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Internet telephony means that IP stations can communicate directly with other IP stations over the Internet or with stations from the conventional telephone network. This type of telephony is also called Voice over IP (VoIP). To use Internet telephony, you will need access to an Internet Telephony Service Provider (ITSP).

Call stations (IP stations) such as IP phones, PCs, and conventional phones connected via special adapters can set up the connection to the Internet.

Connecting to the Internet (to the ITSP)

The communication system can be connected to the Internet either directly or via an additional Internet router.

• Communication system with direct Internet access

This option is offered only on the hardware platforms; it is not supported by the softswitch.

Connection to Service Provider ITSP Access and Internet Telephony

• Communication system with Internet access via existing Internet router:

The internal network is connected to the Internet over an existing Internet router. In order to receive incoming calls over the Internet, the relevant IP user must be able to determine his or her IP address used on the Internet and share this with the communication partner. To do this, a STUN server operated by the ITSP is required. The STUN server is also used at some ITSPs in order to receive incoming calls.

Call Setup and Cleardown

Calls are set up and cleared down via the Session Initiation Protocol (SIP). The voice data is combined in IP packets and transferred over the Realtime Transport Protocol (RTP).

Further information on the network configuration for ITSP including STUN can be found here:

http://wiki.siemens-enterprise.com/wiki/

Network_Configuration_for_VoIP_Providers

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6.2.1 ITSP Requirements

An Internet Telephony Service Provider (ITSP, SIP Provider) lets you conduct calls over the Internet. To do this, an Internet telephony connection must be applied for from the ITSP, and a user account must be set up for the communication system.

Internet Telephony Service Providers do not always offer the same range of SIP features. Consequently, only ITSPs certified for the communication system should be used. A list of certified ITSPs can be found at the following link:

http://wiki.siemens-enterprise.com/wiki/

Collaboration_with_VoIP_Providers

Types of Internet Telephony Connections

• The Internet telephony user connection is a connection with the registration of individual call numbers. With this connection type, a registration and authentication from the ITSP is required for every individual station connection call number.

• The Internet telephony point-to-point connection is a connection with the registration of a call number range. With this connection type, only a single registration and authentication from the ITSP is required for the entire call number range.

INFO: A registration is not necessary if static IP authentication or a VPN tunnel is used by the ITSP.

Connection to Service Provider ITSP Access and Internet Telephony

ITSP user account

The ITSP user account (SIP User Account) must be applied for from the ITSP.

The ITSP provides a SIP Registrar server at which the communication system must first log in (provider-specific) for this purpose.

INFO: Special numbers and emergency numbers, which are not supported by the ITSP, should be routed over fixed network connections.

INFO: In the event of ITSP failure, fixed network connections via least cost routing (LCR) can be used as a fallback solution.

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6.2.2 Configuring an Internet Telephony Service Provider

It is possible to configure predefined and new Internet Telephony Service Providers. You can configure one or several accounts for each ITSP. The ITSP call numbers can be a range of call numbers or individual Internet telephony numbers.

The default is to use a preconfigured ITSP template. To do this, the own access data and phone numbers are entered in the template, and this is then activated.

In Expert mode, you can also edit a preconfigured ITSP template and save it as a new template.

Configuring a new ITSP is seldom required and can be very time-consuming. No guarantee can be provided for the functionality of a newly configured ITSP.

Additional information on ITSPs and their features can be found here:

http://wiki.siemens-enterprise.com/index.php/

Collaboration_with_VoIP_Providers#Overview

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6.2.3 STUN (Simple Traversal of UDP through NAT)

When operating the communication system behind a NAT router, STUN

determines its own public IP address/port (which is required for some ITSPs). The functionality is made available on the Internet on STUN servers, whose

addresses must be stored in the configuration of the communication system.

The required STUN mode depends on the ITSP infrastructure and the used Internet router. STUN is not required for ITSPs that resolve NAT traversal using infrastructure components in the provider network such as the session border controller.

The following STUN modes can be set at the communication system:

Connection to Service Provider trunk access

• Automatic (Default)

If no ITSP is active, STUN is fully disabled. With an active ITSP, STUN determines the used firewall type (NAT type) at system startup and detects IP address changes during runtime. Depending on the detected NAT type, STUN changes certain parameters in SIP messages (NAT traversal).

INFO: Symmetric NAT is not supported.

• Always

STUN is always active, for example. Depending on the detected NAT type, some parameters in SIP messages are adapted.

• Use static IP

The DSL modem or Internet router uses a static a static IP address (public IP address), and the ITSP requires a static IP authentication. The static IP address and port that is used by the modem or router must be specified in addition.

• Port Preserving router

The public IP address is determined using STUN. The port is entered in SIP messages unchanged.

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