Dying Gasp

Dying Gasp

Dying Gasp is a message (or signal) sent by the CPE DSL device to the DSLAM when a power outage occurs. A DSL interface with dying gasp must derive power for a brief period from another source so that the message can be sent without external power. The dying gasp message will end the session and a new session will be able to be made as soon as power returns and the modem retrain. Dying Gasp is referenced in section 7.1.2.5.3 of ITU-T Recommendation G.991.2 (12/2003) as the Power Status bit. (SHDSL)

Dying gasp信号：在系统输入电压无法满足CPE正常工作的时候，CPE会自动发一个信号给DSLAM，说明CPE要不能正常工作了，DSLAM做相应反应。

Dying gasp原理：芯片厂商在设计芯片的时候会设计一个Dying gasp模块在芯片内，此模块通过监测外部输入电压来实现Dying gasp功能。此功能正常使用的前提是芯片必须还能正常工作，并且要向DSLAM发送一定时间长度的信号，所以在Dying gasp信号有效时间内（一般几个ms），供芯片正常工作的电源（一个电容electric capacity而已）电压不能小于此芯片要求的最小工作电压。