switched telephone network (PSTN). It is typically used for providing Voice over Internet Protocol (VoIP) services like voice and fax between IP networks and the PSTN), or entirely within IP networks. Because of the types of devices targeted for control by H.248/Megaco and the low level of its control structure, H.248 is generally viewed as complementary to H.323 and Session Initiation Protocol (SIP). While a media gateway controller (MGC) uses H.248/Megaco to manage media establishment and control with a number of media gateways (MGs), other VoIP protocols, such as SIP and H.323 are used for one communication between controllers. From a SIP perspective, the combination of MGC and MGs are treated together as a SIP Gateway. The H.248/Megaco model describes a connection model that contains the logical entities, or objects, within the Media Gateways (MGs) that can be controlled by the Media Gateway Controller. The main entities are Contexts and Terminations. Terminations These source or sink one or more media streams or control streams. Terminations may be physical or ephemeral Contexts These are star connections created by associating multiple terminations. A logical entity on an MG that is an association between a collection of Terminations. A NULL context contains all non-associated terminations. A Context is a logical entity on an MG that is an association between a collection of Terminations. A ContextID identifies a Context. The normal, "active" context might have a physical termination (say, one DS0 in a DS3) and one ephemeral one (the RTP stream connecting the gateway to the network). Contexts are created and released by the MG under command of the MGC. A context is created by adding the first termination, and it is released by removing (subtracting) the last termination. A termination may have more than one stream, and therefore a context may be a multistream context. Audio, video, and data streams may exist in a context among several terminations. In IP Multimedia Subsystem (IMS), Media Gateway Control Function (MGCF) control Media Gateways (MGW)s to send and receive call to / from the PSTN circuit switched (CS) networks using. H.248. The MGCF uses SIP messages to interact with Call Session Control Function (CSCF) and Breakout Gateway Control Function (BGCF). Although the modeling of the Media Gateway differs in H.248/Megaco when compared to MGCP, there is a similarity between the semantics of the commands in the two specifications. There is almost a one-to-one mapping between the