7-14 Cisco BPX 8600 Series Reference
ATM Connection Configuration
VBR and ATFR Connections
VBR Connections
VBR (variable bit rate) connections may be classified as rt-VBR or nrt-VBR connections.
The rt-VBR (real-time variable bit rate) category is used for connections that transmit at a rate
varying with time and that can be described as bursty, often requiring large amounts of bandwidth
when active. The rt-VBR class is intended for applications that require tightly constrained delay and
delay variation. An example of rt-VBR is video conferencing which requires real-time data transfer
with bandwidth requirements that can vary in proportion to the dynamics of the video image at any
given time. The rt-VBR category is characterized in terms of PCR, SCR (sustained cell rate), and
MBS (maximum burst size).
The nrt-VBR (non-real time variable bit rate) category is used for connections that are bursty but are
not constrained by delay and delay variation boundaries. For those cells in compliance with the
traffic contract, a low cell loss is expected. Non-time critical data file transfers are an example of an
nrt-VBR connection. A nrt-VBR connection is characterized by PCR, SCR, and MBS.
Configuring VBR connections. The characteristics of rt-VBR or nrt-VBR are supported by
appropriately configuring the parameters of the VBR connection.
The parameters for a VBR connection are shown in Figure 7-4 in the sequence in which they occur
during the execution of the addcon command. The VBR policing definitions are summarized in
Table 7-6.
Figure 7-4 VBR Connection Prompt Sequence
VBR
PCR(0+1)
%Util
CDVT(0+1)
FBTC (AAL5 Frame based traffic control, enable/disable)
SCR
MBS
Policing (1, 2, 3, 4, or 5)
For policing prompt:
1 = VBR.1
2 = VBR.2
3 = VBR.3
4 = PCR policing only
5 = policing off
Note: BW allocation = (PCR)x(%Util)
10225
1
1
Trunk cell routing
restrict (Y/N) [Y]
