DSL and two sides

[sarahr202]

Hi Every body!

I can use dial up to connect two PC at different locations. Can i use DSL too? or DSl is only used to connect to Internet ?

Thanks a lot!

[lamav · Accepted solution]

Sarah:

Ive never seen a deployment in which a computer is used to connect to another single computer on a dedicated aDSL line.

From a network perspective, I dont see why this could not be done, since the connection basically consists of running PPP encapsulation over a multiaccess network, like ethernet or ATM connection - usually ethernet. But I cant think of an application in which a PC would have to use a DSL line to connect to one other PC.

ISPs use it to allow multiple users access to their network. To differentiate between different users on a multiaccess PPPoE link, ISPs typically employ an authentication process, which after being negotiated successfully, then allows the end machine to discover the MAC address of the peer machine and then negotiate a session ID. The ethernet address and the session ID combined make for the unique connection identifier for billing purposes.

See RFC 2516.

HTH

Victor

[Giuseppe Larosa · Accepted solution]

Hello Sarah,

the answer is no for ADSL for two reasons

a)

ADSL requires to go through a central office so it is not good for back to back connections.

It is a question of the tramsmission tecniques in use:

ADSL uses 256 tones (each tone is a carrier) : some tones are used for transmit from home to CO (upstream) and others (the most) are used to transmit from CO (ATU-C in DSL terminology) to home (CPE or ATU-R in DSL terminology)

For this reason connecting back to back two ADSL interfaces doesn't work.

Other types of DSL exist.

SHDSL can be used for this because it is a symmetric service.

see for example:

http://www.cisco.com/en/US/tech/tk175/tk274/technologies_configuration_example09186a0080135834.shtml#diag

but this is on a pair of copper wires without no CO in the middle or with a wire cross-connection in CO.

b) no real interaction of DSL with PSTN network

xDSL doesn't use the PSTN calling capabilities at all.

they just share the same wire pair with PSTN at different frequencies:

PSTN uses the smallest frequencies, then the upstream tones and then the downstream tones.

there is no way to call someone on another DSL line.

At the CO special filters (POTS splitters) divide PSTN signal from DSL signal. The first is carried to the PSTN CO switch, the DSL signal is carried to a DSLAM ATU-C where the point-to-point DSL link is terminated.

there is no modem pool in DSL as in dial-up access as explained by Victor in the other thread.

(this is why time based fees for DSL are just money makers for ISPs)

And also there are no network resources to make the call: this means creating a cross connect (in ATM it would be an SVC) Virtual Circuit with bandwidth resources.

Hope to help

Giuseppe

[Joseph W. Doherty · Accepted solution]

In theory, DSL probably could be used for the end circuits as part of a dedicated TelCo circuit, but I don't know if TelCos are currently configured to do so or have any interest in doing so.

PS:

If you had your own long distance (up to about 1 Km?) copper wire between two of your locations, you might find end devices, e.g. Ethernet extenders, that might use DSL like signally technology to communicate across the wire.