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Know Your 800G Transceiver

800 Gigabit (800G) transceivers are optical modules capable of handling data rates of 800 Gbps. With a transmission rate of up to 800 Gbps, 800G transceivers offer double the capacity of their latest predecessor (400G transceivers). 800G transceivers are ideal for:

  • Any host platform with 800G ports

  • Networks with 800 gigabits data transmission

  • Telecommunication networks that require high-speed data transmission with minimal loss

An 800G transceiver uses multiple lanes of optical signals and advanced modulation techniques to achieve higher capacities. 800G transceivers employ multiplexing using multiple fibers. These transceivers also use a combination of fiber and wavelength multiplexing to transmit an optic signal. All 800G client optics use 8 lanes of 100G with Pulse amplitude modulation 4-level (PAM4) modulation. PAM4 has a modulation of 53 Gbaud x 2 bits per symbol. 800G optics do not currently support Wavelength Division Multiplexing (WDM) systems that use only wavelength multiplexing and demultiplexing techniques.

800G transceivers support multiple transmission rates and breakout modes to ensure compatibility with various network transport requirements. This flexibility allows a single physical transceiver to be logically divided into multiple lower-speed Ethernet ports, adapting to different deployment scenarios:

  • 1x800G—The transceiver functions as a single 800G port to achieve a total capacity of 800 Gbps.

  • 2x400G—The breakout cable provides the port as two separate 400G ports to achieve a total capacity of 800 Gbps.

  • 8x100G—The transceiver can break out into eight separate 100G ports to achieve a total capacity of 800 Gbps.

Juniper's 800G transceivers use the OSFP800 and QSFP-DD800 form factors. This document refers to the form factors as OSFP and QSFP-DD.

Modulation Methods

  • PAM4—PAM4 is a modulation method that combines two bits into a single symbol with four amplitude levels. That is, PAM4 effectively doubles the amount of data that you can transmit over a network. PAM4 has a higher than required signal to noise ratio (SNR) and is susceptible to four-Wave Mixing (FWM). FWM is a nonlinear optical phenomenon that occurs in fiber-optic communication systems when multiple optical signals (wavelengths) interact within the fiber. The challenge of achieving 800G optical transmission over distances greater than 10 km using PAM4 modulation is mainly due to FWM. It is necessary to configure forward error correction (FEC) to handle the signal integrity. You must configure FEC at both the transmitter and receiver ends of a communication link that uses 800G optical transceivers. When you configure FEC at both ends, the FEC algorithm encodes data before transmission and decodes and corrects the errors in data upon reception. In summary, PAM4 enables efficient short distance data transmission, but it demands more signal processing and error correction.

    Figure 1: PAM4 Modulation Waveform diagram showing a PAM4 signal for binary sequence 0110100 and an eye diagram illustrating PAM4 signal quality with levels 11, 10, 01, and 00.

  • Non-return to zero (NRZ) modulation—Non-return to zero (NRZ) modulation is commonly used as the modulation format for lower speed client optics up to 100G. However, industry standards for 800G optics do not use NRZ modulation. Hence, Juniper's 800G clients optics do not support this.

800G optical transceivers use the following technologies:

Digital Signal Processing

Advanced digital signal processing (DSP) techniques enhance signal integrity and extend the reach of 800G transceivers over optical fiber.

Clock Data Recovery

Clock data recovery (CDR) extracts timing information from a data signal and ensures accurate data retrieval and transmission in an optic network.

Forward Error Correction

The 800G optical transceiver handles high transmission speeds. Hence, it is susceptible to errors caused by noise, signal distortions, and nonlinear effects. Forward Error Correction (FEC) is a method of error control in which the transmitter adds redundant data or parity bits to the original data stream. This redundancy allows the receiver to detect and correct errors without requiring retransmission. Retransmission is impractical in optical transceivers due to high latency and the need for real-time transmission.

