What is parallel wiring？

Parallel Wiring is a cabling solution used in data centers and high-speed networks that employs multi-core optical fibers or multi-channel electrical interfaces to transmit data simultaneously. It contrasts with traditional serial wiring (dual-fiber single-channel) and significantly enhances single-port bandwidth through a “multi-lane parallel” approach.

Serial vs. Parallel: Core Differences

Serial is like a “dual fiber single channel”, while parallel is like an “8-24-lanes multi-fiber highway”.

Item	Serial wiring	Parallel wiring
Transmission method	Serial transmission of a single logical signal	Parallel transmission of multiple logical signals
Number of fiber cores per port	2-core (one transmit, one receive)	8-24 cores (receive more, transmit more)
Interface type	Duplex LC	MPO/MTP (multi-fiber push-onl connector)
Channel architecture	1 Channel	N channel (4/8/12/16)
Typical rate	10G, 25G, 100G (single channel)	40G, 100G, 200G, 400G, 800G
Port density	Lower (larger LC interface)	Extremely high (1U can accommodate 144+cores)
Power consumption	Higher (requiring optical module+fiber optic)	Lower (multi-channel shared circuit)
Typical Applications	Enterprise Network FTTH, Traditional data center	Ultra large scale data center, AI/HPC cluster

Why is parallel wiring necessary?

With the arrival of the 400G/800G era, the improvement of single channel speed is facing physical limits (copper wire loss, optoelectronic device bandwidth). Parallel cabling adopts mature 25G/50G VCSEL technology, which achieves bandwidth doubling by increasing the number of channels and reducing the single channel rate requirement. This not only simplifies the design of optical modules, but also avoids serious losses in high-speed signal transmission.

The bandwidth doubling is as follows:

• 400G: 8 × 50G PAM4 or 4 × 100G PAM4;
• 800G: 8 × 100G PAM4 or 16 × 50G PAM4

The core technology of parallel cabling

Parallel cable connector:MTP/MPO

The basis of parallel data cable is MPO/MTP multi-fiber push on connector, which accommodate multi-core optical fibers (4/8/12/16/24 cores) in one interface.

• MTP vs MPO: MTP is an improved version of MPO with better optical performance and mechanical accuracy, and the two are physically compatible.

Connector type	Fiber count	Typical application	Parallel channels
MPO-12	12 cores	40G/100G SR4	4Tx 4Rx (8fiber in use, 4 no use）
MPO-16	16cores	400G SR8/PSM8	8Tx 8Rx (16cores all use)
MPO-24	24cores	400G SR8( high density) / 800G	8Tx 8Rx or 16Tx 16Rx

There are several MPO/MTP parallel cabling products that Yingda can provide, including:

Parallel Structure

Parallel cabling relies on multi-channel parallel fiber channel transceivers, and common architectures include:

Structure	Channel qty	Typical rate	Optical module type	Interface
4×25G NRZ	4 channel	100G	QSFP28 SR4	MPO-12
4×50G PAM4	4 channel	200G/400G	QSFP56 FR4 / QSFP-DD FR4	Duplex LC
8×25G NRZ	8 channel	200G	QSFP-DD SR8（at the beginning）	MPO-16
8×50G PAM4	8 channel	400G	QSFP-DD SR8 / PSM8	MPO-16
16×50G PAM4	16 channel	800G	QSFP-DD SR16	MPO-24

The core advantage of parallel cabling

• Ultra high bandwidth density: A single MPO-24 interface can carry 800G (16 × 50G), far exceeding LC duplex solutions
• Save cabinet space: 1U space can accommodate 144 cores (6 x MPO-24), with a 300% increase in port density
• Reduce power consumption: Parallel modules share circuits, with power consumption lower than the sum of multiple serial modules
• Simplified deployment: Pre terminated MPO backbone cable, replacing 12 LC LC patch cords with one cable
• Flexible breakout: Supports 1/4 and 1/8 branches to protect investments

• Future oriented: 400G/800G/1.6T are all based on parallel architecture, with smooth evolution

Parallel cabling scheme

1. Classification by transmission medium

Type	Fiber type	Typical distance	Application scenarios
Parallel multi-mode wiring	OM3/OM4 multimode fiber	70-100 meters	Internal cabinet rooms and TOR Leaf interconnection in data centers
Parallel single-mode wiring	OS2 single-mode fiber	500 meters to 2 kilometers	Park interconnection, DCI short distance
Parallel Active Optical Cable (AOC)	Pre terminated multi-core optical cable	30-100 meters	Short distance, plug and play inside the cabinet

2. Classified by topological structure

Point to point switch direct connection:

In a 400G data center, parallel cabling is the standard solution for achieving high bandwidth and high-density interconnection, using 8/12/16 MPO/MTP patch cords , without breakout kit, simple and efficient, without branches:

• Spine Leaf interconnection: 400G SR8 + MPO 16 cable parallel wiring, single port bandwidth of 400G, transmission distance of 100 meters.
• TOR to Leaf uplink: 100G SR4 + MTP 12 cable parallel wiring, transmission distance of 100 meters.
• Leaf to Spine interconnection: 400G DR4/FR4 + MPO 12 fiber cable parallel wiring, with a transmission distance of 500 meters.

1 to 4 Breakout (most common): 400G → 4 x100G

400G DR4 fiber transceiver → MPO 12 to 4x LC duplex patch cords → 4 x 100G DR1 fiber transceiver

The most common wiring method is to split one 400G port and connect four 100G devices, which not only protects the existing 100G investment but also supports phased network upgrades.

1 to 8 Breakout: 400G → 8 × 25G

400G PSM8 fiber module → MPO 16 to 8 LC fanout cable → 8 × 25G SFP28 fiber module

400G to 8x25G is a commonly used branching scheme in the early days of 400G, with ultra-high density access. One 400G port can be split and connected to eight 25G devices. Note that 400G uses PAM4 modulation, with a single channel 100G rate, while 25G optical modules use NRZ modulation. Therefore, 400G optical modules should remember to use PAM4+NRZ standard chips with Gearbox function.

Challenges and Solutions of Parallel Wiring

Challenge	Solution
Polarity management is complex	Adopting Type B (crossover type) to standardize polarity and simplify inventory
High difficulty in cleaning the end face	MPO one click cleaner for 12/16 core end faces
Bending radius control	G. 657 anti bending fiber, minimum bending radius 7.5mm
Difficulty in troubleshooting	MPO dedicated OTDR, locate specific channels
relatively high cost	TCO lower than serial solution during batch deployment, saving wiring time

Conclusion

Parallel wiring is the cabling standard of the 400G/800G era in data centers – integrating MPO/MTP 8 to 16 fibers into one interface to achieve ultra-high bandwidth of single port 400G / 800G, with a density three times that of traditional LC solutions and an 80% increase in deployment efficiency.

At present, the single channel speed has been continuously upgraded from 25G, 50G, and 100G PAM4. The mainstream parallel solution for 400G uses MPO 24 or MPO 16 cores, while the 800G SR8 is commercially available. The higher density 800G/1.6T will use MPO-32. In the pursuit of lower power consumption, the number of CPOs (co packaged optics) that integrate optical engines with ASICs and eliminate DSP will gradually increase.

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