What problems does 400G solve?

The pressure to increase network capacity is enormous, and as a result, expectations for network providers are also increasing.
To keep up with the demand for data consumption and achieve high bandwidth connectivity, network operators need interfaces with increasingly higher bitrates.

The demand for data collection is constantly growing. The reasons are obvious:

  • increasing access to streaming platforms such as Netflix or HBO MAX.
  • the development of IoT (Internet of Things), intelligent devices that automatically communicate and exchange data via the network, without human intervention
  • storage of data in the cloud.

400G solution in the form of an interface QSFP-DD 400G is the best choice for telecom service providers and large data centers with huge traffic growth.

What does QSFP-DD 400G mean?

QSFP-DD 400G are high-tech optical modules designed in a standardized enclosure. The standard for optical module memory management and host-to-module communication is clearly defined in the specification Common Management Interface Specification (CMIS).

With actual unification and standardization, 400G QSFP-DD modules are entering the market much faster than 100G modules. In this case, there is no concern about whether modules will be available during the development of the network that matches the ports in the currently purchased equipment, because there is one standardized type of interface.

In addition, its specification is flexible enough that it will also cover new modules, which may not appear until some time. The specification of the module is clearly defined in the CMIS system, and power consumption classes are defined with a large margin.

Benefits of 400G QSFP-DD:
  • defining power consumption classes with large stock
  • new CMIS standard for module memory management and how the module communicates with the host
  • backward compatibility of the connector with QSFP28

400G QSFP-DD optical modules transmit the signal through four or eight optical tracks, providing a total bit rate of up to 400 Gbps. On the electrical side, we have eight 53,125Gb/s PAM4 lines.

How do I connect Top of the Rack switches to servers within the Data Center?

In this scenario, we will combine 400G Top of TheRack switches with servers equipped with 100G cards to realize specific services. IN GBC Photonics offer we have a dedicated solution that works at a distance of up to 500 meters, so ideally suited for data center applications.

This solution is based on the selection of suitable optical modules on the side of 400G and 100G interfaces. In addition, we must use a patch cord that works with these interfaces transmitting the signal over a single-mode medium.

In a 400G switch equipped with QSFP-DD interfaces, we need to adopt a module that transmits the optical signal through four 100G lasers. In this operating mode, you need to configure the switch port as 4x100G.

In addition, the QSFP-DD module must have a built-in MPO connector that allows the separation of individual 100G signals. On the other hand, on the side of servers with 100G cards, the QSFP28 100G modules should be used, in which the transmission must take place one lambda each.

Figure 1. Diagram of the QSFP-DD DR4 transmission structure.

Devices with portfolio of GBC Photonics necessary for the construction of this solution:

We will build the solution using the QSFP-DD400G optical module with MPO-12 connector:

QSFP-DD 4x DR1 1310nm500m MPO SINGLE RATE 400GbE Single Mode EML.

Additionally, four QSFP28 Single Lambda modules should be used, which will work with the QSFP-DD module. The products necessary in this case are:

QSFP28 SINGLE LAMBDA DR1 1310nm 500m LC SINGLE RATE 100GbE Single Mode EML.

Need help ordering the right parts for your system? We will be happy to advise you. Schedule an interview with an expert.

To connect two different types of interfaces, we use an optical cable commonly known as an “octopus”. On one side, we use MPO connector to plug into 400G module connector, and on the other side four pairs of LC connectors to plug into 100G module connectors.

GBC Photonics product codes used to build this solution:

QDDSSMOBQE0.5CGP-QSFP-DD 4x DR1 1310nm 500m MPO SINGLE RATE 400GbE Single Mode EML

100G QSFP28 Single Lambda Type

MPTC-SM-MPO-8XLCU-D00X- Patch Cord SM, MPO — 8xLC/UPC, length: xm

How do I connect Top of the Rack switches located in two remote locations?

In the second scenario, we will connect two Top of the Rack switches equipped with 400G ports located in two different server rooms distant from each other. Point-to-point connection without signal regeneration.

GBC Photonics offers a dedicated solution to transmit 400G signal in locations up to 40 kilometers away from each other. It is a pair of optical modules working on a pair of optical fibers, thus having LC connectors.

In 400G switches equipped with QSFP-DD interfaces, we must use the appropriate modules operating at wavelengths located around 1310 nm.

Why do the modules need to operate at wavelengths close to 1310 nm?

Transmissions with high bitrates are sensitive to chromatic dispersion. In order to minimize its influence, the wavelengths along which the transmission is realized are located in the region of 1310 nm, because only at this point the dispersion is equal to “0".

To transmit a signal over a distance of more than 10 km, we reach for modules that, on the optical side, transmit the signal at wavelengths called LAN-WDM.

To transmit a 400G signal without regeneration over a distance of up to 10km, use a pair of QSFP-DD 400G LR8 optical modules equipped with an LC connector. However, to transmit a 400G signal without regeneration over a distance of up to 40 km, you need to reach for a pair of QSFP-DD 400G ER8 optical modules equipped with an LC connector.

These modules, on the optical side, transmit signals at eight LAN-WDM wavelengths tightly focused around 1310 m.

The structure of QSFP-DD 400G LR8/ER8 optical module is as follows:

Figure 2. Construction diagram of QSFP-DD 400G LR8 and QSFP-DD 400G ER8 optical modules.

LAN-WDM wavelengths used by QSFP-DD LR8/ER8
8x50G (1273.5, 1277.9, 1282.3, 1286.7, 1295.6, 1300.1,1304.6, 1309.1 nm)

GBC Photonics products used to build this solution: