Patent Application
20110130032
Embodiments of the present invention generally relate to wired network communications and, more particularly, to an active cable extender assembly for extending the effective length of a direct attach cable assembly.
Network communications demand ever-increasing amounts of transmitted information, and network technologies for higher data rates have been and continued to be developed. For example, the Gigabit Ethernet standard has been available for some time and is quite common. The Gigabit Ethernet standard specifies communicating using Ethernet technology at data rates of at least one Gigabit per second (Gbps), and both optical and copper-based solutions have been implemented to comply with the standard. At 1 Gbps or greater, optical cables tend to be used for longer distances, whereas copper cables tend to be used more for shorter distances due in large part to the promulgation of the 1000 Base-T standard, which permits 1 Gbps communication over standard Category 5 (“Cat-5”) unshielded twisted-pair network cable.
Presently, data rates of at least 10 Gbps have been standardized, while technologies and standards are being developed for 40 Gbps and 100 Gbps data rates using Ethernet technology. As these data rates increase, copper-based solutions become more difficult to realize. For example, the permissible copper cable length becomes shorter or the transmission power requirements increase as the data rate increases due to distortion effects introduced by the high speed signal propagating through the cable. However, because of the cost of current optical solutions, interest in copper-based solutions persists, even at these higher data rates.
Embodiments of the present invention generally relate to an active cable extender assembly or adapter for wired network communications at data rates of at least 10 Gigabits per second (Gbps).
One embodiment of the present invention provides an apparatus. The apparatus generally includes an electrical link, a male connector coupled to a first end of the link, and a female connector coupled to a second end of the link. The female connector typically includes a connector receptacle compatible with data rates of at least 10 Gbps and an active circuit for reducing signal distortion, coupled between the second end of the link and the connector receptacle.
Another embodiment of the present invention provides a method. The method generally includes transmitting a signal into an electrical assembly—wherein the electrical assembly typically includes an electrical link, a male connector coupled to a first end of the link, and a female connector coupled to a second end of the link, the female connector having a connector receptacle compatible with data rates of at least 10 Gbps and an active circuit for reducing signal distortion, coupled between the second end of the link and the connector receptacle—and reducing distortion in the signal as the signal passes through the active circuit of the female connector.
Yet another embodiment of the present invention provides a system. The system generally includes a host, a network access element, and first and second electrical assemblies for transmitting signals between the host and the access element. The second electrical assembly typically includes an electrical link, a male connector coupled to a first end of the link, and a female connector coupled to a second end of the link, the female connector having a connector receptacle compatible with data rates of at least 10 Gbps and connected with the first electrical assembly and an active circuit for reducing signal distortion, coupled between the second end of the link and the connector receptacle.
So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments.
Embodiments of the present invention provide methods and apparatus for reducing distortion in signals propagating through cables at data rates of at least 10 gigabits per second (Gbps). By connecting such direct attach cables with an active cable extender assembly described herein, data signals may be reshaped, retimed, and/or emphasized in an effort to increase the cable length between network devices while still complying with the signal quality requirements of communication standards, such as the SFF-8431 MSA, the SFF-8461 MSA, and the IEEE 802.3ba CR4/10 standards. Copper cable solutions with such increased cable length possible between network devices may provide substantial cost reduction when compared to optical cable solutions. Furthermore, by potentially increasing the signal quality effectively transmitted by a host, solutions utilizing embodiments of the present invention may guarantee host-to-host interoperability.
As an electrical assembly, the direct attach cable assembly 103 may comprise a cable 104, such as copper cable, and a male connector 106 on each end of the cable 104. For high speed Ethernet communications of at least 10 Gbps, the male connectors 106 may comprise enhanced small form factor pluggable (SFP+) or quad small form factor pluggable (QSFP) connectors, for example.
For 10 Gbps Ethernet communication, the physical layer transmitters may not be well-controlled or good enough to fully comply with the SFF-8431 MSA, especially as the transmission length increases. The signal quality from such transmitters is currently the most limiting factor on the cable length that may practically be used. In order to comply with the current SFF-8431 MSA, which defines the 10 Gbps direct attach copper cable assembly, the cable 104 may be limited in length to 7 m. This limitation may likely become more problematic (i.e., the allowed cable length may be further reduced) as 40 Gbps (and especially 100 Gbps) data rate standards are issued.
One way to overcome this cable length limitation may be to connect an electrical assembly, such as an active cable extender assembly 110, to the direct attach cable assembly 103, as shown in
For other embodiments, the cable extender assembly 110 may appear more like an adapter, having a short electrical link coupling the two connectors 202, 204 together. For such embodiments, the electrical link may comprise a ribbon cable or a printed circuit board (PCB) with traces running between the two connectors, for example.
