爱上100G 的10个理由

stupid · 发表于 2012-2-18 14:37

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Before I list the reasons to be excited by the prospect of implementing 100 Gigabit Ethernet and developing its components, let me lay out its essential aspects.

There are two topologies: 10×10 and 4×25; 10×10 has ten separate 10 Gb/s lanes and 4×25 has four at 25 Gb/s. By “10 Gb/s” and “25 Gb/s” I’m referring to the payload. The actual transmission rates are 10.3125 Gb/s and 25.78125 Gb/s, respectively – the excess accounts for the two bits of overhead per 64 bits of data in the 64B/66B encoding scheme.
In particular:

100GBASE-CR10 = 10 x 10 on shielded balanced copper cabling with reach up to 7 m.
100GBASE-SR10 = 10 x 10 on ten separate multimode fibers with reach up to 100 m.
100GBASE-LR4 = 4 x 25 multiplexed (WDM) on one single-mode fiber with reach of at least 10 km.
100GBASE-ER4 = 4 x 25 multiplexed (WDM) on one single-mode fiber with reach of at least 40 km.
As yet there is no backplane specification for 100 GbE, though there is for the 4×10 flavor of 40 GbE.

The electrical aspects of the physical layer specification leverage 10 GbE for each of the 10 Gb/s lanes but is cagey about the 25 Gb/s electrical signaling that will obviously be needed. Don’t worry though, until the 4×25 electrical signaling is specified you can leverage the Optical Internetworking Forum’s work on the common electrical i/o (OIF-CEI) — but feel free to tinker.

In any case, like other high speed serial (HSS) technologies, 100 GbE electrical channels use differential signaling with embedded clocks and de-emphasis is prescribed at the transmitter and equalization at the receiver. The parallel 100 GbE configurations are essentially independent HSS channels with all jitter advantages and clock recovery hassles included at no extra cost! In this sense, 100 GbE is nearly a complete superset of the hassles you face with the 2nd, 3rd, … generations of the other HSS technologies.

Here’s my top ten list of 100 GbE intriguing features:

9. Until the 4×25 electrical signaling is specified you have freedom to tinker and/or can leverage from the Optical Internetworking Forum’s work on the common electrical i/o (OIF-CEI)

8. The physical coding sublayer (PCS) “gearbox” shuffles the issue of interlane skew higher in the protocol stack, so we don’t have to worry about it at the physical layer.

7. Forward error correction (FEC) is optional (so far).

6. Most of the optical issues are well trod, but clever ways to multiplex signals onto single fibers, like DP-QPSK are emerging. Using quadrature phase shift keying with optical signals is one thing, but doubling the data rate by sending another pair of signals on the same fiber with different polarizations is genius.

5. New jargon for crosstalk! Victims will hereby be annoyed by disturbers rather than disturbed by aggressors.

4. Since each lane can use an independently recovered clock, there is no requirement that separate lanes be synchronized which will make diagnosing crosstalk problems considerably more interesting.

3. The integrated crosstalk noise (ICN) requirement combines limits on insertion loss (IL) and crosstalk noise in an ICN vs IL template – we love templates!

2. Flexible and delightfully complicated interference tolerance testing: two tests that probe the receiver’s ability to tolerate crosstalk in the presence of jitter. One with low crosstalk and maximum channel insertion loss, the other with maximum crosstalk and minimum insertion loss.

1. Transmitter de-emphasis amplifies high frequency signal content to compensate the low pass nature of the channels, but those big voltage swings will generate much worse crosstalk.

0. Equalization in the presence of crosstalk is rife with opportunity. While continuous time linear equalization (CTLE) and feed forward equalization (FFE) both amplify crosstalk noise, you can just smell different ways to equalize away crosstalk. They even give you a training sequence during initialization.

It’s rife, I tell you!

113788067 · 发表于 2012-2-20 22:32

强人啊·~~

ymz000 · 发表于 2012-3-19 18:30

呵呵英文的比较强大

pcbchat · 发表于 2012-4-16 14:37

全英文呢太难懂了

amnesia · 发表于 2012-4-21 12:04

嗯，真的假的啊？这么便宜

孔子不能解决的问题，老子帮你解决。12345fanli.com

eda_lxp · 发表于 2012-5-2 15:45

最好是有中文的，哎，看不太懂

stupid · 发表于 2012-8-7 13:46

The path beyond 100G
July 31, 2012
By Randy Eisenach, Fujitsu Network Communications

Carriers face ever-increasing needs for bandwidth and capacity in their metro, regional, and long-haul optical networks due to the demands of high-speed data services, Internet video services, data centers, and higher-bandwidth residential broadband connections. Until recently, most DWDM systems supported up to 88 channels with 10-Gbps data rates per channel. To provide additional network capacity, improved spectral efficiency, and lower cost per bit, the optical transport industry has been developing 100G technologies for the last 3–4 years.

