Copyright © TIBCO Software Inc. All Rights Reserved
Copyright © TIBCO Software Inc. All Rights Reserved


Chapter 10 Managing Rendezvous Client Queues : Functional Description

Functional Description
During the delivery of a routed message to a client, the message passes through the queuing structure shown in Figure 12.
Figure 12 Client Egress Queue Hierarchy
The message first passes through the application message queue to the TCP transmit queue. A scheduler then selects it from the TCP transmit queues and places the message into a TCP send queue.
The act of enqueuing the message triggers the TCP stack to evaluate if the connection can send more data from that queue. If the TCP stack determines that it is acceptable to send data on the TCP connection, then data from the message is copied to a per-port transmit queue on the way to the Ethernet interface. The data remains on the TCP queue until it is acknowledged by the client through a TCP ACK message.
The per-port transmit queue is not strictly bounded in depth. However, its total depth never exceeds:
Note: For more information on LAGs, refer to Configuring 802.3ad Link Aggregation.
The per-client TCP transmit queues have a configurable maximum depth, measured in bytes. When a transmit queue is full, no more data is taken from the message queues.
The per-client message queues also have a configurable maximum depth, measured in work units of 2048 bytes. When these queues become full, messages are discarded, and the dataplane statistic for Transmit Congestion--Slow Consumer is incremented.
Per-client TCP Queues
Each active client has one TCP queue for message delivery.
The TCP queue holds data that is either waiting for delivery out of the P-7500, or is data that has already been sent, but is waiting for acknowledgement.
Before messages are placed in the TCP queue, the current depth of the TCP queue is checked against its configured maximum. If the current depth of the TCP queue is less than its maximum, the entire message is placed on the queue. This can cause the TCP queue to temporarily exceed its configured maximum depth. If the depth is at or greater than the maximum depth, the message is left on the per-client message queues. When a message is placed on the TCP queue, the exact byte length of that message is added to its current depth.
Per-port Transmit Queues
Each active client has one transmit queue for message delivery. The transmit queue holds data that is waiting on the hardware to send data out of one of the four Ethernet ports.
While the size of the per-port transmit queues is not configurable, the P-7500 ensures that ingress traffic cannot be affected by too many buffers in this queuing point.
For TCP connections, the TCP windows of the connections limit the number of buffers that can be on per-port transmit queues.

Copyright © TIBCO Software Inc. All Rights Reserved
Copyright © TIBCO Software Inc. All Rights Reserved