Abstract:
A midspan power sourcing equipment (PSE) for operation with power over Ethernet (PoE). The midspan PSE provides powering over wire pairs that are also used for data communication. To reduce costs by the midspan manufacturer, the midspans can be designed without the use of data transformers. Rather, midspans can include transmit/receive couplers that have blocking capacitors and divider trees for the insertion of power.

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to Power over Ethernet (PoE) and, more particularly, to midspan powering without the use of data transformers in a PoE application. 
         [0003]    2. Introduction 
         [0004]    The IEEE 802.3af and 802.3at PoE specifications provide a framework for delivery of power from power sourcing equipment (PSE) to a powered device (PD) over Ethernet cabling. In this framework, various PDs can be deployed such as voice over IP (VoIP) phones, wireless LAN access points, network cameras, computing devices, etc. 
         [0005]    In the PoE process, a valid device detection is first performed. This detection process identifies whether or not it is connected to a valid device to ensure that power is not applied to non-PoE capable devices. After a valid PD is discovered, the PSE can optionally perform a Layer 1 power classification. 
         [0006]    In one configuration, power can be sourced directly from data terminal equipment such as an Ethernet switch. This type of network device is referred to as an endspan device. In another configuration, power can be supplied by a midspan device.  FIG. 1  illustrates such a midspan configuration, which includes a medium dependent interface (MDI) link between Ethernet switch  110  and PD  130 . As illustrated, midspan PSE  120  is placed in the middle of the MDI link for the insertion of power to be supplied to PD  130 . An advantage of such a midspan configuration is the usage of legacy Ethernet switches that do not have PoE capabilities. 
         [0007]    In one midspan configuration that supports 100BASE-TX, data is transmitted using pins  1  (TX+),  2  (TX−),  3  (RX+), and  6  (RX−) of the Ethernet cable. The remaining pins  4 ,  5 ,  7 , and  8 , which are representative of the two unused pairs of the Ethernet cable, can be used by midspan PSE  120  for the transmission of power to PD  130 . 
         [0008]    In an alternative midspan configuration, power is not transmitted on the two unused pairs, but transmitted on the two signal pairs used for data transmission. In this configuration, data transformers are included within the midspan to facilitate the insertion of power onto the two signal pairs. The inclusion of these data transformers into the midspan can represent a significant cost to midspan manufacturers. What is needed therefore is a mechanism for facilitating midspan powering through the two signal pairs, while maintaining efficiency in areas such as cost. 
       SUMMARY 
       [0009]    Midspan powering without the use of data transformers in a PoE application, substantially as shown in and/or described in connection with at least one of the figures, as set forth more completely in the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    In order to describe the manner in which the above-recited and other advantages and features of the invention can be obtained, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
           [0011]      FIG. 1  illustrates an example of the inclusion of a midspan PSE in an MDI link. 
           [0012]      FIG. 2  illustrates an embodiment of powering a PD by midspan equipment using unused wire pairs. 
           [0013]      FIG. 3  illustrates an embodiment of powering a PD by midspan equipment using the data transmission signal wire pairs. 
           [0014]      FIG. 4  illustrates an embodiment of a midspan equipment in accordance with the present invention. 
           [0015]      FIG. 5  illustrates an embodiment of a transmit/receiver coupler according to the present invention. 
           [0016]      FIG. 6  illustrates an embodiment of a midspan equipment that applies to data transmission using four wire pairs. 
           [0017]      FIG. 7  illustrates an example of the support of non-PDs by midspan equipment. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Various embodiments of the invention are discussed in detail below. While specific implementations are discussed, it should be understood that this is done for illustration purposes only. A person skilled in the relevant art will recognize that other components and configurations may be used without parting from the spirit and scope of the invention. 
