Logical and Physical Channels Flashcards
What is a logical channel?
Logical Channels define the actual information that humans discern from the radio signal, whether that be a text, call, power up command, authentication, etc.
What is a physical channel?
A Physical GSM Channel consists of the physical characteristics of the transmitted radio wave.
What are the 4 types of logical channels
Broadcast Channels (BCH)
Common Control Channels (CCH)
Dedicated Control Channels (DCCH)
Traffic Channels (TCH)
What are the 3 broadcast channels?
Frequency Correction Channel (FCCH)
Synchronization Channel (SCH)
Broadcast Control Channel (BCCH)
What are the 3 common control channels?
Paging Channel (PCH) Random Access Channel (RACH) Access Grant Channel (AGCH)
What are the 3 dedicated control channels?
Standalone Dedicated Control Channel (SDCCH)
Slow Associated Control Channel (SACCH)
Fast Associated Control Channel (FACCH)
What is the role of the FCCH?
The FCCH is a sine wave 67 kHz above the center frequency that helps a handset tune to the center of the ARFCN.
What is the role for the SCH?
The SCH helps the handset tune to the symbol time (aka time sync). Also carries the Base Station Identity Code (BSIC).
What is the role of the BCCH?
The BCCH carries a multitude of cell specific information and network parameters, including the PLMN, LAC, CID, CRO, BA list, temporary offset, penalty timer, and RxLAM.
What is the role of the PCH?
The paging channel is sent on the downlink to notify a user of incoming traffic. Paging Channels carry the TMSI of the user being contacted. Broadcasts on the downlink only.
What is the role of the RACH?
Used by the handset to respond to a page or initiate a network connection. The handset uses this channel to request network resources. Broadcasts on the uplink only.
What is the role of the AGCH?
The AGCH is the “answer” to the handset’s RACH. The AGCH either carries an “Immediate Assignment” message if there are resources, or an “Immediate Reject” if there are no available timeslots. Broadcasts on the Downlink only.
What is the role of the SDCCH?
Performs all dedicated signaling outside of a traffic channel (Authentication, Registration, Caller ID, Call Setup). Sends/Receives SMS. 1/8th of a Timeslot. Can be on timeslot 1-7.
What is the role of the SACCH?
Used for call maintenance, power up/down commands, Timing Advance changes, SMS messages while in a TCH. Can be associate to a TCH or an SDCCH
What is the role of the FACCH?
Used to send priority immediate messages while the user is in a call, such as call waiting messages or handover commands. Uses the method of “stealing flags” where small amounts of bits are replaced with the incoming message. Can only be associated to a TCH.
