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||SackOpts (Selective Acknowledgements - RFC 2018). SACKs allow a receiver to acknowledge non-consecutive data. This is particularly helpful on paths with large TCP Windows (large RWIN / BDP). Selective acknowledgements also allow TCP to recover from IP packet loss without resending packets that were already received by the client.
While SACK is now supported by most operating systems, it may have to be explicitly turned on by the system administrator.
||SAN (Storage Area Network) is a high-speed special-purpose (sub)network that interconnects different types of data storage devices with associated data servers on behalf of a larger network of users. Typically, a storage area network uses Fibre channel framework, or Gigabit Ethernet and is part of the overall network of computing resources for an enterprise.
||Serial ATA (Serial Advanced Technology Attachment). SATA is a newer standard for connecting hard drives in computer systems. It is based on serial signaling technology (as opposed to Parallel ATA, or PATA). SATA cables have only 7 conductors and are more flexible, thinner, use lower voltage, have lower potential for crosstalk/EMI, and can be longer than PATA ones (40-conductors).
Recent SATA hard drives have started implementing NCQ (Native Command Queuing, a technology designed to increase performance by allowing the disk to internally optimize the order in which read/write commands are executed. This bring brings SATA drives performance a step closer to SCSI than IDE PATA drives.
||SCSI (Small Computer System Interface) is an electronic interface allowing computers to communicatd with peripheral hardware such as disk drives, CD-ROM drives, scanners, etc.
SCSI is a very fast, and flexible parallel interface supported by all major Operating Systems. The latest Ultra320 SCSI standard allows for 15 devices to be connected to a single SCSI cable/port with length of up to 12 meters(LVD), having transfer rates of up to 320 MBps (Megabytes per second).
SCSI hard disk drives are often used in server environments, have better specs, and are higher priced than their IDE counterparts.
Top 10 reasons why SCSI is better than IDE:
10. more devices per cable/port (up to 16)
9. you can connect external devices to the SCSI bus (scanners/printers, etc.)
8. better multi-user capabilities (simultaneous access)
7. much lower CPU utilization
6. SCSI ensures data integrity with CRC checks, etc.
5. four times higher MTBF (mean time between failure)
4. longer is better (cables up to 12 meters with LVD)
3. lower access/seek time (HDD spindle speed up to 15K RPMs)
2. higher transfer rates (up to 320 MBytes/sec.)
and the number one reason why SCSI is better than IDE is....:
1. SCSI is just a smarter bus than IDE
||SCTP (Stream Control Transmission Protocol) is a computer networking Transport Layer protocol, serving in a similar role as the popular TCP/UDP protocols.
It provides some of the same service features of both, ensuring reliable, in-sequence transport of messages with congestion control.
Sometimes referred to as "next generation TCP", SCTP is designed to make it easier to support a telephone connection over the Internet (and specifically to support the telephone system's Signaling System 7 (SS7) on Internet connection).
SCTP was defined in 2000 by the IETF Signaling Transport (SIGTRAN) working group in RFC 4960 (RFC 3286 provides an introduction). Defined by RFC 2960 originally, obsoleted by RFC 4960.
In the absence of native SCTP support by operating systems, it is possible to tunnel SCTP over UDP, as well as mapping TCP API calls to SCTP.
||SDM (Space Division Multiplexing) is a method by which metallic, radio, or optical transmission media are physically separated by insulation, waveguides, or space in order to maintain channel separations. Within each physically distinct channel, multiple channels can be derived simultaneously through frequency, time, or wavelength division multiplexing. Some Passive Optical Network (PON) implementations employ space division multiplexing, with the downstream transmissions occurring over one fiber of a duplex fiber optic cable and upstream transmission occurring over the other fiber.
Space Division Multiplexing is an integral part of the new 802.11n wireless standard. It allows for different data streams to be transmited over different antennas simultaneously with the goal of increased capacity (throughput) and better SNR performance. These different data streams can then be recombined at the receiver using multiple antennas as well.
