Cisco BPX-BXM-155-8DX Installation And Configuration Manual page 92

Broadband Controller Card (BCCs)
The arbiter polls each card to see if it has data to transmit. It then configures the crosspoint switching
matrix to make the connection between the two cards. Each connection is unidirectional and has a
capacity of 800 Mbps (616.7 Mbps for cell traffic plus the frame overhead).
Only one connection at a time is allowed to an individual card.
Each card contains a Switch Interface Module (SIM) which merely provides a standardized interface
between the card and the data lines and polling buses. The SIM responds to queries from the BCC
indicating whether it has data ready to transmit.
With the BPX switch equipped with two BCCs, the cell switching is completely redundant in that there
are always two arbiters, two crosspoint switches, two completely independent data buses, and two
independent polling buses.
The BCC incorporates non-volatile flash EEPROM which permits new software releases to be
downloaded over the network and battery-backup RAM (BRAM) for storing user system configuration
data. These memory features maintain system software and configuration data even during power
failures, eliminating the need to download software or reconfigure after the power returns.
The BPX switch cell switching is not synchronized to any external clocks; it runs at its own rate. No
switch fabric clocks are used to derive synchronization nor are these signals synchronized to any
external sources.
Node clocking is generated by the BCC. Because the BPX switch resides as an element in a
telecommunications network, it is capable of synchronizing to higher-stratum clocking devices in the
network and providing synchronization to lower stratum devices. The BCC can be synchronized to any
one of three different sources under software control:
• An internal, high-stability oscillator.
• Derived clock from a BNI module.
• An external clock source connected directly to the BPX.
The BCC clock circuits provide clocking signals to every other card slot. If a function card needs to
synchronize its physical interface to the BPX switch clock, it can use this timing signal to derive the
proper reference frequency. These reference frequencies include DS1, E1, DS3, and E3.
Cisco BPX 8600 Series Installation and Configuration
3-4
Chapter 3 BPX Switch Common Core Components
Release 9.3.0, Part Number 78-10674-01 Rev. D0, July 2001