Ethernet Physical Layer protocol finishing (2)-Gigabit Ethernet

IEEE and 10GEA (Gigabit Ethernet Alliance) are the two most important organizations in Gigabit Ethernet standardization.
Gigabit Ethernet standards and specifications are many, in the standard, the first 2002 years of IEEE 802.3ae, and then continue to have a new Gigabit Ethernet specification, such as the 2006 IEEE 802.3an Standard (10GBASE-T) on the introduction of twisted-pair copper wire-based Gigabit Ethernet specification , the same IEEE 802.3aq standard introduced the 10gbase-lrm;2007-based IEEE 802.3AP standard for optical fiber, which introduced the 10GBASE-KX4 and 10GBASE-KR specifications based on copper wire. 1) IEEE 802.3AE Gigabit Ethernet Physical Layer Architecture

The IEEE 802.3AE Gigabit Ethernet standard mainly includes the following:
-compatible with the minimum and maximum Ethernet frame lengths defined in the 802.3 standard;
-Supports only full duplex mode;
-Lan with Point-to-point links and structured cabling to form a star-shaped physical structure;
-Supports 802.3AD link aggregation protocol;
-10Gbps speed on the Mac/pls service interface;
-Definition of two PHY (physical layer specification), LAN PHY and WAN PHY;
-Define an adaptation mechanism that corresponds to the data transfer rate of the MAC/PLS to the WAN PHY data transfer rate;
-Define physical layer specifications that support specific physical media-related interfaces (PMD), including Multimode and single-mode fibers, and corresponding transmission distances, support for the types of optical media defined in ISO/IEC 11801, and so on.
-With WAN interface (Wis:wan interface sublayer), Gigabit Ethernet can also be tuned to a lower transfer rate, such as 9.584640Gbps (oc-192c, 9953.280*260/270=9584.64), This allows the Gigabit Ethernet device to be compatible with the synchronous Optical Network (SONET) sts-192c transmission format.


In the Gigabit Ethernet technology, one of the more prominent is an interface called Xaui. Xaui borrowed the abbreviation for the original Ethernet add-on interface (Attachment unit interface,aui), and X is derived from 10 of the Roman numerals, representing the meaning of transmitting 10,000 megabits per second. Xaui is designed to be both an interface Extender and an interface. In fact, in the architecture is to refer to the following 10GB/S media Independent interface (Gigabit media independent interface,xgmii), can also be seen as an extension of the XGMII interface. The xgmii is an interface with 74 signal lines, of which 32 data lines are used for sending and receiving data. The xgmii can also be used as the MAC layer of Ethernet to complement PHY. Xaui can also be used to replace the Ethernet MAC layer with the PHY interconnect or as a xgmii extension, which is a typical application of xgmii. The XAUI is developed directly from the 1000base-x PHY in the Gigabit Ethernet standard and has a serial bus with its own clock. The Xaui interface is 2.5 times times the rate of 1000base-x. The 4 serial channels ensure that the data throughput supported by the Xaui interface of the Gigabit Ethernet is 10 times times that of Gigabit Ethernet.

Specifications published in the IEEE 802.3ae standard it includes 10gbase-r (including the 10GBASE-SR, 10GBASE-LR, and 10gbase-er three specifications), 10gbase-w (including 10GBASE-SW, 10GBASE-LW and 10gbase-ew three specifications), 10gbase-x (including 10GBASE-LX4 specifications only) three physical interface standards.

In the architecture of the 10gbase-x sub-series, the physical layer structure is similar to that of Gigabit Ethernet, except that the interface between the PCS sub-layer and the RS sub-layer is changed from the original gmii to the Xgmii, which is the Xaui mentioned earlier. The 10gbase-x uses a special compact package that contains 1 simpler WWDM (Wide wavelength Division) devices, 4 receivers, and 4 lasers working at approximately 25nm intervals around 1300nm wavelengths, using 8B /10B encoding, each pair of transmitters/receivers work at 3.125gbit/s speed (data flow speed of 2.5gbit/s).

And in the 10gbase-r sub-series of the three specifications of the physical layer, in addition to the above interface for Xgmii, there is a difference is the PCS sub-layer encoding from the original 8b/10b changed to 64b/66b. The data stream is 10.000gbit/s, resulting in a clock rate of 10.3125gbit/s.

