A method for communication, comprising: assigning a downlink window to at least a first remote node of a multiplicity of remote nodes, during which downlink window: the at least first remote node is operable for receiving downlink messages transmitted thereto by a central node, using a first frequency hopping function; and at least a second remote node of the multiplicity of remote nodes, which is operable: for ascertaining, during the downlink window, whether there exists at least one outstanding uplink message for transmission to the central node; responsive to said ascertaining that there exists at least one outstanding uplink message, transmitting, during the downlink window, the at least one outstanding uplink message to the central node, using a second frequency hopping function, which is synchronized with but different from the first frequency hopping function; ascertaining, during the downlink window, whether there exists at least one outstanding downlink message for transmission from the central node to the at least first remote node; and responsive to said ascertaining that there exists at least one outstanding downlink message for transmission, transmitting, during the downlink window, the at least one downlink message from the central node to the at least first remote node using the first frequency hopping function; and alternatively responsive to said ascertaining that there does not exist at least one outstanding downlink message for transmission to the at least first remote node, receiving, by the central node, during the downlink window, the at least one outstanding uplink message transmitted thereto by the at least second remote node using the second frequency hopping function. the at least first remote node is operable for receiving downlink messages transmitted thereto by a central node, using a first frequency hopping function; and at least a second remote node of the multiplicity of remote nodes, which is operable: for ascertaining, during the downlink window, whether there exists at least one outstanding uplink message for transmission to the central node; responsive to said ascertaining that there exists at least one outstanding uplink message, transmitting, during the downlink window, the at least one outstanding uplink message to the central node, using a second frequency hopping function, which is synchronized with but different from the first frequency hopping function; ascertaining, during the downlink window, whether there exists at least one outstanding downlink message for transmission from the central node to the at least first remote node; and responsive to said ascertaining that there exists at least one outstanding downlink message for transmission, transmitting, during the downlink window, the at least one downlink message from the central node to the at least first remote node using the first frequency hopping function; and alternatively responsive to said ascertaining that there does not exist at least one outstanding downlink message for transmission to the at least first remote node, receiving, by the central node, during the downlink window, the at least one outstanding uplink message transmitted thereto by the at least second remote node using the second frequency hopping function. for ascertaining, during the downlink window, whether there exists at least one outstanding uplink message for transmission to the central node; responsive to said ascertaining that there exists at least one outstanding uplink message, transmitting, during the downlink window, the at least one outstanding uplink message to the central node, using a second frequency hopping function, which is synchronized with but different from the first frequency hopping function; ascertaining, during the downlink window, whether there exists at least one outstanding downlink message for transmission from the central node to the at least first remote node; and responsive to said ascertaining that there exists at least one outstanding downlink message for transmission, transmitting, during the downlink window, the at least one downlink message from the central node to the at least first remote node using the first frequency hopping function; and alternatively responsive to said ascertaining that there does not exist at least one outstanding downlink message for transmission to the at least first remote node, receiving, by the central node, during the downlink window, the at least one outstanding uplink message transmitted thereto by the at least second remote node using the second frequency hopping function.