High-density QSFP+ SR4 Transceiver Cabling Methods

With the increasing demand for higher speed in fiber optic communications, 40G network is widely deployed in today’s backbone transmission network. 40G QSFP+ SR4 transceivers, for short reach applications, can support distance of up to 150 m over OM4 multimode optical fiber. Inserted in switch, QSFP+ SR4 module utilizes a MTP/MPO interface for dual way transmission.

There are a lot of methods to connect QSFP+ SR4 transceivers to other devices by using different connectivity products. Besides, the cabling for 40G is relatively more difficult than that of 10G network, which requires more cables and space. Here are several high density QSFP+ SR4 transceiver cabling methods.

QSFP+ SR4 40G to 40G Applications

40G to 40G transmission is needed in a 40G fiber optic network. The following picture simply illustrates how 40G to 40G multimode transmission is being achieved by QSFP+ SR4 transceivers. Two QSFP+ SR4 modules interconnected with a MTP trunk cable are separately inserted into two switches. Thus two switches are linked successfully.

Of course, there are also other ways to achieve this connection. The more devices you use, the more complex it is to achieve connections because cable counts increase. As shown in the following figure, a 48-port 1U rack mount MTP fiber patch enclosure is used. Four 12-port MTP fiber adapter panels can be deployed in this standard 1U rack mount enclosure. With the help of this 48-port MTP fiber enclosure, cable management for 40G connections could be easier.

QSFP+ SR4 40G to 10G Applications

QSFP+ SR4 is a parallel fiber optic transceiver which uses four fibers for transmitting and four fibers for receiving at the same time. The 40G fiber optic signal can be separated into four 10G signals to meet the 40G to 10G transferring requirements. The fiber optic cable count will be increased at the 10G distribution end. Usually a breakout MTP-8LC harness cable is used. For better cable management, a 1U 96-fiber enclosure is recommended, which includes four HD MTP cassettes transferring MTP front the 40G end to LC at the 10G end. Four 10G-SR SFP+ modules, inserted in 10G switch/ports, can be connected to the corresponding LC ports on fiber optic enclosures to achieve the duplex transmission between 40G and 10G.

For higher cabling density, the above mentioned 48-port 1U rack mount MTP fiber patch enclosure is still being recommended, which can provide high density 40G MTP cabling environment. And additional MTP-8LC harness cables should be used for transferring signals between 40G and 10G.

Conclusion

Through the above analysis we can see that, QSFP+ SR4 transceivers can meet various cabling applications with different fiber products. Apart from the above-mentioned methods, there are also others way to build connections using QSFP+ SR4 modules and it will depend on the practical applications and cabling environments. All the related products for the above mentioned methods can be found in FS.COM.

QSFP+ Transceiver, DAC, AOC – Which Is Your Choice?

The IEEE 802.3ba committee ratified the 40 Gigabit Ethernet standard and along with the general specification, defined a number of fiber optic interfaces. For 40GbE direct cabling between two devices using QSFP+ port, there are several options including QSFP+ transceiver option, QSFP+ DAC (Direct Attach Copper) cable, and QSFP+ AOC (Active Optical Cable). Among these options, each of them has its own merits. This article will compare them and point out which is more cost-effective for your networks.

QSFP+ Transceiver

The 40-Gigabit QSFP+ transceiver module is a hot-swappable, parallel fiber-optical module with four independent optical transmit and receive channels. These channels can terminate in another 40-Gigabit QSFP+ transceiver, or the channels can be broken out to four separate 10-Gigabit SFP+ transceivers. The QSFP+ transceiver module connects the electrical circuitry of the system with either a copper or an optical external network. The transceiver is used primarily in short reach applications in switches, routers, and data center equipment where it provides higher density than SFP+ modules.

Cables for 40 Gigabit Ethernet

Copper Cables: QSFP + to QSFP + copper cable and QSFP + to 4SFP + breakout copper cable are the two common types of QSFP + cables. QSFP + to QSFP + copper cables are hot-removable and hot-insertable. A cable consists of a cable assembly that connects directly into two QSFP + modules, one at each end of the cable. QSFP + to 4 SFP + breakout copper cable is with one QSFP + on one end and four SFP + on the other end. It allows a 40G Ethernet port to be used as four independent 10G ports thus providing increased density while permitting backward compatibility and a phased upgrade of equipment.

Fiber Cables: Active optical cable (AOC) assemblies were invented to replace copper technology in data centers and high performance computing (HPC) applications. The 40G QSFP + AOC is a parallel 40Gbps quad small form factor pluggable (QSFP +) active optical cable, which supplies higher port density and total system cost. The QSFP + optical modules provide four full-duplex independent transmit and receive channels, each are able of 10Gbps operation 40Gbps aggregate bandwidth of at least 100m multimode fiber.

Which to Choose?

