Specifications

51
Release Notes for Cisco 7000 Family for Cisco IOS Release 12.1 T
78-10811-05
New and Changed Information
probabilities to those packets. This feature adds two new commands, random-detect dscp and dscp.It
also adds two new arguments, dscp-based and prec-based, to two existing WRED-related
commands—the random-detect (interface) command and the random-detect-group command.
Distributed CRTP
Platforms: Cisco 7500 series routers
The Distributed Compressed Real-Time Transport Protocol (dCRTP) feature compresses the combined
40-byte IP/UDP/RTP packet headers to between two and four bytes on packets traveling on a Cisco
7500 series router with a Versatile Interface Processor (VIP) in distributed fast-switching and
distributed Cisco Express Forwarding (dCEF) environments. This compression reduces the packet size,
improves the speed of packet transmission, and reduces packet latency.
Before Cisco IOS Release 12.1(5)T, if compression of TCP or Real-Time Transport Protocol (RTP)
headers was enabled on a Cisco 7500 series router with a VIP, the compression was performed in the
process-switching path. That meant that packets traversing interfaces that had TCP or RTP header
compression enabled were queued and passed up to the Route Switch Processor (RSP) to be switched.
This procedure slowed down transmission of the packet, and therefore some users preferred to
fast-switch uncompressed TCP and RTP packets rather than enable TCP and RTP compression.
If the dCRTP feature is enabled, the header compression of the combined IP/UDP/RTP header occurs
by default in the distributed fast-switched path or the distributed Cisco Express Forwarding-switched
(dCEF-switched) path, depending on which switching method is enabled on the interface.
If distributed fast-switching or distributed Cisco Express Forward switching are disabled, TCP or RTP
header compression will occur in the process-switched path as before.
For additional information on dCRTP, see the Distributed Compressed Real-Time Transport
Protocol feature module on Cisco.com and the Documentation CD-ROM.
Distributed Low Latency Queuing
Platforms: Cisco 7500 series routers
The Low Latency Queueing feature, which was introduced for some router platforms in Cisco IOS
Release 12.0(7)T, is now available for VIP-enabled Cisco 7500 series routers. The VIP-enabled
Cisco 7500 series version of the Low Latency Queueing feature, which contains significant
functionality differences from the standard Low Latency Queueing feature, is called Distributed Low
Latency Queueing.
The Distributed Low Latency Queueing feature brings the ability to specify low latency behavior for a
traffic class. Low Latency Queuing allows delay-sensitive data such as voice to be dequeued and sent
first (before packets in other queues are dequeued), giving delay-sensitive data preferential treatment
over other traffic.
The Distributed Low Latency Queueing feature also introduces the ability to limit the depth of a device
transmission ring. Before the introduction of Distributed Low Latency Queueing, the maximum
transmission ring depth was not a user-configurable parameter. Therefore, particles could accumulate
on a transmission ring without limitation, which could result in unavoidable high latencies. The
Distributed Low Latency Queueing feature allows users to limit the number of particles that may exist
on a transmission ring, effectively lowering the latency incurred by packets sitting on that transmission
ring.
For additional information on Distributed Low Latency Queueing, see the Distributed Low Latency
Queueing feature module on Cisco.com and on the Documentation CD-ROM.