Connection Flow Example; Ingress From Cpe 1 To Bxm 3 - Cisco BPX-BXM-155-8DX Installation And Configuration Manual

Chapter 21 Configuring ATM Connections
Network queues buffer the data at the trunk interfaces throughout the network according to the
connection's class of service. Service classes are defined by standards-based QoS. Classes can consist
of the five service classes defined in the ATM standards as well as multiple sub-classes to each of these
classes. Classes can range from constant bit rate services with minimal cell delay variation to variable
bit rates with less stringent cell delay.
When cells are received from the network for transmission out a port, egress queues at that port provide
additional buffering based on the service class of the connection.
CoS Management provides an effective means of managing the quality of service defined for various
types of traffic. It permits network operators to segregate traffic to provide more control over the way
that network capacity is divided among users. This is especially important when there are multiple user
services on one network.
Rather than limiting the user to the five broad classes of service defined by the ATM standards
committees, CoS management can provide up to 16 classes of service (service subclasses) that can be
further defined by the user and assigned to connections. Some of the CoS parameters that may be
assigned include:
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These class of service parameters are based on the standards-based Quality of Service parameters and
are software programmable by the user. The BPX switch provides separate queues for each traffic class.

Connection Flow Example

The example shown in Figure 21-3 shows the general ATM connection flow through BXM cards in
BPX switches. The cnfport, cnfportq, cnfln, cnftrk, and cnftrkparm commands are used to configure
resources affecting the traffic flow of a connection. Examples are described in Traffic Shaping for CBR,
rt-VBR, nrt-VBR, and UBR, page 21-13.

Ingress from CPE 1 to BXM 3

ATM cells from CPE 1 that are applied to BXM 3, Figure 21-3, are processed at the physical level,
policed per individual VC based on ATM header payload type, and routed to the applicable one of 15
per card slot servers, each of which contains 16 CoS service queues, including ATM service types CBR,
rt-VBR, nrt-VBR, ABR, and UBR.
ATM cells undergoing traffic shaping, for example, ABR cells are applied to traffic shaping queues
before going to one of the 15 per card slot servers. ATM cells applied to the traffic shaping queues
receive additional processing, including congestion control by means of VSVD or ForeSight and virtual
connection queuing.
Cells are served out from the slot servers via the BPX backplane to the BCC crosspoint switch. The
cells are served out on a fair basis with priority based on class of service, time in queue, bandwidth
requirements, and so on.
Release 9.3.0, Part Number 78-10674-01 Rev. D0, July 2001
Minimum bandwidth guarantee per subclass to assure that one type of traffic will not be preempted
by another
Maximum bandwidth ceiling to limit the percentage of the total network bandwidth that any one
class can utilize
Queue depths to limit the delay
Discard threshold per subclass
Cisco BPX 8600 Series Installation and Configuration
ATM Connection Flow
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