Survey on the LAN MCS Gap Analysis (LMGA)

Local Area Network (LAN, also known as Ethernet) is a network technology connecting computer systems through wired communication channels such as copper wires and fibre optical cables but with limited range not exceeding 40 kilometers. [8] The technology is mainly developed by IEEE 802.3 group and adopted into International Standards system through bilateral PSDO agreement with ISO. [9] Another local area network technology is connecting systems through emission of electromagnetic waves. It is called Wireless Local Area Network (WLAN) and is also mainly developed by IEEE and enters international standard through ISO.

Local Area Networks, in the beginning known as carrier sense multiple accesses with collision detection (CSMA/CD) access method and physical layer specifications was approved as an IEEE standard by the IEEE Standards Board in 1983 and subsequently published in 1985 as IEEE Std 802.3-1985. In 2012, the title of the standard was changed to Standard for Ethernet.

Communication speed is the major base to categorize IEEE LAN/Ethernet Standards. [10] The First version of LAN standard in 1985 had a 2.94 Mb/s data rate. IEEE Std 802.3u™ added 100 Mb/s operation (also called Fast Ethernet), IEEE Std 802.3z™ added 1000 Mb/s operation (also called Gigabit Ethernet), IEEE Std 802.3ae™ added 10 Gb/s operation (also called 10 Gigabit Ethernet), IEEE Std 802.3ah™ specified access network Ethernet (also called Ethernet in the First Mile) and IEEE Std 802.3ba added 40 Gb/s operation (also called 40 Gigabit Ethernet) and 100 Gb/s operation (also called 100 Gigabit Ethernet). [11] These major additions are all now included in and are superseded by IEEE Std 802.3-2022 and are not maintained as separate papers. Now, IEEE is working on Ethernet technologies capable of delivering 800 Gbps, 1 Tbps and beyond.

Comparing WLAN and LAN, there are some commonalities but also striking differences in the perspective of MCS Gap Analysis. The differences are summarized in the following table.

With these differences, a lot of MCS related questions need to be answered:

How the different application scenarios and conditions affect MCS systems in these two application fields?

Figure 1.

From the above brief summary, it shows a remarkable trend that over forty years since its start, the data rate of Ethernet has been increased from 10 Mb/s to over 400 Gb/s, which is 40,000 times.

Unlike Wireless LAN and Mobile Communications which transmits radio waves through the air, Ethernet transmits information signals through wired cables. Because of the physical, economic and other considerations in different application scenarios, Ethernet uses different cables and transmission protocols.

The evolution of Ethernet technology indicates that the increase of speed over the past three decades was primary due to the exploration of cabling technology like using different categories of twist pairs, using higher frequencies and optical transmission technologies.

However, due to physical constraints, cable transmission also has maximum performance limits. Has Ethernet reached those limits? How far is from the limits? These questions are relevant to MCS gap analysis.

In IEEE standard systems, there is no uniformed rule for the abbreviation of MCS. [12] It different standards it refers to different technologies.

In IEEE 802.16 for example, MCS is short form for “modulation and coding scheme”. In IEEE 802.11 WLAN standards, MCS is not included in the abbreviation list, but in the text it is clearly indicated that MCS refers to modulation and coding scheme.

In IEEE 802.3, MCS is not listed in the abbreviations tables. [13] In 802.3:2022, MCS is not used to define “Modulation and Coding Scheme”, but as “MAC Control Services”.

Figure 2.

To avoid confusion with modulation and coding scheme, whenever the abbreviation of MCS appears in Ethernet standards, the full term “MAC control service” is included.

It is therefore necessary to restate that in AG 4 produced paper and in our discussion on LAN MCS deficiencies, MCS has always been defined as the abbreviation of “Modulation and Coding Scheme.”

During the discussion on WLAN MCS deficiency before the founding of AG 4, there were questions about the MCS related descriptors such as HT, HE-MCS, VHT and UHT in IEEE 802.11 standards. [14] This issue does not arise in Ethernet standards because of the following factors:

Ethernet categorizes its technology into different speeds (throughput) such as 10M,100M, 10G, 100G, and 400G

IEEE 802.3 standard adopts a rate based classification system for its programs and standards. [15] In this system, from the titles of the groups, their missions and objectives are clearly indicated. The following list is from IEEE website:

Figure 3.

There are two major types of modulation schemes in IEEE Ethernet standards, PAM and QAM. [16] PAM modulation was the major scheme in LAN standards and QAM modulation is introduced into Ethernet only for about five years and in limited application scenarios. In efficiency, PAM modulation belongs to the lower end and QAM modulation is considered as the choice for higher order solutions.

PAM modulation and Ethernet are considered as a perfect match. Most forms of Ethernet use pulse amplitude modulation (PAM) constellations. In PAM signal modulation, information is encoded in the amplitude of a series of signal pulses. [17] The advantages of PAM include simplicity of receiver and transmitter design and easy transmission over a pair of wires.

The following table shows Ethernet PAM modulation types and application scenarios:

In IEEE Std 802.3™-2015, there was only one reference to QAM in 62.3.1 PMD Overview: “The bytes within the frame are encoded to a set of QAM constellation points that are used to modulate the carriers of the DMT symbol. [18] The time-domain symbol is cyclically extended and then windowed to reduce side lobe energy.” And, QAM was not even included in the abbreviation list.

