Project PDA

ADSL or Asymmetric Digital Subscriber Line allows standard phone lines to deliver high-speed data communications. Unlike ISDN (q.v.) which has transmission speeds limited to 64 kbps, ADSL technology can deliver upstream (from the user) speeds of 640 kbps and downstream (to the user) speeds of more than 6 mbps. ADSL also uses the portion of a phone line's bandwidth not utilized by voice, allowing for simultaneous voice and data transmission. You can establish an Internet connection by running adsl-start, either from the command-line or from a startup script. To terminate the connection, run adsl-stop. To check the connection and see the IP address that was assigned to your server, run adsl-status.

ADSL transceiver, also known as a ADSL modem or DSL modem, is a device used to connect one or more computers to a phone line, in order to use an ADSL service. Some ADSL modems also manage the connection and sharing of the ADSL service with a group of machines, making an ADSL router or ADSL modem/router a more accurate name for the device. A DSL modem acts as the ADSL Terminal Unit or ATU-R, as the telephone companies call it.

Apart from connecting to an ADSL service, many modems offer additional integrated features:

• ADSL2 or ADSL2+ support
• Router functionality that uses NAT to share the connection
• An 802.11b or 802.11g wireless access point
• A built-in switch (typically 4 or 5 ports)
• VPN termination
• DHCP server
• Dynamic DNS client
• VoIP functionality including QoS

Many ADSL modems can have their firmware upgraded to support additional features or fix existing problems. This can be done over the network, or using a dedicated serial connection.