Equitel E451 Manual de usuario descargar pdf (Pagina 8)

October 2013 – Ed.1.0

EQUITEL E400 Family – Control and communications protocol

Page 5

Step 5: End of communication

When one of the links decide to end the communication, it cuts the audio stream and sends a message to the

PBX informing about this.

Figure 8. VoIP. End of communication

In all this process there are two parts clearly differentiated: the control of the communication establishment

or session (steps 1, 2, 3 and 5) and the vocal communications (step 4).

The messages format and the data between the units are fixed by several RFCs industrial standards

(3)

Communications establishment

There are currently several open standards: SIP, H.323,… as well as proprietary protocols from other

manufacturers such as Cisco, etc.

The most widely used and the simplest to implement may be SIP, defined under RFC 3261 standard. It is

rather easy to find nowadays commercial telephones and PBX supporting this protocol.

This document has not the purpose of describing the functioning of the SIP protocol although we will see in

Chapter 4 that the units E401 and E451 implement a small part of it.

Vocal communications

In this case, the protocol we use is always RTP, defined under RFC 3550 standard. This protocol sets how the

digitized and coded audio data are encapsulated in UDP packets.

There are several audio codification methods, commonly called codecs. Each one of them has different

characteristics as to the quality sound and the bandwidth. The most commonly used are defined under ITU

(4)

(G.711, G.722, G.723, G.726, G.728, G.729…).

The most widespread and easiest to implement is G.711. It is based in digitalizing audio at 8 kilosamples per

second, with 12 bits per sample. This standard is divided in two: G.711-A Law, which is used in Europe and in

international links, and G.711-µLaw, more commonly used in US and Japan. The bandwidth used is 64 Kb/s.

(3) RFCs are publicly accessible standards managed by IETF (Internet Engineering Task Force). They regulate the different communication protocols used nowadays in

Ethernet / IP networks.

www.ietf.org, www.rfc-editor.org

(4) International Telecommunications Union. It is a UN body regulating the telecommunications at an international level.

1 2 3 4 5 6 7 8 9 10 11 12 13 ... 31 32

Comentarios a estos manuales

Sin comentarios

Equitel E451 Manual de usuario Pagina 8

Comentarios a estos manuales

Relacionado con productos y manuales para Sistemas de intercomunicación de la puerta Equitel E451