Interface and method for interconnecting a host device and a small form factor pluggable module

Abstract

The present invention relates to an interface and method for interconnecting a host device and a small form factor pluggable module. The interface comprises a host device connector (52) arranged to receive a mating small form factor pluggable module connector (51); and a switching device (53, 54) connected to the host device connector and arranged to selectively switch at least one signal carried on the host device connector between at least two separate signal paths (56, 57) of the host device depending on a selected switching mode of the switching device.

Description

Technical Field

[0001] The present invention relates to interfaces and methods that enable interconnection between a host device and a small form factor pluggable module. Background Art

[0002] In a hierarchical mobile telecommunications network, the backhaul portion of the network includes an intermediate link between the core network of the mobile telecommunications network and a small subnetwork at the periphery of the entire hierarchical network. For example, although the user equipment communicating with the base station constitutes a local subnetwork, the connection between the base station and the rest of the world begins with a backhaul link to the core of the telecommunications provider's network. Various passive optical networks (PONs) can be used as mobile backhaul. For example, an optical network that provides multiple access methods (such as a gigabit passive optical network (GPON)) is a suitable mobile backhaul solution (it is called a GPON radio access network (GPONRAN)). However, other PON solutions are possible, such as Ethernet PON (EPON) or wavelength division multiplexing PON (WDMPON). In the following, GPON will be used to illustrate the xPON network.

[0003] GPON is Figure 1 1, wherein an optical network 10 essentially transmits traffic between a base station 11 and a base station controller 12. A plurality of user nodes 15 in the form of optical network units (ONUs) provide telecommunication services to end users via equipment (CPE) in the customer premises (which generally refers to devices such as telephones, routers, switches, set-top boxes, etc.). The ONUs are connected to a central office node 13 in the form of an optical line terminal (OLT) via an optical distribution network 14 (ODN), wherein a plurality (up to 64) of ONUs share a common splitter and a trunk optical fiber connected to the OLT. The OLT acts as an access multiplexer, which aggregates traffic from the ONUs and distributes traffic toward the ONUs. Thus, at one end of the network, the OLT provides an interface (e.g., Ethernet and time division multiplexing (TDM) interfaces, such as SONET) between the GPON and the service provider's network services (e.g., including IP services). At the other end of the network, the ONU provides the interface between the GPON and the end user, where services include voice, such as in the form of plain old telephone service (POTS) or voice over IP (VoIP), data such as Ethernet, video, etc.

[0004] In addition to the optical fiber, the ONU contains a GPON framer (for managing packet data) and a host CPU (for controlling the GPON framer and Ethernet-related logic (switching, service management, L3 functions, etc.) and / or voice-related logic). The ONU also contains flash memory to store software that can be updated remotely by the OLT.

[0005] Recently, highly integrated ONU chipsets have become available that contain many more functions in addition to framers. This allows very small ONUs to be made that can be hosted in small form factor pluggable (SFP) modules. Advantageously, at the ONU, as soon as bandwidth requirements increase, one or more SFP modules can be inserted to make the ONU highly scalable. In addition, because different SFP types have different ranges (1km, 5km, 80km, etc.), different SFPs can be inserted depending on the range requirements.

[0006] SFP is currently the most popular transceiver form factor for Ethernet (1G), SDH / SONET, Fibre Channel, and PON (EPON, GPON, WDM). The SFP module is inserted into the SFP connector mounted on the motherboard of the ONU. The connector is placed inside an EMI shield where the SFP module is connected. The SFF MSA group has standardized the SFP, and the enhanced version SFP+ is currently used for 10G Ethernet with the same connector layout.

[0007] In order for synchronous PON to be usable as mobile backhaul, transmission of synchronization signals is a strict requirement. In the art, this has been addressed by integrating the packet-based 1588 infrastructure in the SFP module, which is referenced in Figure 2 The SFP modules are described in detail in detail. That is, the SFP modules have been modified to comply with the precision time protocol described in a standard called IEEE 1588. Using this protocol, it is possible to synchronize distributed clocks with an accuracy of less than 1 microsecond via an Ethernet network. However, this approach requires significant modification of ordinary off-the-shelf SFP modules, making them both complex and expensive. Summary of the invention

[0008] The object of the present invention is to solve these problems in the art.

