SaaS
Short for Software as a Service, SaaS is software that is provided as a service instead of a product. Users access the software program by visiting a website and instead of paying a single payment for the program pays a monthly service fee or pays by the total time the software is used. A good example of a SaaS is Microsoft Office 365.
Samba
Samba is an open source program that allows end-users utilizing SMB/CIFS clients to access files, printers and other commonly shared network resources. Samba is commonly used on Linux computers, allowing the network shares to be accessed by other computers, such as those running Microsoft Windows.
SAN
A Storage Area Network (SAN) is a sub-network of storage devices that are shared with one another over a high-speed network connection. The purpose of a Storage Area Network is to allow all designated users on the network to access multiple storage devices, not only the storage devices installed within their computer. Once a SAN is constructed, and all storage devices are shared within the SAN, it is then connected to the servers that are accessed by network users.
Thus, one of the primary benefits of a SAN is that it significantly decreases the amount of storage required on a network server in order for multiple users to have the ability to access the same information.
With multiple users' being able to access the actual storage devices, businesses can use the extra network capacity to run more powerful software applications and increase the efficiency of the production of the network. SAN's are also commonly used for storage redundancy purposes in case of unexpected natural disaster and loss of data. Large back-up disk arrays can be stored on an off-site location and shared on a SAN where users can access them remotely.
SAP
1. Short for Service Advertising Protocol, SAP is used by servers to inform clients of availability on the network in a Novell NetWare environment. SAP messages are broadcasted every 60 seconds, if a SAP packet is not received for three minutes, that server is presumed down.
2. An abbreviation for Session Announcement Protocol, SAP provides session setup details to users engaged in a multicast session. It often utilizes Session Description Protocol (SDP) as a format for Real-time Transport Protocol (RTP) sessions.
SATAN
SATAN, which stands for Security Administrator Tool for Analyzing Networks, is a set of testing and reporting tools used to deliver information about networked hosts. It has a web interface, tabulated results, and if a security hole is found it provides context-sensitive tutorials about how to proceed.
The majority of SATAN is written in Perl; requiring a web browser to display the user interface. It was first released in 1995 by authors are Dan Farmer and Wietse Venema and the logo for the software was designed by Neil Gaiman. Though somewhat antiquated, SATAN is still relevant and useful in many situations.
SDLC
1. Short for Synchronous Data Link Control, SDLC is a data transmission protocol developed by IBM in the 1970's that is used by networks utilizing System Network Architecture (SNA.)
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2. Alternatively referred to as the waterfall model, SDLC is short for Systems Development Life Cycle and is a series of steps taken from the beginning to the end of a development.
SDSL
Short for Symmetric DSL, SDSL is similar to HDSL but has a transfer speed of 1.544Mbps for both the upstream and downstream data transmissions, and is capable of operating at a range of up to 10,000 feet.
SDU
Short for Service Data Unit, SDU is a piece of information that is passed by the layer above to the current layer for transmission using the service of that layer.
IPX/SPX
Short for Internet Packet eXchange/Sequential Packet eXchange, IPX/SPX is a local-area network communications protocol developed by Novell that exchanges information between network clients, applications, and network peripherals. This Protocol cannot be used over the Internet.
Serial
Serial is a term used to describe the process of transmitting information one bit at a time, or sequentially. The common opposite of this is parallel transmission.
Server
In a technical sense, a server is an instance of a computer program that accepts and responds to requests made by another program; known as a client. Less formally, any device that runs server software could be considered a server as well. Servers are used to manage network resources. For example, a user may setup a server to control access to a network, send/receive e-mail, manage print jobs, or host a website.
Some servers are committed to a specific task; often referred to as dedicated. As a result, there are a number of dedicated server categories, like print servers, file servers, network servers and database servers.
Because they are commonly used to deliver a services that are required constantly, most servers are never turned off. Consequently, when servers fail, they cause the network users or company many problems. To alleviate these issues, servers are commonly high-end computers setup to be fault tolerant.
Server farm
Sometimes referred to as just a farm, server farms are collections of computers (at least 10) working together or in conjunction with one another. One of the largest, if not THE largest server farms, is maintained by the popular search engine Google. At last report Google had over 10,000 computers in its server farm. The picture shows an example of a server farm with several hundred 1U rack mountable computers.
OSI
1. Short for Open System Interconnection, OSI is a network model developed by ISO in1978 where peer-to-peer communications are divided into seven layers. Each layer performs a specific task or tasks, and builds upon the preceding layer until the communications are complete. Below are the purposes of each of the seven layers.
1 - Physical layer - responsible for the electrical, mechanical, and timing across the link.
2 - Data link layer (also known as the link layer) - responsible for transmitting data across a link.
3 - Network layer - responsible for routing information through the network and allowing systems to communicate.
4 - Transport layer - responsible for transferring information between endpoints on the network and deals with errors such as lost or duplicate packets.
5 - Session layer - responsible for managing a session between two applications.
6 - Presentation layer - responsible for the data formatting and display, allowing for compatibility.
7 - Application layer - responsible for user interaction. An example of an OSI application is the
FTAM.
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2. Short for Open-Source Initiative, OSI is a non-profit corporation dedicated to managing and promoting Open Source. Their page can be found at http://www.opensource.org/.
SFTP
Short for Secure File Transfer Protocol, SFTP is a version of FTP that encrypts any commands and data transfers, helping keep your passwords secure and your session private. Because SFTP is a different protocol than FTP, in order for you to establish a SFTP connection, you must be connecting to a computer that supports it. Using SFTP to connect to an FTP server will not work.
