networking & internet

How RTP Multiplexing Works?

In this modern technological era, the demand of audio and video communication has increased, which requires high volume of bandwidth for audio and video transmission over the internet resulting in bandwidth lacking & network overload. To overcome these difficulties a variety of RTP multiplexing methods has been proposed. This article describes one of the RTP multiplexing methods which will give you the full understanding of how RTP multiplexing works.

The RTP multiplexing scheme relies on the assumption that there are two multiplexing ends, one is the sender and another is the receiver. Both ends are transparent and reciprocal to each other. Multiple RTP packets from different users are received by one multiplexer end which will be multiplexed destined to the same destination packet. Then it is sent to the receiver end which will demultiplex the packet and send it to the destination.

RTP Multiplexing

For the sake of simplicity we are describing RTP multiplexing for audio communication only. As you know there are different types of audio codecs with different audio frame sizes which are combined with IP, UDP and RTP header. Depending on the audio codec frame size varies 10, 20 or 30, 64 bytes etc, on the other hand, the RTP overhead(TCP header- 20 bytes, UDP header - 8 bytes and IP header - 12 bytes) is 40 bytes which is very large compared to the codec frame size. For example, G729 voice codec frame size is 10 bytes where RTP overhead is 40 bytes.

Diagram: G729 Codec Frame Size

Thus causing the header overhead problem. Transmitting a large number of the small packets over the network which is limited by the router capacity or network equipment causes network overload or congestion.

RTP Multiplexer can handle those problems - network overload and header overhead very efficiently. The RTP multiplexing system demands two endpoints. One endpoint multiplexes the packets and another endpoint demultiplexes those packets and vice-versa. RTP packets from different input sources are received by the first endpoint, which checks the destination of every packet and removes the RTP overhead. Then add a mini header to each packet and encapsulate packets into a single multiplexed packet of the same destination. Finally send to another endpoint which demultiplexes the received packets with the information of a mini header attached with the multiplexed packets to rebuild its original RTP packets and send to their destination.

RTP Multiplexing

So the number of packets as well as RTP overhead has been decreased between two endpoints.Thus the problem of network congestion and header overhead has been solved by RTP Multiplexing.

Another point to note, as you know RTP multiplexing process requires two additional endpoints which causes a significant delay for the processing multiplexing and demultiplexing of packets. This issue is overcome by the network Maximum Transfer Unit(MTU) as multiplexed packet sizes are bounded by the MTU.

Advantages of RTP multiplexing

  • Removes Packet overhead
  • Reduce network overload
  • Increase Performance
  • Reduce packet loss and congestion
  • Maintain QoS

Disadvantages of RTP multiplexing

  • Delay
  • Processing Charge
  • Multiplexed packet loss affects whole packets.
  • External Equipments

Natiply as a RTP Multiplexer

Synopi Natiply uses a proprietary communication protocol that ensures all the RTP multiplexing advantages such as reducing network overload, removing packet overhead, increasing performance more efficiently. Moreover, It removes the disadvantages of RTP multiplexing like delay, network congestion, packet loss by its advanced network congestion management system to maintain the highest performance and QoS. For more details about Natiply, please visit