High Speed 25Gbps Connectivity

25 Gigabit Ethernet connecting needing higher density and lower power dissipation, which is still different in optical communications. Therefore, high speed data should be delivered effectively using a small and low-power package. In order to meet the growth of bandwidth in data center, 25G SFP28 takes great benefit for enterprises and system operators to get extraordinary network performance, this article will focus on high speed 25Gbps connectivity.

Introduction

25Gigabit Ethernet is a standard of Ethernet connectivity developed by IEEE 802.3 task force P802.3by in a data center environment, The main form factor of 25G is SFP28, The SFP28 standard depends on the mechanical specification of the 10G SFP+ (small form-factor pluggable) standard, and the electrical specification has been improved from a 10Gbps lane (running at 10.312Gbps) to a 28Gbps lane (25Gbps + error correction). 25G transceivers can be plugged into SFP+ sockets and 10G transceivers can be plugged into SFP28 sockets due to the same electrical and mechanical pin-out, but the associated host needs to provide the software support for the related devices.

25G types

25G types focus on 25G AOC Cables , 25G Copper DAC Cable as well as 25G SR transceivers.

25G AOC Cable

The 25G SFP28 AOC also provides a cost-effective solution for the same data center applications that require longer distances over 5 meters. Typically, AOCs are provided in standard lengths of 1 m, 2 m, 3 m, 5 m and 10 m. However, they are usually limited to around 25 meters due to inventory stock and idle storage issues.A data center is only connected to AOCs for consistency reasons, not a combination of AOCs and DACs.

25G DAC cable

The 25G SFP28 DAC cable is typically used in data center applications to provide the lowest cost fixed-length interconnect for TOR (top-of-rack) switches to connect to high-performance servers. Depending on bandwidth and distance, the DAC can be passive or active, usually based on a Twin-AX cable.

25G DACs can generally operate up to 5 meters without active components in the data path. There is not needed FEC (Forward Error Correction) if up to 2m. but FC-FEC (Fire Code Forward Error Correction) is needed for 3 meters, apart from them , RS-FEC (Reed Solomon Forward Error Correction) is needed to correct errors for 5 meters. Generally, at 25Gbps beyond 5 meters, active components are required in the data path to amplify and correct the signal. These components drive up cost which causes network designers to consider optical interfaces. 25G direct attach cables also exist which adapt a single QSFP28 format 100GbE port to four independent 25G SFP28 connections. Utoptical offers 25G SFP to SFP and QSFP breakout cables that comply with the associated IEEE specifications.

25GBASE-SR SFP28

25GBASE-SR SFP28 internal transmitter is a vertical cavity surface emitting laser (VCSEL, Vertical Cavity Surface Emitting Laser),which is used with standard OM3 or OM4 multimode fiber. Data centers require up 100 meters over OM4 fiber or 70 meters over OM3 fiber for interconnect between TOR switches and leaf or spine switches.

Summary

In these bandwidth-intensive applications, the choice of using 25G is clear. 25G devices are plugged into relative data centers, campus and service provider switches and routers to provide high speed 25Gbps connectivity. 25G Ethernet is more suitable for cloud data centers and network scale data center applications.

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