Understanding 400G Transceivers and Cables: Key Questions Answered
Jan 23, 20221 min read
400G transceivers and cables play a vital role in the process of constructing a 400G network system. So, Do you want to look into 400G transceivers like QSFP-DD (Quad Small Form Factor Pluggable-Double Density) transceivers, as well as 400G cables such as QSFP-DD AOC/DAC cables? Then, what applications do they have? Find answers here.
Definition and Types
Q1: What are 400G transceivers?
A1: 400g optical transceivers are optical modules that are mainly used for photoelectric conversion with a transmission rate of 400Gbps.
They can be classified into two categories according to the applications: client-side transceivers for interconnections between the metro networks and the optical backbone, and line-side transceivers for transmission distances of 80km or even longer.
Concurrently, the electrical port side employs 8 channels of 53Gbps PAM4 electrical signals, packaged in OSFP or QSFP-DD formats. Optical wavelength categorizes 400G optical transceivers into multi-mode (MM) and single-mode (SM), transmission distance classifies them as SR, DR, FR, and LR, and modulation methods distinguish between NRZ and PAM4 (usually favoring PAM4).
Q2: What does it mean when an electrical or optical channel is PAM4 or NRZ in 400G transceivers?
A2: NRZ is a modulation technique that has two voltage levels to represent logic 0 and logic 1. PAM4 uses four voltage levels to represent four combinations of two bits logic-11, 10, 01, and 00. The PAM4 signal can transmit double faster than the traditional NRZ signal.
When a signal is referred to as "25G NRZ", it means the signal is carrying data at 25 Gbps with NRZ modulation. When a signal is referred to as "50G PAM4", or "100G PAM4", it means the signal is carrying data at 50 Gbps, or 100 Gbps, respectively, using PAM4 modulation. The electrical connector interface of 400G transceivers is always 8x 50Gb/s PAM4 (for a total of 400Gb/s).
Q3: What are the 400G transceivers packaging forms?
A3: There are mainly the following packaging forms of the 400g optical transceiver:
QSFP-DD: 400G QSFP-DD (Quad Small Form Factor Pluggable-Double Density) is an expansion of QSFP, adding one row to the original 4-channel interface to 8 channels, running at 50Gb/s each, for a total bandwidth of 400Gb/s.
OSFP: OSFP (Octal Small Formfactor Pluggable, Octal means 8) is a new interface standard and is not compatible with the existing photoelectric interface. The size of 400G OSFP modules is slightly larger than that of 400G QSFP-DD transceivers.
QSFP112: 400G QSFP112 (Quad Small Form Factor Pluggable 112) is a further upgrade of the QSFP series, designed for the next generation of high-speed networks. It is optimized based on the original 4-channel interface, supporting a single-channel 112Gb/s transmission rate and a total bandwidth of up to 400Gb/s.
CFP8: CFP8 is an expansion of CFP4, with 8 channels and a correspondingly larger size.
COBO: COBO (Consortium for On-Board Optics) means that all optical components are placed on the PCB. COBO has good heat dissipation and small-size. However, since it is not hot-swappable, once a module fails, it will be troublesome to repair.
CWDM8: CWDM 8 is an extension of CWDM4 with four new center wavelengths (1351/1371/1391/1411 nm). The wavelength range becomes wider and the number of lasers is doubled.
CDFP: CDFP was born earlier, and there are three editions of the specification. CD stands for 400 (Roman numerals). With 16 channels, the size of CDFP is relatively large.
Q4: What is QSFP-DD cable?
A4: QSFP-DD cable contains two forms: one is a form of high-speed cable with QSFP-DD connectors on either end, transmitting and receiving 400Gbps data over a thin twinax cable or a fiber optic cable, and the other is a form of breakout cable that can split one 400G signal into 2x 200G, 4x 100G, or 8x 50G, enabling interconnection within a rack or between adjacent racks.
