Specifications
Common Equipment Description 2-17
BNM-T3/E3
The major function of the BNM is to provide a T3 or E3 ATM interface to a BNI or BXM-T3/E3
card in a BPX 8620 node. The BNM also provides a number of miscellaneous functions as follows:
• Shelf Mastership
Selects which core card to use as the master and which redundant bus to use.
• Cell Bus Mastership
BNM polls the other cards on the bus and grants permission to transmit cells across the bus.
Polling is performed on a round-robin basis.
• Clock Selection
BNM manages the clock selection and synchronization for the entire MGX 8220 shelf. The BNM
selects, regulates and outputs the selected clock for use by each service module in the shelf. The
BNM back card contains a T1/E1 port for inputting an external T1/E1 clock source. Two versions
of the line module are available. Version T3E3-B has a BNC external clock connector used with
E1 clock timing input. Version T3E3-D has a DB-15 external clock connector used with T1 or
E1 clock timing input. The shelf can also obtain clock from the DS3 or E3 trunk itself or use an
internal clock source.
• External Alarm Interface
BNM provides the activation of four alarm relays which are wired to a DB-15 connector on the
back card faceplate allowing the customer to wire their own cable from the connector to an
indicator panel. The four relays are Major Alarm Audible, Major Alarm Visual, Minor Alarm
Audible, and Minor Alarm Visual. The pinouts for this connector are provided in the
Appendix B, “Specifications”.
• Miscellaneous Monitoring Functions
— Fan performance in the Cooling Assembly
— Input voltage levels
— Shelf intake air temperature
— In-band management
The BNM card provides a separate path for management of the MGX 8220 using an ATM VCC from
across the ATM network
ATM Trunk Interface
The BNM card accepts and transmits ATM cells over a T3 or E3 line interfaces at 44.736 Mbps or
34.368 Mbps respectively, using Cisco STI (StrataCom Trunk Interface) protocol asynchronously.
Framing occurs on the card using C-bit parity. An 8Khz clock is extracted from the received signal
and can be used to synchronize the entire MGX 8220 system.
The physical T3 or E3 ATM interface to the BNM is achieved via the BNM backcard. This physical
connection is made with BNC connectors. There are also relays on the backcard. These relays
provide the continuity or discontinuity between the internal circuitry and the external BNC
connectors for the Transmit and Receive lines.
These relays are also used as a mechanical loopback for the T3 or E3 bit stream.
The MGX 8220 shelf implements the ATM STI cell format by using slot/channel numbers in the
VPI/VCI fields in the cell format used between the BNM and the BPX 8620 BNI port. The cell
format is shown in Figure2-14 and Figure2-15. The format on the left is the general STI format, the
format on the right is the MGX 8220 implementation.