Snom 4S Media Server Use and care manual

Administrator‘s
Manual
snom 4S
SIP Media Server
Version 2.0

snom technology AG • 3
snom 4S Media Server Version 2.0 Administrator Manual
1. Edition 2002
© 2002 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
specically 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.

snom technology AG • 3
“Welcome to the
Media Server!”
When you dial the wrong number with your good old PSTN phone,
you will probably hear something like “The number you have dialled is
temporarily not available”. When you reach the auto attendant of a
company, you will hear something like “Welcome to snom technology!”.
We take messages like these almost for granted.
With most VoIP installations today, you will probably just hear
some beeping of the phone. It is hard to explain why a new technology
can not do what the old technology can do today. Your customers and
your colleagues will expect that a VoIP telephony system will have at least
the same features as your “good old” PBX had.
With a media server you can do exactly this. Together with a
SIP proxy it will provide the functionality that will full the needs of your
telephone users and might also offer some more and helpful features not
known from traditional PBX.
A SIP network consists of several components. Some vendors
group a SIP proxy, registrar, location server and media server to
“SoftSwitch” or iPBX. 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 make 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 ourishing VoIP telephone industry
in which the products of the different vendors work together like the

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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 its 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 www.snom.de — together with their answers!
We hope that you enjoy using the media server and it helps you
setting up a great communication environment!
Sincerely,
Dr. Christian Stredicke Nicolas Peter-Pohland

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Table of Contents
“Welcome to the Media Server!”.................................3
How It Works .............................................................7
Signalling and Media ................................................................... 7
Response Times ......................................................................... 8
Multiprocessing.......................................................................................................................................................................................... 8
Hard Disks ........................................................................................................................................................................................................ 9
Privacy ...................................................................................... 9
Installation ..............................................................11
Windows ................................................................................. 11
Installation................................................................................................................................................................................................... 11
Uninstalling in Windows............................................................................................................................................................ 16
Linux ...................................................................................... 16
Manual Starting..................................................................................................................................................................................... 16
Automatic Starting ........................................................................................................................................................................... 17
Command Line Options.............................................................. 18
Setting Up ................................................................21
Licensing ................................................................................. 21
Hostnames................................................................................................................................................................................................... 22
License Key................................................................................................................................................................................................. 22
Fundamental Settings................................................................ 23
SIP Port............................................................................................................................................................................................................. 23
TCP threshold........................................................................................................................................................................................... 24
Log Level ........................................................................................................................................................................................................ 24
Default SIP Domain.................................................................................................................................................................................
24
HTTP port....................................................................................................................................................................................................... 24
HTTP User and Password......................................................................................................................................................... 25
Codecs .................................................................................... 25
Representing Voice.......................................................................................................................................................................... 25
Representing User Input.......................................................................................................................................................... 27

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Accounts ..................................................................29
Registering Accounts ................................................................. 30
Passwords ............................................................................... 30
Music On Hold .......................................................................... 30
How to use Music On Hold..................................................................................................................................................... 31
Conguration of the MOH account............................................................................................................................. 31
Mailbox ................................................................................... 32
Using the Mailbox Account.................................................................................................................................................... 32
Conguring a Mailbox Account........................................................................................................................................ 32
Answer Delay ......................................................................................................................................................................................... 32
Record Length......................................................................................................................................................................................... 33
MWI Destination................................................................................................................................................................................... 33
Register and Pass............................................................................................................................................................................... 33
Conference Server .................................................................... 33
Auto Attendant......................................................................... 34
Error-Announcement ................................................................. 34
Maintenance.............................................................35
Trace ...................................................................................... 35
Logle..................................................................................... 36
Stored Messages ...................................................................... 37

