• Kilobits vs. kilobytes explained
• What is MTU? What should mine be?
• Where can I test the speed of my internet?
• What is RWIN? How high/low should mine be?
• Does the RWIN affect pings or packet loss?

In data communications, a kilobit is a thousand bits (1,000) bits. It's commonly used for measuring the amount of data that is transferred in a second between two points. Kilobits per second is usually shortened to Kbps (or kbps). For example, 53.333kbps is 53,333 bits per second.

1 kb/s = 1000 b/s
1 KB/s = 1024 B/s
1 KB/s = 8.192 kb/s
1 kb/s = .1221 KB/s

The lowercase b usually stands for bits while the uppercase B stands for bytes.

To find your theoretical download speed for your line, divide your advertised speed by 8.192:
53.333kbps / 8.192 = 6.51 KB/s

or by 10 to include overhead:
53.333kbps / 10 = 5.33 KB/s

got feedback? got feedback?

Any feedback you provide is sent to the owner of this FAQ for possible incorporation and shown publically as well.

by redxii edited by TravisB
last modified: 2006-07-24 23:53:08

Packet size, often referred to as MTU (Maximum Transmission Unit) is the greatest amount of data that can be transferred in one physical frame on the network. For Ethernet, the MTU is 1500 bytes, for PPPoE 1492, dial-up connections often use 576.

Although many say an MTU of 1500 helps, I suggest using 576. If you're still wanting to make your MTU 1500, read the following steps.

1) Download Dr.TCP and change your MTU to 1500.
2) Click save then reboot your computer.
3) Dial-up like normal, then press Start>Run and type command.
4) In the command box, type
ping -f -l 1472 www.yourispswebsite.com
-l is a lowercase L, not a bar |

Simply change it back to 576 if it gives an error of "Packet needs to be fragmented but DF set." That error is telling you that your ISP doesn't support that MTU.

got feedback? got feedback?

Any feedback you provide is sent to the owner of this FAQ for possible incorporation and shown publically as well.

by redxii edited by TravisB
last modified: 2006-07-24 23:53:21

DSLR Speed Tests

PC Pitstop Download Bandwidth Test - 50KB/100KB/200KB/500KB/1,000KB/5,000KB Test Files

Speakeasy Network - Pick a city closest to you to get better accuracy.

got feedback? got feedback?

Any feedback you provide is sent to the owner of this FAQ for possible incorporation and shown publically as well.

by TravisB
last modified: 2006-07-24 23:53:30

RWIN (TCP Receive Window) is the amount of data that your computer can accept without acknowledging the sender. If sender has not received acknowledgement for the first packet it sent, it will stop and wait and if this wait exceeds a certain limit, it may even retransmit. This is how TCP achieves reliable data transfer.

How to find your RWIN:

1) Open up a DOS Prompt box:
Start>Run>command

2) Type: ping -l #### dslreports.com
#### is your MSS. (MSS = MTU - 40)

Example Screenshot

Take your average large packet ping, multiply by 1.5, multiply that by your proposed advertised speed, and divide that value by 8. You now have your raw RWIN.

Example: 450ms average latency (x 1.5) with 53Kbps available downstream bandwidth:

450 x 1.5 = 675. 675 x 53kbps = 35775. 35775/8 = 4472 (RWIN).

3) To change the RWIN:

•Download DrTCP to your Desktop.•Change the TCP Receive Window field to whatever value you got.•Save, Exit, then reboot your PC.

got feedback? got feedback?

Any feedback you provide is sent to the owner of this FAQ for possible incorporation and shown publically as well.

by redxii edited by TravisB
last modified: 2006-11-02 01:45:55

No, the RWIN does not affect your pings. Ping is latency on the Net, and not your computer, therefore it can not be lowered. Latency changes every second on the Net, with the pulse of it's many users.

If your line is already lossy, a higher RWIN from Windows default (ME/2K/XP: 17520, 9x: 8760), then it may cause packet loss.

got feedback? got feedback?

Any feedback you provide is sent to the owner of this FAQ for possible incorporation and shown publically as well.

by redxii edited by TravisB
last modified: 2006-07-24 23:53:42