The invention relates to a method and system for ensuring a PSTN protocol restart procedure as defined by the V5 standard after a failure of a first data link carrying PSTN protocol signalling messages. In the method, a first time-out (TC3) for starting the restart process is observed and, if the time-out has tripped, the restart procedure is started by sending a start message using a Control protocol signalling message consistent with the V5 standard. According to the invention, after the first data link carrying the PSTN protocol has been restored to working order, a check is carried out to establish whether a second data link intended to carry Control protocol signalling messages is in order, and this check is repeated until the second data link intended to carry Control protocol signalling messages is in order, and when the second data link is in order, a message for starting the PSTN protocol restart procedure is sent in the Control protocol.
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