WO2009115780A1

WO2009115780A1 - Connecting a device

Info

Publication number: WO2009115780A1
Application number: PCT/GB2009/000695
Authority: WO
Inventors: Mark Edward Scopes
Original assignee: British Telecommunications Public Limited Company
Priority date: 2008-03-20
Filing date: 2009-03-16
Publication date: 2009-09-24
Also published as: GB0805280D0

Abstract

The present invention relates to the connection of a device, in particular the connection of a device to an optical network. It includes the steps of: making an optical connection between the optical network and the device, which connection is suitable for supporting communication at a first bit rate; transmitting data from the device over the optical connection at the first bit rate; using the transmitted data to determine at least one characteristic of the device; and, in dependence on the or each determined characteristic, modifying a physical aspect of the optical connection such that the connection is suitable for transmitting data at a second bit rate higher than the first bit rate. The connection at the first bit rate can be used to determine whether transmission at the second bit rate is appropriate.

Description

Connecting a device

The present invention relates to the connection of a device, in particular the connection of a device to an optical network.

Various protocols are known for introducing or connecting afresh a device to a network. For example, terminals intended to be connected to a passive optical network are pre- configured to respond in a predetermined manner to instructions from a head end unit within the network. Generally, if a device is not arranged to communicate according to the correct protocol, connecting the device to a network can result in the network operating less efficiently than it would otherwise, or can even result in failure of the network. However, it is not always easy to determine whether a device compatible with a network without first connecting the device to that network.

According to the present invention, there is provided a method of connecting a device to an optical network, including: making an optical connection between the optical network and the device, which connection is suitable for supporting communication at a first bit rate; transmitting data from the device over the optical connection at the first bit rate; using the transmitted data to determine at least one characteristic of the device; and, in dependence on the or each determined characteristic, modifying a physical aspect of the optical connection such that the connection is suitable for transmitting data at a second bit rate higher than the first bit rate.

By first allowing communication at the first bit rate, and using information obtained at the first bit rate to decide whether to modify the optical connection so as to allow communication at the second bit rate, the device can be introduced into the optical network in a controlled and progressive fashion, thereby reducing the risk of damage occurring to the network if the device is inappropriate for that network.

In order to reduce the likelihood that communication with the device at the first bit rate will interfere with traffic from other devices already connected to the network, the connection will preferably have a loss associated therewith, thereby reducing the intensity of light from the device. Once it has been determined that the device is appropriate, the connection may be modified so as to reduce the level of loss and thereby allow communication at the second bit rate. The loss may be reduced by reducing the loss at a releasable optical connector assembly, of the type which for example includes a socket that is a wall mounted at the premises of a customer, the socket being arranged to releasably receive an optical plug connector. Alternatively or in addition, an aspect of the optical connection which is modified may be the geographical route associated with a connection. As a further alternative or in addition, a router may be provided to allow the optical connection to be formed along a selected one of a plurality of optical waveguide. The level of loss when transmitting data at the first bit rate will preferably be at least 30% or at least 50% of the intensity of light used to convey data transmitted at the second bit rate.

According to another aspect of the invention, there is provided an optical network having: a network device; a detachable device; an optical connection for connecting the detachable device to the network device, the connection having a first state for supporting communication at a first bit rate, and a second state for supporting communication at a second bit rate; and, means for allowing a physical aspect of the optical connection to be modified so as to change the state of the connection from one of the first and second states to the other of the first and second states, one of the network device and the detachable device being arranged, in response to traffic at the first bit rate from the other of the network device and the detachable device, to provide an indication of the compatibility of the detachable device with the network device.

The indication may be provided on a user display on the detachable device. Alternatively or in addition, the indication may be a signal from the network device, which signal may be transmitted at the first bit rate over the optical connection.

In a preferred embodiment, the network is a passive optical network and the optical connection has optical loss associated therewith. The optical loss may serve to limit the useful data that can be carried over the connection, such that the detachable device receives useful data only at a reduced rate from the head end until. The state of the connection may be changed from the first state to the second state so as to reduce the loss and thereby allow the detachable device to receive data at a higher rate. Before the state of the connection is changed, data from the detachable device may be received at the first bit rate, from which data an indication of compatibility can be provided. Alternatively or in addition, an indication of compatibility may be provided on the basis of the data received at the detachable device when the connection is still in the first state. According to yet another aspect of the invention, there is provided a method of connecting a device to an optical network, including: making an optical connection between the optical network and the device, which connection is suitable for supporting communication at a first bit rate; transmitting data over the optical connection at the first bit rate; using the transmitted data to determine an indication of compatibility between the device and the network; and, in dependence on the indication of compatibility, modifying a physical aspect of the optical connection such that the connection is suitable for transmitting data at a second bit rate higher than the first bit rate.

