Home Network Terms

Bandwidth

Bandwidth in computer networking refers to the data rate supported by a network connection or interface. Bandwidth is most commonly expressed in terms of bytes per second (bps). The greater the bandwidth (capacity), the more likely that greater performance will follow.

Bit

A single binary digit; a 1 or a 0.

bps vs. Bps

Network performance has traditionally been measured in units of bits per second (bps). Not so long ago, a typical dial-up network connection performed at 9600 bps. As networks have greatly improved in performance, rates are usually now specified in Kbps (thousands of bps) or Mbps (millions of bps).

The unit "Bps" refers to bytes per second. Traditionally units of Bps have been avoided in networking as not all computer architectures implemented a byte with the same number of bits (some used four bits, most used eight bits, and a few used neither of these). As eight-bit byte architectures have become prevalent today, one can generally convert from Bps down to bps safely by multiplying by a factor of eight.

Broadband

The term broadband refers to any type of transmission technique that carries several data channels over a common wire. DSL services, for example, combine separate voice and data channels over a single telephone line -- voice fills the low end of the frequency spectrum and data fills the high end.

Client/Server

Client/Server describes the relationship between two computer programs in which one program, the client, makes a service request from another program, the server, which fulfills the request. Although the client/server idea can be used by programs within a single computer, it is a more important idea in a network. In a network, the client/server model provides a convenient way to interconnect programs that are distributed efficiently across different locations. Computer transactions using the client/server model are very common.

Digital Subscriber Line (DSL)

DSL provides high-speed networking over ordinary phone lines using digital modem technology. It integrates voice and data functionality, bringing the "always on" feature of the telephone to the computer network. The technology theoretically supports data rates of 8,448 Kbps (8.448 Mbps), although typical rates vary from 1,544 Kbps to 512 Kbps and sometimes as low as 90 Kbps.

Domain Name Service (DNS)

The Domain Name Service (DNS) translates Internet domain and host names to IP addresses. DNS implements a distributed database to store name and address information for all public hosts on the Internet.

The DNS database resides on a hierarchy of special-purpose servers. When visiting a Web site or other device on the Internet, 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 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 is delivered to the resolver.

Dynamic Host Configuration Protocol (DHCP)

DHCP allows a computer to join an IP-based network without the need for it to have a pre-configured IP address. DHCP is a protocol that assigns unique IP addresses to devices, and it releases and renews these addresses as devices leave and re-join the network. Many Internet Service Providers (ISPs) use DHCP to allow customers to join the Internet with minimum effort.

DHCP systems require a server setup with the appropriate configuration parameters for the given network. These parameters include the range or "pool" of available IP addresses, the correct subnet masks, and gateway and name server addresses. Devices running DHCP client software can then automatically retrieve these settings as needed. Using DHCP on a network means that system administrators do not need to configure these parameters individually for each device joining the network.

Ethernet

Ethernet is a physical and data link layer technology for Local Area Networking (LAN). When it was first widely deployed in the 1980s, Ethernet supported a maximum theoretical data rate of 10 megabits per second (Mbps). More recently, Fast Ethernet standards have extended traditional Ethernet technology to 100 Mbps peak, and Gigabit Ethernet technology extends performance up to 1000 Mbps.

Extensible Markup Language (XML)

XML is a markup language for writing other markup languages. XML is sometimes called a "meta" language because it describes how to write new languages. It allows for the creation of applications that are streamlined for the use of the owner.

File Transfer Protocol (FTP)

FTP allows the transferral of files between computers on the Internet. Technically, FTP is a simple network protocol based on IP, and is structured on a client/server architecture. An FTP client program initiates a connection to a remote computer running FTP server software. After the connection is established, the client can choose to send and/or receive copies of files, singly or in groups. To connect to an FTP server, a client generally requires a username and password as set by the administrator of the server. Many public FTP archives follow a special convention that accepts a username of "anonymous."

Firewall

A firewall protects a computer network from unauthorized access. Firewalls may be hardware devices, software programs, or a combination of the two. A firewall typically guards an internal network against malicious access from the outside; however, firewalls may also be configured to limit access to the outside from internal users.

