Snom 4S Media Server Use and care manual

Administrator‘s
Manual
snom 4S
SIP Media Server
Version 2.24

snom 4S Media Server Version 2.24 Administrator Manual
3. Edition 2004
© 2004 snom technology Aktiengesellschaft. All Rights Reserved.
This document is supplied by snom technology AG for information purposes only to licensed
users of the snom 4S media server and is supplied on an “AS IS” basis, that is, without any
warranties whatsoever, express or implied.
Information in this document is subject to change without notice and does not represent any
commitment on the part of snom technology AG. The software described in this document
is furnished under a license agreement and may be used only in accordance with the terms
of that license agreement. It is against the law to copy or use this software except as
specifically allowed in the license. No part of this document may be reproduced, republished
or retransmitted in any form or by any means whatsoever, whether electronically or
mechanically, including, but not limited to, by way of photocopying, recording, information
recording or through retrieval systems, without the express written permission of snom
technology AG.

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Table of Contents
1 Foreword .......................................................7
2 Introduction ..................................................9
2.1 Signaling and Media ....................................................... 9
2.2 Response Times ........................................................... 10
2.2.1 Multitasking ....................................................................................................................................................................... 10
2.2.2 Hard Disks ........................................................................................................................................................................... 11
3 Installation .................................................13
3.1 Windows ..................................................................... 13
3.1.1 Installation .......................................................................................................................................................................... 13
3.1.2 Uninstalling in Windows ................................................................................................................................... 18
3.2 Linux .......................................................................... 18
3.3 Command Line Options ................................................. 18
4 Setup ..........................................................21
4.1 Licensing .................................................................... 21
4.1.2 License Key ........................................................................................................................................................................ 22
4.2 System Settings .......................................................... 23
4.2.1 Log Level ............................................................................................................................................................................... 23
4.2.2 Recording File ................................................................................................................................................................. 23
4.2.3 DNS Identity ..................................................................................................................................................................... 24
4.2.4 Default SIP Domain ................................................................................................................................................ 24
4.2.5 Start RTP Port and End RTP Port ........................................................................................................ 24
4.2.6 Max Number of Connections ..................................................................................................................... 25
4.3 Webserver Settings ...................................................... 25
4.3.1 HTTP and HTTPS port .......................................................................................................................................... 25
4.3.2 HTTP User and Password ............................................................................................................................... 26
4.4 SIP Settings ................................................................ 26
4.4.1 Outbound Proxy ........................................................................................................................................................... 26
4.4.2 SIP Port ................................................................................................................................................................................... 27
4.4.3 Session Timer ................................................................................................................................................................. 27
4.4.4 Retry Timeout ................................................................................................................................................................ 27

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4.4.5 Max-Forwards ................................................................................................................................................................. 28
4.4.6 MWI Attachents ........................................................................................................................................................... 28
4.5 Codecs ....................................................................... 28
4.5.1 Representing Voice ................................................................................................................................................. 28
4.5.2 Representing User Input ................................................................................................................................. 30
4.5.3 Codec Negotiation .................................................................................................................................................... 30
4.6 Dial Plan ..................................................................... 31
4.7 Mailbox Template ......................................................... 33
5 Accounts .....................................................35
5.1 Registering Accounts .................................................... 36
5.2 Passwords ................................................................... 36
5.3 Outbound Proxy ........................................................... 37
5.4 Hangup ...................................................................... 37
5.5 Passing Variables ......................................................... 37
6 Specific Account Types ................................39
6.1 Music On Hold ............................................................. 39
6.1.1 How to use MOH ......................................................................................................................................................... 39
6.1.2 Configuration of the MOH account ................................................................................................... 40
6.2 Mailbox ...................................................................... 40
6.2.1 Using the Mailbox Account ........................................................................................................................... 41
6.2.2 Configuring a Mailbox Account ............................................................................................................... 41
6.2.3 Answer Delay ................................................................................................................................................................ 41
6.2.4 Identity .................................................................................................................................................................................... 42
6.2.5 MWI Destination ......................................................................................................................................................... 42
6.2.6 Record Length, Max Messages ............................................................................................................... 42
6.2.7 Jump Out ............................................................................................................................................................................... 42
6.2.8 Time Difference .......................................................................................................................................................... 43
6.2.9 Password ............................................................................................................................................................................... 43
6.3 Conference Server ....................................................... 43
6.3.1 Calling a Conference ............................................................................................................................................. 43
6.3.2 Remote Initiation of Conferences ...................................................................................................... 43
6.4 Auto Attendant ............................................................ 44
6.5 Error-Information ......................................................... 45
6.5.1 Playing Messages using SIP ....................................................................................................................... 46
6.5.2 Playing Messages using HTTP .................................................................................................................. 46
6.6 Other Types ................................................................ 47
7 Email-Support .............................................49
7.1 Sending Emails Directly ................................................ 49