A limited number of vendors introduced 100G transponders and muxponders, based on single-carrier dual-polarization quadrature phase-shift keying (DP-QPSK) modulation and coherent detection, in 2011. Carriers have started to deploy these 100G units for capacity-constrained routes and to support 100-Gigabit Ethernet private line services, a trend that will continue to grow over the next few years. One of the key benefits of 100G transponders and muxponders is the ability to expand existing WDM network capacity by 10X, eliminating the need for costly overbuild networks.

The optical industry now is shifting focus and R&D activities to enable even greater capacity. Some possible options include:
Increasing optical channel rates
Increasing the number of WDM channels
Adding parallel systems over additional fiber pairs
Combinations of the approaches above.
Each option has its own set of tradeoffs, which are being studied and evaluated. For example, increasing channel rates from 100G to 400G also incurs additional optical signal-to-noise ratio (OSNR) requirements, which can limit the overall optical reach of a signal, requiring additional regeneration nodes on long-haul routes. Adding parallel WDM systems over separate fiber pairs to increase capacity offers the benefit of using currently available technology and WDM platforms, but requires significant additional investment, as well as using additional fiber resources.

Carriers are likely to adopt many, if not all, of these approaches in one form or another. In the near term, capacity is being increased by using additional fiber pairs, as well as migrating to 100G interfaces. Future systems will use even higher speed, 400G optical interfaces.
400G – Capacity versus reach
With the introduction of 100G, the industry shifted from very simple modulation techniques (on/off keying) that transported a single bit of data, to much more advanced phase modulation techniques (DP-QPSK) capable of encoding and sending multiple bits at once. Along with coherent receivers, these more advanced modulation techniques enable much higher data rates and improved compensation for optical impairments such as chromatic dispersion, polarization mode dispersion, and optical loss.

The tradeoff with these advanced modulation techniques is they require higher OSNR. OSNR translates directly into the optical distances that can be achieved prior to a regeneration node. In other words, the more sophisticated and powerful the modulation, the shorter the optical reach. This tradeoff between modulation technique, channel size, and OSNR requirements is at the heart of current 400G research efforts.

Researchers are evaluating a number of advanced modulation schemes and channel sizes for use at 400G, as shown in Figure 1. In general, the higher order modulation techniques, such as 16QAM and 64QAM, encode more bits per symbol and can be squeezed into smaller channel sizes, but with the previously mentioned tradeoff of much higher OSNR requirements.

Figure 1. Advancements in optical interfaces, 1980–2015.

As vendors and the optical industry evaluate these different 400G modulation, channel size, and OSNR options, it will be critical to adopt a single, standardized approach. The industry achieved such a consensus at 100G for long-haul applications, working through the Optical Internetworking Forum (OIF). A similar approach to 400G OIF standardization will be needed to ensure a healthy, robust, component supply chain with wide choices and competitive pricing.

Spectral efficiency and subcarriers
While the OIF has not yet started such a standardization process, a number of vendors have active 400G research and development efforts underway. One likely candidate for 400G modulation will be DP-16QAM using two subcarriers to continue the progress that has been made in improving spectral efficiency.

Spectral efficiency is one measure of how efficient an optical interface or modulation scheme is at using the available fiber, and is measured in the number of bits transmitted per second per Hz of optical spectrum (bits/s/Hz). Existing 10G wavelengths use simple OOK for modulation and easily fit within the 50-GHz channel grid spacing, as shown in Figure 2. However, at 10G much of the 50-GHz channel is unused, resulting in relatively low spectral efficiency of only 0.2 bits/s/Hz. With 100G modulation techniques, 10X the data rate is transmitted in the same 50-GHz channel spacing, resulting in 2 bits/s/Hz spectral efficiency.

Figure 2. Capacity versus OSNR advancement modulation.

As mentioned before, efficient transmission of 400G will require the optimum combination of modulation format, channel size, and OSNR requirements. DP-16QAM with two subcarriers looks very promising in this context. Using subcarriers offers a number of key advantages. Subcarriers enable very high data rates to be divided and transported over any number of closely spaced, or slightly overlapping, subcarrier channels. The lower data rates on each subcarrier enable implementations that fit within existing component-level silicon technologies, one example being the high-speed analog-to-digital converters (ADCs) used in the coherent receivers. In addition, subcarrier channels can be spaced on existing 50-GHz grid channels to provide compatibility with existing WDM networks, or future flexible-grid spaced WDM systems.

DP-16QAM modulation using two subcarriers with a total of 87.5 GHz channel spacing is shown in Figure 3. The spectral efficiency of this approach is approximately 4.6 bits/s/Hz.

Figure 3. 10G and 100G spectral efficiency.

Summary
With 100G development efforts largely complete, the optical transport industry is evaluating modulation techniques, channel size, and OSNR requirements for 400G, with the goal of a single, industry-standard approach, working through the OIF. Although still early, one leading candidate is DP-16QAM using two subcarriers.

Randy Eisenach is a WDM product marketing manager at Fujitsu Network Communications, Inc.

晨曦123 · 发表于 2012-8-28 08:17

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