Case 1: Distances Below 5 m If the transmission distances is under 5 m, like the case that two switch ports are connected within the same rack or between racks located within the same room. The QSFP+ passive DAC cable is recommended. Take the Cisco compatible QSFP+ optics for example:

DAC	5m Cisco QSFP-H40G-CU5M Compatible 40G QSFP+ Passive Direct Attach Copper Cable	US$ 65.00
AOC	5m Cisco QSFP-H40G-AOC5M Compatible 40G QSFP+ Active Optical Cable	US$ 140.00
Transceiver & Cable	Cisco QSFP-40G-SR4 Compatible 40GBASE-SR4 QSFP+ 850nm 150m DOM Transceiver	US$ 85.00
	5M OM4 12-fiber MTP Fiber Optic Trunk Cable for 40GBASE-SR4	US$ 73.00

Case 2: Distances Below 100 m (< 5 m) For the case that transmission distance is below 100 m but beyond 5 m, the QSFP+ AOC is an ideal choice for use. In this case, the QSFP+ passive DAC cable cannot achieve such long reach requirement because of its performance limitation. While the 40GBASE-SR4 QSFP+ transceiver can do this but the cost of the MTP trunk cable is higher. Thus, here, the QSFP+ AOC is preferred.

Case 3: Distances Above 100 m If the transmission distance is longer than 100 m, DAC cables and AOCs are usually not recommended. In this case, the 40G QSFP+ modules which are used for short-reach applications are recommended.

40G QSFP+ cables can provide inexpensive and reliable 40G speed connections using either copper cables with distances reaching up to 30ft (10 meters length) or active optical cables reaching even 300ft (100 meters). Of course, all the above are just rough estimates of the optics. In reality, more details should be included according to your specific requirements.

QSFP+ Interconnect Solution for 40 Gigabit Ethernet

The QSFP+ optical transceiver is the dominant transceiver form factor used for 40 Gigabit Ethernet applications. In the year of 2010, the IEEE standard 802.3ba released several 40-Gbps based solutions, including a 40GBASE-SR4 parallel optics solution for multimode fiber. Since then, several other 40G interfaces have been released, including 40GBASE-CSR4, which is similar to 40GBASE-SR4 but extends the distance capabilities.

As is know to all, two switches are connected by either transceiver modules or cables. For example, if you simply wanted to cable up two Nexus 3000s with 40GbE, the options are multi mode fiber or twinax copper. We’ll only cover the fiber throughout this post as that is where most of the questions are in recent years. So, since you are now using fiber, how do we connect these switches into the network? First, you need to insert the QSFP+ optic similar to how you would insert a fiber optic for standard 1G or 10G connectivity. For the Nexus 3000, only multi mode fiber is available, so the Cisco part number needed is QSFP-40G-CSR4. This is the equivalent of the GLC-LH-SMD or SFP-10G-SR, for 1G and 10G, respectively. The connector type for QSFP-40G-CSR4 is no longer LC, but is a MPO (multi-fiber push-on) connector.

It is worth noticing that cables for 40G Ethernet actually have 12 fiber strands internal to them to achieve 40GbE. Distance limitations are 100m using OM3 and 150m using OM4 fiber respectively. Because these cables are connected with MPO connectors, have 12 strands, and are ribbon cables for native 40GbE. They will not be able to leverage any of your existing fiber optic cable plant. So be prepared to home run these cable where needed throughout the data center.

However, you may not always need native 40GbE between two switches. Instead, you may opt to configure multiple 10GbE interfaces instead. In this case, the QSFP-40G-SR4 is still needed, but the cable selection is different with what was previously shown above and the ability to use current cable plants is possible. The cable required here would have an MPO connector on one end that would connect into the QSFP port and then “break out” into 4 individual fiber links on the other end. These breakout cables terminate with LC male connectors. I would like to call it MTP-LC harness cable. The application for this MTP-LC harness cable is to directly connect a QSFP+ port to (4) SFP+ ports. For most Data Center applications, the use of structured cabling is employed via MTP trunks and the use of patch panels.

This is great that they terminate with LC male connectors because this allows customers to leverage the current cable infrastructure assuming existing patch panels have LC interfaces and OM3/OM4 fiber is used throughout the data center. These breakout cables are also nice if you want to attach a northbound switch that only supports 10GbE interfaces. You can easily direct connect or jump through a panel in the data center to connect the Nexus 3000 via multiple 10GbE interfaces to a Nexus 7000 (or any other switch with 10GbE-only interfaces).

Accordingly, direct attach cables which are terminated with QSFP+ connector is an alternative in 40G connectivity. For instance, HP JG331A compatible QSFP+ to 4SFP+ direct attach copper cable is terminated with one QSFP+ connector on one end and four SFP+ connector on the other end.

40G QSFP+ cables can provide inexpensive and reliable 40G speed connections using either copper cables with distances reaching up to 30ft (10 meters length) or active optical cables reaching even 300ft (100 meters). Cost of local NOC connectivity is significantly reduced by avoiding the more costly fiber transceivers and optical cables.