FECs are implemented through FEC algorithms. FEC algorithms are specific mathematical techniques or coding schemes. FEC algorithms detect and correct errors in transmitted data without requiring retransmission. The FEC process involves two steps:

  • Encoding (at the Tx or transmitter)—The FEC algorithm processes the original data and adds redundant bits or parity bits based on a specific mathematical rule. The encoded data is then transmitted over the communication channel.

  • Decoding (at the Rx or Receiver)—The receiver uses the FEC algorithm to analyze the received data, including the redundant bits. If errors are detected, the algorithm attempts to correct them based on the redundancy.

The error correction capability of FEC depends on the specific algorithm used and the amount of redundancy added. Some of the commonly used FEC algorithms include:

  • Reed-Solomon (RS) FEC

  • Soft-Decision FEC (SD-FEC)

  • Low-Density Parity-Check (LDPC) Codes

  • Bose-Chaudhuri-Hocquenghem (BCH) Codes

  • Concatenated FEC

The choice of FEC algorithm depends on the specific requirements of the communication system:

  • Data Rate—High-speed systems require more efficient algorithms. This could be LDPC or turbo codes.
  • Error Characteristics—Burst errors are better handled by block codes such as Reed-Solomon.
  • Latency—Real-time applications such as video streaming require low-latency algorithms.
  • Power and Complexity—Systems with limited computational resources may use simpler codes like Hamming or BCH.

See the Hardware Compatibility Tool for the list of transceivers, their specifications, and the list of devices supported by the transceivers.

Key Characteristics

The following are the key characteristics of an 800G transceiver:

  • Form factor—Common form factors for 800G transceivers include OSFP and QSFP-DD. The OSFP and QSFP-DD transceiver modules are designed to accommodate the higher power and thermal requirements of 800 Gbps of data transmission. The OSFP form factor has larger dimensions than the QSFP-DD form factor. It allows transceivers with OSFP form factor to handle higher power dissipation and provide better cooling solutions.

  • Fiber type and reach—The fiber type specifies the type of optical fiber (singlemode or multimode) compatible with 800G transceivers. The reach provides the maximum supported distance or range for an optical transceiver. It helps you to select the appropriate optical transceiver for different applications, such as inter-data center, intra-data center and so on.

  • Lane distribution—Juniper's 800G optics uses eight parallel lanes, either with multiple fiber pairs or wavelength multiplexing. 800G optics has parallel fibers that are used over shorter distances. Wavelength multiplexing using duplex single-mode fiber is used for longer distance optical communication.

Juniper Optical Product Numbers

Juniper's optical components such as transceivers, cables, and connectors follow a naming convention. Each element in the product name corresponds to a specification. It helps you to better understand and select the appropriate optical component. For example:

  • QDD-2x400G-DR4

    • QDD—Short for QSFP-DD. It identifies the form-factor of the transceiver.

    • 2x400G—It indicates that the transceiver supports break-out into two independent 400G Ethernet interfaces for data transmission.

    • DR4—Stands for 400GBase-DR4. It is a specific standard and indicates that each 400G channel uses four parallel lanes of 100 Gbps to deliver 400 Gbps.

Note:

You can distinguish the Juniper optical cables from transceivers using their product numbers. For example, QDD-800G-AOC-5M and OSFP-800G-AOC-10M are product names for Juniper cables. The product names specify the form factor (OSFP or QSFP-DD), the data transmission speed (800 Gbps, 400 Gbps, and so on), the cable type (AOC or DAC) and distance range (5 meter, 10 meter, and so on) for each cable.

800G (X8) Transceiver Architecture

The 8x100 gigabit architecture for an 800G transceiver uses eight lanes of 100 Gbps each. The following are the different components of an 800G transceiver architecture:

  • Host platforms—Juniper devices that support 800G architecture.

  • 8x100G electrical—The electrical interface between the switch and the transceiver components. It can transmit data over eight separate 100 Gbps electrical lanes.

