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WO1999045677A1 - Dispositif de transmission par reseau - Google Patents

Dispositif de transmission par reseau Download PDF

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Publication number
WO1999045677A1
WO1999045677A1 PCT/GB1998/003611 GB9803611W WO9945677A1 WO 1999045677 A1 WO1999045677 A1 WO 1999045677A1 GB 9803611 W GB9803611 W GB 9803611W WO 9945677 A1 WO9945677 A1 WO 9945677A1
Authority
WO
WIPO (PCT)
Prior art keywords
data
communication device
packet
data packet
receive
Prior art date
Application number
PCT/GB1998/003611
Other languages
English (en)
Inventor
Nigel Horspool
David Law
Quang Tien Trang
Patrick Overs
Original Assignee
3Com Technologies
Butcher, Ian, James
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from GBGB9804846.5A external-priority patent/GB9804846D0/en
Priority claimed from GB9826251A external-priority patent/GB2333675B/en
Application filed by 3Com Technologies, Butcher, Ian, James filed Critical 3Com Technologies
Publication of WO1999045677A1 publication Critical patent/WO1999045677A1/fr

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L49/00—Packet switching elements
    • H04L49/35—Switches specially adapted for specific applications
    • H04L49/351—Switches specially adapted for specific applications for local area network [LAN], e.g. Ethernet switches