[0009] In a first aspect of the invention, this object is achieved by an interface that enables interconnection between a host device and a small form factor pluggable module. The interface comprises a host device connector arranged to receive a mating small form factor pluggable module connector, and a switching device connected to the host device connector and arranged to selectively switch at least one signal carried on the host device connector between at least two separate signal paths of the host device depending on a switching mode selected by the switching device.

[0010] In a second aspect of the invention, this object is achieved by a method of interconnecting a host device and a small form factor pluggable module. The method comprises the steps of receiving a small form factor pluggable module connector in a host device connector, and selectively exchanging at least one signal carried on the host device connector between at least two separate signal paths of a host device on which the host device connector is mounted.

[0011] Advantageously, by enabling the interface to selectively switch one or more signals carried on the host device connector to separate signal paths (i.e., in practice to separate pads on the host device printed circuit board), it is possible to insert different types of SFP modules into the host device. For example, the present invention facilitates the insertion of a Gigabit Ethernet (GE) SFP or a GPON ONUSFP into the same SFP connector of a host device (e.g., a micro / macro / pico radio base station (RBS)).

[0012] In an embodiment of the present invention, the switching device of the interface is arranged to selectively switch a group of signals carried on the host device connector to a corresponding first signal path when in a first switching mode, and selectively switch a group of signals carried on the host device connector to a corresponding second signal path separated from the first signal path when in a second mode. In an exemplary embodiment, a group of signals carried on the host device connector includes TxFault, TxDisable, RateSelect and LOS signals in the first mode, and includes at least 1PPS signals in the second mode. Therefore, in the case of, for example, GE SFP, the signals switched to the host device PCB pad will have their usual functions, but in the case of, for example, GPON ONU SFP, at least one of the signals switched to the host device PCB pad will be a synchronization in the form of 1PPS. The 1PPS signal is a pulse whose rising edge indicates the start of one second. The 1PPS signal must be provided to one of the SFP connector contact pins TxFault, TxDisable, RateSelect and LOS at the SFP module side of the host device. As will be described in more detail, the SFF MSA group has standardized the SFP where TxFault is a transmitter fault indication output that indicates that the SFP module laser driver has detected a laser fault, TxDisable is a transmitter disable input that commands the laser driver to disable the laser, RS is a rate select input that can be used to assume bandwidth selection to support multi-rate standards (e.g., in Fibre Channel), and LOS is a loss of signal output that indicates that no signal is received.

[0013] In an embodiment of the invention, when the set of signals carried on the host device connector includes a 1PPS signal, a time of day (ToD) signal is also arranged to be received on the host device connector via an inter-integrated circuit (I2C) signal. Alternatively, when the switching device is set in the second mode, the ToD signal is arranged to be included in the set of signals carried on the host device connector.

[0014] In another embodiment of the present invention, the switching mode of the switching device is arranged to be controlled by the I2C signal carried on the host device connector. In addition, the I2C signal can be arranged to define the type of the small form factor pluggable device that the host device connector is arranged to be interconnected with it. In addition, the I2C logic circuit can be connected to the I2C signal and the switching device carried on the host device connector, and the I2C logic circuit determines which switching mode should be selected from the I2C signal and switches the switching device to the selected mode. In another embodiment of the present invention, the type of the small form factor pluggable device that the host device connector is arranged to be interconnected with it is defined by the identification data stored in the EPROM of the SFP module and submitted via the I2C signal. It should be noted that the above-mentioned I2C bus is included in the standard SFP connector. However, any other standard bus can be used for this purpose, assuming that it becomes included in the SFP connector.

[0015] Relative to the prior art system in which the packet-based 1588 infrastructure must be integrated in the SFP module, the embodiments of the present invention have many advantages. First, no or few additional hardware components are required. The 1588 infrastructure requires an Ethernet PHY chip, timing logic (e.g., a crystal oscillator and a phase-locked loop, an interface, etc.). The use of a phase-locked loop also means slow and unstable synchronization. Second, the 1588 infrastructure has higher power consumption and larger size. Third, software is required in the SFP module to handle the 1588 protocol stack. With the creative interface for interconnecting the SFP module with the host device, such software is not required.

