Abstract:
An apparatus is provided for deployment in an outdoor environment for managing and distributing Ethernet-type data communication signals. The apparatus includes electrical isolation elements for various electromagnetic effects and a high speed pulse reshaper and repeater. The isolation elements include low capacitance electric pulse suppression devices so that maximum signal distance can be achieved without loss of usable pulse shape and isolation transformers on differential signal pair that retain magnetization at elevated temperatures so that signals are not blocked. As a further feature, a management protocol is included whereby the type of signals can be autonomously distinguished, managed, secured and redirected, thus allowing the apparatus to be operated with compatible devices in a daisy-chained and start switch fabric.

Description:
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     BACKGROUND OF THE INVENTION 
     This invention relates to digital data communications over distance-limited wire media. In particular, this invention relates to an apparatus for managing and distributing Ethernet signals in an outdoor environment. 
     SUMMARY OF THE INVENTION 
     According to the invention, an apparatus is provided for deployment in an outdoor environment for managing and distributing Ethernet-type data communication signals. The apparatus includes electrical isolation means for various electromagnetic effects and a high speed pulse reshaper and repeater. The isolation means includes low capacitance electric pulse suppression means so that maximum signal distance can be achieved without loss of usable pulse shape and isolation transformers on differential signal pairs that retain magnetization at elevated temperatures so that signals are not blocked. As a further feature, a management protocol is included whereby the type of signals can be autonomously distinguished, managed, secured and redirected, thus allowing the apparatus to be operated with compatible devices in a daisy-chained and star switch fabric. The invention will be better understood upon reference to the following detailed description in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of an apparatus according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a block diagram of a packet switch  10  according to the invention. The packet switch  10  is built around a set of pulse shaping and repeating circuits (PHYs)  12 A- 12 D, etc., for shaping and repeating pulses. This circuit set is typically built of an integrated circuit combining independently functional circuits of low-power physical layer transceiver and protocol control devices. Two types are contemplated: a fast Ethernet set  12 C,  12 D for 10/100 MBPS applications such as drops, and a Gigabit Ethernet device  12 A,  12 B, with a copper wire interface through multiple differential pairs (TX and RX) s, t, u, v and w, x, y, z and/or a serial interface port (SX)  102  coupled via a light transceiver (SX XCVR)  104  to a fiber link  106 . These latter ports support the higher speeds associated with trunk transmissions. 
     A specific embodiment of a PHY for use in a 10/100 MBPS application is a Model AC104QF PHY quad (four element) device manufactured by Broadcom, Inc. of Irvine, Calif. This circuit is compliant with specific standards, namely the IEEE 802.3u specification and the RMII (Reduced Media Independent Interface) specification. Each 10/100 MBPS PHY typically uses two unshielded twisted pairs for each transmission port, one pair dedicated to transmit signals (pairs a and e) and a second pair to receive signals (pairs b and f). The higher speed ports employ four pairs (s,t,u and v; and w,x,y and z) for data transmission and for data reception. For the three speeds of 10/100M and 1 Gigabit per second, the higher speed PHYs  12 A,  12 B employ more dedicated channels and transmit and receive according to IEEE 802.3ab. Examples of suitable components are Broadcom Model BCM5402 and Marvel 88E1020 (Sunnyvale, Calif.). The PHY circuit set  12  normally interfaces to a switch or (RS) (Reconciliation Sublayer) of a MAC (media access controller) on one side (not shown) and the hard wired or copper interface on the other side (not shown). 
     To transmit data, the PHY circuit set  12  converts the digital data stream it receives on one side from switch logic  14  to the appropriate signaling format needed to launch the data-containing signal on the other side. To receive data, the PHY circuit set  12  converts the signals it receives into a digital data stream which is passed up to switch logic  14 . The RX ports and the TX ports of the PHYs  12 C,  12 D are protected through isolation mechanisms from the outside environment. The 10/100 RXD and TXD ports provide interface to internal devices through either an RMII bus or an MII bus (or a RGMII or GMII bus for 1000BaseT PHY devices  12 A,  12 B). 
