Техническая Спецификация для Cisco 1-port ATM E3 port adapter PA-A6-E3=
Модели
PA-A6-E3=
Data Sheet
All contents are Copyright © 1992–2007 Cisco Systems, Inc. All rights reserved. This document is Cisco Public Information.
Page 4 of 9
Per-Virtual Circuit and Per-Virtual Path Traffic Shaping
Traffic shaping is a function typically provided on ATM edge devices to ensure that bursty traffic
conforms to a predetermined contract. Specifically, traffic shaping ensures that traffic from one
virtual circuit does not adversely impact another, resulting in data loss. This function is very
important when connecting to an ATM WAN or public ATM network, especially when the ATM
switches enable traffic policing that discards all traffic that exceeds the predetermined contract at
the ingress of the ATM network.
The Cisco ATM Port Adapter supports traffic shaping on a per-virtual circuit basis and per-virtual
path basis. Supporting traffic shaping in hardware means that there is no performance degradation
when shaping is enabled. Providing traffic shaping on a per-virtual circuit and per-virtual path basis
allows flexibility and control over every virtual circuit and virtual path configured.
Depending on the selected ATM service class, the Cisco ATM Port Adapter supports highly
configurable parameters such as peak cell rate (PCR), sustainable cell rate (SCR), maximum burst
size (MBS), and minimum cell rate (MCR). These parameters can be defined based on the specific
bandwidth requirements of an individual virtual circuit, as needed for a specific application.
The Cisco ATM Port Adapter hardware shapes the virtual circuit to the specific parameters using a
wheel-based scheduling algorithm to ensure fairness across the ATM interface. If two cells
compete for the same time slot, the virtual circuits, by default, are prioritized in the following order
(starting with highest priority):
0 CBR, control
1 AAL5 or AAL2 VoATM virtual circuit (any service category)
2 VBR-rt
3 VBR-nrt
4 ABR
5 UBR, UBR+
Prioritizing the virtual circuits in this manner ensures that the high-priority and guaranteed traffic
have precedence over the best-effort traffic. It is also possible to configure a custom prioritization
scheme on a per-virtual circuit basis.
To provide further flexibility, the Cisco ATM Port Adapter allows each of these parameters to be set
over a wide range of small increments.
Supported Traffic-Shaping Granularity - OC-3, DS3, and E3 Versions
Parameter
Range
Increments
PCR
56 kbps to line rate
2.29-kbps increments for OC-3c/STM-1, 0.674-kbps increments for DS3, and
0.515-kbps increments for E3
0.515-kbps increments for E3
SCR
56 kbps to line rate
2.29-kbps increments for OC-3c/STM-1, 0.674-kbps increments for DS3, and
0.515-kbps increments for E3
0.515-kbps increments for E3
MBS
1 to 65535
One cell
High-Performance Architecture
The Cisco ATM Port Adapter is based on advanced dual segmentation and reassembly (SAR)
architecture. One SAR processor is dedicated for transmission and one for reception. Each SAR
supports AAL5 ATM adaptation for high-performance data applications. Many of the Cisco ATM