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   Satellite Internet - How it works?

How 2-Way Satellite Internet Access Works ?

How DIRECWAY Works

Satellite communication systems differ from terrestrial systems in one obvious but important way - the transmitter is moved from the ground to the sky. Because a satellite can "see" about one-third of the Earth's surface from its position in space, it is able to serve a very large geographical area. This leads to a number of advantages:

            - As little as three satellites can cover almost the whole of the Earth's surface, with  the exclusion of the sparsely populated polar regions. To achieve the same coverage by terrestrial means would require a very large and expensive network of ground-based transmitters.

            - Services can be quickly introduced, since coverage is available for everyone from day one. There is no need for a phased introduction of ground-based transmissions with a simple antenna, those located even in the most remote locations can still enjoy the same level of service as someone living in the center of a major city.

            - Satellites naturally span national boundaries, providing numerous possibilities for truly international services.

Direcway provides one of the fastest Internet connectivity available nationwide. For downloading from the Internet, a DIRECWAY system is capable of receiving content distribution or streaming video at bit rates up to 1 MBps. For uploading to the Internet, a satellite return channel provides upload speeds up to 128 kbps.

When DIRECWAY is configured with a satellite return, it uses the ITU (Indoor Transmit Unit) to send data up to the satellite, which in turn sends the data to the Hughes Network Operations Center (NOC). The NOC forwards the request to the Internet, where the data is routed to its final destination.

Data returning from the Internet to the PC is routed to the NOC, where it is sent up to the satellite. The DIRECWAY system's IRU (Indoor Receive Unit) receives and decodes the high-speed data, then presents the data to the user.

Indoor Equipment

The IRU is a DVB-compliant satellite adapter that can be used alone, in the receive-only/dial-up return configuration or together with the ITU for satellite return. When used with a modem or existing network connection, the receive-only configuration can provide hybrid Internet access, where packets travel to the Internet via terrestrial routes and return to the PC via the satellite.

The ITU adds transmit capability to an IRU. If an ITU is installed and configured, the user can select the satellite instead of the modem as the outbound (upload) route. When the ITU is available and the user selects this option, the system essentially is "always on." This means the user never has to wait for the PC to connect.

Outdoor Equipment

The DIRECWAY antenna is equipped with:

An LNB to receive data from the satellite
A radio unit to transmit data to the satellite (for satellite return)

