VoIP Components

In the VoIP network there must be a functionality similar to the one of the PSTN Network.
To connect the VoIP network to the PSTN there is the need of a Hardware called Gateway.

The components of a VoIP Network usually are:

IP PBX

END USER DEVICES

VOIP GATEWAYS/GATEKEEPERS

IP NETWORK


IP PBX

It is the call processing server.
It terminates all VoIP calls on the PSTN Network.
It is usually software based.



END USER DEVICES

They usually are:

VoIP phones

They use the TCP/IP protocol to communicate with the IP network,
they have an IP address for the subnet on which they are installed.

Usually, VoIP phones use DHCP to auto-configure themselves, with the DHCP server telling the phone about the location of the configuration server, which most of the time is identical to the call processing server.

Softphones

They are software application running on computers,
They are usually installed in mobile devices.
They have the same base features as VoIP phones.



VOIP GATEWAYS/GATEKEEPERS

Sometimes you can use indifferently the name Gateway or Gatekeeper.
The last usually performs the Call admission and bandwidth control.
But it is also possible to find all functions in one only hardware.
The main function is to transform the analog call to digital and to create VoIP packets.
They can have additional features as voice compression, echo cancellation, packets prioritation.

Each call is a single IP session transported by a Real-time Transport Protocol (RTP) that runs over UDP.


IP NETWORK

The IP backbone provides the connectivity among the end elements.

The IP Network provides smooth delivery of the voice.

The IP network must treat voice and data traffic in a different way.
To assure good quality of transmission it must be able to prioritize the different traffic types.

Classic Circuitswitching telecommunications dedicate channels, reserving bandwidth as it is needed out of the trunk links interconnecting the switches.
For example, a phone conversation reserves a single DS-0 channel, and that
end-to-end connection is used only for the single conversation.

IP networks are quite different from the circuit-switch infrastructure in that it is a packet-network, and it is based on the idea of needed availability.
Class of service ensures that packets of a specific application are given priority.
This prioritization is required for real-time VoIP applications to ensure that the voice service is unaffected by other traffic flows.