[0016] An interface that enables interconnection between a host device and a small form factor pluggable device according to embodiments of the present invention advantageously allows multiple SFP types to share the same SFP connector in a telecommunications CPE product.

[0017] Further features and advantages of the present invention will become apparent when studying the appended claims and the following description. Those skilled in the art realize that different features of the present invention can be combined to create embodiments other than those described in the following. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention will now be described by way of example with reference to the accompanying drawings, in which:

[0019] Figure 1 Illustrated is a prior art GPON as mobile backhaul in which the present invention can be applied;

[0020] Figure 2 FIGURE 1 illustrates a prior art solution for transmitting a synchronization signal from an OLT to a host device via an SFP module inserted into the host device;

[0021] Figure 3An example prior art SFP ONU is shown;

[0022] Figure 4 A standard SFP module connector is shown;

[0023] Figure 5 illustrates an interface according to an embodiment of the present invention;

[0024] Figure 6 The diagram shows the interconnection between the OLT, SFP ONU and host device;

[0025] Figure 7 Figure 1 shows how to synchronize 1PPS pulses and ToD serial data.

[0026] Figure 8 A flowchart illustrating an embodiment of a method according to the present invention is illustrated; and

[0027] Fig. 9 The diagram shows a flow chart of a further exemplary embodiment of the method according to the invention. DETAILED DESCRIPTION

[0028] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the invention are shown. However, the present invention may be implemented in many different forms, and the present invention should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0029] The present invention is described herein by way of reference to specific examples. In particular, embodiments of the present invention are described in a non-limiting general context with respect to a Gigabit-capable Passive Optical Network (GPON). However, it should be noted that the present invention and its exemplary embodiments are also applicable in all synchronous PON systems.

[0030] Figure 1 The diagram shows GPON as a mobile backhaul. The optical network 10 transmits traffic between a base station 11 and a base station controller 12. The optical network 10 comprises an optical line terminal (OLT) 13, an optical distribution network (ODN) 14 and several optical network units (ONU1, ONU2 ... ONUi) 15, in which the present invention can be implemented.

[0031] GPON is just one of many options when it comes to mobile backhaul. VDSL2, microwave-based, or Gigabit Ethernet (GE) are other well-known backhaul types. Depending on the available backhaul infrastructure, a decision must be made as to which type to use for a particular radio base station (RBS) to be deployed. Therefore, there is a requirement to make different backhaul interfaces pluggable at the RBS. This keeps the RBS PCB utilization small and the CAPEX low. It is even necessary to allow different SFP types (GE SFP, GPON ONU SFP) to be plugged into the same SFP connector at the RBS. In other words, it must be possible to plug a GE SFP module or a GPON ONU SFP module into the same SFP connector at a micro / macro / pico RBS.

[0032] In Ethernet and OTN / Fibre Channel, SFP modules typically contain the physical and media-related layer functions, keeping the actual media access controller (MAC) functions external - typically as part of an Ethernet switch on a motherboard. Therefore, the SFP MSA has specified the functions of the twenty I / O contact pins on the SFP connector.

[0033] A typical SFP module strictly contains physical layer and media related functions, such as connectors to the transmission medium (RJ45 for copper, single SC or single / dual LC for fiber), line driver components (analog front end for copper, laser / photodiode for fiber - usually BOSA and laser driver and limiting amplifier), and a CPU with ROM / RAM memory to control the line driver, support module / characteristic identification and optical supervision functions.

[0034] Figure 2 The diagram shows the current solution for transmitting synchronization signals from the OLT to the host device via an SFP module that is plugged into the host device. The standard SFP interface only defines the Ethernet serial link and I2C management signals as well as typical transceiver signals (in Figure 4). Thus, the OLT 20 receives a time of day (ToD) signal and data traffic via an interface 22, both of which are provided to the GPON MAC 24 and further to the GPON transceiver 25 via an ODN / optical fiber compliant with G.984.3, for example, from a base station controller (not shown) for a submitting service provider. The SFP ONU 30 receives the signal at the GPON transceiver 31 and the GPON MAC 32. However, because there is no support for synchronization signals at the SFP module, the packet-based 1588 infrastructure must be integrated in the SFP module (IEEE 1588 is a standard for a precise clock synchronization protocol). Therefore, the ToD signal is extracted and provided to the ToD circuit 34 and the IEEE 1588 master device 35 to the Ethernet transceiver 36, while the data traffic is provided to the switching and packet processing circuit 38. The Ethernet transceiver 36 is interconnected to the corresponding transceiver 41 at the host device 40 via an SFP connector 39. The ToD signal is extracted by the IEEE 1588 slave device 43 and provided to the interface 44 for further transmission. The transceiver provides data traffic to switching and packet processing circuitry 46 .

