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Glossary: CCNA & General Networking Terms 


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Service Access Point. The point at which the services of an OSI layer are made available to the next higher layer. The SAP is named according to the layer providing the services, e.g., Transport services are provided at a Transport SAP (TSAP) at the top of the Transport Layer. [Source: RFC1208]
Scottish and Northern Ireland JANET User Group (SNIJUG)
The Scottish and Northern Ireland JANET User Group (SNIJUG) presents the views of the users on JANET and UKERNA services to the JISC Committee on Networking through the JANET National User Group. See also: JANET National User Group.
See: Synchronous Digital Hierarchy
The identifier used by an OSI entity to distinguish among multiple SAPs at which it provides services to the layer above. See port. [Source: RFC1208]
Serial Line IP (SLIP)
A protocol used to run IP over serial lines, such as telephone circuits or RS-232 cables, interconnecting two systems. SLIP is defined in RFC 1055. See also: Point-to-Point Protocol. [Source: RFC1392]
See: South East JANET Regional User Group
A provider of resources (e.g., file servers and name servers). See also: client, Domain Name System, Network File System. [Source: RFC1392]
Service Level Agreement
A contractual agreement between a service provider and a service user about the level of performance of the service, and indeed the provider. An example is the SLA between JISC and UKERNA for the JANET service.
Session Layer
The OSI layer that provides means for dialogue control between end systems. [Source: RFC1208]
Simple Gateway Management Protocol. The predecessor to SNMP. See SNMP. [Source: RFC1208]
See: Standardized Generalized Markup Language
Special Interest Group [Source: RFC1392]
signal-to-noise ratio
When used in reference to Usenet activity, signal-to-noise ratio describes the relation between amount of actual information in a discussion, compared to their quantity. More often than not, there's substantial activity in a newsgroup, but a very small number of those articles actually contain anything useful.
The three or four line message at the bottom of a piece of email or a Usenet article which identifies the sender. Large signatures (over five lines) are generally frowned upon. See also: Electronic Mail, Usenet. [Source: RFC1392]
Simple Mail Transfer Protocol (SMTP)
A protocol, defined in RFC 821, used to transfer electronic mail between computers, with extensions specified in many other RFCs. It is a server to server protocol, so other protocols are used to access the messages. See also: Electronic Mail, Post Office Protocol, RFC 822. [Source: RFC1392]
Simple Network Management Protocol (SNMP)
The Internet standard protocol developed to manage nodes on an IP network. The first version is defined in RFC 1157 (STD 15). SNMPv2 (version 2) is defined in too many RFCs to list. It is currently possible to manage wiring hubs, toasters, jukeboxes, etc. See also: Management Information Base. [Source: RFC1392]
Simple Object Access Protocol (SOAP)
A lightweight messaging framework designed for exchange of structured information in a distributed, decentralised environment, of which the provision of services over the World Wide Web is an example. SOAP is issued by the World Wide Web Consortium (W3C) XML Protocol Working Group.
See: Service Level Agreement
See: Serial Line IP
See: Switched Multimegabit Data Service
See: Structure of Management Information
See: Simple Mail Transfer Protocol
See: Systems Network Architecture
snail mail
A pejorative term referring to the U.S. postal service.
See: Scottish and Northern Ireland JANET User Group
See: Simple Network Management Protocol
See: Start of Authority Record
See: Start of Authority Record
See: Synchronous Optical NETwork
South East JANET Regional User Group (SERJUG)
The South East JANET Regional User Group (SERJUG) presents the views of the users on JANET and UKERNA services to the JISC Committee on Networking through the JANET National User Group. See also: JANET National User Group.
South West JANET Regional User Group (SWJRUG)
The South West JANET Regional User Group (SWJRUG) presents the views of the users on JANET and UKERNA services to the JISC Committee on Networking through the JANET National User Group. See also: JANET National User Group.
SPAG (1)
Standards Promotion and Application Group. A group of European OSI manufacturers which chooses option subsets and publishes these in a "Guide to the Use of Standards" (GUS). [Source: RFC1208]
SPAG (2)
Service Performance Advisory group, formerly MSC, a subgroup of JISC, responsible for development and trend analysis of JANET.
send an email message or news message to large numbers of email distribution lists or Usenet newsgroups, to the annoyance of most recipients, and contrary to Netiquette.
Spread Spectrum
Transmission of a signal using a carrier whose frequency spectrum varies over a wide range in a pseudo random manner. Detection and interception are difficult as transmissions appear similar to background noise. Reception is done by cross correlation of the wide band signal with a replica of the spectrum of the sender, synchronised between sender and receiver.