The invention will now be further described, by way of example only, and with reference to the following drawings in which:

Figure 1 shows an optical connector assembly in an un-coupled state, in accordance with the present invention;

Figure 2 shows the optical connector of figure 1 in a partially coupled state;

Figure 3 shows the optical connector of figure 1 in a fully coupled state;

Figure 4 shows, in transverse cross section, a connector of the connector assembly of figure 1 ; Figure 5 shows a first device and a second device optically coupled using the optical connector of figure 1 ;

Figure 6 shows a further embodiment having an optical switch arrangement; and,

Figure 7 shows a connector assembly with an electrical actuator.

Figure 1 illustrates schematically, in longitudinal cross section, an optical fiber connector assembly 10 having a male connector 12 arranged to releasably receive a female connector 14. The male connector has a ferrule assembly 16 with a tubular passage 18 in which is is held a first optical fiber 20 along a longitudinal axis. With reference to figure 4 which shows the male connector in cross section transverse to the longitudinal axis, the ferrule assembly 16 is mounted within a main body member 22 having a cylindrical hollow portion, the ferrule assembly 16 being arranged centrally within the cylindrical portion so as to provide an annular cavity 24 between the ferrule assembly and an inner wall of the main body member. The ferrule assembly 16 has a forward projecting portion 26 which projects beyond the main body member 22. A retention member 28 is provided to retain the optical fiber within the ferrule assembly. The main body member has a forward face 30 arranged transverse to the longitudinal axis along which the fiber that is held. Towards the lower end of the forward face (in the orientation of figure 4), there is provided and an abutment region that is generally normal to the longitudinal axis.

The main body member is generally rectangular in cross section having a flat underside 34 and generally flat upper surface 36. Generally parallel side surfaces 58 are provided normal to the underside 34. A respective cutout portion 40 is provided towards the upper end of each side surface, the cutout portions being defined by respective faceted surfaces 42. The faceted surfaces are arranged between the upper surface and each side surface, each faceted surface extending at approximately 45° from a respective side surface.

In the main body member is located within a frame 44, the frame having openings 46 arranged to allow access to releasable engagement means (not shown) located on the side surfaces of the main body member. An upstanding ridge portion 48, elongate in the longitudinal direction, is provided on an upper surface of the frame.

In a similar fashion to the male connector, the female connector 14 has a main body member 50 with a retaining portion 52 at a rearward end thereof, for retaining an optical cable 54 having an optical fiber 56 therein. A female a ferrule assembly 58 for holding the optical fiber 56 is provided in a central longitudinal axis of the female connector 14. The (female) main body member 50 is held in a connector housing 60, which housing has a main cavity 62 dimensioned so as to receive. the male connector 12.

Held within the housing 60 is a cylindrical sleeve 64, in which is located in the female ferrule assembly. The sleeve 64 extends beyond the female ferrule assembly so as to project into the main cavity 62 of the connector housing 60. The main cavity has internal walls 66 that are shaped so as to cooperate with the frame 44 of the male connector 12_r and to guide the male connector such that when the male connector is introduced into the main cavity, the ferrule assembly 26 of the male connector is received in the cylindrical sleeve 64 through an opening 65 thereof. The internal walls of the main cavity serve as coarse guide means to guide the relative movement of the male and female connectors, whereas the cylindrical sleeve 64 serves to guide and retain the optical fibers in precise axial alignment with one another. The female connector housing 60 has a transverse channel 68 (transverse to the longitudinal axis), in which there is provided, in sliding engagement with the transverse channel, an abutment member 70. The abutment member 70 can move between three positions as shown in figures 1-3. In figure 1 , the abutment member is in a closed position. In the closed position, an end portion 72 of the abutment member is positioned in front of the opening 65 in the cylindrical sleeve 64, thereby acting as a closed shutter to the female connector. In this position, the male connector is prevented from optically coupling with the female connector. Furthermore, the optical fibre 56 is protected from dirt as well as unwanted light.

