Abstract: A soft decision maximum likelihood detection method and apparatus. Both encoding and decoding schemes are provided for a forward error correcting code. The decoding technique utilizes soft decision maximum likelihood decoding especially suited for codes that operate on symbols rather than bits. The decoding technique utilizes a maximum likelihood function in combination with an erasure correcting coding scheme to correct b+1 errors in a block wherein the erasure correcting code itself can correct up to b erasures. The decoding method uses likelihood values for all possible symbol values for each received symbol in addition to hard decisions. First, the (b+1)th error is corrected by assuming a single error in each symbol location. Then, for each symbol in a codeword all valid symbol possibilities are tested. For each symbol possibility, the metric of the resulting codeword is calculated using the likelihoods provided by the receiver.

Abstract: A mechanism and associated protocol for performing Service Level Agreement (SLA) measurements in a communications network. The measurements obtained are used to perform various SLA parameter calculations such as delay, round trip delay, one way jitter and bandwidth related calculations. SLA measurement request and response messages are stamped with time and bandwidth counters by the client and remote ends of a connection. The resultant data is used to perform the calculation of SLA parameters.

Abstract: An apparatus for and a method of locating and releasing stuck virtual circuits in an ATM network device. Memory resources are freed that would otherwise be lost due to the last cell of a frame not being received on a particular virtual circuit. Two flags: a sticky first_cell flag and a last_cell flag, track the status of the receipt of a frame over a virtual circuit. The software periodically examines the two flags and if both the first_cell flag and last_cell flags are found cleared then a ‘stuck’ virtual circuit is identified indicating that the hardware did not detect a first cell of a frame on this particular virtual circuit since the last time the software cleared this bit to ‘0’. In response to the identification of a stuck virtual circuit, the software releases the memory resources consumed by the incomplete frame.

Abstract: A method of notification and handling of device status changes in MPOA enabled ATM based networks. In a first method notification of changes in device status configuration are provided by selectively releasing one or more Data Direct VCs that were previously established be LECs connecting MPOA Servers and MPOA Clients. An MPOA Server, upon detecting a change to its device configuration status, releases the Data Direct VCs connecting its associated LEC to known MPSs and MPCs that are neighbors to it. All MPOA devices for which a Data Direct VC was released delete all LE_ARP cache entries associated with the ATM destination of the released Data Direct VC. In a second method, each MPOA device periodically sends keep alive messages as targetless LE_ARP messages having a time to live TLV appended. An MPOA device receiving the keep alive message, refreshes (i.e., restarts) a validation timer for each association made by the corresponding MPOA identification TLV.

Abstract: An apparatus for and a method of extending the ATM Forum LAN Emulation standard to support 802.1Q VLAN tagging with Independent VLAN Learning. A standard LEC entity is modified to perform the VLAN tagging method that supports Independent VLAN Learning. Since the LES may also respond to LE_ARP messages, it is optionally modified to perform the VLAN tagging method of the invention so as to provide support for 802.1Q Independent VLAN Learning. Support for 802.1Q Independent VLAN Learning is provided by adding a VLAN-ID TLV to LAN Emulation control messages such as LE_ARP and LE_REGISTER messages. The TLV added comprises the VLAN Tag Header information that is normally carried by the Ethernet frame in 802.1Q networks.

Abstract: An apparatus and associated method for performing flow switching (tag switching) in a frame switching environment. The flow switching apparatus provides a mechanism whereby flows are identified and tags assigned to them. The identification and assignment of tags to flows is made Independently of other network entities and does not require communications with any other entities within the box itself or other entities in the network. The forwarding decisions are calculated once and stored in a cache or a look up table which can be accessed very quickly. The tag is used as an index into the cache or LUT such that if an entry is found in the cache or LUT for that particular tag, the forwarding decision does not have to be made again. This serves to greatly reduce the time to obtain a forwarding decision which is used by the switching fabric in steering the input frame to the appropriate output port(s). Multiple queues are used along with the cache to facilitate the forwarding of the frames.

Abstract: A method of controlling the route used for a flow in an environment comprising a default routing path and a shortcut path in an MPOA enabled ATM based network. A data field is added to the Ingress Cache table in the Ingress MPOA Client (I-MPC) to indicate whether the flow is to be routed through an MPOA shortcut towards the Egress MPOA Client (E-MPC) or is to be routed through the default path towards the Ingress MPOA Server (I-MPS). A first embodiment comprises a method of controlling the routing of a data flow from a source to a destination for security purposes. A second embodiment comprises a method of load sharing a plurality of data flows. A third embodiment comprises a method of learning about past MPOA resolution successes and failures and utilizing past establishment history to bypass the MPOA resolution process.

