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Glossary

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sliding window

The method of flow control used by TCP, as well as sev-

eral Data Link layer protocols. This method places a buffer between the
receiving application and the network data flow. The "window" available
for accepting data is the size of the buffer minus the amount of data already
there. This window increases in size as the application reads data from it and
decreases as new data is sent. The receiver sends the transmitter announce-
ments of the current window size, and it may stop accepting data until the
window increases above a certain threshold.

SLIP

Serial Line Internet Protocol: An industry standard serial encapsula-

tion for point-to-point connections that supports only a single routed
protocol, TCP/IP. SLIP is the predecessor to PPP. See also: PPP.

SMDS

Switched Multimegabit Data Service: A packet-switched, data-

gram-based WAN networking technology offered by telephone companies
that provides high speed.

SMTP

Simple Mail Transfer Protocol: A protocol used on the Internet to

provide electronic mail services.

SNA

System Network Architecture: A complex, feature-rich, network

architecture similar to the OSI reference model but with several variations;
created by IBM in the 1970s and essentially composed of seven layers.

SNAP

Subnetwork Access Protocol: SNAP is a frame used in Ethernet,

Token Ring, and FDDI LANs. Data transfer, connection management, and
QoS selection are three primary functions executed by the SNAP frame.

snapshot routing

Snapshot routing takes a point-in-time capture of a

dynamic routing table and maintains it even when the remote connection goes
down. This allows the use of a dynamic routing protocol without requiring the
link to remain active, which might incur per-minute usage charges.

SNMP

Simple Network Management Protocol: This protocol polls SNMP

agents or devices for statistical and environmental data. This data can
include device temperature, name, performance statistics and much more.
SNMP works with MIB objects that are present on the SNMP agent. This
information is queried then sent to the SNMP server.

socket

1) A software structure that operates within a network device as a

destination point for communications. 2) In AppleTalk networks, an entity
at a specific location within a node; AppleTalk sockets are conceptually sim-
ilar to TCP/IP ports.

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