Q5: What are the main 400G transceivers and 400G DAC/AOC cables available on the market?
A5: The tables below show the main types of 400G transceivers and cables provided by FS. Each module is tested in targeted devices to ensure compatibility, with low BER, precise eye diagram, optical spectrum, and temperature tests verifying high performance. With a variety of packaging options available, please contact our solutions experts to customize your network upgrade solution.
Category | Product | Max Cable Distance | Connector | Media | Power Consumption | Application |
400G OSFP Modules | 50m@OM4 or OM5 | MPO-12/APC | MMF | ≤8.5W | InfiniBand | |
500m | MPO-12/APC | SMF | ≤10W | |||
100m@OM4 | MPO-16/APC | MMF | ≤10W | Ethernet | ||
500m | MPO-12/APC | SMF | ≤10W | |||
400G QSFP-DD Modules | 100m@OM4 | MPO-12/APC | MMF | ≤8W | Ethernet | |
100m@OM4 | MPO-16/APC | MMF | ≤10W | |||
150m@OM5 | MPO-12 | MMF | ≤12W | |||
500m | MPO-12/APC | SMF | ≤9W | |||
500m | MPO-12/APC | SMF | ≤10W | |||
2km | MPO-12 | SMF | ≤11W | |||
2km | Duplex LC/UPC | SMF | ≤9W | |||
2km | MPO-12/APC | SMF | ≤9W | |||
6km | Duplex LC UPC | SMF | ≤10W | |||
10km | Duplex LC/UPC | SMF | ≤10W | |||
10km | Duplex LC/UPC | SMF | ≤9W | |||
10km | MPO-12/APC | SMF | ≤9W | |||
40km | Duplex LC/UPC | SMF | ≤10W | |||
400G QSFP112 Modules | 50m@OM4 | MPO-12/APC | MMF | ≤9W | InfiniBand | |
500m | MPO-12/APC | SMF | ≤10W | |||
2km | Duplex LC/UPC | SMF | ≤10W | |||
2km | MPO-12/APC | SMF | ≤10W | |||
10km | Duplex LC UPC | SMF | ≤10W | Ethernet | ||
400G DAC Cables | 2m | OSFP to OSFP | Copper | ≤0.1W | InfiniBand | |
2m | OSFP to OSFP | Copper | ≤0.1W | Ethernet | ||
3m | QSFP112 to QSFP112 | Copper | ≤1.5W | |||
5m | QSFP-DD to QSFP-DD | Copper | ≤2.5W | |||
400G AOC Cables | 100m | QSFP-DD to QSFP-DD | Optic Fiber | ≤8W | Ethernet | |
400G Breakout Cables | 30m | OSFP to 2x QSFP56 OSFP to 4x QSFP56 | / | ≤8W | InfiniBand | |
70m | OSFP to 2x QSFP56 OSFP to 4x QSFP56 QSFP-DD to 2x QSFP56 QSFP-DD to 4x QSFP56 QSFP-DD to 8x SFP56 QSFP-DD to 4x QSFP28 QSFP-DD to 8x 50G SFP56 | / | ≤12w | Ethernet |
Q6: What do the suffixes "SR8, DR4 / XDR4, FR4 / LR4 and 2FR4" mean in 400G transceivers?
A6: The letters refer to reach, and the number refers to the number of optical channels:
SR8: SR refers to 100m over MMF. Each of the 8 optical channels from an SR8 module is carried on separate fibers, resulting in a total of 16 fibers (8 Tx and 8 Rx).
DR4 / XDR4: DR / XDR refers to 500m / 2km over SMF. Each of the 4 optical channels is carried on separate fibers, resulting in a total of 4 pairs of fibers.
FR4 / LR4: FR4 / LR4 refers to 2km / 10km over SMF. All 4 optical channels from an FR4 / LR4 are multiplexed onto one fiber pair, resulting in a total of 2 fibers (1 Tx and 1 Rx).
