Interface for upgrading serial backplane application from ethernet to gigabit ethernet

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] Not Applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0002] Not Applicable.

REFERENCE CITED

FIELD OF THE INVENTION

[0003] This invention relates generally to serial backplane application and more particularly to apparatus and methods for seamlessly upgrading Ethernet to Gigabit Ethernet while allowing Gigabit Ethernet and Ethernet to coexist in the same system for a serial backplane with 2-pair copper transmission infrastructure.

BACKGROUND OF THE INVENTION

[0004] Typical telecom equipment such as SONET, SDH, ATM or Gigabit Ethernet switches use modular designs. Modules such as communication line cards are inserted in the sockets of an electronic circuit board to allow them to communicate with each other. The interface design of modules and backplanes constitute the “backbone” for the equipment. The backbone can be a traditional parallel mode bus with single-ended signaling, or a serialized interface with low voltage differential signaling. The topology of the backplane design can vary from point-to-point to multi-drop to multi-point connection.

[0005] As the need for bandwidth expands in LANs, WANs and SANs, serial backplanes become the ideal alternative for solving information bottlenecks. The current use of parallel buses in networking systems does not provide the performance required. Serial backplanes have clear advantages over parallel buses in that they utilize fewer wires and connectors, consume less power, can carry signals for longer distances, and ultimately offer higher performance and reliability. This allows the designer to connect boards that are separated by larger distances, together in the system. In addition, wiring harnesses are simplified because the designer does not need to run a large number of wires (as in a parallel bus), when a single pair of wires (as in a serial backplane) can be employed. This results in lower costs and higher performance. High performance is also achieved because serial approaches generate less crosstalk between parallel wires.

[0006] Many data communication vendors use 10BASE-T (10 Mbps) or 100BASE-T (100 Mbps) Ethernet as a communication channel between the different cards in a piece of telecom equipment. 10BASE-T or 100BASE-T form the communication channel among cards in the system. They do this by providing a physical link consisting of two pairs of signals routed on the backplane. One par of signals is used for the receive channel and one pair is used for the transmit channel. The 100BASE-T communications channel can be used for general card control, software maintenance, establishing in-band NMS (Network Management System) links and for alarm reporting. It is not used for processing or switching data. As the system grows and more cards are added, the bandwidth of the 10BASE-T or 100BASE-T channels gets consumed, thus slowing down the performance of the system.

[0007] Gigabit Ethernet offers a solution to the problem. However the Gigabit Ethernet standard for transmission over copper, 1000BASE-T, requires four pairs of signals: two pairs of signals for transmit and two pairs for receive. It is very difficult and expensive to redesign the backplanes to accommodate this standard because of the installed customer base that would not be able to benefit from this enhancement. Replacing a backplane in the field would mean that the entire system would have to be replaced. Furthermore, it is desirable to stay backwards compatible with the existing installed legacy cards. This problem is not unique to a single system vendor because the standard for using four pairs of wires for 1000BASE-T was not formally completed when the backplanes for many system vendors were first designed. To differentiate Gigabit Ethernet from other versions of Ethernet, those versions of Ethernet that operate at or below 100 Mbps are classified as high-speed Ethernet.

[0008] It would, therefore, be desirable to provide an interface device and method to seamlessly upgrade 2-pair copper transmission lines based serial backplane from Ethernet to Gigabit Ethernet while allowing both Ethernet and gigabit Ethernet based cards to coexist in the same system.

SUMMARY OF THE INVENTION

[0009] The present invention provides an interface device and method to seamlessly upgrade 2-pair copper transmission lines based serial backplane from Ethernet to Gigabit Ethernet while allowing both Ethernet and gigabit Ethernet based cards to coexist in the same system.

[0010] An interface device has a plurality of ports with a plurality of speed configurations for a serial backplane with 2-pair copper transmission lines. The interface device has a plurality of high speed Ethernet ports and a plurality of Gigabit Ethernet ports. A switch mechanism for selecting between the high speed Ethernet ports and the Gigabit Ethernet ports connects the selected port to the serial backplane via the 2-pair copper transmission lines.

[0011] A serial backplane has 2-pair copper transmission lines having two interface devices. The interface devices have a plurality of communication cards with different Ethernet speed configurations connected via the ports. A communication method for two of the communication cards on each of two interface devices to communicate with each other across the serial backplane includes the following steps: a first card initiates contact with a second card via a negotiating method and then initiates the switching mechanisms to connect either a high speed Ethernet port or a Gigabit Ethernet port of the two cards to the serial backplane via the 2-pair copper transmission lines.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0013]FIG. 1 is a schematic diagram of a typical conventional high speed Ethernet based serial backplane for a communication system.

