Setup guide
3-5
Cisco 6400 Software Setup Guide
OL-1183-04
Chapter3 Basic NRP Configuration
NRP-1 Configuration
Segmentation and Reassembly Buffer Management
In Cisco IOS Release 12.1(1)DC, the following segmentation and reassembly (SAR) buffer management
enhancements were introduced:
• Reduced Segmentation Buffer Size—Prior to this release, the default size of the PVC segmentation
buffer was 256 packets. This meant that each PVC could queue up to 256 packets to be segmented
and sent. Now the default size is 32 packets, and a new command allows you to manually change
the segmentation buffer size.
• Increased Input/Output Memory Size—Prior to this release, the default input/output (I/O) memory
size was 16 MB for NRP-1s with 64 MB or 128 MB DRAM. Now the default I/O memory size is
18 MB for an NRP-1 with 64 MB DRAM, and 36MB for an NRP-1 with 128 MB DRAM. You can
also manually set the I/O memory size with an environment variable under ROM monitor
(ROMMON).
• Reserved Segmentation Buffer Slot for High-Priority Packets—For each PVC, a segmentation
buffer slot is reserved for high-priority packets.
These SAR buffer management enhancements reduce the amount of memory resources that can be held
by congested PVCs. This prevents a small group of congested PVCs from using all available memory
resources and adversely affecting the performance of other PVCs. The enhancements also improve
high-priority packet transmission. With a segmentation buffer slot reserved for high-priority packets,
each PVC accommodates high-priority packets even when the segmentation buffer is full.
Note Because of process memory usage, setting the I/O memory size to a larger value might reduce the
number of sessions that your NRP-1 can handle.
Setting the Segmentation Buffer Size
Caution Entering the atm vc tx command can cause service disruption. Only enter this command during
maintenance windows.
To manually set the size of all PVC segmentation buffers, complete the following steps beginning in
global configuration mode:
Example
In the following example, the PVC segmentation buffer size is set to 64 packets.
!
interface atm 0/0/0
atm vc tx 64
!
Command Purpose
Step1
Router(config)# interface atm 0/0/0
Specifies the ATM interface.
Step2
Router(config-if-atm-vc)# atm vc tx queue-depth
Sets the maximum number of packets in the PVC
segmentation buffers.