Two RG-6 coaxial cables connect the outdoor equipment to the indoor equipment.


~~~~~~~~~~~~~~~~~~~~~~~~~
Equipment Details

The DIRECWAY DW4000 systems consist of a oval satellite antenna, matching integrated outdoor electronics, and the indoor units (see below for further descriptions).

Indoor Equipment

The indoor equipment consists of one or two USB satellite adapters:

  • ITU (Indoor Transmit Unit, Model DW4000 only)
  • IRU (Indoor Receive Unit, Models DW3000/4000).

The DW4000 indoor equipment package is shown in Figure 1. Include are the ITU, IRU, power supply, USB cable, and ITU-IRU interconnection cable.

The IRU is a DVB compliant satellite adapter that can be used alone, in the one-way configuration, or together with the ITU for two-way operation.

The DIRECWAY ITU is designed to be an add-on capability to a standard receive-only DIRECWAY IRU. When the ITU is installed and configured, the user will have the ability to select the satellite instead of the modem as the outbound route. When this option is selected and the ITU is available, the system is essentially "always on". This means you never have to wait for your PC to connect, or worry about ISP busy signals. And because the ITU is connected to the IRU through the ITU-IRU interconnection cable, only one USB port on your PC is required to operate the DIRECWAY indoor equipment.

Outdoor Equipment

The DIRECWAY antenna is equipped with the following:

  • A single LNB to receive DIRECWAY data from the satellite (Models DW3000/4000)
  • A radio unit to transmit DIRECWAY data to the satellite (Model DW4000 only).

In addition each DIRECWAY system can be optionally equipped with an additional dual- LNB to receive DIRECTV using the same antenna. This configuration is called DirecDUO.

Figure 2 shows the DIRECWAY antenna configured without the DirecDUO option.

The outdoor equipment is connected by two RG-6 coaxial cables to the indoor equipment.


DiRECWAY Security

The packets destined for Internet hosts are sent first to the DiRECWAY Network Operations Center (NOC). The NOC forwards the request to the Internet, where the data is routed to the destination Internet host. Data received back from the Internet host is routed to the NOC, up to the satellite, and back down to the user's PC.

DiRECWAY Download (Receive) Security

DiRECWAY Conditional Access utilizes encryption technology to protect the various DiRECWAY services against unauthorized access by interlopers on the satellite downlink to a user's PC. Conditional access provides privacy protecting transmissions to a site (email, etc.) from being intercepted by any other site over the space link. It protects multimedia streams and digital file transmissions from being intercepted by any site except those designated by the information provider to the DiRECWAY NOC.

The DiRECWAY NOC individually encrypts each multimedia stream or package with a unique session key. Access to a stream or package is controlled by the NOC's only making its session key available in usable form to authorized DiRECWAY receivers. The NOC passes to a DiRECWAY receiver its session keys in a scrambled format only usable by that specific receiver. Each receiver includes a tamper-resistant crypto-facility (secure ASIC) in which is stored at manufacturing time unique key material. The crypto-facility is only capable of decrypting with session key material created by the NOC especially for the crypto-facility. As such, the receiver is only capable of decrypting DiRECWAY satellite services.

The NOC utilizes the Data Encryption standard (DES) with 56 key length as the bulk encryption algorithm. Triple-DES with 112 bit key length is used within the key-distribution algorithms.

DiRECWAY Return Channel Security

There is no encryption algorithm applied to data traveling, from the user, to the NOC, and eventually to the Internet. However, inroutes are inherently secure because of their method of operation. Inroutes use a Time Division Multiple Access (TDMA) method of access and transmission, which means that multiple DiRECWAY transmitters will be using the same inroute or set of inroutes for transmission. transmissions occur in almost random bursts on the inroutes, and timing of the transmissions is controlled via the receive/downlink channel, so compromise of outroute security is necessary to even have a chance of compromising the inroutes. In addition, error correction algorithms applied to the data make it more difficult to monitor transmissions and make sense of the data.

The expense and effort necessary to extract useful data from the inrout is prohibitive, especially since the data is destined for a public network, the Internet.

DiRECWAY NOC Configuration