[0035] Figure 3 An example prior art SFP ONU 30 is shown. The SFP ONU 30 includes a GPON transceiver 61 and a GPON MAC 62 for communicating with the OLT. The GPON transceiver basically includes a laser diode (for data transmission) and a light detection sensor (for data reception). A switching / packet processing circuit 63 (for managing data packets) and a packet buffer 64 (for queuing packet data) are included. In addition, an Ethernet MAC unit 65 (for processing Ethernet MAC addressing in the link layer) and a GE PHY circuit 66 (for connecting the link layer with the Gigabit Ethernet physical layer and thus communicating with the host device via the SFP connector 67) are included. In addition, the SFP module 30 includes an EEPROM 68, for example, for storing SPF identification data. The EEPROM and identification data will be discussed in more detail below. The SFP ONU 30 also includes a power supply circuit 69 (for powering the various components included in the SFP module) and a crystal 70 (for generating a clock signal with a very precise frequency). The main components of the SFP module are the system CPU 71 and peripheral devices (e.g., system I / O 72, RAM 73 for software execution, and flash memory 74 for software storage). The functions of the system CPU 71 include processing management control interfaces, controlling other components (e.g., packet processing), performing monitoring and reporting to the OLT, etc.

[0036] Figure 4 A standard SFP connector is shown. Such an SFP connector has 20 contact pins for carrying signals on the SFP / host device interface. Figure 4 The functionality of the corresponding pin is indicated in the figure. In the following, the functionality of each pin will be briefly described and the connector pinout will be indicated. The data to and from the SFP module is typically differential serial with two contact pins in each direction (TD+ (pin 19) / TD- (pin 18) for transmission; RD+ (pin 12) / RD- (pin 13) for reception).

[0037] VccT (pin 16) and VeeT (pins 10, 17, and 20) provide DC power to the transmitter circuit, while VccR (pin 15) and VeeR (pins 1, 2, 11, and 14) provide DC power to the receiver circuit. All contact pins are required to allow enough current to the SFP (GPON ONU SFP requires more power than Ethernet SFP).

[0038] TxFault (pin 9, Transmitter Fault Indication, output) indicates that the SFP laser driver has detected a laser fault, and TxDisable (pin 8, Transmitter Disable, input) commands the laser driver to disable the laser.

[0039] MOD-DEF are three contact pins that define the I2C communication interface of the SFP module. MOD-DEF 0 (pin 5) is grounded to indicate the presence of the SFP module, MOD-DEF 1 (pin 6) is the clock line of the I2C EEPROM, and MOD-DEF 2 (pin 7) is the data line of the I2C EEPROM.

[0040] RS (Pin 4, Rate Select, Input), bandwidth selection to support multi-rate standards (for example, in Fibre Channel). In PON, this pin is used for TX signal detection (indicating TX data transmission). On ONU and OLT, it is used for RSSI triggering.

[0041] LOS (Pin 3, Loss of Signal, Output), no receive signal indication.

[0042] Figure 5 An embodiment of the invention is illustrated in which an interface is provided that facilitates insertion of a GE SFP module or a GPON ONU SFP module into the same SFP connector of a host device. Thus, the host device 40 is interconnected to the SFP module 30 via a host device connector 52 (which is arranged to receive a mating SFP connector 51).