Abstract: A method of determining an Ethernet LAN switch topology including the steps of a) establishing a communications link between a network management server and a switch in an Ethernet LAN, thereby defining the switch as a root switch, b) identifying each of a plurality of switches attached to the Ethernet LAN, the each of the plurality of switches includes at least one identifiable port, c) generating a mapping of each of the switches, the mapping including a list for each of the ports of the switches that each of the ports sees, d) eliminating from the mapping each upwardly looking one of the ports, e) identifying in the mapping at least one leaf connected to at least one of the ports, f) maintaining in a topological mapping at least one relationship between the leaves and the ports connected to the leaves, g) eliminating from the list for each of the ports each of the leaves that each of the ports sees, and h) repeating steps e)-g) until all of the leaves are identified.

Abstract: A transmitter apparatus and method for use in a spread spectrum data communications system that utilizes the Differential Code Shift Keying (DCSK) or non-differential Code Shift Keying (CSK) modulation technique. The transmitter transmits data in the form of packets to the receiver. Each packet is consists of a header, one or more data symbols followed by a CRC checksum. The preamble comprises a sequence of one or more zero rotated symbols and one or more predetermined non-zero rotated symbols. In one embodiment, a shift index is calculated based on the input data. The shift index is used to form the address in a PN sample ROM. The PN sequence is read out using a counter of length modulo the PN sequence length. Samples of the PN sequence are read out and input to a Manchester encoder whose output is amplified and filtered to obtain a particular spectrum shape. In a second embodiment, the shift index is loaded into a counter and used as a starting address to address the PN sample ROM.

Abstract: An apparatus for and method for acquiring synchronization for use in communications systems, i.e., acquiring the presence of a packet of data and associated timing information. A sequence of symbols having known rotation and phase is transmitted to the receiver. The receiver attempts to match the received vectors in a predefined manner in order to determine whether a signal or noise is being received. CSK modulation is used for the synchronization acquisition stage and, any desired data carrying modulation may be switched to once synchronization is obtained, which may or may not be CSK. The transmitter transmits data in the form of packets to the receiver, wherein each packet is preceded by a preamble comprising a number of symbols. The length of the preamble can be any suitable number of symbols such that the receiver is able to synchronize with the transmitter. The preamble comprises a sequence of rotated or non-rotated symbols, inverted or non-inverted (or generally phase-rotated by some amount).

Abstract: A method of performing flow control in a PNNI network wherein a node that becomes congested advertises this fact to the network thus eliminating additional call requests and other messages that it cannot handle due to the current load. The method utilizes the Maximum Cell Rate (MCR) and Available Cell Rate (ACR) parameters provided for in the PNNI standard. When the congestion level on a local node exceeds a predetermined threshold, a PTSE with MCR set to zero and ACR set to zero is advertised to the network. The PTSE causes nodes (originating nodes in particular) to not consider that node in route calculations. When the congestion level recedes on the local node, another PTSE is generated with the original MCR and ACR that existed before the congestion occurred causing the resumption of call request messages to be forwarded to the network.

Abstract: A proxy MPOA client in a VLAN that is otherwise populated by legacy LECs such that the MPOA services for these LECs are provided centrally by the proxy MPC. A standard MPC enabled edge device is adapted to provide MPC services to legacy LECs that are not MPOA aware. Such an edge device provides MPOA services to legacy LECs located in other edge devices connected to the ATM cloud. The proxy MPC is configured to have at least two LECs: one residing on a legacy ELAN and another residing on an MPOA ELAN. Traffic from the legacy LEC arriving from the legacy ELAN is forwarded to an Ethernet port that is looped back to a second Ethernet port on the proxy MPC edge device. Upon ingress at the second Ethernet port, the traffic is treated as if it arrived from a regular port and provided with MPC services. The loopback may be implemented either internally or externally via one or more cables.

Abstract: A method of detecting a signaling congestion situation in a transmitter within a communications switch and for handling and recovering from the congestion. The method functions to (1) monitor the level of the transmit queue for each output port and (2) to monitor the level of the signaling message buffer memory pool for all ports. When the levels of either pass predetermined thresholds, the signaling congestion state is declared. Once the signaling congestion state is declared, the call control or equivalent entity in the communications device stops routing new calls from/towards all ports that are in the signaling congestion state. The call control continues to handle existing calls from/towards ports that are in the signaling congestion state.

Abstract: An apparatus and method for providing synchronization in a data transmission system via the use of a short cyclic synchronization sequence inserted in the header of cells to be transmitted. A 2-bit sync sequence is inserted at the beginning of the header in each cell. At the receiving end, a pair of state machines search for and track the sync sequence. A feedback signal is generated that is used by the receiver to adjust its framing so as to align the received data with the boundaries of the cells. To aid in detecting the sync sequence, the two sync bits are rotated each cell cycle. To avoid confusion with data that mimics the sync sequence, the transmitter transmits idle cells containing all ones except for the 2-bit sync sequence field during the period that the receiver is attempting to sync up with the transmitter.