Shared directory
Alternatively referred to as a share or network share, a shared directory is a directory or folderthat is made accessible to multiple users or groups on a network. This the most common method of accessing and sharing information on a local area network. Any file or document contained within the directory is often referred to as a shared document.
STP cable
Short for Shielded Twisted-Pair cable, STP is a cable originally developed by IBMfor Token Ring that consists of two individual wires wrapped in a foil shielding to help provide a more reliable data communication.
Short-haul
When referring to data communications, short-haul refers to a communication that only needs to travel a very short distance to reach its final destination.
Sign off
1. Alternatively referred to as log, log off, log out, disconnecting, and sign out, sign offis a term used to describe the process of disconnecting from a network or what occurs when your connection is lost. For example, a user using a modem to connect to the Internet may sign off from the Internet to free up the phone line but still be able to use the computer.
• See the Windows logoff command page for additional information about this command.
• Information about the Linux command can be found on our logout page.
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2. The term sign off is also used to describe the process of disconnecting from a network service such as IRC.
3. When in a Windows FTP session the disconnect command will disconnect from the current session. See the how to use ftp help page for information about disconnect and other FTP commands.
4. Finally, sign off is also a message commonly displayed when a user disconnects from a chat service. Most sign offs are witty quotes, sayings, or advertisements created by the user.
Sign on
Alternatively referred to as log on, sign in, or connecting, sign on is the process of connecting to a network or a software program that utilizes a network identification. The sign on process requires that the user specify the username and password and, in some cases, additional network or server information.
Single-mode fiber
A single-mode fiber is a fiber optic cable that transmits its signal over a single light pulse. Single-mode fiber is used over long distances; however, the cable and equipment used for single-mode fiber is often much more expensive when compared to multi-mode fiber.
Hostname
Alternatively referred to as a computer name or sitename, a hostname is the name of the computer you're currently logged into or visiting. Below is an example of a hostname, that is assigned to a computer connecting to the Internet using Comcast
c-61-123-45-67.hsd1.co.comcast.net
As can be seen in the above example, this hostname has the IP address (61.123.45.67), "CO" for Colorado, and comcast.net, which is the ISP hosting the customer.
When referring to an Internet web page or location a hostname is more often referred to as a domain name. Hostname is also a command that can be run on some versions of Microsoft Windows and Linux.
SLA
1. Short for Service Level Agreement, SLA is the measurable level of service a company guarantees to offer the user. Many ISPs and web hosts provide their customers with an SLA that outlines the measurable expectations the user can expect. Below are some examples of what may be included in an SLA.
• The percentage of uptime, e.g. 99.9% guaranteed uptime.
• The guaranteed response time from a help desk, e.g. a response time of 15 minutes or less.
• The overall expected performance or benchmark of a connection or product.
• The expected penalty or credit if the SLA is not met.
2. Short for Sealed Lead Acid, SLA most economical for larger power applications where weight is of lesser concern.
SLIP
Short for Serial Line Internet Protocol, SLIP is an Internet protocol that allows users to gain Internet access using a computer modem. Today, SLIP is not used as frequently as its successor, Point-to-Point Protocol (PPP), which provides enhancederror detection and automatic configuration.
Smart terminal
Alternatively referred to as an intelligent terminal, a smart terminal contains all the necessary hardware to function by itself.
SMS
1. Short for Short Message Service, SMS is a widely accepted wireless service that allows individuals to send short text messages with wireless devices such as mobile phones and pagers. See the text message definition for additional information about this term.
2. Short for Systems Management Server, SMS are tools developed by Microsoft that help administrators perform diagnostics, maintain, and create an inventory of computers that are connected to the Network and are running SMS. See our SCCM definition for full information on this term.
3. Short for Storage Management Subsystem, SMS was developed by IBM to help manage storage resources. With SMS a user is capable of managing backup, data security, data migration, data recovery, and data deletion.
SMTP
Short for Simple Mail Transfer Protocol, SMTP is an Internet standard for the sending of e-mail messages over port 25. While it is mostly used for transfer from one mail server to another, some client mail applications use SMTP for relaying messages; whereas receiving happens via POP or IMAP.
SNA
Short for System Network Architecture, SNA was introduced in 1974 and is a communications format developed by IBM, used on local-area networks (LANs) to allow multiple systems access to centralized data.
Sneakernet
Alternatively referred to as a Floppy-Net, Shoenet, TennisNet, and Walknet. A sneakernet is slang used to describe the transfer of data through physical means, mainly by walking diskettes or storage tapes from one location to another instead of using a real network.
Sniffing
A packet sniffer is a utility that has been used since the original release of Ethernet. Packet sniffing allows individuals to capture data as it is transmitted over a network. Packet sniffer programs are commonly used by network professionals to help diagnose network issues and are also used by malicious users to capture unencrypted data like passwords and usernames in network traffic. Once this information is captured, the user can then gain access to the system or network.
If you want to keep information confidential or are concerned about packet sniffing, it is advised that you work on encrypted protocols and encrypt all sensitive data, such as e-mails, being sent over the Internet or network. A great encryption program is PGP, users who are using Telnet should consider using SSH instead.
SNMP
Short for Simple Network Management Protocol, SNMP was first introduced in1988 and is a query, command, and response protocol to examine and change configuration parameters of LAN and WAN connected repeaters, bridges, routers,switches, and other devices connected to a network.
