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snom 4S N AT Filter Admin Man ual snom 4S NAT Filter Version 2.11.
snom 4S NAT Filter Version 2.11 © 2004-2005 snom technology Aktiengesellschaft. All Rights Reserv ed. This document is supplied by snom technology AG for information purposes only to licensed users of the snom 4S NA T filter and is supplied on an “ AS IS” basis, that is, without any warranties whatsoev er , express or implied.
snom technology AG • 3 Table of Contents 1 Overview .......................................................... 5 1.1 Applications ...................................................................... 6 1.2 Features .................................
4 • Contents [ S N O M 4S NA T F I L T E R ] 4.3.4 Media Ports .............................................................................................................................................................................. 35 4.3.5 Port Budgets .
snom technology AG • 5 1 Overview Network address translation (NA T) is a reality today . There have been man y discussions about the evil and the good of this network topol- ogy and the replacement by IP version 6. However , operators and busi - ness want to offer V oIP services today and therefore must address the problem.
6 • Overview [ S N O M 4S NA T F I L T E R ] 1.1 Applications The filter can be used in the following scenarios: • Corporations. Corporations which operate their infrastructure be - hind NA T and/or firewalls can talk to the public Internet through the filter .
snom technology AG • 7 [ S N O M 4S NA T F I L T E R ] • Both http and https as web interface for simple access from any- where on the Internet. • The filter supports Inter active Connectivity Establishment (ICE). User agents that support this feature will optimize the media path for the shortest possible delay .
8 • Overview [ S N O M 4S NA T F I L T E R ] • The first exception is a REGISTER request. When a user agent tries to register and needs the support of the filter , the filter will set up a local data structure representing the user agents. It will make sure that the connection to the user agents stays alive.
snom technology AG • 9 2 Architecture 2.1 The NAT Filter and SIP In the SIP architecture, the SBC acts as the first proxy that is contacted by user agents. There are two ways to make sure that the rel- evant tr affic gets routed trough the filter: • User agents can be set up to use the filter as outbound pro xy .
10 • Architecture [ S N O M 4S NA T F I L T E R ] to register and needs the support of the SBC, the SBC will set up a local data structure representing the user agents. It will make sure that the connection to the user agents stays alive. It will also make sure that requests destined to the user agents will be forwarded properly .
snom technology AG • 11 [ S N O M 4S NA T F I L T E R ] 2.2.1 How does NAT work? NA T is essentially a translation table that maps public IP address and ports combinations to private IP address and port combinations. The translation table is implicitly set up when a packet is sent from the priv ate network to the public network.
12 • Architecture [ S N O M 4S NA T F I L T E R ] In SIP it is legal to send from a different port than the receiving port. When this is being done, there is no way of supporting these de- vices behind NA T . However , some phones offer an option that disables this mechanism so that the sending port is the same as the receiving port.
snom technology AG • 13 [ S N O M 4S NA T F I L T E R ] devices that have been designed without ha ving NA T in mind. These devices can register only for a short period of time, so that the REG- ISTER messages keep the port association open (the SIP messages are used to keep the port association).
14 • Architecture [ S N O M 4S NA T F I L T E R ] When the NA T Filter sees a message that contains information about sending media (session description protocol, SDP), it opens a local globally routable port on behalf of the user agent and patches these mes- sages in a wa y that the destination will send media via this port.
snom technology AG • 15 [ S N O M 4S NA T F I L T E R ] 2.3 SBC Behaviour 2.3.1 Registering When a user agent registers, it puts its IP address in the top Via. If the user agent is on public Internet or properly supports NA T , this Via will match the perceived IP address.
16 • Architecture [ S N O M 4S NA T F I L T E R ] 0637ced821ef40a3;ua=c9b140ab598290e5bb491e9c3aaca440 Via: SIP/2.0/UDP 203.145.183.113:12975;branch=z9hG4bK- abx3au3mxb01;rport=17401 From: <sip:denny@snomag.de>;tag=k9p6fmeg7h To: <sip:denny@snomag.
snom technology AG • 17 [ S N O M 4S NA T F I L T E R ] simply not programmed to allocate an address properly or because it is behind symmetrical NA T , which makes it impossible to properly allocate this address. In this case, the help of the media SBC will make sure that media will always be deliv ered properly .