In the three specifications of the 10gbase-w sub-series, the relative change in the physical layer of the Gigabit Ethernet is greater, in addition to two changes in the 10gbase-r sub-series, a new sub-layer is added between the PCS sub-layer and the PMA sub-layer--wis (WAN Interface sublayer) child layer. With WIS, Gigabit Ethernet can also be tuned to a lower transfer rate with a clock of 9.953gbit/s and a data stream of 9.584640gbit/s, which allows the Gigabit Ethernet device to be compatible with the synchronous Optical Network (SONET) sts-192c transmission format.

10G Ethernet LAN and 10G Ethernet wide Area network (with oc-192c) physical layer of different rates, 10G Ethernet LAN Data rate is 10GBIT/S, and 10G Ethernet WAN Data rate is 9.58464gbit/s, but the two rates of physical layer shared a MAC layer, The MAC layer has a working rate of 10gbit/s.
The problem that 10G Ethernet WAN needs to be solved is to reduce the 10gbit/s transfer rate of 10GMII interface to match the transfer rate 9.58464gbit/s of the physical layer with the adjustment strategy.
At present, there are 3 adjustment strategies for 10gbit/s rate adaptation to 9.58464gbit/s oc-192c:
-A hold signal is sent at the Gmii interface, and the MAC layer stops sending at a clock cycle;
-Using "Busy idle", the physical layer sends "Busy idle" to the MAC layer during IPG, and when the MAC layer receives it, it pauses sending the data. The physical layer sends "Normal idle" to the MAC layer during IPG, and after the MAC layer receives, resend the data;
-Use the IPG extension mechanism: Mac frames are passed one frame at a time, dynamically adjusting IPG intervals based on the average data rate2) LAN Gigabit Ethernet based on fiber

For the time being, the fiber-based Gigabit Ethernet specification for LAN is: 10GBASE-SR, 10GBASE-LR, 10gbase-lrm, 10gbase-er, 10GBASE-ZR, and 10gbase-lx4 six specifications. 2.1) 10GBASE-SR

The "SR" in 10GBASE-SR stands for "short Reach", which supports a short-wave (850nm wavelength) multimode fiber (MMF) encoded in 64b/66b with an effective transmission distance of 2~300m, To support 300m transmission requires an optimized 50μm wire diameter OM3 (Optimized multimode 3, optimized multimode 3) fiber (no optimized wire diameter 50μm fiber is called OM2 fiber, and the wire diameter of the 62.5μm fiber is called OM1 fiber). The 10GBASE-SR has the advantages of lowest cost, lowest power consumption and minimal fiber modules. 2.2) 10GBASE-LR

The "LR" in 10GBASE-LR represents the meaning of long Reach, which supports 64b/66b (1310nm) Single mode optical fiber (SMF), which is encoded in the form of an effective transmission distance of 2m to 10km, in fact up to 25km. The 10GBASE-LR fiber modules are cheaper than the 10GBASE-LX4 fiber modules that will be described below. 2.3) 10gbase-er

The "ER" in the 10gbase-er means "ultra long Distance" (Extended Reach), which supports the ultra high-wave (1550nm) single-mode optical fiber (SMF) with a valid transmission distance of 2m to 40km. 2.4) 10gbase-lx4

10GBASE-LX4 uses wavelength division multiplexing (WDM) technology to achieve 10GB/S transmission through the use of 4-channel wavelengths of 1300 nm, which work in 3.125gb/s separate light sources. The effective transmission distance of the specification in Multimode fiber is 2~300m, and the effective transmission distance under single mode fiber is up to 10km. It is primarily suitable for environments where multimode and singlemode fibers are supported simultaneously in a single fiber module. Because the 10GBASE-LX4 standard uses 4-channel laser light source, so in the cost, fiber optic line diameter and power cost more than 10GBASE-LRM specifications have shortcomings. 2.5) 10gbase-lrm

Prior to 10GBASE-LRM, there were two 10GE ports that supported multimode fibers, namely 10GBASE-SR and 10gbase-lx4. Why IEEE 802.3aq creates another multimode fibre port type 10GBASE-LRM.
Only the new high-bandwidth OM3 (UM core) multimode fiber is installed, and the 10GBASE-SR can support distances of up to 300 meters. On commonly installed multimode fiber OM1 (62µm fiber cores) and OM2 (50µm cores) with low bandwidth, 10GBASE-SR can only be used for inter-device interconnection in the room. 10GBASE-LX4 is an expensive wavelength-division multiplexing solution.
The installation of OM1 and OM2 fibers is large and growing, and it requires a truly economical 10G Ethernet solution.
The "LRM" in 10GBASE-LRM stands for "Long Reach multimode", which corresponds to the IEEE 802.3aq published in 2006. Wavelength 1300 nm, the effective transmission distance in the FDDI network and 100BASE-FX network of FDDI 62.5μm multimode fiber installed before 1990 is 220m, while in OM3 fiber can reach 260m, in connection length, it is inferior to the previous 10GBASE-LX4 specification, But its fiber-optic module has lower cost and lower power consumption than the 10GBASE-LX4 specification. 2.6) 10GBASE-ZR

