Multiple-port lan selector switch for token-ring networks

The subject of the invention is a data transmission block in a data transmission network and a data transmission network.

In digital data transmission systems, complex clock and data signals in binary form are sent, via wires or optical fibers, from a transmission line transmitter to a transmission line receiver. The transmitter or receiver in a data transmission system can be a single computer or it can be a local area network (LAN). A specific computer or station on a LAN can send information to other stations on a LAN or receive information from other stations. The station joins the LAN when it needs to connect to another station and disconnects from the LAN when the connection is completed.

A common topology of a LAN is a token-ring network, i.e. a network with a ring architecture and a relay transmission method. The token-ring network architecture is used to connect devices connected to the network. The token-ring network enables unidirectional data transmission between stations using the tag forwarding procedure. Ring architecture allows tags to be forwarded from a node associated with a specific device attached to the network, such as a personal computer, to another node in that network. A node that is ready to send data can capture the flag and then issue the data for transmission. If the information received by the node or station is intended for a station further along the network, then the receiving station must forward the information along the LAN, to the next adjacent station, and so on until the information reaches its final destination. A device or computer station trying

179 711 to access the token-ring network node should have an adapter that is physically connected to the token-ring network. The access device must implement the token-ring network access procedure in accordance with the standard protocol.

The token-ring network has two data transmission rates: 4 Mbps and 16 Mbps. Typically, both of these transfer rates are used, and often 4 Mbps data rates can be used in one network, while 16 Mbps data rates in another network, and the user may wish to have access to both networks.

Many LANs use hubs or hubs, known as multi-access units, to connect multiple stations on one network node. Individual multi-user access units connect to each station via a 4-wire cable. Many such cables go from the hub to the individual stations, forming a star-shaped structure. Physically, each station is separately connected to the hub with its cable, where it can access the network node. All stations attached to a specific hub operate at the same network speed, e.g. 4 Mbps. When the hub is connected to a token-ring network, then the logical network configuration places each station connected to the hub in a separate node within the network. The hub itself can connect attached devices into a token-ring network, or it can be connected to other hubs, forming a larger token-ring network, including all devices connected to all hubs. An intelligent hub is a hub that contains a processor that controls switching electronics and is designed to control access to the network.

The term hub usually refers to a multi-available MAU. Such a system is introduced by the IEEE 802.5 specification, referring to such a system as an inter-network interface unit. Individual cables consist of two pairs of twisted pair cables that connect the network adapter or other communication device to the hub port. Individual cables connect with other identical cables to form a complete hub. Although the number of cables in the hub can vary, the most popular configuration uses eight cables, which is mainly due to the physical size of the terminal block used in the token-ring network that matches the standard equipment rack.

Each computer connected to the network is connected with a cable to the appropriate port on the concentrator cable, with the computer exercising control over the switch-on / bypass mechanism by means of phantom-type excitation in the form of DC voltage. This constant voltage is transparent when the data transmitted by the computer passes, hence the name of the phantoms. The applied voltage is used as part of the hub's cable port to affect the serial introduction of the computer's integration into the network. Loss of phantom forcing causes a derive action that bypasses the computer and causes the computer to enter a looped state.

A network-connected computer contains a network adapter card consisting of hardware and electronic components that are necessary for connecting to the MAU via a cable, as well as for entering data and communicating in a token-ring network. The IEEE specification requires that existing token-ring network adapters send data in an orange-black pair of wires and receive through a red-green pair of wires in a carrier interface cable. The token-ring network adapters connect directly to the MAU in such a way that the MaU receives data on an orange-black pair of wires and transmits via a red-green pair of wires. Phantom excitation current, i.e. phantom current excitation, is controlled by the token-ring adapter on a red-green pair of wires to allow connection to the token-ring network. Phantom excitation current has a dual function, i.e. it is used to detect a faulty cable connection and to turn on the relay in the MAU unit for serial connection of the computer to the token-ring network. Hence, the adapters are the source of the phantom excitation current, and the MAU is the outlet for it.