18 • Architecture [ S N O M 4S NA T F I L T E R ] a=rtpmap:0 pcmu/8000 a=rtpmap:8 pcma/8000 a=rtpmap:3 gsm/8000 a=rtpmap:18 g729/8000 a=rtpmap:2 g726-32/8000 a=rtpmap:101 telephone-event/8000 a=fmtp:101 0-15 a=sendrecv a=silenceSupp:off - - - - The NA T Filter changes the private address to a globally routable address and inserts the local port.
snom technology AG • 19 [ S N O M 4S NA T F I L T E R ] The distribution of user agents to a server is performed using DNS SRV (RFC 2782). This means that you need to list the available serv - ers on DNS level; the user agents must perform DNS SRV look ups and pick one of the servers (possible using the detection algorithms described below).
20 • Architecture [ S N O M 4S NA T F I L T E R ] The snom 4S NA T Filter includes a STUN server that operates on the SIP UDP port. User agents should send their test packets to the SIP port. 2.6 Requirements on User Agents Generally , there are two categories of user agents: The non NA T aware user agents and the STUN/ICE capable user agents.
snom technology AG • 21 [ S N O M 4S NA T F I L T E R ] 2.7 Defining the Maximum Session Time There are a couple of timeout -related settings that terminate a call when certain events fire (see below). However , when prepaid cards are being used, operators w ant to limit the call duration to a certain time.
22 • Architecture [ S N O M 4S NA T F I L T E R ] 2..
snom technology AG • 23 3 Installation If y ou want to install the product on your own, this chapter will provide you with the necessary information. 3.1 Windows The Windows v ersion of the NA T Filter comes with an InstallShield application that should make the installation very simple for y ou.
24 • Installation [ S N O M 4S NA T F I L T E R ] netstat command to check which ports are being used on that machine. Y ou can change the ports later; however you should at least make sure that y ou can access the administration web interface of the NA T Filter with an open port.
snom technology AG • 25 [ S N O M 4S NA T F I L T E R ] If you agree to the license agreement, the next screen will ask you to enter the license code and to select the ports of the NA T Filter . The hostnames are a list of host identifications that identify this installation.
26 • Installation [ S N O M 4S NA T F I L T E R ] forget the port number , you need to look it up later , using the netstat command. After entering the license information and the port numbers, the InstallShield program will ask you for the installation directory .
snom technology AG • 27 [ S N O M 4S NA T F I L T E R ] may manually start the application using the services manager . The last InstallShield dialog offers you the option to start the NA T Filter . If you choose this option, you don’t have to go to the services manager .
28 • Installation [ S N O M 4S NA T F I L T E R ] 3.2 Linux After you downloaded the RPM from our web site you can either install it via the gr aphical administration frontend of your Linux distribu- tion or you can use the command line interface (CLI).
snom technology AG • 29 [ S N O M 4S NA T F I L T E R ] this is the first installation of the snom 4S proxy on this host from a RPM package please use the following command to install the software: rpm -ihv snomnatf-2.
30 • Installation [ S N O M 4S NA T F I L T E R ] 3..
snom technology AG • 31 4 Configuration 4.1 Logging In First of all, you need to log in to the server (see figure 2). The default login name is “admin” and there is no password set (you should change this if it has not already been done for you).
32 • Confi gur ation [ S N O M 4S NA T F I L T E R ] For http and https, you need to know the port numbers when y ou want to log in. W e recommend not using the standard ports. Oper ating a server on the public internet usually leads to a lot of denial of service at- tacks on the standard ports.
snom technology AG • 33 [ S N O M 4S NA T F I L T E R ] 4.3 System Settings 4.3.1 Logging The Log Level defines the granularity with which messages are written into the log.
34 • Confi gur ation [ S N O M 4S NA T F I L T E R ] messages are written, a log level of 9 means that all possible log mes- sages are written. If the Log Filename is set, all log messages are also written to the indicated file. If the file name contains a dollar character , the dollar will be replaced with the current date.
snom technology AG • 35 [ S N O M 4S NA T F I L T E R ] NA T Filter . Because the NA T Filter itself can be operated in a server farm, you can set up a completely redundant server setup .
36 • Confi gur ation [ S N O M 4S NA T F I L T E R ] The Hide Routing flag will replace route sets with a unique route index when requests or responses are sent to a registered user agent. Via headers are also replaced with one Via header . This feature has sev- eral advantages.
snom technology AG • 37 [ S N O M 4S NA T F I L T E R ] Unfortunately , only a small percentage of existing user agents deal properly with this situation. When y ou turn the flag on, the filter will only let the first 2xx response pass through to the user agent.
