Good afternoon Kurt, : 1. head of line blocking : 2. queuing on remote side [ description snipped: 16 kByte link, 1500 byte MTU ] With a 1500-byte packet and its serialization delay there's not much to be done. With only 128kbit (an ISDN line), you'll have to suffer some serialization delay and a bit of jitter. Queue on the provider's side is full? Take care of the shaping yourself (keep the provider's queues empty) and you'll see the best responsiveness you can expect. : I have two ideas how to handle this: : : 1. fragmentation : : Once VoIP traffic starts, I send an ICMP message that fragmentation is : neccessary and the maximum size is somethink like 150 bytes. That might allow you to reduce the jitter associated with transmitted traffic, but it won't begin to solve the problem, and will have a host of side effects. : 2. reduction of tcp window size : : Here I alter the packages to report a window size of 1 which should : reduce the downstream data rate. Aiee! This would have some pretty severe side-effects. : Can someone give me any hints if this has been done before or where to : start implementing this? I thought the QoS code should be a good start. Join the LARTC mailing list [0], review the venerable LARTC site [1], read some of my documentation [2], Jason Boxman's HOWTO [3], Stef Coene's descriptions, graphs and scripts [4] and Leonardo Balliache's technical docs on the Linux QoS system [5]. If you are interested in the code, start with Leonardo Balliache's documentation first. If you are interested in practical solutions, check out my docs and Jason Boxman's docs. In particular, I think you should be able to support VoIP on your ISDN line by planning an HTB deployment. And please note that the traffic control crowd is fairly active on the LARTC mailing list. Good luck Kurt, -Martin [0] http://mailman.ds9a.nl/mailman/listinfo/lartc [1] http://lartc.org/howto/ [2] http://tldp.org/HOWTO/Traffic-Control-HOWTO/ [3] http://edseek.com/~jasonb/articles/traffic_shaping/ [4] http://www.docum.org/ [5] http://opalsoft.net/qos/ -- Martin A. Brown --- SecurePipe, Inc. --- mabrown@xxxxxxxxxxxxxx - : send the line "unsubscribe linux-net" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
