> ## 5 Transport mechanisms

> ### 5.1 Callback interface

> The callback interface of the transport module contains several functions. Some of which are mandatory while others are only optional:

> - `send_message` - Send a message. Mandatory
> - `block` - Block the transport. Optional
>   This function is usefull for flow control.
> - `unblock` - Unblock the transport. Optional

> ### 5.2 Examples

> The Megaco/H.248 application contains implementations for the two protocols specified by the Megaco/H.248 standard; UDP, see megaco_udp, and TCP/TPKT, see megaco_tcp.

Copyright © 1991-2003 Ericsson Utvecklings AB