Technology sharing | anyrtc service single port design

Conventional CDN such as RTMP live broadcast , Is based on tcp Service for , There is no case of too many ports ; and RTC Most services use udp port , such Udp The model has many advantages , But compared to RTMP The single port of the live broadcast server goes around the world ,RTC The service needs to open hundreds of ports, which is a little embarrassing .

RTC Most of them are udp Communications , Many ports need to be opened during interworking , One sound / The video channel needs to open multiple channels , If it is a multi person audio and video call, more ports need to be opened . It is a great waste of port resources , Some firewalls limit the number of udp The opening of ports . If you want to deploy on the server , The development of multi ports will cause great inconvenience to the operation and maintenance .

Some people would say , There's nothing wrong with opening multiple ports , There is no problem in using it in the actual scene . Indeed, there is no problem with multiport itself , Safe to use , We just propose an optimization scheme on this basis .

What are the disadvantages of so many ports ？

1） Many network exit firewalls can pass through UDP Ports are limited .

2） For the server, open up so many ports , Security itself has some problems , It's easy to be scanned by hackers to attack , Especially my classmates , Even more refuse .

3） Open up so many ports in Server carry carefully , Port overhead and performance have a certain impact .

4） Industry specific requirements , Especially finance 、 Public security and other industries with particularly high security requirements , Multi port is not acceptable .

How to reduce RTC Use of ports in services , Can you even just use 1 There are two ports ？

So far, there are many mature strategies to reduce port use :

1）Rtp/Rtcp Scheme of multiplexing ports Rtcp-mux.

2） Audio and video Boundle, You can reuse the audio and video connection channel .

3） Multiplexed stream with single connection plan b and unified plan programme ;PS：WebRTC Of M89 The version is officially abandoned plan b, all WebRTC Standards have shifted unified plan.

These strategies are constantly reducing the use of ports , But even if all of the above strategies are turned on , A single user still needs to occupy at least one port , If one RTC The server should serve 500 Users , It's about to open 500 Ports .

How to realize single port , Because we need to know some technical points , In this way, the idea will be clearer ：

1）SDP offer and answer Internally configured ice-ufrag The content in the field ,STUN Binding Request Inside USERNAME The field is from the top Offer and answer Of ice-ufrag The content is spliced , This is used as stun Packet authentication , Therefore, it can be used as a logo for us .

2） send out STUN Binding Request Client local udp socket, And ice Sending media data after successful connection establishment udp socket Is the same , So for the server , Client's ip port Is the same .

Let's look at the implementation details ：

1） From the server to the client SDP Answer Set in ice-ufrag The only in this service ID, among ID It can be designed as the content allocated by the business layer , It can also be used to distinguish between each pair of calls and participants . Go ahead and do Ice candidate negotiation , The client starts to do connectivity detection , That is to say stun binding request Inside USERNAME by SDP local and remote Of ice-ufrag Specify content .

2） Server received stun binding request The client of ip And port , And normal return stun binding response.

3） The server records the mapping relationship between the client address and the user's information .

4） The server received a rtp/rtcp Media packets , Through the source of the package ip And port , Query the mapping table to identify which connected stream the package belongs to .

In this way, a single port mode can be realized RTC service , Very simple . Here's another tip for closing the pit , In the real world , The client's network is prone to change , For example, cell phones wifi Switch to 4/5G The Internet , At this time, the external exit of the mobile phone ip The port has changed , It needs to be updated on the server in time , Otherwise, a black screen will appear .