Nortel Circuit Card, Installation Manual, Page: 397 / 908

NT6D80 MSDL card Page 397 of 906
Circuit Card Description and Installation
Data flow
The MSDL transmit interface, managed by the MSDL handler, sends data
from the system to the MSDL. This interface receives packetized data from
the system and stores it in the transmit buffer on the MSDL. The transmit
buffer transports these messages to the appropriate buffers, from which the
messages travel over the MSDL port to the I/O equipment.
The MSDL uses the MSDL receive interface to communicate with the
system. The MSDL card receives packetized data from the I/O equipment
over the MSDL ports. This data is processed by the MSDL handler and sent
to the appropriate function.
The flow control mechanism provides an orderly exchange of transmit and
receive messages for each operation. Each operation has a number of
outstanding messages stored in buffers waiting to be sent to their destinations.
As long as the number of messages does not exceed the threshold specified,
the messages queue in the buffer in a first-in-first-out process.
If the outstanding number of messages for an operation reaches the threshold,
the flow control mechanism informs the sender to wait until the number of
messages is below the threshold before sending the next message.
If buffer space is not available, the request to send a message to the buffer is
rejected and a NO BUFFER fault indication is sent.
Engineering guidelines
Available network card slots
The number of available network slots depends on the system option, the
system size, and the number of available network slots in each module for the
selected system option.
Some of these network card slots are normally occupied by Network cards,
Superloop Network cards, Conference/TDS, and others, leaving a limited
number of unused slots for MSDL and other cards.