38 • Confi gur ation [ S N O M 4S NA T F I L T E R ] If you set this variable, the NA T filter will attempt to compress the message until it fits into the size. By default, it will use the short names (e.g. “l” instead of “Content -Length”).
snom technology AG • 39 [ S N O M 4S NA T F I L T E R ] packet. This setting does not only help you in making the packets shorter , it can also help you to keep some parts of the SIP message secret.
40 • Confi gur ation [ S N O M 4S NA T F I L T E R ] 4.4 Timeout Settings In contrast to previous v ersions, the time related settings have been summarized on this new management web page. The filter differentiates between registration related settings and call related settings.
snom technology AG • 41 [ S N O M 4S NA T F I L T E R ] 4.4.2 Call Timeouts Unfortunately , in SIP little attention has been given to the prob- lem of a user agent disconnecting from the network without further no- tification. This situation typically occurs on power failure or system crash or when the Internet connection becomes una vailable.
42 • Confi gur ation [ S N O M 4S NA T F I L T E R ] is not answered after a certain timeout, the filter assumes that the call is over and will not start again. The setting Timeout for Unestablished Calls addresses this problem. Please keep in mind that the ringing phone also falls into this category .
snom technology AG • 43 [ S N O M 4S NA T F I L T E R ] T o restrict the login, you should set a username („admin“ is the default) and a password.
44 • Confi gur ation [ S N O M 4S NA T F I L T E R ] 4.6 Outbound Proxy List In addition to the previously mentioned outbound proxy you may specify a number of dedicated outbound proxies. This feature is typically being used in the following scenarios: • Integration of PSTN gateway .
snom technology AG • 45 [ S N O M 4S NA T F I L T E R ] The algorithm for searching the outbound proxy is simple. The filter first goes through to the list of outbound proxies and tries to match the hostname in the request-URI of the request to the provided Domain .
46 • Confi gur ation [ S N O M 4S NA T F I L T E R ] 4.9 Trace The NA T Filter keeps a list of the last tr ace entries in memory . Y ou may view this list by selecting the trace link. The handling of the page is similar to the handling of the log page.
snom technology AG • 47 [ S N O M 4S NA T F I L T E R ] The Source/Destination indicates the IP address where the packet was sent or received. The Header column contains the abstr act. By clicking on the header link, you may see the complete pack et.
48 • Confi gur ation [ S N O M 4S NA T F I L T E R ] was terminated because the maximum session time has been reached. This time is indicated by the P-Session- Timeout header . 4.11 Current Ports It is important to see which calls are active on the filter .
snom technology AG • 49 [ S N O M 4S NA T F I L T E R ] 4.12 Currently Handled UA This table shows the currently handled UA with their SIP URI and their associated IP address. The third column shows the SIP request type that this binding is using. T ypically , this will be a REGISTER or SUBSCRIBE request.
50 • Confi gur ation [ S N O M 4S NA T F I L T E R ] 4..
snom technology AG • 51 5. Web Server Integration The SBC can use a web server as application server . This way you can use PHP , ASP and anything you like to implement the logic for your SIP traffic. F or example, if you want to redirect a call to a specific gateway , you can do this easily on the web server .
52 • W eb Server Integration [ S N O M 4S NA T F I L T E R ] 5.1 Interface to the Web Server The interface to the web serv er is built upon http. The communi- cation is a request/response protocol. The SBC requests information from the application server , and the application server answers.
snom technology AG • 53 [ S N O M 4S NA T F I L T E R ] • If the packet was already authenticated or internally generated, the further processing of the packet can start. • If the request is a register request and the registration is still valid, the packet forwarded to the further processing.
54 • W eb Server Integration [ S N O M 4S NA T F I L T E R ] correctly . The web requests that the SBC sends to the application server has the following parameters: • The parameter “action” is set to “auth” . By looking at this parameter , the application server can easily find out that it should do a pass - word lookup.
snom technology AG • 55 [ S N O M 4S NA T F I L T E R ] is authenticated. • If realm, username and password are set, the request is regularly processed. Because it is possible to send more than credential with one au - thentication request, the applications server can update passwords that have just been changed.
