Users who use public network walkie-talkies know that they must press the PTT button and hear a "beep" before they can speak, which is obviously different from traditional analog or digital conventional walkie-talkies, and some users I am not used to using the public network walkie-talkie for the first time. Why when I use the public network walkie-talkie, if I press the PTT button to start talking, the receiving end is prone to the phenomenon that the first few words (the first lost words) cannot be heard? This is Because, there is a time difference between the public network walkie-talkie pressing the PTT button and the completion of the intercom group establishment. This time difference is called "group call establishment delay".
 

As we all know, traditional walkie-talkies are divided into "regular walkie-talkies" and "cluster walkie-talkies". For conventional intercom, each intercom group needs to occupy a wireless channel (frequency point) exclusively, and multiple intercom groups need to occupy multiple independent wireless channels (frequency points); cluster intercom, controlled by a central base station, can realize wireless Channel sharing, each intercom group occupies the wireless channel only when an intercom call occurs, and the channel resources are released after the intercom, and the same channel can be used by different intercom groups.

It is precisely because the conventional walkie-talkie adopts the exclusive channel mechanism. As soon as the user presses the PTT key, the walkie-talkie starts to transmit signals. There is no process of channel resource application and allocation, so there is no need for a speech prompt tone. Press the PTT key to speak. .

The trunking intercom system is different, such as TETRA, iDEN, etc., using the shared channel mechanism, the number of user groups will be much larger than the number of available physical channels. After the allocated resources are confirmed, the wireless channel can be occupied and the speech can be started. Therefore, users who have used the trunking walkie-talkie know that after pressing the PTT key, they can only speak after hearing the voice confirmation prompt.

The working principle of the public network intercom is similar to that of the digital trunking system. Therefore, it should be more precisely called "public network trunking system" or "public network trunking intercom system". In fact, users of public network intercom not only share wireless channel resources with other public network intercom users, but also share wireless channel resources with mobile phone users. However, due to the large number of base stations, large system capacity and large coverage area of ​​the mobile public network, it has many advantages compared with the private network digital trunking system. Especially under the condition of large bandwidth and low latency of 4G network, its advantages in business function, performance and system capacity are more obvious.

The delay of group call establishment is one of the key indicators of the public network cluster intercom service, which has a great impact on the user's intuitive experience. The group call establishment delay index of the traditional Tetra digital trunking system is less than 300ms. The early public network intercom system based on 2G mobile network is due to the long delay and instability of group call establishment. Sometimes it takes several seconds to establish, resulting in poor user experience and poor market development. Under the 3G and 4G network, this indicator has been greatly improved.