# Common Control Channels **GSM CCCHs(Common Control Channels)** are used for conveying information from network to the Mobile Subscribers(MSs) and provide access to the Mobile Subscribers. GSM CCCHs include PCH,RACH,AGCH and CBCH. Can be used on Uplink or Downlink but only one at time --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://gsm.learn-telecom.com/gsm-channels/signalling-channels/common-control-channels.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.