Abstract: The invention relates to an electronic device chassis, comprising at least an opening on the chassis and an inward guide apparatus along the opening; the guide apparatus comprises at least a first guide part and a second guide part which are respectively a concave slide and a convex slide, to guide modules in at least two different structural specifications into the electronic device to establish electrical connection with the electronic device. The module is inserted through the opening along the slides, and is fitted to the corresponding connector on the mainboard. The invention can solve the problem that traditional switch devices can not support different transmission speeds and transmission modes between networks. With the slides, a device can be compatible with data transmission modules with different speeds and different interface forms.

Abstract: The invention relates to an electronic device chassis, comprising at least an opening on the chassis and an inward guide apparatus along the opening; the guide apparatus comprises at least a first guide part and a second guide part which are respectively a concave slide and a convex slide, to guide modules in at least two different structural specifications into the electronic device to establish electrical connection with the electronic device. The module is inserted through the opening along the slides, and is fitted to the corresponding connector on the mainboard. The invention can solve the problem that traditional switch devices can not support different transmission speeds and transmission modes between networks. With the slides, a device can be compatible with data transmission modules with different speeds and different interface forms.

Abstract: An Ethernet data packet including a VLAN tag header and a VLAN identification field is modified. The modification is accomplished by inserting in place of the VLAN tag header a field of the same size including selected information. The VLAN identification may be retained. The inserted field may include a first field indicating the presence of the VLAN identification field and a second field of selected information, the second field being longer than the first field.

Abstract: A network switch (10) for a packet-based data communication network, comprises a plurality of ports for the reception and transmission of data and means for establishing a database for controlling the passage of data between the ports. The database comprises a data table (17) for holding data entries each comprising a media access control address and an identification of a port, and a pointer table (16) of which the entries each comprise a network address and an associated pointer to an entry in the said data table. The pointers are accessed by hashing network addresses in received packets.

Abstract: A network switch maintains transmit queues and for each transmit queue a table which identifies the contributions of traffic received at the ingress ports to that queue. When a queue is too long, a pause frame is dispatched from a selected one of the ingress ports. The ingress port may be selected as that making the greatest contribution to the transmit queue. However, a control algorithm allows ports carrying high priority traffic to be excluded from the selection.

Abstract: The present invention is based on a ring architecture wherein each chip in the multiplicity of chips is connected in a chain so that it can receive packets from the next previous chip in the chain and forward packets to the next following chip in the chain, whereby to form a ring. Before a packet is placed on the ring by a device it is provided with a ‘masking’ field which identifies each of the other devices and the ports within any such device to which the packet must be sent in order to achieve a multicast. When a device in its turn receives such a packet it will examine the masking field to determine whether the field identifies that device. If so, the packet, which may be held in temporary storage, may be processed for forwarding from a port of that device. The device will strip from the masking field the identification of the respective device and transmit the packet with a thus modified masking field to the next device in turn.

Abstract: A method of operating a network device in a communication system for the transmission of data packets which include network addresses identifying sources and destinations of data, the network device being capable of both bridging and routing decisions and including a forwarding database by means of which a packet including network address data can be forwarded to at least one port and thereby to at least one network path identified by a network address, and packets can be forwarded to at least one port in response to a media access control address. The method comprises establishing a data table which contains entries comprising a network address of an end station to which a packet is destined, a respective media access control address and an identification of at least one port to which the packet will be directed within the device. The table is accessed in response to network addresses and media access control addresses, whereby the same table can be used for both routing and bridging decisions.

Abstract: A system including an ordered data table containing linked lists of MAC addresses has a multiplicity of search engines which have their access to an LRU engine under the control of a token which is passed from one search engine to the next when the LRU engine has completed reordering the table after an address look-up. The system avoids conflicts between searching and reordering and allows reordering to be performed at a controlled rate.

Abstract: A last-in first-out data stack is able to store a plurality (n) of elements wherein the plurality is greater than two. For each of n storage locations in the stack a selector is adapted to receive n elements read out from the stack and a new element. The selector is arranged to make a controllable selection of its received elements. Combinational logic capable of performing logic manipulations on the selection of elements provides a resultant for pushing onto the stack.

Abstract: A data connection between two network stations such as an Ethernet hub and an end station which are both capable of exchanging data at the higher of two rates, the higher rate being selected by an auto-negotiation process, is monitored for the occurrence of error represented by a symbol representing the start of a data packet immediately followed by an idle symbol. The rate of occurrence of such errors is compared against a threshold and the speed of the data connection is downgraded to the lower rate.

Abstract: A forwarding database in a network switch is established and maintained by performing a look-up for a source address read from an incoming frame to find a match between the source address in the frame and the source address in an entry which includes that source address, a port number and an age field. New entries are made if matches are not found, so that the forwarding database facilitates the dispatch of frames to destination addresses corresponding to source addresses in the table. The switch maintains a system age, such as a two-bit field, which is changed from time to time and the current system age is entered in the table as the age field when a source address entry is made. When said source address is found by a look-up process, it is updated with the current system age only if the age field of the entry and the current system age do not correspond. There is a saving of bandwidth arising from the avoidance of write cycles when an age field of an entry corresponds to the current system age.

