Cisco Systems 8600 Series manual VBR and Atfr Connections, VBR Connections

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 7-4in 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

1

Policing (1, 2, 3, 4, or 5)

Trunk cell routing restrict (Y/N) [Y]

1For policing prompt:

1 = VBR.1

2 = VBR.2

3 = VBR.3

4 = PCR policing only

5 = policing off

Note: BW allocation = (PCR)x(%Util)

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7-14Cisco BPX 8600 Series Reference