255-700-019
2-3
PacketStar
™
PSAX 20 Access Concentrator User Guide
, Issue 1
Release 6.3.0
Chapter 2 Hardware Description
Central Processing Unit (CPU) Component
The chassis backplane has a single bus, which supports 600 Mbps of ATM
bandwidth, and live insertion and removal of the I/O and server modules.
Power is distributed through the backplane to the cooling fans and the I/O
and server modules.
Central Processing Unit (CPU) Component
The Central Processing Unit (CPU) component provides the processing,
switching, and storage functions for the PSAX 20 system. The RISC-based
microprocessor has the processing power to maintain data flow, perform
numerical calculations, and manage the DMA interfaces. While the interface-
specific physical and link layer protocol functions, in addition to the queuing
and traffic management functions, are performed on each of the various I/O
modules, the CPU module has 64 MB of memory for routing and signalling
functions, forward error correction, processing of SVC connections, and
network management capabilities.
Stratum 3–4 Component
The Stratum 3–4 component provides synchronization and monitoring for
the PSAX 20 system. This component supports the backplane bus and
furnishes 600 Mbps of ATM bandwidth. In addition, the PSAX 20 system can
obtain network clock synchronization through the backplane from any of its
I/O modules except for the DSP2A/B/C Voice Server, Ethernet, High-Speed,
Tones and Announcements Server, Route Server, Voice 2-Wire Station, and
Voice 2-Wire Office modules. The Multi-Serial module can be used for
network timing, but it is not recommended. With the ability to accept a
timing reference from any physical interface at low transmission rates, the
system provides the network with a reliable transport and access
infrastructure. The Stratum 3–4 clock timing is accurate to Stratum 3
requirements, allowing the PSAX 20 system to freely run even after losing
external synchronization, for as long as 24 hours, without synchronization
problems.
Figure 2-1. PSAX 20 System with Enclosed Chassis
FAIL
ACTIVE
T1
FAIL
ACTIVE
DSP
FAIL
ACTIVE
CPU
1
1
2
2
3
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6
LOS
ETHERNET CONSOLE
PSAX 20