Access credentials is a set of criteria for gaining access to a protected resource. Security system will compare a user's credentials with other user credentials stored in a database.

If the credentials match, the user is granted access.  If the credentials are at variance, authentication fails and access is denied.

An Access Point (AP) is a device to have a wireless enabled device, such as a laptop, join a wireless local area network (WLAN).  An Access Point may be a computer or a dedicated device.

An AP can be attached to a wired LAN or to another Access Point. Interconnected Access Points can provide a wide LAN topology. An Access Point exchanges radio-frequency signals with a wireless device to start a connection with it and to exchange data.

A wireless device shall be capable to migrate from an Access Point to another Access Point without losing the connection. Feature is known as ‘handover’An Access Point shall be capable of using several frequency bands to avoid the interference with foreign devices, due to the limited number of available frequency bands. An Access Point can behave as a simple signal repeater or as an interface between a wireless LAN and a wired LAN in the same way as a bridge or router would interconnect two wired LAN segments. 

Each Access Point may be thought as generating a radio cell around it.

An account is all of the information about a user in a given context. Such information may include personal data as well as access rights granted to the account in the given context. Name, address, initials, e-mail address, but also the right to access the Internet or the right to create other accounts, to name a few, are elementary properties of  an account, sometimes known as a user’s profile.

The term 'Account' shall not be confused with 'Account ID', which is a unique account identifier. Examples of account ID are a fully qualified telephone number, such as +390244656000, which uniquely identifies a line in the world, or an e-mail address, such as john.smith@eutelia.it, which uniquely identifies a mailbox across the Internet.

'Account' is sometime used in spoken language as shorthand for account ID. The two concepts, however, should be carefully kept distinguished.

Acronym of Asymmetric Digital Subscriber Line, a data transmission technology for high-speed connection to the Internet over traditional unshielded twisted pair (UTP) wiring, generally available in home and small offices.

ADSL features are:

1)    Transmission rate (up to 1280 Kbps) is quite different from receiving rate (up to 12 Mbps), hence the term ‘asymmetric’; Italian providers offer up to 256 Kbps transmission rate and up to 1280 Kbps receiving rate, higher by 10 times the rates that can be obtained by using a traditional modem;

2)    Phone line remains available to voice calls during ADSL connection; if user agreed by contract to be charged a flat rate tariff, not a time-based one, he or she may stay permanently connected to the Internet;

3)    Categories of DSL are Adsl,R-Adsl, Hdsl,Sdsl, Vdsl.

A quantity is said to be analogue when it can assume an infinite set of values within a range, according to a physical phenomenon, such as, for instance, the signal generated by a microphone. On the other hand, a digital signal can only take discrete values.

An example:  Let a signal describe the journey taken by a person, when trying to reach a platform about one meter over the ground level. A slip of access will go through all values from zero to 105 cm, representing an analogue signal in time. A stairway with 15 cm steps will go through values 15, 30, 45, 60, 75, 90, 105, representing a discrete values signal in time (digital signal, for short).

ASCII Coding is the standard encoding of characters in computers. Original ASCII coding uses patterns of 7 bits to  code a set of 128 characters including numbers, lowercase, uppercase, punctuation marks and other graphic symbols, such as ‘@’; first 32 characters are reserved for control of peripherals and communication devices.

Extension of the ASCII coding into an 8-bit pattern has been subsequently provided to accommodate other characters, such as the accented characters typical of most national languages.

Acronym with two meanings:

1. Application Service Provider, an organisation providing application software running on its server systems to user connected through a dedicated network or the Internet;

2.  Active Server Page, a language developed by Microsoft to implement dynamic HTML pages.

Any signal can be decomposed into an infinite series of sinusoids having frequencies value f, 2f, 3f etc.

Bandwidth is the range of most significant frequencies in a signal. A communication channel can provide an amount of bandwidth depending on its physical characteristics.

A relation holds between bandwidth and the data rate that can be transmitted over the channel.  In ideal conditions, a data rate of W bits per second can be accurately transmitted over a 2*W Hz channel.