SNMP is currently available in three versions:
• SNMP version 1 (SNMPv1): SNMP v1 is the first implementation of SNMP and is described in RFC 1157. SNMP v1 operates within the specifications of SMI and has support for such protocols as CLNS, DDP, IP, IPX, and UDP.
• SNMP version 2 (SNMPv2): SNMP v2, more appropriately known as SNMP v2c (as described in RFC 1901), was first introduced in RFC 1441 and includes improved support increasing efficiency and error handling.
• SNMP version 3 (SNMPv3): SNMP v3 was introduced in RFC 3410 and improves in security and privacy.
Socks
Socks is a protocol for handling client to server requests and communications made through a proxy server.
SPI
1. Short for Stateful Packet Inspection, SPI, also known as stateful firewall, is a feature found in networking devices, like routers, that keeps track of the state of network connections. Keeping track of a connection's state allows the device to better filter unwanted or harmful network traffic.
2. Short for Serial Peripheral Interface, SPI bus is a serial data link coined by Motorola. It is a de facto standard, used with SD cards and sensors.
3. Short for System Packet Interface, SPI is set of interoperability agreements that specify packet operations on ethernet applications and optical networking.
Spoof
In general, the term spoof refers to hacking or deception that imitates another person, software program, hardware device, or computer, with the intentions of bypassing security measures. One of the most commonly known spoofing is IP spoofing.
IP spoofing
A method of bypassing security measures on a network or a method of gaining access to a network by imitating a different IP address. Some security systems have a method of helping to identifying a user by his or her IP address or IP address range. If the attacker spoofs their IP address to match this criteria it may help bypass security measures. This technique is also used to deceive a web page, poll, or other Internet contest into thinking the user is someone else allowing him or her to get more hits or falsely increase a votes rank.
E-mail or address spoofing
Process of faking a senders e-mail address. This form of spoofing is used to fool the recipient of the e-mail into thinking someone else sent them the message. This is commonly used to bypass spam filters or to trick the user into thinking the e-mail is safe when in reality it contains an attachment that is infected with a virus or spam.
• Getting bounce back e-mails from addresses I don't know.
Phone number spoofing
Anyone can fake the number or area code of from where they are calling. This type of spoofing is done by telemarkers to hide their true identity and by hackers to gain access to unprotected phone voicemail messages.
Web page spoof
A fake web page or spoof on another commonly visited page. For example a malicious user may create a spoof page of Microsoft's, eBay, PayPal or Google's home page that looks identical but is hosted on a different server. These pages are commonly used inphishing e-mails to extract information from the user such as usernames and passwords or to send malicious files to them. Web page spoofing may also be done through IP cloaking.
SSAP
Short for Source Service Access Point, SSAP is the individual address for access into the upper layers of the network protocol stack.
SSH
Short for Secure Shell, SSH (developed by SSH Communications Security Ltd.) is a secure protocol for remote logins. Using an SSH client, a user can connect to a server to transfer information in a more secure manner than other methods, such as telnet. The image to the right is an example of how an SSH session, which uses a command line interface, may look .
SSHD
1.A daemon that implements the Secure Shell protocol, sshd acts as a server; providing encrypted communication between two hosts and is typically used in conjunction with the client software ssh. The sshd starts when the system boots, then listens for connections. It forks a new daemon for each established connection and the daemon handles the exchange of keys, encryption, authentication, command execution, and data exchange.
SSID
Short for Service Set IDentifier, SSID is a 32alphanumeric identification given to devices on awireless network. A device wanting to connect to a wireless network with a SSID enabled must have the same SSID in order to communicate. When connecting to a home network you may see multiple SSIDs from your neighbors wireless routers.
A BSSID, short for Basic Service Set Identifier unlike the SSID is unique to the access point and does not transfer between multiple access points.
SSTP
Short for Secure Socket Tunneling Protocol, SSTP is a type of VPN tunnel that utilizes an SSL 3.0 channel to send PPP or L2TP traffic. SSL allows for transmission and data encryption, as well as traffic integrity checking. Due to this, SSTP can pass through most firewalls and proxy servers by using the SSL channel over TCP port 443.
SSTP is available to use in a Windows environment (since Windows Vista SP1), in RouterOS and in SEIL (since firmware version 3.50). SSTP can be used with Winlogon or smart card authentication, remote access policies and the Windows VPN client because of being integrated with the RRAS architecture. As with other IP-over-TCP tunneling protocols, SSTP only performs well if there is sufficient bandwidth on the un-tunneled network link. If enough bandwidth is not available, the tunneled TCP timers will possibly expire, causing a large decrease in SSTP performance.
Stack
1. In computer networking, a stack is a frequently used method of describing TCP/IP.
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2. In computer programming, a stack is a special data structure that removes items in the reverse order from which they were added.
3. A stack may also refer to a collection of computers that are stacked upon each other or a series of caseless computer components a computer farm.
4. In some video games, multiple players join to defeat a creature, creating a party or raid. When fighting some creatures, it is necessary to stack together. When players stack, they are moving to a common spot, standing in a tight group to create a smaller target for the creature to hit or to share incoming damage.
Star Topology
Alternatively referred to as a star network, star topology is one of the most common network setups. In this arrangement, every node connects to a central hub, switch or computer; the hub acting as a server and the peripheral devices as clients. A major disadvantage of this network topology is that if the central hub fails, all of the connected devices are disconnected. The visual example shows how this setup gets its name as it is shaped very much like a star.
