Description

Optical Data Communications

Technical field

[0001] This invention relates to techniques for use in optical data communication networks. In particular, the invention relates to techniques for use in resolving differences in communication standards between devices in a network.

Background art

[0002] There are a number of different standards for data communication in networks. The most common form of network to which this invention relates is an Ethernet network. There are a number of communication standards which govern the speed at which data is transferred over such networks. Current Fast Ethernet networks operate at a theoretical maximum transmission speed of 100Mbit/s. There are a number of standards for such communication, collectively known as 100BASE-T, such as 100BASE-TX (using two pairs of Cat 5 cable). Standards exist for transmission speeds of 10Mbit/s to 1000Mbit/s (1 Gbit/s) and above

[0003] The usual form of physical link is a copper wire-based infrastructure.

When two devices are connected by a copper wire Ethernet network, and operate at different speeds (standards), there is an Ethernet procedure called 'auto-negotiation' which allows the two devices to choose common transmission parameters such as speed and duplex mode to allow them to communicate. Auto-negotiation resides in the physical layer of the OSI model and is currently covered by the international standard IEEE 802.3ab.

[0004] Auto-negotiation operates by connected devices detecting failure of a data communication link and then exchanging data relating to the technology abilities of each device. Upon receipt of this information, the devices decide on a mode of operation based on a priority list which forms part of the standard, currently spanning 10Mbit/s to 1 Gbit/s.

[0005] The possibility of auto-negotiation on copper wire networks means that it is possible to progressively upgrade the capabilities of the various devices

connected while still permitting full operation of the network. In this respect, the technology is backward compatible. [0006] It is also possible to implement Ethernet networks using optical fibre links.

These can also be configured to operate at different speeds. However, current standards covering such networks do not include anything comparable to auto-negotiation and so are not backward compatible. This invention is intended to address this problem. Disclosure of the invention [0007] A first aspect of this invention comprises a method of communicating data between a network communication device and a data network which are connected to each other by means of an optical fibre data link, the method comprises the steps of: within the device, monitoring the connection to detect data communication at a first standard, and either: a) if data communication is detected at the first standard, establishing data communication between the network device and the data network using the first standard; or b) if no data communication is detected at the first standard, monitoring the connection in the device to detect data communication at the second standard and if data communication is detected at the second standard, establishing data communication between the network device and the data network using the second standard.

[0008] Preferably, this comprises cycling connection monitoring of the device between the first standard and the second standard until communication is detected. After a predetermined period of time if no communication is detected at either standard, the step of monitoring the connection in the device is ceased.

[0009] Monitoring at one or more further standards may take place if no communication is detected on either the first or second standard.

[0010] Typically, the first, second and/or further standards are mutually incompatible such that a device operating at one standard cannot communicate with a device operating at one of the other standards.

[0011] Each standard may provide communication at a different speed, for example the first standard operating at 1 Gbit/s and the second standard operating at 100 Mbit/s.

[0012] Each standard also typically uses different coding algorithms.

[0013] A second aspect of the invention provides a communication device to provide access to a data network, comprising: data communication means for communicating data to and from an optical fibre data link at a first or second standard; and monitoring means to control the data communication means; characterized in that the monitoring means are configured so as to monitor the connection to detect data communication at a first standard, and either: a) if data communication is detected at the first standard, apply the first standard to the data communication means such as data communication between the network device and the network uses the first standard; or b) if no data communication is detected at the first standard, monitor the connection to detect data communication at the second standard and if data communication is detected at the second standard, apply the second standard to the data communication means such as data communication between the network device and the network uses the second standard.

[0014] The monitoring means preferably is configured to cycle connection monitoring at the first standard and at the second standard until communication is detected. The monitoring means may be configured to cease to operate after a predetermined period of time if no communication is detected at either standard.

[0015] The data communication means may also be capable of data communication at one or more further standards and the monitoring means monitors communication at the one or more further standards if no communication is detected on either the first or second standard.

[0016] A third aspect of the invention provides a system comprising at least first and second data communication devices connected by means of a fibre optic data link, at least one of which is a device according to the second aspect of the invention.

Brief description of the drawings

[0017] Figure 1 shows a schematic diagram of a generic broadband network; and Figure 2 shows a schematic view of the operation of a device according to an embodiment of the invention.