Because the token-ring network described above allows each network adapter to connect to any other network adapter, then each such connection in

179 711 token-ring networks must be carried out through a hub. Consequently, two computers next to each other within a LAN must connect using a limited bandwidth that is shared between each adapter connected to the network. There are two problems that do not allow two network adapters to be connected directly to each other. The first is a direct connection of two network adapters that meet the standard set out in the IEEE 802.5 specification, would lead to a direct connection of a pair of transmitting twisted pair adapters (orange-black pair) and their receiving wires (a pair of red-green twisted pair), not allowing any connection between two network adapters. The second problem is that currently available network adapters cannot be an outlet for phantom excitation current, they can only be their source. Without the possibility of creating an outlet for phantom excitation current, an adapter trying to connect would be a source of phantom excitation current for a receiving adapter that could not be an outlet for phantom excitation current. Hence, the source adapter could detect the wiring error condition, i.e. wiring error or damage. After detecting the wiring error condition, the adapter could automatically stop data transfer.

The essence of the data block in the data transmission network, according to the invention, in which each port contains the first port connection and the second port connection as well as the transmitter and receiver system, is that each port of the data block includes the first transformer, with the first winding connected to the first port and second winding connections, and a second transformer with the first winding connected to the second port connection and with the second winding, whereas in the first operating mode the second winding of the first transformer is connected to the transmitter system and the second winding of the second transformer is connected to the receiver system, while in the second operating mode the second winding of the first transformer is connected to the receiver system and the second winding of the second transformer is connected to the transmitter system .

Preferably, each port includes a first switch connecting a DC voltage source to the first port connection and a second switch connecting the second port connection to the DC return path in the first position and to the first port connection in the second position.

Preferably the port is attached to the hub.

The essence of the data transmission network, according to the invention, comprising network adapters and a hub connecting one or more network adapters forming a token-ring network, is that it contains a data transmission block with one of a number of network adapters connected to the first port of this transmission block data, with the concentrator connected to the next port of this data block.

An advantage of the solution according to the invention is the possibility of crossing network adapter cables for sending and receiving to allow direct connection between adapters. In addition, the advantage is the implementation of an outlet for phantom forcing, to prevent detection of a false condition wiring error when two network devices connect directly, and to provide a direct link between two network devices with a full network bandwidth, e.g. 16 Mbps, rather than shared bandwidth provided over token-ring connections.

The invention in the embodiment is illustrated in the drawing, in which Fig. 1 shows a data transmission system forming a network according to an embodiment of the invention, Fig. 2 - a diagram of a single port of a multi-port LAN switch as a data transmission block according to the invention in adapter mode, Fig. 3 a single port of a multi-port LAN switch configured in port mode, fig. 4 - diagram of a standard adapter connected to a LAN switch port configured in port mode, Fig. 5 - diagram of a multi-port LAN switch port configured in adapter mode for connection to a standard MAU, Fig. 6 - block diagram of the port of the first LAN switch in adapter mode and port of the second LAN switch in port mode, Fig. 7 - flowchart for automatically determining the type of connected device

179 711 and the multi-port LAN switch configuration, while Fig. 8 is a flowchart that is a continuation of the flowchart of Fig. 7.. ,

Figure 1 is a block diagram of a communication system forming a network including a multi-port LAN switch as a data block according to the invention. In more detail, Figure 1 shows a data transmission system forming a network 10 into which LAN multi-switches 40, 46, 47 are included. Network 10 includes a local area network (LAN) formed by a number of attached devices or stations 12, such as personal computers or workstations. Stations 12 are connected to each other through hubs 14, 44 and through LAN switches 40, 46, 47. A typical hub can support up to 8 connected devices and can be the end of a network connection between attached free-standing devices. This hub can also be connected to a main network connecting many hubs forming a larger network in a larger geographical area.

Each station 12 connects to concentrators 14, 44, such as MAU, connection port 16 via cable 22. The specified attached device or station 12 is connected to the network by means of the network adapter 24, 36, 37, 42, 43, located in station 12. This adapter provides a direct connection to the cable and ensures that each station gains access to the network to send and receive data, the adapter also includes the hardware and / or software necessary to physically connect to and operate within the network.

Concentrators 14, 44 are such a physical termination of the connection between ports 16 that the attached device 12 can connect to another connected device 12. The concentrators 14, 44 are intelligent concentrators having control logic and relay mechanisms for controlling the connection of various stations 12.