The male connector 202 at one end of the cable may comprise any of various suitable male connectors compliant with high speed Ethernet communications of at least 10 Gbps. For example, the male connector 202 may comprise an SFP+ or a QSFP/CX connector and may be capable of being plugged into any host supporting a CX1 direct attach interface or a CR4/10 QSFP interface. The male connector 202 may be compliant to the SFF-8431 MSA and SFF-8461 MSA standards.
The female connector 204 (also called a cage) at the other end of the cable may house a connector receptacle 206 and an active circuit 208 for reducing distortion in signals propagating between the cable 104 and the connector receptacle in either direction. The connector receptacle 206 may be any of various suitable female connectors for receiving a male connector compliant with high speed Ethernet communications of at least 10 Gbps. For example, the connector receptacle 206 may comprise a female SFP+ or QSFP connector for receiving a male SFP+ or QSFP connector, respectively.
The PCB 300 may comprise any suitable connector interface 304 for electrically connecting the connector receptacle 206 with the PCB. Similarly, the PCB 300 may comprise any suitable cable interface 306 for connecting the cable 104 with the PCB. Traces 308 fabricated in or on the PCB 300 may connect the connector interface 304 with the EDC 302, while traces 310 may connect the EDC 302 with the cable interface 306.
Furthermore, the active circuit 208 (e.g., the EDC 302) may be powered via one or more power supply rails 312 routed through the cable extender assembly 110 and provided as traces on the PCB 300. For example, the host 100 may supply power to one or more pins of the male connector 202, and these pins may be connected with the power supply rails 312 via one or more wires or other suitable connections through the cable 104 and the cable interface 306. The power pins of the male connector 202 used to supply power to the active circuit 208 may be specified by one of the MSAs (e.g., SFF-8431 or SFF-8461) to supply power to the optic interfaces. Such pins may be capable of supplying 1 A of current via a 1 V rail, which may be sufficient to power the EDC 302 or other active circuitry in the female connector 204.
Various circuits supporting the active circuit 208, the connector interface 304, and/or the cable interface 306 may be mounted on the PCB 300 or otherwise disposed within the female connector 204. This support circuitry may include active and/or passive electrical components.
The active circuit 208 in the female connector 204 (including the EDC 302, for example) may compensate the distorted signal received from the direct attach cable assembly 103 via the connector interface 304. After compensation, a clean, reshaped, retimed, and/or emphasized signal may be sent through the cable interface 306, the cable 104, and the passive side (P) of the cable extender to the host 100. In this manner, the signal reaching the host 100 may have reduced distortion compared to a similar length of passive cable between the host and the access element 102, thereby allowing for an increased cable length (e.g., 14 m) between the host and access element. Eye diagram 420 illustrates the example distortion reduction of the cable extender assembly 110. Moreover, because the properties of the fixed length of cable 104 in the cable extender assembly 110 are known, the active circuit 208 may compensate the signal propagated from the access element 102 such that the signal reaching the host 100 is compliant with the SFF-8431 MSA, SFF-8461 MSA, and/or the IEEE 802.3ba for CR4/10 standards. For example, the output of the active circuit 208 on the transmitting side of the cable interface 306 may be set to an appropriate emphasis level in an effort to increase the signal quality of the data 400 received at the host after propagation through the cable extender assembly.
Returning to the direction of data transmission of
In this manner, the cable length between the host and the access element may be increased up to 14 m, for example, without any changes to the device hardware or firmware upgrades. Furthermore, the cable extender assembly 110 described above may provide substantial cost savings since the combined cost of the passive direct attach cable and cable extender assemblies is less than half the cost of short reach optical cable solutions. Most users do not require the significantly greater length capability of optical solutions, even though the 7 m length limitation of contemporary passive copper cable solutions for data communications of at least 10 Gbps may not be sufficient for such users. Embodiments of the cable extender assembly described herein may offer a solution allowing for increased cable length between network devices, while maintaining signal quality compliance with various communications standards supporting data rates of at least 10 Gbps, such as the SFF-8431 MSA, the SFF-8461 MSA, and the IEEE 802.3ba for CR4/10 standards.
Moreover, by providing at least the same or increased signal quality compared to the signal quality transmitted directly by the host, embodiments of the active cable extender assembly described herein may guarantee host-to-host interoperability, such as between different types of hosts from the same vendor or between hosts manufactured by different vendors. Furthermore, embodiments of the active cable extender assembly permit using long copper cable between network devices even if the host EDC alone is not capable of guaranteeing compliance and signal propagation quality. For example, a host guaranteeing CX1 compliance only up to 3 m may be extended up to 10 m by utilizing an active cable extender assembly having a length of 7 m.
For some embodiments, the active cable extender assembly may be connected with any cable type. For example, the cable extender assembly may be connected with an optical active cable. In this case, the active side (A) may function as a media converter, too, converting signals between the electrical and optical domains as signals are propagated through the active circuit and increased in signal quality.
While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
