3Com MSR 50 Series, Configuration Manual

Page: 2238 / 2443

2238 C
HAPTER
129: V
OICE
O
VERVIEW
There are two kinds of voice entities: plain old telephone service (POTS) entity and
VoIP entity.
■
The POTS entity corresponds to the local telephone or PSTN. POTS entity
configuration is to associate a voice subscriber line on the VoIP gateway with a
local telephone. The POTS entity configuration implements the binding
between telephone numbers and voice subscriber lines.
■
The VoIP entity relates a call entity with a routing policy. Compared with the
POTS entity, the VoIP entity corresponds to the IP network. VoIP configuration
implements the binding between telephone numbers and destination
addresses (IP addresses or server addresses).
Voice Protocols The VoIP gateway can transfer voice or fax over the IP network by using different
protocols. The basic voice protocols that the router supports are H.323 and session
initiation protocol (SIP), and 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 the IP
network. An H.323 network usually consists of VoIP gateway, gatekeeper
(optional), multipoint control unit (MCU), and terminals. According to the ITU-T
specifications, the gatekeeper (GK) should provide H.323 terminals, 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, you
need to perform related configurations on the router. For detailed configurations,
refer to
“H.323 Configuration” on page 2355 .
2
SIP
SIP is the core protocol of the IETF multimedia data and control architecture and is
used for signaling control and communication with a softswitch platform in the IP
network. A SIP network consists of user agent (namely, SIP endpoint), proxy server,
registration server, location server, and redirect server. Here, the proxy server,
registration server, location server, and redirect server are only functional entities.
In practice, multiple functional entities may 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