Serial Line Internet Protocol (SLIP)

An industry standard protocol developed in 1984 for UNIX environments that supports TCP/IP networking over serial transmission lines. These serial lines are typically dial-up connections using a modem. Serial Line Internet Protocol (SLIP) can provide TCP/IP hosts with dial-up access to the Internet by using SLIP servers located at Internet service providers (ISPs).

Simple Mail Transfer Protocol (SMTP)

A standard application-layer protocol for delivery of e-mail over a TCP/IP internetwork such as the Internet. The basics of Simple Mail Transfer Protocol (SMTP) are defined in Request for Comments (RFC) 821 and 822.

Simple Network Management Protocol (SNMP)

An Internet-standard application layer (layer 7) protocol for exchanging device management information between network devices on a TCP/IP network. Simple Network Management Protocol (SNMP) is most often used for collecting statistical and configuration information about network devices such as computers, hubs, switches, routers, and even network printers. The statistical information includes the number of packets or frames sent or received per second, the number of errors per second, and so on. The configuration information includes the IP address of an interface on the device, the version of the operating system running on the device, and so on. Management systems are used to monitor network health, trap errors, perform diagnostics, and generate reports. SNMP is the most popular network management protocol in use.

Static address

An IP address that is manually assigned to a host on a TCP/IP internetwork. Computers running Microsoft Windows support both static Internet Protocol (IP) addressing and dynamic IP addressing through the Dynamic Host Configuration Protocol (DHCP).

Static IP addresses are usually used for

• Small workgroups whose machine configurations will not change often. Peer-to-peer networks that use Windows 95 or Windows 98 don’t have a DHCP server to assign IP addresses to stations on the network.
• Servers on a network, which should have an IP address that does not change. An alternative is to assign a DHCP reservation to these servers so that they receive their IP addresses automatically from a DHCP server but always receive the same reserved address.
• Windows NT–based and Windows 2000–based servers that are running certain services, such as DHCP, Windows Internet Name Service (WINS), or Domain Name System (DNS). Servers running these services normally require static IP addresses.

Static routing

A routing mechanism that is handled by the Internet Protocol (IP) and that depends on manually configured routing tables. Routers that use static routing are called static routers. Static routers are generally used in smaller networks that contain only a couple of routers or when security is an issue. Each static router must be configured and maintained separately because static routers do not exchange routing information with each other.

Statistical multiplexing

A multiplexing technique that allows information from a number of channels to be combined for transmission over a single channel.

Subnet mask

A 32-bit number that is used to partition IP addresses into a network ID and a host ID. Subnet masks are used by TCP/IP services and applications to determine whether a given IP address on an internetwork is a local network address or a remote network address

Subnetting

The process of partitioning a single TCP/IP network into a number of separate networks called subnets. These subnets are then joined using routers. Advantages of subnetting a network include the following:

• Reducing network congestion by limiting the range of broadcasts using routers
• Enabling different networking architectures to be joined

Switched virtual circuit (SVC)

A form of telecommunications service that provides a path between two nodes in a packet-switched network. The path is set up and configured at the beginning of a session and is dismantled at the end. Each new session requires a switching path to be established, and this path differs during each session depending on the available switches.

A switched virtual circuit (SVC) provides a temporary, point-to-point connection between the two nodes. SVCs offer the advantage of bandwidth on demand but suffer from some latency in establishing a connection. They are cheaper than permanent virtual circuits (PVCs) because they use whatever telco resources are available at a given time; after the session, these resources are released for other purposes. Because the actual switching path varies with each session, SVCs also suffer from inconsistent connection quality.

Symmetric Digital Subscriber Line (SDSL)

A type of Digital Subscriber Line (DSL) technology in which upstream and downstream speeds are equal. Symmetric Digital Subscriber Line (SDSL) technology can provide subscribers with permanent, high-speed data connections for Internet access and other uses much more cheaply than T1 lines can. SDSL is sometimes interpreted to stand for "Single-line DSL" instead of "Symmetric DSL" because it uses a single twisted-pair copper wire.

Synchronous Data Link Control (SDLC)

A data-link layer protocol developed in the 1970s by IBM for its Systems Network Architecture (SNA) networking environment. Synchronous Data Link Control (SDLC) is primarily used in wide area networks (WANs) that use leased lines to connect mainframe SNA hosts and remote terminals.

Synchronous Optical Network (SONET)

A physical layer specification for broadband synchronous transmission of voice, video, and data over long distances of fiber-optic cabling at speeds of more than 1 Gbps. Synchronous Optical Network (SONET) networks can carry voice, video, and data simultaneously and are often used by telecommunications providers to provide the underlying transport mechanism for Asynchronous Transfer Mode (ATM) networking in internal telco and long-distance carrier networks. SONET can also be used as the underlying transport for Fiber Distributed Data Interface (FDDI), Integrated Services Digital Network (ISDN), and Switched Multimegabit Data Services (SMDS) communication. SONET was developed by Bellcore in the mid-1980s and has been standardized by the American National Standards Institute (ANSI). A European version called Synchronous Digital Hierarchy (SDH), which has been standardized by the International Telecommunication Union (ITU), is essentially equivalent to SONET.

Synchronous transmission

A mode of serial transmission for digital modems, ISDN terminal adapters, Channel Service Unit/Data Service Units (CSU/DSUs), and other telecommunications devices.

Systems Network Architecture (SNA)

A set of IBM mainframe networking standards and protocols introduced in 1974. Systems Network Architecture (SNA) originally defined a centralized architecture with mainframe hosts controlling terminals, but it has also been adapted for peer-to-peer communication and distributed client/server computing environments. SNA includes services for configuring and managing system resources within an IBM mainframe networking environment.

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