Several manufacturers proposed the transmission distance can reach 80km ultra long Distance module interface, this is the 10GBASE-ZR specification. It also uses an ultra-long-wave (1550nm) Single-mode fiber (SMF). However, the 80km physical layer is not within the Eee 802.3ae Standard, is the manufacturer's own description in the oc-192/stm-64 sdh/sonet specification, and will not be accepted by the IEEE 802.3 working Group. 3) LAN Gigabit Ethernet based on twisted pair (or copper wire)

including 10gbase-cx4, 10gbase-kx4, 10gbase-kr, 10gbase-t. 3.1) 10gbase-cx4

IEEE 802.3ak proposed the 10GBASE-CX4 on coaxial copper cable to achieve Gigabit Ethernet transmission, was approved in March 2004, but the transmission distance is limited to 15 meters. The 10gbase-cx4 uses the Xaui (Gigabit add-on interface) defined in 802.3ae and the 4X connector in the InfiniBand, which is referred to as the "CX4 copper cable" (in fact, a shielded twisted pair). Instead of transmitting gigabit data using a single copper link, the 10GBASE-CX4 specification uses 4 transmitters and 4 receivers to transmit the gigabit data and operate on a coaxial cable in a differential manner, each with a 8B/10B encoding that transmits at 3.125GHz baud rate per channel 2.5gb/ S of data. This requires 4 pairs of differential cables in each direction for a total of 8 dual coaxial channels in each cable group. In addition, unlike the Class 5, Super 5 twisted pair that can be terminated in the field, the CX4 cable needs to be terminated at the factory, so the customer must specify the cable length. The longer the cable, the greater the general diameter. The main advantages of 10gbase-cx4 are low power consumption, low cost, low response time delay, but the interface module is larger than spf+. 3.2) 10gbase-kx4/10gbase-kr

10gbase-kx4 and 10gbase-kr correspond to the IEEE 802.3AP Standard, which was released in 2007. They are primarily used for backplane applications such as cluster line cards for blade servers, routers, and switches, so they are also referred to as "Backplane Ethernet".
The gigabit Backplane is now available in parallel and serial versions of two. The parallel version (10GBASE-KX4 specification) is the universal design of the backplane, which splits the Wan Shaoxin number into 4 channels (similar to Xaui), 10gbase-kx4 using the same physical layer encoding as the 10GBASE-CX4 specification, and the bandwidth of each channel is 3.125gb/s. In the serial version (10GBASE-KR specification) only one channel is defined, using the same physical layer encoding as the 10GBASE-LR/ER/SR three specification-64/66b encoding method for 10gb/s high-speed transmission. In the 10GBASE-KR specification, in order to prevent the signal from decay at a higher frequency level, the backplane itself needs higher performance and can maintain the quality of the signal over a larger frequency range. 3.3) 10gbase-t

10GBASE-T corresponds to the IEEE 802.3an standard published in 2006, and the goal of 10GBASE-T is to:
-10-bit error rate (BER);
-Data transmission speed of 100 meters long F-Class cabling (Class 7) up to million megabits per second;
-Data transfer speed of 55 to 100 meters long E-Class cabling (class 6) reaches million megabits per second. The new CAT6A can reach a transmission distance of 100 meters, and the main differences between the 6a class and Class 6 include: The 6a class will extend beyond the 500MHz frequency, and 6 classes may stop at 250MHz.

10GBASE-T uses the 1000BASE-T transmission mode, still adopts four differential pair simultaneous bidirectional transmission, full duplex, but the total transmission rate of up to 10Gbps, the rate of each pair of lines up to 2.5Gbps. In terms of coding, instead of using the original 1000base-t PAM-5, the PAM-16 encoding method is adopted.