In fiber optics, SDM is the condition in which each fiber of a bundle carries a separate channel.
||SDSL (Single line DSL, Symmetric DSL) is a DSL variation that uses just one twisted pair. SDSL is also symmetric, ie, the maximum data rate both upstream and downstream is the same, as opposed to ADSL.
||SLA (Service Level agreement) is a document outlining the service that a carrier provides to a customer. SLAs normally include acceptable levels of latency, packet loss, availability, as well as other expectations of the customer and carrier. In the event that the carrier does not meet their SLA (customer experiences carrier-caused outage, for example), the customer may be eligible for billing credit.
||SMTP (Simple Mail Transfer Protocol) is a TCP/IP protocol used in sending and receiving e-mail. It is usually used together with POP3 or IMAP, protocols that let the user save messages in a mailbox and download them periodically from a server. In other words, client programs typically use SMTP for sending e-mail and POP3/IMAP for downloading email messages from their local mail server.
||sneakernet (jargon, generally ironic, a.k.a. floppy-net, foot-net) - transfer of data by physically carrying floppy disks, hard disks, tape or other removable medium from one place to another.
"Never underestimate the bandwidth of a station wagon filled with magtape, or a 747 filled with CD-ROMs."
||SNMP (Simple Network Management Protocol) is an internet standard protocol defined in RFC 1157, developed to manage nodes on an IP network.
SNMP is used most often by network administrators to monitor and map network availability, performance, and error rates. To work with SNMP, network nodes utilize a distributed database of object definitions called the Management Information Base (MIB). All SNMP compliant devices contain a MIB which supplies the pertitent attributes of a device. Some of the attributes are hard coded in the MIB while others can be dynamic values suplied by software running on the device.
||SNR or S/N (Signal-to-Noise Ratio)
In communications, signal-to-noise ratio is a measure of signal strength relative to background noise (measured as signal level divided by noise). The ratio is usually measured in decibels (dB).
Higher SNR numbers repesent cleaner signals, with less noise. Decreasing noise, and/or increasing signal increases/improves the SNR value.
||Small Office/Home Office (SoHo) - a market for relatively inexpensive consumer electronics targeted towards individuals and small companies.
||SONET (Synchronous Optical Network) is an optical networking standard, defining specific aspects of how the network will be automatically restored during service outages via redundant links, as well as how it will be synchronized to facilitate time division multiplexing (TDM).
||SPI (Stateful Packet Inspection) is a firewall technology that monitors the state of a transaction to verify the destination of an inbound packet matches the source of a previous outbound request.
||SSD (Solid State Drive) is a data storage device that uses solid-state memory to store persistent data in the same manner as traditional block i/o mechanical hard disk drives (HDDs).
SSDs retain data in non-volatile memory chips, contain no moving parts, they're faster, less susceptible to physical shock, quieter, with much lower access time and latency, and use less power than traditional traditional HDDs.
||SSID (service set identifier) is a 32 byte set of characters that uniquely names a WLAN (Wireless LAN). This name allows stations to connect to the desired network when multiple independent networks operate in the same physical area.
A set of wireless devices communicating directly with each other is called a basic service set (BSS). Several BSSs can be joined together to form an extended service set (ESS), a logical WLAN segment. A Service Set Identifer (SSID) is simply a 32 byte alphanumeric name given to such ESS.
||STBC (Space-Time Block Coding) is a technique used in wireless communications to transmit multiple copies of the same data stream across a number of antennas (and frequency channels) to improve the reliability of data transfer.
Wirelessly transmitted signal traverses a potentially difficult environment with scattering, reflections, noise, etc. Data redundancy results in a higher chance of being able to use one of more of the received copies to correctly decode the received signal. Space-Time Block coding combines all the copies of the received signal to extract as much information as possible.
TCP interprets frame/packet loss as sign of network congestion and cuts the transmission rate to half whenever thoese error events occur. STBC essentially presents a smoother transmission to TCP, allowing for a more reliable wireless communication with a minimal throughput impact.
||Scientific Wild ass Guess :D
||SysAdmin (systems administrator). Knows the answer to life, the universe and everything.
...and how to fix a server.
