Snom 4S Media Server Use and care manual

Administrator‘s
Manual
snom 4S
SIP Proxy/Registrar
Version 2.21

snom technology AG • 3
snom 4S Registrar Proxy Version 2.21 User Manual
© 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 registrar proxy 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
SIP World!
SIP is becoming more and more accepted in the area of VoIP.
Many companies are working on SIP solutions and making great products
that will make telephony much easier and better.
SIP without a proxy makes no sense. Entering IP addresses to nd
another user cannot be the future of telephony. Locating http web content
and nding email users has become a part of todays communication
behavior and sure will be part of telephony in the near future. However,
for the small and medium size ofce, we are missing a simple yet powerful
solution that is available for a standard-software price. That is why we are
making this simple and straightforward proxy available.
snom 4S stands for “snom soft switch for small and medium
enterprises“. That means, the snom 4S proxy was designed for
environments handling up to 1000 users with normal trafc. In
environments where you need more features and better scalability, we
would be happy to refer you to other companies offering carrier grade and
feature-rich proxies that solve these problems.
This product is a proxy/locations server with built-in registrar
which means this software is responsible for locating users. Features
like follow me and group calling are therefore supported; however media
services like mailbox and music on hold are not part of the software. You
should use a media server for this.
Interoperability is important to us. We have tried to stick to the
SIP standard as well as possible and tested the phones of other vendors.
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 products in the computer industry do today. We believe that having a
choice is good for you and therefore good for us.
This manual gives you a brief introduction to VoIP and SIP,
explains the installation process for Windows and Linux and shows how

4 • Welcome
[ S N O M 4S PR O X Y / R E G I S T R A R M ANUAL ]
snom technology AG • 5
to run the SIP proxy. For additional snom 4S information, please visit our
Web site at http://www.snomag.de and if you have any comments and
suggestions about snom 4S, please contact us through snom technology
AG’s support link Web site. We would appreciate your feedback.
And, of course, you can reach us at sip:[email protected].
Thank you and have fun using the snom 4S!
Dr. Christian Stredicke Nicolas Peter-Pohland

4 • Welcome
[ S N O M 4S PR O X Y / R E G I S T R A R M ANUAL ]
snom technology AG • 5
Table of Contents
Welcome to the SIP World! ........................................3
The Voice over Internet Protocol................................7
Why SIP?................................................................................... 7
Open Standards ......................................................................... 8
What You Can Expect and What Not .............................................. 9
The SIP Architecture ................................................11
User Agents ............................................................................. 11
Proxies.................................................................................... 12
Location Server ........................................................................ 12
Registrars ................................................................................ 12
Media Server............................................................................ 13
Gateways ................................................................................ 13
snom 4S Framework.................................................15
Proxy ...................................................................................... 15
SIP NAT Gateway...................................................................... 16
Media Server............................................................................ 17
Installation ..............................................................19
Windows Installation ................................................................. 19
Uninstalling in Windows ............................................................. 23
Linux Installation ...................................................................... 24
General Concepts .....................................................27
Security ................................................................................. 27
Reliabilty ................................................................................. 28
State ...................................................................................... 29
Overlap Dialling........................................................................ 30
Sequential Forking .................................................................... 30
Network Address Translation ...................................................... 31
Routing ................................................................................... 32

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Conguration ...........................................................33
Licensing ................................................................................. 33
General Settings....................................................................... 35
Registration ............................................................................. 38
Routing ................................................................................... 40
Domain Administration .............................................................. 43
User Administration .................................................................. 44
Dial Plan.................................................................................. 45
Error-Information ..................................................................... 49
Welcome Message..................................................................... 52
DNS........................................................................................ 53
Server Farm Operation .............................................................. 54
Registering Phones ..................................................57
snom 100 Registration............................................................... 57
Microsoft Messenger Registration ................................................ 58
Maintenance.............................................................61
Registered Users ...................................................................... 61
Call Logs ................................................................................. 62
SIP Message Flow ..................................................................... 65
Logging ................................................................................... 67
More Information .....................................................69
Open Issues............................................................................. 69
Standards................................................................................ 69
Other useful information ............................................................ 70
Footnotes ................................................................................ 70
Index .......................................................................71