Abstract: A method for distributing addressed data packets from an input channel to a multiplicity of packet queues includes receiving said addressed data packets and, responsive to first hashed addresses, distributing the addressed data packets to said queues in accordance with said first hashed addresses. A first hash function is applied to selected address data of each of said addressed data packets to produce said first hashed addresses. At the same time a succession of different hash functions is applied to said selected address data in each of the packets to produce second hashed addresses and occurrences of each of the second hashed addresses are counted so as to obtain for each of said different hash functions a respective one of a plurality of set of counts, each such set representing the distribution of said packets that would occur in said queues if the respective one of the different hash functions had been applied to said addressed data packets.

Abstract: Trunking or other relationship is defined between ports on different devices in a cascade-connected stack of network devices. When network communications are passed via the cascade connection an indication is included of whether it originated from a port that is part of a trunk and thereby port-mismatch errors can be avoided.

Abstract: A method of computing statistics relating to the flow of data by way of a packet-switched data transmission system wherein a packet includes path address data and network address data, and the network includes means, such as an RMON1 matrix table, for providing traffic flow data indexed according to each of a plurality of traffic flow paths identified by the path address data. Data packets are sampled and, for each of a multiplicity of packet types indexed according to selected address data within the packets, traffic flow counts are respectively incremented in response to each new sample data packet of the respective type. For each traffic flow path indicated in sample packets a respective one of a plurality of reference traffic flow counts is incremented in response to each new relevant sample data packet. Values corresponding to said traffic flow data are stored for each of the traffic flow paths for which said reference traffic flow counts are accumulated.

Abstract: A method of controlling access to a common physical data transmission link from a multiplicity members of a packet-based local area network, wherein the members are partitioned into a plurality of virtual local area networks (VLANs) and wherein packets are identified according to the virtual local area network from which they come, comprises (a) monitoring packet traffic from the virtual local area networks on the link and thereby obtaining measures of the traffic flow from each of the virtual local area networks; (b) determining whether the traffic flow for each respective VLAN is above or below a threshold; (c) denoting a VLAN which is above its threshold as in a restricted state and denoting a VLAN which is below its threshold as in a priority state; (d) arbitrating between requests from the VLANs to transmit data packets on the link; and (e) according priority in the arbitration to a VLAN which is in a priority state over any VLAN which is in a restricted state.

Abstract: Trunking or other relationship is defined between ports on different devices in a cascade connected stack of network devices. When network communications are passed via the cascade connection an indication is included of whether it originated from a port which is part of a trunk and thereby port-mismatch errors can be avoided.

Abstract: A network switch comprises a first device which includes a store for data packets, a second device which includes a plurality of ports from which the packets may be transmitted, a plurality of temporary stores each associated with one of the ports, a data bus connecting the first device to the second device, a unit for maintaining a count of units of storage space in respect of each of the ports, a unit for incrementing the respective count on transmission of data from one of the stores, and a unit for decrementing the count in response to dispatch of data from the temporary store in the first device to the second device.

Abstract: A forwarding database in a network switch is established and maintained by performing a look-up for a source address read from an incoming frame to find a match between the source address in the frame and the source address in an entry which includes that source address, a port number and an age field. New entries are made if matches are not found, so that the forwarding database facilitates the dispatch of frames to destination addresses corresponding to source addresses in the table. The performance of a source address look-up is inhibited in the absence of a token, a reservoir of tokens being decremented each time a source address look-up is performed and incremented from time to time, at a selectable rate. The process facilitates the performance of a destination address look-up for every received frame by restricting the bandwidth made available for source address look-ups.

Abstract: A method of operating a repeater for a packet-based data transmission system wherein the repeater has a receiving port associated with a buffer whereby packets received at the port are temporarily stored before they are onwardly transmitted and wherein the repeater performs a contention resolution process such that if an attempted onward transmission of a packet is prevented by virtue of contention with a prior or an existing transmission, a subsequent attempt at transmission of that packet is delayed for a time which is likely to be substantially greater than a selected minimum time. The method includes examining a received packet to determine whether the packet is a multi-media packet, and giving the packet a higher priority in the contention resolution process such that if the packet is not transmitted onwardly owing to contention with a prior transmission, a fresh attempt at transmission of the packet is made on the expiry of the selected minimum time.

Abstract: Port mirroring is achieved between ports on separate devices in a stack of communication devices by establishing a protocol for communications within a cascade connection forming the stack in which an indication is given of whether the communication is being sent to the mirror port in addition to its intended destination. This avoids increasing the volume of traffic in the cascade connection as would be the case if the original and mirror copy were sent separately.