R2511-HP MSR Router Series Voice Configuration Guide(V5)

• A POTS entity corresponds to the local telephone (or PSTN) side. POTS entity configuration

associates a voice subscriber line on the VoIP gateway with a local telephone. The POTS entity

configuration also implements the binding between telephone numbers and voice subscriber lines.

• 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).

• A VoFR entity is used to transmit voice data over a frame relay network.

• 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