Linha fale a vontade todos os dias, aquela que você só paga a assinatura www.telefonevesper.com.br ----- Original Message ----- From: "Jonathan Lynch" <jlynch@xxxxxxxxxxxxxxxxxx> To: <lartc@xxxxxxxxxxxxxxx> Sent: Tuesday, October 11, 2005 6:04 PM Subject: The effects of queueing on delay > > I have a router with 3 network interfaces like in the following ASCII > diagram below. All interfaces are 100mbit. There is tcp traffic being > sent from net1 to net3 and from net2 to net3 and the tcp connections > consume as much bandwidth as possible. There is a pfifo queue on the > egress interface eth0 of the core router with a limit of 10 packets. > > > net1 --> (eth1) router (eth0) -> net3 > (eth2) > ^ > | > net 2 > > I police traffic on the edge of net1 to 48.4375 Mbit and shape the > traffic on exit of net 2 to 48.4375 Mbit. There are no packets in the > queue of the egress interface eth0 of the router at any stage. (every > packet is enqueued by pfifo_enqueue() to an empty queue. I have > confirmed this by adding adding a counter in sch_fifo.c that is > incremented every time there is a packet in the queue when a new packet > is enqueued.) The delay is at a maximum of 2ms. > > When I increase the policing rate and shaping rates to 48.4687. The > combined increase is 31.2 kbit which is very small. there are some > packets queued for a short period and some dropped which clears the > queue. The maximum number of packets dropped was 20 per second. But the > delay goes up to 30ms. > > check out the graphs at > http://frink.nuigalway.ie/~jlynch/queue/ > > > I cant seem to explain this. Even if the queue was full all the time and > each packet was of maximum size, the delay imposed by queueing should be > a maximum of 10 * 1500 * 8 /100,000,000 which equals 1ms. > > How can so much delay be added by such a small increase in the > throughput coming from net1 and net2 ? > > I would appreciate if someone could explain it to me. > > Btw im using a stratum 1 NTP server on the same LAN to ensure > measurement accuracy. > > > Jonathan > > _______________________________________________ > LARTC mailing list > LARTC@xxxxxxxxxxxxxxx > http://mailman.ds9a.nl/cgi-bin/mailman/listinfo/lartc _______________________________________________ LARTC mailing list LARTC@xxxxxxxxxxxxxxx http://mailman.ds9a.nl/cgi-bin/mailman/listinfo/lartc
