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Time to live

Time to live (TTL) or hop limit is amechanism that limits the lifespan or lifetime of data in a computer ornetwork. TTL may be implemented as a counter or timestamp attached to or embeddedin the data. Once the prescribed event count or timespan has elapsed, data isdiscarded. In computer networking, TTL prevents a data packet from circulatingindefinitely. In computing applications, TTL is used to improve performance ofcaching or to improve privacy.

IP packets

Under the Internet Protocol, TTL is an8-bit field. In the IPv4 header, TTL is the 9^th octet of 20. In theIPv6 header, it is the 8^th octet of 40. The maximum TTL value is255, the maximum value of a single octet. A recommended initial value is 64.

DomainName System

The Domain Name System (DNS) is ahierarchical decentralized naming system for computers, services, or anyresource connected to the Internet or a private network. It associates various informationwith domain names assigned to each of the participating entities. Mostprominently, it translates more readily memorized domain names to the numericalIP addresses needed for the purpose of locating and identifying computerservices and devices with the underlying network protocols. By providing aworldwide, distributed directory service, the Domain Name System is anessential component of the functionality of the Internet.

The Domain Name System delegates the responsibilityof assigning domain names and mapping those names to Internet resources by designatingauthoritative name servers for each domain. Network administrators may delegateauthority over sub-domains of their allocated name space to other name servers.This mechanism provides distributed and fault tolerant service and was designedto avoid a single large central database.

Burst error

In telecommunication, a burst error orerror burst is a contiguous sequence of symbols, received over a datatransmission channel, such that the first and last symbols are in error andthere exists no contiguous subsequence of m correctly received symbols withinthe error burst.

SecurityIdentifier

In the context of the Microsoft Windows NTline of operating systems, a Security Identifier (commonly abbreviated SID) isa unique, immutable identifier of a user, user group, or other securityprincipal. A security principal has a single SID for life, and all propertiesof the principal, including its name, are associated with the SID.

Man-in-the-middle-attack

In cryptography and computer security, aman-in-the-middle attack (often abbreviated MitM, MiM attack, MitMA or the sameusing all capital letters) is an attack where the attacker secretly relays andpossibly alters the communication between two parties who believe they aredirectly communicating with each other. Man-in-the-middle attacks can bethought about through a chess analogy. Mallory, who barely know to play chess,claims that she can play two grandmasters simultaneously and either win onegame or draw both. She waits for the first grandmaster to make a move and thenmakes this same move against the second grandmaster. When the secondgrandmaster responds, Mallory makes the same play against the first. She playsthe entire game this way and cannot lose. A man-in-the-middle attack is asimilar strategy and can be used against many cryptographic protocols. Oneexample of man-in-the-middle attacks is active eavesdropping, in which theattacker makes independent connections with the victims and relays messagesbetween them to make them believe they are talking directly to each other overa private connection, when in fact the entire conversation is controlled by theattacker. The attacker must be able to intercept all relevant messages passingbetween the two victims and inject new ones. This is straightforward in manycircumstances; for example, an attacker within reception range of anunencrypted Wi-Fi wireless access point can insert himself as aman-in-the-middle.

As an attack that aims at circumventingmutual authentication, or lack thereof, a man-in-the-middle attack can succeedonly when the attacker can impersonate each endpoint to their satisfaction asexpected from the legitimate other end. Most cryptographic protocols includesome form of endpoint authentication specifically to prevent MITM attacks. Forexample, TLS can authenticate one or both parties using a mutually trustedcertificate authority.

Metropolitanarea network (MAN)

A metropolitan area network (MAN) is anetwork that interconnects users with computer resources in a geographic areaor region larger than that covered by even a large local area network (LAN) butsmaller than the area covered by a wide area network (WAN). The term is appliedto the interconnection of network in a city into a single larger network (whichmay then also offer efficient connection to a wide area network). It is alsoused to mean the interconnection of several local area networks by bridgingthem with backbone lines. The latter usage is also sometimes referred to as acampus network.

Examples of metropolitan area networks ofvarious sizes can be found in the metropolitan areas of London, England; Lodz,Poland; and Geneva, Switzerland. Large universities also sometimes use the termto describe their networks.

From: http://searchnetworking.techtarget.com/definition/metropolitan-area-network-MAN

Memory footprint

Memory footprint refers to the amount of main memory that a program uses or references while running.

The word footprint generally refers to theextent of physical dimension that an object occupies, giving a sense of itssize. In computing, the memory footprint of an executable program indicates itsruntime memory requirements, while the program executes. This includes allsorts of active memory regions like code segment containing (mostly) programinstructions (and occasionally constants), data segment (both initialized anduninitialized), heap memory, call stack, plus memory required to hold anyadditional data structures, such as symbol tables, debugging data structures,open files, shared libraries mapped to the current process, etc., that theprogram ever needs while executing and will be loaded at least once during theentire run.

Larger programs have larger memoryfootprints. Excessive number of utility classes and methods in a programminglanguage design would increase the footprint for API users even if they did not use non-standard plug-ins orapplications. Programs themselves often do not contribute the largest portionsto their own memory footprint; rather, structures introduced by the run-timeenvironment take up most of the memory.

Qualityof service

Quality of service (QoS) is the overallperformance of a telephony or computer network, particularly the performanceseen by the users of the network.

To quantitatively measure quality ofservice, several related aspects of the network service are often considered,such as error rates, bit rate,throughput, transmission delay, availability, jitter, etc.

Quality of service is particularlyimportant for the transport of traffic with special requirements. Inparticular, developers have introduced technology to allow computer networks tobecome as useful as telephone networks for audio conversations, as well as supportingnew applications with even stricter service demands.

Definitions

In the field of telephony, quality ofservice was defined by the ITU in 1994. Quality of service comprisesrequirements on all the aspects of a connection, such as service response time,loss, signal-to-noise ratio, crosstalk, echo, interrupts, frequency response,loudness levels, and so on. A subset of telephony QoS is grade of service (GoS)requirements, which comprises aspects of a connection relating to capacity andcoverage of a network, for example guaranteed maximum blocking probability andoutage probability.

Bitrate

In telecommunications and computing, bit rate (sometimes written bitrate oras a variable R) is the number of bits that are conveyed or processed per unitof time.

The bit rate is quantified using the bitsper second unit (symbol: “bit/s”), often in conjunction with an SI prefix. Thenon-standard abbreviation “bps” is often used to replace the standard symbol “bit/s”,so that, for example, “1 Mbps” is used to mean one million bits per second.

Salt

In cryptography, a salt is random data thatis used as an additional input to a one-way function that “hashes” a passwordor passphrase. Salts are closely related to the concept of nonce. The primary function of salts is to defend against dictionary attacks versus a list ofpassword hashes and against pre-computed rainbow table attacks.

A new salt is randomly generated for eachpassword. In a typical setting, the salt and the password are concatenated andprocessed with a cryptographic hash function, and the resulting output (but notthe original password) is stored with the salt in a database. Hashing allowsfor later authentication while protecting the plaintext password in the eventthat the authentication data store is compromised.