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7.2 Logging Email Reception ............................................... 50
7.3 Using Multiple Email Accounts ........................................ 50
8 Maintenance ................................................51
8.1 Trace .......................................................................... 51
8.2 Open Calls .................................................................. 52
8.3 Logfile ........................................................................ 52
8.4 Memory Usage ............................................................ 52
8.5 System Information ..................................................... 52

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1 Foreword
In today’s telephone networks, there are many situations when
you are talking to a machine. Typical examples include the mailbox,
auto attendant or just music on hold. Over time, the telephone industry
has developed many advanced interactive voice dialogs like arranging
meetings, reservation systems, tracking systems and so on. In a VoIP
network, these features must also be present. By having a media server in
the network, a VoIP telephony system will have at least the same features
as your “good old” PBX had.
Technically, the snom 4S Media Server is much more than a
SIP media server. It includes the logic to handle complex applications.
Together with a SIP proxy the media server provides the functionality that
fulfils the needs of your telephone users and might also offer some more
and helpful features not known from traditional PBX.
We chose the term media server to indicate that this component
takes care about everything that is related to audio streams. This makes
sense because handling audio is a real time task and sets different
requirements on the underlying hardware than not-so-critical requirements
of the call control. SIP allows and encourages this distinction and thus
makes scalable systems easier to implement. However, practically all
components of a small to medium size installation will run on the same
machine.
Interoperability is the glue of the growing VoIP industry. We have
tried to stick to the SIP standard as well as possible and tested together
with the equipment of other vendors whenever that was possible. We
hope that this will help to build up a flourishing VoIP telephone industry in
which the products of the different vendors work together like the products
in the computer industry do today. We believe that having a choice is good
for you and therefore good for us.
This manual is the best way to get started with the snom 4S
media server. However, because it’s hard to keep a manual up-to-date
with all the issues that come up, we provide a list of frequently asked
questions (FAQ) on out web site http://snom.com.
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We hope that you enjoy using the media server and it helps you
setting up a great communication environment!
Sincerely,
Dr. Christian Stredicke
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2 Introduction
This chapter explains the functionality of the media server and
gives you a feeling on what is important. You will learn the difference
between signaling and media and what is important to operate a media
server.
This is not intended to serve as introduction into VoIP and SIP in
general. You find great introductions and numerous links in the Internet
and in the literature. The snom 4S Proxy manual also gives a brief overview
on SIP.
If you are already with the underlying problems with a media
server, go can go straight to the next chapter.
2.1 Signaling and Media
In short words, there are two fundamental problems with
telephony: Finding the user you want to talk to and talking.
Finding the user is done with signaling. SIP is one way to find the
party you want to talk to. This job is characterized by a complexity, for
example when a user redirected his phone or can be reached on several
locations. If the finding process takes a second more or less, this is not
so critical.
When the user has been found, the problem shifts to transporting
the speech as fast as possible between the participants. One second
for transporting the voice from one user to another is a big burden for
the communication. It takes a lot of discipline if you want to establish a
conversation like this. When users are talking, typically every 20 ms a
piece of the conversation is transported over the network. If this stream
of packet gets delayed or stalls, the other side will experience a bad audio
quality.
While operating systems are very good at scheduling tasks (so
nothing gets forgotten), reacting very fast sometimes gives problems. If
you need to send a packet every 20 ms, you usually don’t have the time
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to get audio data from a network server and even accessing the local hard
disk can degrade the quality.
2.2 Response Times
A modern PC is an unbelievable workhorse. An off-the-shelf
PC can process several billion operations per second and store easily a
month of a conversation. The bandwidth of a standard Ethernet card is
enough to handle more than a thousand uncompressed media streams.
Set up correctly, it can handle tens and hundreds of parallel calls without
a problem. However, in order to operate this workhorse you need to follow
a few rules.
2.2.1 Multitasking
All modern operating systems like Windows 32 and Linux support
multiprocessing or multitasking. Several processes share the same CPU
in a way that the CPU works for a short time on the first process and then
continues with the next process. The switching is done around a hundred
times per second and typically the user does not recognize this.
In a VoIP environment we are talking about sending packets at
a rate of fifty packets per second per call and that might result in a high
frequency of process switches.
The operating system knows that the media server has higher
requirements on time critical task switching (this is signaled during the
starting of the media server). However, when there are other tasks on
this computer, the operating system might not be able to give all of them
the CPU attention that they need. So in short words, if you run the media
server and some video games on the same machine don’t get surprised if
your users complain about stuttering voice.
The best approach to solve this problem is to run the media server
on a dedicated the host. Because the proxy usually does not request time
critical priority from the operating system, it is usually not a problem to
run the proxy on that machine as well. However, it is not a good idea to
run the media server on a file server.
This is the reason why snom offers the media server as a
preconfigured product in a dedicated box. Although this box has limited
resources compared to a modern PC, it can do a good job because the
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