先决条件 – 时分复用 (TDM)
1. 同步时分复用：
在同步 TDM 中，存在于其中的每个设备都给出了相同的时隙来传输数据。它不考虑设备是否包含数据。当它们的时隙到达时，设备将它们的数据放置在链路上，如果不知何故任何设备不包含数据，则其时隙保持为空。有多种时隙被组织成帧，每一帧由一个或多个专用于每个发送设备的时隙组成。
2.异步TDM：
异步 TDM 的另一个名称是统计分割复用。之所以这样称呼是因为时隙不是固定的，即时隙是灵活的。由于时隙不固定，要发送数据的设备分配时隙。
同步 TDM 和异步 TDM 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. |