In figure 2, the abutment member 70 is in an intermediate position. In the intermediate position, the end portion 72 of the abutment member 70 is clear of the cylindrical sleeve deepening 65, allowing the ferrule assembly 26 of the female connector 12 to be partly inserted into the cylindrical sleeve. However, the male connector 12 is prevented from being fully introduced into the female connector by the abutment member 70, in particular the end portion thereof. The end portion has an engagement surface 75 which abuts the front face of the main body member. This abutment prevents any further forward movement of the ferrule assembly of the male connector into the cylindrical sleeve. Thus, there remains an air gap between the ferrule assemblies of the male and female connectors. However, the air gap is sufficiently narrow to allow partial optical coupling between the optical fibers of the male and female connectors. That is, the ferrule assembly of the male connector is sufficiently long in the longitudinal direction that when the male connector is advanced as far as is permitted by the abutment member 70 (when the abutment member is in the intermediate position), the optical fiber 20 of the male connector 12 is in partial optical coupling with the optical fiber of the female connector 14. Typically, the distance between the ends of the male and ferrule assemblies (that is, air gap between the ends of their respective fibers) will be about 1 mm.

The effect of the air gap will be to introduce optical loss, that is, to cause a reduction in the intensity of the light as it travels from one connector to the other. This loss is due to the fact that light exiting an optical fiber will disperse over an area that is greater than the optical fiber cross section, whereas only some of this disbursed light will be captured by the fiber at the other optical connector. If the optical fibers are single mode fibers, the number of available modes in the air gap will increase, and these modes will not couple perfectly to the single mode of the fibers. Generally, the greater the length and cross section of the air gap, the greater the loss will be between the connectors. The greater the loss, the lower the signal level will be, and the higher will be the probability that binary data will be corrupted by noise (for a given noise level). Furthermore, the lower the signal level relative to the noise level, the longer in duration a given bit must be in order to average out the noise over the bit period, and thus the lower the maximum possible bit rate for a given error rate. Clearly, the optimum gap between the optical fibers of the male and female connectors in the intermediate position will depend on various factors, such as the noise level, optical input power, and the bit rate. However, a gap of 1 mm is expected to be capable of allowing data communication at rates of above 1 kHz, whereas when full coupling is achieved, data rates of at least 1 MHz of possible.

Clearly, a gap wider than 1 mm is possible if it is desired to further reduce the power level through the connector assembly. Conversely, a narrower gap can be chosen if higher bit rates or higher losses are required in the intermediate position.

In figure 3, the abutment member 70 is in an open position; that is, the abutment member is in a retracted state in which the forward face 13 of the main body member 22 can advanced past the abutment member 70, and in which the ferrule assembly of the male connector 12 can move sufficiently into the sleeve 64 so as to be in good optical coupling with the corresponding ferrule assembly 58 of the female connector 14. Normally, good optical coupling will be achieved when the ferrule assemblies of the male and female connectors are an abutment.

The abutment member 70 will normally be biased towards the closed position by a resilient member 76 (such as a spring), as indicated schematically in figures 1-3. The abutment member has a grip portion 78 arranged to allow a user to pull the abutment member into the open position. Thus, without the intervention of a user, and in the absence of a male connector received in the female connector, the abutment member resides in the closed position shown in figure 1. In the example of figures 1-3, the abutment member 70 has an angled surface 80, oriented at an angle less than 90° to the longitudinal axial direction. The angled surface 80 is arranged to engage with the forward face 30 of the (male) main body member 22, so that when a forward force is exerted on the male connector to introduce the male connector into the female connector, this force is partially translated into a transverse force which urges the abutment member from the closed position and into the intermediate position. As can be seen from figure 2, once the abutment member 72 has been moved into the intermediate position as a result of the forward movement of a male connector into the female connector, the front face all the main body member engages with the engagement surface 75 of the abutment member. Because the engagement surface 75 is arranged normal to the longitudinal axial direction, any further forward force exerted on the on the male connector does not result in any further transverse displacement of the abutment member 72. Thus, the abutment member prevents further forward movement of the male connector unless a user moves the abutment member manually into the open position by pulling on the grip portion 78 against bias off the resilient member 76.

One effect of the present embodiment is that the male and female connectors can be connected in a two-stage process in which, in a first stage, partial coupling is possible, and in a second stage, full coupling (that is, at least improved coupling) is possible, full coupling being possible only after manual or other intervention.

The partial coupling provided at the first stage can be used to perform one or more tests which determine whether full coupling is appropriate. For example, information can be transferred between the connectors (in one or both directions), which information can then be used to decide whether or not to allow full coupling. In one embodiment, the information transferred during partial coupling is used to reduce the risk of a user inadvertently making a full optical connection between devices which should not be so connected.