Static allocation
1. When referring to computer memory, static allocation is a section of memory that has been set aside for an application when it is first loaded. This section of memory is kept to be only used with that application, and is made available again once the program is closed.
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2. When referring to a network or network device, static allocation or a static IP address is the assignment of a fixed address. For example, assigning a computer a fixed IP address of 192.168.123.114 never changes unless done so manually. This address is designated by the user and not the network.
Assigning a computer a static IP address that is not compatible with the netmask or with your network configuration will not allow the computer to communicate properly with the network.
STM
Short for Synchronous Transport Module, STM is a standard for data transmissions over SONET.
Store and forward
A relay system that stores all outgoing messages in an intermediate location until the receiving end requests them. E-mail is a good example of store and forward; messages are stored on a server and can be retrieved at any time.
STP
1. Short for Spanning Tree Protocol, STP is a networking protocol designed to create a single path over a network, preventing any loops from occurring on a network even if there are multiple paths to the same destination.
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2. Short for Shielded Twisted Pair, see the STP cable definition for further information.
3. Short for Software Test Plan, STP is a plan developed as a guideline to test computer software.
STP cable
Short for Shielded Twisted-Pair cable, STP is a cable originally developed by IBM for Token Ring that consists of two individual wires wrapped in a foil shielding to help provide a more reliable data communication.
Straight through
A network cabling that connects a computer to a network device. For example, straight through cables connect a computer to a network hub, network switch, and network routers. These are the standard network cables you would find at the store unless labeled as a cross-over cable.
Streaming content
Streaming content is an audio or video file on the Internet that is partially downloaded and then played as the remainder of the file is being downloaded. More specifically, live streaming is the method of constantly sending and receiving content over the Internet. Streaming content or streaming media are beneficial in that they significantly reduce, if not eliminate, wait times for online content; usually depending on the speed of their connection.
Online radio stations and YouTube videos are both good examples of streaming content.
The first live streaming was done by the band Severe Tire Damage on June 24, 1993. The event was seen live in Australia and other locations over the Internet. While streaming audio is not quite as bandwidth-intensive, streaming video does require more bandwidth to achieve. Users wanting to view streaming movies should have an Internet speed of at least 2.5 Megabits (Mbit) per second. For high definition content, 10 Mbit/sec is recommended.
STS
Short for Synchronous Transport Signal, STS is a standard for data transmissions over SONET.
Subdomain
Alternatively referred to as a child domain, a subdomain is a domain name with a prefix. For example, "www.computerhope.com" is the URL for Computer Hope and "www" is the subdomain. If we wanted to have a FQDN for a sub page or another external domain such as our help section, we would create "help.computerhope.com" as a subdomain.
Subnet Mask
Short for subnetwork mask, a subnet mask,subnet, or subnetting is a method of dividing a network of IP addresses into groups. Subnetting allows each computer or networking device in its own subnet to communicate with each other and still allow communication between subnets by routing the traffic through the network router. By dividing a network into subnets, it can improve network security and keep overall network traffic balanced. A common example of a subnet mask for class C IP addresses is 255.255.255.0 and is the default subnet mask for many computers and network routers.
Switch
1. A piece of a physical circuitry component that governs signal flow. Having a switch or toggle switch allows a connection to be opened or closed. When opened the switch allows a signal or power to flow through the connection. When closed the switch stops the flow and breaks the circuit connection.
2. On a network, a switch is a hardware device thatfilters and forwards packets through the network, but often not capable of much more. The first network device that was added to the Internet was a switch called the IMP, which helped send the first message on October 29, 1969. A network switch is more advanced than a hub but not as advanced as a router. The picture shows an example of a NETGEAR 5 port switch.
SYN
Short for synchronize, SYN is a TCP packet sent to another computer requesting that a connection be established between them. If the SYN is received by the second machine, an SYN/ACK is sent back to the address requested by the SYN. Lastly, if the original computer receives the SYN/ACK, a final ACK is sent.
3. A button or lever that can be switched to turn a device on or off.
4. When referring to the switches command, this command is loaded through config.sysand allows you to add and remove various functions of MS-DOS. See the switches command for further information about this command.
5. When referring to another command, a switch is an available option that can be used with the command. For example, the command: "fdisk" can be used with the /MBR switch, using "FDISK /MBR" would allow the user to recreate the master boot record and not just run the fdisk program.
6. Switches is also a config.sys command that allows the user to add and remove features of early versions of MS-DOS and Windows. See the switches page for further information on this command.
SYN Attack
Alternatively referred to as an SYN flood, an SYN attack is a Denial of Service (DOS)attack on a computer or network that floods the network with spoofed SYN packets or packets that contain an address that never responds to the SYN/ACK requests. Essentially, the connection queues fill up with bad connections and service is denied to legitimate users.
Syslog
Short for Systems Log, syslog was originally developed for Unix based systems to collect error, warning, or other system messages sent to the central location through UDP port 514.
Today, syslog is available the majority of operating systems, as well as hardware devices such as network switches and routers.
SYSOP
Short for SYStem OPerator, the term SYSOP is used to describe an individual in charge of a multi-user system, such as a BBS. Today, this term has been replaced by admin, Moderator, Root, or System Administrator.