Gateway

"Gateway" is a generic term for an internetworking system (a system that joins two networks together). Gateways can be implemented completely in software, completely in hardware, or as a combination of the two. Depending on their implementation, gateways can operate at any level of the OSI model from application protocols to low-level signaling.

Because a gateway by definition appears at the edge of a network, related functionality like firewalling tends to exist at the same location.

Hyper-Text Transfer Protocol (HTTP)

HTTP is an application layer network protocol built on top of TCP. HTTP allows Web browsers and Web servers to communicate. HTTP clients and servers communicate via request and response messages, and utilize TCP port 80 by default, though other ports such as 8080 are also used.

Integrated Services Digital Network (ISDN)

ISDN is a network technology that supports transfer of simultaneous voice and data traffic. Similar to DSL in this respect, an ISDN Internet service works over ordinary telephone lines. ISDN Internet service generally supports data rates of 128 Kbps.

ISDN emerged as an alternative to traditional dial-up networking during the 1990s. However, the relatively high cost of service limited its popularity with home users. The much higher speeds supported by newer cable and DSL technologies diminish the importance of ISDN for home networking, but ISDN technology may still have applications in other areas of business.

Internet

The term Internet today refers to the global network of public computers running Internet Protocol. The Internet supports the public World Wide Web (WWW) and many special-purpose client/server software systems. Internet technology also supports many private corporate intranets and private home LANs.

Internet Protocol (IP)

IP is probably the world's most popular network protocol. Data travels over an IP-based network in the form of packets. Each IP packet includes both a header (specifying source, destination, and other information about the data) and the message data itself.

IP supports the notion of unique addressing for computers on a network. Current IP (IPv4) addresses contain four bytes (32 bits), sufficient to address most computers on the Internet.

IP supports protocol layering as defined in the OSI reference model. Popular higher-level protocols like HTTP, TCP, and UDP are built directly on top of IP. Likewise, IP can travel over several different lower-level data link interfaces like Ethernet and ATM.

Internet Protocol (IP) Address

An IP address is the logical address of a network adapter. The IP address uniquely identifies computers on a network.

An IP address can be private, for use on a LAN, or public, for use on the Internet or other WAN. IP addresses can be determined statically (assigned to a computer by a system administrator) or dynamically (assigned by another device on the network on demand).

IP addresses consist of four bytes (32 bits). Each byte of an IP address is known as an octet. Octets can take any value between 0 and 255, but various rules exist for ensuring IP addresses are valid.

Internet Service Provider (ISP)

An ISP is a company that provides Internet connectivity to home and business customers. ISPs choose what form of access to provide customers, ranging from traditional modem dial-up to DSL and cable modem to T1/T3 lines.

Intranet

An intranet is the generic term for a collection of private computer networks within an organization. Intranets generally use standard network technologies like Ethernet, TCP/IP, Web browsers and Web servers. An organization's intranet often enjoys Internet access but is firewalled so that its computers cannot be reached directly by the public.

Local Area Network (LAN)

A Local Area Network (LAN) supplies networking capability to a group of computers in close proximity to each other such as in an office building, a school, or a home. LANs are useful for sharing files and providing access to printers and the Internet (among other things).

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.

Depending on the protocol(s) they need to support, packets are constructed in some standard packet format. 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.

Peer-to-Peer (P2P)

A peer-to-peer architecture allows hardware or software to function on a network without the need for central servers. Peer-to-peer is commonly used in configuring home computer networks where the cost of a server can be difficult to justify. The approach has also been popularized by some Internet software applications such as Groove and Napster.

Ping

Ping is the name of a standard network utility packaged with popular network operating systems. The utility can be used to determine if a remote device, such as a Web or game server, can be reached on the network and, if so, how fast the current connection is.

Port

A port represents an endpoint or channel for network communications. Port numbers allow different applications on the same computer to utilize network resources without interfering with each other.

Repeater

Network repeaters regenerate incoming signals. On physical media like Ethernet, data transmissions can only span a limited distance before the quality of the signal degrades. Repeaters attempt to preserve signal integrity and extend the distance over which data can safely travel.

RJ-45

A serial connector looks very much like a standard telephone connector, except it houses eight wires instead of four. RJ-45s are not typically found on computers or normal serial equipment. Because they are so small they are often used on devices such as terminal servers which have many ports.

