In Voice over IP (VoIP) communication, there are two main methods of
initiating a call setup: early offer and delayed offer. Both methods have
their own advantages and disadvantages, and it is essential to understand
the differences between them to ensure optimal call setup and quality.
Early Offer:
Early offer, also known as early media, is a method where the originating
device sends the Session Description Protocol (SDP) message containing the
audio and video codec information in the initial INVITE message. This
message is sent before the called party answers the call. This method
enables the called party to see and hear the caller’s information while the
call is being set up.
The early offer approach can be used for both inbound and outbound calls,
and it has the advantage of reducing the call setup time. This is because
the negotiation of the audio and video codecs takes place before the call is
established. Another advantage of early offer is that it enables the caller
to know if the called party is available before the call is fully
established.
Delayed Offer:
Delayed offer is a method where the originating device sends the INVITE
message without any SDP information. The called party must respond with a
180 Ringing message before the originating device sends the SDP message with
codec information in a subsequent message. In this method, the caller is
unable to hear or see any media until the called party answers the
call.
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The delayed offer approach is generally used for outbound calls and has the
advantage of being more secure than early offer since the originating device
only reveals the codec information once it has received confirmation that
the call has been accepted. Additionally, this method can conserve network
bandwidth since the SDP information is only sent when it is necessary.
The choice between early offer and delayed offer depends on the specific
needs of the organization. Early offer is generally used for video
conferencing, while delayed offer is used in voice-only calls. Ultimately,
it is up to the network administrator to determine which method to use based
on the organization’s requirements and network infrastructure.
In conclusion, the main difference between early offer and delayed offer is
the timing of when the SDP message containing audio and video codec
information is sent. The early offer method sends this information in the
initial INVITE message, while the delayed offer method sends it after
receiving a 180 Ringing message from the called party. Understanding these
methods is crucial in optimizing call setup and quality.