropriate return code when a specific one for the situation is not available; it also helps Call Agent developers ensure that there is consistent behavior for the return code that is received. 1.2. Document Organization In addition to categorizing return codes (section 2.1), section 2.2 provides a consolidated list of return codes in terms of "situations" that may have triggered and the "categories" that they fall under. This provides some additional implementation guidelines for the use of these return codes. Section 2.3 includes a summary of the return codes and their categories. Section 3 provides some additional implementation guidelines for Call Agent and gateway developers. 2. Return Code Usage 2.1. Return Code Categories The following categorizes return codes from gateways based on expected Call Agent behavior. Category normal: These return codes are used in normal operation and do not represent error conditions. Category none (specific errors requiring specific action): A return code associated with a specific situation in the gateway that will invoke a corresponding specific Call Agent behavior. As such, these return codes are not categorized into a common behavioral category. Category "Service Failure": A category in which the endpoint is either out-of-service or the treatment by the Call Agent is expected to be the same as for an out-of-service endpoint. Foster & Sivachelvan Informational