1G	It is a first-generation wireless telephone technology, cellphones. It is an analog cellphone standards.
2G	The second generation of mobile telephony systems uses digital encoding.
3.5G	It can provide an end-to-end IP solution where voice, data and streamed multimedia can be served to users on an "Anytime, Anywhere" basis at higher data rates than previous generations.
3G	Third generation of mobile phone standards and technology. It can provide wider range of network. That is means that can make wide-area wireless voice telephony and broadband wireless data, all in a mobile environment.
Access Point (AP)	A specially configured node on wireless local area networks (WLAN). It is used as a central transmitter and receiver of WLAN radio signals
ADSL	It is a form of Digital Subscriber Line (DSL) Internet service. ADSL provides greater bandwidth for downloads at the expense of upload speeds.
Address Resolution Protocol (ARP)	ARP converts an Internet Protocol (IP) address to its physical network address, also known as Media Access Control (MAC) address. ARP operates at Layer 2 of the OSI model.
Analog data	Data that can have any value in a range and that can change continuously; the time of day represented by clock hands, or the temperature represented by a liquid thermometer are examples of analog data.
Analog signal	A type of signal that encodes data transmitted over wire or through the air, and is commonly represented as an oscillating wave. An analog signal can take any value in a range, and changes smoothly between values. An analog signal can transmit analog or digital data. For example, a radio station sends analog music data using analog signals, while a modem transmits digital data using analog signals.
ANSI	American National Standards Institute is a organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States.
ARPANET	ARPANET is the predecessor of the global Internet. It built by  United States Department of Defense. ARPANET  used packets to send information which can be routed different paths and reconstructed at their destination.
Asynchronous Transfer Mode (ATM)	ATM is a high-speed networking standard designed to support both voice and data communications. ATM operates at the data link layer (Layer 2 in the OSI model) over either fiber or twisted-pair cable. ATM switches establish point-to-point connections between endpoints and data flows directly from source to destination. Additionally, ATM utilizes fixed-sized cells. ATM cells are 53 bytes in length that includes 48 bytes of data and five (5) bytes of header information.
Asynchronous  PPP	One of the modes in which the point-to-point protocol is utilized. Asynchronous means that the characters which form data packets are sent at irregular intervals. There is no clocking signal to time transmission. Asynchronous PPP is commonly used in lower-speed transmission and less-expensive transmission systems.
Asynchronous transmission	A mode in which the sending and receiving serial hosts know where a character begins and ends because each byte is framed with additional bits, called a start bit and a stop bit. A start bit indicates the beginning of a new character; it is always 0 (zero). A stop bit marks the end of the character. It appears after the parity bit, if one is in use.
Attenuation	When we using medium to transmission a signal, the power of the signal will be attenuation. Attenuation can reduce the signal strength during transmission.
Backbone	A backbone is a central hub designed to transfer network traffic at high speeds. Network backbones are designed to maximize the reliability and performance of large-scale, long-distance data communications. The best known network backbones have been those used on the Internet.
Bandwidth	Bandwidth refers to the data rate supported by a network connection or interface.
Bit	A bit is the smallest unit of data transfer on a computer network. Bits represent the two binary values "on" or "off." Bits are often stored on computers as the digital numbers '1' and '0', but in networking, bits can also be "encoded" by electrical signals and pulses of light.
Bluetooth	Bluetooth is a specification for the use of low-power radio communications to wirelessly link phones, computers and other network devices over short distances. Bluetooth technology was designed primarily to support simple wireless networking of personal consumer devices and peripherals, including cell phones, PDAs, and wireless headsets. Wireless signals transmitted with Bluetooth cover short distances, typically up to 30 feet (10 meters). Bluetooth devices generally communicate at less than 1 Mbps.
BONDING (Bandwidth On Demand Interoperability Group)	A consortium of over 40 data communications equipment vendors and service providers who joined together to create a standardized inverse multiplexing protocol so that inverse multiplexers from different vendors could interoperate. Also refers to the resultant specification, sometimes known as the "BONDING specification".