Figure 5 shows a first optical device 82 connected by a first optical fiber 18 to the female connector 14 of figures 1-3, and a second optical device 86 connected to the corresponding male connector 12 by a second optical fiber 88. Each of the first and second devices have a respective controller stage 90,92 operating in the electrical domain, and a respective optoelectrical interface 94, 96 for receiving data from the respective controller stage in the electrical domain and transmitting that data in the optical domain, and vice versa. Each controller stage has a respective memory 90,92 for storing executable instructions, as well as other data, and a processor facility 102,104 for executing the stored instructions and otherwise processing data in the electrical domain. A respective use interface 106, 108 is provided at the each device, each user interface having user input means 110, 112 to allow a user to input data, and a user display 114,116 to display information for a user.

The first and second devices are configured to initially communicate at a lower bit rate using a protocol that is tolerant to the error rate expected when the connector assembly is partially coupled as indicated in figure 2. That is, in response to a user input indicating that the second device is partially coupled to the first device, controller stage 92 of the second device causes the optoelectrical interface 94 to transmit an ID stored in the local memory. The ID is transmitted at the low bit rate, here at 1 kHz. (Alternatively, the first device may be arranged to transmit signals at intervals in a continuous fashion, the partial coupling at the connector assembly being sufficient to allow the second device to sentence the signals and in responders transmit its ID). In accordance with the executable instructions stored in the local memory, the controller stage of the first device is arranged, in response to receiving the ID, to compare the received ID with a set of stored IDs, and to either authorize or refuse a full connection to the second device in dependence on whether a match is found between an ID in the stored set and the received ID. If a match is found, a response message authorizing the second device is transmitted thereto. Otherwise, the response message is a refusal message refusing a full connection.

The second device is arranged to process the response message from the first device, and, if the response message indicates that the first and second devices are permitted to be coupled, to display an indication on the user display, from which a user can infer that full coupling is appropriate. Otherwise, if a refusal message is received, the controller of the second device causes the display to display an indication of this refusal. Based on the displayed indication, the user can decide whether to pull the abutment member into the open position so as to allow any male and female connectors to be brought into full coupling.

The second device is arranged to sense whether full coupling has been achieved (e.g., by monitoring the input power level) and if so, to transmit data at the normal bit rate, the normal bit rate being higher than the low (initial) bit rate. In this way, a user is given the opportunity to test whether full coupling is appropriate. Furthermore, since without user intervention, full coupling is prevented by the abutment member, the likelihood is reduced that a user will fully couple the first and second devices without previously testing whether such coupling is appropriate.

Alternatively (or in addition), the second device has a code associated therewith, which code is stored in the local memory facility. The first device has a list of one or more allowed codes stored in its local memory facility, the code or codes corresponding to devices for which full coupling is permitted. The second device is arranged to transmit its code at the low bit rate when . coupling is only partial. In response to receiving the code from the second device, the first device is arranged to transmit an indication of whether the code matches an allowed coded.

In a further modification to the embodiment of figure 5, the first device has a local optical switch arrangement 117 as shown in figure 6, which switch arrangement is controlled by the controller stage 90, such that if the correct code or ID is received, the switch connects the second device to an operational module 118 of the first device. In this way, the operational module is protected from full coupling with a device that transmits an excessive power level, since one effect of partial coupling is to reduce the through-power coupled by the connector.

Figure 7 shows a yet a further embodiment in which the connector assembly 10 has an electrical actuator 120 (such as a solenoid actuator) arranged to control the position of the abutment member in response to electrical signals. The actuator in this example is connected to the first device by an electrical link 122, such as a telephony connection, although a radio link or an optical link could be used instead. The electrical actuator may be locally powered. Upon detecting that the second device is suitable for full coupling, as described above for example using code information, the first device is arranged to transmit an electrical signal to the actuator 120 over the electrical link 118, the electrical signal clausing the actuator to move the abutment member 70 into the open position.

In a yet further embodiment, the first device and the second device are each part of an optical network, here a Passive Optical Network or (PON) 124, as shown in figure 8. The optical network has a head end 126, also known as an ONT, corresponding to the first device, and a plurality of network units 128, each also know as an ONU (components in figure 8 having a corresponding function to those in figure 5 have corresponding numerals). The head end is connected to a trunk fiber 130 of an optical distribution network or ODN 132, the optical distributional network having at least one power splitter 134 which distributes downstream light from the trunk fiber to a plurality of branch fibers 136. The splitter also serves to combine light from different branch fibers travelling in the upstream direction, and to direct of the combined light onto the trunk fiber 130.