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How It Works
This chapter explains how a media server works in principle and
gives you a feeling on what is important. You will learn the difference
between signalling 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 nd great introductions and numerous links in the Internet
(e.g. at http://iptel.org) and in the literature. The snom 4S Proxy/
Registrar 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.
Signalling 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 signalling. SIP is one way to nd 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 nding 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. A second for transporting the
voice from one user to another is unacceptable. 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 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.
Response Times
A modern PC is an unbelievable workhorse. An off-the-shelf PC
can process more than a 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. You would have to spend ten or hundred times more money to
have such a working horse as traditional PBX hardware.
However, in order to operate this workhorse you need to follow
a few rules.
Multiprocessing
All modern operating systems like Windows 32 and Linux support
multiprocessing. Several processes share the same CPU in a way that
the CPU works for a short time on the rst 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.
However, in a VoIP environments we are talking about sending
packets at a rate of fty 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 signalled 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 le server.
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We would like to point out that from a media server perspective,
both Windows and Linux are great operating systems to run the media
server process.
Hard Disks
Hard disks are another miracle of the computer industry. I was
told modern off-the-shelf hard disk can store more information that the
human brain and so it should be good enough to store some mailbox
messages.
The price to pay for this is access time. When information on the
hard disk is scattered, the time to gather information can become too long
to answer requests within twenty milliseconds.
Missing the twenty millisecond answer time does not mean the
end of the call. Phones usually tolerate late packets to a certain degree
and if the packet is missing it will ll the gap with other information. Only
when too many packets get lost, the call will stop.
The general strategy to avoid situations like these is called
caching. Operating systems usually keep les which have already been
opened in the main memory until they are not used and are replaced with
information which is needed more urgently. As long as a le stays cached
there will be no problem.
Needless to say, accessing les (which are also stored on hard
disks) via the network is not an option if a continuous media stream is
wanted.
Privacy
There is another reason to use a dedicated server for the media
server: privacy. Remember that voicemails are normally strictly private,
and therefore it makes sense to separate them from normal le access.
There is nothing better than a physically separated server for this.
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Installation
Windows
Installation
Tip: If you are doing an update, you need to stop and uninstall
the old proxy rst (see below).
After double clicking on the setup executable, the installations
program starts up. Press Next to begin the installation.
At the beginning of the installation the setup program asks you to
accept the license conditions. Please read them carefully, then select the
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“accept” button and press “next” to accept the conditions. If you decline,
the installation will be aborted.
After accepting the license agreement, the next screen asks you
to enter your personal information. Enter your name and the name of
organization. This information is not linked to the licensing, which is done
after the installation
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You can then select the location where the media server’s les
will be put. The installation program proposes a reasonable location but
if you want to you can change it. After this, the installation asks you
for the location where the media information will be put. This directory
needs write access and will contain the information for registered users.
The installation program proposes a location relative to the media server
installation directory, but it might be useful to specify a different location
for this, e.g. a temporary directory. It is important that the directory
exists; the media server will not create this directory.
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Remember that for a good performance of the media server, the
media directory should be one the local hard disk.
In the next step you can select the installation type. We
recommend using the Typical installation. If you select Minimal, the
documentation is not installed.
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Before the installation nishes, you need to dene on which ports
the media server will operate. This is important because otherwise it will
be hard for you to nd the right port.
The http port denes where the web server of the media server
can be accessed. The default port for web servers is 80, and if you are
not running any other web services on the computer, port 80 is a good
choice. Otherwise, choose a free port and write the port number down
somewhere so you don’t have to search for it. If you don’t ll in any data
or cancel the dialog, port 80 will be used.
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The SIP port denes where the SIP trafc is expected. The default
port is 5060, but in case you are running a proxy on the same host you
will probably have to choose a different port. In this case, port 5062 is a
