The Difference Between 40G CSR4 and ESR4

CSR4 and ESR4 modules are both abbreviations for QSFP 40G SR multimode optical modules , using an 850nm operating wavelength, MPO/MTP interface, and parallel 4-channel transmission (4 × 10G) through multimode fiber (MMF). Their core difference lies in transmitting data and some performance parameters.

Taking SFP+ 40GB optical modules as an example, QSFP 40G CSR4 and ESR4 are essentially “enhanced versions” of 40G SR4. They achieve longer transmission distances than standard SR4 (100-150 meters) by increasing transmission power and reception sensitivity. XSR4 is a customized version for extremely short distances within 50 meters.

Why do we need these type of SFP+ 40Gb module?

In large data centers, sometimes the distance between two racks exceeds 150 meters (the limit of SR4 under OM4), but it is not enough to use single mode QSFP+ LR4 (10km). At this moment:

• QSFP+ SR4: Too short to connect.
• QSFP+ LR4: Too expensive and requires the installation of single-mode fiber.
• 40G CSR4/ESR4: Optimal solution. Using existing multi-mode fiber optic cabling, it is easy to run 300-400 meters.

Below, we will take the most common 40G QSFP+optical module as an example for analysis.

Comparison Table of Core Parameters

Item	QSFP 40G SR4	QSFP 40G CSR4	QSFP 40G ESR4 / eSR4
Full name	Short Reach 4	Custom Short Reach 4	Extended Short Reach 4
Standard properties	IEEE International Standard	Manufacturer defined standards (non-standard extensions), commonly found in the general market and some second tier brands	Manufacturer defined standards (enhanced extensions), mainly promoted and used by Juniper
OM3 transmission distance	100 m	300 m	300 m
OM4 transmission distance	150 m	400 m	400 m
Transmitting optical power	normal range	Higher (enhanced laser)	Higher (high-performance laser)
Power consumption and heat generation	lower	moderate	slightly higher
Interface type	MPO-12	MPO-12	MPO-12
One quarter function	✅  support	✅  support	✅  support

Depth Detail Differences

QSFP 40G SR4 (Short Reach)

• Positioning: The most standard and basic multi-mode short-range optical module.
• Features: Strictly following the IEEE 802.3ba international standard, with the best compatibility and the cheapest price.
• Scenario: Fully meet the short distance interconnection between the same computer room, the same cabinet, or adjacent cabinets.

QSFP 40G CSR4 (Customize/Extended Short Reach)

• Positioning: The upgraded version of 40Gb SR4 belongs to the non-standard “long-distance multimode optical module”.
• Features: By improving the specifications of optical transceiver components (such as better lasers and more sensitive receivers), the transmission distance can be extended to 300m/400m without changing the existing high-density multimode fiber.
• Scenario: Suitable for interconnection scenarios in medium-sized data centers that span across data centers and floors, but do not want to spend high costs switching to single-mode fiber (LR4). It is designed to fill the huge distance gap between SR4 (150m) and LR4 (10km).  
• Compatibility: It is fully compatible with the standard SR4 at the physical level. That is to say, you can use a CSR4 module to dock with a regular SR4 module (but in this case, the maximum distance will be limited by the module with lower performance).

ESR4/eSR4 (Extended Short Reach)

Positioning: The performance and transmission distance of CSR4 are almost identical, both aimed at running further on multimode fiber (OM3/OM4).

Difference: This is mainly due to the naming conventions of different hardware manufacturers.

• Cisco and other manufacturers usually like to name this 300m/400m long-distance multi-mode module CSR4.
• Juniper, Arista, and some third-party module vendors are more accustomed to naming it ESR4 or eSR4.
• Note: Some manufacturers’ ESR4 also optimizes eye diagram and bit error rate (BER), supporting low latency transmission without enabling error correction code (FEC).

XSR4 (Extra Short Reach)

• Positioning: The ultra short distance concept proposed by certain specific manufacturers (such as certain customized high-density network devices).
• Features: Typically optimized for extreme cost and power consumption over extremely short distances within 50 meters (similar to the VR4 concept evolved in the 400G era).

Buying Advice

1. Within 100 m: Choose SR4 without thinking, with the lowest cost and highest degree of standardization.
2. Between 100 m and 400 m: If the wiring is already multimode fiber (OM3/OM4), please choose CSR4 or ESR4 according to your switch brand to avoid the high wiring cost of replacing single-mode fiber.
3. Hybrid compatibility: In actual deployment, CSR4 and ESR4 can usually interface with standard SR4 optical modules, but the transmission distance of the entire link will be limited to SR4’s short distance standard (i.e. 100m/150m)
4. If you are using Juniper equipment, you will usually see ESR4 when looking for the model number; If you are using other brands (such as Huawei, H3C, Cisco), look for CSR4. The two are almost interchangeable in terms of functionality. Your current wiring length is approximately within 300 meters, both of which are very reliable choices.

Yingda provides above types of SR multimode modules, compatible with various brands: Juniper, Finisar, Cisco, Hisense, Avago, Oclaro, Huawei, Ruijie, Mikrotik, HPE, DELL, Arista, Aruba, Intel, Netgear, Lumentum, etc. Contact us now for best quotation!