The two main methods are Frequency Hopping (FH or FHSS) and Direct Sequence (DS or DSSS). In FH the output frequencies hop around the desired range according to a pseudo random sequence of numbers fed into the frequency synthesiser. In DS a narrow band signal is spread into a wideband signal using a pseudo random chipping code sequence (a rather higher data rate bit sequence) which determines the spreading ratio. This is also known as Phase Shift Keying or phase modulation. For 802.11b Wireless Local Area Networks the modulation scheme is known as Complementary Code Keying (CCK) and for 802.11a it is known as Orthogonal Frequency Division Multiplexing (OFDM). The signal is despread at the receiver with the same code sequence, using the redundant information in the code sequence to aid error correction in case of interference. See also: 802.11, Wireless Local Area Network.

Structured Query Language. The international standard language for defining and accessing relational databases. [Source: RFC1208]
A Web proxy cache package.
Secure Shell, a package for eliciting secure (i.e. encrypted) interactive connections across a public network such as the Internet.
Secure Socket Layer protocol, a method for eliciting secure (i.e. encrypted) connections (e.g. to web services) across a public network such as the Internet. Now extended as Transport Layer Security (TLS).
JANET Spam-relay Tester And Notification system, for checking electronic mail servers for weaknesses which might promote spam.
Standardized Generalized Markup Language (SGML)
An international standard for the definition of system- independent, device-independent methods of representing text in electronic form. Different applications can be developed using Document Type Definitions (DTDs) e.g. HTML. See also: Hypertext Markup Language. [Source: RFC1983]
Start of Authority Record (SOA Record)
A DNS resource record type indicating which host is authorative for a particular domain. See also: Domain Name System.
A subseries of RFCs that specify Internet standards. The official list of Internet standards is in STD 1. See also: For Your Information, Request For Comments. [Source: RFC1392]
A type of transport service that allows its client to send data in a continuous stream. The transport service will guarantee that all data will be delivered to the other end in the same order as sent and without duplicates. See also: Transmission Control Protocol. [Source: MALAMUD]
Structure of Management Information (SMI)
The rules used to define the objects that can be accessed via a network management protocol. This protocol is defined in STD 16, RFC 1155. See also: Management Information Base. [Source: RFC1208]
stub network
A stub network only carries packets to and from local hosts. Even if it has paths to more than one other network, it does not carry traffic for other networks. See also: backbone, transit network. [Source: RFC1392]
A portion of a network, which may be a physically independent network segment, which shares a network address with other portions of the network and is distinguished by a subnet number. A subnet is to a network what a network is to an internet. See also: internet, network. [Source: FYI4]
subnet address
The subnet portion of an IP address. In a subnetted network, the host portion of an IP address is split into a subnet portion and a host portion using an address (subnet) mask. See also: address mask, IP address, network address, host address. [Source: RFC1392]
subnet mask
See: address mask
subnet number
See: subnet address


A collection of OSI end systems and intermediate systems under the control of a single administrative domain and utilizing a single network access protocol. Examples:- private X.25 networks, collection of bridged LANs. [Source: RFC1208]
Scottish University for industry.
To encapsulate a number of responses into one coherent, usable message. Often done on controlled mailing lists or active newsgroups, to help reduce bandwidth.
SuperJANET 4 is a very high performance backbone network based on optical fibre technology, offering up to 2.5 Gigabits/sec transmission rates in April 2001. This new network is needed to support advanced applications requiring a mixture of voice, data, image and video communications. The network is designed to use the most up-to-date communications technology - synchronous digital hierarchy (SDH) access - within the backbone between Core Points of Presence (C-PoPs) and to Backbone Access Routers (BARs) at the boundary of each regional MAN. A testbed network using DWDM is also in use.
South West England Regional Network.
Switched Multimegabit Data Service (SMDS)
An emerging high-speed datagram-based public data network service developed by Bellcore and expected to be widely used by telephone companies as the basis for their data networks. See also: Metropolitan Area Network. [Source: RFC1208]
See: South West JANET Regional User Group
Data communications in which transmissions are sent at a fixed rate, with the sending and receiving devices synchronized.
Synchronous Digital Hierarchy (SDH)
The European standard for high-speed data communications over fiber-optic media. The transmission rates range from 155.52Mbps to 2.5Gbps. [Source: RFC1983]
Synchronous Optical NETwork (SONET)
SONET is an international standard for high-speed data communications over fiber-optic media. The transmission rates range from 51.84Mbps to 2.5Gbps. [Source: RFC1983]
Systems Network Architecture (SNA)
A proprietary networking architecture used by IBM and IBM- compatible mainframe computers. [Source: NNSC]


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