BNI (Trunk) Cards

In the transmit direction (from the BPX switching matrix towards the transmission facility, referred to as egress), the BNI performs these functions:

• Software controlled line buildout to match up to 900 feet (275 meters) of ABAM cable.

• Receives incoming cells from the switch matrix on the BCC.

• Queues and serves the cells based on the class-of-service algorithm.

• Sets congestion indication (EFCN) in cell header when necessary.

• Adds frame sync pattern and PLCP or G.804 overhead and transmits cells onto the T3 or E3 trunk.

In the receive direction (from the transmission facility towards the BPX switching matrix, sometimes referred to as ingress), the BNI performs these functions:

• Receives incoming ATM cells from the DS3 transmission facility, stripping the framing and overhead from the received bit stream.

• Determines the address of the incoming cells by scanning the Virtual Path Identifier (VPI)/Virtual Circuit Identifier (VCI) in the cell header.

• Queues the cells for transmission through the switch matrix.

• Extracts receive timing from the input framing and makes it available for node timing. Line can operate in looped timing mode.

• Recovers clock and data from the bipolar B3ZS (T3) or HDB3 (E3) line signal and converts data to unipolar.

• PLPP—Receiver Side

  • Provides frame sync for either the M23 or C-bit parity frame format.

  • Provides alarm detection and accumulates B3ZS code violations, framing errors, parity errors, C-bit parity errors, and far end bit error (FEBE) events.

  • Detects far end alarm channel codes, yellow alarm, and loss of frame.

  • Provides optional cell descrambling, header check sequence (HCS) error detection, and cell filtering.

  • Small receive FIFO buffer for incoming cells.

• PLPP—Transmitter Side

  • Inserts proper frame bit sequence into outgoing bit stream.

  • Inserts proper alarm codes to be transmitted to the far end.

  • Provides optional ATM cell scrambling, HCS generation and insertion, and programmable null cell generation.

  • Small transmit FIFO for outgoing cells.

In the BNI-3E3 the PLPP is replaced by a G.804 framer. The E3 framer obtains end-to-end synchronization on the Frame Alignment bytes. And a E3 transmitter/receiver replaces the DS3 transmitter/receiver for the BNI-3E3.

A Serial Interface Module (SIM) provides cell interface to the StrataBus backplane. This operates at 800 Mbps. It provides a serial-to-parallel conversion of the data and loopback and pseudo-random bit generation for test purposes.

• A non-disruptive self test
  This is automatically performed on a routine basis.

• A more complete, disruptive test
  This may be initiated manually when a card failure is suspected. If the card self-test detects a failure, the card status LEDs displays an indication of the failure type.

Loopback paths are provided:

• A digital card loopback path
  This is used by the node for self-test. It loops the data at the serial DS3 or E3 interface back toward the node.

• A digital line loopback
  This loops the data at the electrical transmitter/receiver at the card output.

Internally, the PLPP circuit in the BNI-T3 has several loopbacks for use by diagnostic routines. These loopbacks loop the signal in both directions, toward the StrataBus as well as toward the output. Therefore, they can be used to support both near-end and far-end maintenance loopback testing:

• A digital loopback at the DS3 or E3 transmitter/receiver
  This checks both the transmit and receive signal paths in the near-end BNI card.

• A digital loopback capability on the BNI-3T3 to the PLPP processor
  This is used for the internal self test to basically check the operation of the signal processor.

When a trunk has been assigned to a BNI card but is not yet activated (upped), it is put in a loopback mode and a diagnostic test is continuously performed. This loopback is disruptive so it cannot be performed on a card that has an active trunk. This diagnostic test checks the data path through the BNI out to the BCC, through the switch matrix, and back to the BNI.

Active trunks are constantly checked by the Communications Fail test routine which is part of system software.

The Line Module connects to the BNI through the StrataBus midplane. You can make two adjacent cards of the same type redundant by using a Y-cable at the port connectors. All three ports on a card must be configured the same.

• BNC connectors for 75-ohm unbalanced signal connections to the transmit and receive of each of the three ports.

• Transformer isolation from the trunk lines.

• Metallic relays for line loopback when in standby mode.

A final node loopback is at the end of the LM-3T3 or LM-3E3 card. This is a metallic loopback path that uses a relay contact closure. It is a near-end loopback path only; the signal is looped at the final output stage back to circuits in the node receive side. It is operated only when the corresponding front card is in standby.

• Single-mode fiber intermediate range

• Single-mode fiber long range

• Multimode fiber backcard

The Line Modules connect to the BNI through the StrataBus midplane.