         [0019]      FIG. 2  illustrates an example of a midspan PoE configuration that uses the two unused wire pairs for the transmission of power to the PD (referred to as Alternative B). As illustrated, the two unused wire pairs are terminated at midspan equipment  220 . The remainder of the link of the two unused wire pairs is then used to transmit power from PSE  222  to PD  230 . As power is inserted onto the link by midspan equipment  220 , Ethernet switch  210  need not have PoE capabilities. Ethernet switch  210  can therefore represent legacy Ethernet equipment. In general, a PD is capable of receiving power from either wire pair in 802.3af and two-pair powering in 802.3at. 
         [0020]    In a four-pair Ethernet cable, two signal wire pairs can be used for data transmission. In one implementation such as 100BASE-TX, pins  1  (TX+) and  2  (TX−) are used for the transmission (TX) portion of the link, while pins  3  (RX+) and  6  (RX−) are used for the receiving (RX) portion of the link. Pins  4 ,  5 ,  7 , and  8  represent the two unused wire pairs, which are not used in the portion of the link between Ethernet switch  210  and midspan equipment  220 . 
         [0021]    At midspan equipment  220 , power is inserted using PSE  222 . Specifically, PSE  222  provides power to PD  230  using the two unused wire pairs (pins  4 ,  5 ,  7 , and  8 ), which are terminated at midspan equipment  220 . The power carried on the two unused wire pairs is then extracted at PD  230  to power load  232 . 
         [0022]    As further illustrated in  FIG. 2 , the two signal wire pairs used for data transmission (pins  1 ,  2 ,  3 , and  6 ) are passed through midspan equipment  220  onto PD  230 . This pass-through connection can be implemented as an undisrupted channel connection between Ethernet switch  210  and PD  230 . In other words, the characteristics of the wired channel connection between Ethernet switch  210  and PD  230  can be left largely undisturbed as the data transmissions pass through midspan equipment  220 . 
         [0023]      FIG. 3  illustrates an alternative midspan powering configuration that uses the two data transmission signal wire pairs for powering, instead of the two unused wire pairs. Thus, in the context of the example of  FIG. 2 , the two signal wire pairs represented by pins  1 ,  2 ,  3 , and  6  can be used for both data transmission and powering. To facilitate this alternative midspan powering scheme, midspan equipment  320  adds data transformers  322 ,  324 . As illustrated, PSE  326  inserts power onto the data transmission signal wire pairs through transformer taps on the end device side of the transformer. 
         [0024]    Consider, for example, the signal wire pair represented by pins  1  and  2 . In this signal wire pair, data is transmitted from Ethernet switch  310  and received at midspan equipment  320 . After passing through data transformer  322 , the data is then transmitted to PD  330 . Similarly, for the signal wire pair represented by pins  3  and  6 , data that is transmitted by PD  330  is received at midspan equipment  320 . After passing through data transformer  324 , the data is then transmitted on to Ethernet switch  310 . 
         [0025]    While the provision of power onto the two signal wire pairs does result in efficiency in the number of wire pairs used, it also results in the increased costs of the midspan equipment. Specifically, the midspan equipment manufacturer would now add the cost of two data transformers  322 ,  324  that enable data and power to be transmitted onto the same wire pairs. This is in contrast to the relatively simple design of  FIG. 2 , which provides an undisrupted channel connection between the switch and the end device. 
         [0026]    In some applications, data transformers  322 ,  324  would be required to meet certain inductance requirements. Consider, for example, the inductance requirement that is specified by the 100BASE-TX specification for the transmit side. As the 100BASE-TX specification sets forth, the minimum inductance measured at the transmit pins shall be greater than or equal to 350 μH with any DC bias current between 0-8 mA injected. As would be appreciated, other inductance ranges (higher or lower) can also be specified for a given application. For example, a higher inductance range can be specified to accommodate higher DC bias currents that would be expected in an application such as 802.3at. 
         [0027]    In general, the inductance requirement of the transmitter transformer in the midspan equipment is designed for operation with legacy PHY receivers. These legacy PHY receivers expect to see the effective inductance on the channel so that the signal quality and BER of the link is not impacted. This minimum inductance level can be specified to present sufficient inductance that would overcome killer patterns that cause baseline wander so that the receiver can recover. In other words, the inductor at the source slows down the edges. 
