• klseesea
• Jul 28,2010
• In: Internet & Broadband

Streamyx Attenuation and SNR Margin explaination

Streamyx technology relies on ADSL. To provide high speed connection, ADSL relies on unused frequency bands of your telephone cable. A twisted pair copper cable can carry analog voice as well as digital signals simultaneously. The diagram below shows the bandwidth available for a typical telephone cable.

Red block: Analog voice signals. Your normal voice calls are allocated to a maximum of 4kHz.
Green block: Digital Upstream signals. For uploading data to your ISP.
Blue block: Digital Downstream signals. For downloading data from your ISP.
Notice that blue block is larger than green block. Because ADSL users typically download data more than upload, ISPs will allocate a bigger portion of bandwidth for downloading. That’s why your Streamyx download speed is much higher than upload speed.

Downstream traffic is located at the far end of your cable frequency range. Low quality cables cannot provide the entire frequency spectrum and will severely degrade downstream capacity. That’s why some customers have full upload speeds but crippled download speeds.

Analysing signal quality

Using an Alcatel Speechtouch 510 DSL modem and Alcatool, you can analyse the quality of your phone line as shown below. One single bar represents a 4.3kHz slot.

This graph is split into Up and Down portions. Higher bars means better signal quality. In this example, the DSL signal starts from 138kHz and above. Notice that on the far right portion (966kHz) the signal starts to drop. This could due to signal loss, distance from HQ or other attenuation issues.

Overall, this chart represents a very high quality DSL signal. The maximum physical attainable speed is about 10Mbps due to short distance to Telekom exchange(about 3km). This is the best signal quality I’ve got back in 2003.

Simple signal quality measurement for everyone

Your DSL modem that came with Streamyx could probably do simple signal quality analysis. Although it can’t provide data to reproduce a complex chart like the above, you can tell the signal quality by looking at the following parameters. You need to login to your modem homepage to get these statistics.

Distance versus speed

Basic rule of the thumb: the nearer you are to the Telekom DSLAM, the better it is for your Streamyx connection. From Wikipedia, here’s a rough guide of wiring distance versus maximum data rate:

• 25 Mbit/s at 1,000 feet (~300 m)
• 24 Mbit/s at 2,000 feet (~600 m)
• 23 Mbit/s at 3,000 feet (~900 m)
• 22 Mbit/s at 4,000 feet (~1.2 km)
• 21 Mbit/s at 5,000 feet (~1.5 km)
• 19 Mbit/s at 6,000 feet (~1.8 km)
• 16 Mbit/s at 7,000 feet (~2.1 km)
• 1.5 Mbit/s at 15,000 feet (4.5 km)
• 800 kbit/s at 17,000 feet (~5.2 km)

Most customers who are using Basic 384k or 512k packages will not have much problems regarding physical connection speeds. The real problem starts with 1Mbps packages and above if their phone lines distance is almost 5km and beyond.

Source - nicky.my

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