Main ring 26 connects concentrator 14 to a plurality of concentrators, such as concentrator 44, which are connected in series along a ring network. The main ring may include an optical fiber cable or other type of medium used for data transmission, for example shielded or unshielded twisted pair of copper wires. Each concentrator is connected to the main ring 26 via a ring in / out (RI / RO) device included in the concentrator. The I / O ports on concentrators 14, 44 connect to each other through the main ring, forming a ring of the transmission system that the data moves in a clockwise direction around the ring network. This allows you to connect stations connected to port 16 not only with other stations 12 connected to hub 14, but also with other stations and servers on the network that are connected to various hubs, such as hub 44.

Preferably, the token-ring network architecture is used to connect attached devices or stations 12 within a LAN. The token-ring network enables unidirectional data transmission between stations in a ring-like system using the tag transfer procedure. The ring topology allows the transfer of markers from a specific station 12 to another station connected to concentrator 14 or to another station connected to concentrator 44. Station 12, when ready to send data, can capture the tag and then enter the data for transmission on the network.

A preferred token-ring network is a token-ring network compliant with the IEEE 802.5 standard, which allows peer-to-peer broadband connection for individual stations. This token-ring network can operate at either 4 Mb / sec or 16 Mb / sec and supports up to 260 stations in one ring. The token-ring network uses the Manchester differential code, a digital coding technique in which each period allocated to one bit is divided into two complementary halves to encode a digital baseband wave. The transition, i.e. the change of signal state at the beginning of the bit period, represents one of the binary digits, namely 0, while the lack of transition, i.e. the change of the signal state at the beginning of the bit period, represents the binary digit 1.

Attached station 12, attempting to access the network and having its network adapter, starts enabling its port by entering Phase 0 of the process I will turn on

179 711 adapter. During this phase, the network adapter sends frames addressed to each other to determine if the cable and the transmitting and receiving systems are working properly. Therefore, during this phase, all frames are returned back to the adapter through the hub, so that if the link is good, the adapter will receive exactly what it sends through the cable.

After completing Phase 0, the network adapter introduces Phase 1 by supplying the phantom excitation current to the cable. The concentrator port 16 detects the presence of current and sends a phantom detection interrupt to the concentrator CPU which controls the concentrators 14, 44. The phantom detection interrupt is used to identify the cable trying to connect to the network. The central unit, unless otherwise set up by the network management system, enables relays connected in series with port 16 to connect a station trying to access the network. Alternatively, some hubs are not intelligent hubs and do not need to have a central unit or even be powered. In this type of concentrator, the phantom excitation current charges the capacitor, which then activates the relay in the concentrator to turn on the included adapter.

As you know, LAN switches are known in the field of data transmission and computer networks and are used to provide data transmission between devices or segments of a LAN connected to many ports of the LAN switch. A LAN segment can be defined here as a group of nodes in which all nodes use the same physical layer of the open system connection (OSI) model. To connect two devices or two network segments, the LAN switch activates a node in one LAN segment to connect to a node in a different LAN segment. Typically, a LAN switch receives data from a node in one LAN segment and forwards this data to another LAN segment that contains the destination node. Preferably, the LAN switch is a multi-port LAN switch, such as a LAN 40 switch.

The LAN switch performs several functions. Namely, the LAN switch port provides media access control (MAC) and implements the physical layer (PHY) necessary for coupling and communication with devices connected to the port. In addition, the LAN switch port maintains current port statistics, including the number of passes, valid and invalid frames, and port operational status. Invalid frames are those that contain errors. The port also maintains address tables containing a list of node addresses connected to other ports on the multi-port LAN switch. Along with maintaining these address tables, the port also contains systems for determining and selecting destination ports. The port also includes buffers for buffering incoming and / or outgoing frames. Buffering may be needed when the destination port is busy or when the frames arrive at a total bit rate exceeding the capacity of the destination port. Finally, the LAN switch port provides interface logic for the switch matrix. The term switch matrix refers to systems that transfer data from one port to another. Such a switch matrix may be a fast transmission bus or a cross switch.

The network adapter 42 is connected to the port a of the LAN switch 40, while the network adapter 43 connects to the port b of the LAN switch 40. The MAU 44 unit is connected to the port c of the LAN switch 40 via cable 32. Also, the two LAN switches 40 and 46 are connected from port d of the LAN 40 switch to port e of the LAN switch 46. The LAN 40 switch is also connected from its e port to the e port of the LAN switch 47. Each of the above connections of a multi-port LAN 40 switch with a hub, network adapters and switches is implemented via a standard cable, with standard cabling in the form of two pairs of twisted pairs, as required by the IEEE 802.5 standard.

