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segment. (1) A section of cable between components
or devices. A segment may consist of a single patch
cable, several patch cables that are connected, or a
combination of building cable and patch cables that are
connected. (2) In Internet communications, the unit of
transfer between TCP functions in different machines.
Each segment contains control and data fields; the
current byte-stream position and actual data bytes are
identified along with a checksum to validate received
data.
segmenting. In OSI, a function performed by a layer
to map one protocol data unit (PDU) from the layer it
supports into multiple PDUs.
sequence number. In communications, a number
assigned to a particular frame or packet to control the
transmission flow and receipt of data.
Serial Line Internet Protocol (SLIP). A protocol used
over a point-to-point connection between two IP hosts
over a serial line, for example, a serial cable or an
RS232 connection into a modem, over a telephone line.
server. A functional unit that provides shared services
to workstations over a network; for example, a file
server, a print server, a mail server. (T)
service access point (SAP). (1) In Open Systems
Interconnection (OSI) architecture, the point at which
the services of a layer are provided by an entity of that
layer to an entity of the next higher layer. (T) (2) A
logical point made available by an adapter where
information can be received and transmitted. A single
service access point can have many links terminating in
it.
Service Advertising Protocol (SAP). In Internetwork
Packet Exchange (IPX), a protocol that provides the
following:
v A mechanism that allows IPX servers on an internet
to advertise their services by name and type. Servers
using this protocol have their name, service type, and
address recorded in all file servers running NetWare.
v A mechanism that allows a workstation to broadcast
a query to discover the identities of all servers of all
types, all servers of a specific type, or the nearest
server of a specific type.
v A mechanism that allows a workstation to query any
file server running NetWare to discover the names
and addresses of all servers of a specific type.
session. (1) In network architecture, for the purpose of
data communication between functional units, all the
activities which take place during the establishment,
maintenance, and release of the connection. (T) (2)
A logical connection between two network accessible
units (NAUs) that can be activated, tailored to provide
various protocols, and deactivated, as requested. Each
session is uniquely identified in a transmission header
(TH) accompanying any transmissions exchanged
during the session. (3) In L2TP, L2TP creates a session
when an end-to-end PPP connection is attempted
between a dial user and the LNS; regardless of whether
the user initiates the session or the LNS initiates an
outbound call. The datagrams for th session are sent
over the tunnel between the LAC and LNS. The LNS
and LAC maintain the state information for each user
attached to an LAC.
Simple Network Management Protocol (SNMP). In
the Internet suite of protocols, a network management
protocol that is used to monitor routers and attached
networks. SNMP is an application layer protocol.
Information on devices managed is defined and stored
in the application’s Management Information Base
(MIB).
SNA management services (SNA/MS). The services
provided to assist in management of SNA networks.
socket. (1) An endpoint for communication between
processes or application programs. (2) The abstraction
provided by the University of California’s Berkeley
Software Distribution (commonly called Berkeley UNIX
or BSD UNIX) that serves as an endpoint for
communication between processes or applications.
source route bridging. In LANs, a bridging method
that uses the routing information field in the IEEE 802.5
medium access control (MAC) header of a frame to
determine which rings or token-ring segments the frame
must transit. The routing information field is inserted into
the MAC header by the source node. The information in
the routing information field is derived from explorer
packets generated by the source host.
source routing. In LANs, a method by which the
sending station determines the route the frame will
follow and includes the routing information with the
frame. Bridges then read the routing information to
determine whether they should forward the frame.
source service access point (SSAP). In SNA and
TCP/IP, a logical address that allows a system to send
data to a remote device from the appropriate
communications support. Contrast with
destination
service access point (DSAP)
.
spanning tree. In LAN contexts, the method by which
bridges automatically develop a routing table and
update that table in response to changing topology to
ensure that there is only one route between any two
LANs in the bridged network. This method prevents
packet looping, where a packet returns in a circuitous
route back to the sending router.
sphere of control (SOC). The set of control point
domains served by a single management services focal
point.
sphere of control (SOC) node. A node directly in the
sphere of control of a focal point. A SOC node has
exchanged management services capabilities with its
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