[0043] This is Figure 6 , which shows an OLT 20, an ODN / Fibre Channel, an SFP ONU 30, and a host device 40, all of which are referenced Figure 2 To describe. Figure 6As can be seen in FIG. 1 , an interface according to an embodiment of the present invention is arranged at a host device and includes a host device connector 52 arranged to receive an SFP module connector 51. The physical interconnection created by attaching the host device connector 52 to the SFP module connector 51 corresponds to Figure 2 SFP connection 39 in (and corresponds to Figure 3 SFP connection 67).

[0044] Reference again Figure 5 One or more switching devices implemented in the form of multiplexers 53, 54 are connected to the host device connector and are arranged to selectively switch a set of signals TxFault (TxF), TxDisable (TxD), RS and LOS carried on the host device connector to corresponding first signal paths 56 indicated by pads TxF, TxD, RS, LOS on the host device printed circuit board (PCB) when in a first switching mode, and selectively switch the set of signals to corresponding second signal paths 57 separated from the first signal paths and indicated by pads P1, P2, P3 and P4 when in a second switching mode. Figure 5 The rightmost pad in is connected to various components at the host device, such as, for example, the main CPU.

[0045] As can be seen, TxFault, TxDisable, LOS and RS are typical transceiver specific lines used by GE SFP and are usually controlled / used externally by the SFP module. In GPON ONU SFP, those lines are controlled by GPON MAC (or its integrated host CPU) and are functionally redundant. Therefore, any one of these four contact pins can be used to pass synchronization signals in the form of 1PPS signals and ToD signals required by GPON ONU SFP.

[0046] The transmission of 1PPS and ToD signals on the SFP interface from the ONU SFP module to the host device contains two signal paths: a 1PPS pulse (whose rising edge indicates the start of one second), and ToD serial data (which includes detailed descriptions of the 1PPS pulse (e.g., the absolute time of the 1PPS, the status and quality indication of the 1PPS pulse, etc.).

[0047] The ToD serial data needs to be transmitted periodically. Its period should be synchronized with the 1PPS pulse and the serial data transmission must be completed before the start of the next 1PPS pulse. Figure 7 Figure 1 shows how to synchronize the 1PPS pulse and ToD serial data.

[0048] Different operators may require different formats for the ToD serial data. One possible format is set forth in the NMEA 0183 specification. However, any format may be used.

[0049] Now, refer again Figure 5 , in order to determine which switching mode should be selected (i.e., whether a GE SFP module is connected and the SFP connector contact pins have their standard functionality and therefore the signals transmitted thereon should be passed to the corresponding pads TxF, TxD, RS and LOS, or a GPON ONU SFP module is connected and the ToD and 1PPS signals should be passed to any one of the pads P1-P4), the signals transmitted via the I2C pads should be evaluated. In this regard, the type of SFP that requires synchronization signals is exemplified using the GPON ONU SFP. It should be noted that other types of SFP modules that require synchronization signals and should be able to be inserted into the interface of the present invention include fiber channel SFP, optical transport network (OTN) SFP, coarse wavelength division multiplexing (CWDM) or dense wavelength division multiplexing (DWDM) SFP and WDM-PON SFP.

[0050] In the SFP module 30 connected to the host device connector 52, there is an EPROM for hosting data about a specific SFP module. This data is read by the I2C logic circuit 55 and controls the multiplexers 53, 54 via the selection input S to select the appropriate exchange mode. That is, either the SFP module is an Ethernet SFP module and the signals TxD, TxF, RS and LOS have their conventional functions and are exchanged to the corresponding pads TxD, TxF, RS and LOS respectively in the first mode, or the SFP module has the type of synchronization required as stated above, and the impact is that the 1PPS signal and the ToD signal are carried on any two of the four SFP connector pads and are exchanged to any two of the P1-P4 pads at the host device in the second mode. Other signals may be further carried on the interface and exchanged to any one of the pads P1-P4 in the second mode, such as faster data channels or general signals. For example, the I2C logic may be a dedicated circuit in the form of an ASIC or FPGA, but may alternatively be implemented by the host device CPU. The multiplexer can also be implemented by dedicated circuits or the host device CPU. Figure 5 5, their functionality can be very well implemented in a single multiplexer. In the case where the multiplexers are implemented by dedicated circuits, their power supply can be taken from the SFP interface. Instead of having a host device CPU providing the selection signal, the advantage of having dedicated hardware controlling the multiplexer is that the SFP module itself can select the switching mode. On the other hand, by implementing the multiplexer and I2C logic circuit in the host device CPU, no additional hardware is required because this functionality is implemented in software.