Each network unit 128 is connected to a respective branch fiber 136 (at an end thereof that is remote from the splitter) by a respective connector assembly 10, of the type shown in figures 1-3. Typically, the connector assembly is used to releasably connect customer equipment to the network, at an edge or demarcation point of the network; that is, at a far end of one of the branch fibres. In such a situation, the connector assembly is normally located at customer premises, the female connector 14 being wall-mounted and terminating a branch fiber, whilst the male connector 12 terminates a fiber leading to a network unit 128.

When the optical network is in normal operation, the network units will be fully coupled to the optical distribution network (that is, the connector assembly will be in a state shown in figure 3). The head end 126 will broadcast, in the downstream direction, information to the network units 128 over the optical distribution network 132. In the head end will also receive information from the network units in the upstream direction. The light in the upstream and downstream directions will normally be the in infra red region, but at different wavelength to allow duplex traffic over a common fibre path.

In addition to the components of the first device shown in Figure 5, the head end 126 has a scheduler stage 138 for controlling the timing of signals from the respective network units 128, such that there is essentially no risk (or a reduced risk) that upstream signals from one network unit will collide with signals from another network unit where optical paths are combined at a splitter. The network units are configured to transmit short bursts of data in response to scheduling instructions from the head end, the scheduler stage 138 of the head end being arranged to perform a scheduling function such that the transmission of bursts are timed so as not to overlap. Hence, data from the different units is passively interleaved or equivafently multiplexed (in this example temporally, that is, in a time-division manner), in the normal way of a PON. The head end can then access data from each network unit using a TDMA (Time Division Multiplexed Access) protocol. It will be understood that the term "passive" refers to the manner in which data is multiplexed at a splitter, in particular to the way in which the timing function is carried out remotely from the splitter itself, so that the splitter may be passive. However, the splitter may function in the electrical domain, having an upstream interface and a downstream interface to convert data between the optical and electrical domain and vice versa. Furthermore, the optical network may include one or more repeaters or amplifiers.

The scheduling instructions from the head end contain an instruction for a given network unit to transmit data for a predetermined time interval at a predetermined time, with respect to a centralised time (although other in protocols data transmission is timed with respect to the local arrival time of a control signal). Accordingly, each network unit has, in addition to the components of the second device shown in Figure 5, a respective timing unit 140 for measuring the time at which a data burst is to be transmitted in response to a scheduling signal from the head end. Each network unit 128 will normally be connected to customer equipment such as telephony equipment or other communications equipment (not shown), and will be arranged to buffer data from the customer equipment in order to transmit it at the correct time in the upstream direction.

The network units each have an address or identity associated therewith stored in the local memory, and the head end is arranged to transmit broadcast instructions which associate given data with a given address. Each network unit is arranged to monitor the broadcast information from the head end, to capture data addressed to it, and to forward where appropriate the captured data towards the correct customer equipment.

Data in the upstream and downstream directions is transported as a series of cells arranged as a series of frames. A frame includes a plurality of sequentially arranged data cells or time slot, each of which has a data payload for carrying traffic data intended for costumer equipment, and a header, which header includes protocol-specific fields for defined types of information, such as an identifier field for the identity of the network unit for which a given data cell is intended (each network unit is arranged to forward data in the payload to customer equipment, whereas data in the header is not normally so forwarded). Signalling cells are provided between some of the data cells at predetermined positions within a frame (in the present example, two signalling cells and data cells are provided per frame). The signalling cells (also known in some protocols as PLOAM or "Physical Layer Operation, Administration and Maintenance" cells) contain the scheduling instructions (also know as "grants") from the head end which permit one or more specified network units to transmit a specified number of upstream data cells at a respective specified time. The signalling cells also contain dedicated fields for synchronisation information to allow the network units to achieve synchronisation. Additional fields are provided for other control instructions used for ranging, error control, and maintenance. Examples of known protocols for governing signalling, traffic transmission and other aspects of network operation include the ITU standards G983.1 and G983.4.

In the upstream direction, the network units are instructed, by means of the downstream signalling cells, to each transmit upstream data cells at an appropriate time so that the cells from the different network units come together at a junction in an interleaved fashion so as to form a downstream frame structure as described above, guard bands being provided between the cells to allow for timing irregularities. Consecutive cells may or may not originate from the same network unit.