The network architecture of the DiRECWAY NOC also provides protection for DiRECWAY end users. A single IP address is assigned to each DiRECWAY end station. The IP addresses assigned are in general "non-routable", which means that if the appear on the Internet, Internet routers will not know where to route the packets. Because of this, the DiRECWAY NOC employs Network Address Translation, or NAT, on the interface to the Internet and translates the non-routable address to a routable address for the duration of a DiRECWAY users's session. The assignment of the routable address is dynamic, and means that a DiRECWAY user will in general use a different routable IP address each time they use their DiRECWAY system.

In addition, gateway systems in the NOC preclude other Internet systems or hackers from initiating a connection with DiRECWAY remote, even if a hacker could "guess" the routable IP assigned to the DiRECWAY system. Because of this, it would be difficult for hackers to launch an attack on a DiRECWAY system from the Internet.


Most satellite broadband companies advertise speeds of "up to" 400-500kbs down. Actual download speeds very widely. Your results will depend upon your provider, transponder and gateway assignment, and your registry tweaks, among other things. But the good news is nearly everyone gets better than the advertised download speeds. One-way systems usually average in the 500-1,300kbs range and two way systems in the 600-2,000kbs range. Many DirecPC based two-way systems when fully tweaked have attained speeds in excess of 3,000kbs and average 1,500kbs - 2,500kbs. You should note however, that depending upon transponder assignment, many users with identical systems can only get download speeds in the 600-1,300kbs range


How do you find out what satellite and transponder you are on? 
 

a. Start/Programs/DirecWay (or DirecPC)
b. right click Antenna pointing
c. select Properties
d. find the line that says Target
e. place your cursor immediately after the last letter (G)
f. push your spacebar once
g. type /manual
h. click OK

Return to Start/Programs/DirecWay (or DirecPC) and
a. launch the Antenna Pointing utility.
b. Put in your ZIP code (manual latitude/longitude is more accurate - if you know it)
c. depending on which version of software you have report the info on the next screen, or
d. report the info found on the Satellite and Transponder tabs.

There is a shorter way to do this, but because of bugs in several versions of the software, it's not always as accurate as the above technique. To see if you have the buggy software, do this:
a. find the icon down by the clock that represents your satellite connection; it's usually a DW or a NAV.
b. right click it and select About
c. select System Info
d. compare Satellite Information and Transponder information to that which you found using the Antenna Pointing utility.

Satellite locations, transponders & frequencies in use
In the Sat forum you see many posts about a certain transponder and optimum settings for them. Currently DirecPC (DirecWay) has 4 transponders in use on the Galaxy 11 satellite at 91 degrees west longitude, 7 on Satmex5 at 116.8 (117) degrees west and 7 on G4R at 99 degrees W. The "Powered by" partners currently use one of the transponder on G11, that we refer to as 1410. Recently some new Earthlink customers have been put on 1370 on G11.

Galaxy 3C at 95 degrees west and SatMex 5 at 116.8 degrees west all have 1 to 5 transponders in use for broadband internet. G3C is used by the "older" gray dish systems sold as DirecPC Classic and AOL+ One way systems. AOL+ also has customers on Satmex5 and G4R at 99 degrees W.

AMC1, formerly GE1, at 103 degrees west was also a "Classic" bird with 1 transponder, but was discontinued in Oct. 2002.


The frequencies we refer to in our posts are actually the down-converted (IF) frequencies coming down our coax after being converted in the LNB at the dish. The satellite frequencies transmitted and received are much higher and not easily routed to and from your sat modems.

You will find many DSLR members have added the down-converted frequencies to their signatures as well for ease of passing along our setup information.

Specifically, the transponders in use on each satellite are:

Galaxy 11 (91) - 990, 1350, 1370, 1410
Galaxy4R (99) - 970, 1110, 1210 (AOL+), 1230, 1250, 1350, 1370
Satmex5 (117) - 990, 1050, 1070, 1090, 1130, 1170, 1250


Your system is set up to use 1 of these during the running of Websetup and you have no control over which one your system uses. The determination of which transponder you use is based upon your provider and your geographical location. Your installer can get your system moved at commissioning if there is a problem with the line of sight or signal from a certain bird.

You can see which transponder you are assigned to by right clicking the NAV or DW icon in the system tray, click "About" and click "System Information". Your transponder down-converted frequency is the second line from the bottom listed as Frequency. You can gain more valuable information by clicking  http://www.lyngsat.com/america.shtml  then clicking on a particular satellite and browsing through the information