LAN switches 40, 46 and 47 act as high-speed bridges, as is known in the field of data transmission and networking. The lAn switch can connect any two devices connected to its ports, hence it provides a link between these devices. A LAN switch can connect an attached adapter with another attached adapter, an attached adapter with another hub, or an attached adapter with another attached LAN switch. Also, the LAN switch allows you to connect local loops, channels or rings by adjusting circuits and facilities for the accuracy of data transmission.

Each LAN switch port is configured in the appropriate operating mode, i.e. either in port mode or in adapter mode. In port mode, the LAN switch is configured to properly transmit and receive data and provide an outlet for phantom excitation current. In adapter mode, the LAN switch is configured to correctly transmit and receive data and provide a source of phantom excitation current, for example as shown in Fig. 1 ports a, b of the LAN switch 40 could be configured in port mode to receive and transmit data from network adapters 42 and 43, respectively. Port c of the LAN switch 40 could be configured in adapter mode to allow receiving and transmitting data to MAU 44. When connecting to a token-ring network, the 42 network adapter must be shown to be connecting to the MAU port. Therefore, ports a, b of the LAN switch 40 must be configured to appear identical to the MAU port. Similarly, the inclusion of MAU 44 must present itself as a direct connection to the adapter. Consequently, LAN switch c port 40 must be configured to emulate the adapter. According to the present invention, when the network adapter 42 attempts to join the token-ring network and initiates communication, then the LAN switch 40 provides an outlet for the phantom excitation current. Therefore, to allow network adapter 42 to communicate with network adapter 36, one LAN switch port could be set in adapter mode, while the other in port mode, allowing data transmission between port d of LAN switch 40 and port e of LAN switch 46.

Fig. 2 is a schematic of a single port of a multi-port LAN switch as a data block according to the invention. The port is configured in adapter mode. When the IEEE 802.5 standard cable connects the device to the port, then the first port 50 connection connects to the black-orange twisted pair and the second port 52 connection connects to the red-green twisted pair. The first port 50 connection connects to the first winding of transformer 58 and the second port 52 connects to the first winding of the second transformer 60. The second winding of the first transformer 58 and the second winding of the second transformer 60 connect to the relay 62. Both the transmitter system 54 and receiver circuit 56 is connected to relay 62.

The port includes transmitter 54 and receiver 56 circuits that perform the transmitter and receiver functions necessary to support connectivity and connectivity with any attachable device, including network adapters, MAUs, and other switches. LAN. Relay 62 creates an electrical connection between circuits 54 and 56 and transformers 58 'and 60 as a function of relay 3 control signal. The control signal of relay 3 sets relay 62 into the connection shown in figure 2 when the port is in adapter mode. When the control signal of relay 3 indicates adapter mode, then relay 62 connects the transmitter system 54 to the first transformer 58 and connects the receiver system 56 to the second transformer 60. When the control signal of relay 3 indicates port mode, then relay 62 electrically connects the transmitter system 54 to the second transformer 60 and connects the receiver system 56 to the first transformer 58 as shown in Figure 3.

Referring back to Figure 2, the DC phantom source is connected to the switches 64 which are controlled by the relay 1 control signal. The switches 64 connect the two poles of the DC phantom source to the first winding of the first transformer 58 to allow the phantom forcing current to be drawn from this port, through the attached device from the output of the first port connection via black and orange twisted pair. In addition, when the port is configured in adapter mode, then it must provide a return path for phantom current through the second connection of port 52. Switches 66 are controlled by the relay 2 control signal and are switched to connect the first winding of the second transformer 60 to ground when the port is in adapter mode.

In an alternative embodiment, the optical coupler 69 is connected in series to the return path. The output of the optical coupler 69 indicates whether the port is in mode

179 711 adapter or port through the presence or absence of phantom extortion. When the port is configured in port mode, the optical coupler 69 will indicate the current flowing in the return path.

Fig. 3 shows the port of a multi-port LAN switch configured in port mode. As described previously, the relay 62 is set in a cross configuration by the signal controlling relay 3 in port mode to connect the transmitter system 54 to the second transformer 60 and to connect the receiver system 56 to the first transformer 58. Signal control relay 1 has opened switches 64 to disconnect the phantom source from the first port 50 connection so that the phantom excitation current does not flow when the port is in port mode. Switches 66 have also been switched by the control signal of relay 2 to connect the first windings of transformers 58 and 60 (via resistors 68) and provide a return path (i.e. ground) for the current from which the source is connected via a black and orange twisted pair device.

