Digital Equipment Corporation

Cabletron Systems, Inc.

Enterasys Networks, Inc.

Digital Equipment International Limited

Harvey, George A.

Hawe, William

Koning, Gerard

Miles, Kevin

Lauck, Anthony

Harper, John

Oran, David

Anthony G Lauck

Kadangode K Ramakrishnan

Henry S Yang

Bruce Eric Mann

William R Hawe

William D Strecker

Darrell Duffy

Anna Charny

John A Harper

Radia Joy Perlman

George Varghese

Ian M Shand

K K Ramakrishnan

Richard L Szmauz

Stuart R Soloway

David R Oran

George A Harvey

Kevin Miles

Darrell J Duffy

Gerard Koning

David Oran

John Harper

A rate based, end to end flow control system is disclosed for a communications network. The disclosed rate based flow control system includes each source end station selecting its transmission rate from a set of permitted discrete transmission rates. The set of permitted discrete transmission rates is based on a logarithmic encoding. The disclosed rate based traffic control system further requires each source end station to send one end to end control cell every time period T. The time period T is also known by switches in the communications network and is used to periodically calculate an available allocation (&ldquo;fair share&rdquo;) of bandwidth at a switch for a given virtual circuit.

Traffic control system having distributed rate calculation and link flow control

The rate based end system may provide feasible transmission rates for end source stations. As an extension to the rate based end to end system, there is disclosed a hybrid link by link flow control system. The link by link control system is built upon the end to end, rate based traffic control system. The link by link system utilizes bandwidth un accounted for by the end to end system. The link by link system uses feasible transmission rates obtained by the end to end system to determine the size of the buffers required for overbooking and for updating credit information to sustain the calculated rate.

Traffic control system having distributed rate calculation and link by

A system has a node connected to a network, the node generating a separate session message for each of a plurality of users. The node places each of the separate session message in a slot in a single virtual circuit message, and transmits the virtual circuit message onto the network. A server is connected to the network, and the server receives the virtual circuit message, and the server identifies each of the separate session messages. The server then transmits each of the separate session message to a user having a session corresponding to each of the separate session messages.

Computer network having a virtual circuit message carrying a plurality

A rate based, end to end flow control system is disclosed for a communications network. The disclosed rate based flow control system includes each source end station selecting its transmission rate from a set of permitted discrete transmission rates. The set of permitted discrete transmission rates is based on a logarithmic encoding. The disclosed rate based traffic control system further requires each source end station to send one end to end control cell every time period T. The time period T is also known by switches in the communications network, and is used to periodically calculate an available allocation (or 'fair share') of bandwidth at a switch for a given virtual circuit.

A technique for modifying the IEEE 802.3 standard for selecting backoff times in a Carrier Sense Multiple Access with Collision Detection (CSMA/CD) network, in the event that a collision is sensed by a node that has captured the network communication channel. If there is a small number of active nodes on the network, one node may capture the channel and the standard backoff algorithm makes it increasingly unlikely for another node to transmit. The new technique provides for less aggressive, i.e. longer, backoff times before at least the first retransmission attempt made by a node that has captured the channel. Three specific examples of the technique are disclosed. Even though the invention represents a departure from the standard CSMA/CD backoff algorithm, the overall average backoff times provided by the invention can be selected to be consistent with the average times provided by the standard. Moreover, nodes using the invention interoperate successfully with nodes that do not.

Method and apparatus for use in a network of the ethernet type, to

A communications network has a plurality of users connected by virtual circuits to a plurality of service providers. A server has the plurality of users connected thereto. A node provides the plurality of service providers. Both the server and the node are connected to the network. A first session is established between one user and the server, and a second session is established between the node and a selected one of the service providers. A virtual circuit is established linking the first service session and the second service session to establish message transmission between the one user and the selected service provider. A message sent between the user and the service provider is sent over the network, and the message identifies the virtual circuit. Messages between a server and a node are multiplexed by having slots, and a slot contains a message from a sending session to a receiving session.

Local area network with server and virtual circuits

A node operating in a network using the International Standard Organization (ISO) High-Level Data Link Control (HDLC) network protocol includes a mechanism for encoding information such that frames including the encoded information can be correctly interpreted by nodes operating in either of the standard 16-bit or 32-bit ISO-HDLC operating modes. The encoding mechanism produces a preliminary frame check sequence by encoding the information in an encoder using a generator polynomial G.sub.48 (x), which is a combination of the generator polynomials G.sub.16 (x) and G.sub.32 (x) which are used to produce frame check sequences for nodes operating in 16-bit or 32-bit modes, respectively. Before the information is encoded, the encoding mechanism sets the encoder to an initial condition using an initializing polynomial I.sub.48 (x). The preliminary frame check sequence is further encoded by adding to it a complementing polynomial C.sub.48 (x). The result is a 48-bit frame check sequence. The encoding mechanism appends the 48-bit frame check sequence to the information, and transmits the information and the appended 48-bit frame check sequence over the network as part of a frame.