     The packet switch  10  employs an N×N switch fabric  14  for the PHY  12 A,  12 B,  12 C,  12 D a switch logic device  14  for coupling, timing and logic control. The functions provided by switch logic devices may include (but are not limited to) the following: 1) storing, switching and forwarding of data for multiple ports at line speed for layer  2  and layer  3  packets, 2) triple speed connectivity (10/100/1000MBPS), 3) MAC address tables with autolearning and aging, 4) four QoS priority levels, 5) stacking support for linking multiple switch logic devices together to increase the number of switched ports and 6) optional management processor support for setup, configuration, maintenance and management. Examples of suitable components are Broadcom Model AL125 with A1320, Broadcom BCM5680, Switchcore CXE-1000 (San Jose, Calif.), and Marvel GT-48370. 
     The packet switch  10  must deal with arbitrary types of packet signals, so a mechanism is needed to recognize and respond to assure compatibility between signal sources and signal destinations and to manage the routing of the switch fabric  14 . To this end, a processor  18  is provided which is coupled to the switch logic  14  via a CPU bus so it can read the status and set up speed and mode of each PHY element (to the extent the Phy elements do not perform these tasks autonomously) and set up the paths through the switch logic  14 . Optional processor  18  provides setup, configuration, maintenance and management of switch logic  14  through a PCI bus, DMA bus or other conventional bus. The processor  18  boots and runs embedded management software that resides in off-chip or on-chip memory. A wide variety of management processors (and software suites) is available commercially to service specific switch logic device capabilities. Several types of popular processors include ARM, MIPS and PowerPC. Examples of suitable components are ARM7-based NetSilicon Net +50 (Waltham, Mass.) and Motorola PowerPC MPC850 or 8245 (Phoenix, Ariz.). Some product offerings include processors that are integrated with switch logic devices and attendant memory and “glue” logic, for example, a MIPS processor is integrated into Infineon PLB2800 (Munich, Germany). 
     A variety of software suites is available commercially to service specific switch logic device capabilities and configuration/management protocols. Operating systems include: proprietary systems sold as VxWorks (Windriver, Alameda, Calif.), RADLAN (Israel) and NET OS of Net Silicon. So-called public domain or open operating systems include Linux. The management software suites include functions that permit the processor to communicate with specific registers called MIBs (Management Information Bases) in the switch logic device  14 . Other functions include: 1) TCP/IP stacks for opening packets for Layer  3 + packet management, filtering and security protocols; 2) SNMP (Simple Network Management Protocol) for providing communications security, reading status and statistics registers and controlling switch port operating parameters; and DHCP (Dynamic Host Control Protocol). 
     A standard has been adopted for electrical and magnetic isolation of electronic circuitry intended to be operated in a severe outdoor environment. The standard is referenced as IEEE 802.3u, IEEE 802.3ab and ANSI X3.236. The specifications provide for operation in a temperature range between 0 and 70 C. For extended operation between −40C and +85C., which is more typical of actual experience in some environments, as well as the extremes of current and of voltage transients, construction of devices merely compliant with this standard is inadequate for reliable operation. 
     Accordingly, the packet switch  10  of the invention incorporates a number of features that go beyond standards compliance. Connectors  22 ,  23 ,  24 ,  25  used on the switch  10  are female DB-9 connectors that mate with DB-9 connectors  20 ,  21 ,  26 ,  27 . This type of connector is an industry standard but it is not known to have been commercially used for Ethernet signals. However, its pins provide 360 degree surface area coverage, and mating connectors provide 360 surface coverage for the pin area and are connected through solid mechanical connections and held together with two screws. The signal connectors would normally be expected to be of type RJ-45. However, such connectors are not as robust or as reliable for the intended use as the chosen connectors. 
     In order to provide the needed electrical isolation, isolation elements  28 ,  29 ,  30  and  31  with an extended temperature rating are used for voltage isolation and EMI suppression. The isolation elements  28 - 31  typically provide one isolation transformer per twisted pair or 2 to 4 isolation transformers per port in addition to common mode and EMI suppression chokes/filters and line impedance resistors (not illustrated.) Isolation elements  28 - 31  may be incorporated into a single, dual or quad port isolation module. Shunted across each of the wiring connections  34  and  36  to ground between the connectors  22 ,  23 ,  24  and  25  and the isolation elements  28 - 31  are for example SiBar (a brand of Raychem Corporation of Menlo Park, Calif.) (Model TVB170) or SIDACtor (a brand of Teccor of Irving, Tex.) (Model P2604UA) bi-directional overvoltage suppression devices  38 ,  40 . They suppress voltages above a certain threshold, typically around +/−170 V. This voltage protection is intended to protect the packet switch  10  from damage or destruction by indirect lightning strikes or other causes such as power line faults. Low capacitance suppression devices permit operation of Ethernet signals over cable distances of 150 m. 