Mode(s) for carrying out the invention

[0018] Figure 1 shows a generic description of a broadband network for providing telephone, internet and TV/video services to subscribers in a number of locations. The present invention finds particular use in such systems. A series of service providers provide the various services (SP1 , SP2, SP3) to the network 10 via conventional access points 12. The network 10 provides connection to these subscribers via routers 14 located close to the subscribers. These can include business locations that can include routers in commercial property 16, and domestic subscribers with routers located in a central office 18 for a neighbourhood of separate dwellings (houses 17), or in a single building such as an apartment. The network operator manages the network function by the use of a control and provisioning system 20. The present invention is particularly applicable to such networks.

[0019] The physical structure of the network comprises the routers 14 and other such devices connected by means of data cables 22. Each subscriber is provided with a local device (often called 'customer premise equipment' or 'CPE') that is connected to its respective router by a cable 24. In systems to which the present invention relates, the cables 22, 24 are optical fibre cables and data communication between the devices including routers 14 and CPE takes place via the appropriate standard. Common standards used in such cases are 100BASE-FX and 1000BASE-FX. These standards provide data transmission speeds equivalent to the corresponding copper wire standards 100BASE-T, 1000BASE-T.

[0020] The CPE can take a number of forms, for example the DRG range of devices from PacketFront of Sweden. Such devices include optoelectronic devices (data communication means) for the actual transmission and reception of signals under the control of a programmable control system (monitoring means) which forms part of the device. The software

control is programmed to apply the selected standard when transmitting or receiving data. This includes the coding applied to the data for transmission or reception to or from the connected device.

[0021] In previous systems, the devices have been provided with a set standard programmed, for example 100BASE-FX, for fast Ethernet communications. For example, if a router 14 is programmed to operate at 100BASE-FX, under normal conditions, the connected CPE must also operate at 100BASE-FX. Connecting a CPE programmed to operate at 1000BASE-FX will not work (and vice versa). This means that it would be necessary to upgrade both the routers and the CPEs if it was desired to upgrade the performance of that section of the network to 1000BASE-FX. This can make the process expensive for the network operators and the subscribers. In this normal case, there is no way to install upgraded equipment in only part of the network while continuing to run at the old rate until there is sufficient upgraded equipment in use to justify a system level upgrade.

[0022] This invention is based on the ability of the connected equipment to be controlled to operate at two or more standards. This is particularly the case when the operation is under software control. By programming the device to monitor the data connection and switch to another standard when no communication is detected, the device can be made to hunt for the appropriate standard and operate at this until a change is detected.

[0023] Figure 2 shows schematically the steps executed in the device when connected to a network so as to implement the invention. When first connected, the device tests first T1 for a connection at a first speed (e.g. 100Mbps) 100, checking downlink 100d connections on the connected cable (checking of the uplink 100u may also be possible using Ethernet loopback OAMs and receiving the correct link symbols). If up and down links are detected, communication is established at this speed and continues until the device is again caused to establish a link (e.g. following a restart, disconnection, etc.).

[0024] If no link is detected at the first speed, the device changes mode dM1 and initiates a test T2 at a second speed (e.g. 1 Gbps) 1000, again checking

uplink 100Ou and downlink 100Od connections. Again if up and down links are detected, communication is established at this speed and continues until the device is again caused to establish a link (e.g. following a restart, disconnection, etc.).

[0025] If no link is detected at this second speed, the device again changes mode dM2 and returns to the first speed operation for testing the link T1.

[0026] The link test runs for a predetermined period and if no link is detected, it times out. The device will cycle between the two speeds until a link is detected or until a predetermined time has elapsed at which time it ceases. In most cases, only one device will incorporate the invention. However, where two devices incorporating this invention are connected, there is a risk that their cycling can be permanently out of phase so that they never reach a situation where both are using the same speed. In this case, no communication would ever be detected. This can be avoided by randomising the timeout so that each device has a different timeout period.

[0027] The two speeds given here describe the common case for optical fibre connections at 100BASE-FX and 1000BASE-FX which may be encountered in domestic CPE connections to a broadband network. However, any two operating speeds can be selected. Alternatively, more than two options can be available, the device cycling through the options in a predetermined order or in a random order (which may also assist in avoiding the situation where two devices are out of phase when cycling through the options so that they never achieve a matching speed).

[0028] This invention is best embodied in physical layer equipment under software control. Such devices are capable of monitoring link status and configuring operation speed of the device so as to enable operation at the appropriate speed. It is only necessary for one end point of the final link to have the capability of the invention. In most cases, this is the CPE since it allows progressive upgrades of CPE installations before the whole network is reconfigured to operate at another speed.

[0029] Other changes can be made within the scope of the invention.