Definitions

  • the present invention relates to computer networking technology and in particular to communication devices such as Repeaters for interconnecting network devices in such networks.
  • a Repeater is a very important component of computer networks such as local area networks as it provides the medium through which other devices can communicate with each other.
  • a Repeater is provided with a number of communications ports and in the simplest configuration an end station, such as a computer is attached to each of the ports.
  • a repeater functions such that any communication which is received on one port is retransmitted on all of the other ports, so that a communication sent out by any one device attached to the network is received by all of the others.
  • the retransmission by a Repeater of a communication should be simultaneous with its reception at the receiving port.
  • One very common type of communications protocol in such networks is a carrier sense multiple access protocol of which Ethernet is a well known example.
  • communications between computers attached to the network are by way of data packets having a pre defined format.
  • a network user wishes to transmit a communications packet it simply attempts to access the communications medium provided by the Repeater or interconnected Repeaters and transmits the packet.
  • the repeating function of the Repeater device mentioned above means that the communication packet reaches all of the other users on the network including the intended destination.
  • the two or more transmitting units sense that a collision has occurred on the network and therefore that the transmitted data packet will not have been successfully received.
  • the collision In order for the collision to be sensed and properly acted upon, the collision must be sensed by the transmitting station before it has completed the transmission of a packet. If this occurs, the transmitting station will simply attempt, at the end of a predetermined period to retransmit the packet. If it completes transmission of the packet without receiving a collision detector signal, it will assume that the transmission was successful.
  • the above mentioned physical characteristics of the Repeater device have an impact on the operation of such protocol for the following reasons.
  • the transmitted packet In order for a collision to be properly sensed by a transmitting station, the transmitted packet must be received by the Repeaters and repeated to all segments of the network quickly enough so that if a collision occurs on any one of the network segments this can be relayed back, via the Repeaters, to the transmitting station before the end of the transmission of the packet in order that the collision can be properly sensed.
  • computer networks such as local area networks operating the Ethernet protocol can handle communications at 10 megabits per second (Mbps) for some while and it has been relatively easy to implement Repeaters for such network speeds which propagate data quickly enough so that up to approximately five Repeaters could be connected together and still obtain satisfactory network performance.
  • Class I Repeater is directly connected to an end station or to a bridge or switch, which are other well known types of communications hub.
  • the communication standards do not allow any alterations in the lengths of the preambles to the data packets passing through the network. Therefore, as well as re-transmitting the packets quickly, a
  • Class II Repeater must take considerable care to ensure that the whole of any received data packet, including the preamble, is accounted for and properly handled.
  • a preferred Repeater architecture provides a receive data bus to which each PHY device is connected and which has a single connection to the Repeater core. Such an arrangement involving a data bus is advantageous as it reduces the 4 number of connections, and therefore physical pins, which must be made on the ASIC.
  • This architecture is further explained, insofar as it is relevant to the present invention, with reference to Figure 2 which shows the interconnections made between ASIC 1 and PHY devices 2 in order to enable the reception of data.
  • a Repeater device would of course also include interconnections for the retransmission of the received data but the present invention is related principally to the receive side of a Repeater device and therefore the relevant portions of the receive side are shown.
  • a bus 10 to which all of the PHY devices 2 may put their received data (RXD) in order that the received data can be received at ASIC 1.
  • RXD received data
  • Figure 3b illustrates the start of a received data packet and in particular is illustrated according to the known defined 100Mbps protocol.
  • the communications packet begins with a predetermined sequence of symbols (in particular J, K followed by a plurality of 5s) which are present to enable functions such as synchronising with the packet to be done before the information bearing portion of the packet arrives, and other known functions.
  • the imminent arrival is sensed by the PHY device 2 and the device asserts its carrier sense signal (CRS) as illustrated in Figure 3a.
  • CRS carrier sense signal
  • ASIC 1 permits access to the data bus by the PHY device in question by asserting the corresponding receive enable (RXEN) signal.
  • the corresponding PHY device 2 then has access to data bus 10 in order to write the received data to the bus.
  • Another signal generated by PHY device 2 on reception of a data packet which is important for the proper reception of the data is the receive data valid (RXDV) signal and this signal is asserted by PHY device 2 in synchronism with the beginning of the communications packet, as illustrated in Figure 3 c.
  • RXDV receive data valid
  • time interval tl was sufficiently long to allow this to occur.
  • the speed of reception of the data by the PHY device must be high in order to meet the overall timing requirements and therefore data needs to be put onto data bus 10 very quickly upon its reception.
  • the problem with this is that there is insufficient time for ASIC 1 to receive and respond to the carrier sense signal and to return the appropriate RXEN signal before the time at which the PHY device 2 is ready to put the beginning of the packet onto data bus 10 and to assert its RXDV signal. Therefore, either the PHY device 2 must delay the transmission of the data to the data bus 10, which is not acceptable in the context of a Class II Repeater, or an unknown amount of the preamble of the receive data packet would be lost due to the bite assertion of RXDV, which loss is not allowed in 100Mbps networks.
  • the RXEN signal would have to be asserted by ASIC 1 within 20ns of receiving the carrier sense signal and this is very difficult if not impossible to achieve.
  • the present invention provides a communication device for a computer network comprising: a plurality of ports arranged to receive and transmit communications in the form of data packets from and to the network; communication core means arranged to receive communications received at said ports and to implement a desired functionality for re-transmission of said communications via said ports; data transfer means arranged to carry communications received at said ports to said communication core means; receive means associated with each of said ports arranged to send received data packets to said data bus means without a predetermined portion from 6 the beginning of the data packets; and transmit means associated with each said port arranged to receive data packets for transmission from said communication core means and to replace said predetermined portion at the beginning of the data packet for transmission from the respective port.
  • the present invention provides a Repeater for use in computer networks of the general type discussed above, in which the PHY device associated with each port, on reception of a communications packet for retransmission to the other ports, delays the assertion of its RXDV signal to a predetermined time within the preamble to the received packet and transmits all of the symbols subsequent to this predetermined time to the Repeater core.
  • this invention is the first two symbols of the communications packet preamble which are not transmitted through the Repeater.
  • this invention generally accelerates the reception and handling of data packets by network devices and therefore is also applicable to other network devices such as bridges and switches.
  • the invention therefore takes advantage of the fact, that in 7 communication protocols such as Ethernet, no important data is contained in the first portion of a communications packet, this portion of the packet being generally a non- data carrying preamble to assist in sensing and synchronising with the packet.
  • the removal of a predetermined number of bits from the beginning of the packet by the physical layer device on reception of the packet allows more time for the Repeater to enable access to the Repeater core and get the remainder of the communications packet to the other physical layer devices for retransmission whilst still enabling the fast transmission times necessary to meet requirements of fast operating networks, and preserving the correct length of preamble as required by the 100Mbps Ethernet standard as mentioned above.
  • the preamble is completed by a physical layer device on retransmission of the packet so as to conform to network protocols.
  • Figure 1 is a schematic diagram of a communication device according to the invention in an exemplary network environment
  • Figure 2 is a schematic diagram illustrating the architecture of the receive side of a Repeater according to the preferred embodiment
  • Figure 3 is a timing diagram illustrating the operation of Repeater devices.
  • a network communications device is arranged to have a fast throughput of data packets. This is achieved by recognising that, in protocols such as Ethernet, the first symbols in a data packet do not carry any data and therefore do not necessarily require to be properly carried through a communications hub. Rather, a known number of symbols are discarded from the start of a packet on receipt and replaced on re-transmission. This discarding reduces the reception delays particularly in bussed-architecture repeaters where bus arbitration must take place for each received packet. 8
  • FIG. 1 illustrates in schematic form a communication device 10 according to the preferred embodiment in a network context.
  • the network includes network devices 20 which may be terminal equipment such as PCs or printers or may be other communication devices connected to other portions of the network.
  • network devices 20 which may be terminal equipment such as PCs or printers or may be other communication devices connected to other portions of the network.
  • communication device 10 which is, in the preferred embodiment, a repeater, has a plurality of ports 12 to which network devices 20 are connected for the transmission of communications in the form of data packets.
  • PHY physical layer device
  • core means generally implemented as an ASIC, which provides the repeater functionality.
  • ASIC application-specific integrated circuit
  • PHY device 2 is in communication with ASIC 1 as will be discussed in more detail below to enable ASIC 1 ro receive and re-transmit data packets from and to the required ones of ports 12.
  • Figure 2 illustrates a schematic outline of the receiver side of a Repeater device, comprising ASIC 1 performing the core functions of the Repeater and a plurality of PHY devices 2, one being provided for each port of the Repeater.
  • Incoming communications are received at PHY devices 2 and are passed via the RXD bus 10 to ASIC 1 for retransmission from the other ports. Also as outlined above, access to the bus is requested by asserting the carrier sense signal (CRS) and access to the bus is granted by the return of the RXEN signal from ASIC 1.
  • the other signal illustrated in Figure 2 is receive data valid (RXDV) which is asserted by a PHY device 2 in synchronism with the transmission of a data packet to bus 10.
  • Figure 3a illustrates the assertion of CRS at time interval tl before the beginning of the communications packet illustrated in Figure 3b. In a 100Mbps per second network time interval tl may be as small as 20ns.
  • the PHY device 2 on receipt of the RXEN signal the PHY device 2 does not immediately assert its RXDV signal and start sending receive data to the bus 10. Because there is no specific knowledge of the time at which RXEN will be provided, this would mean that an unknown portion of the preamble of the data packet would potentially be lost.
  • the PHY device 2 waits until a specific predetermined time during the preamble of the data packet before it asserts RXDV and transmits the remainder of the data packet to the data bus 10.
  • the PHY device 2 asserts RXDV at the time at the end of the second symbol (commonly known as the "K" symbol) as shown in Figure 3e.
  • RXDV therefore usefully and properly signals the timing of the received data packet to ASIC 1 and it is known with certainty which portions of the data packet passed before the assertion of RXDV.
  • ASIC 1 can then retransmit the received parts of the receive data to the other PHYs for retransmission, and the other PHY devices 2 are arranged so as to re-complete the preamble to the data packet by the addition of the J and K symbols so that a complete data packet is retransmitted in the form it was received.
  • RXEN is in fact asserted within 80ns of the assertion of CRS and therefore the above described timing can be properly implemented.
  • the present invention therefore permits the implementation of a Class II 100Mbps per second Repeater having a bus architecture.