On a more serious note, a SysAdmin is a person whose responsibility is the integrity and security of a network. The job often includes maintaining networked computers and peripherals as well.
||TC-PAM (Trellis Coded Pulse Amplitude Modulation) is the modulation format that is used in both HDSL2 and SHDSL, and provides robust performance over a variety of loop conditions.
SHDSL uses TC-PAM to provide a rate/reach adaptive capability, offering enhanced performance (increased rate or reach) and improved spectral compatibility with ADSL when compared to today's 2B1Q SDSL offerings. Compared to HDSL2, SHDSL offers lower power consumption through the use of lower-power, intelligently shaped transmit waveforms.
||TCP/IP (Transmission Control Protocol/Internet Protocol) is the suite of communications protocols (the main ones being TCP and IP) used to connect hosts on the Internet.
TCP/IP is used by the Internet, making it the de facto most widely spread standard for transmitting data over networks. TCP and IP were developed by a DOD (Department of Defense) research project to connect a number different networks designed by different vendors into a network of networks (the Internet).
||Tcp1323Opts - TCP Large Window support ( Windows 98 and later ). Used when an application requests a Winsock socket to use buffer sizes greater than 64KB. In previous implementations the TCP window size was limited to 64KB, this limit is raised to 2**30 through the use of TCP large window support as defined in [RFC1323] and implemented in Winsock 2. Tcp1323Opts also controls Timestamps.
||TDM (Time Division Multiplexing) is a type of multiplexing that combines data streams by assigning each stream a different time slot in a set. TDM repeatedly transmits a fixed sequence of time slots over a single transmission channel.
See also: WDM, FDM.
||TDMA (Time Division Multiple Access) is a wireless technology using TDM (time-division multiplexing). TDMA is used by the GSM digital cellular system. It works by dividing a frequency into multiple time slots, and then allocating them to multiple calls. This way, a single frequency can support multiple data channels simultaneously.
||tethering refers to using an internet-capable mobile phone as a modem to share its internet access with other devices, such as laptops and PCs. This internet sharing can be accomplished over Wi-Fi, Bluetooth, or by physical connection using a cable.
In the case of tethering over Wi-Fi, the mobile phone acts as a portable router and the feature is aslo called a mobile hotspot.
Many modern mobile phones, including Windows Phone 7 (from version 7.5 Mango), Android (from version 2.2 Froyo), and iOS (4.3 or higher) offer tethered Intnernet access. The feature is sometimes disabled, or requires extra monthly fees by operators to reduce strain on their networks.
||TFTP (Trivial File Transfer Protocol) is a simplified version of FTP that uses UDP, rather than TCP for data transport. It is easier to implement than FTP, but it is insecure (no authentication), lacks directory services, and UDP is not a reliable transport protocol.
TFTP is intended for use with small file transfers, often used to allow diskless devices to boot over the network, or for firmware transfers.
||Throughput (or transfer rate) in data transmission is the amount of data moved successfully from one place to another in a given time period.
For data networks, throughput is usually measured in number of bits per second (bps) that are transmitted, also quoted as Kilobits per second (Kbps) or Megabits per second (Mbps).
||Timestamps is defined in TCP Options ( RFC 1323 ) and used for two distinct mechanisms: RTTM (Round Trip Time Measurement) and PAWS (Protection Against Wrapped Sequences).
The disadvantage of using Timestamps is it adds 12 bytes to the 20 byte TCP header.
||TKIP (Temporal Key Integrity Protocol) is an enhancement to WEP security, part of a draft standard 802.11i.
TKIP enhances WEP security by adding functions for remixing keys per packet, making it more resistant to attacks involving key reuse (the main WEP weakness).
TKIP utilizes RC4 stream cipher with 128-bit keys for encryption and 64-bit keys for authentication.
||The shape of a local-area network (LAN) or other communications system (either physical or logical).
