Speed Test — About Broadband Speed

Here's some information to help you understand your results.

There are many factors that impact your speed test results. Throughput problems in your local area network, IP or access overhead, and network design all play a role. Please read the definitions and examples below to learn more about these factors.

  • Download
    Download is a measure of how fast your connection delivers content to your computer or local area network.
  • Upload
    Upload is the measure of how fast content is delivered from your computer or local area network to others on the Internet.

    For businesses or power-users, download and upload speed should match or at least be very close. This is important for applications like VoIP, on-line gaming and other interactive programs. Upload speed is even more important if you are operating a server at your location. If achieving optimal upload speed is a concern, consider Ethernet, T1 or DSL services.
  • Kbps
    Kbps transfer rate = kilobit per second transfer rate. There are 8 bits in a byte, so we would divide kbps by 8 to get KB/sec transfer rate.
  • Mbps
    Mbps transfer rate = megabits per second transfer rate. 1000 kilobits equals one megabit. One megabit per second equals 1 million bits per second. Mbps is the industry-standard used by ISPs.
  • MBps
    MegaBytes per second. There are 8 megabits in one megabyte.
  • Latency
    In a network, latency, a synonym for delay, is an expression of how much time it takes for a packet of data to get from one designated point to another. In some usages, latency is measured by sending a packet that is returned to the sender and the round-trip time is considered the latency. Low latency is extremely important for businesses and power-users.
  • Transfer Rate
    Transfer rate is speed at which data can be transmitted between devices. As files to download become increasingly larger, the highest data transfer rate is most desirable.
  • Throughput
    Throughput is the maximum amount of communication or messaging that can be transmitted through a communication channel during an elementary unit of time, usually, in a second.

    Depending on the type of channel, the addressing mechanism used in that channel, the type of messages are being transmitted and how secure the transmission needs to be—along with physical attributes like temperature, humidity and signal-to-noise ratios—actual measured throughput will vary.

An Example of Throughput

You have Ethernet 8.0 Mbps service and need to transmit an email which is exactly 1MB in size You may expect it will take exactly 1 second to transmit that message. But it will actually take longer as the total information that needs to be transmitted is more than 1MB. The total information is called Payload. The channel needs to not only transmit the payload but also some addressing details like where it is coming from and where it is destined to.

The device that sends this email will break down the message into smaller pieces and package them into what are called IP Packets. The size of these packets is usually determined by your Local Area Network. Some have smaller size, so the message will take more IP Packets to transmit; while others may have larger size which needs fewer IP Packets. Each IP Packet also contains an IP Header. This is where the information like the source IP Address, the destination IP Address and additional information about the payload is included. IP Header is usually 20 Bytes (160 Bits) long.

Assuming that this customer uses 100 Byte payload, each IP Packet will now be 120 Bytes long. And that 1MB message will have to be broken down into 10,000 payload pieces. That means to transmit the whole message the channel really needs to transmit about 1,200,000 Bytes or 1.2 MB or 9,600,000 bits. It will take at least 1.2 seconds to transmit all these bytes on this 8 Mbps service assuming that all these IP packets with the payload arrive without any errors and not needing re-transmission. This is called IP Overhead.

Actual Throughput will always be less than line rate of the access service that is communicated by your provider—and this is all based on IP Overhead only. Ethernet services also have a Layer 2 or Ethernet Overhead. Other services may have ATM, Frame Relay or other kinds of Overhead depending on the design. All of this may contribute to a slower bandwidth throughput than what you are expecting.

Other frequent factors influencing throughput:

  • The number of devices sharing the access circuit and the activity the other devices are generating while speed test is being run on one of the devices
  • A rogue LAN port that is clogging the LAN with transmission
  • A leaky LAN port which degrades LAN performance
  • LAN signaling issues which create a lot of packet re-transmission for the devices on the LAN
  • LAN Router with performance issues, low processing power or Deep Packet Inspection and advanced security features like URL blocking enabled
  • Wireless Access Points on the LAN side
  • Distance (both geographical as well as number of hops) between the speed testing client and the server

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