Subnet

A subnet is a logical grouping of connected network devices. Nodes on a subnet tend to be located in close physical proximity to each other on a LAN.

Network designers employ subnets as a way to partition networks into logical segments for greater ease of administration. When subnets are properly implemented, both the performance and security of networks can be improved.

In IP networking, nodes on a subnet share a contiguous range of IP address numbers. A mask (known as the subnet mask or network mask) defines the boundaries of an IP subnet.

Transmission Control Protocol/Internet Protocol (TCP/IP)

Technically, Transmission Control Protocol (TCP) and Internet Protocol (IP) are two distinct network protocols. TCP and IP are so commonly used together, though, that TCP/IP has become standard terminology to refer to either, or both, of the protocols.

IP roughly corresponds to the Network layer (layer 3) in the OSI model, whereas TCP corresponds to the Transport layer (layer 4) in OSI. In other words, the term TCP/IP refers to network communications where the TCP transport is used to deliver data across IP networks. The average person on the Internet works in a predominately TCP/IP environment. Web browsers, for example, use TCP/IP to communicate with Web servers.

User Datagram Protocol (UDP)

UDP squeezes extra performance from IP by not implementing some of the features a more heavyweight protocol like TCP offers. Specifically, UDP allows individual packets to be dropped (with no retries) and UDP packets to be received in a different order than they were sent. UDP is often used in videoconferencing applications or games where optimal performance is preferred over guaranteed message delivery.

Uniform Resource Locator (URL)

A URL is a specially-formatted text string that defines a location on the Internet. URL strings contain three parts or substrings:

1. Network Protocol
2. Host Name or Address
3. File Location

The network protocol substring determines the underlying Internet protocol to be used in reaching the location. These strings consist of a standard protocol name followed by the :// characters. Typical protocols found in URLs include http://, ftp://, and mailto://.

The host substring immediately follows the protocol definition. Hosts may be defined by Internet-standard naming (DNS) or by IP address. For example, a URL of http://compnetworking.about.com or, equivalently, http://209.143.212.20 contains the protocol and host information needed to access this Web site.

The file location portion of a URL defines the location of a network resource. Resources are files that can be plain text files, documents, graphics, or programs, and resource names are relative to a local root directory. Technically, a URL like http://compnetworking.about.com contains an implied file location of /, that Web servers like Apache automatically translate to a specific file name like index.htm. All other specific files exist in a hierarchy or directory tree underneath the root, such as the following:

Relative File Location

Complete URL

http://compnetworking.about.com/library/glossary/blglossary.htm

Wide Area Network (WAN)

A WAN spans a large geographic area, such as a state, province or country. WANs often connect multiple smaller networks, such as LANs or MANs.

The most popular WAN in the world today is the Internet. Many smaller portions of the Internet, such as extranets, are also WANs.

Wired Equivalent Privacy (WEP)

WEP is a protocol that adds security to wireless local area networks (WLANs) based on the 802.11b standard. WEP is a data link layer (Layer 2) security technology that can be "turned on" and "turned off." It is designed to afford wireless networks the same level of protection as a comparable wired network.

WEP security is based on a scheme called RC4 that involves a combination of secret user keys and system-generated values. The original implementations of WEP used so-called 40-bit encryption, that implements a key of length 40 bits and 24 additional bits of system-generated data (64 bits total). Research has shown that 40-bit WEP contains security flaws, and consequently most product vendors today employ so-called 128-bit encryption (key length of 104 bits, not 128 bits).

Wireless Fidelity (Wi-Fi)

Wi-Fi is the industry name for wireless LAN (WLAN) communication technology related to the IEEE 802.11 family of wireless networking standards. To some, the term Wi-Fi is synonymous with 802.11b, as 802.11b was the first standard in that family to enjoy widespread popularity. Today, however, Wi-Fi can refer to any of the three established standards 802.11b, 802.11a and 802.11g.

World Wide Web (WWW)

The term WWW refers to the open development phase of the Internet in the 1990s. The WWW consists of all the global public "Web sites" hosted on server computers and the client devices (computers, cell phones, etc.) that access their "Web content."