Chapter 3 System Features
AC 60 Software Features
3-42
255-700-025
PacketStar
™
Access Concentrator 60 User Guide
, Issue 1
Release 6.3.0
The algorithm processes traffic moving out of the input cell selection buffer
according to the SCR of the particular VPC/VCC. The MBSs of traffic-shaped
output are set as follows:
The OC-3c and the STM-1 modules can perform traffic shaping on multiple
high-rate connections (such as three 40-Mbps connections). Assigning a SCR
to a connection above 75 Mbps, however, is not recommended in sensitive,
bursty traffic environments. Assigning a SCR above 120 Mbps will essentially
eliminate any traffic shaping, and thus is strongly discouraged.
•
The OC-3c and the STM-1 modules perform only limited traffic
management on the output side. The output buffer is limited to 2 Mbps
for VBR traffic and 128 cells for CBR traffic, with only three priority levels
supported: CBR, VBR1, and VBR2. The maximum-capacity level for
congestion control is 32,000 cells, and the minimum-capacity level is
24,576 cells, with VBR traffic being shut off first from the backplane.
Voice Compression
A noncompressed voice channel uses 64 Kbps of bandwidth. Voice
compression reduces the 64 Kbps bandwidth to a lower value, based on the
algorithm chosen. Compressed voice messages can be carried over ATM
Adaptation Layer 2 (AAL-2) only. The software on the CPU module assumes
a 30 percent bandwidth savings.
Voice compression over AAL-2 will only work for a voice channel that is
connected to an Access Concentrator through an ISDN PRI line. This is
because AAL-2 does not transfer the voice channel signaling bits. If silence
detection is enabled for a voice compression channel and no voice is
detected, no ATM cell will be sent.
Voice Processing
With the DSP2C module, the Access Concentrator system can process voice
traffic on selected DS0 circuits within the DS1 connections of the system.
This module, a significant improvement over the earlier DSP2A and DSP2B
server modules, processes ciruit emulation voice messages and can apply
voice compression, echo cancellation, silence suppression, and comfort noise.
Used with the channelized circuit emulation service modules, the DSP2C
offers superior voice processing capability through the
PacketStar
™
line for
the Lucent voice traffic over ATM (VToA) solution.
Sustained Cell Rate
(SCR) of VPC/VCC
Maximum Burst Size (MBS) of Traffic-
Shaped Output
0–20 Mbits/sec.
< 4 cells
20–30 Mbits/sec.
< 5 cells
30–40 Mbits/sec.
< 6 cells
75–120 Mbits/sec.
approximately 20–50 cells