Glossary of Terms
A router is a computer networking device that forwards data packets across a network toward their destinations, through a process known as routing. A router acts as a junction between two or more networks (in this case internal and external, or Internet) to transfer data packets among them.
A network switch is a networking device that performs transparent connection of multiple network segments with forwarding based on MAC addresses. It allows the "splitting" of one network connection into many ports, so more devices can be connected to that segment.
The Internet Protocol (IP) is a data-oriented protocol used for communicating data across a packet-switched internetwork. IP is a network layer protocol in the internet protocol suite and is encapsulated in a data link layer protocol (e.g., Ethernet). As a lower layer protocol, IP provides the service of communicable unique global addressing amongst computers. This implies that the data link layer need not provide this service. Ethernet provides globally unique addresses except it is not globally communicable (i.e., two arbitrarily chosen Ethernet devices will only be able to communicate if they are on the same bus). The difference is that IP is concerned with the final destination of data packets. Ethernet is concerned with only the next device (computer, router, etc.) in the chain. The final destination and next device could be one and the same (if they are on the same bus) but the final destination could be on the other side of the world.
A Private Branch eXchange (also called PBX, Private Business eXchange or PABX for Private Automatic Branch eXchange) is a telephone exchange that is owned by a private business, as opposed to one owned by a common carrier or by a telephone company.
Asymmetric Digital Subscriber Line (ADSL) is a form of DSL, a data communications technology that enables faster data transmission over copper telephone lines than a conventional modem can provide. It does this by utilizing frequencies that are normally not used by a voice telephone call, in particular, frequencies higher than normal human hearing. This signal will not travel very far over normal telephone cables, so ADSL can only be used over short distances, typically less than 5 km. Once the signal reaches the telephone company's local office, the ADSL signal is stripped off and immediately routed onto a conventional internet network, while any voice-frequency signal is switched into the conventional phone network. This allows a single telephone connection to be used for both ADSL and voice calls at the same time.
Symmetric Digital Subscriber Line (SDSL) is a Digital Subscriber Line (DSL) variant with E1-like data rates (72 to 2320 kbit/s). It runs over one pair of copper wires, with a maximum range of about 3 kilometers. The main difference between ADSL and SDSL is that SDSL has the same upstream data transfer rate as downstream (symmetrical), whereas ADSL always has smaller upstream bandwidth (asymmetrical). It is quite expensive. Equipment routing SDSL support is usually proprietary equipment which only speaks to SDSL equipment from the same vendor, or to SDSL equipment from other vendors that use the same DSL chipset. Most new installations use G.SHDSL equipment instead of SDSL.