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GSM Issue-Handover from UTRAN failed due to physical channel failure

On this page we will examine most common issue where in handover from UTRAN failed due to physical channel failure. This failure is usually followed by timer T313 timeout.

This scenario explains handover from UTRAN to GSM. The UTRAN network starts handover procedure by initiating "handover command" to the mobile subscriber (i.e. UE) on the main DCCH channel. After the initiation UE starts timer T3103.

While sending of handover command by network and reception of the same by UE, transmission of signalling messages are suspended by the network. The exception is for RR messages needed for handover procedure as well as for abnormal cases.

After mobile receives the handover cmd message, it will release link layer connections and disconnects the physical channels. It then switches to the channels assigned by network. Now UE initiates lower layer connection establishment including channel activation and data link connection establishment.

Four procedures are defined. The support of three of them is mandatory in the mobile station. The pseudosynchronization case is optional in the mobile station. A pseudo-synchronised handover can be commanded only to a mobile station that can support it, as indicated in the classmark.

•  Finely synchronized cell case
•  Non synchronized cell case
•  Pseudo-synchronised cell case
•  Pre-synchronised cell case

Upon successful lower layer connection establishment, mobile station(MS) returns HANDOVER COMPLETE message. It will set cause as 'normal event' in the message to the network on the main DCCH channel.

After the reception of 'HANDOVER COMPLETE' message, the network will stop the timer T3103 and will release the old channels.

If requested by the network, mobile subscriber corrects the transmission of HANDOVER COMMAND message to the half value of timing advance as measured it.

The handover failed when UE moves from UTRAN cell to the GSM cell due to physical channel failure followed by T313 timer expiry.
Timer T313 Starts when UE detects consecutive N313 "out of sync" indication from Layer-1(PHY)
Timer Stops when UE detects consecutive N315 "in sync" indication from Layer-1(PHY)
Time T313 will get expired when either radio link failure will occur or physical channel failure will happen.

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