As you can see from the description above, the LAN switch is able to emulate on each of its own ports either a network adapter or a hub port. During network adapter emulation, the LAN switch will be a source of phantom forcing current and will transmit data through a black and orange twisted pair and will receive data and provide ground for phantom forcing current on a red and green twisted pair. During emulation of the hub port, the LAN switch will receive data via a black and orange twisted pair and will transmit data via a red and green twisted pair. In addition, while in port mode, the LAN switch port provides a DC voltage connection between the first and second port connections to provide a return path via a red-green twisted pair for a phantom power source.

Figs. 4, 5 and 6 show three diagrams, each showing a LAN switch port either in adapter mode or in port mode, respectively, for the attached device. Fig. 4 shows a standard adapter connected to the port of a multi-port LAN switch configured in port mode. The standard adapter includes transmitter 70, receiver 72 and transformers 74, 76. Due to the fact that the LAN switch port must be in port mode to communicate with the standard adapter, the relay 62 is appropriately crossed to connect the transmitter system 70 to the receiver system 56 and to connect the transmitter system 54 to the receiver system 72. Also, switches 66 are switched to connect the first windings of port 58 and 60 transformers to provide a return path for phantom excitation current.

Fig. 5 shows the LAN switch port configured in adapter mode for connection to a standard MAU. In adapter mode, switches 64 are closed to provide phantom excitation current for a standard MAU through a pair of black and orange strands. The MAU unit returns the phantom excitation current through a pair of red-green strands to ground via switches 66.

Fig. 6 shows the port of the first LAN switch in adapter mode and the port of the second LAN switch in port mode. The two LAN switches are connected here using a standard cable rather than a crossover cable, as would be required by previously known LAN switches.

The LAN switch is an intelligent device that has data processing capabilities, including determining the destination node for the data frame based on the address information received with the data and forwarding the received data to the port connected to the destination node. As will be described below, the LAN switch automatically determines the type of device attached to each of its ports, and then configures these ports either in port mode or in adapter mode, allowing proper communication between each of the attached devices. In this way, all wiring can have the same polarity, i.e., no crossover cables are needed, and no manual operation is required, such as installing special cables or setting port configuration switches, at a low cost and higher installation reliability and maintenance.

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An additional property of the LAN switch port is therefore its ability to automatically determine the type of device attached to the port, configuring the port in the appropriate operational mode required to ensure communication with the device (for example, the LAN switch connection - the LAN switch requires reverse polarity to transmit and receive data between two ports switch (s), i.e. one is in port mode and the other is in adapter mode). The following method detects the attached LAN switch and correctly configures the port to allow connectivity to the attached LAN switch.

The port also has the ability to determine whether the attached LAN adapter or switch is a half-duplex or full-duplex device, for example, as shown in Figure 1, adapter 42 is a half-duplex adapter (HDX) and adapter 43 is a full-duplex adapter (FDX) . Also the LAN switch 47 is the FDX switch and the LAN switch 46 is the HDX switch. In token-ring network terminology, half duplex (HDX) refers to the usual token forwarding access protocol as defined in the IEEE 802.5 standard. Full duplex (FDX) refers to an immediate broadcast access protocol, currently defined by the IEEE 802.5 standard. The FDX operation is based on a point-to-point connection of two devices and does not use a tag. In FDX mode, any device can transmit and receive at any time, i.e. without waiting for a marker.

Each LAN switch port has a token-ring driver, including the introduction of PHY physical layer and MAC control. In addition, each token-ring controller includes a central unit, called a port central unit. The port CPU controls the determination of the connection type and then turns on the attached device by configuring the LAN switch port in the appropriate operating mode. The LAN switch port is configured by controlling one or more mode signals, in particular, relay control signals 1-3, as described above when configuring the adapter or port mode. This process is described in detail below in connection with Figs. 7 and 8. Thus, two configurations are possible for the port in adapter mode (FDX adapter or HDX adapter) and two configurations for the port in port mode (FDX port or HDX port).

