A SIP server is the main component of an IP PBX, dealing with the setup of all SIP calls in the network. A SIP server is also referred to as a SIP Proxy or a Registrar.
Although the SIP server is the most important part of the SIP based phone system, it only handles call setup and call tear down. It does not actually transmit or receive any audio. This is done by the media server in RTP.
An example of a SIP server is 3CX Phone System - a Windows-based SIP server
A SIP URI is the SIP addressing schema to call another person via SIP. In other words, a SIP URI is a user’s SIP phone number. The SIP URI resembles an e-mail address and is written in the following format:
SIP URI = sip:x@y:Port
Where x=Username and y=host (domain or IP)
Examples:
sip:joe.bloggs@212.123.1.213
sip:support@phonesystem.3cx.com
sip:22444032@phonesystem.3cx.com
The SIP URI standard has been defined in the RFC 3261 standard. 3CX Phone System for Windows uses SIP URIs
Links:
RFC 2396 - Uniform Resource Identifiers (URI): Generic Syntax.
A STUN (Simple Traversal of User Datagram Protocol [UDP] Through Network Address Translators [NATs]) server allows NAT clients (i.e. computers behind a firewall) to setup phone calls to a VOIP provider hosted outside of the local network.
The STUN server allows clients to find out their public address, the type of NAT they are behind and the internet side port associated by the NAT with a particular local port. This information is used to set up UDP communication between the client and the VOIP provider and so establish a call. The STUN protocol is defined in RFC 3489.
The STUN server is contacted on UDP port 3478, however the server will hint clients to perform tests on alternate IP and port number too (STUN servers have two IP addresses). The RFC states that this port and IP are arbitrary.
More information about STUN and VoIP in general can be found in our SIP / VoIP Video tutorials, 'Voip Nuggets'. VoIP Nuggets are short youtube technical training tutorials about VoIP. Click here for the latest list of VoIP Nuggets
Stun functionality is seamlessly handled by 3CX Phone System for Windows - an easy to install windows based PBX.
Unified Communications is defined as the process in which all means of communication, communication devices and media are integrated, allowing users to be in touch with anyone, wherever they are, and in real time.
The objective of Unified Communications is to optimize business procedures and boost human communications by simplifying processes.
Read more about Unified Communications.
H323 is a set of standards from the ITU-T, which defines a set of protocols to provide audio and visual communication over a computer network.
H323 is a relatively old protocol and is currently being superceded by SIP – Session Initiation Protocol. One of the advantages of SIP is that its much less complex and resembles the HTTP / SMTP protocols.
Therefore most VOIP equipment available today follows the SIP standard. Older VOIP equipment though would follow H 323.
FXS and FXO are the name of ports used by Analog phone lines (also known as POTS - Plain Old Telephone Service) or phones.
FXS - Foreign eXchange Subscriber interface is the port that actually delivers the analog line to the subscriber. In other words it is the ‘plug on the wall’ that delivers a dialtone, battery current and ring voltage.
FXO - Foreign eXchange Office interface is the port that receives the analog line. It is the plug on the phone or fax machine, or the plug(s) on your analog phone system. It delivers an on-hook/off-hook indication (loop closure). Since the FXO port is attached to a device, such as a fax or phone, the device is often called the ‘FXO device’.
FXO and FXS are always paired, i.e similar to a male / female plug.
Without a PBX, a phone is connected directly to the FXS port provided by a telephone company.
FOIP stands for Fax over IP and refers to the process of sending and receiving faxes via a VOIP network.
Fax over IP works via T38 and requires a T38 capable VOIP gateway as well as a T38 capable fax machine, fax card or fax software. Fax server software that can talk 'T38' allows sending and receiving faxes directly via a VOIP gateway and, consequently, does not need any additional fax hardware.
3CX includes a T38 compatible network fax server in its 3CX Phone System for Windows. Faxes are converted to PDF files and forwarded via email. Outbound faxes are sent via Microsoft Fax from anywhere in the network. Other fax servers currently in the market require the use of separately licensed and expensive Dialogic SoftIP drivers.
How does FAX work in VOIP environments?FAX was designed for analog networks, and does not travel well over a VOIP network. The reason for this is that FAX communication uses the signal in a different way to regular voice communication. When VOIP technologies digitize and compress analog voice communication it is optimized for VOICE and not for FAX. Subsequently, there are a number of things you need to take note of when you move to a VoIP Phone System. If you want to continue using your old fax machine, and you want to connect to your VoIP phone system, its best to use aVoIP Gateway and an ATA that supports T38. T38 is a protocol designed to allow fax to 'travel' over a VoIP network. An example configuration of such a setup can be found here It is also possible to convert to computer based fax and choose a VoIP phone system that supports fax. 3CX Phone System for Windows includes a full featured fax server that is able to receive faxes and forward them in PDF format to e-mail. Faxes can be sent from anywhere in the network using theMicrosoft Fax client & fax server (which comes free with Windows Server 2003 and 2008) Another way to deal with fax when you switch to voip are to connect the fax machine directly to the existing analog phone line and bypass your VOIP system. |
