What Protocols are used during a VOIP Call?

As today we are using Voice Over IP on a larger scale and you have to know about the protocols used for this process so that we can use it for our system. The two main protocols for the VOIP are session control protocol and media control protocol. The first one is the Session Control Protocol. These main protocols are used during a VoIP call.

Session Control Protocol

The session control protocols have different standards. H.323 standard is used for the commands and messages such as the H.225 family which is called as Registration Admission Status which have such protocols for different purposes.

In this family we have  Registration request(RRQ), Registration Confirm(RCF), Registration Reject(RRJ), Admission Request (ARQ), Admission Confirm (ACF), Admission Reject (ARJ), Status Info Request (IRQ), Status Info Reject (IRJ), Info ACK (IACK), Info (INAK), Bandwidth Request (BRQ), Bandwidth Confirm (BCF), Bandwidth Reject (BRJ) for the different registration and admission purposes. 

The family for the call control Setup control the signal Alerting Called user to check the slot is free for a call or not and also alter the user to the specific purpose and it also Connect the user by having the connection purpose protocol which is in the call control protocol. Also, we have the Release Complete sent by terminal which acknowledges the user for successful connection.

SIP (Session Initiation Protocol) consists of the main entities in which we have the  User Agent Client (UAC) which is used to  Caller application that initiates and sends SIP requests. User Agent Server (UAS) which is used to Receives and responds to SIP requests and also accepts, redirects, or refuses calls.

Proxy Server is used to Contact the sued and control and pass the call to the network and also redirect it to the next hop and it contains the UAS and UAC which have same function as mentioned above Redirect Server it doesn’t initiate SIP request or accept the calls but maps the address into new address and return those address to the client who are using it.

The main message Methods of SIP are INVITE which invite the user or service to participate in a session where is required by the user. Acknowledge  is the used for the  Client to receive a final response to the invited request. And then it would use BYE command to indicate the server to release  the call.

Media Control Protocol

The Media Gateway Control Protocol is composed of the following major commands and messages. In which we have some different the first is CRCX  which create the interconnection between different end points and  also uses SDP for the defining the capabilities of the network.

MDCX which modify the connection characteristics where required for the connection also we have DLCX which used to delete connection message and also be used to originate from the gateway if the line is broken or disturbed. RQNT, it Request Notification regarding the occurrence of specific events. NTFY which inform the MGC when see events occurs on Fax and modem tones. AUCX.

Along with this it also have some others protocols which do the work of media control on the layer and is responsible for the media on the link.

By allowing voice and other media to be transmitted over the internet, Voice over Internet Protocol (VoIP) has completely altered the way we interact with one another. Multiple protocols collaborate invisibly to keep your VoIP calls running smoothly and reliably. These protocols make it possible to send and receive data with minimal disruption and maximum clarity. In this article, we’ll examine the protocols at play in a VoIP connection, elucidating how and why they form the bedrock of contemporary voice communication.

Real-Time Transport Protocol (RTP)

The voice and video information in a VoIP connection is transferred via the Real-Time Transport Protocol (RTP). It compensates for packet loss, jitter, and delay to guarantee the timely and secure transmission of voice packets. The RTP Control Protocol (RTCP) is a companion protocol that keeps tabs on the state of the network and reports back on the call’s quality.

Internet Protocol (IP)

VoIP relies on Internet Protocol (IP) since it enables the transfer of data packets across networks. It establishes the rules for packet routing and addressing and gives each device its own unique IP address. When talking over long distances, IP ensures that voice data is broken up into packets, sent across the internet, and then reassembled at the other end.

Real-Time Control Protocol (RTCP)

A VoIP call’s quality can be monitored and adjusted with the help of RTCP, which operates in tandem with RTP. It measures things like packet loss, delay, and jitter to compile statistics regarding the transmission’s reliability. Callers periodically exchange RTCP packets, which can be used to monitor and adjust call settings to improve audio quality.

Session Description Protocol (SDP)

SDP is a protocol for describing and bargaining over the properties of a multimedia session. Codecs, video formats, and network addresses are only some of the data that can be transmitted. SDP allows for a standardization of audio and video communication across various VoIP gadgets, hence facilitating their interoperability.

Secure Real-Time Transport Protocol (SRTP)

SRTP provides encryption and authentication procedures for the sent data to secure the confidentiality, integrity, and privacy of VoIP calls. Protecting the voice packets from snooping and manipulation improves the safety of VoIP calls.


Voice over Internet Protocol (VoIP) calls rely on a group of protocols that cooperate to provide high-quality, real-time voice communication across networks. Each protocol, from SIP’s signaling skills to RTP’s fast transportation, is essential to delivering a faultless VoIP service. The need of a stable and secure network infrastructure is underscored by an awareness of the protocols used in a VoIP call, which in turn helps us grasp the technical complexity of this cutting-edge method of communication. To keep up with the ever-increasing requirements of modern communication, VoIP protocols are constantly being updated to provide greater voice quality, higher levels of security, and more cutting-edge tools.