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g-17
GLOSSARY
SAR (Segmentation And Reassembly) - the SAR accepts PDUs from the CS
and divides them into very small segments (44 bytes long). If the CS-PDU is
less than 44 bytes, it is padded to 44 with zeroes. A two-byte header and
trailer are added to this basic segment. The header identifies the message type
(beginning, end, continuation, or single) and contains sequence numbering
and message identification. The trailer gives the SAR-PDU payload length,
exclusive of pad, and contains a CRC check to ensure the SAR-PDU integrity.
The result is a 48-byte PDU that fits into the payload field of an ATM cell.
SCSI (Small Computer Systems Interface) - a standard for a controller bus
that connects disk drives and other devices to their controllers on a computer
bus. It is typically used in small systems.
SDLC (Synchronous Data Link Control) - IBM’s data link protocol used in
SNA networks.
SDU (Service Data Unit) - a unit of interface information whose identity is
preserved from one end of a layer connection to the other.
SEAL (Simple and Efficient Adaptation Layer) - also called AAL 5, this ATM
adaptation layer assumes that higher layer processes will provide error recov-
ery, thereby simplifying the SAR portion of the adaptation layer. Using this
AAL type packs all 48 bytes of an ATM cell information field with data. It also
assumes that only one message is crossing the UNI at a time. That is, multiple
end-users at one location cannot interleave messages on the same VC, but
must queue them for sequential transmission.
Segment - a single ATM link or group of interconnected ATM links of an ATM
connection.
Semipermanent Connection - a connection established via a service order or
via network management.
SGMP (Simple Gateway Management Protocol) - the predecessor to SNMP.
Shaping Descriptor - n ordered pairs of GCRA parameters (I,L) used to
define the negotiated traffic shape of an APP connection. The traffic shape
refers to the load-balancing of a network. In this context, load-balancing
means configuring the data flows to maximize the efficiency of the network.
SIR (Sustained Information Rate) - the long-term average data transmission
rate across the User-to-Network Interface.
SMDS (Switched Multimegabit Data Service) - a high-speed, datagram-
based, public data network service expected to be widely used by telephone
companies in their data networks.
SMTP (Simple Mail Transfer Protocol) - the Internet electronic mail protocol
used to transfer electronic mail between hosts.