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Page updated Tuesday
26th 2002f February 2002
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  ADSL by Mr. Simon Hackett of Internode

Date:November 9, 2001
Time:7:00 pm.
Place:WEA, 223 Angas Street, ADELAIDE
Presenter:Mr Simon Hackett

Mr. Simon Hacket of Internode will give a presentation on ADSL at our November meeting.
Mr Hacket co-founded Internode in 1991 and has been involved with the Internet since before it was trendy. He also helped to build the first appearance of the Internet in Australian in the late 80's (AARNet, for the university and research sectors).
The presentation is expected to include;

  • Who they/he are/is (briefly!)
  • How ADSL works in general
  • How the Telstra ADSL system works
  • How Internode have built their own ADSL service as an extension of that Telstra wholesale structure
  • What the challenges, issues and pitfalls are
  • How it actually works out in practice.
Mr. Hacket designed the Internode ADSL implementation so this should be a very informative evening.

Some background/general ADSL information follows...

ADSL - Asymmetric Digital Subscriber Line

Twisted Pair Access to the Internet

Asymmetric Digital Subscriber Line (ADSL) provides multimedia and high-speed data communications over ordinary existing twisted-pair telephone lines. With bandwidths of up to 100 times more than existing bandwidths, ADSL readily provides movies, television, LANs, and the Internet to homes or small businesses.

 

ADSL includes:

- a telephone or ISDN service,

- a high speed downstream channel,

- a medium speed duplex channel.

 

Transmission rates

Transmission rates largely depend on line length, wire gauge, existence of back-ended pairs, and whether other ADSL services share the same cable. Attenuation increases with line length and frequency and decreases with wire diameter.

 

 

 

Data Rate

Wire Size

Distance

1.5 or 2 Mbps

0.5 mm

5.5 km

1.5 or 2 Mbps

0.4 mm

4.6 km

6.1 Mbps

0.5 mm

3.7 km

6.1 Mbps

0.4 mm

2.7 km

 

The phone/ISDN channel is separated from the ADSL digital modem by filtering which allows them to operate independently - even if one fails!

The high speed channel ranges from 1.5 to 6.1 Mbps, while duplex rates range from 16 to 832 kbps.

 

Error Correction

ADSL uses forward error correction to enable real-time streaming video to be used over the link, as well as other data types.

 

Transmission Methods

ADSL modems divide the available bandwidth to provide either:

- Frequency Division Multiplexing (FDM) which assigns one band for upstream data and another band for downstream data.

- Echo Cancellation which assigns the upstream band to over-lap the downstream, and separates the two by means of local echo cancellation as per V.32 and V.34 modems.

 

With either technique, ADSL splits off a 4 kHz region for the phone/ISDN at the low end of the band.