[Asterisk-Users] QoS - Routers

[Harold Workman]

asterisk-users-admin at lists.digium.com wrote:
> Looking at the wiki on QoS is very helpful.
>
> But just wondered if there is anyone who
> would want to comment on "ip rtp header-compression"?
>
> Is it a good thing, does it help on T1 or slower connections?
>
> Also why does Cisco often suggest the MultiLink thing?

Heres the RFC on rtp header-compression.  it helps better with slower
connections. http://www.faqs.org/rfcs/rfc2508.html   Read the Assumptions
and Tradeoffs.


the Multilink "thing", commonly used on PPP links provide load balancing
functionality over multiple WAN links, while providing multivendor
interoperability, packet fragmentation and proper sequencing, and load
calculation on both inbound and outbound traffic. It allows packets to be
fragmented and the fragments to be sent at the same time over multiple
point2point links to the same remote address.

Heres an example.  you have an isdn line with 2 64k B channels. You have
your load threshold set for 50% meaning when you are using 50% of the
bandwidth of the first channel the second channel connects. Now, you want to
download a file. The first B channel connects, as the file downloads you
reach that threshold and the second channel connects.  Now you have 2
completly seperate channels connected, and in order for that same 1 file to
now go across both links, the ISP router fragments the packets and sends
them over both links.  The fragments get to your isdn router and pieces it
back together.



There are many different types of QOS.  And each one helps in the type of
enviroment you are in.
Class-based weighted fair queueing (CBWFQ)
Priority queueing
Weighted fair queueing (WFQ)
Low latency queueing (LLQ)
Link Fragmentation and Interleaving (LFI)
Frame Relay Traffic Shaping (FRTS) for Voice
ATM Traffic Shaping
IP RTP Priority



im sure theres more i just cant think of any off the top of my head..