Softswitches�Part III: The Media Gateway Controller
Core of the Call Control and Signaling plane, the MGC is responsible for setting up and dismantling the end-to-end network connections necessary to support phone calls.
In the first tutorial in this sub-series regarding softswitches, we briefly discussed the concepts of telephone switching and three key functions, routing, transmission, and billing, which are involved in connecting a call from the source to the destination. We also considered the distinction between the switching fabric which makes the physical connection, and the switching logic, which handles routing, billing, and associated functions. One of the key concepts behind the softswitch is the separation between the hardware (physical) and software (logical) functions, which allow different devices, in perhaps different geographical locations, to handle these separate functions. This provides significant flexibility advantages over monolithic legacy switches, which can be challenging to upgradeand even harder to replace with newer technology.
In the second softswitch tutorial we looked at the architecture of a softswitch, as defined by the International Packet Communications Consortium (IPCC) in their IPCC Reference Architecture Document. This document details the architecture of a softswitch, and describes four major functional areas, called Telephone calls transported by either a VoIP network or the Public Switched Telephone Network (PSTN) share a common requirement for end-to-end reliability, and with that, the ability to establish and disconnect the end-to-end connection. The Media Gateway Controller, or MGC (which is also known as the Call Agent or the Call Controller) is the device that provides those functions, and therefore contains a substantial amount of the network intelligence. Thus, call routing, control of the connection, and the control of network resources are all functions that the MGC provides. These specific operations include: The IPCC Architecture defines two additional functions that are considered subsets of the MGC. The first is called the Call Agent Function, which provides the call control and call state maintenance operations. This function may involve a number of protocols, including the Session Initiation Protocol (SIP), defined by the Internet Engineering Task Force, or the H.323 protocol, defined by the International Telecommunications UnionTelecommunications Standard Sector (ITU-T). The second is called the Interworking Function, which is used when a connection is needed to/from a network that deploys another type of networking protocol. Examples of interworking functions would include H.323/SIP or Internet Protocol/Asynchronous Transfer Mode (IP/ATM) network connections.
Our next tutorial will describe the Media Gateway, another significant part of the softswitch reference architecture.
Copyright Acknowledgement: © 2005 DigiNet ® Corporation, All Rights Reserved
Author's Biography
Mark A. Miller, P.E. is President of DigiNet ® Corporation, a Denver-based consulting engineering firm. He is the author of many books on networking technologies, including Voice over IP Technologies, and Internet Technologies Handbook, both published by John Wiley & Sons.