Reasons for buying the highest speed DSL line available?

You may have a number of requirements for buying the highest speed line available:

4 To be able to download more data (e.g. for largescale software or file download, data file transfer or data backup applications). In a 60 minute ‘busy hour’ window each day you are able to transfer a maximum of 450 Mbytes for each 1 Mbit/s of linespeed

4 To support bandwidth-hungry applications (e.g. as you may require in order to enjoy higher speed or higher quality/higher resolution live video streaming – e.g. for IPTV and HDTV – high definition television downloads across the Internet). Without a high speed line, you will have to make do with poorer quality, poorer resolution pictures and videos.

4 For faster response of interactive applications: where you are running interactive applications (such as games) it may be critical to ensure fastest possible delivery of data and messages in both directions. A faster bitrate reduces the elapsed time until full receipt of a given length of message at the receiving end. Note however, that a line with double the bitrate does not deliver the message in half the time. The length of the line (propagation distance) is also critical to the overall elapsed time for message conveyance. In the example below a 20x increase in ADSL connection bitrate reduces the message propagation to a half of its previous value.

Message transfer time example:

Let us compare the time for message transfer of a message of 64 byte (64 x 8 bits = 512 bits) length

Let us assume that the total distance the message will be carried is 100km.

Therefore the propagation time across the connection of a single ‘bit’ of data is ≈ 100 km /(¾ x 3 x10⁵ km/s*)

Propagation time of single bit of data (due to length of connection) is 0.444 ms

[*Note: 3 x 10⁵ km/s is the speed of light through space. Digital signals in a telecommunications network travel at about ¾ of this speed]

Connection 1: 1.024 Mbit/s download rate time to transmit 512 bits = 0.5 ms total time elapsed to message receipt = latency = 0.444 ms + 0.5 ms = 0.944 ms

Connection 2: 20.480 Mbit/s download rate (20x speed) time to transmit 512 bits = 0.025 ms total time elapsed to message receipt = latency = 0.444 ms + 0.025 ms = 0.469 ms delivery in half the time, but requiring 20x bitrate

If you are a software application designer:

The most significant improvement in the speed at which your application runs may be achieved by reducing the ‘conversational’ exchange of the user’s client software with the server. In particular, eliminating the need to wait for ‘acknowledgement (ACK)’ messages as confirmation of particular actions will considerably reduce the time required for process execution. (In the example above, each ‘acknowledgement’ required from the distant end will ‘cost’ at least double the time which elapses during a simple message receipt – since a message transmission and an ACK reply must be conducted – a minimum PING response time of 2 x 0.469 ≈ 1 ms delay or latency)

4 As an insurance against future needs (‘future-proofing’): Given that most modern equipment (e.g. DSL modems) already supports the latest ADSL2+ standard, it is easy to predict the development of future applications and services exploiting the higher bitrates (up to 25 Mbit/s) which it makes possible. It may simply be prudent to avoid the costs of a later equipment and line connection bitrate upgrade by contracting to the higher bitrate from the start.

In order that you can make most benefit from the highest speed of ADSL connection, you may need new or more equipment to deal with the increased speed and data (e.g. DSL modem compatible with the ADSL2+ standard, or ‘always on’ home entertainment server to capture the large volumes of data associated with video downloands).