Abstract: A line protection circuit for an ISDN device includes a pair of identical, NMOS field effect transistors connected between the device and opposite terminals of one winding of an isolation transformer. Each device has one N region connected to an output line from the ISDN device, a second N region connected to one winding terminal, a grounded channel or P region and a gate connected to a source of positive logic voltage. During normal operation, the FETs pass current provided by a constant current source within the ISDN device without attenuation. If a power surge occurs elsewhere in the ISDN network, the voltage at one of the FETs is be clamped to ground while the voltage at the other FET rises only until FET cut-off occurs. If power is removed from the FETs, at least one PN junction will always be reverse biased to isolate the protected ISDN device from the remainder of the network.

Abstract: An end-to-end, closed loop flow and congestion control system for packet communications networks exchanges rate request and rate response messages between data senders and receivers to allow the sender to adjust the data rate to avoid congestion and to control the data flow. Requests and responses are piggy-backed on data packets and result in changes in the input data rate in a direction to optimize data throughput. GREEN, YELLOW and RED operating modes are defined to increase data input, reduce data input and reduce data input drastically, respectively. Incremental changes in data input are altered non-linearly to change more quickly when further away from the optimum operating point than when closer to the optimum operating point.

Abstract: Access agents in nodes at the LAN/WAN interface are formed into a group of access agents so that the access agents may be managed by the WAN as a group. The group must maintain group operation integrity in that if communications between agents in the group are broken, the access agents will coalesce into subgroups and continue performing communication jobs as a group activity. Each of the access agents contains a finite state machine to perform the tasks of group formation and maintenance. The formation of interconnected access agents into a group is accomplished by one access agent being identified as a group leader. All other access agents communicating with the group leader within the LAN may then join the group. The maintenance of group activity integrity is accomplished by detecting a break in group communication integrity and thereafter reforming the group into multiple smaller groups.

Abstract: Access control for a packet communications network includes a dynamic bandwidth updating mechanism which continuously monitors the mean bit rate of the signal source and the loss probability of the connection. These values are filtered to remove noise and then used to test whether the values fall within a pre-defined acceptable adaptation region in the mean bit rate, loss probability plane. Values falling outside of this region trigger bandwidth updating procedures which, in turn, result in acquiring a new connection bandwidth, and determining new filter parameters and new parameters for a leaky bucket access mechanism.

Abstract: In a multicast network communication system, administration of the communication path making up the multicast tree itself has been separated from control and administration of the network. Creation of a multicast distribution tree and control over the membership thereof, is separately controlled independently from the creation and use of the tree transmission path used to communicate among the members of a multicast set. Transmission distribution trees are set up when a transmission request is received and the properties of the transmission path that is required are known. Transmission paths are created and controlled by all nodes in the communications system, each node having necessary control code and processors for responding to requests from set members to transmit a message to groups of users by creating and activating the necessary tree communication path distribution linkages. A distribution tree is created by the Tree Leader by generating a tree address using a random number generator.

Abstract: In a packet communications network, the addition or deletion of a connection to the network by a user is governed by a link traffic metric which represents the effective capacity of each link in the network which participates in the packet connection route. A new connection (or deletion) is represented by a compatible metric which allows updates in the link metric by simple vector addition or subtraction. Separate link metrics for a plurality of classes of service permit a much higher efficiency in the exploitation of the link bandwidth than is possible with a single link metric. A packet network using multiple link metrics and efficient metric updating techniques provides increased packet throughput while, at the same time, preserving all class of service guarantees.

Abstract: An enhanced intervention list is used in a data communication network used to route messages from a source or originating user to a destination user in the network. The enhanced intervention list includes an intervention type field which defines how an intercepted distribution is to be processed. For an Associative Redirection intervention type, the message is redirected to a destination user identified in the intervention list. For a Predirecting Intervention type, the message is diverted to an intervening agent or program identified in the intervention list. After the message is processed by the intervening agent, it is routed to a user directory which identifies the destination node serving the destination user. For a Postdirecting Intervention type, the message is sent to the local user directory first and is then checked against the intervention list entries to see if intervention is still warranted.

Abstract: A method is disclosed for determining whether to use a preempt/resume protocol or an alternate protocol in transmitting data packets from a local system to a remote system. Each system informs the other whether it supports preempt/resume and provides the sizes of the largest low priority data packets it can send and receive. The local system always elects the alternate protocol unless both support preempt/resume. The local system then selects the lesser of (a) the largest low-priority data packet it can send and (b) the largest low-priority data packet the remote system can receive. Use of prompt/resume is initiated by the local system only where a packet of the selected size would be delayed in reaching the remote system by more than a predetermined interval.

Abstract: A process for selecting a least weight path between two nodes in a data communication network uses partial trees created and cached in prior route selection operations. All root nodes on possible paths between the two nodes are identified. Any cached tree having a root matching one of the identified root nodes is retrieved from storage. If necessary, each retrieved tree is extended until it includes all possible destination nodes. The extended and/or retrieved trees are used to select the least weight path between the two nodes. The extended tree is then cached for possible use in future route selection operations.

Abstract: In a focal point network, adjacent nodes may agree to a relationship where one node (a focal point or server node) supplies network management services to the other node (a non-focal point or served node). A served node forwards management services data to its server node without waiting for any request. There is a risk that the nodes will become configured into a closed loop within which data, once introduced, will circulate endlessly. To eliminate this risk, a loop-detection message is generated when a node acquires a new server node and is itself a server node for other nodes. The message, which includes the originating node's name, is passed from served node to server node. Each node inspects the message. If it does not find its own name, it appends its name to the message and passes it on to its own server node. If the node does find its own name, it generates a loop-detected message that revokes the server/served relationship with the current server node.

