Bandwidth, Monthly Transfer Limit, Latency, Network Speed
Some of the questions that we got asked a lot are
- What is the speed to/from so-and-so location?
- What is the bandwidth we are getting?
- How much data can I transfer in a month?
- Why is my connection to so-and-so so slow?
Often the various terms - bandwidth, network speed, monthly data transfer and latency are used very loosely and interchanged. (Those in China - yes I know the links are to Wikipedia, read on for a summary.)
Bandwidth describe how much data can travel over a connection in given time. An analogy would be a water pipe, more water can flow through a wider pipe than a thinner pipe. So if a connection has high bandwidth, more data can flow across in a given time.
However in hosting, the term “bandwidth” is often used metaphorically, to describe the amount of data that can be transferred to or from the website or server, measured in bytes transferred over a prescribed period of time. This can be more accurately described as “Monthly Data Transfer”.
Before going further, it is important to mention that different kinds of Internet usage has different effect on bandwidth and data transfer limit. Two typical Internet usage are web browsing and downloading files.
Web pages are typically small files that take just seconds to download transfer from the server. In between web pages virtually no traffic occurs between the user and the server.
Download files, especially large files, caused a sustained transfer from the server to the user.
You can see that bandwidth is more a limiting factor for downloading than web browsing. The same bandwidth that can support a few hundreds web browsing but may be taken up by just a few download.
Now consider monthly transfer limit. If the limit is low, no matter how wide is the bandwidth, that is the limit to amount of data you can transfer. If the limit is too high, you will never reach it anyway since it is the bandwidth that determines the upper limit.
Next, network speed. Many people use the ping command as a measure of network speed. It is an indication but not a true measure of the network speed. Due to the way the Internet works, there are many factors that affects the perceived speed. In fact ping measures what is known as latency rather than speed.
Speed, as we know, measures something per unit time - in this case how much data per unit time.
Latency is measured in unit time - in this case how long (duration) it takes to go from source to destination and back.
Bandwidth and latency are also connected in that when the bandwidth is saturated, congestion occurs and latency is increased.
An example may help to illustrate the concept. During a recent earthquake near Taiwan, a number of submarine cables were damaged. The speed that data is moving through your ADSL has not significantly changed. The bandwidth was fully utilized as all traffic channeled through the few remaining cables. The latency raised to incredible level that it just stopped at certain choke points. The nett effect is that the perceived speed slowed to almost zero.
With the basic understanding of these term in mind, here are some take away for hosting and Internet usage in China
- Latency can be high when access sites overseas or when an overseas user access a site within China.
- Bandwidth between different telecom provider can be low leading high latency and what is known as the north-south divide. This situation however is improving.
- Very typically shared hosting in China do not provide a guarantee on bandwidth or monthly transfer limit.
- If you are running a website, monthly transfer limit is usually not an issue. (Unless your website is very popular)
- To be guaranteed of certain bandwidth you would have to buy from the datacenter direct or through the hosting company.
This can be a confusing topic. Please let me know if I missed anything. Hope this article helps you understand better while using the Internet and when selecting hosting.
Add comment April 19th, 2007