  • PAM4 clock data recovery (CDR)/digital signal processor (DSP)—A PAM4 CDR/DSP supports 100 Gbps electrical lanes. PAM4 effectively doubles the amount of data that you can transmit. The CDR is responsible for re-timing incoming data to reduce jitter. The DSP handles functions like equalization, error correction, and other signal processing tasks.

  • Driver x8—Drivers are electronic components that amplify the electrical signal. The x8 transceiver architecture has eight drivers. Each driver corresponds to a 100 Gbps electrical lanes.

  • Modulator x8—Eight modulators correspond to 100 Gbps electrical lanes (x8). 800G optics uses the following types of modulators:

    • Vertical cavity surface emitting Lasers (VCSEL)—VCSEL is used for multimode optics such as SR8/VR8.

    • Directly modulated lasers (DMLs)—DMLs are used for single-mode optics such as DR8. DMLs use distributed feedback (DFB) structures that incorporate a diffraction grating for stable direct modulation. Their modulation speed and transmission distance depend on the spectral line-width. A narrower line-width allows higher speeds and longer distances. In DMLs, data is modulated by adjusting the injection current on the laser diode, resulting in a compact design suitable for low-power applications.

    • Electro-absorption Modulated Laser (EMLs)—An EML integrates a laser diode with an electro-absorption modulator on a single chip. The laser operates continuously and the modulator turns the signal on and off.

    Unlike DMLs, EMLs maintain constant laser properties during modulation, offering advantages in higher speed and longer distance transmissions due to lower chromatic dispersion. EMLs are primarily used for speeds over 25 Gbps and distances of 10 kilometers to 40 kilometers in telecom applications.

  • 8x100G optical module—Optical interfaces that carry data in the form of light pulses. Each fiber in this model carries 100 Gbps of data.

  • Transimpedance amplifiers (TIA) x8—A TIA converts and amplifies the electrical current from the photodiode into an electrical voltage level. It can operate with very low signal levels that are typical for optical communication.

  • Photo-detector x8—It works in tandem with the TIA to convert the optical information back into electrical form.

An 8x100G architecture employs eight lanes to achieve a total data transmission rate of 800 Gbps. Each lane handles 100 Gbps.

Figure 2: 800G (X8) Transceiver Architecture Block diagram of 800G optical transceiver system: data flows from 800G switch through PAM4 CDR/DSP, Driver x8, Laser Modulator x8, Photo Detector x8, and TIA x8, handling 8x100G electrical inputs and outputs 8x100G optical signals.

Optical PMD in 800G Transceiver Architecture

Optical physical medium dependent (PMD) sublayer is a component of an optic fiber's physical layer. It is responsible for the physical transmission of data. PMD formats the data correctly, then transmits and receives it through the optical medium. The following are some of the optical PMD models:

Parallel Single-mode Fiber Optics and Parallel Multi-mode Fiber Optics

Parallel single-mode fiber optics uses multiple single-mode fibers to send separate data streams simultaneously. It supports high-speed transmissions over long distances. Parallel multi-mode fiber optics involves multiple multi-mode fibers for simultaneous data streams. It is ideal for high-speed connections over shorter distances due to the larger core size of the fibers. For more information on single-mode fiber (SMF) and multi-mode fiber (MMF) optic cables, see Active Optical Cable (AOC).

  • 1λ single-mode fiber (SMF) solution for 800G DR8 and 800G DR8-2—It is designed for a single wavelength (1λ), SMF solution. 1λ SMF indicates the use of a single wavelength for light propagation. That is, only one mode or one path in the optical fiber allows light propagation. These optics use a single-wavelength but eight parallel fiber pairs. 1λ SMF benefits data transmission by minimizing loss. Also, it enables transmission over longer distances with less signal loss than multimode fibers. The 800G DR8 or DR8-2 transceivers utilize eight-channel, direct-reach modules that are preferred in Tunable DWDM optics. See Figure 3. The 1λ SMF solutions for 800G DR8 and 800G DR8-2 from Juniper include OSFP-2X400G-DR4, QDD-2X400G-DR4-P, QDD-8X100G-FR1, and QDD-8X100G-LR1.