2FR4: 2FR4 refers to 2 x 200G-FR4 links with 2km over SMF. Each of the 200G FR4 links has 4 optical channels, multiplexed onto one fiber pair (1 Tx and 1 Rx per 200G link). A 2FR4 has 2 of these links, resulting in a total of 4 fibers, and a total of 8 optical channels.
Applications
Q1: What are the benefits of moving to 400G technology?
A1: 400G technology can increase the throughput of data and maximize the bandwidth and port density of the data centers. With only 1/4 the number of optical fiber links, connectors, and patch panels when using 100G platforms for the same aggregate bandwidth, 400G optics can also reduce operating expenses. With these benefits, 400G transceivers and QSFP-DD cables can provide ideal solutions for data centers and high-performance computing environments.
Q2: What are the applications of QSFP-DD cables?
A2: QSFP-DD cables are mainly used for short-distance 400G Ethernet connectivity in the data centers, and 400G to 2x 200G / 4x 100G / 8x 50G Ethernet applications.
Q3: 400G QSFP-DD vs 400G OSFP/QSFP112: What are the differences?
A3: The table below includes detailed comparisons for the three main form factors of 400G transceivers.
400G Transceiver | 400G QSFP-DD | 400G OSFP | 400G QSFP112 |
Application Scenario | Data Center | Data Center Compatible with NVIDIA ConnectX-7 Adapters | |
Size | 18.35mm× 89.4mm× 8.5mm | 22.58mm× 107.8mm× 13mm | 40mm× 102mm× 9.5mm |
Max Power Consumption | 12W | 15W | 24W |
Backward Compatibility with QSFP28 | Yes | Through adapter | Yes |
Modulation | 8x 50G-PAM4 | 4x 100G-PAM4 | 4x 100G-PAM4 |
Switch Port Density (1RU) | 36 | 36 | 16 |
Media Type | MMF & SMF | ||
Hot Pluggable | Yes | ||
Thermal Management | Indirect | Direct | Indirect |
Support 800G | No | Yes | No |
For more details about the differences, please refer to the blog: Differences Between QSFP-DD and QSFP+/QSFP28/QSFP56/OSFP/CFP8/COBO
Interface Compatibility
Q1: Can I plug an OSFP module into a 400G QSFP-DD port, or a QSFP-DD module into an OSFP port?
A1: No. OSFP and QSFP-DD are two physically distinct form factors. If you have an OSFP system, then 400G OSFP optics must be used. If you have a QSFP-DD system, then 400G QSFP-DD optics must be used.
Q2: Can a QSFP module be plugged into a 400G QSFP-DD port?
A2: Yes. A QSFP (40G or 100G) module can be inserted into a QSFP-DD port as QSFP-DD is backward compatible with QSFP modules. When using a QSFP module in a 400G QSFP-DD port, the QSFP-DD port must be configured for a data rate of 100G (or 40G).
Q3: Is it possible with a 400G OSFP on one end of a 400G link, and a 400G QSFP-DD on the other end?
A3: Yes. OSFP and QSFP-DD describe the physical form factors of the modules. As long as the Ethernet media types are the same (i.e. both ends of the link are 400G-DR4, or 400G-FR4 etc.), 400G OSFP and 400G QSFP-DD modules will interoperate with each other.
Q4: How can I break out a 400G port and connect to 100G QSFP ports on existing platforms?
A4: There are several ways to break out a 400G port to 100G QSFP ports:
QSFP-DD-DR4 to 4x 100G-QSFP-DR over 500m SMF
QSFP-DD-XDR4 to 4x 100G-QSFP-FR over 2km SMF
QSFP-DD-LR4 to 4x 100G-QSFP-LR over 10km SMF
OSFP-400G-2FR4 to 2x QSFP-100G-CWDM4 over 2km SMF
Apart from the 400G transceivers mentioned above, 400G to 4x 100G breakout cables can also be used.