Session Description Protocol (SDP) Nedir?


SDP is responsible for announcing the session and providing information about it by sending the necessary invitations.

Specifically, it is a compass that guarantees that the media flow is delivered to the parties without losing its way, in conversations involving multimedia based on audio or video transmission over IP. You can find details about SDP in this article.

Session Description Protocol (SDP) Nedir?

SDP, which we know as the session identification protocol, unlike SIP, deals with the session itself, not its media.

It allows the session to adapt to the transferred media. It is necessary to create the necessary conditions for multimedia sessions such as video calls and voice calls (voIP).

It processes and defines a variety of metadata, from codecs to participants’ transmission addresses and protocols.

At first glance, we can actually compare SDP to operators who install and test devices such as barcovision, headphones, microphones and speakers in a meeting room.

Indeed, SDP is not a protocol that provides media transmission on its own. It has a structure that reveals parameters and supports communication.

In other words, it deals with the installation scheme, not the materials installed. It works in concert with protocols that determine session initiation and streaming, and can take part in many different media-based searches.

However, SDP does not specify individual media protocols. It presents the types of media it can support to SIP and asks it to choose among them. The session takes shape from here on.

What Does the Session Description Protocol (SDP) Do?

When a VoIP call is made over SIP, an invitation message will be added to the dialed number.

This message serves as an information note about the codec to be used in accordance with SDP, the addresses, and communication channels where communication will take place.

In other words, when there is a media transfer, the principles on which that transfer will be possible are determined.

At its most basic, the SIP phone determines the purpose and identity of the session and then transfers the SDP information from the caller to the called SIP phone.

After this initial contact, as soon as the call is received, the embedded SDP data will be sent again to the SIP phone from which the call was first made.

Thanks to this process, when the call in question is activated, the identifying phones of this SIP-based session are not only aware of the media to be transferred.

That media; It also knows where it will be sent, in what medium (audio, video, music) and through what type of codec.

In summary, after SDP, IPs and the media transfer-based function of the session are determined, it is useful to determine the parameters of that media stream.

At the end of the work, a compatible protocol is created for the SIP-based call by adjusting the available media, channels and codecs according to the type of media to be transferred.

The session definition protocol (SDP) consists of sequential arrays of <character> = <value> lines.

Here, the <character> line consists entirely of alphabetic characters and its function may differ depending on the use of uppercase or lowercase letters. The line we see next to it as <value> is within a structured text.

There are three parts in the SDP schema that we can define as “session”, “scheduling” and “media descriptions.”. Of course, there is only one session defined.

What are session description protocol terms?

SDP terms can be listed as follows;

  • Conference:It is a set consisting of the parties between whom communication, communication and media transfer takes place, as well as the software that these parties use for the action in question.
  • Session:It consists of components that send and receive the medium in question and ensure that this medium can be transmitted continuously.
  • Session Notification:We can also call this term “invitation”. It defines the session for users who will attend the conference and allows planning by including time and environment information. Also known as session announcement.
  • Session Identification:It is a programmed format to detect and include the necessary information in a session involving multiple media. We can say that it defines the function of SDP.

We have completed our terminology about SDP, which is known as “Session Description Protocol” in English and “Session Description Protocol” in .

The session identification protocol, which does not provide any media flow but acts as a communication bridge, includes many terms.

Although the SDP initially appeared as a component of the Announcement Protocol, it began to serve other purposes over time. We will see together what will happen in the future.


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