[0051] In either case, the interface is set up (i.e., the switching mode of the multiplexer is selected) by having the I2C logic read the SFP EPROM via I2C signals. For example, this can be done by reading the transceiver code (stored at a standard address in the SFP EPROM), or by reading the part number, serial number, copyright string, password (stored in a user-defined segment of the SFP EPROM). The I2C logic can then provide appropriate selection signals to the multiplexer to adapt the switching mode to the type of SFP module inserted into the host device. In addition, by reading the serial number, copyright string, and / or password, the interface can block illegal SFP module types (unsupported types, invalid copyright strings / passwords). In such a case, the multiplexer drives some or all of the contact pins to a high-ohmic (open drain) state, effectively lifting it from the bus (if necessary).

[0052] Further references Figure 5 In yet another embodiment of the interface of the present invention, the 1PPS signal is passed on the host device connector via any of the TxF, TxD, RS or LOS contact pins and switched by multiplexers 53, 54, while the ToD signal is transmitted via the I2C contact pins. Thus, the ToD signal is transmitted from the SFP EPROM (the RAM segment of the EPROM) via the I2C contact pins, and the CPU on the host device copies the timestamp provided by the ToD signal to a memory location once per second (dictated by the 1PPS pulse) sent on the other connector contact pins.

[0053] Modern optical SFP transceivers support digital diagnostic monitoring (DDM) functionality via I2C according to industry standard SFF-8472. This feature is also known as digital optical monitoring (DOM). This feature gives the end user the ability to monitor real-time parameters of the SFP module (e.g., optical output power, optical input power, temperature, laser bias current, and transceiver supply voltage). Diagnostic monitoring is available via I2C signals of the SFP EPROM starting at address A2h, and a 120-byte user-writable address interval (at addresses 127-247) is typically used as an extended area for communication between the host and the SFP module. In the user-writable address interval, a 38-byte ToD message can be included at addresses 127-165 and transmitted on the I2C contact pins.

[0054] Figure 8 The diagram shows a flow chart of an embodiment of the method according to the present invention. In a first step S101, a host device receives an SFP module connector in its host device connector. Thereafter, in a second step S102, at least one signal carried on the host device connector is selectively exchanged between at least two separate signal paths of the host device.

[0055] Fig. 9 The diagram shows a flow chart of a further embodiment of the method according to the invention. In a first step S201, a host device receives an SFP module connector in its host device connector. Thereafter, in a second step S202, a switching mode is determined, wherein in the case of determining the occurrence of a first switching mode, a set of signals carried on the host device connector are switched to a corresponding first signal path, and in the case of determining the occurrence of a second switching mode, the set of signals carried on the host device connector are switched to a corresponding second signal path separate from the first path.

[0056] Further references Fig. 9 In another embodiment of the method according to the present invention, the exchange mode of step S202 is determined by a signal carried on the host device connector; when the group of signals carried on the host device connector includes TxFault, TxDisable, RateSelect and LOS signals, the first mode is selected, however, if the group of signals includes at least a 1PPS signal, the second mode is selected.

[0057] For synchronization purposes, the ToD signal should additionally be carried on the host device connector, as already mentioned before. Therefore, in yet another further embodiment of the method according to the invention, when the set of signals carried on the host device connector comprises a 1PPS signal, the ToD signal is arranged to be transmitted on the host device connector via an I2C signal, while in an alternative embodiment of the method, the ToD signal is included in the set of signals determining the exchange mode.

[0058] Even though the invention has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent to those skilled in the art. Therefore, the described embodiments are not intended to limit the scope of the invention as defined by the appending claims.

