通信术语

1.guard time

A time interval left vacant (i.e., during which no data is sent) on a transmission channel that can be used for synchronization and/or compensating for a signal distortion. The guard time provides a safety margin against symbol interference in the time between sequential operations such as transmission, encoding, decoding or switching.
2.Preamble:

A sequences of 56 bits having alternating 1 and 0 values that are used for synchronization. They serve to give components in the network time to detect the presence of a signal, and being reading the signal before the frame data arrives.