Short for Software as a Service, SaaS is software that is provided as a service instead of a product. Users access the software program by visiting a website and instead of paying a single payment for the program pays a monthly service fee or pays by the total time the software is used. A good example of a SaaS is Microsoft Office 365.
Samba
Samba is an open source program that allows end-users utilizing SMB/CIFS clients to access files, printers and other commonly shared network resources. Samba is commonly used on Linux computers, allowing the network shares to be accessed by other computers, such as those running Microsoft Windows.
SAN
A Storage Area Network (SAN) is a sub-network of storage devices that are shared with one another over a high-speed network connection. The purpose of a Storage Area Network is to allow all designated users on the network to access multiple storage devices, not only the storage devices installed within their computer. Once a SAN is constructed, and all storage devices are shared within the SAN, it is then connected to the servers that are accessed by network users.
Thus, one of the primary benefits of a SAN is that it significantly decreases the amount of storage required on a network server in order for multiple users to have the ability to access the same information.
With multiple users' being able to access the actual storage devices, businesses can use the extra network capacity to run more powerful software applications and increase the efficiency of the production of the network. SAN's are also commonly used for storage redundancy purposes in case of unexpected natural disaster and loss of data. Large back-up disk arrays can be stored on an off-site location and shared on a SAN where users can access them remotely.
SAP
1. Short for Service Advertising Protocol, SAP is used by servers to inform clients of availability on the network in a Novell NetWare environment. SAP messages are broadcasted every 60 seconds, if a SAP packet is not received for three minutes, that server is presumed down.
2. An abbreviation for Session Announcement Protocol, SAP provides session setup details to users engaged in a multicast session. It often utilizes Session Description Protocol (SDP) as a format for Real-time Transport Protocol (RTP) sessions.
SATAN
SATAN, which stands for Security Administrator Tool for Analyzing Networks, is a set of testing and reporting tools used to deliver information about networked hosts. It has a web interface, tabulated results, and if a security hole is found it provides context-sensitive tutorials about how to proceed.
The majority of SATAN is written in Perl; requiring a web browser to display the user interface. It was first released in 1995 by authors are Dan Farmer and Wietse Venema and the logo for the software was designed by Neil Gaiman. Though somewhat antiquated, SATAN is still relevant and useful in many situations.
SDLC
1. Short for Synchronous Data Link Control, SDLC is a data transmission protocol developed by IBM in the 1970's that is used by networks utilizing System Network Architecture (SNA.)
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2. Alternatively referred to as the waterfall model, SDLC is short for Systems Development Life Cycle and is a series of steps taken from the beginning to the end of a development.
SDSL
Short for Symmetric DSL, SDSL is similar to HDSL but has a transfer speed of 1.544Mbps for both the upstream and downstream data transmissions, and is capable of operating at a range of up to 10,000 feet.
SDU
Short for Service Data Unit, SDU is a piece of information that is passed by the layer above to the current layer for transmission using the service of that layer.
IPX/SPX
Short for Internet Packet eXchange/Sequential Packet eXchange, IPX/SPX is a local-area network communications protocol developed by Novell that exchanges information between network clients, applications, and network peripherals. This Protocol cannot be used over the Internet.
Serial
Serial is a term used to describe the process of transmitting information one bit at a time, or sequentially. The common opposite of this is parallel transmission.
Server
In a technical sense, a server is an instance of a computer program that accepts and responds to requests made by another program; known as a client. Less formally, any device that runs server software could be considered a server as well. Servers are used to manage network resources. For example, a user may setup a server to control access to a network, send/receive e-mail, manage print jobs, or host a website.
Some servers are committed to a specific task; often referred to as dedicated. As a result, there are a number of dedicated server categories, like print servers, file servers, network servers and database servers.
Because they are commonly used to deliver a services that are required constantly, most servers are never turned off. Consequently, when servers fail, they cause the network users or company many problems. To alleviate these issues, servers are commonly high-end computers setup to be fault tolerant.
Server farm
Sometimes referred to as just a farm, server farms are collections of computers (at least 10) working together or in conjunction with one another. One of the largest, if not THE largest server farms, is maintained by the popular search engine Google. At last report Google had over 10,000 computers in its server farm. The picture shows an example of a server farm with several hundred 1U rack mountable computers.
OSI
1. Short for Open System Interconnection, OSI is a network model developed by ISO in1978 where peer-to-peer communications are divided into seven layers. Each layer performs a specific task or tasks, and builds upon the preceding layer until the communications are complete. Below are the purposes of each of the seven layers.
1 - Physical layer - responsible for the electrical, mechanical, and timing across the link.
2 - Data link layer (also known as the link layer) - responsible for transmitting data across a link.
3 - Network layer - responsible for routing information through the network and allowing systems to communicate.
4 - Transport layer - responsible for transferring information between endpoints on the network and deals with errors such as lost or duplicate packets.
5 - Session layer - responsible for managing a session between two applications.
6 - Presentation layer - responsible for the data formatting and display, allowing for compatibility.
7 - Application layer - responsible for user interaction. An example of an OSI application is the
FTAM.
• Computer network and network card help and support
2. Short for Open-Source Initiative, OSI is a non-profit corporation dedicated to managing and promoting Open Source. Their page can be found at http://www.opensource.org/.
SFTP
Short for Secure File Transfer Protocol, SFTP is a version of FTP that encrypts any commands and data transfers, helping keep your passwords secure and your session private. Because SFTP is a different protocol than FTP, in order for you to establish a SFTP connection, you must be connecting to a computer that supports it. Using SFTP to connect to an FTP server will not work.