Spead Tweaks 

  • What is DrTCP and how do I use it?
     DrTCP is a small utility that provides a window to the area of your registry that stores adjustable TCP settings. Using this program is a very easy way to adjust settings that can make a huge difference in your download speed.

    You can download DrTCP now by clicking  


When you load up DrTCP, go to the field marked "Adapter Settings". If you are tweaking the computer that is directly connected to the satellite modem, in that field, use the small arrow to the right to select "Satellite USB Device". If you are tweaking a network client computer, choose the Network Interface Card (NIC) for that computer.

Don't forget to save your changes and re-boot to have them take effect.

In the actual tweak instructions, we assume you are using DrTCP.

  • Important Info for WIN2K SP1 users using DrTCP!!
    When you installed the DirecPC, DirecWay, Earthlink or Pegasus software on your computer, it installs a registry key called GlobalMaxTcpWindowSize. If you are using WIN2K you should upgrade to Service Pack 2 to fix a bug in this key that causes DrTcp changes to have no effect on RWIN. If you don't want to upgrade to SP2, then you must delete the key. Note: You do not need to delete this key if you are using Win2K SP2 or above or XP.

    Using Regedit you can find the key at: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
    Open the Parameters folder and locate the key GlobalMaxTCPWindowSize, right click on it and choose delete.

    After the key is deleted you can set your RWIN with DrTCP, reboot, and the RWIN you selected will be used.

    Remember, that if you upgrade or re-install your satellite software, you will need to use regedit to delete this key again.

  • Optimal Settings for Satellite Return (Two-Way) Systems
    Tcp Receive Window (RWIN): 224360
    Window Scaling: YES
    Time Stamping: NO
    Selective Acks: YES
    Path MTU Discovery: YES
    Black Hole Detection: NO
    Max Duplicate Acks: 3
    TTL: 64
    MTU: 1500

    Try these settings first. If you find that your download speeds are at or over 1,500kbs with these settings, then increase the RWIN to 474280, so that you can get the full download speed potential available to you. If your speeds are ALWAYS below 1,500kbs, raising your RWIN any higher than 224360 won't help, and may actually hurt your connection speed.

  • Is there something I can do to improve my upload speeds with SRS?
    One tweak for upload speed is to turn Path MTU Discovery to YES in DrTCP. Without this switch turned on, Windows treats the Satellite Upstream path as a dial-up path, and changes the MTU for the path to 576, regardless of what you have the MTU set for on the adapter. By turning Path MTU Discovery on, Windows will see that the upstream path minimum MTU is 1460-1500 bytes, and will adjust accordingly. - PD

    2. A registry tweak has been found and tested to improve upload speeds on Satellite Return Systems. The only problem is that it only pertains to certain operating systems, with certain processors, with certain amounts of memory. This tweak requires modifying the registry, so please be sure to back up your registry before doing any of these modifications. This tweak has been extensively tested, and has not shown any signs of being problematic with any system. The details for the certain systems that this works on are below, but don't be afraid to try them if you fall out of these parameters. The registry modification can easily be deleted if it doesn't work for you or if you just want rid of it.

    The following details have found to have the best impact of this tweak:

    Operating system:
    Windows XP (Home and Pro)
    Windows 2000

    Processor:
    Pentium 3
    Pentium 4
    AMD

    Minimum memory:
    384mb SDRAM
    256mb DDRAM
    256mb RDRAM

    *512mb of any RAM seemed to be the platform where things work the best. Any more than 512mb didn't see any improvements.


    There are 2 different values to enter in the registry for the 2 different operating systems:
    Windows XP - 18000
    Windows 2000 - 17a00
    Don't be afraid to try either one though - throughout the testing these values coupled with these operating systems seemed to get the best results.


    Here are the instructions for the tweak. Please be sure to back up your registry first!

    \HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\AFD\Parameters

    Open Run and type in regedit click ok.

    click on
    HKEY_LOCAL_MACHINE
    SYSTEM
    CurrentControlSet
    Services
    AFD

    Right Click on AFD and select New, and Key name the new Key Parameters
    Click on Parameters.
    On the right side you will see (Default) right click in the empty area and select New, DWORD Value.
    Name this Dword value DefaultSendWindow
