QSFP-40G-SR-BiDi vs QSFP-40G-SR4, Which to Choose?
There are two common types of 40G QSFP+ multimode optical modules, SR4 and SR-BiDi. What are the differences between these two multimode optical modules? And how to choose and purchase them?
QSFP-40G-SR4 & QSFP-40G-SR-BD at a Glance
QSFP-40G-SR4 Overview
QSFP-40G-SR4 is a standard module, which comply with the QSFP+ MAS and 40GBase-SR4. It adopts MPO/MTP multimode fiber connectors and is usually connected by MPO-12 fiber jumpers. It has four fiber channels, with each channel having a transmission rate of 10Gbps, and it achieves a transmission rate of 40Gbps through a 4-transmit-4-receive mode.
When paired with OM3 multimode fibers, the transmission distance can reach 100 meters, and when paired with OM4 multimode fibers, the transmission distance can reach 150 meters.
QSFP-40G-SR-BD Overview
QSFP-40G-SR-BD It complies with the standards of QSFP+ MSA, is connected by duplex LC fiber jumpers, and its interface is of the LC type. There are only two channels, with each channel having a transmission rate of 20Gbps. It adopts the single-fiber bidirectional technology and utilizes WDM to simultaneously achieve bidirectional transmission on a single fiber, thus reaching a transmission rate of 40Gbps.
Usually, when used in combination with OM3 multimode fibers, the transmission distance can also reach about 100 meters, and when used with OM4 multimode fibers, the transmission distance can likewise reach about 150 meters.
QSFP-40G-SR4 vs QSFP-40G-SR-BD, What’s the Difference?
The Working Principle of QSFP-40G-SR4
The QSFP-40G-SR4 working principle and structure are relatively simple. It consists of 4 independent optical channels, and each channel has a transmission rate of 10Gbps. All of the 4 optical channels’ wavelength are the same, so each channel needs to occupy one optical fiber, usually a standard MPO-12 connector is used.
QSFP-40G-SR4 Function Diagram
The Working Principle of QSFP-40G-SR-BD
The QSFP-40G-SR-BD working principle and structure are relatively complex.
There are four electrical signal channels on the HOST side, with each channel having a transmission rate of 10Gbps. There are two single-fiber bidirectional optical channels on the line side, and the upstream and downstream rates of each channel are 20Gbps.
Inside the module, a Gearbox is used to synthesize the four 10Gbps electrical signals at the transmitting end into two 20Gbps electrical signals, and then respectively modulate the two 20Gbps electrical signals onto two different optical carriers and convert them into two 20Gbps optoelectronic signals.
On the optical path, the Wavelength Division Multiplexing (WDM) technology is used to couple two pairs of 20Gbps transmitting and receiving signals onto two bidirectional fiber channels for transmission respectively.
QSFP-40G-SR-BD Function Diagram
10G-40G Migration: QSFP-40G-SR4 or QSFP-40G-SR-BiDi?
Unstructured Cabling System
In an unstructured cabling system, devices are directly connected via fiber cables. The QSFP-40G-SR-BD uses LC multimode fibers, which is consistent with the cabling used by 10G SR.
This means that the QSFP-40G-SR-BD modules can reuse the existing cables when upgrading and migrating from 10G to 40G.
However, the QSFP-40G-SR4 uses MTP patch cords, which are incompatible with the 10G SR cabling. Therefore, it’s not easy to upgrade from 10G unstructured cabling to 40G if the QSFP -40G-SR4 modules are used.
Structured Cabling System
In structured cabling System, QSFP-40G-SR-BD can still directly use the cabling network of 10G SR to achieve a zero-cost upgrade. However, for QSFP-40G-SR4, it is necessary to replace the LC splitters at the ends of the structured cabling system with MTP splitters.
Summary
With the current rapid development trend of big data in the network, servers require higher data transmission rates. Most data centers have already upgraded from 10G to 40G.
The 40G BIDI QSFP+ optical modules contribute to the construction of 40G data center platforms. The short-distance transmission solution of the QSFP-40G-SR-BD optical module can reuse the existing 10G fiber infrastructure for 40G connections, greatly saving construction costs.
FAQ
What is a BiDi QSFP?
A BiDi QSFP module is designed to transmit and receive data in a bidirectional manner over a single fiber. It uses different wavelengths for transmitting and receiving.
What does BiDi mean in SFP?
BiDi uses WDM technology to achieve simultaneous bidirectional transmission within an optical channel over a single optical fiber. For example, it might transmit data at one wavelength (such as 1310 nm) and receive data at another wavelength (such as 1550 nm).
What is QSFP 100g/40g BiDi?
QSFP 100g/40g BiDi can adapt to 100Gbps or 40Gbps transmission rates automatically.
What is the difference between BiDi and full duplex?
BiDi means one fiber channel support bidirectional transmission, both transmitter and receiver signal are in the same fiber. Duplex has 2 optical channels, the transmitter and receiver channels are independent.
