There are several other protocols and standards used
in VoIP systems, including RTCP, Real‑time Transport Control Protocol.
Imagine you're playing a game with a friend and you want to keep score. RTCP
is like the scorekeeper for a VoIP call. It keeps tracks of the quality of the
call, like how many packets of audio or video are being sent and received, or
if there's any problem with the call.
This information is then used to improve the call quality for future calls.
RTCP is used in conjunction with RTP to monitor the quality of the multimedia
transmission. RTCP periodically sends control packets between the sender and
the receiver to exchange information about the quality of the transmission,
such as the number of lost packets and the amount of jitter. This information
is then used to adjust the transmission parameters, such as the rate at which
packets are sent,
to ensure the best possible quality of the multimedia stream. You
would often need your VoIP system to call the normal landline, or a
mobile phone, or maybe a toll free number,
which is on the PSTN side, but there is a glitch,
PSTN networks have different protocols and standards than VoIP
systems. In these situations, you would need a gateway to let your
VoIP system talk to the external PSTN world.
The job of the gateway is to translate between two different
protocols, like ISTN protocol on the PSTN side and IP protocol on the
LAN side. Between the two different protocols, the gateway is
typically a router you could configure to let your voice system be
integrated with the PSTN world.
There are many cloud‑based gateways as well that are hosted in different
clouds, which you could use if you don't want to purchase dedicated hardware
on‑prem. Now let's discuss a protocol that works on the gateways, MGCP, Media
Gateway Control Protocol. It is used to control and manage media gateways in a
VoIP network. Media gateways are responsible for handling the conversion of
analog voice signals into digital ones to be transmitted over the IP network,
and vice versa.
MGCP controls and manages these gateways, ensuring that
calls are properly routed and managed,
and the call quality is maintained. MGCP is a client/server protocol that
allows the call agent CA to take control of a specific gateway endpoint,
that is the port, to send or receive calls. Real‑world applications of MGCP
include large enterprise networks, service provider networks,
and public switch telephone networks, PSTN,
that are being transitioned to Voice over IP. Then we have the H.248
protocol, known as Megaco, which is more flexible and scalable than the
MGCP protocol. H.248 can control a large number of media gateways in large
enterprises or service providers. H.248 controls the communication between
a media gateway and a media gateway controller, a server that manages the
gateway. The protocol is responsible for setting up, maintaining, and
tearing down calls,
and for controlling media streams that carry voice and video
traffic. There is N number of protocols used today, and, what I discussed are just the popular ones.