In this section to learn about the physical layer of Ethernet, the IEEE802.3 standard gives the physical layer structure of the Ethernet, as indicated in the red box shown.
We can see that physics can be broadly divided into: gmii media independent interface, PCS physical coding sub-layer, PMA Physical media connection layer, PMD physical media related layer, MDI interface, Medium physical medium.
From the bottom up, we look at the physical media layer first.
1. Physical media layerHere the so-called physical media, our most common is our network cable, which is a kind of Ethernet transmission of physical media. Common physical media also have coaxial cable, fiber, and so on, and now basically no one with coaxial cables.
Look at the table below, where 10-100-1000 represents the speed of the Ethernet 10m-100m-1000m. The letter number after base indicates the type of the current media. The last few are gigabit network transmission media, Gigabit Ethernet can operate on the following four kinds of media: single-mode fiber (LX), the maximum connection distance of at least 5 km, multimode fiber (SX), the maximum connection distance of at least 550 meters, coaxial cable (CX), the maximum connection distance of at least 25 meters; Super Five class/six class line , the maximum connection distance is 100 meters.
10BASE2: IEEE 802.3 10mb/s Physical layer specification with fine coaxial cable interface (see IEEE 802.3 Clause 10.) |
10BASE5: IEEE 802.3 10mb/s Physical layer specification with coarse coaxial cable interface (see IEEE 802.3 Clause 8.) |
10base-f: IEEE 802.3 10mb/s Physical layer specification with fiber optic cable interface (see IEEE 802.3 Clause 15.) |
10BASE-T: IEEE 802.3 10mb/s Physical layer specifications with telephone twisted pair (see IEEE 802.3 Clause 14.) |
100BASE-FX: IEEE 802.3 100mb/s Physical layer specifications with two optical fibres (see IEEE 802.3 clauses and 26.) |
100BASE-T2: IEEE 802.3 physical Layer Specification (see IEEE 802.3 Clause 32) with two pairs of 3 lines or better balance cables. |
100BASE-T4: IEEE 802.3 four MB/S physical layer specification (see IEEE 802.3 Clause 23) for unshielded twisted pair 3, 4, and 5 lines. |
100BASE-TX: IEEE 802.3 5 MB/S physical layer specification with two pairs of unshielded twisted pair or shielded twisted pair (see IEEE 802.3 clauses and 25). |
1000base-cx:1000base-x interface specifications for transmission in a specially shielded cable (see IEEE 802.3 Clause 39.) |
The 1000base-lx:1000base-x is available in single-mode or multimode long-wavelength lasers (see IEEE 802.3 Clause 38.) |
The 1000base-sx:1000base-x uses the specifications of the multimode shortwave lasers (see IEEE 802.3 Clause 38.) |
1000BASE-T: four MB/s physical layer specification for five-pair balanced cables (see IEEE 802.3 Clause 40.) |
The
various specifications are mentioned here, in fact, each of the corresponding physical layer of the specification is not the same. Let's take a look at the physical layer of 1000base-x.
Here is the physical layer of the 1000base-t. You can see that 1000base-t's self-negotiation is not the same as the 1000base-x location.
2. MDI interface
MDI is the interface between the PHY chip and the physical medium, the RJ45 interface is common. Hundred gigabit Nets, MDI four lines, two pairs of differential signals, only with the RJ45 1,2,3,6 line,. Gigabit Network, MDI altogether 8 lines, four pairs of differential signals, with the RJ45 8 lines again RJ45 on the two lights-green: Long bright, indicating that the link is complete. Yellow light: Flashing, indicating that there is data sent and received.
3. PMD \pma\pcs LayerOriginally wanted to introduce the three layers, but finally gave up, because under different specifications, each layer is not the same, it is difficult to unify the introduction. The author also did not study in depth. Here is a brief description of the approximate functions of this three-time completion. PCS: Physically encoded sub-layers. The 8B/10B encoding is used for 1000base-x. For 1000BASE-T, the PAM5 encoding conversion method is used.
