3 New Versions of Ethernet You Should Know About - EDA365电子工程师网

以太网路(Ethernet)是现今重要的网路技术之一，对现代人来说习以为常。从1973年创始至今，以太网路依然持续进化，未来仍有许多成长空间。根据Communique报导，最早的标准化以太网路是IEEE802.3，传输速度只有10MB/s，共有2种铜轴版本，后来还有未屏蔽双绞线(UTP)版本10BASE-T。其传输速度一路从10Mb/s，成长至100Mb/s、1Gb/s、10Gb/s。其中以UTP版本人气最高，但也有些特殊应用会使用光纤作为传输媒介。不过，随着以太网路的最高频宽发展到100Gb/s，10BASE-T，也就是每一代以太网路的频宽都比上一代增加10倍这条发展路线，现在已经难以为继。100Gb/s以太网路的传输速度对大多数应用来说，显得大材小用，且成本过于高昂，并没有真正广泛应用。

The firststandardized version of Ethernet was IEEE 802.3 and it had a speed of 10 Mb/s.There were two coax versions and a later unshielded twisted pair (UTP) version10BASE-T. Enhanced versions came along with decade increases in speed from 10Mb/s to 100 Mb/s next to 1 Gb/s and then 10 Gb/s. UTP versions are the mostpopular, but fiber versions are available. And today we have several 100 Gb/sfiber versions on the shelf. These decade speed increases were difficult toachieve. Often they were overkill and too expensive for some applications. Thefirst sign of this was the creation of a 40 Gb/s version that was lessexpensive with more range than the 100 Gb/s versions. That got the networkingcommunity thinking that decade advances were not always necessary for a widerange of applications. Lower cost was more often the rationale for interimspeed versions. As a result, we will soon be seeing some more intermediatespeed variants at 2.5/5, 25/50, and 400 Gb/s.

One of these is theso-called NBASE-T that uses speeds of 2.5 or 5 Gb/s. One of the main reasonsfor developing this version was the need to upgrade the widespread 1 Gb/s LANsso they could accommodate the extra speeds available in the new 802.11ac Wi-Fiaccess points (APs). This version of Wi-Fi can achieve speeds up to 6 Gb/sunder some conditions only to be limited by the APs Ethernet connection.

One obvious solution is toupgrade to the 10 Gb/s version. However, most of the installed Ethernet cablenetworks are Cat 5e or Cat 6, which do not support 10Gb/s to 100 m—not tomention the much higher equipment costs. Ten Gigabit Ethernet needs new Cat 6acabling and who wants to have to rewire the office or campus. Severalmanufacturers came along and defined a new version that uses the installedcabling to achieve 2.5 or 5 Gb/s.

NBASE-Tuses a new Ethernet PHY based upon heavy DSP. This new PHY usesauto-negotiation to select just the right speed and is even backward-compatiblewith 100 Mb/s and 1 Gb/s equipment. It is ideal for the new 11ac Wi-Fi APs andwill also benefit other applications in industry, video surveillance, and storage.

This newversion of Ethernet is supported by the 40-plus member companies of the NBASE-TAlliance. The IEEE now has a working group in progress to make this version aformal standard 802.3bz. Ratification is expected in September 2016. In themeantime, several companies like Cisco already have NICs and switches availablefor you early adopters.

基于成本考量，中等速度的NBASE-T已成为业界选择的发展方向，例如2.5Gb/s或5Gb/s版本的以太网路。这种频宽不是10倍数的以太网路标准之所以出现，主要是为了解决Wi-Fi无线基地台快速升级所造成的瓶颈问题。目前Wi-Fi标准已经发展到802.11ac，1台采用该标准的无线基地台(AP)，理论上最大通讯频宽可达6Gb/s，若以太网路仍停留在1Gb/s版本，将会构成传输瓶颈

造成NBASE-T标准崛起的另一个原因，则出在网路线上。目前最主流的网路线是Cat 5e与Cat 6，但这2种网路线都无法以10Gb/s的传输速率将资料传到100公尺远的地方，不符合以太网路的距离标准要求，因此业界才会发展出降速版本来应对。毕竟，更换网路线不仅麻烦，且会对用户造成额外的费用。

NBASE-T最主要的技术特性在于，其实体层(PHY)经过重新设计，使用了大量数位讯号处理(DSP)技术。这种实体层可支持自动协商(Auto Negotiation)，可自动判断其所连接的装置适用100Mb/s或1Gb/s频宽，并做出对应的调整。

目前国际电子电机工程师协会(IEEE)正在将NBASE-T制定为正式标准，2.5Gb/s与5Gb/s的标准将定名为802.3bz，预料标准出炉的时间将落在2016年9月。目前许多网通大厂都已经推出对应的硬体设备，例如思科(Cisco)。

Faster versions ofEthernet have made the standards far more complex and expensive. The 100 Gb/sversions are available now, but expensive, and are excessive for someapplications. That is why intermediate speed versions are getting attention.802.3by is the 25 Gb/s version under development. It is designed for datacenter interconnects between servers and switches. The goal is to createsingle-lane (wire, fiber, etc.) alternatives that are less expensive. Severalphysical layer versions are envisioned including a PCB backplane, copper twinaxial cable, and one for multimode fiber (MMF). While there is usually no needfor 100 meter versions in a data center, the standard includes thisalternative. A version with four twisted pairs is also an option. The finalstandard is estimated to be done by fall of 2016.

在10Gb/s到100Gb/s之间，IEEE另外制定了1个名为802.3by的标准，其频宽为25Gb/s。这项标准锁定的应用领域是资料中心，目标是在伺服器到交换设备之间，提供更低成本的网路连接选项。通常在资料中心里，资料传输距离不会高达100公尺，但IEEE仍将100公尺列为选择性标准。802.3by标准预计在2016年秋季出炉。

Yes, 400Gb/s. It had to happen. The leap of x10 from 100 Gb/s to One Terabit (1 Tb/s)is just too great. And with multiple parallel lane versions of 100 Gb/savailable as a base, it is doable. The 400 Gb/s standard effort is designated802.3bs. The development program centers around different variants usingmultiple parallel paths either separate fibers or separate wavelengths (λ) onone single mode fiber (SMF). Four 100 Gb/s lanes will do the job. Othervariations include eight 50 Gb/s lanes or 16 25 Gb/s lanes using NRZ. Otheroptions use PAM4 modulation that encodes two bits per symbol and cuts thenumber of lanes in half at those speeds.

There aremany variations under consideration and these will address the different rangeversion from PCB backplanes to 100 and 500 meters as well as 2, 10, and 40 km.Work on 802.3bs will probably run into 2017.

至于100Gb/s以上的以太网，虽然目前看来将是个肯定的市场，一口气将频宽从100Gb/s拉高到1Tb/s过于不切实际，恐重蹈100Gb/s的覆辙，因此IEEE还是决定未雨绸缪，先定义出400Gb/s版本的802.3bs标准。这个标准可能会等到2017年才制定完成。4条 100Gbps通道可以实现，其他的变种包括采用NRZ的8条50Gbs通道，或者16条16.25通道，也有采用PAM4的调制选项。