Abstract: A method of determining information on network resources in a packet-based internetwork comprising multiple routing nodes, the method comprising: distributing user software to each of multiple end-user terminals connected to the internetwork, the user software having a primary user function other than the collection of network data; in association with the user software, distributing secondary code configured to participate in the collection of data by probing different routes from the respective end-user terminal to a destination terminal over the internetwork, each route passing via a plurality of said routing nodes; receiving data resulting from the probing performed by the secondary code on the multiple end-user terminals, including data resulting from routes involving the routing nodes of different network service providers; and determining estimates of network resources based on the received data.

Abstract: A communication system includes a plurality of nodes, the communication system being arranged to assign each of the plurality of nodes a certificate by means of which it can authenticate itself to other nodes in the communication system and periodically distribute to the plurality of nodes an update formed by compressing a data set representing the validity of the certificates assigned to the plurality of nodes. The update is such that a node may not be able to unambiguously determine from the update whether or not a particular certificate is valid. The system further provides the plurality of nodes with a source of information about the validity of the plurality of certificates that is different from the update and by means of which a node may resolve an ambiguity in the update regarding a particular certificate's validity.

Abstract: A communication system includes a plurality of nodes, the communication system being arranged to assign each of the plurality of nodes a certificate by means of which it can authenticate itself to other nodes in the communication system. The communication system further includes an authentication node arranged to determine that a certificate should be revoked and to, responsive to that determination, write an indicator of that certificate's revocation to a location in the communication system that is external to the authentication node and to which the node assigned the revoked certificate is not permitted to write.

Abstract: A method of determining information on network resources in a packet-based internetwork comprising multiple routing nodes, the method comprising: distributing user software to each of multiple end-user terminals connected to the internetwork, the user software having a primary user function other than the collection of network data; in association with the user software, distributing secondary code configured to participate in the collection of data by probing different routes from the respective end-user terminal to a destination terminal over the internetwork, each route passing via a plurality of said routing nodes; receiving data resulting from the probing performed by the secondary code on the multiple end-user terminals, including data resulting from routes involving the routing nodes of different network service providers; and determining estimates of network resources based on the received data.

Abstract: A communication system includes a plurality of nodes, the communication system being arranged to assign each of the plurality of nodes a certificate by means of which it can authenticate itself to other nodes in the communication system and periodically distribute to the plurality of nodes an update formed by compressing a data set representing the validity of the certificates assigned to the plurality of nodes. The update is such that a node may not be able to unambiguously determine from the update whether or not a particular certificate is valid. The system further provides the plurality of nodes with a source of information about the validity of the plurality of certificates that is different from the update and by means of which a node may resolve an ambiguity in the update regarding a particular certificate's validity.

Abstract: A communication system includes a plurality of nodes, the communication system being arranged to assign each of the plurality of nodes a certificate by means of which it can authenticate itself to other nodes in the communication system. The communication system further includes an authentication node arranged to determine that a certificate should be revoked and to, responsive to that determination, write an indicator of that certificate's revocation to a location in the communication system that is external to the authentication node and to which the node assigned the revoked certificate is not permitted to write.