Method and apparatus for generating a 48-bit frame check sequence

A technique for modifying the IEEE 802.3 standard for selecting transmit-to-transmit interpacket gap (IPG) intervals in a Carrier Sense Multiple Access with Collision Detection (CSMA/CD) network, to provide fairness and good channel utilization in the event that a node has captured the network communication channel. If there is a small number of active nodes on the network, one node may capture the channel and the standard backoff algorithm makes it increasingly unlikely for another node to transmit. The new technique provides for use of a longer interpacket gap (IPG) interval to be used by a node that has been initially unsuccessful in contention for the channel, thereby ensuring that the other node may continue to transmit back-to-back data packets without interruption or collision. After a preselected time interval, the nodes reverse their roles by selecting the opposite IPG intervals. The initial receiver now selects the shorter IPG interval and captures the channel for the preselected time interval.

Apparatus and method for realizing a parallel implementation of run length coding. The system encodes control and data information into the respective link control and data streams and merges the same onto the communication link for transmission. In addition, the system separates link data information from control information upon receipt of the information stream and decodes the received link data and control information into the original information.

Parallel implementation of run length coding apparatus and method

A technique for modifying the IEEE 802.3 standard for selecting backoff times in a Carrier Sense Multiple Access with Collision Detection (CSMA/CD) network, in the event that a collision is sensed by a node that has captured the network communication channel. If there is a small number of active nodes on the network, one node may capture the channel and the standard backoff algorithm makes it increasingly unlikely for another node to transmit. The new technique provides for less aggressive, i.e. longer, backoff times before at least the first retransmission attempt made by a node that has captured the channel, and in addition provides for the use of a stopped backoff algorithm. Three specific examples of methods to choose a backoff time and two methods of using a stopped backoff algorithm are disclosed. Even though the invention represents a departure from the standard CSMA/CD backoff algorithm, the overall average backoff times provided by the invention can be selected to be consistent with the average times provided by the standard. Moreover, nodes using the invention interoperate successfully with nodes that do not use the invention.

A technique for modifying the IEEE 802.3 standard for selecting transmit-to-transmit interpacket gap (IPG) intervals in a Carrier Sense Multiple Access with Collision Detection (CSMA/CD) network, in the event that a node has captured the network communication channel. If there is a small number of active nodes on the network, one node may capture the channel and the standard backoff algorithm makes it increasingly unlikely for another node to transmit. The new technique provides for less aggressive, i.e. longer, interpacket gap (IPG) intervals to be used by a node that has captured the channel, thereby increasing the likelihood that another node will gain access.

A ring purging station for a token-ring network is disclosed. The station performs purging operations to remove no-owner frames and frame remnants from the network. The station begins a purging operation by detecting the token on the network and removing it. The station then begins stripping all frames and remnants of frames that it receives from the network, and transits one or more purge marker frames. When the station detects one of the one or more purge marker frames it transmitted, it ends the purging operation, and releases the token back onto the ring. In this way no-owner frames and frame fragments are removed from the network, while the ring is otherwise normally operating. In an embodiment of the invention, a sequence number is associated with each purging operation, included in the purge marker frame(s), and verified upon receipt of the purge marker frame(s). The station also corrects multiple token conditions when a multiple token condition is detected during a purging operation. A further aspect of the invention is an election method for selecting a purging station from the stations on the ring.

No-owner frame and multiple token removal mechanism for token ring

A method of providing loop free and shortest path routing of data packets in a network having a plurality of switches, routing messages for communicating network topology information between the switches, a plurality of links connecting the switches and a plurality of channels connecting the switches to the links. The loop free routing of data packets is achieved through modifications to known link state packet (LSP) routing protocols and permits each switch to inform adjacent switches in the network of the information in the switch's database used to compute forwarding tables. A switch uses a received LSP to compute a forwarding table and informs neighboring switches on attached links of the routing change. The switch discards any subsequent data packets whose path would be affected by the changed routing information. The discarding of data packets continues until the switch receives notification from each adjacent switch affected by the changed routing information that all affected routing paths have been recalculated and the forwarding table of each affected switch has been updated. Thus, while adjacent switches temporarily contain inconsistent LSP databases and possibly inconsistent forwarding tables, the looping of data packets is prevented. Shortest path routing for data packets from a source endnode to a destination endnode is achieved by assuring that the first switch to forward the packet is on the shortest path to the packet's destination endnode. A source endnode transmits a data packet with an appropriate destination header and the determination of the actual routing path is performed transparently to endnodes. A data packet reaches its destination endnode by following the shortest path possible based on the network topology as represented in the database of the first switch that forwards it.

Synchronization mechanism for link state packet routing

A method and related apparatus for establishing a point-to-point cross-link between two bridges in a bridged communication network. The bridged communication network is first configured in a loop-free arrangement by a spanning tree algorithm that selects which links of every bridge to activate in order to form the spanning tree active configuration. Then at least one cross-link not defined by the spanning tree configuration is established for routing of messages as an alternative to a spanning tree path. A protocol in each bridge ensures that no loops are formed and that only messages to preselected locations are passed over the cross-link. An optional optimization procedure measures message propagation times in both directions between the two bridges and over both the cross-link path and the spanning tree path, to determine whether to modify usage of the cross-link. Selection of the bridges for the formation of the cross-link, and selection of the destination stations for cross-link traffic, are independent of the location of a root bridge in the spanning tree configuration.

Growing community of inventors

Wellesley, MA, United States of America

Anthony G Lauck