先决条件–时分复用(TDM)
1.同步TDM：
在同步TDM中，其中存在的每个设备都已指定了相同的时隙来传输数据。它不考虑设备是否包含数据。设备在其时隙到达时将其数据放置在链接上，如果某种设备不包含数据，则其时隙将保持为空。存在被组织成帧的各种时隙，并且每个帧由专用于每个发送设备的一个或多个时隙组成。
2.异步TDM：
异步TDM的别称是统计划分多路复用。之所以这样称呼，是因为时隙不是固定的，即时隙是灵活的。由于时隙不是固定的，因此要发送分配时隙的数据的设备。
同步TDM和异步TDM之间的区别：
| S. No. | Synchronous TDM | Asynchronous TDM |
|---|---|---|
| 1. | In this, multiplexer allocates same time slots to each device without considering fact that device contains data or not. | In this, multiplexer does not allocates same time slots to each device without considering fact that device contains data or not. |
| 2. | Number of slots per frame are equal to number of input lines i.e., If it contains n input lines, then it must have n slots in one frame. | Number of slots per frame are less than number of input lines i.e., If there are n input lines, then there are m slots in one frame (m |
| 3. | There is no guarantee that full capacity link is used. | There is guarantee that full capacity link is used. |
| 4. | Total speed of input lines cannot be greater than capacity of path. | Total speed of input lines can be greater than capacity of path. |
| 5. | Usage of devices is less. | Usage of devices is more. |
| 6. | Number of time slots in a frame as always based on number of input lines. | Number of time slots in a frame as always based on statistical analysis of number of input lines that are likely to be transmitting at any given time. |
| 7. | Time slots are fixed and pre-defined. | Time-slots are not pre-defined. |