The snom 4S (which stands for "SIP SME Soft Switch") is a commercial but affordable and feature rich SIP based system. It fills the existing gap for a simple solution in the small and medium enterprise (SME) environment for SIP network components that are necessary to run SIP telephony.
The system currently consists of these components:
| ||The SIP Proxy/Registrar is an obligatory component that routes the SIP calls to the right destination.|
| ||The SIP Media Server that takes care of media related issues like mailbox and auto attendant.|
| ||A SIP NAT Gateway that translates SIP traffic in the private network to the public Internet.|
| ||A STUN Server that acts as "mirror" in the Internet and helps measuring identities out. |
Combined with snom and/or other SIP compliant phones and a SIP PSTN GW, it is well suited to accommodate the needs of a SME.
Why snom 4S?
A phone can only work if it is used in an environment that is able to transport the voice and store and play messages. This has been true for PSTN networks and it is true for VoIP networks as well.
We believe that VoIP will function like the computer industry is doing today. That means that specialists contribute products that work together with components of other vendors.
The core of our strategy is to deliver the phones to this industry. We believe that this is the most important and most valuable component in a network of distributed intelligence. In contrast to the PBX model, the phones do a lot more than play the role of a soundcard with attached keyboard.
However, while several vendors focused on large network infrastructure components, an affordable solution for the small and medium enterprise was missing and open source projects did not have the necessary maturity yet. As we have all necessary software components for solving the problems in a small network, we decided to offer a solution: The snom 4S.
What do you need?
Setting up a working SIP environment in your network usually does not require any additional hardware. If you want to terminate your calls to the PTSN you need a SIP gateway. We recommend using a separate standard PC as standalone server for the telephony functions so that other processes on the same machine don't disturb them.
The snom 4S runs both on Windows and Linux. Although we use Linux on our phones as underlying (and invisible) operating system, for the snom 4S Windows is also a great platform that can be used for telephony. We leave this decision up to you.
SIP is open to any vendor. Most users do already have a SIP client and are not aware of this. The Microsoft Messenger, which comes with Windows XP already, supports SIP, and you may use it for your first trials with a SIP-enables telephony network in your office. Again, our FAQ library gives a few tips about using Messenger with the snom 4S.
A SIP telephony infrastructure built on a snom 4S fulfils all requirements on modern telephony. This includes:
Hold, Divert, Transfer with and without consultation
CWI - call waiting indication
MWI - message waiting indication
Music on hold
Call List, Deny List
National Language Support (NLS)
DTMF selectable actions
Graphical Interface with Animations.
Sequential Call Forking (Group pickup)
Power Over LAN (IEEE 802.3af)
G.711, GSM 6.10, G.729a and GIPS Codecs
Internet telephone calls
Interoperability with devices from other vendors
3. Overview - A SIP Infrastructure with snom 4S
The 4S stands for SIP SME Soft Switch. It is software that makes up parts of a SIP infrastructure intended to be used in SMEs.
This section will give you an overview on of which components a SIP infrastructure is made up of with the components of the snom 4S.
The illustration above outlines a SIP infrastructure consisting of the following base components:
| ||SIP user agents such as snom 100. These are the terminals the users have to communicate. This includes soft clients that use standard PC to communicate.|
| ||snom 4S Proxy/Registrar. This component is used the register and find clients. Call logging is also done here.|
| ||snom 4S NAT Gateway. With this component, you can make calls to the Internet.|
| ||snom 4S Media Server (not shown in picture). The media server hosts services like mailbox, music on hold, auto attendant and conferencing. It can be located in the private network as well as in the public network.|
| ||LDAP Server (not shown in picture). Here you can place a global address book.|
| ||HTTP server for mass deployment (not shown in picture). Your company http server can also store the configuration files for your phones. This makes it easier to set them up.|
| ||SIP PSTN GWs. VegaStreams Vega 50 or 100 for instance can be used to connect to PSTN networks. |
To give the phone system some advanced features, the following servers can be added:
4. snom 4S RP
| ||snom 4S MOH - Music on hold|
| ||snom 4S VMS - Voice Mail System|
| ||snom 4S AA - Auto Attendant|
| ||snom 4S MCU - Multiple Conference Unit|
| ||snom 4S NAT GW - an application layer gateway needed to get across NAT GWs|
| ||LDAP server - a global phone book|
| ||snom 4S MDS - Mass Deployment System |
The snom 4S Proxy/Registrar combines several SIP components in one program.
The registrar is used by user agents to indicate under which address a user agent can be found and what the probability of finding the user there is. Clients can register the same number multiple times; the proxy will try to find them on any of the registered contacts.
The proxy is used for forwarding SIP requests. This includes finding a user in several contacts. The proxy stays in the signaling path all the time, so it is able to trace the calls and generate call data records. Some user agents are not able to find the server on their own; the proxy will help out in these cases.
The included location server is used when the call is not destined to a local registered user. In this case, calls can be forwarded to one or more PSTN gateways. The location server also checks if the user may dial the number or if additional digits are required to complete the call.
The Proxy/Registrar features among other things:
HTTP interface for configuration and maintenance
Sequential Call Forking
Record Routing (RFC 3261 compliant)
5. snom 4S Media Server
When you dial the wrong number with your PSTN phone, you most probably hear "the number you have dialed is temporarily not available". Someone has to generate this announcement.
In SIP, this (amongst other things) is done with a media server. The snom 4S media server is a generic machine interpreting XML configuration documents that describe the behavior of mailboxes, auto attendants, conference servers and simple error-announcers. It is able to understand DTMF user interaction (both inband and out-of-band) and it can record messages.
The configuration may write variables and remember how the account was set up. Authentication is supported in the standard SIP way (Digest MD5). The transcoding module supports several low rate codecs and makes the media server also usable as Internet server. The programmability makes it very flexible for all kinds of accounts. However, the initial set up is easy to use in a standard environment.
Current types include:
6. Additional Servers
snom 4S STUN Server
| ||Mailbox including absence messages, customized announcements, sending of message waiting indications.|
| ||Auto Attendant featuring default target and a variable length of extension digits.|
| ||Music on Hold can be easily setup by your own personal. WAV-Files|
| ||The conferencing server supports conferencing with a number of participants bigger than two or three users (limited only by the CPU performance).|
| ||The error explanation can be used to inform users about mistakes and failures.|
This server operated according to the STUN (Simple Traversal of UDP through NAT) draft. It is used in environments where it is not possible to use a SIP NAT application layer gateway for translating SIP messages in NAT environments. See the FAQ for details on this topic.
snom 4S NAT Gateway
The NAT Gateway acts as SIP proxy that puts itself automatically into the signaling path. It patches the SDP attachments of the session initiations and opens RTP ports for forwarding packets to the right destinations in the private network. See the FAQ for details on this topic.
SNOM Featured Products:
us for information on other SNOM products.