Bridge	Bridges reduce the amount of traffic on a LAN by dividing it into two segments. Bridges operate at the data link layer (Layer 2) of the OSI model. Bridges inspect incoming traffic and decide whether to forward or discard it. An Ethernet bridge, for example, inspects each incoming Ethernet frame - including the source and destination MAC addresses, and sometimes the frame size - in making individual forwarding decisions.
Broadband	Broadband refers to any type of transmission technique that carries several data channels over a common wire. For example, DSL, Cable, etc.
CAT5	CAT5 is an Ethernet network cable standard defined by the Electronic Industries Association and Telecommunications Industry Association (commonly known as EIA/TIA). CAT5 is the fifth generation of twisted pair Ethernet technology and the most popular of all twisted pair cables in use today. CAT5 cable contains four pairs of copper wire. It supports Fast Ethernet speeds (up to 100 Mbps). As with all other types of twisted pair EIA/TIA cabling, CAT5 cable runs are limited to a maximum recommended run length of 100m (328 feet). A newer specification for CAT5 cable - CAT5 enhanced (CAT5e) - supports networking at Gigabit Ethernet speeds (up to 1000 Mbps) over short distances by utilizing all four wire pairs, and it is backward-compatible with ordinary CAT5.
CAT6	CAT6 is an Ethernet cable standard defined by the Electronic Industries Association and Telecommunications Industry Association (commonly known as EIA/TIA). CAT6 cable contains four pairs of copper wire and unlike CAT5, utilizes all four pairs. CAT6 supports Gigabit (1000 Mbps) Ethernet and supports communications at more than twice the speed of CAT5e, the other popular standard for Gigabit Ethernet cabling.
CCITT	CCITT is short of International Telephone and Telegraph Consultative Committee, now known as ITU(International Telecommunications Union-Telecommunication),  who has defined many important telecommunications standards.
CDMA	Code division multiple access is a communication channel access principle, it can make differents codes in the same channel, but only same code can understand each other.
CHAP	Challenge Handshake Authentication Protocol. This security protocol allows access between data communications systems prior to and during data transmission. CHAP uses challenges to verify that a user has access to a system.
Cisco Certified Internetwork Expert (CCIE)	CCIE is the most advanced level of networking certification available from Cisco. CCIE is highly prestigious and renowned for its difficulty. Four different CCIE certifications can be earned, in these areas: Routing and Switching Communications and Services Security Voice
Cisco Certified Network Associate (CCNA)	CCNA is an entry or "apprentice" level networking certification. Cisco created the CCNA to recognize basic competency in computer networking, particularly for installation and support of LAN/WAN networks having 100 nodes or fewer. The CCNA covers both IP and non-IP networks including Novell IPX and AppleTalk.
Cisco Certified Network Professional (CCNP)	CCNP is a professional or "journeyman" level networking certification. Cisco created the CCNP to recognize advanced skills in computer networking, particularly for installation and support of medium-sized LAN/WAN networks (having 100-500 nodes). The CCNP focuses on routing and switching of scalable networks including intranets and campuses.
Cisco Systems	Cisco Systems is a large corporation that produces computer networking products and services. The Linksys brand of consumer networking products is also an owned subsidiary of Cisco Systems.
Classless Inter-Domain Routing (CIDR)	CIDR is an efficient method for specifying IP addresses to Internet routers. Before CIDR, Internet routers used an inefficient IP addressing scheme based on classes. In contrast, CIDR makes the IP addressing space classless. CIDR associates network masks with IP network numbers independent of their traditional class. Routers that support CIDR recognize these networks as individual routes, even though they may represent an aggregation of several traditional subnets.
Coaxial cables	It is used as a high-frequency transmission line to carry a high-frequency or broadband signal for trasfer data. It is very cheap and widely using in TV and Internet transmission system etc.
Cookies	It more like the history of you visiting Internet. Some website using cookies to remember user's activities.
CPE	Customer Premises Equipment. Terminal equipment located on the customer premises which connects to the telephone network.
