NCAUUI 14-9
Digital Switching Systems DMS-250 ISDN Reference Manual MWC14 (CSP14)
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User Information message counter N, initialized to X
• the replenishment parameter Y, initialized to X/2
• the DMS-250 switch timer TUUS is 10 seconds
A burst capability to send N User Information messages is available to each
access/egress agent. The value of N decrements by one for each User
Information message sent by the user and increments by Y at regular
intervals of TUUS subject to the limitation that N does not exceed X. If the
DMS-250 switch receives more than N User Information messages within
the TUUS timer setting, “network congestion” occurs. The network sends a
Congestion Control message to the user with Congestion Level parameter
set to “Receiver Not Ready.” The DMS-250 switch sets the Cause
Parameter in the Congestion Control message to a value of 42, “Switching
Equipment Congestion,” Location “Transit,” and Coding Standard “CCITT.”
When network congestion clears, the DMS-250 switch sends a Congestion
Control message is to the user with Congestion Level parameter in the
Congestion Control message set to “Receiver Ready.” The DMS-250 switch
sets the Cause Parameter to a value of 42, “Switching Equipment
Congestion,” Location “Transit” and Coding Standard “CCITT.” The
DMS-250 only sends a Congestion Control message with “Receiver Ready”
to the user previously notified of congestion.
User Congestion and Network Flow Control Interaction
The DMS-250 switch considers the congestion status of both end users and
itself before sending or forwarding Congestion Control messages to the end
users.
The network notifies the end user that the network or the end user is
congested. The end user only receives one Congestion Control message with
an indication of “Receive Not Ready” and an optional Cause parameter.
Once a user receives a Congestion Control message for that user must have
an indication of “Receiver Not Ready,” the next Congestion Control
message for that user must have an indication of “Receiver Ready” with the
optional Cause parameter identical to the one received in the Congestion
Control message with an indication of “Receiver Not Ready.”
If the access DMS-250 switch goes into ”network congestion” due to
congestion flow control, the DMS-250 switch sends a Congestion Control
message to the access user with an indication of “Receiver Not Ready.” If
the far-end user is congested, the DMS-250 sends a Congestion Control
message with an indication of “Receiver Not Ready.” The network forwards
this user generated Congestion Control message across the network until it
reaches the access switch that sent the first Congestion Control message with
an indication of “Receiver Not Ready.” If the access switch is still in
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