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25G Bandwidth Drivers:
Dramatic advancements within video conferences have derived the bandwidth demands in current enterprise networks through systems like Cisco's Telepresence, including real-time implementations like Mixed Reality, Virtual Reality, and Augmented Reality. These have taxed traditional 10 Gigabit infrastructure's limits. We have built modern enterprise networks with equipment of excessive speed that now needs 25 Gigabit Ethernet interfaces. It does not matter if it is direct electrified equipment with fiber/copper ports that need 1 Gigabit/2.5 Gigabit/5 Gigabit/10 Gigabit backhaul interfaces or IEEE802.1 AX Wireless Access Points.
Cisco’s latest Small Form Factor Pluggable-10/25 Gigabit-LR-S optical transceiver enables SMF interconnection for Cisco’s recently developed programs with 25 Gigabit interfaces, involving the modern Catalyst 9500, 9400,9300, 9200’s, other modern switches, new NICs/servers, and new routers.
A Description of “LR”:
“LR” for SFP optical transceiver technology signifies Long Reach and traditionally represents a range of 10 kilometers. We have standardized the form factor 25G SFP, which we also call SFP28. The LR details are accessible in IEEEP802.3cc™-Amendment 11 2017: Management Parameters and Physical Layer for serial 25 Gigabits per second Ethernet Operation above SMF.
The 25G fiber optic transceiver is like a 10G optical transceiver because it utilizes an easy NRZ modulation. However, it has a high bandwidth receiver and transmitter for 25G communication. It also involves the CDR circuit for cleaning the signs. The 25G optical transceiver also needs the support of host ports to RS-FEC, which we don't require for 10G.
Cisco's recently developed 25G products involving the Catalyst switches 9500, 9400, 9300, and 9200's have developed ASIC that apply RS-FEC for 25 Gigabit communication. Therefore, the communication error rate can improve from a 5x10-5 BER to 1x10-12. We traditionally consider a 1x10-12 BER as "error-free" and associate it with different Ethernet rates wherein ULP (upper-layer protocols) can handle the infrequent communication error.
Intra-building and Inter-building Implementations for Small Form Factor Pluggable-10/25 Gigabit-LR:
We now use the 25 Gigabit-LR SMF optical transceivers for both intra-building and inter-building campus implementations to provide excessive speed connectivity.
Intra-Building Implementations:
We often use SMF to link the switches to distribution cables. Within these applications, architects and network builders are moving beyond the typical 300 meters above OM3 (and 400 meters above OM4) by utilizing SMF for great spans, which we find in huge airports, significant manufacturing buildings, and large shopping malls. With Cisco's Small Form Factor Pluggable-10/25 Gigabit-LR, networks connect at 25 Gigabit without any change in the SMF optical fiber infrastructure.
Inter-Building Implementations:
In extensive campus conditions, we use 25G to link from the distribution switches of the building to core switches in some other campus buildings. The connection of the core switches is typical to the supplier's core/metro network system with 40G/100G connections. However, those connections may also utilize 25 Gigabit LR technology. Due to the 25 Gigabit-LR's range of 10 kilometers, the optical transceiver gives an excellent cost-effective solution for relatively extensive campus conditions like hospitals, college campuses, business parks, and medical offices.
Movement from 10 to 25G:
The latest Small Form Factor Pluggable-10/25 Gigabit-LR optical transceiver possesses dual-rate capacity that facilitates interoperability with SMF-10 Gigabit-LR optical transceivers. Therefore, incrementally upgrades the network at both ends of the optical fiber. The following diagram depicts how we have replaced a distribution switch with a modern one equipped with the Small Form Factor Pluggable-10/25 Gigabits-LR. However, it still meets up with the old Catalyst 10G switch utilizing 10G. Then when we replace the wired closet switch with a modern 25 Gigabit Catalyst switch, its communication is through the distribution switches using 25 Gigabit without replacing the optical transceiver in the last end.
Interworking of 100G and 40G:
Under certain circumstances, a distribution switch can only possess Quad Small Form Factor Pluggable interfaces. The latest Small Form Factor Pluggable-10/25 Gigabit-LR interoperates with Cisco's Quad Small Form Factor Pluggable-100 Gigabit-PSM-S optical transceiver and Cisco's Quad Small Form Factor Pluggable-4x10 Gigabit-LR-S optical transceiver through fiber optic breakout cassettes or cables. Thereby links Quad Small Form Factor Pluggable ports with Small Form Factor Pluggable ports. The 25 Gigabit mode needs RS-FEC's use on each host, which is accessible on Cisco 25G and 100G ports.
