Faster Internet Action

Two options for speeding up Dialup Networking in Windows 95

Computers are getting faster, modems are getting faster, but we still want more speed from our Internet connections where the World Wide Web has become known in some circles as the World Wide Wait. Internet delays can be caused by a number of factors including net congestion, overloaded servers or MTU speed problems. So what is an MTU?

The acronym stands for Maximum Transmission Unit and is the greatest unit of data that the network can transfer at one time. Data is transferred along the network in blocks or packets that are individually routed between hosts, with no previously established communication path. Packets are routed to their destination through the most expedient route, and not all packets travelling between the same two hosts, even those from a single message, will necessarily follow the same route. The destination computer reassembles the packets into their appropriate sequence.

The MTU is usually determined through negotiation between the sending and receiving computers with the lower MTU value usually, but not always, being accepted. Packets carry header and trailer information that enable them to be re-assembled, and the combined size is known as a frame. Each medium has a maximum frame size that cannot be exceeded, and frames can be broken up or fragmented as they pass through different interfaces with a smaller MTU than the packet length, resulting in delays with data having to be resent. Frame sizes are listed below:

Default MTU size for different media.

Network MTU(Bytes)

-----------------------------------

16 Mbit/Sec Token Ring 17914

4 Mbits/Sec Token Ring 4464

FDDI 4352

Ethernet 1500

IEEE 802.3/802.2 1492

X.25 576 (X.25 is an international standard packet switching network.)

The header information takes 40 bytes, and if these are subtracted from the MTU what is left is the MSS or Maximum Segment Size. The MSS is the largest segment of data that the receiving Winsock can accept, and the header is stripped off before the data is placed in the window buffer. The Winsock is at the heart of the TCP/IP (Transmission Control Protocol/Internet Protocol) on which the Internet is constructed. TCP is the most common transport layer protocol used on the Internet, and allows computers with different architectures to communicate with each other. It is built on top of Internet Protocol (IP). The IP is a packet switching protocol providing packet routing, fragmentation and re-assembly through the data link layer. Essentially it defines the form in which the data will be exchanged.

The MSS must be taken into account in determining the size of the TCP Receive Window, known as RWIN. This window sets how much data the receiving computer can accept and is a multiple of the MSS. It would seem that anything other that an integer value must result in fragmentation of data packets arriving at RWIN. Recommended multiples are usually four, six or eight. Too small a multiple will result in slow transmission because of having to process more units of data. Too large a multiple can also result in slow transmission if data in the MSS is lost or damaged and larger blocks have to be retransmitted. So we can see where delays might occur in trying to contact a remote web site through multiple interfaces.

Another factor that comes into consideration is Time To Live (TTL). TTL is the number of hops a packet of data is permitted to make before being discarded. Win95 defaults to 32, but with an ever increasing - and increasingly busy - Internet a value of 64 is generally recommended. It is possible that a value of 32 could produce a site not found message when the site does, in fact, exist.

Windows 95 has a default MTU of 1500 bytes set in the registry, which is great for Local Area Networks on cable connections but seemingly bad news for dialup connections proceeding through several routers. The most common setting for MTU throughout the Internet is 576 bytes, and this is recognised as a defacto Internet standard. Obviously then, a packet of 1500 bytes is liable to suffer severe fragmentation and consequent delay. Optimising the MTU and RWIN in the registry and changing TTL should materially increase throughput using the Point to Point Protocol (PPP) of modem connections to the Internet. PPP is the Internet standard for transmitting IP packets over serial point-to-point links. It can configure connections to a remote network dynamically, and test that the link is usable.

Manually editing the registry is fraught with danger, and there are programs that make the task safer and easier here. I will mention three that I am aware of.

PPP-Boost is freeware from www.sysopt.com or www.c3sys.demon.co.uk. It sets Windows Default, Recommended, and Custom values for MTU, RWIN and TTL. It is small, fast and simple. Recommended starting points for optimisation are MaxMTU = 576; TTL = 64; and RWIN = 2144 (MSS{576-40=536} x 4).
MTUSpeed is also freeware from Tucows or www.sysopt.com; (author's home page mike@mjs.u-net.com). Documentation is comprehensive and responsible; it warns about backing up the registry before making changes to it in case of glitches. The program permits much more customisation for those intrepid enough to want to experiment, and introduces more variables like 'Black Holes' and NDI Cache size. There are several recommended sites for background reading and I suggest that you visit these sites for additional information.
The third program is TweakDUN, available through www.sysopt.com. This is a professional shareware program at a very modest price that appears to be the Rolls Royce of these programs. It introduces an even wider range of settings than MTUSpeed.

