Re: [ns] queue limit

[Brian Lee Bowers <bowersb@lanl.gov>]

On Monday 16 July 2001 12:45, Alfredo Grieco wrote:
> Hi at all,
> what is the meaning of queue-limit over the queue of the first link
> of a connection? Is the limit able to create congestion?

Every node you create has a queue.  Every queue has a limited amount 
of space.  If you have a long fat network and big receive window 
size, your sending node can put out a burst of packets too large for 
its own queue to handle.  The packets will be dropped before they 
"officially" get onto the network.

Here is an informal, contrived example.  Node A is transmitting to 
node B.  A sends 50 packets to B.  B receives all of the packets and 
sends back 50 ACKs.  Due to other network traffic, all of the ACKs 
get compressed on a router.  When the traffic backlog clears, 50 ACKs 
get bursted to A.  Every time A gets an ACK, it puts out another 
packet.  A can only hold 30 packets in its internal queue; if it gets 
the 50th ACK before it can get 20 packets onto the wire, then one or 
more packets must be dropped from A's queue.

-- 
Brian Lee Bowers	|	RADIANT Team (Summer Intern)
bowersb@lanl.gov	|	Los Alamos National Laboratory