Cell Relay Archive

[pmandal@ix.netcom.com]

Ruth,

Some sort of QOS, in my personal opinion, is necessary not
only from video or audio perspective, but also from just
regular TCP traffic perspective.

Why?

Suppose some intermediatary device (e.g. a DSLAM or a switch)
is a receiver of packets and this receiver has a relatively
small buffer size; that is a buffer size that is less than
the sender's TCP window size.  If the transmitter sends the number
of TCP packets that is dictated by it's window size, and
the receiver can't keep up with processing of these packets,
then there is a high probability that the packets might get
dropped.  If this happens, then you have TCP retransmissions going on
and the TCP connection slows down.

This is a case of not being able to handle "bursty" traffic.

(Of course, I'm giving a very simplistic example here)

This "Burstiness" of traffic can be handled in one of 2 ways:
1)  Add more memory  and/or
2)  Have the Transmitter not send bursty traffic.

Hence, the reason why Burst Tolerance on VBR-NRT circuits are
valuable.

Anyway, in the ATM world, you have other QOS parameters (e.g. MCR,
PCR, SCR, CDVT, etc.) but, in my opinion, a lot of these
are currently ineffective because they require end-to-end solution
and, currently, the Internet is not end-to-end "QOS-ready".

Hope this helps.

Praveen Mandal
RedBack Networks
praveen@rback.com

In article <35694183.72ED@enternet.com.au>,
  rpm@enternet.com.au wrote:
>
> Hi,
>
>  I was wondering if you could help me.  I have a few questions about
> QOS, such as
>      What are the problems the existing Internet causes for these media
> types?
>      How does QOS help alleviate these problems?
>      What are the main QOS implementations?
>      What alternative solutions exist that don't rely on QOS
> mechanisms?"
>
> Can you possibly direct me to some answers either available on the
> interent or just from your knowledge.
>
> Thanks so much,
>
> Ruth
>


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