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Cisco BPX 8600 Series Installation and Configuration
Release 9.3.10, Part Number 78-11603-01 Rev. D0, July 2001
Chapter 21 Configuring ATM Connections
rt-Vbr and nrt-Vbr Connections
Example of cnftrk:
pubsbpx1 TN silves BPX 8620 9.3 Aug. 1 2000 14:43 PDT
TRK 2.4 Config OC3 [353207cps] BXM slot: 2
Transmit Rate: 353208 Line framing: STS-3C
Protocol By The Card: No coding: --
VC Shaping: No CRC: --
Hdr Type NNI: Yes recv impedance: --
Statistical Reserve: 1000 cps cable type: --
Idle code: 7F hex length: --
Connection Channels: 256 Pass sync: No
Traffic:V,TS,NTS,FR,FST,CBR,NRT-VBR,ABR, T-VBR clock: No
SVC Vpi Min: 0 HCS Masking: Yes
SVC Channels: 0 Payload Scramble: Yes
SVC Bandwidth: 0 cps Frame Scramble: Yes
Restrict CC traffic: No Virtual Trunk Type: --
Link type: Terrestrial Virtual Trunk VPI: --
Routing Cost: 10 Deroute delay time: 0 seconds
This Command: cnftrk 2.4
Transmit Rate [ 1-353208 ]:
rt-Vbr and nrt-Vbr Connections
Vbr (variable bit rate) connections may be classified as either:
• real time (rt-Vbr)
This 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 such as
compressed voice video conferencing—for example, 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).
• non-real time (nrt-Vbr)
This 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.
When configuring a rt-Vbr connection, the trunk cell routing restriction prompt does not display,
because rt-Vbr connection routing is automatically restricted to ATM trunks.