VoIP phone

SIP phones are a type of phones based on Voice over IP and to use the Session Initiation Protocol ( SIP). The conversation is here shipped in individual data packets over the Internet. SIP phones can be implemented as a single device ( hard phone ), telephone adapter plus classic phone or as a software solution on a PC or PDA ( softphone). There are both wired (usually Ethernet) and wireless ( mostly WLAN ) variants.

Features and Functions

The solution than hard phone can be operated like an ordinary telephone and looks it. Apart from the phone numbers can be applied to SIP phones and SIP addresses choose (also called URI) that are shaped just like e- mail addresses, and the schema prefix sip: take, for example sip: [email protected]. If the SIP address of the caller is known, this can for example sip: [email protected] directly instead of the number in the phone can be entered. Requirement is that the phone or the software supports entering alphanumeric SIP address.

Supports the SIP client, so a hardware or softphone that ENUM look-up method, it is checked after the election of the phone number from the SIP client for a registrar if the dialed number is present, a SIP URI entry. If this is the case, the call to the stored SIP URI entry is made ​​, one speaks of the real ENUM look-up (public ENUM look-up ). Consequently, the conversation runs completely as an IP call. An ENUM look-up can also be performed by a VoIP provider, but not all providers support this function. Some providers limit this to its own members or to members of its partner providers, we speak here of any real ENUM look-up ( private ENUM look-up ). This means that a call can be billed as a normal landline call, although a SIP phone is selected. When ENUM look-up in this case the selected E.164 number is converted into a corresponding ENUM domain. This domain is searched by the resolver after NAPTR resource records. The evaluation of these resource records results in one or more URI where / which the desired service of the specified domain or telephone number can be addressed.

The LAN can be used for the transmission of telephone calls, whereby the separate wiring of telephone lines is superfluous and thus costs can be saved. With Power over Ethernet ( PoE) power cable required for office phones also fall away in addition.

SIP telephony is designed for worldwide use and therefore used as a rule, in the national use international address formats. For example, the connection could be achieved anywhere on the world always the same telephone number. So may be allocated for a SIP phone, a geographical telephone number for London, but the SIP phone registers, for example, in Stuttgart. If the London number is being called, indicates that the SIP phone in Stuttgart. This functionality of mobility is currently being used in IMS -based multimedia next-generation networks.

A selection of so-called codec allows transmission of language in different levels of quality. This can range from cell phone quality with the GSM codec, up to hi-fi quality with wideband codecs such as iLBC and G.722 standard, which is also understood by UMTS terminals, rich. See also HD voice.

Disadvantages

Since the end of 2004 German VoIP provider must not provide geographic numbers more to their clients, if they have a residence is not in this number range. To compensate for this a separate number range with the area code 032 has been made available since the beginning of 2005. The same applies to Austria, where the number range is 0720th

A very restrictive firewall can complicate the configuration and makes the use of sometimes quite impossible. Also, a uniform voice quality can now be not usually guaranteed, it is dependent on bandwidth and network load.

Emergency numbers:

  • (110, 112) - Local office: Emergency numbers are restricted from many providers available and often do not run to the nearest services, but at a specified by the provider.
  • (110, 112) - Röchelruf: If the caller is unable to speak (so-called Röchelanrufe ) the transmission of the address data to the department is particularly important. In nomadic use of VoIP connection the customer must call the location provider so that it can pass the address in emergency case. The updating of the emergency address can not be made from many providers. Taking its VoIP connection with the stay abroad, there is no jurisdiction for the German emergency services more.

Encrypting the possibility of signaling and payload (eg, language ), is not always given, which substantially facilitates eavesdropping. To correct the situation - as available - give SRTP (voice, video ) and TLS ( signaling).

Synonyms

  • SIP User Agent (UA)
  • SIP client
  • SIP terminal
Avaya Client (computing) internet Low Bitrate Codec Wideband audio 112 (emergency telephone number) Secure Real-Time Transport Protocol
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