Figure 4.9 REGISTER Message Flow
4.3.2.3.2 Invite authentication
Authentication of INVITE requests is not really required, but it is a good practice to do so. A SIP
Proxy Server can only challenge requests that are coming from users belonging to an administrative domain that the proxy server is responsible for.This means that a proxy responsible for, e.g., the iptel.org domain can challenge only requests that have iptel.org in the From header field.
Requests coming from foreign users can not be challenged because foreign users usually do not have a username and password registered at this server. Requiring authentication would make incoming calls from foreign users impossible.
Figure 4.10 is a call flow of challenged INVITE.
Figure 4.10 INVITE with authentication
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[IP Telephony Cookbook] / Setting Up Basic Services
~ 4.4. Examples
This section lists some examples of how a zone setup could look like, depending on the requirements.
~ 4.4.1. Example 1: Simple use of IP Telephony like legacy telephony Assumption: an institution currently using a PBX with internal numbers of four digits length.
There are telephone numbers from 6000 to 6999 available for IP Telephony.There are no requirements regarding authentication. Because only calls into the PSTN will be billed, the PBX
is the only place where billing will take place.There are no special requirements regarding availability and there is no demand for IP Telephony research.
Components: any kind of IP Telephony server (H.323 Gatekeeper or SIP Proxy), even productions using proprietary protocols are usable.The gateway must be able to translate signalling between the protocol that the server uses and the PBX.The protocol to the PBX
usually uses one of the protocols described in Section 5.1.1.
Structure: See Figure 4.11.
Call Routing: the PBX is configured to route every call to a number, starting with 6, to the gateway.The IP Telephony server either has the gateway as a default route for unknown/unregistered targets or is configured to route every call to a number that does not start with 6 to the gateway too.The gateway can either be configured to always route a call from one side to the other or needs to have a configuration similar to the IP Telephony server.
Authentication: authentication on the IP-side is either done using the H.323 or SIP
authentication mechanisms or can be done on the link layer. In the latter case, a telephone number is bound to a specific port or MAC address.
Billing: the billing mechanisms that were already in use for PBX calls can be used for IP
Telephony as well as all outgoing calls passing the PBX.
default -> PSTN
6xxx ->IP
Billing
Legacy PBX
Gateway
IP telephony
PSTN