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Universal T1 WAN (UTWAN)
UTWAN connection
The UTWAN connection supports frame relay or Point-to-Point protocol (PPP) at the link layer.
The link protocol you use depends on the existing network or on the service you buy from your
Internet service provider.
Frame Relay
In Frame Relay mode, the UTWAN interface allows up to 50 PVCs (permanent virtual circuits) to
be configured. You can assign the same IP for multiple PVCs, or a unique IP for each PVC. To
avoid IP routing confusion, it is important that each unique IP belongs to a unique subnet.
The available Data Link Control interface numbers are 0-1023. Of the 1024 PVCs, 16 are
reserved. The maximum number of PVCs allowed is 1008.
The range of the Data Link Control Interface (DLCI) numbers is between 0 and 1023. However,
within this range, only 16 through 991 are available for user connections. The other ports are
reserved as follows:
•
0 and 1023 are reserved for the Local Management Interface (LMI) handshake
•
992 through 1007 are reserved for Frame Relay management at layer 2
•
1 through 15 and 1008 through 1022 are reserved for future use
Point-to-Point-Protocol (PPP)
Point-to-Point Protocol (PPP) is a full-duplex transmission protocol for communication between
two computers using a serial interface. A typical PPP connection is a personal computer connected
by telephone line to a server. For example, your Internet service provider (ISP) provides you with
a PPP connection so that the ISP server can respond to your requests, pass them on to the Internet,
and return your requested Internet responses to you.
Fragmentation
Frame Relay fragmentation and PPP fragmentation are link-layer fragmentation schemes.
Over a slow link, the major advantage of using link-layer fragmentation over IP layer
fragmentation is that while it reduces the jitter effect for voice packets, it also reduces the
end-to-end delay for data packets that is introduced by IP layer fragmentation.
RTP Header compression
The RTP Header Compression feature allows you to compress the 40 byte IP/UDP/RTP header to
2 or 4 bytes. This reduces the header-to-payload ratio of a data transmission. This is particularly
true of data transmissions with smaller payloads, such as a IP telephony packets. By reducing the
header-to-payload ratio, you can increase your bandwidth utilization. With slower links, this
allows more data or simultaneous IP telephony conversations to be carried over the link at the
same time.
N0008589 3.3
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