Quality of Service (QoS)

QoS (Quality of Service) refers to a broad collection of networking technologies and techniques. The goal of QoS is to provide guarantees on the ability of a network to deliver predictable results. Elements of network performance within the scope of QoS often include availability (uptime), bandwidth (throughput), latency (delay), and error rate.

QoS involves prioritization of network traffic. QoS can be targeted at a network interface, toward a given server or router's performance, or in terms of specific applications. A network monitoring system must typically be deployed as part of QoS, to insure that networks are performing at the desired level.

QoS is especially important for the new generation of Internet applications such as VoIP, video-on-demand and other consumer services. Some core networking technologies like Ethernet were not designed to support prioritized traffic or guaranteed performance levels, making it much more difficult to implement QoS solutions across the Internet.

Repeater

Network repeaters regenerate incoming electrical, wireless or optical signals. With physical media like Ethernet or Wi-Fi, 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.

Request For Comments (RFC)

RFC documents have been used on the Internet for more than 30 years. Researchers from universities and corporations publish these documents to solicit feedback on new technologies for the Internet. Most popular networking technologies like IP and Ethernet have been historically documented in RFCs.

Registered Jack 45 (RJ45)

RJ45 is a standard type of connector for network cables. RJ45 connectors are most commonly seen with Ethernet cables and networks.

RJ45 connectors feature eight pins to which the wire strands of a cable interface electrically. Standard RJ-45 pin outs define the arrangement of the individual wires needed when attaching connectors to a cable.

Router

Routers are physical devices that join multiple wired or wireless networks together. Technically, a wired or wireless router is a Layer 3 gateway, meaning that the wired/wireless router connects networks (as gateways do), and that the router operates at the network layer of the OSI model.

Home networkers often use an Internet Protocol (IP) wired or wireless router, IP being the most common OSI network layer protocol. An IP router such as a DSL or cable modem broadband router joins the home's local area network (LAN) to the wide-area network (WAN) of the Internet.

By maintaining configuration information in a piece of storage called the "routing table," wired or wireless routers also have the ability to filter traffic, either incoming or outgoing, based on the IP addresses of senders and receivers. Some routers allow the home networker to update the routing table from a Web browser interface. Broadband routers combine the functions of a router with those of a network switch and a firewall in a single unit.

Recommended Standard 232 (RS-232)

RS-232 is a telecommunications standard for connecting certain types of electronic equipment. In computer networking, RS-232 cables were commonly used to connect modems to the compatible serial ports of personal computers. So-called null modem cables could also be connected directly between the RS-232 ports of two computers to create a simple network interface suitable for transferring files.

Today, most uses of RS-232 in computer networking have been replaced by USB technology. Some computers and network routers possess RS-232 ports to support modem connections. RS-232 also continues to be used in some industrial devices, including newer fiber optic cable and wireless implementations.

Symmetric DSL (SDSL)

SDSL is a form of Digital Subscriber Line (DSL) service that provides equal bandwidth for both uploads and downloads. Originally developed in Europe, SDSL was one of the earliest forms of DSL to not require multiple telephone lines.

SDSL possesses all of the common characteristics of DSL, including an "always on" combination of voice and data services, availability limited by physical distance, and high speed access compared to analog modems. SDSL supports data rates up to 3,088 Kbps.

Serial Port

serial port enables external modems to connect to a PC or network router via a serial cable. The term "serial" signifies that data sent in one direction always travels over a single wire within the cable.

Server

A network server is a computer designed to process requests and deliver data to other (client) computers over a local network or the Internet.

Network servers typically are configured with additional processing, memory and storage capacity to handle the load of servicing clients. Common types of network servers include: Web server, Proxy server, FTP server and Gaming server.

SFTP

SFTP can refer to either the SSH File Transfer Protocol or the Simple File Transfer Protocol. SFTP is one of the two primary technologies for secure FTP networking.

SSH File Transfer Protocol

SSH File Transfer Protocol was designed to be used with SSH for secure file transfers. Both command-line and GUI programs exist that support SFTP, including the Java-based Rad SFTP and MacSFTP for Mac OS.

