[Asterisk-Users] QoS for improvements

[Jean-Christophe Heger]

I've spent may hours to play with HTB QoS settings on the firewall, but with absolutely no effect. In fact, this is normal, because the time required to let a data packet going through the ADSL line will break the voice jitter. The only right way to handle this issue is to modify the MTU on the router.

Without setting a TOS for voip, data where going through and voice was unusable.
With a lowdelay (0x10) TOS set for voip, voice was going through, but data was blocked.
With a lowdelay TOS and an HTB QoS on the router, data where going through slowly and voice was scambled.

After many tests, an MTU of 700 did work quite well. I did loose 15% of bandwidth for data (twice more overheads), but data and voice may be used together.

Those tests have been done on a 256 kbps up stream.

There is a quite good explenation about this issue on Cisco's web
site, and about they're LFI technology (link fragmentation and interleaving):
http://www.cisco.com/warp/public/788/voice-qos/voip-mlppp.html#link_frag

Jean-Chrsitophe




Kumara Jayaweera a écrit :

>Hello! Everybody!!,
>I want to run VoIP in the same LAN (15 windows clients) which we use for
>surfing the Internet. 6-7 softphones in the same client's machines is 'the
>target'. My DSL is 128kbps, (I can go to 256kbps if required). So, I am told
>to install some QoS's in the LAN to improve the voice quality. Frankly, I
>don't know what it (QoS= Quality of Service) is. I hope you may help me
>giving "Links" to read and briefing me your ideas.
>Thanks to everybody in the list.
>So far my success and progress are your help.
>Thanks again
>Kumara
>
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