Glossary

A

ADSL

Asymmetric Digital Subscriber Line

Special form of DSL.

ALG

Application Layer Gateway

NAT control mechanism of a router.

Many routers with integrated NAT use ALG. ALG lets the data packets in a VoIP connection pass and adds the public IP address of the secure private network.

The router's ALG should be deactivated if the VoIP provider offers a STUN server or an outbound proxy.

See also: Firewall, NAT, Outbound proxy, STUN.

Authentication

Restriction of access to a network/serv- ice by use of a password to log in.

Automatic ringbackSee Ringback when the number is busy.

B

Block dialling

Enter the complete phone number, and correct it if necessary. Then pick up the receiver or press the handsfree key to dial the phone number.

Broadband Internet access

See DSL.

Buddy

Subscriber with whom you exchange brief messages on the Internet in real time (chatting).

See also: Instant messaging.
Glossary

C

Call forwarding

CF

Automatic forwarding of a call to a different telephone number. There are three kinds of call forwarding:

–CFU, Call Forwarding Unconditional

–CFB, Call Forwarding Busy

–CFNR, Call Forwarding No Reply

Call waiting

CW

VoIP provider feature. A beep during a call indicates that another caller is wait- ing. You can accept or reject the second call. You can activate/deactivate the feature.

Chatting

Form of communication on the Inter- net. During a chat, brief messages are exchanged between the communicating parties in real time. Chatting in this sense is understood to be a written form of communication.

Client

Application that requests a service from a server.

Codec

Coder/decoder

Codec is a procedure that digitises and compresses analogue voice before it is sent via the Internet and decodes – i.e.translates into analogue voice – digital data when voice packets are received. There are different codecs that vary, for instance, according to the level of compression.

Both parties involved in the telephone connection (caller/sender and recipi- ent) must use the same codec. This is negotiated between the sender and the recipient when establishing a connec- tion.

The choice of codec is a compromise between voice quality, transmission speed and the necessary bandwidth.

A high level of compression, for exam- ple, means that the bandwidth

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