good choice.
After nishing the setup wizard, check that the media server is
running. If you do not want to reboot your system (because it is running
other critical applications), you can also manually start the service in the
services section of the Windows control interface.
Check that the installation has been successful by checking the
Services eld of Windows. Open the services Window and look for “snom
4S SIP Media Server”. The status should be “Started”. If this is not the
case you should invoke the media server by selecting “start”. In this case,
we recommend rebooting the system to make sure that the media server
is running after the reboot.
After making sure the media server is running, you should
connect to the media server to a web browser. In order to do this, you can
connect to the address of the local computer (http://127.0.0.1:8080 if
you are running the web browser on the same machine). If the http port
is already occupied by other programs, the media server will try to use
ports 5068, 5069, 5070 and so on. It is important that you connect to the
media server to a web browser, because that is the only way to control
the media server.
Uninstalling in Windows
To uninstall the media server, rst stop it in the services window.
Then go to the Software Window and click on “remove” for snom 4S SIP
Media Server.
Linux
Manual Starting
If you just want to try the media server, it should be enough to
start the media server manually. Load the tarball to a directory of your
choice and start the media server with the command “mediaserver”. You
can use the command line arguments shown in the next chapter. You
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don‘t need to have root permissions to run the media server in this mode,
normal user rights are enough.
Automatic Starting
If you want the media server to be started automatically after
a reboot, you need to set up some les as a root. Make sure that you
are logged in as root and go to the directory where you want to put the
media server. This directory will have subdirectories for the different
media server versions and for registrations. It typically also contains the
conguration information.
cd /usr/local
mkdir mediaserver
cd /usr/local/mediaserver
Extract the les from the tarball:
su -
cd /usr/local
tar xvfz ~/snom_sip_mediaserver-i386-linux-2.0.tgz
If you are updating a version, you may stop the proxy with
rcmediaserver stop and remove the symbolic link pointing to the old
installation. This will force a completely new installation. After this you
can continue the installation in the directory where you extracted the new
version.
cd snom_sip_mediaserver -i386-linux-2.0
The tarball includes a shell script with the name install.sh which
sets up the necessary les and links for you.
./install.sh
The le /etc/rc.cong (for SuSe Linux) and /etc/init.d/functions
(for RedHat) are appended with the variable „START_MEDIASERVER“ and
the MEDIASERVER_OPTS variable is set to a value depending on the html
port that you specify. You can edit the le and modify the value.
The installation script will install a command rcmediaserver.
rcmediaserver start starts the media server while rcmediaserver stop
terminates the media server process.
After the installation you should see that the media server
is running. Open a web browser to see if the media server is up and
running. Reboot the system and check whether the sip media server was
started automatically after the reboot. You can then continue with the
installation using the web browser. Stop and restart the media server with
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the rcmediaserver command to check whether the conguration has been
saved.
After several installations, the directory could look like this:
lrwxrwxrwx 1 root root 30 Aug 24 11:42 mediaserver -> snom_
mediaserver-i386-linux-2.12
-rw------- 1 root root 1472 Aug 22 16:17 mediaserver.txt
lrwxrwxrwx 1 root root 57 Aug 24 11:42 mediaserver_manual.pdf ->
snom_ mediaserver -i386-linux-2.12/snom 4S SIP Proxy-2.12.pdf
drwx--x--x 3 root root 4096 Jul 19 15:04 snom_mediaserver -i386-
linux-2.10
-rw------- 1 root root 3900938 Jul 19 15:04 snom_mediaserver -i386-
linux-2.10.tgz
drwx--x--x 3 root root 4096 Aug 12 14:09 snom_mediaserver -i386-
linux-2.11
-rw------- 1 root root 3902694 Aug 12 14:09 snom_mediaserver -i386-
linux-2.11.tgz
To update a version, copy the latest tarball into the directory and
run the install script of the new version. It will automatically shut down
the old media server and run the new one.
Unfortunately, the media server keeps a lot of stateful information
which makes it hard to do a smooth software update where user don‘t
experience any service interruptions. Therefore, we recommend two
approaches:
1. Do the software upgrade when service disruptions are ok
with the users (e.g. at night, early morning). This is probably the
easiest approach and should be easy in small and medium enterprise
environment.
2. If you are running the service in a server farm, take out one
server after another from the DNS SRV list and update when they are not
used any more. This makes the software update completely smooth and
users don‘t feel any interruptions.
Command Line Options
--log n: Specify the log level between 0 and 9. 9 means as much
messages as possible, 0 means only the most important messages.
--cong f: Specify the le where the conguration information
is saved. This option is only in the Linux version available.
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--html-port n: Explicitly specify the html port number.
--sip-port n: Explicitly specify the sip port number.
--no-daemon: Don’t run the process as daemon in the background,
run it as normal process.
--dir d: Specify the root directory for the media server. This is
important as the media server will search les in this directory.
--version: Print the version number and exit.
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