         [0028]    In the midspan example of  FIG. 3 , the satisfaction of the inductance requirement by transmitting transformers  322 ,  324  in midspan equipment  320  would enable operation with legacy PHYs in the receivers of PD  330  and switch  310 , respectively. Satisfaction of this additional inductance requirement by transmitting transformers  322 ,  324  further adds to the costs of the midspan equipment manufacturer. 
         [0029]    In accordance with the present invention, the costs of the midspan manufacturers can be reduced through the elimination of the expensive data transformers. As will be described in greater detail below, the elimination of the data transformers does not compromise on the performance of the midspan in enabling power to be injected onto the signal wire pairs. 
         [0030]      FIG. 4  illustrates a midspan equipment in accordance with the present invention that has replaced the data transformers with TX/RX couplers  422 ,  444 . An embodiment of TX/RX couplers  422 ,  44  is illustrated in  FIG. 5 . As illustrated, TX/RX coupler  500  includes blocking capacitors C 1 , C 2  that enables DC isolation between the two sides of TX/RX coupler  500 . Specifically, blocking capacitors C 1 , C 2  are coupled to receive ports RX+_in and RX−_in on a receiving side (i.e., from the switch or from the end device). On the transmitting side of TX/RX coupler  500 , power is injected by the PSE onto the TX+_out and TX−_out ports through two divider trees created by elements E 1 , E 2 . In one embodiment, elements E 1 , E 2  are inductor elements. In another embodiment, elements E 1 , E 2  are low loss resistive elements. As would be appreciated, other variations of elements E 1 , E 2  can be used to deal with various transients. 
         [0031]    In one embodiment, TX/RX coupler  500  can be designed to present a low effective impedance at a frequency range of operation. This particular TX/RX coupler design would enable the support of legacy Ethernet switches and end devices. In general, the midspan equipment design on the transmit side is critical for ensuring proper compatibility with legacy equipment. 
         [0032]      FIG. 6  illustrates another midspan embodiment that is applied to data transmission applications such as 1000BASE-T. In this embodiment, four wire pairs are used for data transmission. Accordingly, four data transformers can be replaced by four TX/RX couplers  621 - 624 . While the power connections are not shown, PSE  625  can be designed to inject power into one or both (e.g., 802.3at) of the two wire pair groupings. Specifically, power can be injected through TX/RX couplers  621 ,  622  and/or through TX/RX couplers  623 ,  624 . 
         [0033]    As would be appreciated, the principles of the present invention would apply regardless of whether power was applied to the signal wire pairs. As such, the midspan equipment design can also support non-PD devices. These non-PD devices would not receive power since they would not be discovered as valid PD devices.  FIG. 7  illustrates an example of such a scenario where PDs  732 ,  734  and non-PD  736  are supported by midspan PSE  720 . Here, each of PDs  732 ,  734  and non-PD  736  can be a link partner that is attached to midspan PSE  720  and switch  710 . If a TX/RX coupler in midspan PSE  520  is designed with a low effective impedance at the frequency of operation, then midspan PSE  520  can support a legacy PHY in non-PD  536 , regardless of whether Ethernet switch  510  could present an appropriate inductance level. 
         [0034]    Finally, the principles of the present invention can also be applied to medium dependent interface crossover (MDIX) ports. 
         [0035]    These and other aspects of the present invention will become apparent to those skilled in the art by a review of the preceding detailed description. Although a number of salient features of the present invention have been described above, the invention is capable of other embodiments and of being practiced and carried out in various ways that would be apparent to one of ordinary skill in the art after reading the disclosed invention, therefore the above description should not be considered to be exclusive of these other embodiments. Also, it is to be understood that the phraseology and terminology employed herein are for the purposes of description and should not be regarded as limiting.