The principal network topologies are listed below:
bus topology: (a.k.a. linear topology) All devices are connected to a central cable, called the bus or backbone. Bus networks are relatively inexpensive and easy to install for small networks.
star topology: All devices are connected to a central hub(switch). Star networks are relatively easy to install and manage, but bottlenecks can occur because all data must pass through the hub.
ring topology: All devices are connected to one another in the shape of a closed loop, so that each node is connected directly to two other devices, one on either side of it. Ring topologies are relatively expensive and difficult to install, but they offer high bandwidth and can span large distances.
mesh topology: A network topology in which there are at least two nodes with multiple paths between them.
hybrid topology: A combination of any two or more network topologies. For example, a bus-star hybrid network consists of a high-bandwidth bus (the backbone), which connects a collections of slower-bandwidth star segments.
tree topology: a hybrid topology that combines characteristics of linear bus and star topologies. It consists of groups of star-configured nodes connected to a linear bus backbone cable.
||TR-069 (Technical Report 069) is a Broadband Forum technical specification entitled "CPE WAN Management Protocol" (CWMP). It defines an application layer protocol for remote management of end-user devices (e.g. modems, routers, gateways, set-top boxes, VoIP phones).
TR-069 provides the communication between customer-premises equipment (CPE) and Auto Configuration Servers (ACS). It includes auto configuration, dynamic service activation, firmware updates/version management, status and performance control, diagnostics, logs, etc. It is a platform that works through the Internet, and regardless of the device(s) manufacturer.
||traceroute is a utility that records the route between your computer and a destination computer on the Internet. It measures the time it takes to reach each node (specific gateway computer at each hop) needed to make the connection.
Traceroute is a handy tool both for understanding where problems are in the network (packet loss, high latency) and for getting a detailed sense of the network itself. The traceroute utility sends 3 ICMP packets to each node, increasing the "time to live" value of packets and seeing how far they get until they reach the given destination; thus, a trail of hosts passed through and time to them is built up.
The traceroute utility comes included with most current operating systems as part of the TCP/IP package. In Windows, traceroute can be used from the Command Prompt, by typing:
||transponder is the portion of a communications satellite that acts as a receiver, amplifier, and retransmitter for the signals communicated up to and down from the satellite.
||trojan (a.k.a trojan horse) - a program that pretends to be something else. Usually a piece of malicious code contained in another seemingly harmless program in such a way that it can get control and/or damage your PC. It could erase some files (even your entire hard disk) and/or give other people full access to your system... Sounds ridiculous? It happens every single day to computer users near you.
According to legend (Homer's Iliad), the Greeks won the Trojan war by hiding warriors in a huge, hollow wooden horse, who later opened the gates and helped them get into the fortified city of Troy. This a symbolic explanation of what a computer trojan horse is: it can open your PC to anyone, even if no immediate damage is done.
Note: In a much more limited use the term was also used for counter-measures, such as a program for cleaning a virus.
||TTL (Time To Live) is a value set in the header of outgoing IP packets. TTL determines the maximum amount of time (in seconds) an IP packet can live, or the number of routers an IP packet may pass through before being discarded (whichever is lower).
||Tunneling refers to the ability to encapsulate packets of data formatted for one network protocol (or a private secure network) in packets used by another protocol (or a public network). Tunneling allows the use of the (public) Internet to transfer data on behalf of a private network. See also: VPN, PPTP.
Note that tunneling and VPN is not intended as a substitute for data encryption by itself. For a higher security level strong encryption should be used within the VPN.
||TurboQAM is a Broadcom 802.11 wireless technology that makes it possible for the 2.4GHz band with 40MHz channels to achieve a maximum transfer rate of 200 Mbps per data stream, instead of the standard 150 Mbps. This is achieved by using QAM-256, instead of the standard QAM-64 used until now by 802.11n wireless networks.
TurboQAM requires 40MHz channels and clients that support QAM-256. Current routers revert back to 20MHz channels when there is interference from another radio that is within two channels of them.
||Two single core copper wires twisted around ach other to reduce crosstalk or electromagnetic induction. Twisted pair is usually installed in two or more pairs, all within a single cable. For some locations, twisted pair is enclosed in a shield that functions as a ground, and is known as shielded twisted pair (STP). Ordinary wire to the home is unshielded twisted pair (UTP).
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