What problems does 400G solve?

The demand for data is ever increasing in our interconnected world. Widespread access to video-on-demand(VoD) platforms — such as Netflix and HBO MAX — coupled with the growing popularity of IoT technologies like AI, machine learning or cloud storage, place a significant pressure on networks.

To keep up with this demand and achieve high-capacity connectivity, users need an interface with a bit rate of 400G.

400G in QSFP-DD form factor solutions are ideal for Telco providers and large data centres with huge traffic growth.‍

What is QSFP-DD 400G?‍

With QSFP- DD 400G, operators donot need to worry about matching the ports in their existing equipment with thenew transceiver, as the new module was designed in a standardised form factor.The specifications of the module are clearly defined in the CommonManagement Interface Specification (CMIS).

 There is one standard of QSFP-DD,whose power consumption classes are defined with a large margin.

‍Benefits of 400G QSFP-DD

• definition of power consumption classes with a large margin
• new CMIS standard for managing the module memory and the way of communication between the module and the host
• connector is backward compatible with QSFP28 100G

The transceivers also have four optical lanes that operate at 100Gbps PAM4modulation, providing solutions of up to 400 Gbps. They come equipped with eight lanes on the electrical side of 53.125Gbps PAM4.

How to connect top of the rack switches with servers within the data centre?

‍In this scenario, we will connect 400G top of the rack switches in our server room with servers equipped with 100G cards in order to provide specific services — you can find dedicated solutions of up to 500 meters in our GBC Photonics portofolio. Our solution uses appropriate transceivers with 400Gand 100G interfaces and is ideal for data centres.

Additionally, in this example we will need to use a patch cord that works with these interfaces and transmits the signal over a single-mode medium.

In the 400G switch equipped with QSFP-DD interfaces, we will use a transceiver transmitting the optical signal via 4x100G lasers. In this operating mode, we 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.

In the case of servers with 100G cards, QSFP28 100G modules should be used, where the transmission is over 100G lambda.

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We will build the solution using the QSFP-DD 400G optical module with an MPO-12 connector. To make ordering easier, here are the products’ part codes from the GBC Photonics portofolio:

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

Additionally, four pieces of QSFP28 single lambda modules should be used, which will work with the QSFP-DD module.

In this case, products’ part codes are: QSFP28 SINGLE LAMBDA DR1 1310nm 500m LC SINGLE RATE 100GbE Single Mode EML.

If you need additional help in ordering the most suitable parts for your system, we are happy to provide a personalised, free consultation. Schedule yours here.

To connect two different types of interfaces, we will also use a specific optical cable. On one side, an MPO connector will be plugged into the 400G module connector, and on the other, four pairs of LC connectors to be plugged into the 100G module connectors.

GBC Photonics PN’s products used to build this solution

400G QSFP-DD

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

100G QSFP28 Single Lambda type

Q28SSLOBSE0.5CGP -QSFP28 SINGLE LAMBDA DR1 1310nm 500m LC SINGLE RATE 100GbE Single Mode EML

Patchcord

MPTC-SM-MPO-8xLCU-D00x - Patchcord SM, MPO – 8xLC/UPC, lenght: xm

How to connect top of the rack switches located in two remote locations?

In our second scenario, we will connect two top of the rack switches equipped with 400G ports located in two different server rooms that are far away from each other. We will use a point-to-point connection without signal regeneration.

You can find a dedicated solution that allows the transmission of 400G signals in distant locations of up to 40 kilometers in our GBC Photonics offer.

The solution involves a pair of optical modules working on optical fibres and has LC connectors.

In 400G switches equipped with QSFP-DD interfaces, we need to use specific transceivers operating at wavelengths located around 1310 nm.

Why do modules have to work at wavelengths close to 1310 nm?

This is because high bit rate transmissions are sensitive to chromatic dispersion while the dispersion is "0" at 1310 nm. Therefore, in order to transmitt the signal over a distance of over 10 km, we need  transceivers that transmit optical signal at wavelengths called LAN-WDM.

To send the 400G signal without regenerating the signal up to a distance of 10 km, we should use a pair of QSFP-DD 400G LR8 optical modules equipped with an LC connector.

However, to send the 400G signal without regenerating the signal at a distance of up to 40 km we should use a pair of QSFP-DD 400G ER8 optical modules equipped with an LC connector.

The structure of the  QSFP-DD 400G LR8/ER8 transceiver look as follows:

LAN-WDM wavelengths used by QSFP-DD LR8/ER8

8x50G (1273.5, 1277.9, 1282.3, 1286.7, 1295.6, 1300.1, 1304.6, 1309.1nm)

‍GBC Photonics PN’s products used to build this solution:

400G QSFP-DD

QDDSSLOLOE010CGP -QSFP-DD LR8 1310 nm 10 km LC SINGLE RATE 400GbE Single Mode EML

QDDSSLOLOE040CGP -QSFP-DD ER8 1310 nm 40 km LC SINGLE RATE 400GbE Single Mode EML

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