Cisco BPX 8650, Installation And Configuration Manual

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5-8
Cisco BPX 8600 Series Installation and Configuration
Release 9.3.30, Part Number 78-12907-01 Rev. E0, May 2005
Chapter 5 BXM Card Sets: T3/E3, 155, and 622
BXM Capabilities
Both DX and EX versions have the same connection density, providing you with the ability to
upgrade networks with the high connection density on trunk side, port side, or a combination of
trunks and ports. You can smoothly upgrade BXM cards to BXM-E capabilities; see the Upgrade
BXM to BXM-E Cards section of Appendix A, “Upgrade Information.”
• Support an improved traffic shaping granularity for each virtual interface (VI) to allow any desired
shaping rate.
On regular BXM cards, the VI traffic shaping rate is limited to OC-12/n. For example, where n is an
integer. On the Enhanced BXM cards, the VI traffic shaping rate is any desired shaping rate with a
precision of 9-bit mantissa and 4-bit exponent.
•
Provide ABR support for connections with non-AAL5 traffic
On the current BXM cards, the ABR support is limited to connections with AAL5 traffic. These
connections allow early packet discard to be applied to avoid queue congestion and thus maintain
RM cell flow. The Enhanced BXM cards extend the ABR support to connections with non-AAL5
traffic also. The Enhanced BXM cards minimize the problem of RM cell discard when RM cells are
injected into a congested VC by reserving room for 8 RM cells even when the VC begins to drop
data cells. The RM cell reserve can be globally configured for VS/VD and nonVS/VD connections.
• Support unidirectional ForeSight connections
On the current BXM cards, the ForeSight ABR (Cisco's prestandard ABR implementation) support
is limited to bidirectional connections only. The current BXM cards also support ATM Forum
standard ABR for both bidirectional and unidirectional connections. The Enhanced BXM cards will
extend the ForeSight ABR support to include unidirectional connections also.
• Support interworking of the port ABR segment controlled with ATM Forum ABR algorithm and the
network ABR segment controlled with ForeSight ABR algorithm.
The Enhanced BXM cards provide coupling between the port ABR segment with ATM Forum ABR
algorithm and the network ABR segment with ForeSight ABR algorithm.
•
Merging of multiple frame-based VCs onto a single frame-based VC
The Enhanced BXM card hardware supports VC merge to facilitate Label Switching with simple
software upgrade. With VC merge, the Enhanced BXM cards allow the BPX to aggregate multiple
incoming frame-based VCs with the same destination address into a single outgoing frame-based
VC. Cells from different VCIs going to the same destination are transmitted to the same outgoing
VC using multipoint-to-point connections.
Where VC merge occurs, several incoming labels indicated by VCIs are mapped to one single
outgoing label. This sharing of labels reduces the total number of virtual circuits required for label
switching. Without VC merge, each source-destination prefix pair consumes one label VC on each
interface along the path. VC merge reduces the label space shortage by sharing labels for different
flows with the same destination.
For a more detailed description, see Chapter 23, “Configuring BXM Virtual Switch Interface.”
The Enhanced BXM cards include a feature that is enabled by future firmware and switch software,
which is to separate frame discard CLP0 and frame discard CLP1 thresholds for each class-of-service
(CoS) queue.The Enhanced BXM cards support separate frame discard CLP0 and frame discard CLP1
thresholds for each CoS queue. This feature enables preferential treatment for conforming traffic within
CIR (frames with CLP=1 start-of-frame cell) compared to nonconforming traffic (frames with CLP=0
start-of-frame cell) when applying early packet discard (EPD).