[0014]FIG. 2 is a schematic representation of an embodiment for a Gigabit Ethernet capable 2 pair copper transmission line based serial backplane in accordance with an embodiment of the present invention.

[0015]FIG. 3 is a flowchart illustrating the communication process for two cards connected to serial backplane via the interface devices in the illustrative embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0016] Referring to the drawings, FIG. 1 schematically illustrates a typical conventional high speed Ethernet based serial backplane for a communication system, such as an SN 16000 optical switch from Sycamore Networks, Chelmsford, MASS. Two communication cards <b>10</b>-<b>1</b> and <b>10</b>-<b>2</b> are plugged into ports of 10/100 BASE-T interface devices <b>20</b>-<b>1</b> and <b>20</b>-<b>2</b> respectively and then connected to a serial backplane via two backplane connectors <b>60</b> and <b>70</b>. A communication card can be one of many field-replaceable microprocessor-based slave cards responsible for handling network traffic or it can be a field-replaceable microprocessor-based master card that is responsible for managing the slave cards. The backplane is the non-replaceable fixed medium by which the slave cards communicate with the master card. The backplane in FIG. 1 is delineated by the region between the backplane connectors <b>60</b> and <b>70</b>. There are two pair copper transmission lines <b>50</b>-<b>1</b> and <b>50</b>-<b>2</b> in the serial backplane. Correspondingly, interface device <b>20</b>-<b>1</b> for card <b>10</b>-<b>1</b> communicates with the serial backplane via 2 pairs <b>30</b>-<b>1</b> for transmit and <b>30</b>-<b>2</b> for receive, and interface device <b>20</b>-<b>2</b> for card <b>10</b>-<b>2</b> communicates with the serial backplane via two pairs <b>40</b>-<b>1</b> for receive and <b>40</b>-<b>2</b> for transmit. The span of backplane, such as the distance between backplane connector <b>60</b> and <b>70</b>, is relatively short, normally in the range 2″ to 40″. Cards <b>10</b>-<b>1</b> and <b>10</b>-<b>2</b> communicate with each other across the backplane via the two pair copper transmission lines for purposes such as general card control, software maintenance, establishing in-band NMS (Network Management System) links and alarm reporting. The two pair copper transmission lines are not used for processing or switching network traffic. The interface device can be a custom ASIC (application specific IC), or an off-the-shelf 10/100 Mbs Ethernet MAC (media access device) coupled with a 10/100BASE-T Ethernet Layer 1 transceiver.

[0017] As the system grows and more cards are added, the bandwidth of the 10BASE-T or 100BASE-T channels gets consumed, thus slowing down the performance of the telecom device. Gigabit Ethernet offers a solution to the problem, however, the Gigabit Ethernet standard for transmission over copper, 1000BASE-T, requires four pairs of signals: two pairs of signals for transmit and two pairs for receive. Fortunately a Serdes (SERializer-DESerializer) interface provides a point-to-point path from parallel to serial that uses 2 pairs lines, which is ideal to connect with a 2 pair copper transmission lines based serial backplane. The higher the data rate, the shorter the transmission distance must be. This means that closer attention must be paid to data integrity. One reason for Gigabit Ethernet over Copper standard to use 4 pair transmission lines is to support relatively long distance (100 meters) so each pair equivalently carries data at a rate of 250 Mbps. For general serial backplane applications, due to the relatively short distance (around 40″), 2 pairs using a Serdes interface is sufficient to maintain data integrity.

