Improving Windows Networking

  • Thread starter Thread starter Geoff Bennett
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G

Geoff Bennett

Comrades,



I'm a technology journalist working for Light Reading, and on-line
publication We focus on core network technologies like optical, IP, MPLS,
etc.



This week I've put up a column about some of the issues that people have
with Windows in the context of IP networking. Right now I've highlighted
one that seems to be a big one - that Windows Media Player tends to cause IP
Packet Fragmentation (according to the report I cite, 52% of fragmented
flows on the Internet are caused by Media Player, although I stress that
this conclusion is being challenged).



http://www.lightreading.com/document.asp?doc_id=37874



Given that most of our readers are infrastructure experts, and not Windows
experts I thought I'd invite you folks to put forward your comments. The
idea is to come up with a consolidated feature request document we can
forward to Microsoft, hopefully for inclusion in Longhorn.



I stress this is just about networking aspects of Windows, hence my posting
here. Also, if any of you know about other consolidation efforts in this
area, please let me know. We're not trying to re-invent the wheel here,
just to make constructive comments.



You can post right onto our message boards, or send me a mail with your
coments (remove the nospam).



We're in contact with Microsoft too, both through their PR folks and through
at least one Product Management group, so hopefully this will have some
official recognition.



Cheers,

Geoff



Geoff Bennett

Chief Technologist, Heavy Reading
 
My guess is to get more data treaming down the Internet highway then use
larger packets. The end node routers are bringing them down to the standard
thus fragmentation. The superhighway routers are designed to handle larger
packets for better efficiency.
Bob
 
Hi Bob,
Actually packet size (or more correctly MTU) depends on the nature of the
transmission interface.

Regular Ethernet used to have an MTU of 1,518 bytes, which was increased to
1,524 bytes when IEEE 802.1Q tags were added for VLANs. Then various
Gigabit Ethernet manufacturers began allowing "jumbo frames" of up to about
9,000 bytes (since jumbos are non-standard, different manufacturers support
different MTUs from 9k to about 16k bytes). Regular and Fast Ethernet LANs
do not support jumbos.

Since the Internet was designed to be independent of the underlying
transmission technology, IP contains a feature called Path MTU Discovery
that allows hosts (it's the originating host that sets the initial packet
size) to determine the minimum MTU for the total path.

Apparently versions of Windows Media Player prior to v9 did not support RFC
1119 Path MTU Discovery, which can lead to a high proportion of fragments.
However, as Microsoft are pointing out, it's not Media Player that sets the
packet size for transmission, but the codec.

Bottom line is you cannot change the packet sizes supported by installed
base of routers, as that's fixed by the hardware. But instead you have to
get the hosts (and routers) to implement the right protocols to negotiate an
appropriate MTU size. That, amongst other things, is what we're trying to
explain to Microsoft.

Cheers,
Geoff
 
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