    Double click on DefaultSendWindow and enter either 17a00 or 18000 leave it on Hexadecimal.

    Click OK, close and then reboot.

    If you don't like it, all you have to do is delete the Parameters entry. Remember, always backup your registry.


    This tweak has been found to double our upload speeds for Satellite Return Systems. 

     

  • Is there anything I can do to improve the performance of the DW proxy server
    Try changing your proxy port from 83 to 85. To do this open up control panel and go to internet options.Then click on connection tab. Then click on LAN settings. Then click on advanced. Then change port from 83 to 85. If you have Internet Explorer open you can get to the same place by clicking on tools at top. Then internet options and go from there.

  • Reduce your cache for better browsing
    This technique has been reported by many users to enhance the "snappiness" of browsing with these high latency connections.

    It seems that Satellite Return Systems (SRS) get more of a benefit than Dial Return Systems (DRS) from this tweak, because of the greater latency with SRS.

    Try reducing your browser's cache to 1mb size.

    In IE, go to Tools -> Internet Options. Under "Temporary Internet Files" press the "settings" button. Under "Temporary Internet Files Folder" change the number in the box to 1. Press OK, then OK again.

  • Should I try speed patches I see at other sites?
    Using "one size fits all" speed tweak patches is an incredibly bad idea. Here are just a few reason why:

    1. These patches were never developed with the high latency and high speed combination of satellite in mind.

    2. Because the developers don't know how many TCP adapters are on your system, they play tricks to make sure all adapters get "tweaked". One of the most common tricks is to assume there will be no more than 10 adapters, and therefore to create registry entries for 10 adapters. Since almost no one has 10 TCP adapters on their computer, this creates many excess registry entries causing extra overhead and great confusion if you ever need to figure out what is what in your registry.

    3. Many of the patches give you no way to undo the changes you made after they have completely destroyed your connection, or only to undo themselves incompletely. Many people have had to re-format their drives and re-install a clean copy of their o/s to fix the problems created by speed patches.

    The bottom line is that by using DrTCP, you control the changes and you can always change things back to if you like.

  • I Tweaked with DrTCP but the Tweak Tester doesn't report the changes.
    With DirecPC/Direcway systems, including Earthlink and Pegasus express since you have no public IP, the tweak tester gets confused as to what machine to test. The result is you are seeing results from an intermediate machine at the DPC NOC.

    Ignore any results you get from the DSLR tweak tester if you are on a DirecPC/Direcway based system. The results you are getting from the tweak tester are not for your computer.

  • I'm sharing my connection on a LAN. Do I need to do more?
     Yes. In order to get the client computers on a network to have the same performance as the host computer, there is a bit more work to be done. A three-step process. You can skip step one if you are not using Windows 98SE with ICS on the host computer.

    1. First if you are using Windows 98SE and ICS, a registry key is created that is killing your speed, even on the host. This key was originally put in to support dial-up internet connections and has been removed from subsequent versions of Windows. You need to delete the key or at least give it a null value. Since you have DrTCP it's easy. Open DrTCP on the host computer. Find the section entitled "ICS Settings". In that section, there is a window marked "Internet MTU". Delete any value in that window. Make it blank. Push "Save", exit, and re-boot.

    Now you need to get the client computer(s) up to speed.

    2. Load DrTCP on each client. In the "adapter settings" window, choose the Network Interface Card (NIC) for that machine. Make the settings exactly the same as the settings you put on the host machine for "Satellite USB Device". Push Save, exit and re-boot.

    3. Your host machine was set up by the DPC software install to use several simultaneous TCP connections. This is done to reduce the effects of latency on browsing, and the result can be quite dramatic. You will want your client(s) to have the same advantage, but for them you will have to make the registry keys manually using regedit. (Start->Run->Regedit)

    Basically you need to add two registry keys. Below you will find where in the registry to put the keys and what to name the keys. Navigate to the locations specified in the left pane, then in the right pane, right click and choose to create a "New" Dword value. Name them exactly as shown. Once they are there, double click on each and insert the value 15 (HEX). Once you've done that, exit regedit, re-boot. Your work is done.