[0018] As illustrated in FIG. 2, in accordance with one aspect of the invention, two interface devices <b>110</b>-<b>1</b> and <b>110</b>-<b>2</b> are located at two sides of a serial backplane, having 2 pair copper transmission lines <b>180</b>-<b>1</b> and <b>180</b>-<b>2</b>. The interface device can be one or more custom ASICs (application specific ICs), or an off-the-shelf 10/100/1000 Mbs Ethernet MAC (media access device) coupled with a 10/100BASE-T Ethernet Layer 1 transceiver (PHY) that also provides an IEEE 802.3z interface to which a SERDES can be connected. To complete the interface device, a bank of analog switches or relays are used to switch between the serial interface on the SERDES and the 10/100BASE-T interface on the PHY. A plurality of cards <b>100</b>-<b>1</b>, . . . <b>100</b>-N are plugged into the interface device <b>110</b>-<b>1</b> via ports on the interface device <b>110</b>-<b>1</b>. A communication card can be one of many intelligent slave cards responsible for handling network traffic or it can be an intelligent master card that is responsible for managing the slave cards. A card that does not have a microprocessor on it is not an intelligent card and therefore is not a communication card. The interface device <b>110</b>-<b>1</b> is further connected to the backplane using 2 pair copper lines <b>170</b>-<b>1</b> for transmit and <b>170</b>-<b>2</b> for receive via backplane connector <b>200</b>-<b>1</b>. A detailed schematic of the same interface card <b>110</b>-<b>2</b> as <b>110</b>-<b>1</b> is described as in FIG. 2, which further includes a traditional 10/100 BASE-T interface <b>140</b> having a plurality of legacy cards <b>120</b>-<b>1</b>, . . . <b>120</b>-M connected, and a Gigabit Ethernet interface <b>150</b> having a plurality of new Gigabit Ethernet capable cards <b>130</b>-<b>1</b>, . . . <b>130</b>-K connected. The Gigabit Enabler logic <b>190</b> controls the connection of either legacy 10/100 BASE-T interface <b>140</b> or Gigabit Ethernet interface <b>150</b> to serial backplane using 2 pair copper lines <b>220</b>-<b>1</b> for receive and <b>220</b>-<b>2</b> for transmit via backplane connector <b>200</b>-<b>2</b>. The Gigabit Enabler logic <b>190</b> functions by controlling switch mechanism <b>210</b>-<b>1</b>, <b>210</b>-<b>2</b>, <b>210</b>-<b>3</b> and <b>210</b>-<b>4</b>. The Gigabit Ethernet interface <b>150</b> is first connected to a Serdes interface <b>160</b> before switched to the 2 pair transmission lines <b>220</b>-<b>1</b> and <b>220</b>-<b>2</b>. The 10/100 BASE-T interface <b>140</b>, Gigabit Ethernet interface <b>150</b> and Serdes interface <b>160</b> can be implemented using Off the shelf products such as Intel's 82546 integrated dual MAC/PHY/SERDES device, or Broadcom's BCM5700 coupled with Broadcom's BCM5421S.

[0019] To further demonstrate how the interface device works, FIG. 3 illustrates the communication process between two cards <b>100</b>-<b>1</b> (which is a new Gigabit Ethernet enabled card) and <b>120</b>-<b>1</b> (which is a legacy 100 BASE-T card). First, the default mode for card <b>100</b>-<b>1</b> and <b>120</b>-<b>1</b> are reset to the lowest Ethernet speed such as 10BASE-T or 100BASE-T. Then a first card, such as <b>100</b>-<b>1</b>, initiates the contact with card <b>200</b>-<b>1</b> by first identifying card <b>200</b>-<b>1</b>'s Gigabit capability. One way of doing this is by reading card <b>200</b>-<b>1</b>'s identification stored in PROM, among many possible implementations. Card <b>100</b>-<b>1</b> starts negotiating for speed process by trying different speeds such as 10 Mbps, 100 Mbps, 1000 Mbps until the highest common speed between cards <b>100</b>-<b>1</b> and <b>120</b>-<b>1</b> is found. Card <b>100</b>-<b>1</b> and <b>100</b>-<b>2</b> default to 100BASE-T upon power-up. If card <b>100</b>-<b>1</b> is the master (management entity) and it is capable of Gig-E, it queries the slave or examines its ID PROM to determine this. If the Gig-E capable slave responds favorably to the query, the master switches to Gig-E and tries to establish communication. If the link drops as a result of either the master or slave being reset the interface resets to its default state (100BASE-T). Depending on the negotiated speed, the Gigabit enabler logic will switch either 10/100BASE-T or Gigabit Ethernet interface to the backplane via 2 pair copper transmission lines. For the illustrated example, the negotiated speed is 100BASE-T, the Gigabit enabler logic on the left side will connect Gigabit Ethernet interface within <b>110</b>-<b>1</b> to the backplane and the Gigabit enabler logic on the right side will connect 10/100BASE-T <b>140</b> interface within <b>110</b>-<b>2</b> to the backplane.

[0020] The illustrated embodiment provides a seamless upgrade path to a Gigabit Ethernet for a legacy 2 pair copper transmission lines based serial backplane when next generation Gigabit Ethernet based cards come on line. The illustrated interface device with multiple Ethernet speed configurations allows next generation cards to be backward compatible with the legacy cards while both next generation and legacy cards coexist in the same system.

[0021] Numerous modifications and alternative embodiments of the present invention will be apparent to those skilled in the art in view of the foregoing description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the best mode for carrying out the present invention. Details of the structure may vary substantially without departing from the spirit of the invention, and exclusive use of all modifications that come within the scope of the appended claims is reserved. It is intended that the present invention be limited only to the extent required by the appended claims and the applicable rules of law.