Author Topic: MTU (packet size) Info and Question for Skuzzy  (Read 273 times)

Offline CRASH

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MTU (packet size) Info and Question for Skuzzy
« on: April 12, 2000, 11:27:00 AM »
Got this off the MS knowledge base.  My question is this, if we're connecting by dial up modem and using ppp (do we connect using this?) to connect to HT, by default aren't we already sending the minimum packet size (576).  BTW, I'm using a 5 year old us robotics 28,8 internal and have great connects most of the time.
CRASH

Description of the Internet Protocol Packet Size Setting

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The information in this article applies to:

Microsoft Windows 98

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SUMMARY
In Windows 98, it is possible to modify the default Maximum Transmission Unit (MTU) settings. This article describes these settings, and why it may be beneficial to alter them.

To view these settings, use the following steps:

Click Start, point to Settings, click Control Panel, and then double-click Network.


On the Configuration tab, click Dial-Up Adapter, and then click Properties.


On the Advanced tab, click IP Packet Size. The following list shows the values you can select in the Values box:
    - Automatic    Programmatic control, this is the default setting
    - Large        1500
    - Medium       1000
    - Small        576
 
NOTE: When you use Automatic mode, all Point-to-Point Protocol (PPP) connections at speeds below 128kbps are made with an MTU of 576. At speeds above 128kbps, all connections are made with an MTU of 1500. Regardless of the MTU setting, the MTU will be further reduced to account for the network overhead if Virtual Private Networking (VPN) is used.

MORE INFORMATION
MTU is the Maximum Transmission Unit of a network. This is the greatest amount of data or "packet" size that can be transferred in one physical frame on a network. Fragmentation of packets occurs if a packet is sent across a network that has an MTU smaller than the packet's frame length. This leads to reduced performance levels as fragments need to be reassembled.

The Internet standard for MTU is 576. When you connect to an Internet resource, your data may have to go through a router that has an MTU of 576. This results in fragmentation if your MTU is greater than 576, which can result in a Web resource being loaded slowly.

Microsoft recommends using the default setting of Automatic for the Internet Protocol (IP) packet size.

NOTE: By default, the Windows 95 MTU is 1500. This setting can only be changed by editing the registry. For information about how to do this, see the following article in the Microsoft Knowledge Base:


ARTICLE-ID: Q158474
TITLE : Windows TCP/IP Registry Entries

Additional query words: 98

Keywords : kbenv kbnetwork win98
Version : WINDOWS:
Platform : WINDOWS
Issue type : kbinfo
 


Last Reviewed: April 2, 1999
© 2000 Microsoft Corporation. All rights reserved. Terms of Use.
 


Offline Lephturn

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MTU (packet size) Info and Question for Skuzzy
« Reply #1 on: April 12, 2000, 05:03:00 PM »
Should be largely irrelevant for Win 98.  Note the "Automatic" setting.  It will adjust the MTU as necessary, or it should.

If in doubt, try different settings yourself and test them, then use the faster one.  

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Offline tshred

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MTU (packet size) Info and Question for Skuzzy
« Reply #2 on: April 13, 2000, 03:47:00 AM »
I can't remember where I read it, but one of the conncection optimization sites recommended calling your ISP and finding out what their MTU setting is and adjusting yours to that for the best possible connect. That was back when I was using Win95 however.

ts

Offline Skuzzy

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MTU (packet size) Info and Question for Skuzzy
« Reply #3 on: April 13, 2000, 09:03:00 AM »
Although Windows 98 is supposed to automatically adjust according to the speed of the connection, there are times when this does not appear to be true.

Our basic philosophy is to force everything you can to any specific state you can, rather than let the software guess at what may be correct.

Dial-Up connections are PPP based, and part of the PPP specification allows for negotiation of the MTU and MRU sizes.  If your providers terminal servers you are dialing into do not accept any other vaules than 1500 or 1524, which many do, then Windows or any other operating system will be forced to accept those values.

Many providers, us included, used to use 576 as the MTU until Windows 95 / NT 4.0 came out.  These operating systems had a problem reassembling fragmented packets and would hang on occasion.  This forced most ISP's to return the MTU back to 1500 for dial-up.

Dial-up Networking update 1.3 for Windows 95/NT 4.0 and Windows 98 finally fixed the problem, but we still have to live with legacy systems.

If you are an avid game player, and that is your priority, then it is best to manually set the MTU to 576, for best overall performance.


------------------
Roy "Skuzzy" Neese
President, AppLink Corp.
http://www.applink.net
skuzzy@applink.net
Roy "Skuzzy" Neese
support@hitechcreations.com

Offline CRASH

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MTU (packet size) Info and Question for Skuzzy
« Reply #4 on: April 13, 2000, 12:37:00 PM »
Thanx fer such a well thougth out and complete response   I'm gonna try changing to 576.

CRASH

[This message has been edited by CRASH (edited 04-13-2000).]