Abstract: An apparatus for and a method of learning MAC addresses in a Local Area Network (LAN) Emulation (LANE) network implemented over an Asynchronous Transfer Mode (ATM) network. The LEC or LES is adapted to detect when the ATM address associated with a MAC address is no longer valid. Once an invalid ATM address is detected the existing entry can be updated or deleted. A LEC_ID table holding LEC_ID to ATM address bindings is created. Each frame received by the LEC is sniffed in order to find mismatches between the ATM address and the LEC_ID. Optionally, an LE_ARP request message can be forwarded to the LES for learning the new binding. If the MAC address is not found in the LE_ARP table, an entry can be created and added to the table. In another embodiment, the LES is adapted to detect when the MAC to ATM address binding stored in the internal LE_ARP cache is no longer valid. The LE_ARP table is populated by examining LE_ARP request and response sent and received by the LEC.

Abstract: An apparatus for and method of encapsulating Ethernet frame data in Very high speed Digital Subscriber Line (VDSL) frames. The VDSL frames are transmitted over a point to point VDSL link where they are subsequently extracted and forwarded as standard Ethernet frames. The VDSL facility transport system comprises an Ethernet to VDSL Consumer Premises Equipment (CPE) coupled to a DSL Access Multiplexer (DSLAM) over a VDSL transport facility. The Ethernet to VDSL CPE functions to receive a 10BaseT Ethernet signal and encapsulate the Ethernet frame into a VDSL frame for transmission over the VDSL facility. The DSLAM is adapted to receive VDSL frames, extract Ethernet frames therefrom and output a standard Ethernet signal. Ethernet frames are encapsulated within VDSL frames and transmitted on the wire pair without regard to the state of the SOC signals thus overcoming the problems associated with syncing the transmission of the Ethernet data with the SOC signals.

Abstract: A method of avoiding collisions among a plurality of transmitters that communicate asynchronously in relation to each other with a single receiver. The transmission scheme utilizes a randomization process to minimize the probability of collision among transmitted signals from different non synchronized transmitters, thus achieving improved overall link quality for each transmitter and improved system performance. The method has applications to many types of communications systems including frequency hopping spread spectrum communications systems. Transmitters send data in a burst of data packets, each sent during a time slot within the burst. Each time slot is divided into two or more sub time slots. During each time slot, one of the sub time slots is randomly chosen and the data packet is transmitted during that particular sub time slot. The larger the number of sub time slots used results in lower probability of complete transmission loss.

Abstract: A method of establishing calls between an ingress MPC (the calling party) and an egress MPC (the called party) in MPOA enabled ATM based networks. The call establishment method utilizes the call request SETUP, CONNECT and CONNECT_ACK messages in creating the shortcut VCC between ingress and egress MPCs. The calling party is adapted to send a READY_IND message in a reliable manner to the called party indicating that it is ready to receive frames over the shortcut VCC. The called party starts sending data over the shortcut VCC only when it knows that the calling party is ready. The called party knows the calling party is ready upon receipt of a READY_IND message or at least one data frame on the shortcut VCC. The calling party knows that the called party is ready to receive frames when it receives the CONNECT message. Since the READY_IND message sent by the calling party may get lost, the calling party is adapted to re-send the READY_IND message repeatedly until it is certain the called party has received it.

Abstract: A method of triggering reroutes in an ATM network based on a call optimization value being reduced beyond a predefined threshold. The method utilizes a signaling element in the SETUP message called a PNNI optimization reservation signaling element that includes an optimization type, value and percentage. A switch accumulates the optimization value and passes this value to the next node along the path. In addition, the hardware in the node is configured to measure and monitor the optimization value. The optimization value is monitored for changes that exceed the predefined optimization percentage. When this is detected, the software calculates a reroute. If the new route is better than the current route and is within the optimization percentage constraints, a reroute is performed using the newly calculated route. The reroute procedure provided by the ATM Forum can be used to implement the reroute.

Abstract: A queue having a ‘duplicate’ counter associated with each entry whereby duplicate data is not stored in the queue. Before data is placed in the queue, the queue is searched for an entry matching the data to be written. If a match is found, the duplicate counter associated with the entry is incremented. Further, if a match is found and the data stored therein is inconsistent with the current data, the contents of the queue are updated and the duplicate counter associated with the entry is reset to one. If a match is not found, the data is written to the queue and the duplicate counter associated with the entry is initialized to one.