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Cell: A unit of transmission in ATM, consisting of a fixed-size frame containing a 5-octet
header and a 48-octet payload.
CHAP: Challenge Handshake Authentication Protocol. It is typically more secure than PAP
and CHAP. It uses username and password in combination with a randomly generated
challenge string, which has to be authenticated using a one-way hashing function.
CLP: Cell Loss Priority. ATM cells have two levels of priority, CLP0 and CLP1. CLP0 is of
higher priority, and in times of high traffic congestion, CLP1 error cells may be discarded to
preserve the Cell Loss Ratio of the CLP0 cells.
CO: Central Office. In a local loop, a Central Office is where home and office phone lines
come together and go through switching equipment to connect them to other Central Offices.
The distance from the Central Office determines whether or not an ADSL signal can be
supported in a given line.
CPE: Customer Premises Equipment. This specifies equipment on the customer end, or LAN
side.
CRC: Cyclic Redundancy Checking. It is a method for checking errors in a data transmission
between two computers or devices. CRC applies a polynomial function (16 or 32-bit) to a
block of data. The result of that polynomial is appended to the data transmission. Upon receipt,
the destination computer applies the same polynomial to the block of data. If the host and
destination computer share the same result, the transmission was successful. Otherwise, the
sender is notified to re-send the data block.
DHCP: Dynamic Host Configuration Protocol. It is a communications protocol that allows
network administrators to manage and assign IP addresses to computers within the network.
DHCP provides a unique address to a computer in the network, which enables it to connect to
the Internet through Internet Protocol (IP). DHCP can lease an IP address or provide a
permanent static address to those computers who need it (servers, etc.).
DMZ: Demilitarized Zone. It is a computer host or network that acts as a neutral zone
between a private network and a public network. A DMZ prevents users outside of the private
network from getting direct access to a server or any computer within the private network. The
outside user sends requests to the DMZ, and the DMZ initiates sessions in the public network
based on these requests. A DMZ cannot initiate a session in the private network; it can only
forward packets to the private network as they are requested.
DNS: Domain Name System: A method to locate and translate Domain Names into Internet
Protocol (IP) addresses, where a Domain Name is a simple and meaningful name for an
Internet address.
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