X-Mailer: ELM [version 2.3 PL11]
Newsgroups: bit.listserv.novell
Date:         Tue, 25 Aug 1992 21:35:22 CDT
Reply-To:     Novell LAN Interest Group <NOVELL@SUVM.BITNET>
From:         rfranken@CS.UMR.EDU
Subject:      Re: Pburst - dream or reality
X-To:         NOVELL@suvm.acs.syr.EDU
              at Aug 25, 92 8:51 pm

>
> Will PBURST improve the throughput of an IP tunnel?
>
> The overhead of the protocol encapsulation (IPX within IP) and
> the design of the ODI drivers induces some degregation in performance.
>
> I don`t expect PBURST to improve that aspect, but will it improve it
> in other areas to compensate for the tunnel?
>
> Thanks.
>
> --tony
>
Yes.  The protocol used for workstation to server communication (for
file reads / writes etc.) is NCP (Netware core protocol).  NCP provides
all acknowledgements, retrnasmissions, etc.  NCP is then put in an IPX
frame for transmission, routing, etc.  If you are using tunneling, then
that IPX frame is put in an IP frame before it is sent.

NCP was originally designed as a non-streaming, non-windowed protocol,
meaning that one frame was sent, and an acknowledgement waited for,
and then another frame sent, etc.  This means that if you
were going across a router at, say 64KB, the servers first packet sent in
response to your request, was received in its entirety by the router, which
then out it out on the 64KB line, to be received entirely by the other
router, which put it out on your network.  Then your workstation issued an
acknowledgement, which took the recerse path, and then the next packet
was sent.

In such a situation, the theoretical maximum throughout is 64KBPS (actually
less for various reasons, but 64KB is close); however, because the server
must wait a round-trip time (doing nothing) between packets, your actual
throughput is much less.

Packet Bursting is essentially a modification to the NCP protcol that
makes it windowed.  With it, the server can send a second packet to you
before it has received an acknowledgement for the first packet.

In the above example, the second packet can be on its way before the
acknowledgement for the first has made it back across the serial line.
Thus, if only one session is going through the router, the line can be
used at close to 100% efficiency for your traffic.

Because Packet Bursting is just a change to NCP, the means used to
transport NCP is irrelevant.

I would expect the PBurst vs. Non-PBurst performance ratio to be higher
on a tunneled connection than on a non-tunnelled connection. The reason
is that with or without PBurst, you will never run faster that your slowest
LAN line (including serial links).  However, anything along the path
that adds a constant delay (the times it takes for a router to
figure out where to put a packet, the time it takes a machine to put
an IPX packet in an IP packet, etc) causes delays in the acknowledgement that
make the server wait longer before sending the next packet.  By using
PBurst, the constand delays in the loop increase the response time by
one times (delay time) per request rather than one times (delay time) per
packet.

Sldo note that PBurst works both ways, so the above would also apply to
a PC saving a file on the file server.

 - Brett   (rfranken@cs.umr.edu)
Newsgroups: bit.listserv.novell