ZyXEL Communications P-870HN-51B - V1.0 Manual page 88

Chapter 5 WAN Setup
Variable Bit Rate (VBR)
The Variable Bit Rate (VBR) ATM traffic class is used with bursty connections.
Connections that use the Variable Bit Rate (VBR) traffic class can be grouped into
real time (VBR-RT) or non-real time (VBR-nRT) connections.
The VBR-RT (real-time Variable Bit Rate) type is used with bursty connections that
require closely controlled delay and delay variation. It also provides a fixed
amount of bandwidth (a PCR is specified) but is only available when data is being
sent. An example of an VBR-RT connection would be video conferencing. Video
conferencing requires real-time data transfers and the bandwidth requirement
varies in proportion to the video image's changing dynamics.
The VBR-nRT (non real-time Variable Bit Rate) type is used with bursty
connections that do not require closely controlled delay and delay variation. It is
commonly used for "bursty" traffic typical on LANs. PCR and MBS define the burst
levels, SCR defines the minimum level. An example of an VBR-nRT connection
would be non-time sensitive data file transfers.
Unspecified Bit Rate (UBR)
The Unspecified Bit Rate (UBR) ATM traffic class is for bursty data transfers.
However, UBR doesn't guarantee any bandwidth and only delivers traffic when the
network has spare bandwidth. An example application is background file transfer.
IP Address Assignment
A static IP is a fixed IP that your ISP gives you. A dynamic IP is not fixed; the ISP
assigns you a different one each time. The Single User Account feature can be
enabled or disabled if you have either a dynamic or static IP. However the
encapsulation method assigned influences your choices for IP address and default
gateway.
Full Cone NAT
In full cone NAT, the NAT router maps all outgoing packets from an internal IP
address and port to a single IP address and port on the external network. The NAT
router also maps packets coming to that external IP address and port to the
internal IP address and port.
In the following example, the ZyXEL Device maps the source address of all
packets sent from the internal IP address 1 and port A to IP address 2 and port B
on the external network. The ZyXEL Device also performs NAT on all incoming
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P-870HN-51b User's Guide