Sunday, February 22, 2009

The Need for Speed

Broadband Internet service has become the norm for every connected home today. We expect high speed Internet service, with web pages loading in an instant and live videos playing without a hiccup. But are you getting what you are paying for? Every ISP labels its service as "high speed", be it a DSL connection, or a cable connection or a wireless "air card".

Your overall Internet experience actually depends on throughput and not just speed. A higher speed does not necessarily mean a better Internet connection. The quality of the connection matters equally, if not more. When evaluating an Internet service, one has to pay attention to three factors - speed, error rate and latency.

Speed refers to the amount of data that can be transmitted per second - measured in Kilobits or Megabits per second. A high speed connection in my view should provide a minimum of 256 Kbps speed, for decent performance.

Error rate refers to the percentage of messages lost during data transfer. This term is also referred to as "packet loss". Data networks are not perfect, and from time to time messages get dropped. Fortunately, the networking software in our computers will automatically re-transmit the messages if no confirmation of delivery is received. Error rates should be minimal. Anything above 1% is not acceptable. The performance of a 64 Kbps connection with a 0.5% error rate is way better than a 512 Kbps line with a 2% error rate.

Latency is the time it takes for data to travel from your computer to its destination, measured in milliseconds. It is analogous to the delay we perceive in an overseas phone conversation. A higher latency implies that your quality will suffer more under errors. An average latency of 300 milliseconds is acceptable. Anything higher than that will severely impact throughput during errors.

It is easy for us to evaluate the quality of an Internet connection. The Broadband Speed Test website measures the latency, upload and download speeds of your Internet connection. Before you purchase a new Internet service, ask for a demonstration and check out the performance yourself.

More details on how to use the Broadband Speed Test can be found here on the Cyberwatch blog along with a comparison between popular Internet services available in India.

Speed Test your Broadband Internet Connection

This article explores some quick and easy ways to determine the overall performance of your broadband Internet connection. There are three factors that affect the performance, or throughput of your Internet connection.

Line Speed: The speed of your Internet connection is the most advertised factor when selling you the service. We measure the line speed in kilobits per second (Kbps) or megabits per second (Mbps). The line speed tells us how fast can signals travel across the wire. A 256 Kbps speed implies 2,56,000 bits can be transmitted or received in one second. However, speed is not the only factor that boosts your throughput.

Error Rate: Errors hamper data communication. When a transmission error occurs, the data packet being transmitted is lost, and has to be re-transmitted. If your Internet connection suffers from a high error rate, your throughput will be miserable. This is because most of the time is spent in re-transmission of packets in the event of errors. Data packets travelling on the Internet travel like cars on a highway. If you are driving and see an obstacle on the highway, you would naturally apply the brakes and slow down the car. Now, once you clear the obstacle, you would accelerate slowly until you reach the desired speed limit. The time spent in braking and accelerating again is analogous to what happens when a data packet needs to be retransmitted. Now, even if your car can travel at 100 kms per hour, if you have to brake and accelerate repeatedly, your average speed will be less than half of the maximum speed. The maximum tolerable error rate should not exceed 1%. You may be able to tolerate one out of every hundred data packets being dropped. Any more and your throughput is drastically degraded.

Latency: Latency is the time it takes for data to travel from your computer to its destination, measured in milliseconds. It is often referred to as the "round trip time" or RTT for short. Latency is the time it takes for your computer to establish the initial connection with the destination computer on the Internet. A higher latency implies that your throughput will suffer more under errors. For every error that occurs, your computer has to re-establish the connection with its destination. The longer it takes to re-establish the connection, the slower is your performance. Another factor that is based on latency is "jitter".

Jitter is the variation in latency for every data packet sent. If the time taken for every packet varies greatly, it implies a higher jitter. Jitter impacts real-time services such as Voice over IP or watching videos directly from the Internet. Low jitter means a more steady throughput.

With these concepts introduced, let us look at a few quick methods to test how your Internet connection really performs. The Broadband Speed Test website can test your Internet connection's performance in a matter of minutes, without you requiring to install any software. The Broadband Speed Test requires you to select a testing server, to measure how fast the connection is between your computer and the test server. For the first set of tests, choose a server nearest to your location. This will determine how fast the connection is between your computer and your ISP. For the second set of tests, choose a server far away, like in the United States or Europe or Asia Pacific. Most overseas Internet connections from India land in Europe or the US. Testing with a European or a US server will determine the overall speed you can hope to get with servers all over the Internet.

At the end of the test, your results will be displayed as follows:

Tata Indicom (VSNL) - Testing between Ahmedabad and Mumbai

Tata Indicom (VSNL) - Testing between Ahmedabad and San Jose

I conducted tests with three broadband connections - BSNL's 2 Mbps Business Data plan, Tata Indicom (VSNL)'s 2 Mbps Unlimited Data plan and Iqara's 256 Kbps cable connection.

Here is a summary of the tests.

ISPTest ServerLatency (ms)Download Speed (Kbps)Upload Speed (Kbps)Comments
BSNLMumbai, IN751436173Very high latency, and not enough speed for a 2 Mbps connection
BSNLSan Jose, CA382426516An aberration. Usually upload speeds are slower than download speeds.
Tata IndicomMumbai, IN871113496Fast and steady throughput.
Tata IndicomSan Jose, CA323955491Not much difference between Mumbai and San Jose. This indicates a high quality connection. The only difference is the latency.
IqaraMumbai, IN45238240Good enough for a 256 Kbps connection. Low latency and speeds approaching 256 Kbps.
IqaraSan Jose, CA287249187Not much variation in speed between Mumbai and San Jose. Upload speed is reduced, but the download speed is increased.