SSH File Transfer Protocol is not backward compatible with the traditional FTP protocol, meaning that SFTP clients cannot communicate with FTP servers and vice versa. Some client and server software embeds support for both protocols to overcome this limitation.

Simple File Transfer Protocol

Simple FTP was designed many years ago as a lightweight version of FTP running on TCP port 115. Simple FTP was generally abandoned in favor of TFTP.

Secure FTP

SSH File Transfer Protocol is one method for implementing so-called secure FTP. The other common method utilizes SSL/TLS technology. To avoid confusing these two methods, use the acronym SFTP only to refer to SSH File Transfer Protocol and not to secure FTP generally.

Symmetric High-speed DSL (SHDSL)

SHDSL technology can transport data symmetrically at data rates from 192 Kbps to 2,320 Kbps. SHDSL utilizes a single copper wire pair, making it an affordable DSL option attractive to small businesses.

Session Initiation Protocol (SIP)

Session Initiation Protocol - is a network communications protocol commonly employed for Voice over IP (VoIP) signaling. In VoIP networking, SIP is an alternative approach to signaling using the H.323 protocol standards.

SIP is designed to support the calling features of traditional telephone systems. However, unlike the traditional SS7 technology for telephone signaling, SIP is a peer-to-peer protocol. SIP is also a general-purpose protocol for multimedia communications not limited to voice applications.

Server Message Block (SMB)

SMB is a network file sharing protocol. Communication over SMB occurs mainly through a series of client requests and server responses. SMB client and server software exists within nearly all versions of Microsoft Windows. File sharing systems using SMB, such as LAN Manager for UNIX, have also been produced for many non-Windows operating environments.

SMB runs at a higher level on top of other network protocols such as TCP/IP, NetBEUI, or IPX. A new version of SMB, Common Internet File System or CIFS, has been developed by Microsoft for "open" use on the Internet.

Sniffer

Sniffers monitor network data. A sniffer can be a self-contained software program or a hardware device with the appropriate software or firmware programming. Sniffers usually act as network probes or "snoops." They examine network traffic, making a copy of the data without redirecting or altering it. Some sniffers work only with TCP/IP packets, but the more sophisticated tools can work with many other protocols and at lower levels including Ethernet frames.

Simple Network Management Protocol (SNMP)

SNMP is a standard TCP/IP protocol for network management. Network administrators use SNMP to monitor and map network availability, performance, and error rates.

To work with SNMP, network devices utilize a distributed data store called the Management Information Base (MIB). All SNMP compliant devices contain a MIB which supplies the pertitent attributes of a device. Some attributes are fixed or "hard coded" in the MIB while others are dynamic values calculated by agent software running on the device.

Developed in the 1980s, the original version of SNMP, SNMPv1, lacked some important functionality and only worked with TCP/IP networks. An improved specification for SNMP, SNMPv2, was developed in 1992. SNMP suffers from various flaws of its own, so many networks remained on the SNMPv1 standard while others adopted SNMPv2.

Socket

A socket represents a single connection between two network applications. These two applications nominally run on different computers, but sockets can also be used for interprocess communication on a single computer. Applications can create multiple sockets for communicating with each other. Sockets are bidirectional, meaning that either side of the connection is capable of both sending and receiving data.

Synchronous Optical Network (SONET)

SONET is a physical layer network technology designed to carry large volumes of traffic over relatively long distances on fiber optic cabling. SONET was originally designed by the American National Standards Institute (ANSI) for the USA public telephone network in the mid-1980s.

SONET possesses several characteristics that make it appealing on the Internet today:

• SONET defines clear interoperability standards between different vendors' products
• SONET can carry nearly any higher-level protocol (including IP), and
• SONET includes built-in support for ease of management and maintenance.

Generally speaking, SONET performs at very high speeds. At the base signalling level called "STS-1," SONET supports 51.84 Mbps. The next level of SONET signalling, STS-3, supports triple the bandwidth, or 155.52 Mbps. Higher levels of SONET signalling increase the bandwidth in successive multiples of four, up to approximately 40 Gbps!

