is defined in an informational (nonstand- ard) IETF document, RFC 3435. Megaco is less widely implemented than MGCP. Megaco and MGCP are client/server protocols, SO they allow service providers to have more control over subscribers through the use of more network intelligence. This is in contrast to H.323 and SIP, which are both peer-to-peer protocols. With peer-to-peer protocols, all the intelligence is distributed to the network edge, embedded in the terminating devices or endpoints, requiring only a simple core network and great scalability but reducing the network's control over the user. Megaco addresses the relationship between a media gateway, which converts circuit-switched voice to packet-based traffic, and a media gateway controller (also referred to as a call agent or softswitch), which dictates the service logic of that traf- fic. Megaco instructs a media gateway to connect streams coming from outside a packet or cell data network onto a packet or cell stream such as RTP. Megaco is similar to MGCP from an architectural standpoint and in terms of the controller-to-gateway relationship, but Megaco supports a broader range of networks, such as ATM. As shown in Figure 9.5, MGCP is a VoIP protocol used between elements of decomposed multimedia gateway that consists of a call agent, which contains the MGC or Call Agent or Global Signaling Softswitch H.323, MGCP, SIGtrans H.248/Megaco One Logical VolP Gateway Signaling Media Media Gateway Gateway Media Transport Gateway RTP/UD/IP, ATM AAL 1, 2, 5 ISDN, Q.Sig T1/E1/PR1, OC-x, E&M Figure 9.5 Megaco and MGCP Chapter 9 IP Services call control intelligence, and a media gateway, which contains the media functions (i.e., conversation from TDM voice to VoIP). Media gateways contain endpoints on which the call agent can create, modify, and delete connections in order to establish and control media sessions with other multimedia endpoints. A media gateway is typically a network element that provides conversion between the audio signals car- ried on telephone circuits