56 • W eb Server Integration [ S N O M 4S NA T F I L T E R ] • The parameter “explanation” contains the explaining text that is added behind the code in the SIP response. T ypical values are “Ok” or “Not F ound” . • The parameter “contact ” contains the contact that should be re - turned by the registration response.
snom technology AG • 57 [ S N O M 4S NA T F I L T E R ] • The parameter “to_ua” is set to “true” if the SBC believ es that the call will go to a client endpoint.
58 • W eb Server Integration [ S N O M 4S NA T F I L T E R ] ter , the From-header will be set to the value that y ou pass here. Please note that requests may loop through sever al SBC. This will typically happen in data centres that use a SBC server farm.
snom technology AG • 59 [ S N O M 4S NA T F I L T E R ] Currently , the following reasons are av ailable: • “BYE” means that the call was terminated by a regular BYE mes - sage. • “No 200 Ok” is used when the call did not establish (4xx code or other final error codes).
60 • W eb Server Integration [ S N O M 4S NA T F I L T E R ] 5..
snom technology AG • 61 6. SNMP The simple network management protocol (SNMP) is a widely used protocol for checking what’s going on in your network. When you run the SBC, you probably also want to see statistics about the usage and get alarms when something goes wrong.
62 • SNMP [ S N O M 4S NA T F I L T E R ] space etc.), the setup is a little bit more difficult that the setup of a stan- dard sensor . A readable parameter is described by its object identifier (OID). The object identifies are described in the next par agraph.
snom technology AG • 63 [ S N O M 4S NA T F I L T E R ] F or the SIP packets, the SBC measure only the received pack ets. It measures the number of packets as well as the total number of bytes received on the SBC SIP ports. The information does not include IP header like the UDP header .
64 • SNMP [ S N O M 4S NA T F I L T E R ] 6..
snom technology AG • 65 7 Checklist for Installation When snom or one of their partners perform the installation for you, the following information is necessary: 6.1 Linux • Please provide secure shell login to the system that can be ac- cessed at least from the snom.
66 • Checklist for Installation [ S N O M 4S NA T F I L T E R ] tion tool. • Please tell us the login address (host and port), user name and password. W e need administr ative rights on that host. • Please tell us for which domains you plan to use the server .
Reader‘s Feedback snom technology AG welcomes y our evaluation of this manual and any sugges- tions you may have. These help us to improv e the quality and usefulness of our documentation. Please send your comments and suggestions to: snom technology AG Attention: Marketing Department Pascalstr .
© 2004-2005 snom technology AG All rights reserved. snom technology Aktiengesellschaft Gradestr . 46, 12347 Berlin, Germany Phone: +49 (30) 39833-0 mailto:info@snom.
Een belangrijk punt na aankoop van elk apparaat Snom 4S (of zelfs voordat je het koopt) is om de handleiding te lezen. Dit moeten wij doen vanwege een paar simpele redenen:
Als u nog geen Snom 4S heb gekocht dan nu is een goed moment om kennis te maken met de basisgegevens van het product. Eerst kijk dan naar de eerste pagina\'s van de handleiding, die je hierboven vindt. Je moet daar de belangrijkste technische gegevens Snom 4S vinden. Op dit manier kan je controleren of het apparaat aan jouw behoeften voldoet. Op de volgende pagina's van de handleiding Snom 4S leer je over alle kenmerken van het product en krijg je informatie over de werking. De informatie die je over Snom 4S krijgt, zal je zeker helpen om een besluit over de aankoop te nemen.
In een situatie waarin je al een beziter van Snom 4S bent, maar toch heb je de instructies niet gelezen, moet je het doen voor de hierboven beschreven redenen. Je zult dan weten of je goed de alle beschikbare functies heb gebruikt, en of je fouten heb gemaakt die het leven van de Snom 4S kunnen verkorten.
Maar de belangrijkste taak van de handleiding is om de gebruiker bij het oplossen van problemen te helpen met Snom 4S . Bijna altijd, zal je daar het vinden Troubleshooting met de meest voorkomende storingen en defecten #MANUAl# samen met de instructies over hun opplosinge. Zelfs als je zelf niet kan om het probleem op te lossen, zal de instructie je de weg wijzen naar verdere andere procedure, bijv. door contact met de klantenservice of het dichtstbijzijnde servicecentrum.
