Voice Protocols - HP FlexNetwork MSR Series Configuration Manual

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A VoIP entity relates a call entity with a routing policy. Compared with the POTS entity, the VoIP
entity corresponds to the IP network side. VoIP configuration implements the binding between
telephone numbers and destination addresses (IP addresses or server addresses).
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A VoFR entity is used to transmit voice data over a frame relay network.
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An IVR entity is used to set a customizable interactive voice response system.

Voice protocols

The VoIP gateway can transfer voice or fax over the IP network by using different protocols. The
basic voice protocols that routers support are H.323 and SIP. The fax protocol is T.38.
1. H.323
H.323 is a standard protocol established by ITU-T. The H.323 protocol stack, implemented at
the application layer, mainly describes terminals, devices, and services used for multimedia
communication without QoS guarantee over an IP network. An H.323 network usually consists
of VoIP gateway, an optional GK, an MCU, and terminals. According to the ITU-T specifications,
the GK should provide H.323 terminals, a gateway, or MCU in LANs or WANs with the following
functions:
Address translation
Access permission
Bandwidth control and management
Area management and security check
Call control signaling and call management
Routing control and accounting
The GK not only controls the call service, but also functions as the central control point within its
management area. The GK implements the control function by exchanging information with the
VoIP gateway. If there is any GK, the router will be under the control of the GK. To implement
the control function of the GK, perform related configurations on the router. For more
information, see "Configuring H.323."
2. SIP
SIP is the core protocol of the IETF multimedia data and control architecture. SIP is used for
signaling control and communication with a softswitch platform in the IP network. A SIP network
consists of a user agent (SIP endpoint), proxy server, registration server, location server, and
redirect server. Here, the proxy server, registration server, location server, and redirect server
are functional entities. In practice, multiple functional entities can be integrated into one
physical entity.
In a complete SIP system, all SIP endpoints serve as user agents and should register with
the registration server to inform of their locations, session capabilities, and call policies. The
registration server then sends the registration information to the location server for storage.
SIP endpoints use the proxy server to set up calls. SIP endpoints send signaling messages
to the proxy server, and then the proxy server forwards them to the next hop. In this process,
multiple proxy servers might be involved. Eventually, channels are established to transfer
the upper layer voice service.
Unlike the proxy server, the SIP redirect server will not forward the received session request
messages. Instead it will inform the originating SIP endpoints of the addresses of the
terminating SIP endpoints by returning reply messages. The originating SIP endpoints
directly re-originate a session request message to the terminating SIP endpoints. The
terminating SIP endpoints also directly return a reply message to the originating SIP
endpoints.
As a SIP endpoint, the voice router needs to exchange information with the servers to
accomplish functions such as registration. For more information, see "Configuring SIP."
3. Fax protocol
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