Abstract: A congestion control system for packet communications networks in which access to the network is controlled to prevent such congestion. Packets within the prespecified statistical description of each packet source are marked as high priority ("green" packets) while packets exceeding the pre-specified characteristics are marked with a lower priority ("red" packets). The overall red packet rate is limited to prevent red packet saturation of the network. Packets are marked red for a continuous train of successive red packets. The introduction of red packets into the network is subjected to a degree of hysteresis to provide better interaction with higher layer error recovery protocols. The amount of hysteresis introduced into the red packet marking can be fixed or varied, depending on the statistics of the incoming data packets at the entry point to the network.

Abstract: A packet communications system provides for point-to-point packet routing and multicast packet routing to limited subsets of nodes in the network, using a routing field in the packet header which is processed according to two different protocols. A third protocol is provided in which a packet can be multicast to the limited subset even when launched from a node which is not a member of the subset. The routing field includes a first portion which contains the route labels necessary to deliver the packet to the multicast subset. A second portion of the routing field contains the multicast subset identifier which can then be used to deliver the packet to all of the members of the multicast subset. Provision is made to backtrack deliver the packet to the last node identified before the multicast subset if that last node is itself a member of the subset.

Abstract: Modifications to existing frame relay communication protocols are described which permit both voice and data frames to be handled in an integrated frame relay system. A Voice Frame Identifier bit is defined in the address field of a frame. When an intermediate node detects a voice frame, a CRC operation is performed using only the frame header; that is, voice information is excluded from the computation. The frame is flagged for priority processing in the node. When the intermediate node detects a data frame the CRC operation uses both the header and the data fields.

Abstract: In a packet communications network, the addition or deletion of a connection to the network by a user is governed by a link traffic metric which represents the effective capacity of each link in the network which participates in the packet connection route. The link metric is calculated in real-time and updated by simple vector addition or subtraction. Moreover, this link metric is also used to calculate leaky bucket parameters which govern the access of packets to the network once the connection is set up. A packet network using these link metrics and metric generation techniques provides maximum packet throughput while, at the same time, preserving grade of service guarantees.

Abstract: Each node in a multinode communication system is provided with programming to act as a Set Manager for a given set of nodes and users. Functions of the Set Manager include operation processes for creating distribution trees for efficient multicast and bandwidth reservation tasks. Because set membership is not necessarily fixed or accurate at the time the distribution tree is created, the Tree Leader task that creates and maintains the trees needs accurate and updated information showing the number of users at the nodes it serves which are participating in the distribution tree. The count of active users at nodes served by the Tree Leader is provided in response to an indicia established at the time the Tree Leader sets up the tree.

Abstract: A packet communications network relies on a few simple parameters to characterize the wide variety of traffic offered to that network, such as peak bit rate, mean bit rate and average packet burst length. A better representation of many types of traffic relies on an equivalent burst length which produces the same loss probability distribution, but assumes that the distribution is uncorrelated and exponential. Access control and bandwidth management based on such an equivalent burst length produces improved decisions due to the more accurate representation of the actual traffic distribution.

Abstract: A packet communications system utilizes a route determining mechanism by identifying principal paths between the source and the destination in the system. Principal paths are minimum hop count paths with a transmission delay less than a specified threshold. Principal path links are accepted as legs of the optimum path, if feasible, i.e., if the resulting load on the link is less than a specified principal threshold. Secondary links are accepted only if the resulting load on the link is less than a specified secondary threshold, where the secondary threshold is less than the principal threshold. All paths must also have a transmission delay less than a specified threshold. Each request for a route includes the source node, the destination node, the load required, the maximum transmission delay and, if desired, the quality of service parameters which all of the legs of the route must satisfy.

Abstract: A Transport Layer Protocol Boundary (TLPB) architecture is described which will permit an application program to run over a non-native transport protocol without first generating a protocol compensation package tailored to the transport protocols assumed by the program's application programming interface and by the available transport provider. All transport functions required by the program are converted to standardized or TLPB representations. When a connection between the first application program and a second remote application is requested, the individual required TLPB transport functions are compared to corresponding functions supported by the transport provider. Compensations are invoked only where there is a mismatch. The node on which the remote application program runs is informed of the compensations so that necessary de-compensation operations can be performed before the data is delivered to the remote application program.

Abstract: The present invention is an improvement in a known LOCATE process used to locate resources in a computer network. The known LOCATE process always requires that information about a target resource be verified by forwarding a LOCATE request to the node owning the target resource. The present invention improves upon this process by use of selective verification. If predetermined conditions are met, a node in the network may reply to a received LOCATE request by using information about the target resource found in its cache directory. The LOCATE request need not be propagated to the node owning the target resource except for predetermined types of sessions or where past attempts to use selective verification have not been successful.

Abstract: A computer-aided process for calculating the orientation and strength of trim magnetic fields for a monochrome CRT uses a machine vision camera to establish the shape of the uncorrected raster. Using the distortion information and sensitivity mappings representing the effect of a single trim magnet on a raster, a linear optimization technique is employed to compute the strength and orientation of each magnetic field which must be used to correct for raster distortions.