Spanning Tree

Spanning trees are a standard technique used in local area network (LAN) switching. Spanning tree algorithms were developed to prevent redundant transmission of data along intermediate hops between a source and destination host on a mesh network topology. Without spanning trees, a mesh network can be flooded and rendered unusable by messages circulating in an infinite loop between hosts.

The primary Spanning Tree Protocol (STP) is IEEE standard 802.1D, an algorithm commonly used on Ethernet networks. This algorithm works by limiting the paths messages can travel at any given time to a fully connected tree rather than a mesh. As hosts join and leave the network, this protocol dynamically updates the tree accordingly.

A variant of STP called Rapid Spanning Tree Protocol (RSTP) is also now part of the IEEE standard and is the recommended version for use today. RSTP improves the performance of spanning tree updates when the network configuration changes.

Signaling System 7 (SS7)

SS7 supports the exchange of special-purpose messages on public telephone networks. For example, using SS7, telephone companies can implement modern consumer telephone services such as call forwarding.

SS7 messages pass over a separate channel than that used for voice communication. This technique is commonly referred to as "out of band" signaling.

Out-of-band communication techniques like those in SS7 are commonly utilized in computer networking. The File Transfer Protocol (FTP), for example, communicates out-of-band by utilizing two different channels and TCP port numbers, one for data traffic and one for "control" information.

Secure Shell (SSH)

SSH is a remote login technology useful for making command line connections between two computers. Common applications of SSH include file transfer and network system administration. Several different SSH packages are available for Windows, Linux and other operating systems.

SSH offers improved security over older Unix-oriented utilities such as rlogin or telnet. As a network protocol, SSH also provides secure tunneling facilities that can be used to create a type of Virtual Private Network (VPN).

Service Set Identifier (SSID)

An SSID is the name of a wireless local area network (WLAN). All wireless devices on a WLAN must employ the same SSID in order to communicate with each other.

The SSID on wireless clients can be set either manually, by entering the SSID into the client network settings, or automatically, by leaving the SSID unspecified or blank. A network administrator often uses a public SSID, that is set on the access point and broadcast to all wireless devices in range. Some newer wireless access points disable the automatic SSID broadcast feature in an attempt to improve network security.

Secure Sockets Layer (SSL)

SSL security technology helps to improve the safety of Internet communications. SSL is a standard for encrypted client/server communication between network devices.

A network protocol, SSL runs on top of TCP/IP. SSL utilizes several standard network security techniques including public keys, symmetric keys, and certificates. Web sites commonly use SSL to guard private information such as credit card numbers.

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, devices on a subnet share contiguous ranges of IP address numbers. A mask (known as the subnet mask or network mask) defines the boundaries of an IP subnet. The correspondence between subnet masks and IP address ranges follows defined mathematical formulas. IT professionals use subnet calculators to map between masks and addresses.

Switch

A network switch is a small hardware device that joins multiple computers together within one local area network (LAN). Technically, network switches operate at layer two (Data Link Layer) of the OSI model.

Network switches appear nearly identical to network hubs, but a switch generally contains more "intelligence" (and a slightly higher price tag) than a hub. Unlike hubs, network switches are capable of inspecting data packets as they are received, determining the source and destination device of that packet, and forwarding it appropriately. By delivering each message only to the connected device it was intended for, a network switch conserves network bandwidth and offers generally better performance than a hub.

Transmission Control Protocol / Internet Protocol (TCP/IP)

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

IP 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.

Torrent

In peer-to-peer networking, Bit Torrents are small text files. A torrent contains the location of data files that can be downloaded from the Bit Torrent peer to peer network. The torrent file also contains some identifying information about P2P files.

Trojan

Named after the Trojan Horse of ancient Greek history, a trojan is a network software application designed to remain hidden on an installed computer. Trojans generally serve maliciious purposes and are therefore a form of malware, like viruses.