Figures 7 and 8 show a flowchart for automatically determining the type of device attached and configuring the LAN switch port for a multi-port LAN switch. The process starts at step 100, in which the CPU starts the inactivity time measurement timer T. This timer measures the time for inactivity detection mode. The total time of inactivity T is determined using a random number generator, this time is between 3 and 3.2 seconds. By using the random number generator, it is ensured that both connected LAN switch ports will not always be in inactivity detection mode at the same time, but as a consequence one will try to connect to the other. Thus, at step 100, the switch port is set to port mode.

In step 105, it is determined whether the inactivity time T has run out. If the inactivity time T has been exhausted, the process goes to step 145. If the inactivity time T has not been exhausted, the process goes to step 110, where it is determined whether an FDX frame has been received. If so, the LAN switch port is opened, it is configured as the FDX port, as shown in step 115. If the FDX frame was not received at step 110, then the LAN switch port determines whether the phantom excitation current was actuated by the attached device as shown in step 120. If the phantom excitation current was not detected at step 120, the process returns to step 105. Current Phantom excitation can be detected by a sensor such as the optical coupler 69 shown in Fig. 2. If one of the two decision stages 110 or 120 is affirmative, then the attached device attempts to connect to the port.

If phantom excitation current was detected at step 120, then the port determined that the adapter or LAN switch port in adapter mode is attached to this port. The process proceeds to step 125, in which the port transmits the FDX frame from the transmitting system 54 via a red-green twisted pair to the receiving system of the attached device. So in

179 711 step 125, the T response timekeeping timer starts for timing the response wait time. The response time T provides the time period during which the LAN switch port waits for the transmission of the FDX registration frame response. The response time T value is 800 milliseconds.

The process then proceeds to step 130, in which the port listens whether the attached adapter or switch transmits the FDX frame. If an FDX frame is received, the LAN switch port will be opened, i.e. it will be configured as an FDX port, as shown in step 115. If the FDX frame was not received in step 130 and the response time T was not exhausted, as specified in step 135, then the process returns in a loop to step 130, in which the port extends listening, whether the attached adapter transmits the FDX frame. If the timer response time T has run out, the process proceeds to step 140, at which the LAN switch port is opened, it is configured as the HDX port. Thus, at step 140, the port transmits the ring purifying frame. The purge frame is a MAC frame defined by the IEEE 802.5 standard, used to reset a ring segment from frames or markers.

When the process proceeds to step 145 as a result of the inactivity time T having run out of the timer specified in step 105, the wrapping time timer T starts. The wrapping time T value is 30 milliseconds. Thus, at step 145, the relay 62 at the LAN switch port is set to no crossing or in adapter mode, where, as defined in the IEEE 802.5 standard, the port sends a MAC control frame with an address duplication test (DAT).

Then, the port listens for any type of frame that its receiving system is to receive at step 150. If no frame is received, the port continues looping back to step 150 until the wrapping time T in step 155 has expired, and the process returns to stage 100. If any frame was received by the port before the wrapping time T runs out, the process goes to step 160, where the error time measurement timer T starts, preferably the error time value T is from 10 to 15 seconds, with the port being the source of phantom force current (switches 64 closed), providing the phantom excitation current on the black-orange twisted pair. If the error time T has not expired, as determined in step 165, then in step 170 the port determines whether any type of frame has been received. If no frame has been received, the process returns to step 165. If any frame has been received, the port determines whether this frame is an FDX frame, in step 175. If this frame is an FDX frame, the port sets the phantom excitation current off and configures itself in FDX adapter mode. If it was determined in step 175 that this frame is not an FDX frame, then the attached port must be an HDX port. In this case, the LAN switch port sets the phantom excitation current off and configures itself as an HDX adapter as indicated in step 185.

If the error time T runs out, as determined in step 165, before the port receives any frame, the process proceeds to step 190, in which it is determined whether a wiring error condition has been detected. If a wiring error condition occurs, for example, the cable is not attached to the port, then the phantom excitation current will not have a return path and an error will be detected. When the error is detected in step 190, the process returns to step 100. If no error was detected in step 190, the process proceeds to step 185, in which the phantom excitation current is turned off and the port is configured as an HDX adapter.

In summary, the LAN switch as a data block is able to emulate either a network adapter or a hub port on each of its ports. During network adapter emulation, the LAN switch port will be a source of phantom forcing current and will transmit data via black-orange twisted pair and will receive data and provide grounding for phantom forcing current via red-green twisted pair. In addition, while in port mode, the LAN switch port provides an electrical DC connection between the first and second port connections to provide a return path via a red-green twisted pair for a phantom power source.

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