    WinXP and Win2k: All DWORD Values

    HKEY_USERS.DEFAULTSoftwareMicrosoftWindowsCurrentVersionInternet Settings

    MaxConnectionsPerServer
    MaxConnectionsPer1_0Server

    HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionInternet Settings

    MaxConnectionsPerServer
    MaxConnectionsPer1_0Server

    WINME / 98 All DWORD Values

    HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionInternet Settings
    MaxConnectionsPer1_0Server
    MaxConnectionsPerServer

    4. (Submitted by Seagreen) There are a few more settings that need to be added to the client machine's NIC Network properties.

    Add the Host's IP address (192.168.0.1) as the Default Gateway and as the preferred DNS server. Add a Hughes DNS server (usually 198.77.116.8) to the DNS servers list as an alternate after the Host machine's IP address. Adding these helps speed up the client machine's Domain Name Resolution and consequently, browsing. It also helps the client machine get email from POP accounts.

    Follow the instructions below for your particular OS:

    Windows 98:

    Start => Settings => Control Panel => click on the Network icon or right-click on the Network Neighborhood icon and choose 'Properties'. Either way gets you into the Network configuration screens.
    From the list of installed clients, protocols and services, locate TCP/IP bound to the NIC It will look something like this: TCP/IP -> your network card. The arrow indicates the protocol is bound to that adapter. Highlight that and then click the Properties button. This gets you into the TCP/IP configuration screens. Click the DNS Configuration tab. Put as dot in the 'Enable DNS' radio button.
    Then add the DNS servers, starting with the Host machine's IP address (192.168.0.1). Add the Hughes' DNS servers' IP addresses (198.77.116.8) in after that. For domain, enter "direcway.com."
    Next click the Gateway tab and enter 192.168.0.1 as an installed gateway. 'OK' your way out, you'll be asked for the Windows 98 CD if the CAB files are not on your HD and you'll be asked to reboot.

    Windows ME:

    Start => Settings => Control Panel => click on Network icon, or right-click on My Network Places icon on desktop, and choose 'Properties'. Either way gets you into Network Configuration screens. From the list of installed clients, protocols and services, locate TCP/IP bound to the NIC It will look something like this: TCP/IP -> your network card. The arrow indicates the protocol is bound to that adapter. Highlight that and then click the Properties button. This gets you into the TCP/IP configuration screens. Click the DNS Configuration tab. Put a dot in the 'Enable DNS' radio button.
    Then add the DNS servers, starting with the Host machine's IP address (192.168.0.1). Add the Hughes' DNS servers' IP addresses (198.77.116.8) in after that. For domain, enter "direcway.com."
    Next click the Gateway tab and enter 192.168.0.1 as an installed gateway. 'OK' your way out, you'll be asked for the Windows ME CD if the CAB files are not on your HD and you'll be asked to reboot.

    Windows 2000:

    Start => Settings => Network and Dialup Connections. Highlight and right-click on your LAN listing (usually called Local Area Connection) and choose 'Properties.' Highlight TCP/IP and click 'Properties.'
    On the following screen, enter the host's IP (192.168.0.1) address as the default gateway and as the Preferred DNS server. Add a Hughes DNS server (198.77.116.8) as an alternate.

    Windows XP:

    Right click on My Network Places icon on the desktop or Start => Settings => Network Connections. Select "properties". Right click on the Local Area Connection icon and chose Properties. Highlight TCP/IP and click the 'Properties' button. If you are not configuring the IP address manually, but obtaining it from the Host machine, you will not be able to enter a default gateway on the initial screen. Add the DNS servers, starting with the Host's IP address (192.168.0.1) followed by a Hughes DNS server (198.77.116.8). Click the 'Advanced' button. On the IP Settings tab, add the host machine's IP address (192.168.0.1) as the default gateway. Click the DNS tab and add direcway.com as the DNS suffix for this connection. 'OK' your way out and close the network properties interface. 

     

    Where do the tweak numbers come from?

    All of the recommended "optimal settings" were formulated by a combination of theory, long hours of testing, and results reported by DSLR members. The specifics of what the settings mean and why we set them a certain way for satellite connections follow.

