# 1 Introduction

Megaco/H.248 is a protocol for control of elements in a physically decomposed multimedia gateway, enabling separation of call control from media conversion. A Media Gateway Controller (MGC) controls one or more Media Gateways (MG).

This version of the stack supports version 1, 2 and 3 as defined by:

- version 1 - RFC 3525 and H.248-IG (v10-v13)

- version 2 - draft-ietf-megaco-h248v2-04 & H.248.1 v2 Corrigendum 1 (03/2004)

- version 3 - Full version 3 as defined by ITU H.248.1 (09/2005) (including segments)

The semantics of the protocol has jointly been defined by two standardization bodies:

- IETF - which calls the protocol Megaco

- ITU - which calls the protocol H.248

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1.1 Scope and Purpose

This manual describes the Megaco application, as a component of the Erlang/Open Telecom Platform development environment. It is assumed that the reader is familiar with the Erlang Development Environment, which is described in a separate User's Guide.

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1.2 Prerequisites

The following prerequisites are required for understanding the material in the Megaco User's Guide:

- the basics of the Megaco/H.248 protocol

- the basics of the Abstract Syntax Notation One (ASN.1)

- familiarity with the Erlang system and Erlang programming

The application requires Erlang/OTP release R10B or later.

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1.3 About This Manual

In addition to this introductory chapter, the Megaco User's Guide contains the following chapters:

- Chapter 2: "Architecture" describes the architecture and typical usage of the application.

- Chapter 3: "Internal form and its encodings" describes the internal form of Megaco/H.248 messages and its various encodings.

- Chapter 4: "Transport mechanisms" describes how different mechanisms can be used to transport the Megaco/H.248 messages.

- Chapter 5: "Debugging" describes tracing and debugging.

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1.4 Where to Find More Information

Refer to the following documentation for more information about Megaco/H.248 and about the Erlang/OTP development system:

- version 1, RFC 3525

- old version 1, RFC 3015

- Version 2 Corrigendum 1

- version 2, draft-ietf-megaco-h248v2-04

- H.248.1 version 3

- the ASN.1 application User's Guide

- the Megaco application Reference Manual

- Concurrent Programming in Erlang, 2nd Edition (1996), Prentice-Hall, ISBN 0-13-508301-X.