Each network unit has stored, in the local memory thereof (preferably in a read only portion), details of the protocol according to which the optical network is operating. Such details include a set of rules which govern the way in which a network unit responds to the various control instructions from the head end, as well as rules to a now a network unit to correctly interpret the frame structure broadcast by the head end. The tiles of the protocol will normally be entered into memory during manufacture, so that network units which operate according to the protocol are standardized.

Because the terminals communicate with the head end using a time division multiplex protocol, it is particularly important that non-standardized network units or other equipment units are not connected to the optical distribution network. Should non- standardized equipment connected, there is a risk that light from this equipment may superpose with light from another network unit. Thus, the two stage connection described above provides a useful way of reducing the risk of exposing the head end to an excessive power level, since when the connector assembly is in the intermediate position, and coupling is and in the postural, the intensity of light from the Pasha be connected equipment is less than walked the power would be were the equipment fully coupled. In one embodiment, part of the data broadcast by the head end is recognizable by a standardized terminal even when it is only partially coupled to the optical distribution network; that is, when the connector assembly is in the intermediate position. In response to recognizing the data, a network unit is arranged to display a user message informing a user that the network unit is appropriate for the network. The user can then manually move the abutment member to allow full coupling.

In a yet further embodiment, the network units are arranged to recognize one or more pre- agreed control instructions from the head end (although not necessarily other data such as custom of data in a cell payload), even when the connector assembly is in the intermediate position. Thus in a set-up phase, for example when a network unit is being connected to the optical network, the network unit is only partially coupled at the connector. In the partially coupled state, the network unit is configured to respond to a control instruction inviting the network unit to transmit data at a particular time (albeit at the lower bit rate). Because the network unit being connected to the network can be controlled by the head end to transmit data at the correct time, initial communication can be established with a reduced risk of excessive light levels reaching the head end. Once, on the basis of this initial communication in the partially coupled state, the head end has established that the partially connected network unit is a standardized unit, the connector assembly can be allowed to move into the full coupling state.

Claims

1. A method of connecting a device to an optical network, including:

(i) making an optical connection between the optical network and the device, which connection is suitable for supporting communication at a first bit rate;

(ii) transmitting data from the device over the optical connection at the first bit rate;

(iii) using the transmitted data to determine at least one characteristic of the device; and,

(iv) in dependence on the or each determined characteristic, modifying a physical aspect of the optical connection such that the connection is suitable for transmitting data at a second bit rate higher than the first bit rate.

2. A method as claimed in claim 1, wherein a decision to authorize communication between the device and the optical network is made in dependence on the or each determined characteristic, the optical connection being modified if the communication is authorized.

3. A method as claimed in claim 1 or claim 2, wherein the data transmitted from the device includes an identifier for that device.

4. A method as claimed in any of the preceding claims, wherein the connection formed in step (i) has an optical loss associated therewith.

5. A method as claimed in claim 4, wherein the step of modifying a physical aspect of the connection includes modifying the connection such that the extent of optical loss associated with the connection is reduced.

6. A method as claimed in claim five, wherein the connection is modified at an optical connector assembly for making a releasable optical connection, the connector assembly having a loss associated therewith, the connection being modified such that the loss at the connector assembly is reduced.

7. A method as claimed in any of the preceding claims, wherein the connector assembly connects waveguides operating in a single mode fashion.

8. A method as claimed in any of the preceding claims, wherein the optical network is a passive optical network.

9. A method as claimed in claim 8, wherein in step (ii), data is transmitted from the device at the first bit rate in response to an instruction transmitted over the optical network.

10. An optical network having: a network device; a detachable device; an optical connection for connecting the detachable device to the network device, the connection having a first state for supporting communication at a first bit rate, and a second state for supporting communication at a second bit rate; and, means for modifying a physical aspect of the optical connection so as to change the state of the connection from one of the first and second states to the other of the first and second states, one of the network device and the detachable device being arranged, in response to traffic at the first bit rate from the other of the network device and the detachable device, to provide an indication of the compatibility of the detachable device with the network device.

11. A method of connecting a device to an optical network, including:

(ii) transmitting data over the optical connection at the first bit rate;

(Hi) using the transmitted data to determine an indication of compatibility between the device and the network; and,

(iv) in dependence on the indication of compatibility, modifying a physical aspect of the optical connection such that the connection is suitable for transmitting data at a second bit rate higher than the first bit rate.