Shared directory
Alternatively referred to as a share or network share, a shared directory is a directory or folderthat is made accessible to multiple users or groups on a network. This the most common method of accessing and sharing information on a local area network. Any file or document contained within the directory is often referred to as a shared document.
STP cable
Short for Shielded Twisted-Pair cable, STP is a cable originally developed by IBMfor Token Ring that consists of two individual wires wrapped in a foil shielding to help provide a more reliable data communication.
Short-haul
When referring to data communications, short-haul refers to a communication that only needs to travel a very short distance to reach its final destination.
Sign off
1. Alternatively referred to as log, log off, log out, disconnecting, and sign out, sign offis a term used to describe the process of disconnecting from a network or what occurs when your connection is lost. For example, a user using a modem to connect to the Internet may sign off from the Internet to free up the phone line but still be able to use the computer.
• See the Windows logoff command page for additional information about this command.
• Information about the Linux command can be found on our logout page.
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2. The term sign off is also used to describe the process of disconnecting from a network service such as IRC.
3. When in a Windows FTP session the disconnect command will disconnect from the current session. See the how to use ftp help page for information about disconnect and other FTP commands.
4. Finally, sign off is also a message commonly displayed when a user disconnects from a chat service. Most sign offs are witty quotes, sayings, or advertisements created by the user.
Sign on
Alternatively referred to as log on, sign in, or connecting, sign on is the process of connecting to a network or a software program that utilizes a network identification. The sign on process requires that the user specify the username and password and, in some cases, additional network or server information.
Single-mode fiber
A single-mode fiber is a fiber optic cable that transmits its signal over a single light pulse. Single-mode fiber is used over long distances; however, the cable and equipment used for single-mode fiber is often much more expensive when compared to multi-mode fiber.
Hostname
Alternatively referred to as a computer name or sitename, a hostname is the name of the computer you're currently logged into or visiting. Below is an example of a hostname, that is assigned to a computer connecting to the Internet using Comcast
c-61-123-45-67.hsd1.co.comcast.net
As can be seen in the above example, this hostname has the IP address (61.123.45.67), "CO" for Colorado, and comcast.net, which is the ISP hosting the customer.
When referring to an Internet web page or location a hostname is more often referred to as a domain name. Hostname is also a command that can be run on some versions of Microsoft Windows and Linux.
SLA
1. Short for Service Level Agreement, SLA is the measurable level of service a company guarantees to offer the user. Many ISPs and web hosts provide their customers with an SLA that outlines the measurable expectations the user can expect. Below are some examples of what may be included in an SLA.
• The percentage of uptime, e.g. 99.9% guaranteed uptime.
• The guaranteed response time from a help desk, e.g. a response time of 15 minutes or less.
• The overall expected performance or benchmark of a connection or product.
• The expected penalty or credit if the SLA is not met.
2. Short for Sealed Lead Acid, SLA most economical for larger power applications where weight is of lesser concern.
SLIP
Short for Serial Line Internet Protocol, SLIP is an Internet protocol that allows users to gain Internet access using a computer modem. Today, SLIP is not used as frequently as its successor, Point-to-Point Protocol (PPP), which provides enhancederror detection and automatic configuration.
Smart terminal
Alternatively referred to as an intelligent terminal, a smart terminal contains all the necessary hardware to function by itself.
SMS
1. Short for Short Message Service, SMS is a widely accepted wireless service that allows individuals to send short text messages with wireless devices such as mobile phones and pagers. See the text message definition for additional information about this term.
2. Short for Systems Management Server, SMS are tools developed by Microsoft that help administrators perform diagnostics, maintain, and create an inventory of computers that are connected to the Network and are running SMS. See our SCCM definition for full information on this term.
3. Short for Storage Management Subsystem, SMS was developed by IBM to help manage storage resources. With SMS a user is capable of managing backup, data security, data migration, data recovery, and data deletion.
SMTP
Short for Simple Mail Transfer Protocol, SMTP is an Internet standard for the sending of e-mail messages over port 25. While it is mostly used for transfer from one mail server to another, some client mail applications use SMTP for relaying messages; whereas receiving happens via POP or IMAP.
SNA
Short for System Network Architecture, SNA was introduced in 1974 and is a communications format developed by IBM, used on local-area networks (LANs) to allow multiple systems access to centralized data.
Sneakernet
Alternatively referred to as a Floppy-Net, Shoenet, TennisNet, and Walknet. A sneakernet is slang used to describe the transfer of data through physical means, mainly by walking diskettes or storage tapes from one location to another instead of using a real network.
Sniffing
A packet sniffer is a utility that has been used since the original release of Ethernet. Packet sniffing allows individuals to capture data as it is transmitted over a network. Packet sniffer programs are commonly used by network professionals to help diagnose network issues and are also used by malicious users to capture unencrypted data like passwords and usernames in network traffic. Once this information is captured, the user can then gain access to the system or network.
If you want to keep information confidential or are concerned about packet sniffing, it is advised that you work on encrypted protocols and encrypt all sensitive data, such as e-mails, being sent over the Internet or network. A great encryption program is PGP, users who are using Telnet should consider using SSH instead.
SNMP
Short for Simple Network Management Protocol, SNMP was first introduced in1988 and is a query, command, and response protocol to examine and change configuration parameters of LAN and WAN connected repeaters, bridges, routers,switches, and other devices connected to a network.