     Use of DB-9 connectors permits the use of shielded pair network cable of shielded CAT5/6 type that reduces EMI radiated from the network cables to levels acceptable for deployment in certain sensitive jurisdictions and residential areas. The shield ring of the DB-9 connector can be connected to the chassis ground to permit extension of this ground to the n shield of the network data cable. 
     A high efficiency isolated power supply system  42  is used to convert power received from upstream (24-240 VAC/VDC) to provide low voltage (15-22 VDC) for powering remote line extenders and remote packet switches and for driving a high efficiency switching regulator  43  that provides the voltage needed to power the PHYs, switch logic and processor, namely 2.5 VDC and 3.3 VDC, and to the other active devices. An auto resettable positive temperature coefficient (PTC) fuse  44  is used to stop current flow when it becomes too high. This provides short circuit protection. When excessive current flows through the fuse, the characteristics of the material change from low impedance to high impedance causing the current flow to cease. The fuse  44  stays in this state until the power is turned off and the fuse has cooled down enough that the material changes back to a low impedance. This permits remote reset of the fuse  44  by momentarily turning off network power. The ambient temperature has an effect on the threshold at which the fuse  44  takes on the high impedance state. The higher the temperature, the lower the amount of current required to cause the fuse to go into a high impedance state. 
     EMI filters  45 - 48  are placed in the ground and positive lines of the power source lines from both connectors. The EMI filters  45 - 46  together with associated shunt capacitors suppress both voltage and current anomalies. In addition, there is both a differential transient voltage filter capacitor  50  built around a double Zener diode or TVS  52  (transient voltage suppressor) placed between the positive voltage and ground return line and a common mode transient voltage protector built around a double Zener diode or bi-directional TVS  54  placed between the ground return line (neutral) and the chassis ground. Similar isolation  50  is provided between the power supply  42  and the regulator  43  where line extender (LE) power or network power is derived. In this manner, the packet switch  10  is effectively isolated from both unwanted common mode and differential transients. Hot and neutral leads are isolated, while the ground lead is tied to the chassis. The regulator  43  is tied to earth ground so the modules can be daisy chained with a common power source. 
     Additional EMI filters  57 ,  59  are placed in the 20 VDC ground and positive lines that transfer power through the DB-9 connectors to other switches, line and drop extenders. SW 1 , SW 2 , SW 3  and SW 4  are representative of switches for enabling power to their respective ports only when the packet switch  10  is connected to that port. PTCs  61 ,  63  in series with the positive 20 VDC lines protect the power supply  42  against short circuits to the data cables. 
     Network power may be provided from a variety of network power sources and voltages. The connector  60  provides for connection from 12-2 shielded outdoor Romex-type power cable. Shielding is required by the electrical code in certain jurisdictions for specific voltage ranges. The connector  60  can be a push tab, barrier lug strip or standard NEMA equipment receptacle for equipment closet AC power. The push tab strip permits connection of up to 4 or more cables for distribution of network power to branches/segments of the network. Also illustrated is a coax connector  61  for optional alternative connection to cable TV power systems carried by the signal-bearing coax. An RF filter is illustrated that blocks RF while passing 50/60 Hz 60-90 VAC quasi square wave cable system power to power supply  42 . The RF filter  64  has a series RF choke  65 , and a shunt capacitor  66  and a termination resistor  67  between hot and neutral, and the neutral is tied to chassis ground. 
     Two important but competing practical considerations are addressed by the device  10 : power consumption and ease of identifying status. Components are employed that are inherently high efficiency and low in power consumption so that heat generation is minimized and power is not wasted. To provide status indication, LED status indicators  101  are provided to monitor and report the status of each port of the switch logic  14 . LEDs are inherently high in power consumption. Therefore, a power switch  103  is provided which is manually engaged by the user/service worker, and an LED power timer  105  is provided that automatically times out the status indicators  101  when not in use for a period of time. 
     Other features that save power is the disable control  107  which disables the PHY  12 A SX ports s, t, u, v whenever the SX transceiver has been engaged. This is a hard-wired feature, since the fiber port is an alternative to the copper port. 
     The invention has been explained with reference to specific embodiments. For example, the 100BaseT RMII PHY has been illustrated because it particularly requires the use of the present invention for implementation. Other embodiments will be evident to those of ordinary skill in the art. It is therefore not intended that this invention be limited, except as indicated by the appended claims.