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Preface

Datacenters are in constant expansion, requiring ever higher capacity and bandwidth. To meet the increasing demand, datacenters are migrating to 25G ethernet technology by installing 25G optical transceivers, AOCs (Active Optical Cables) and DACs (Direct Attached Cables) in their infrastructure.

A 25G transceiver is commonly called SFP28 and is an enhanced version of the well-known 10G SFP+. The SFP28 is physically identical to the SFP+ but with electrical interface upgraded to support 25G data rates. If the SFP+ is coming in plenty of variants, the SFP28 comes with only a few like SR, LR and bidi. Of course, the number of variants is now increasing with the increasing number of deployed 25G ports.

Datacenter Application

25G SFP28 are today mainly used in Top-Of-Rack (TOR) configuration. Indeed, the 25G SFP28 offers a smooth migration from 10G to 25G using existing fiber installations for people working with 1/10G or 10/25G servers.

Figure 1: Datacenter Application

Enterprise Application

The increase of video conferencing and business applications being so fast, the enterprises have no choice but to upgrade their backbone networks from standard 10G to higher data rates. Being compatible with their legacy 10G equipment, the 25G SFP28 transceivers are the best solution to increase bandwidth allowing enterprises to use the existing infrastructure and save money.

Figure 2: Enterprise Application

Mobile Application

  • Classical” backhaul
Figure 3: Mobile Backhaul Application
  • Centralized RAN and fronthaul

Mobile Fronthaul allows for network cost reductions by moving power consumption from the towers. Co-location of BBUs saves power as capacity can be reallocated depending on traffic load. Latency is reduced as switching and routing functions are moved from the towers deeper into the network.

The connection between centralized BBUs and cell sites (≥ 20km*) can be either based on CPRI or eCPRI protocols.

The links (one per sector and carrier) can be either TDM (dual fibre), BiDi (single fibre) or xWDM. Data rates up to 25G (25GE or CPRI option 10) are envisioned. Connections at 50G are being considered in Asia.

* Limited by roundtrip latency

Figure 3: Mobile Fronthaul Application

Standards

With new technology comes new standards, the below are the current IEEE standards in place or considered for 25GBASE SFP28 transceivers

SR (802.3bm-2015) LR (802.3cc-2017) ER (802.3cc-2017)
Media / Configuration MM /Dual SM / Dual SM / Dual
Reach £ 100m* £ 10km* £ 40km*
Fiber Count 2 2 2
Optical Lanes 1 (850nm) 1 (1310nm) 1 (1310nm)
Data Rate per Lane/ Modulation 25Gbps/NRZ 25Gbps/NRZ 25Gbps/ NRZ

 

BR-10 (P802.3cp) BR-20 (P802.3cp) BR-40 (P802.3cp) BR-40+ (P802.3cp)
Media / Configuration SM/Single SM/Single SM/Single SM/Single
Reach £ 10km* £ 20km* £ 40km* £ 40+km*
Fiber Count 1 1 1 1
Optical Lanes 1 (1270/1330nm) 1 (1288/1314nm) 1 (1288/1314nm) 1 (1288/1314nm)
Data Rate per Lane/ Modulation 25Gbps/NRZ 25Gbps/NRZ 25Gbps/ NRZ 25Gbps/NRZ

* FEC (Forward Error Connection) is mandatory

 

 

Skylane portfolio

Skylane PN Standard Reach Power Class & Consumption Wavelengths Laser Type Application
DAPSSMxx2500 25GBASE (DAC) ≤ 3m Low N/A N/A DataCenter
DAOSSMxx250D 25GBASE (AOC) ≤ 100m 1W, Class I, per terminal 850nm VCSEL DataCenter
S2885P102R2F 25GBASE-SR/ 10GBASE-SR* 100m 1W, Class I 850nm VCSEL Mobile FH, DataCenter
S2885P10252F 25GBASE-SR 100m 1W, Class I 850nm VCSEL Mobile FH, DataCenter
S28130102R2F 25GBASE-LR/ 10GBASE-LR* 10km 1.5W, Class II 1310nm DML Mobile FH, DataCenter
S2813010252F 25GBASE-LR 10km 1.5W, Class II 1310nm DML Mobile FH, DataCenter
S28130202R2F 25GBASE/10GBASE 20km 1.2W, Class II 1310nm DML Mobile FH
S28130402R2F 25GBASE-ER/ 10GBASE-ER* 40km 1.8W, Class III 1310nm DML Mobile FH
S2885P10320C 32GFC (SWL) 100m 1W, Class I 850nm VCSEL SAN
S2813010320C 32GFC (LWL) 10km 1.5W, Class II 1310nm DML SAN
S2B[23,32]0102R2F 25GBASE/10GBASE* 10km 1.5W, Class II 1270nm/1330nm DML Mobile FH
S2B[23,32]0202R2F 25GBASE/10GBASE* 20km 1.5W, Class II 1270nm/1330nm DML Mobile FH
S2B[71,17]0402R2F 25GBASE/10GBASE* 40km 1.8W, Class III 1270nm/1310nm DML Mobile FH
S2Cxx0102R2C (xx = 27 to 37) 25GBASE/10GBASE* 10km 1.5W, Class II 6 channels DML Mobile FH
S2Cxx0202R2C (xx = 27 to 37) 25GBASE/10GBASE* 20km 1.5W, Class II 6 channels DML Mobile FH
S2Dxx010252C  (xx = 17 to 61) 25GBASE/10GBASE* 10km 2W, Class III 44 channels EML Mobile FH

*Rate Select (10G/25G) SFP28 transceivers can be deployed in a 10G environment, which later can be upgraded to 25G without changing the optics. Cisco NCS5500 and Cat9500 are examples of hosts supporting 10G/25G operation. Single rate (25G) versions are also available in Skylane portfolio in case where 10G operation is not required.

 

Sources:

  • Finisar: Latest Trends in Data Center Optics
  • Fiber Optical Networking: 25g-sfp28-transceivers-applications

 

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