In using any of these programs there are simple precautions to be observed and procedures to be followed. The first precaution is to backup the registry before altering it. This means copying the User.dat and System.dat files from the Windows folder to a safe medium like a floppy disk. User.dat may only be small but System.dat will almost certainly be too big to fit on a conventional floppy. You may want to compress it or use a removable Zip disk. In restoring these files remember they are protected and will need to have the attributes changed before they can be overwritten. I would also recommend exporting the registry to the root directory using Regedit and selecting Registry | Export. | All. Give this file a .REG extension, and double clicking on it will restore the registry (so I'm told; I haven't tried it).

To get an objective view of the benefits of your changes you will have to monitor modem speeds before and after making changes. There are third-party programs to do this but Win95 has a perfectly satisfactory facility built into its Programs | Accessories | System Tools folder. It is called System Monitor. For the monitor to display its readings you must set your modem to Record a Log File in its Properties options.

Run this after you are connected to the Net and you will be able to set Bytes sent and Bytes received by the modem. Display options include bar and line graph and numbers. I prefer numbers updated about every three seconds. Once you have set this up you will be able to reload it at any time with these settings retained.

Recommendations here are that you clear your cache before each test to provide a level playing field. This is done in Internet Explorer through View | Options | Advanced | Settings. Also the computer has to be rebooted after changing the settings for them to take effect.

There is an enormous amount of enthusiasm out there for these programs, and obviously people are achieving figures that convince them of the benefits of changing these values in the registry. Some users report success after changing only the MTU, others only after changing the RWIN as well. Anecdotal evidence was quoting throughput for streaming video increasing from 1.8kbps to 4.5kbps with peaks at 6kbps. My experience was different. I ran my tests on a three-minute streaming video with a lot of throughput, and a 600k QuickTime movie that had to be downloaded before running. In my early experiments I was able to lift Bytes received from around 2.5-3.0kbps to 3.0-3.7kbps, which was hardly encouraging. I am running a Pentium 100 with a 33.6kbps modem.

At this point my story diverges drastically. In the course of researching this article I found an MSDUN1.2 (Dial-Up Networking) upgrade on the Microsoft site. With a degree of trepidation I installed this and ran my tests again. The results were astounding. Reverting to Win95 defaults for MTU, RWIN and TTL I am regularly seeing throughput of 3.6-5.1kbps with peaks well over 7.0kbps. For one brief instant I recorded 3.1Gbps. Speeds in this range appear when only small amounts of information are transferred, but the overall performance on the Internet has jumped dramatically. It seems that Microsoft have addressed the problem and solved it. To prove the point, I have run my previous tests with the upgrade installed. Every test degrades performance significantly. Here is what Microsoft have to say about the upgrade in their Release Notes:

"Windows95 Dial-Up Networking 1.2 Upgrade

The WindowsÒ95 Dial-Up Networking 1.2 upgrade is a significant enhancement to the Dial-Up Networking features that were originally delivered with Windows95. This upgrade provides client support for a single PPTP connection, support for internal ISDN adapters, multilink capabilities, connection-time scripting to automate non-standard logins, and improved performance and stability. All of the improvements included in the OSR2 release of Windows95 and the ISDN1.1 Accelerator Pack have been included in this package.

The Windows95 Dial-Up Networking 1.2 upgrade replaces all of the Dial Up Networking components, and installs new versions of the TCP/IP stack and the NDIS layer. A new version of Winsock is included as an optional component in order to correct name resolution limitations in the original Windows95 software.

This Dial-Up Networking 1.2 upgrade can be applied to existing Window95 systems, including the retail release and OEM Service Release 2 (OSR2)."

The MSDUN12 upgrade is easily found on the Microsoft site in the free download area, and installation is done on line. With this upgrade installed you will not need to Record a Log File in your modem properties. The System Monitor is upgrade with several new features and I now find my readings on Dial Up adaptor #2.

You should try one of these speedup options.

Enjoy your computing.

Terry Bibo.