    Note: As per Juniper naming convention, DR8-2 refers to 8x100G-FR1.

  • 1λ multimode fiber (MMF) solution for 800G VR8 and 800G SR8—It is designed for a single-wavelength (1λ) operation in multimode, parallel fiber solutions with MPO-16 and 2xMPO-12 connectors. 1λ refers to the use of a single wavelength. That is, the architecture can handle only one wavelength for the propagation of light. The use of single wavelength allows data transmission with minimal loss. The SR8 transceiver employs eight channels in the Short Reach (SR) mode that offers high data rates over a shorter distance. The VR8 transceiver employs eight channels in the Very Short Reach (VR) mode, which offers high data rates over an even shorter distance compared to SR8. The 1λ MMF solutions for 800G VR8 from Juniper include OSFP-2X400G-VR4-P.

    Note: Juniper does not currently support 800G SR8 optics.
    Figure 3: 1λ SMF Solution: 800G DR8, SR8, and DR8-2 Block diagram of Switch ASIC with 800GAUI-8 interface showing data flow from OSFP connector pins RX1-RX8 and TX1-TX8 through 8x100G or dual 4x100G PAM4 CDR to optical modules, used in high-speed data systems. 1λ SMF Solution: 800G DR8, SR8, and DR8-2
    Note:

    Juniper's 800G optics use both OSFP and QSFP-DD form factors.

Duplex Single-mode Fiber Optics

  • 4λ SMF solution for 2xFR4—It is designed for a quad-wavelength (4λ) operation in SMF solutions. 4λ represents the usage of four differentiated wavelengths signaling four distinctive paths for light propagation. It can transfer more data per fiber pair and can breakout to 2x400G, with each 400G using duplex SMF fiber for transmission. It uses the four-level Pulse Amplitude Modulation (PAM4) technology.

    Figure 4: 4λ SMF Solution: 2xFR4 4λ SMF Solution: 2xFR4

  • 4λ SMF solution for FR4—It is designed for a quad-wavelength (4λ) operation in SMF solutions that employ duplex fiber connectors. 4λ represents the use of four varying wavelengths. Thereby, it indicates four distinct wavelengths for light propagation. Due to the multiplicity of wavelengths, it can handle larger volumes of data transmission with manageable loss. It uses the four-level Pulse Amplitude Modulation (PAM4) technology. Each wavelength uses 200G PAM4 modulation with a 4x200G optical input and output. The FR4-500 is suitable for medium-reach transmissions of 500 meters or less. The PAM4 design enables the architecture to effectively convert eight-channel transmission into four-channel transmission.

    Note: 4λ SMF solution for FR4 is currently not available from Juniper.
    Figure 5: 4λ SMF Solution: FR4 Block diagram of optical transceiver module architecture showing data flow from an 800GAUI-8 interface through a gearbox ASIC to optical receivers and transmitters. Includes 1:4 DEMUX, 4:1 MUX, and duplex fiber connector for 800G data rates using PAM4 modulation and wavelength division multiplexing.

  • 4λ SMF solution for LR4—It is designed for quad-wavelength (4λ) operation in single-mode fiber (SMF) systems that use duplex fiber connectors. The 4λ configuration involves four distinct wavelengths for light propagation, allowing it to handle larger volumes of data transmission with manageable loss. It utilizes four-level Pulse Amplitude Modulation (PAM4) technology, which enables the transmission of more data by encoding two bits per symbol. The LR4 is suitable for long-reach transmissions of up to 10 kilometers. The PAM4 design facilitates the architecture in effectively consolidating data transmission across four channels.

The duplex single-mode fiber optics from Juniper include QDD-2X400G-FR4, QDD-2X400G-FR4-P, QDD-2X400G-LR4-10, and QDD-2X400G-LR4-P.