    By far, the most important setting is the TCP Receive Window or RWIN. The Tcp Receive Window is nothing more than a data buffer. Think of it as a bucket. Your RWIN setting determines how big the bucket is. Data is coming down from the satellite, filling the bucket. Your computer is emptying the bucket as it processes the contents. We can't let the bucket overflow, or we would have to ask the sender to re-send what got spilled on the floor. That's inefficient.

    If the bucket gets empty, your computer is doing nothing, just waiting for the stream to start again, also inefficient.

    The other problem is there is a lag between the time your computer says "Send more, my bucket is almost empty" or "My bucket is almost full, please stop" and the time the sender gets that message. And another lag between when the sender starts sending again or stops, and the result hits your computer. That's latency.

    If the bucket is the perfect size, it is never completely full nor completely empty until there is no more stuff to send. The perfect size bucket allows your computer to send the messages at the right time such that the data stops just before the bucket fills and starts just before the bucket empties. Now you can have too large a bucket, because the sender expects to hear those messages now and then. If it doesn't hear from you, it thinks your bucket isn't getting anything at all so it keeps sending the same stuff, over and over, until it gives up on you and stops sending anything. Very inefficient!

    RWIN is determined mathematically. The required variables for the equation are Maximum Potential Speed (MPS) of the line, Maximum Segment Size (MSS) of the packet and Return Trip Time (RTT)(which most people measure with "ping" tests). Depending on the type of connection, a multiplier is usually applied to RTT to account for bad ping days. But generally the simple construction of the equation would be (MPS * Average Worst RTT)/8. The result is then converted to the nearest multiple of MSS.

    Selective Acks enables re-transmissions of data to consist only of lost packets, rather than entire receive windows. It is very important to enable selective acks when using large receive windows.

    Window Scaling allows for RWIN values above 65535. Since Windows only allocates 2 bytes to represent the RWIN value, a value greater than 65535 cannot be represented. By turning Window Scaling on, a scaling factor is applied to the value found in the two bytes to represent larger numbers.

    TTL is Time To Live and determines how many hops a packet is allowed to take before being declared lost. If the value is too small, unnecessary packet loss occurs as packets that just haven't reached their destination are lost. If it's too large, then too much time is spent waiting on packets that are truly lost.

    Time Stamping: Time stamping adds timing header information to each packet so that Windows can calculate RTT on the fly and use this information to estimate the best points in the empty/full cycle of the receive window to send AKS. Logic would say that would have to make a Long Fat Pipe (meaning high latency, high speed) connection such as satellite more efficient. The reality is that with DirecPC/DirecWay based systems, while it slightly but measurably increases speed, it also prevents certain web sites from loading correctly and can make some email attachments cause email to hang. So the recommendation is for it to be off for DPC, because a number of us have had problems with it turned on.

    Path MTU Discovery: This setting changes your MTU on the fly to match the smallest MTU on your path to the server you are communicating with. Testing has shown that tunring it on can, in some cases significantly improve upload speed on two-way systems. Please note that you may notice little or no difference in upload speed "tests" as the file size used on test sites (about 50KBS) is just too small to measure the speed without being skewed by the high latency of a satellite system. To more accurately measure your results, use an FTP client and do an FTP upload to a server of a 750KB file or larger.

    Black Hole Detection: Does absolutely nothing if Path MTU Discovery is disabled, may cause problems even when it is enabled...leave it off

    Max Dup Acks: Valid values are 1, 2 or 3. Win2k defaults to 2, 98 and ME default to 3. Probably makes absolutely no difference one way or another which value is chosen. It defines the number of duplicate AKS that are allowed to be sent before Windows invokes Fast Re-Transmission. This would occur in a packet loss situation. Windows gets an out of sequence ACK. It figures some packets must have been lost. It sends an ACK back for the lost packet. When the receiver sees the first ACK for a packet, then either 1, 2 or 3 more for the same packet, depending upon how max dup acks is set, it re-sends the whole segment again figuring that it must be lost...that's fast re-transmission.


 

 
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