B-48
Appendix B: Glossary
SHDSL Symmetric High Bit Rate DSL. SHDSL provides a guaranteed level of high
symmetric bandwidth and low interference with other telecommunications
services. SHDSL is a single-wire HDSL and is also called G.SHDSL. SHDSL
provides a higher transmission speed than HDSL2 or SDSL over longer dis-
tances. SHDSL is adaptive and has the capability to determine the highest
possible transmission speed when initialized.
Showtime For ADSL, the time after the training phase during which the router and the
DSLAM establish an ADSL connection and exchange physical-layer packets.
At this point, the two devices have not yet begun to exchange ATM cells or to
communicate at the Data Link Layer.
Single Mode Fiber Optical fiber that carries data using a single ray (or mode) of light. Single mode
fiber is used for long-distance signal transmission.
SIP Session Initial Protocol. An Application Layer control protocol that hosts use
to establish sessions for exchanging packets with multimedia data. SIP
enables such features as audio/videoconferencing, interactive gaming, and
call forwarding to be deployed over IP networks. It also enables service
providers to integrate basic IP telephony services with Web, e-mail, and chat
services. Although, in theory, SIP is a user-to-user protocol, in practice, SIP
relies on proxy and register servers, which help the user initiating a session
to find the intended remote user. For more detailed information on SIP, see
RFC 3261 (at http://www.ietf.org/rfc/rfc3261.txt)
SLA Service Level Agreement. A Frame Relay contract between the subscriber and
service provider that specifies the amount of bandwidth that a PVC is guaran-
teed (the CIR) when the network is congested. The SLA can also specify such
parameters as how far past the CIR traffic is allowed to burst when the
network is not congested (the EIR).
SMART Jack Self-Monitoring, Analysis, and Reporting Technology jack. An access port to
public carrier services. The smart jack is usually owned and maintained by
the service provider. See NIU.
SMB Small-to-Medium Business. Typically, a company with fewer than 250
employees.
SMDS Switched Multimegabit Data Service. A type of high-speed packet-switched
data communications service that operates at T1 or T3 speeds. SMDS uses the
SIP protocol to encapsulate packets into cells for transport.
SNA Systems Network Architecture. IBM’s proprietary mainframe-to-terminal
networking architecture. Developed and implemented in the 1970s, SNA maps
to all seven layers of the OSI model.
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