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  • Small-Scale Networks (AREA)
  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)

Abstract

L'invention concerne un dispositif de transmission par réseau configuré pour acheminer des paquets de données à un débit rapide. Pour ce faire, le dispositif prend en compte le fait que, dans des protocoles de type Ethernet, les premiers symboles dans un paquet de données ne contiennent aucune données, et n'exigent donc pas d'être acheminés normalement à travers un concentrateur. Aussi, un nombre connu de symboles est d'emblée écarté du paquet à la réception, puis remis en place au moment de la retransmission. Ce rejet diminue les retards de réception, en ce qui concerne en particulier les répéteurs à architecture en bus dans lesquels l'arbitrage du bus doit intervenir pour chaque paquet reçu.
PCT/GB1998/003611 1998-03-06 1998-12-03 Dispositif de transmission par reseau WO1999045677A1 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
GBGB9804846.5A GB9804846D0 (en) 1997-11-28 1998-03-06 Repeater
GB9804846.5 1998-03-06
GB9826251A GB2333675B (en) 1997-11-28 1998-11-30 Network communication device
GB9826251.2 1998-11-30

Publications (1)

Publication Number Publication Date
WO1999045677A1 true WO1999045677A1 (fr) 1999-09-10

Family

ID=26313241

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1998/003611 WO1999045677A1 (fr) 1998-03-06 1998-12-03 Dispositif de transmission par reseau

Country Status (1)

Country Link
WO (1) WO1999045677A1 (fr)

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4627052A (en) * 1984-03-19 1986-12-02 International Computers Limited Interconnection of communications networks
US5274631A (en) * 1991-03-11 1993-12-28 Kalpana, Inc. Computer network switching system
US5550803A (en) * 1995-03-17 1996-08-27 Advanced Micro Devices, Inc. Method and system for increasing network information carried in a data packet via packet tagging
US5598581A (en) * 1993-08-06 1997-01-28 Cisco Sytems, Inc. Variable latency cut through bridge for forwarding packets in response to user's manual adjustment of variable latency threshold point while the bridge is operating

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4627052A (en) * 1984-03-19 1986-12-02 International Computers Limited Interconnection of communications networks
US5274631A (en) * 1991-03-11 1993-12-28 Kalpana, Inc. Computer network switching system
US5598581A (en) * 1993-08-06 1997-01-28 Cisco Sytems, Inc. Variable latency cut through bridge for forwarding packets in response to user's manual adjustment of variable latency threshold point while the bridge is operating
US5550803A (en) * 1995-03-17 1996-08-27 Advanced Micro Devices, Inc. Method and system for increasing network information carried in a data packet via packet tagging

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