On 22 Nov. 2016, IEEE approved 802.3bn- 2016 Physical Layer Specifications and Management Parameters for Ethernet Passive Optical Networks Protocol over Coax (EPoC ). The new amendment contains 169 references to QAM.

Three years later when IEEE released IEEE Std 802.3™-2018, QAM was cited 209 times. In IEEE Std 802.3™-2022, QAM was cited 202 times.

Because EPoC is the first IEEE Ethernet standard that adopts QAM modulation, the development time line is needed to indicate the exact time of QAM enters Ethernet.

Spectral Efficiency is one of the most important indicators of the capabilities of MCS system. [19] It affects the data rates (throughput) and bandwidth utility efficiency. In different application scenarios, however, the weight of Spectral Efficiency in the development of communication capacity varies.

IEEE Ethernet standard does not offer spectral efficiency tables for PAM modulation schemes. The following table is based on theoretical estimates:

This table reveals a fact that Ethernet PAM modulation has lower Spectral Efficiencies (SE) with highest SE not exceeding 4 bps/Hz.

Comparing the two major Ethernet modulation schemes, PAM modulation has much lower Spectral Efficiency rates, and QAM modulation can deliver several times higher Spectral Efficiency thus could significantly increase the capacity of Ethernet communication systems.

One observation is that in other applications fields, the evolution of MCS technology is through the path of FSK/PSK to QPSK, 16-QAM, 64- QAM, 256-QAM and 1024-QAM. [20] In

Ethernet, the evolution of MCS technology is from PAM, to PAM 4, PAM 5 and PAM 16 and then to M-QAM. However, not only older Ethernet protocols continue to rely on PAM technology, the newer groups such as IEEE P802.3dcw 400 Gb/s over DWDM systems, IEEE P802.3df 400 Gb/s and 800 Gb/s Ethernet, IEEE P802.3dj 200 Gb/s, 400 Gb/s, 800 Gb/s, and 1.6 Tb/s Ethernet all adopt PAM 4 as the modulation scheme.

The major reason for not adopting higher order QAM modulation in systems over 200Gb/s Ethernet standards are the complexity factor. [21] It is not clear how long this factor will remain a barrier since higher order modulation schemes such as 256-QAM and 1024-QAM have because state of the art MCS technology and Ethernet is adopting M-QAM since 2018. It is likely that Ethernet will follow the main-stream in higher order MCS applications.

During the pre-AG 4 discussions between August 2021 and July 2022 over the issue of WLAN MCS deficiency, the trend of higher and higher MCS power consumption was one of the major factors demonstrating the need for MCS Innovation.

In IEEE 802.3 Ethernet standard, the term Energy Efficiency (EE) was used instead of Power Efficiency (PE) .The purpose of Energy Efficiency is to lower power consumption of Ethernet systems, so the term of Energy Efficiency and Power Efficiency are interchangeable.

Look at the history of 802.3 Ethernet, it is noticeable that IEEE 802.3 standard is very dedicated to achieve Energy Efficiency for Ethernet motivated by the following factors:

Legislative pressure: legislative action worldwide is demanding improvements in energy efficiency of networked systems.

Green Ethernet is a common name for a set of features that is designed to be environmentally friendly, and to reduce the power consumption of a device. [22] The Green Ethernet feature can reduce overall power usage in the following ways:

Energy-Detect Mode: On an inactive link, the port moves into inactive mode, saving power while keeping the Administrative status of the port Up. Recovery from this mode to full operational mode is fast, transparent, and no frames are lost. This mode is supported on both GE and FE ports.

In addition to the above Green Ethernet features, the 802.3az Energy Efficient Ethernet is found on devices supporting GE ports. EEE reduces power consumption when there is no traffic on the port.

The differences between EEE and Green Ethernet are that the later is enabled on all devices whereas only Gigabyte ports are enabled. [23]. With EEE. [24] 802.3az EEE is designed to save power when there is no traffic on the link. And, in Green Ethernet, power is reduced when the port is down but when using 802.3az EEE, systems on both sides of the link can disable portions of their functionality and save power during periods of no traffic.

From MCS perspective, there are some observations:

The Green Energy and EEE are out of scope, just as the Target Wake Time (TWT) energy saving technology in WLAN. [25] The Ethernet power saving technologies such as disabling port LEDs when not needed are Port Management functions irrelevant with MCS operations.

In conventional MCS technology, the C means channel coding and usually refers to FEC coding system. [28] The deficiency of FEC coding has been discussed in 6N 17675 but a through analysis is needed to fully understand the issue and to provide guidelines for coding scheme innovation.

In Ethernet, there are three FEC coding systems used in different application scenarios. Coding gains, latency and complexity are the factors considered in Ethernet FEC coding selections.

LDPC has higher coding gain (only 0.66 dB gain) but higher latency and complexity.

MCS Coding deficiencies is a general and theoretical issue having impact over almost all ICT fields, LAN/Ethernet is no exception. AG 4 needs to have a special study on this topic. IEEE does not have a work plan to work on MCS Coding theory and innovation. There are coding related technical proposals but they are related to specific application scenarios.