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||RAID - Redundant Array of Independent (or Inexpensive) Disks. Type of disk storage configuration often used on servers, where several physical disks are combined into an array for better speed and/or fault tolerance.
RAID 0 (data striping) - file blocks are written to separate drives. Does not provide fault tolerance, because failure of one drive will result in data loss.
RAID 1 (data mirroring) - data is duplicated on two drives either through software or hardware. Provides faster read performance than a single drive and good fault tolerance.
RAID 2 (not used in practice) - data is split at bit level at written to multiple drives.
RAID 3 (requires 3+ drives) - data block is striped at byte level across drives and error correction codes (parity info) is recorder on another drive. Provides fault tolerance but slower writing performance.
RAID 4 - similar to Level 3 but provides faster performance because it uses blocks for striping.
RAID 5 - similar to Level 4 but improves performance by also striping parity info across multiple drives.
RAID 6 - similar to Level 5 but also uses second parity scheme for better fault tolerance.
RAID 7 - proprietary RAID design by Storage Computer Corporation. Faster than other levels because it uses multiple levels of cache and asynchronous I/O transfers.
||RARP - Reverse Address Resolution Protocol (RFC 903).
RARP is a Link layer networking protocol used by a host computer to obtain its Internet Protocol (IPv4) address when it has available its link-layer address, such as an Ethernet MAC address.
||RC4 is a symetric stream cipher with an arbitrary key size designed by RSA Security, Inc. in 1987. It is essentially a pseudo random number generator, with the output of it being XORed with the data stream to produce encrypted data. The source code for an RC4 algorithm (or a code that produces the same results) was posted on Usenet in 1994. It is fast, it has been extensively analyzed and proven to be secure.
The RS4 cipher is used in SSL (Secure Socket Layer), WEP (Wireless Equivalent Privacy), WPA (Wi-Fi Protected Access), TKIP, MS XBOX, Oracle SQL, Adobe Acrobat, etc.
||Regedit is a commonly used editor (provided with Windows) for accessing the Windows Registry. It can be accessed from the Start Menu ( START > Run > type "regedit" ). Many of the registry values require rebooting the PC before they take effect.
Note: Modifying some registry settings can cause serious problems and damage your operating system to a point where it needs to be reinstalled. Make backups and use the information at your own risk.
Again, backup the Windows Registry before changing anything !
||RFCs (Requests for Comments) are the official documents of the Internet Engineering Task Force (IETF) that specify the details for protocols included in the TCP/IP family.
IETF has published over 4000 RFCs, all of which can be viewed at IETF.org, or RFC-Editor.
||RFI (Radio Frequency Interference) - signal interference on the radio frequency electromagnetic spectrum (from 3 KHz to 300 GHz).
||RIAA (Recording Industry Association of America) is a special interest trade group formed in 1952, representing the US recording industry.
The RIAA has been at the heart of the P2P file-sharing controversy, as well as any new technology that can be used to record media content (the VCR for example). RIAA is continuously lobbying and waging an aggressive legal campaign attempting to defend the interests of its members (the larger record labels).
||RIR (Regional Internet Registry) is an organization overseeing the allocation and registration of Internet number resources within a particular region of the world. Resources include IP addresses (both IPv4 and IPv6) and autonomous system numbers (for use in BGP routing).
There are currently five RIRs in operation:
American Registry for Internet Numbers (ARIN) for North America and parts of the Caribbean
RIPE Network Coordination Centre (RIPE NCC) for Europe, the Middle East and Central Asia
Asia-Pacific Network Information Centre (APNIC) for Asia and the Pacific region
Latin American and Caribbean Internet Addresses Registry (LACNIC) for Latin America and parts of the Caribbean region
African Network Information Centre (AfriNIC) for Africa
||RJ-11 (Registered Jack 11) - a standard connector that is used to connect to the telephone line, the most common telephone jack.
||RJ-45 (Registered Jack 45) is a standard connector for the ends of a Category 5 network cable. Though it is similar in apperance to a phone plug (RJ-11), it has 8 wires rather than 6, and is slightly wider.
||Rolling On Floor, Laughing
||rootkit is a type of malicious software that is activated each time your system boots up. Rootkits are generally difficult to detect, since they run before the Operating System has completely booted up.
||Router is the central switching device in a packet-switched network that directs and controls (routes) the flow of data.
A traditional router routes packets within a single address realm, while a NAT router directs datagrams between different address realms. A NAT router sits on the border between two adress realms and performs such "transparent routing" by modifying addresses in IP headers, so that when packets enter another address realm they can be valid and routed properly.
Routers are differentiated from data communications switches by the ability to perform higher-level functions necessary to the interconnection of different networks.
||RPC (Remote Procedure Call) is a protocol that a program can use to request a service from a program located on another computer in a network. RPC helps with interoperability because the program using RPC does not have to understand the network protocols that are supporting communication. In RPC, the requesting program is the client and the service-providing program is the server.
Two newer object-oriented methods for programs to communicate with each other, CORBA and DCOM, provide the same types of capabilities as traditional RPCs.
||RSN (Robust Security Network) is a WPA (Wi-Fi Protected Access) replacement built on 802.1x and the AES (Advanced Encryption Standard).
||RSS (Really Simple Syndication) is a popular, lightweight XML format designed for sharing headlines, and other web content between sites. It is most often used for gathering and distributing news and other web content.
RSS (Receive-side Scaling) is also a method allowing for parallelized processing of received network packets on multiple processors, while avoiding packet reordering.
||RTT ( RoundTrip Time ) is the amount of time it takes for a packet of data to get from one designated point to another and back to the sender. RTT is usually used to measure latency.
||In Ethernet networks, any frame shorter than the minimum 64 bytes but with a valid CRC is considered a runt.
See also: jabber
||RWIN (TCP Receive Window) is a buffer that determines how much data the receiving computer is prepared to get at one time.
A RWIN value that's too large will result in greater loss of data if a packet is lost or damaged. A too small RWIN will be very slow, as each packet will have to be acknowledged before the next packet is sent.
RWIN is one of the most important parameters in tweaking any TCP/IP connection.
||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
||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.
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