6 • Contents
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The Voice over
Internet Protocol
Today there is a wide choice of different switched network
products. Telephones have now been being built for more than a century,
and their technology is well-understood and proven. Why choose a
different technology?
Modern communication infrastructures transport much more than
just one application: email, http, les, instant messages, videos, music,
so it is only natural to include voice in the list of applications and use one
infrastructure for all of them.. Voice is a real time application. Sending
voice over the Internet Protocol is called “VoIP”. The delay between
sending a packet to the network and receiving it needs to be minimal and
constant and this makes specic demands on this application.
Most network equipment can already full this real time
requirement. Virtually all switches currently on sale support a VLAN with
different priorities in the network, and the vast majority of higher layer
network equipment supports some means of transporting packets with
different qualities (DiffSrv). The LAN usually supports a bandwidth of
100 MBit/s, which is more than enough to allow voice to ow through
the network, and adherence to a certain set of rules ensures that this
bandwidth is enough to supply superior telephone quality. The Internet
backbone’s ability to transport large loads is increasing on a daily basis,
and global communications are now ruled by the Internet.
Why SIP?
There has been a “protocol war” regarding the “best” way to set
up a phone call. In the mid 90s, H.323 was the rst attempt to unify the
VoIP industry under a common standard,and move the world of telephony
into the computer industry, using most of the methods known from ISDN.
Seen however, from today’s perspective, the resulting technology was
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8 • About VoIP
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[ S N O M 4S PR O X Y / R E G I S T R A R M ANUAL ]
far too complex, so products based on this technology did not work well
together. The late introduction of “supplementary services” (H.450.x) not
only introduced another level of complexity, but was also simply too late.
By the late 90s, the Session Initial Protocol (SIP) had been
proposed (RFC 25431). SIP follows the paradigms of the Internet, and is
built upon the same principles used by http and email. Moreover, it has
found an enthusiastic community of researchers and developers who like
the idea of applying Internet technology to real time communications.
More and more applications are being put into SIP, telephony being just
one of them.
So far more than 150 drafts have been proposed for extending
the SIP protocol. All kinds of solutions are being addressed in these
documents, and the highly dynamic eld of this new real time
communication technology is resulting in evolutionary pressure to nd
the best common denominator.
Most of the “big players” have jumped on the SIP train. Microsoft
Messenger is based on SIP and Cisco Systems offers SIP extensions
to most of its products. International organizations like ETSI host SIP
interoperability events, and next generation mobile technology will be
integrated with, if not based on, SIP (see the 3GPP for more details).
Open Standards
Open standards dene the rules of the game. Interoperability
allows customers to choose between the products of different vendors and
opens up competition below the system level. This can be advantageous
for the customer, as the computer hardware industry has shown.
Many vendors therefore advertise their usage of an “open
standard”, dening this term as “we make the way our standard works
public”. However, this cannot really be called “standard” if only one vendor
is using it. The disadvantage is that customers still have a limited choice
of products they can buy.
There is no one objective denition of an open standard. However,
something approaching an open standard could be reached if a signicant
number of vendors offered products using the same standard, giving
customers the possibility of combining products to create a system. SIP
is just such a standard.
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8 • About VoIP
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What You Can Expect and What Not
Telephony is more than making calls from A to B. SIP supports
all kinds of transfers, call parking and call picking, user searches (Follow-
me), mailbox support, and all the other features known from traditional
telephony. In addition to this, telephones can now indicate their willingness
to receive calls and the probability of nding a specic user.
You can call a PSTN number from a SIP phone just as you did ten
years ago. The network will usually be set up to terminate these calls on
a gateway which translates the packet stream into a switched network
signal. You can also dial email-like numbers like “sip:fred.intstone@
megaportal.com”, and you can reach your sales team under the same
telephone number and email address.
Internet telephony is still a “best effort” communications
technology and does not always necessarily support the quality of
transport telephony requires. If you are placing a phone call over the
public Internet, there is no guarantee that a packet will be transported
within a reasonable time. Usually there is acceptable quality, but it may
happen that calls suddenly break off, that there is signicant delay, or
that packet loss causes stuttering. It is important that users know what
to expect: Cell phone users know that driving through a tunnel may break
the call, and Internet telephony users must be aware that talking for free
may compromise call quality.
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10 • About VoIP
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