The Q3 interface of the access network can request that a port be blocked for non-urgent configuration or reconfiguration. If the port is routed through a V5 interface to a local exchange, then this request can only be granted by the local exchange via the V5 interface. This is intended to avoid interference with calls in progress, or calls being set up or cleared down. The Q3 interface on the access network can request that a port be blocked for urgent configuration or reconfiguration. If the port is routed through a V5 interface to a local exchange, the other side of the interface shall be informed of this blocking via the V5 interface. Valid values are: * 'blocked' - the user port can be unblocked by both accelerated port alignment (i.e. group unblocking) and sequential port alignment. * 'shuttingDown' - same as 'blocked' except active calls will not be blocked until the calls are completed. * 'unblocked' - port will be unblocked regardless of its previous port block state. * 'blockedNotSuitableForGroupUnblocking' - the user port cannot be unblocked by accelerated port alignment unblocking but can be unblocked by sequential unblocking. Default value is blocked.