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Frame Relay for Sangoma Cards (C) Sangoma Technologies Inc. 1999,2000,2001 Page 72 of 78
10. Managing Information Rates
The Sangoma Frame Relay implementation is designed to allow user control of the information rates.
You can limit the information rate on any or all logical channels to the CIR, while maintaining optimum
use of the line.
Where the card is being used on a network configured for all zero CIR, or one where the CIRs are at
the line speed, there is no point in limiting the CIRs. The Backward and Forward CIR, Bc and Be can
be set at the maximum, or preferably, CIR checking may disabled when configuring the code. The card
will then act as a "dumb" router, sending and receiving data without trying to control the rate at which
data is sent on any DLCI.
On networks where the CIR for each DLCI is a finite value less than line speed, set the Backward and
Forward CIR, Bc and Be by using the SET_DLCI_CONFIGURATION call. The card will then only
transmit on each DLCI at a rate such that the network will never set the DE bit. It will select frames
from the transmit buffer so that as far as possible, line utilization is maximized while still staying below
individual Forward CIRs. When in the CPE mode, the Backward CIR, Bc and Be have no effect on
operation, they are simply used to keep statistics of incoming frame CIRs.
The data obtained from the READ_DLC_STATISTICS call can be used to monitor system
performance and "tune" the network to reduce subscribed facilities to the minimum.
Buffering
The SDLA card has input and output buffering of frames. The smaller the maximum frame size set in the
SET_DLC_CONFIGURATION call, the more efficiently the buffering is used.
The buffering can only deal with short term bursts. Obviously, the system can only work if the long term
total data rate is below the line speed, and if the long term data rate on any DLCI is less than the CIR.
When the system is congested, and board buffers are full, data will not be accepted by the board. It is
up to the application to either retry the INFORMATION_WRITE command or to discard the data and
recover at the protocol level.