Written by Craig Pasek, Product Manager

Transceiver Modules Group, Cisco


Enterprise networks are now being stressed by video conferencing and other demanding video applications that push beyond the speed limits of traditional 10G infrastructure.  Whether it’s IEEE802.11ax WiFi Access Points, that require 1G/2.5G/5G/10G backhaul interfaces or 1G/2.5G/5G/10G direct copper/fiber Ethernet to the desktop, new enterprises are being built for high speed that now requires 25G interfaces.

Using Cisco’s new enterprise Catalyst 9000 Family Switches and Cisco’s new SFP-10/25G-CSR-S transceivers, customers can connect Wiring Closet Switches to Aggregation Switches with 25G over MultiMode Fiber (MMF).

What is “CSR”?

“CSR” stands for Cisco Short Reach.  Using advanced optical technology, Cisco is able to provide 25Gbps bandwidth at distances up to 300/400m* over OM3/4 MMF. While providing these extended reaches, the new SFP-10/25G-CSR-S transceiver is fully interoperable with traditional IEEE 802.3by 25G transceivers that only provide 25Gbps at distances up to 70/100m over OM3/4 MMF.

Why is 300/400m over OM3/4 MMF important?

Traditional 10G networks are being built (or have been built) based upon IEEE802.3 specifications (10GBASE-SR) that allow 300/400m distances over OM3/4 MMF.   These distances are well established by network installers which has resulted in Wiring Closets being located up 300 (or 400m) from Computer Rooms/Data Centers.

Cisco’s new SFP-10/25G-CSR transceiver enables 25G over MMF at the same distance as 10GBASE-SR, which means that if the fiber infrastructure worked at 10G, it will also work with SFP-10/25G-CSR. This is not the case with IEEE 25GBASE-SR because its reach is shorter.


Interoperability with 10G

The new SFP-10/25G-CSR transceiver has dual rate capability that allows interoperability with both 25GBASE-SR and 10GBASE-SR MMF transceivers**. This allows the network to be incrementally upgraded at either the end of the fiber.

Interoperability with 40G and 100G

The new SFP-10/25G-CSR can also interoperate with 100GBASE-SR4 and 40GBASE-SR4 transceivers using 3rd party MMF breakout cables. For 100G interoperability, 25G requires the use of RS-FEC (Forward Error Correction), which is available on Cisco’s 100G ports.

*) depends upon fiber quality
**) may require 4dB attenuator


See this video for further information


Learn more about how Cisco’s 25G transceiver products are transforming the industry here.



Pat Chou

Product Manager

Service Provider - Transceiver Modules Group