Datagram (also known as packet)	A packet is one unit of binary data capable of being routed through a computer network. To improve communication performance and reliability, each message sent between two network devices is often subdivided into packets by the underlying hardware and software. Packet formats generally include a header, the body containing the message data (also known as the payload), and sometimes a footer (also known as the trailer). The packet header lists the destination of the packet (in IP packets, the destination IP address) and often indicates the length of the message data. The packet footer contains data that signifies the end of the packet, such as a special sequence of bits known as a magic number. Both the packet header and footer may contain error-checking information. The receiving device is responsible for re-assembling individual packets into the original message, by stripping off the headers and footers and concatenating packets in the correct sequence.
DCE (Data Circuit-Terminating Equipment)	As defined in the RS-232 specification, equipment to which DTE (Data Terminal Equipment) is connected, often to enable access to network facilities. A DCE converts the format of the data coming from the DTE into a signal suitable to the communications channel. DCE often refers to equipment such as network access equipment, and DTE refers to application equipment, such as a videoconference terminal.
Dynamic Domain Name System (DDNS)	DDNS is a service that maps Internet domain names to IP addresses. Unlike DNS that only works with static IP addresses, DDNS works with dynamic IP addresses, such as those assigned by an ISP or other DHCP server.
Dynamic Host Configuration Protocol (DHCP)	DHCP allows a computer to join an IP-based network without having a pre-configured IP address. DHCP is a protocol that assigns unique IP addresses to devices, then releases and renews these addresses as devices leave and re-join the network. DHCP environments require a DHCP server set up with the appropriate configuration parameters for the given network. Devices running DHCP client software can then automatically retrieve these settings from DHCP servers as needed.
Demilitarized Zone (DMZ)	DMZ is a firewall configuration for securing Local Area Networks (LANs). In a DMZ configuration, most computers on the LAN run behind a firewall connected to a public network like the Internet. One or more computers also run outside the firewall, in the DMZ. The computers outside intercept traffic, adding an extra layer of protection for computers behind the firewall.
Digital data	Data that can have only a limited number of separate values. The time of day represented by a digital clock, or the temperature represented by a digital thermometer are examples of digital data; the digital values do not change continuously, but remain at one discrete value and then change to another, discrete value.
Digital signal	A type of signal that encodes data transmitted over a wire using a limited number of discrete values. The value of the data encoded in a digital signal depends upon the state of the signal during a particular time period. Therefore, the sender and the receiver must synchronize their clocks. Each clock runs at a baud rate, the number of times per second the state of the signal is read or set. Several clocking schemes are available, and digital signals often include clock timing cues.A digital signal can transmit analog or digital data. For example, a CD encodes music data into digital signals, while the wires between computers transmit digital data in digital signals.
Domain Name System (DNS)	The DNS translates Internet domain and host names to IP addresses. DNS automatically converts the names we type in our Web browser address bar to the IP addresses of Web servers hosting those sites. The DNS database resides on a hierarchy of special database servers. When clients like Web browsers issue requests involving Internet host names, a piece of software called the DNS resolver (usually built into the network operating system) first contacts a DNS server to determine the server's IP address. If the DNS server does not contain the needed mapping, it will in turn forward the request to a different DNS server at the next higher level in the hierarchy. After potentially several forwarding and delegation messages are sent within the DNS hierarchy, the IP address for the given host eventually arrives at the resolver, that in turn completes the request over Internet Protocol.  DNS additionally includes support for caching requests and for redundancy. Most network operating systems support configuration of primary, secondary, and tertiary DNS servers, each of which can service initial requests from clients. ISPs maintain their own DNS servers and use DHCP to automatically configure clients, relieving most home users of the burden of DNS configuration.
Denial of Service (DoS)	Denial of Service (DoS) refers to a form of attacking computer systems over a network. DoS is normally a malicious attempt to render a networked system unusable. Denial of service relies on methods that exploit the weaknesses of network technology.
Digital Subscriber Line (DSL)	DSL is a high-speed Internet service like cable Internet. DSL provides high-speed networking over ordinary phone lines using broadband modem technology. DSL technology allows Internet and telephone service to work over the same phone line without requiring customers to disconnect either their voice or Internet connections.
DTE (Data Terminal Equipment)	As defined in the RS-232 specification, equipment to which DCE (Data Communications Equipment) is connected, such as personal computers or data terminals. DTE often refers to application equipment, such as a videoconference terminal or LAN bridge or router, while DCE refers to equipment such as network access equipment.