PMA: If you can see that the PMA layer mainly implements the serial and conversion. The PMD:PMD layer is primarily responsible for transferring the serial signal to the appropriate physical media. The following supplementary 4D-PAM5 encoding methods are explained:
In the communication network, the receiving end needs to recover the clock information from the received data to ensure synchronization, which requires the transmission of the line in the binary stream has enough to jump, that is, there can not be too many consecutive high or low level, otherwise unable to extract clock information. The 4B/5B encoding and MLT-3 encoding combination of the 100BASE-T Ethernet, the transmission code stream first 4B/5B encoding, then nrz-i, finally MLT-3 coding, and finally on the line transmission; 1000base-x in Gigabit Ethernet 8b/ The combination of 10B encoding and NRZ encoding, 64B/66B encoding for Gigabit Ethernet, and 128b/130b encoding for PCIE 3.0. In the final analysis, these codes are all designed to restore the clock from the data.
4. Self-negotiated auto_negotiation
Self-negotiation is generally done at the physical level. However, the specific physical media specification determines which layer of PHY is completed. The basic principle is to send the self-negotiated information through a series of pulses called the FLP. The characteristics of this series of pulses are as follows. The pulse is divided into clock pulse and data pulse, the data pulse clip in the middle of the clock pulse, the first pulse is a clock pulse, the data pulse is 1, no pulse is 0. A FLP pulse sequence contains 17 clock pulses and 16 data pulses. Clock pulses occur once per 125us.
The following is from Huawei's "Ethernet standards and physical layer, data link layer," which is mainly the hundred trillion network self-negotiation. The gigabit network is similar, equivalent to adding some bit definitions.
Fast connection pulse (FLP) information coding can be divided into two categories, one is the basic Connection code word (Basic page), support the exchange of basic information. The other is the next page number to support the exchange of additional information pages.
The information encoding of the basic page can be represented by.
Figure 1-1 The information encoding diagram for the basic page
Select Domain (Selector field)
S[0:4] is used to identify the type of self-negotiated message. The defined types are shown in the following table, and the meanings of all unlisted combinations are preserved, and the reserved encoding combinations should not currently be present in the transport.
Type meaning of self-negotiation
S4 |
S3 |
S2 |
S1 |
S0 |
Selector description |
0 |
0 |
0 |
0 |
0 |
Reserved for the future auto-negotiation development |
0 |
0 |
0 |
0 |
1 |
IEEE STD 802.3 |
0 |
0 |
0 |
1 |
0 |
IEEE STD 802.9 islan-16t |
1 |
1 |
1 |
1 |
1 |
Reseerved for the future auto-negotiation development |
Technical Competency field (Technology ability field)
A[0:7] is used to describe the various operating modes supported by this network interface. Different choice domain types correspond to different technical capability domain definitions. The following table gives the various technical capabilities and their codes defined under the IEEE 802.3 standard.
The meaning of the self-negotiated technical support domain.
Bit |
Technology |
Minimum Cabling Requirement |
A0 |
10base-t |
Two-pair Category 3 |
A1 |
10base-t Full DUPLEX |
Two-pair Category 3 |
A2 |
100base-tx |
Two-pair Category 5 |
A3 |
100BASE-TX Full DUPLEX |
Two-pair Category 5 |
A4 |
100base-t4 |
Four-pair Category 3 |
A[5:7] |
Reserved for Furure Technology |
|
5. Rgmii Interface
Here I mainly introduce the Rgmii interface. Because my development Board is this interface. RGMII (Reduced Gigabit media independent Interface) is a reduced GMII (a Gigabit media independent interface). The RGMII uses 4-bit data interface, working clock 125MHz,
and transmit data at the same time along the rising and falling edges ., so the transfer rate can be up to 1000Mbps. Typically used for communication between Mac and PHY. Transmitter:
- gtx_clk--Gigabit TX.. Clock of the signal (125MHZ)
- txd[3..0]--is sent data
- tx_ctl--Send Control
Note: At gigabit rates, the GTX_CLK signal is provided to the PHY, and the TXD, Txen, and txer signals are synchronized with this clock signal. Otherwise, at the 10/100m rate, the PHY provides a TXCLK clock signal, and the other signals are synchronized with the signal. The operating frequency is 25MHz (100M network) or 2.5MHz (10M network). Receiver:
- rx_clk--Receive clock frequency (extracted from received data, therefore not associated with GTXCLK)
- rxd[3..0]--receiving data
- rx_ctl--Receive control
- col--Conflict Detection (only for half-duplex state)
- crs--Carrier Monitoring
Manage configuration (Control and status information):
- mdc--Configuring Interface Clocks
- mdio--Configuring interface I/O
The Rgmii interface reduces a total of 8 data lines on TXD and rxd, relative to the Gmii interface. Rgmii timing such as
The physical layer of Ethernet
