Firstly, a busy tone is adopted to indicate the channel status and the data packet transmission [18-20].
For the applications of employing a half-duplex transceiver at each node, we propose the slotted dual-channel ETE-MAC protocol to efficiently resolve multichannel hidden-terminal type and exposed-terminal type problems in multihop wireless networks without using the busy tone scheme and the channel state tables.
Later, when the officers tried to reach him, the phone returned the busy tone
. He was unreachable even by other means," a source said.
Many reported after calling the 0845 6006400 number they were met by a busy tone
Imagine the trauma of a bullied or abused child who finally finds the courage to pick up the phone only to receive a busy tone
The typical cooperative MAC protocols of sender-specified helper include the CD-MAC protocol , the CoopMAC protocol , the rDCF protocol , the adaptive distributed cooperative MAC (ADC-MAC) protocol , the relay-contention-free cooperative MAC (RCF-CMAC) , the cooperative access with relay's data (CARD) protocol  and the busy tone based cooperative MAC (BTAC) protocol .
The helper with higher priority can choose the earlier minislot to send its busy tone. The 1st, 2nd, 3rd and 4th priority helpers are those with packet to send, and higher [R.sub.SH] and [R.sub.HD].
A BT spokeswoman said: "For the whole of the UK network there will be call-gap in place which staggers the calls slightly so that everybody should get through which means they will be connected or get a busy tone
- Silence, ring-back, busy tones
or any Custom Tones from the PCM wave file / wave streams
"That's usually the most intensive piece," Murawski says, "because we have to learn all the dial tones, ringtones, busy tones
. And everybody's phone system handles that a little differently."
The simplest seemed to be hiring more agents to handle calls, so that callers wouldn't be put on hold or get busy tones
. "But hiring more personnel, which represents the largest cost in any business today, didn't fit our needs," Widengren recalls.