SNMP is currently available in three versions:
• SNMP version 1 (SNMPv1): SNMP v1 is the first implementation of SNMP and is described in RFC 1157. SNMP v1 operates within the specifications of SMI and has support for such protocols as CLNS, DDP, IP, IPX, and UDP.
• SNMP version 2 (SNMPv2): SNMP v2, more appropriately known as SNMP v2c (as described in RFC 1901), was first introduced in RFC 1441 and includes improved support increasing efficiency and error handling.
• SNMP version 3 (SNMPv3): SNMP v3 was introduced in RFC 3410 and improves in security and privacy.
Socks
Socks is a protocol for handling client to server requests and communications made through a proxy server.
SPI
1. Short for Stateful Packet Inspection, SPI, also known as stateful firewall, is a feature found in networking devices, like routers, that keeps track of the state of network connections. Keeping track of a connection's state allows the device to better filter unwanted or harmful network traffic.
2. Short for Serial Peripheral Interface, SPI bus is a serial data link coined by Motorola. It is a de facto standard, used with SD cards and sensors.
3. Short for System Packet Interface, SPI is set of interoperability agreements that specify packet operations on ethernet applications and optical networking.
Spoof
In general, the term spoof refers to hacking or deception that imitates another person, software program, hardware device, or computer, with the intentions of bypassing security measures. One of the most commonly known spoofing is IP spoofing.
IP spoofing
A method of bypassing security measures on a network or a method of gaining access to a network by imitating a different IP address. Some security systems have a method of helping to identifying a user by his or her IP address or IP address range. If the attacker spoofs their IP address to match this criteria it may help bypass security measures. This technique is also used to deceive a web page, poll, or other Internet contest into thinking the user is someone else allowing him or her to get more hits or falsely increase a votes rank.
E-mail or address spoofing
Process of faking a senders e-mail address. This form of spoofing is used to fool the recipient of the e-mail into thinking someone else sent them the message. This is commonly used to bypass spam filters or to trick the user into thinking the e-mail is safe when in reality it contains an attachment that is infected with a virus or spam.
• Getting bounce back e-mails from addresses I don't know.
Phone number spoofing
Anyone can fake the number or area code of from where they are calling. This type of spoofing is done by telemarkers to hide their true identity and by hackers to gain access to unprotected phone voicemail messages.
Web page spoof
A fake web page or spoof on another commonly visited page. For example a malicious user may create a spoof page of Microsoft's, eBay, PayPal or Google's home page that looks identical but is hosted on a different server. These pages are commonly used inphishing e-mails to extract information from the user such as usernames and passwords or to send malicious files to them. Web page spoofing may also be done through IP cloaking.
SSAP
Short for Source Service Access Point, SSAP is the individual address for access into the upper layers of the network protocol stack.
SSH
Short for Secure Shell, SSH (developed by SSH Communications Security Ltd.) is a secure protocol for remote logins. Using an SSH client, a user can connect to a server to transfer information in a more secure manner than other methods, such as telnet. The image to the right is an example of how an SSH session, which uses a command line interface, may look .
SSHD
1.A daemon that implements the Secure Shell protocol, sshd acts as a server; providing encrypted communication between two hosts and is typically used in conjunction with the client software ssh. The sshd starts when the system boots, then listens for connections. It forks a new daemon for each established connection and the daemon handles the exchange of keys, encryption, authentication, command execution, and data exchange.
SSID
Short for Service Set IDentifier, SSID is a 32alphanumeric identification given to devices on awireless network. A device wanting to connect to a wireless network with a SSID enabled must have the same SSID in order to communicate. When connecting to a home network you may see multiple SSIDs from your neighbors wireless routers.
A BSSID, short for Basic Service Set Identifier unlike the SSID is unique to the access point and does not transfer between multiple access points.
SSTP
Short for Secure Socket Tunneling Protocol, SSTP is a type of VPN tunnel that utilizes an SSL 3.0 channel to send PPP or L2TP traffic. SSL allows for transmission and data encryption, as well as traffic integrity checking. Due to this, SSTP can pass through most firewalls and proxy servers by using the SSL channel over TCP port 443.
SSTP is available to use in a Windows environment (since Windows Vista SP1), in RouterOS and in SEIL (since firmware version 3.50). SSTP can be used with Winlogon or smart card authentication, remote access policies and the Windows VPN client because of being integrated with the RRAS architecture. As with other IP-over-TCP tunneling protocols, SSTP only performs well if there is sufficient bandwidth on the un-tunneled network link. If enough bandwidth is not available, the tunneled TCP timers will possibly expire, causing a large decrease in SSTP performance.
Stack
1. In computer networking, a stack is a frequently used method of describing TCP/IP.
• Computer network and network card help and support
2. In computer programming, a stack is a special data structure that removes items in the reverse order from which they were added.
3. A stack may also refer to a collection of computers that are stacked upon each other or a series of caseless computer components a computer farm.
4. In some video games, multiple players join to defeat a creature, creating a party or raid. When fighting some creatures, it is necessary to stack together. When players stack, they are moving to a common spot, standing in a tight group to create a smaller target for the creature to hit or to share incoming damage.
Star Topology
Alternatively referred to as a star network, star topology is one of the most common network setups. In this arrangement, every node connects to a central hub, switch or computer; the hub acting as a server and the peripheral devices as clients. A major disadvantage of this network topology is that if the central hub fails, all of the connected devices are disconnected. The visual example shows how this setup gets its name as it is shaped very much like a star.
