A RESTART message is sent by the network or user equipment in order to return channels or interfaces to the Null state. The Restart indicator information element shall be present in the RESTART message to indicate whether an Indicated channel, Single interface or All interfaces are to be restarted. If the Restart indicator information element is coded as"Indicated channel", or "Single interface" and the interface is one other than the one containing the D-channel, then the Channel identification information element shall be present to indicate which channel or interface is to be returned to the idle condition. If the Restart indicator information element is coded as "Single interface" and the interface is the one containing the D-channel, then the Channel identification information element may be omitted. If the Restart indicator information element is coded as "All interfaces" then the Channel identification information element shall not be included.
Upon transmitting the RESTART message the sender enters the Restart Request state, starts timer T316, and waits for a RESTART ACKNOWLEDGE message. Also, no further RESTART messages shall be sent until a RESTART ACKNOWLEDGE is received or timer T316 expires. Receipt of a RESTART ACKNOWLEDGE message stops timer T316, frees the channels and call reference values for reuse, and enters the Null state.
If a RESTART ACKNOWLEDGE message is not received prior to the expiry of timer T316 one or more subsequent RESTART messages may be sent until a RESTART ACKNOWLEDGE message is returned. Mean while, no calls shall be placed or accepted over the channel or interface by the originator of the RESTART message. A network shall limit the number of consecutive unsuccessful restart attempts to a default limit of two. When this limit is reached, the network shall make no further restart attempts. An indication will be provided to the appropriate maintenance entity. The channel or interface is considered to be in an out-of-service condition until maintenance action has been taken.
Note - If a RESTART ACKNOWLEDGE message is received indicating only a subset of the specified channels, an indication shall be given to the maintenance entity. It is the responsibility of the maintenance entity to determine what actions shall be taken on the channel(s)which have not been returned to the idle condition.
The RESTART and RESTART ACKNOWLEDGE message shall contain the global call reference value (all zeros) to which the Restart Request state is associated. These messages are transferred via the appropriate point-to-point data link in the multiple frame mode using the DL-DATA request primitive.