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# 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

## 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.

## 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.

## 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.

## 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](https://www.rfc-editor.org/rfc/rfc3525.txt)
- [old version 1, RFC 3015](http://www.ietf.org/rfc/rfc3015.txt)
- [Version 2 Corrigendum 1](https://web.archive.org/web/20100704020645/http://www.erlang.org/project/megaco/standard/H.248.1-Corr1-200403.doc)
- [version 2, draft-ietf-megaco-h248v2-04](https://web.archive.org/web/20100620185420/http://erlang.org/project/megaco/standard/draft-ietf-megaco-h248v2-04.txt)
- [H.248.1 version 3](https://www.itu.int/rec/T-REC-H.248.1/en)
- [ASN.1 application User's Guide](https://www.erlang.org/doc/apps/asn1/asn1_introduction.html)
- [Megaco API reference](https://www.erlang.org/doc/apps/megaco/api-reference.html)
- Concurrent Programming in Erlang, 2nd Edition (1996), Prentice-Hall, ISBN
  0-13-508301-X.