Static allocation
1. When referring to computer memory, static allocation is a section of memory that has been set aside for an application when it is first loaded. This section of memory is kept to be only used with that application, and is made available again once the program is closed.
• Computer memory help and support.
2. When referring to a network or network device, static allocation or a static IP address is the assignment of a fixed address. For example, assigning a computer a fixed IP address of 192.168.123.114 never changes unless done so manually. This address is designated by the user and not the network.
Assigning a computer a static IP address that is not compatible with the netmask or with your network configuration will not allow the computer to communicate properly with the network.
STM
Short for Synchronous Transport Module, STM is a standard for data transmissions over SONET.
Store and forward
A relay system that stores all outgoing messages in an intermediate location until the receiving end requests them. E-mail is a good example of store and forward; messages are stored on a server and can be retrieved at any time.
STP
1. Short for Spanning Tree Protocol, STP is a networking protocol designed to create a single path over a network, preventing any loops from occurring on a network even if there are multiple paths to the same destination.
• Computer network and network card help and support.
2. Short for Shielded Twisted Pair, see the STP cable definition for further information.
3. Short for Software Test Plan, STP is a plan developed as a guideline to test computer software.
STP cable
Short for Shielded Twisted-Pair cable, STP is a cable originally developed by IBM for Token Ring that consists of two individual wires wrapped in a foil shielding to help provide a more reliable data communication.
Straight through
A network cabling that connects a computer to a network device. For example, straight through cables connect a computer to a network hub, network switch, and network routers. These are the standard network cables you would find at the store unless labeled as a cross-over cable.
Streaming content
Streaming content is an audio or video file on the Internet that is partially downloaded and then played as the remainder of the file is being downloaded. More specifically, live streaming is the method of constantly sending and receiving content over the Internet. Streaming content or streaming media are beneficial in that they significantly reduce, if not eliminate, wait times for online content; usually depending on the speed of their connection.
Online radio stations and YouTube videos are both good examples of streaming content.
The first live streaming was done by the band Severe Tire Damage on June 24, 1993. The event was seen live in Australia and other locations over the Internet. While streaming audio is not quite as bandwidth-intensive, streaming video does require more bandwidth to achieve. Users wanting to view streaming movies should have an Internet speed of at least 2.5 Megabits (Mbit) per second. For high definition content, 10 Mbit/sec is recommended.
STS
Short for Synchronous Transport Signal, STS is a standard for data transmissions over SONET.
Subdomain
Alternatively referred to as a child domain, a subdomain is a domain name with a prefix. For example, "www.computerhope.com" is the URL for Computer Hope and "www" is the subdomain. If we wanted to have a FQDN for a sub page or another external domain such as our help section, we would create "help.computerhope.com" as a subdomain.
Subnet Mask
Short for subnetwork mask, a subnet mask,subnet, or subnetting is a method of dividing a network of IP addresses into groups. Subnetting allows each computer or networking device in its own subnet to communicate with each other and still allow communication between subnets by routing the traffic through the network router. By dividing a network into subnets, it can improve network security and keep overall network traffic balanced. A common example of a subnet mask for class C IP addresses is 255.255.255.0 and is the default subnet mask for many computers and network routers.
Switch
1. A piece of a physical circuitry component that governs signal flow. Having a switch or toggle switch allows a connection to be opened or closed. When opened the switch allows a signal or power to flow through the connection. When closed the switch stops the flow and breaks the circuit connection.
2. On a network, a switch is a hardware device thatfilters and forwards packets through the network, but often not capable of much more. The first network device that was added to the Internet was a switch called the IMP, which helped send the first message on October 29, 1969. A network switch is more advanced than a hub but not as advanced as a router. The picture shows an example of a NETGEAR 5 port switch.
SYN
Short for synchronize, SYN is a TCP packet sent to another computer requesting that a connection be established between them. If the SYN is received by the second machine, an SYN/ACK is sent back to the address requested by the SYN. Lastly, if the original computer receives the SYN/ACK, a final ACK is sent.
3. A button or lever that can be switched to turn a device on or off.
4. When referring to the switches command, this command is loaded through config.sysand allows you to add and remove various functions of MS-DOS. See the switches command for further information about this command.
5. When referring to another command, a switch is an available option that can be used with the command. For example, the command: "fdisk" can be used with the /MBR switch, using "FDISK /MBR" would allow the user to recreate the master boot record and not just run the fdisk program.
6. Switches is also a config.sys command that allows the user to add and remove features of early versions of MS-DOS and Windows. See the switches page for further information on this command.
SYN Attack
Alternatively referred to as an SYN flood, an SYN attack is a Denial of Service (DOS)attack on a computer or network that floods the network with spoofed SYN packets or packets that contain an address that never responds to the SYN/ACK requests. Essentially, the connection queues fill up with bad connections and service is denied to legitimate users.
Syslog
Short for Systems Log, syslog was originally developed for Unix based systems to collect error, warning, or other system messages sent to the central location through UDP port 514.
Today, syslog is available the majority of operating systems, as well as hardware devices such as network switches and routers.
SYSOP
Short for SYStem OPerator, the term SYSOP is used to describe an individual in charge of a multi-user system, such as a BBS. Today, this term has been replaced by admin, Moderator, Root, or System Administrator.