QSFP-DD (Double Density QSFP): Something You Want to Know

With the rapid growth of data center and 5G development, density, power limits in servers, switches, and other network equipment are being pushed by rising demand and data volume. Data center is required to support faster processing, more bandwidth, and increased density without sacrificing reliability. In this situation, QSFP-DD came out, which is a new module and cage/connector system similar to current QSFP, but with an additional row of contacts providing for an eight lane electrical interface. In this article, we will introduce you something about QSFP-DD that you may be interested in.

1. What Is QSFP-DD?

QSFP-DD stands for Quad Small Form Factor Pluggable Double Density. What Double Density means? The “double density” means the doubling of the number of high-speed electrical interfaces that the module supports compared with a standard QSFP28 module. QSFP-DD is a “double-density” module and cage/connector system which is similar to the current QSFP system. But QSFP-DD has an additional row of contacts providing for an eight-lane electrical interface. The new optical module will be able to operate 25 Gb/s NRZ modulation or 50 Gb/s PAM4 modulation over 16 pairs of twinaxial conductors or optical fibers to support 200 Gb/s or 400 Gb/s aggregate bandwidth.

2. An Introduction on QSFP-DD MSA Group

QSFP-DD Specification for QSFP Double Density 8X Pluggable Transceiver is currently under development by the QSFP-DD MSA Group. The group includes 13 members which are all the leading vendors in the optical communication industry, like Cisco, Brocade and Finisar, aiming to create a upgraded version of QSFP transceiver, which is called QSFP-DD and is able to support 200G/400G Ethernet.
QSFP-DD MSA Group participants have developed an improved management interface. The MSA project may split into separate management interface and form-factor documents. There is a possibility that the OSFP MSA Group, the uQSFP MSA Group, and the Consortium for On-Board Optics (COBO) will adopt the improved QSFP-DD management interface.

3. QSFP-DD vs. QSFP28

QSFP28, with increased data rates ranging up to 28 Gbps on each of four lanes, supports next-generation 100 Gbps Ethernet and 100 Gbps InfiniBand. Now it is quite popular in datacenter computing, switches, routers, and storage. With enhanced Data Rate applications, the QSFP28 interconnect transmits up to 25 Gbps per-serial lane data rates with excellent signal integrity, EMI protection, and thermal cooling.
The QSFP-DD is similar to the current QSFP, but there are still some differences. If modulated by NEZ, each lane of the QSFP-DD can support data rate up to 25G, thus, it can support a total data rate of 200G. If modulated by PAM4, QSFP-DD transceiver can support data rate up to 400G with each lane supporting data rate of 50G. The MSA group also announced that the QSFP-DD can enable up to 14.4Tbps aggregate bandwidth in a single switch slot, which can definitely satisfy the increasing need for higher bandwidth.

4. 200G QSFP-DD

To achieve 400 Gbps, the interconnect industry is developing next-generation Quad Small Form Factor Pluggable Double Density (QSFP-DD) modules. And Gigalight also took the opportunity to release out the new 200G QSFP-DD in this summer. The 200G QSFP-DD integrates eight data lanes in each direction with 8x25.78125Gbps bandwidth. Each lane can operate at 25.78125Gbps up to 70m by using OM3 fiber or 100 m using OM4 fiber. The module is designed to operate over multimode fiber systems using a nominal wavelength of 850nm. It is a high performance module for short-range multi-lane data communication and interconnection applications. It is four-Channel, pluggable, parallel, fiber-optic QSFP+ SR4 for 100 or 40 Gigabit Ethernet, Infiniband FDR/EDR and applications. This transceiver is a high performance module for short-range multi-lane data communication and interconnects applications.

Conclusion

The QSFP-DD optical transceiver is also forward/backward compatible with QSFP, QSFP28 optical transceiver, AOC/DAC and so on. We believe that the rapid development of QSFP-DD will greatly benefit on the whole optical interconnect and communication industry. Let’s wait and see what will happen in the future.

CWDM and DWDM Comparison: What’s the Difference?

DWDM (Dense Wavelength Division Multiplexing) is undoubtedly the popular technology in today's optical fiber applications. However, because of its expensive price, many operators without enough money are quite hesitated to use it. Can we use wavelength division multiplexing at a lower cost? Faced with this demand, CWDM (Coarse Wavelength Division Multiplexing) came into being. And in the post, we will take an introduction on the main difference between CWDM and DWDM and which one is your better choice.

CWDM, as the name suggests, is a DWDM close relative. When comparing CWDM vs. DWDM, their differences are mainly two points as follows:
1. CWDM carrier channel spacing is wide, so the same fiber can only reuse 5 to 6 or so wavelength. This is why we call “Dense” and “Coarse”.
2. CWDM modulates laser by using non-cooling laser, but DWDM is used to cooling laser. The cooled laser is thermally tuned and the non-cooled laser is electronically tuned. Since the temperature distribution is very uneven in a wide wavelength range, the temperature tuning is difficult and costly to achieve. CWDM avoids this difficulty, therefore the cost is significantly reduced, the entire cost of CWDM system is only 30% of DWDM.
CWDM provides very high access bandwidth for low cost, and is suitable for popular network structures such as point-to-point, Ethernet, SONET ring, especially for short distance, high bandwidth, and point-intensive communication applications. Building communication between buildings or buildings. In particular, it is worth mentioning that CWDM and PON (passive optical network) with the use. PON is an inexpensive, point-to-multipoint optical fiber communication method. By combining with CWDM, each individual wavelength channel can be used as the virtual optical link of PON to realize the broadband data transmission between the central node and multiple distributed nodes.
At present, several companies are introducing CWDM-related products. Here we mainly introduce CWDM Mux/Demux and DWDM Mux/Demux.
(1). CWDM Mux/Demux Module:
CWDM Mux and CWDM Demux are designed to multiplex multiple CWDM channels into one or two fibers. The core of CWDM Module application is the passive MUX DEMUX unit. The common configuration is 1×4, 1×8, 1×16 channels. Available in 19″ Rack Mount or LGX module package, optional wide band port is available to multiplex with CWDM Channels wavelength.
(2). DWDM Mux/Demux Module:
DWDM Mux and DWDM DeMux are designed to multiplex multiple DWDM channels into one or two fibers. The common configuration is 4, 8, 16 and 40 channels. These modules passively multiplex the optical signal outputs from 4 or more electronic devices, send them over a single optical fiber and then de-multiplex the signals into separate, distinct signals for input into electronic devices at the other end of the fiber optic link.
However, CWDM is the product of cost and performance compromise; inevitably there are some limitations on performance. Industry experts pointed out that CWDM currently exist below the following four points: First, CWDM in a single fiber to support the number of multiplex wavelengths less, resulting in higher cost of expansion in the future; second, multiplexers, multiplexers, etc. The cost of the equipment should be further reduced, these devices can not only DWDM corresponding equipment, a simple modification; Third, CWDM does not apply to metropolitan area networks, metro nodes between the shorter distance, operators in the CWDM equipment expansion on the money can Used to lay more fiber optic cable, get better results; Fourth, CWDM has not yet formed a standard.
From the CWDM and DWDM comparison above, we can know both the benefits and drawbacks of CWDM and DWDM. If the transmission distance is short and cost is low, then CWDM may be your first choice. On the contrary, you can consider DWDM. For more information about CWDM and DWDM, you can visit: Gigalight.