Claims

1. An interface enabling interconnection between a host device and a small form factor pluggable module, the interface comprising: a host device connector (52) arranged to receive a small form factor pluggable module connector (51); a switching device (53, 54) connected to the host device connector and arranged to selectively switch at least one signal carried on the host device connector between at least two separate signal paths (56, 57) of the host device depending on a selected switching mode of the switching device, The switching device (53, 54) is arranged to selectively switch a set of signals carried on the host device connector to a corresponding first signal path (56) when in a first switching mode, and to selectively switch a set of signals carried on the host device connector to a corresponding second signal path (57) separate from the first signal path when in a second switching mode, When the set of signals carried on the host device connector (52) includes TxFault, TxDisable, RateSelect and LOS signals, the switching device (53, 54) is arranged to be set in the first switching mode; as well as When the set of signals carried on the host device connector includes at least a 1PPS signal, the switching device is arranged to be set in the second switching mode, wherein when the set of signals carried on the host device connector includes the 1PPS signal, a time of day (ToD) signal is further arranged to be received on the host device connector (52) via an I2C signal, The interface further comprises: an I2C logic circuit (55) arranged to receive the I2C signal carried on the host device connector (52) and further arranged to determine from the I2C signal which switching mode should be selected and cause the switching device to switch to the selected mode, The I2C signal carried on the host device connector (52) is arranged to identify the type of the small form factor pluggable module, and the host device connector (52) is arranged to interconnect with the small form factor pluggable module.

2. An interface as claimed in claim 1, wherein when the switching means (53, 54) is arranged in the second switching mode, the set of signals is further arranged to include a time of day (ToD) signal.

3. An interface as claimed in any one of claims 1 to 2, wherein: The switching means (53, 54) are arranged to change switching modes in dependence on an I2C signal carried on the host device connector (52).

4. An interface as claimed in claim 1, wherein the type of the small form factor pluggable module is defined by identification data, the identification data is stored in an EPROM of the small form factor pluggable module and submitted via the I2C signal, the host device connector (52) being arranged to interconnect with the small form factor pluggable module.

5. The interface of claim 1, wherein the type of small form factor pluggable (SFP) module is selected from the group consisting of Ethernet SFP, GPON ONU SFP, Fibre Channel SFP, OTN SFP, C / DWDM SFP, and WDM-PON SFP.

6. An interface as claimed in any one of claims 1-2, wherein the switch means (53, 54) is arranged to be powered by VccR and VeeR signals carried on the host device connector (52).

7. An interface according to any of claims 1-2, the switching means (53, 54) being a multiplexer arranged with a selection input (S), the multiplexer switching mode being controlled via the selection input.

8. The interface of any of claims 1-2, wherein the host device connector (52) is arranged to interconnect with a mating small form factor pluggable connector of an SFP selected from the group consisting of SFP, SFP+, CFSP, QSFP and XFP.

9. A host device (40) comprising the interface according to any one of claims 1-8.

10. A method of interconnecting a host device and a small form factor pluggable module, the method comprising the steps of: receiving (S101) a small form factor pluggable module connector (51) in a host device connector (52); selectively exchanging (S102) at least one signal carried on a host device connector between at least two separate signal paths (56, 57) of a host device, the host device connector being arranged at the host device, The method further comprises the steps of: Determine (S202) the exchange mode; wherein, The determining (S202) the exchange mode comprises: receiving an I2C signal carried on the host device connector (52), and determining from the I2C signal which exchange mode should be selected, wherein the I2C signal carried on the host device connector (52) is arranged to identify the type of the small form factor pluggable module, the host device connector (52) being arranged to interconnect with the small form factor pluggable module, Wherein selectively exchanging (S102) at least one signal carried on a connector of the host device between at least two separate signal paths (56, 57) of the host device comprises: upon determining the occurrence of a first switching mode, switching a set of signals carried on the host device connector to a corresponding first signal path (56), and upon determining the occurrence of a second switching mode, switching a set of signals carried on the host device connector to a corresponding second signal path (57), in: determining the occurrence of the first switching mode when the set of signals carried on the host device connector (52) includes TxFault, TxDisable, RateSelect, and LOS signals; and determining the occurrence of the second exchange mode when the set of signals carried on the host device connector includes at least a 1PPS signal, The method further comprises the steps of: When the set of signals carried on the host device connector includes a IPPS signal, a time of day (ToD) signal is received on the host device connector (52) via an I2C signal.

11. The method of claim 10, wherein when determining the occurrence of the second exchange pattern, the set of signals further includes a time of day (ToD) signal.

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