Let's review the PAM5 (5-stage pulse modulation) modulation technique used by 1000base-t. In PAM5 mode, the transmitted signals in the media are no longer simple 0 and 1, but are divided into 5 levels ( -2,-1,0,1,2). This is divided into 5 levels of level signal called the code element, 1 code elements can carry a number of bits of information depending on the characteristics of the code element and encoding method. For example PAM5, each PAM5 code element carries a maximum of 2.32 bit (22.32=5), taking into account the efficiency of the coding and the need for error correcting code and synchronization code, so the final 1000base-t each code element carries 2 bit of information.
According to the Nyquist criterion, the highest code transfer rate =2* bandwidth under the ideal low communication channel, we know that the 1000base-t is 125m/seconds, so at least 62.5Mhz of transmission bandwidth is required.

If the 1000BASE-T technology is used, the 10GBASE-T transmission rate is 1250m/seconds, and the minimum transmission bandwidth of the system is 625MHz. This is a high demand for the performance of the transmission system.
But if the performance of the code element, so that a code element to carry more bits, reduce the system's minimum bandwidth, the need for a powerful processor codec processing, which means that the cost increases, this is a pair of contradictions. Finally through the balance of performance and cost, 10GBASE-T uses the PAM16 technology (16-stage pulse amplitude modulation, using -15,-13,-11,-9,-7,-5,-3,-1,1,3,5,7,9,11,13,15), PAM16 modulation, Pulse voltage amplitude is divided into 16 levels, so that each voltage amplitude (called "Symbol") can represent 4 bits of information, where 3.125bit is valid data, the other 0.875 bits for auxiliary and calibration. Of course, both 3.125 and 0.875 are averages. 800M per second of the code element rate, the minimum bandwidth requirements of 400Mhz.

In order for the PAM16 to safely transmit 10Gbps (ber=10-12), it is necessary to set certain encoding rules. In order to improve BER, but also to add a check code for forward error correction, 10gbase-t used LDPC code (low density parity check code) is a linear block code, with superior error correction performance and great practical value, is considered to be the best performance error correction code. The performance of LDPC code can approximate Shannon limit, and this approximation is realized in the less high decoding complexity, the hardware is simple, the same balance of performance and cost.
During the 10GBASE-T encoding process. Each of the 64 bit information, plus the control/data flag bits constitute a 65bit block (block), 50 blocks into a group (groups), each with a 8bit CRC check code. Generate a total of 65*50+8=3258 bit, and then attach the last channel add-on code is 3,259 bit altogether.
3,259 bits are divided into 2 parts, 3*512bit (including the Channel additional code) through the unprotected way, the other 1723 bit plus 325 check code, through the LDPC (1723,2048) protection mode transmission, so that 512 128DSQ codes are required (3*512+4 *512), which is 1024 PAM16 symbols. Ultimately equivalent to 3.125 bit information per PAM16 (64*50/1024=3.125)
Transfer rate =3.125*800m*4=10g BP4) Fiber-based WAN Gigabit Ethernet

The 10GBASE-SW, 10GBASE-LW, 10gbase-ew, and 10GBASE-ZW specifications are all physical layer specifications applied to the WAN, and are designed to work in oc-192/stm-64 sdh/sonet environments, using lightweight sdh/sonet frames, The run rate is 9.953gb/s.
The types of fibers they use and the effective transmission distances correspond to the 10GBASE-SR, 10GBASE-LR, 10gbase-er, and 10GBASE-ZR specifications described previously.
The 10GBASE-LX4 and 10GBASE-CX4 specifications do not have a WAN physical layer, since the previous SONET/SDH standards are all working in serial mode, while the 10GBASE-LX4 and 10GBASE-CX4 specifications use parallel transmission. 5) Gigabit Ethernet Specification Comparison

Million Gigabit Ethernet Specification	The transport media used	Effective distance	Application areas
10gbase-sr	850nm Multi-mode fiber	300m	Lan
10gbase-lr	1310nm Single Mode fiber	10km
10gbase-er	1550nm Single Mode fiber	40km
10gbase-zr	1550nm Single Mode fiber	80km
10gbase-lrm	1310nm Multi-mode fiber	260m
10gbase-lx4	1300nm Single Mode or multimode fiber	300m (multimode), 10km (Single mode)
10gbase-cx4	Shielded twisted pair Cable	15 m
10gbase-t	Class 6, 6a twisted pair	55m (when Class 6), 100m (When 6a class line)
10gbase-kx4	Copper wire (Parallel interface)	1m	Back-panel Ethernet
10gbase-kr	Copper wire (Serial interface)	1m
10gbase-sw	850nm Multi-mode fiber	300m	Sdh/sonet Wan
10gbase-lw	1310nm Single Mode fiber	10km
10gbase-ew	1550nm Single Mode fiber	40km
10gbase-zw	1550nm Single Mode fiber	80km