Voice Media Transmission When a VoIP call is established, using the signaling protocols, the digitized voice samples need to be transmitted. RTP carries the actual digitized voice samples in a call. Specifically, the combined IP, UDP, and RTP headers are approximately 40 bytes in size, whereas a common voice payload size on a VoIP network is only 20 bytes, which includes 20 ms of voice by default. In that case, the header is twice the size of the payload. Figure 2. In addition, sRTP provides message authentication, integrity checking, and protection against replay attacks.
Voice Activity Detection Voice Activity Detection VAD is a technology that works with the human nature of voice conversations, mainly that one person listens while the other talks. VoIP Bandwidth Requirements The amount of bandwidth required varies by the codec and the transmission media.
Table 1. Table 2. Explanation of Terms Codec Bit Rate kbps Based on the codec, this is the number of bits per second that need to be transmitted to deliver a voice call. For example, the G. Codec Sample Interval ms This is the sample interval at which the codec operates. With MOS, a wide range of listeners judge the quality of a voice sample on a scale of one bad to five excellent. The scores are averaged to provide the MOS for the codec. Voice Payload Size Bytes The voice payload size represents the number of bytes or bits that are filled into a packet.
The voice payload size must be a multiple of the codec sample size. For example, G. Voice Payload Size ms Payload Size ms The voice payload size can also be represented in terms of the codec samples. For example, a G. For example, for a G. The following codecs are supported: Table 4.
Enter your password if prompted. Step 3 dial-peer voice number voip Example: Device config dial-peer voice 1 voip Enters dial peer configuration mode for the specified VoIP dial peer. Step 5 Do the following to configure a video codec: video codec codec Example: For Video Codec Device config-dial-peer video codec h Configures a video codec at the dial peer level.
Step 3 voice class codec tag Example: Device config voice class codec 10 Enters voice-class configuration mode for the specified codec voice class.
This becomes part of a preference list Step 5 exit Example: Device config-class exit Exits the current mode. Step 6 dial-peer voice number voip Example: Device config dial-peer voice 1 voip Enters dial peer configuration mode for the specified VoIP dial peer.
Step 7 voice-class codec tag offer-all Example: Device config-dial-peer voice-class codec 10 Applies the previously configured voice class and associated codecs to a dial peer.
Step 4 video codec codec Example: video codec h Configures a video codec within the voice class. Step 5 exit Example: Device config-class exit Exits the current mode. Step 7 voice-class codec tag offer-all Example: Device config-dial-peer voice-class codec 10 Applies the previously configured codec voice class and associated codecs to a dial peer.
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Asked 4 years, 1 month ago. Active 4 years, 1 month ago. Viewed 2k times. Improve this question. Madhumita Madhumita 1 2 2 bronze badges. Add a comment. Active Oldest Votes. Even though the second stream is unidirectional, Alice receives RTCP packets on port from the media server. Alice adds a video stream that is accepted by Bob.
In a second exchange, Bob deletes the video session, resulting in an audio-only session. Call hold and resume flows are also common in 3pcc. In the second exchange, Alice adds an audio stream that Bob accepts.
Hold and Unhold 2 The first offer from Alice contains the connection address 0. Bob accepts with normal SDP. In the second exchange, Alice changes the connection address, Bob accepts, and a media session is established. Hold and Unhold 3 The first offer from Alice contains an audio stream, but the answer from Bob contains the connection address 0. In the second exchange, Bob changes the connection address, Alice accepts, and a media session is established.
Security Considerations SDP offer and answer messages can contain private information about addresses and sessions to be established between parties. If this information needs to be kept private, some security mechanism in the protocol used to carry the offers and answers must be used.
It is important that SDP offer and answer messages be properly authenticated and authorized before they are used to establish a media session. Informative References [ 1 ] Rosenberg, J. Sparks Estacado Systems EMail: rjsparks estacado. This document is subject to the rights, licenses and restrictions contained in BCP 78 , and except as set forth therein, the authors retain all their rights.
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