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NE40E-M2 V800R010C10SPC500 Feature Description - LAN Access and MAN Access 01

This is NE40E-M2 V800R010C10SPC500 Feature Description - LAN Access and MAN Access
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Huawei uses machine translation combined with human proofreading to translate this document to different languages in order to help you better understand the content of this document. Note: Even the most advanced machine translation cannot match the quality of professional translators. Huawei shall not bear any responsibility for translation accuracy and it is recommended that you refer to the English document (a link for which has been provided).
Ethernet Physical Layer

Ethernet Physical Layer

Introduction to Ethernet Cable Standards

The following Ethernet cabling standards exist:

  • 10BASE-2

  • 10BASE-5

  • 10BASE-T

  • 10BASE-F

  • 100BASE-T4

  • 100BASE-TX

  • 100BASE-FX

  • 1000BASE-SX

  • 1000BASE-LX

  • 1000BASE-TX

In these cabling standards, 10, 100, and 1000 represent the transmission rate (in Mbit/s), and BASE represents baseband.

  • 10M Ethernet cable standard

    Table 2-1 lists the 10M Ethernet cabling standard specifications defined in IEEE 802.3.

    Table 2-1 10M Ethernet cable standard

    Name

    Cable

    Maximum Transmission Distance

    10BASE-5

    Thick coaxial cable

    500 m

    10BASE-2

    Thin coaxial cable

    200 m

    10BASE-T

    Twisted pair cable

    100 m

    10BASE-F

    Fiber

    2000 m

    The greatest limitation of coaxial cable is that devices on the cable are connected in series, so a single point of failure (SPOF) may cause a breakdown of the entire network. As a result, the physical standards of coaxial cables, 10BASE-2 and 10BASE-5, have fallen into disuse.

  • 100M Ethernet cable standard

    100M Ethernet is also called Fast Ethernet (FE). Compared with 10M Ethernet, 100M Ethernet has a faster transmission rate at the physical layer, but has the same rate at the data link layer.

    Table 2-2 lists the 100M Ethernet cable standard specifications.

    Table 2-2 100M Ethernet cable standard

    Name

    Cable

    Maximum Transmission Distance

    100Base-T4

    Four pairs of Category 3 twisted pair cables

    100 m

    100Base-Tx

    Two pairs of Category 5 twisted pair cables

    100 m

    100Base-Fx

    Single-mode fiber or multi-mode fiber

    2000 m

    10Base-T and 100Base-TX have different transmission rates, but both apply to Category 5 twisted pair cables. 10Base-T transmits data at 10 Mbit/s, while 100Base-TX transmits data at 100 Mbit/s.

    100Base-T4 is now rarely used.

  • Gigabit Ethernet cable standard

    Gigabit Ethernet developed from the Ethernet standard defined in IEEE 802.3. Based on the Ethernet protocol, the transmission rate increased by 10 times, reaching 1 Gbit/s in GE. Table 2-3 lists the Gigabit Ethernet cable standard specifications.

    Table 2-3 Gigabit Ethernet cable standard

    Interface Name

    Cables

    Maximum Transmission Distance

    1000Base-LX

    Single-mode fiber or multi-mode fiber

    316 m

    1000Base-SX

    Multi-mode fiber

    316 m

    1000Base-TX

    Category 5 twisted pair cable

    100 m

    Using Gigabit Ethernet technology, you can upgrade an existing Fast Ethernet network from 100 Mbit/s to 1000 Mbit/s.

    The physical layer of Gigabit Ethernet uses 8B10B coding. In the traditional Ethernet technology, the data link layer delivers 8-bit data sets to the physical layer. After processing, the 8 bit data sets are sent to the data link layer for transmission.

    This process is different on the Gigabit Ethernet of optical fibers, in which the physical layer maps the 8-bit data sets to 10-bit data sets before sending them to the data link layer.

  • 10GE cable standards

    IEEE 802.3ae is the 10GE cable standard. For 10GE, the cables are all optical fiber in full-duplex mode.

    The development of 10GE is well under way, and will be widely deployed in future.

CSMA/CD

  • Concept of CSMA/CD

    Ethernet was originally designed to connect stations, such as computers and peripherals, on a shared physical line. However, the stations can only access the shared line in half-duplex mode. Therefore, a mechanism of collision detection and avoidance is required to enable multiple devices to share the same line in way that gives each device fair access. Carrier Sense Multiple Access with Collision Detection (CSMA/CD) was therefore introduced.

    The concept of CSMA/CD is as follows:

    • CS: carrier sense

      Before transmitting data, a station checks to see if the line is idle. In this manner, chances of collision are decreased.

    • MA: multiple access

      The data sent by a station can be received by other stations.

    • CD: collision detection

      If two stations transmit electrical signals at the same time, the signals are superimposed, doubling the normal voltage amplitude. This situation results in collision.

      The stations stop transmitting after sensing the conflict, and then resume transmission after a random delay time.

  • Working process of CSMA/CD

    CSMA/CD works as follows:

    1. A station continuously checks whether the shared line is idle.

      • If the line is idle, the station sends data.

      • If the line is in use, the station waits until the line is idle.

    2. If two stations send data at the same time, a conflict occurs on the line, and the signal becomes unstable.

    3. After detecting an instability, the station immediately stops sending data.

    4. The station sends a series of pulses.

      The pulses inform other stations that a conflict has occurred on the line.

      After detecting a conflict, the station waits for a random period of time, and then resumes the data transmission.

Minimum Frame Length and Maximum Transmission Distance

  • Minimum frame length

    Due to the CSMA/CD algorithm limitation, an Ethernet frame cannot be shorter than a certain length. The minimum frame length is 64 bytes. This length was determined based on Ethernet maximum transmission distance and the collision detection mechanism.

    The use of a minimum frame length prevents situations in which station A finishes sending the last bit of a frame, but the first bit has not arrived at station B. Station B senses that the line is idle and begins to send data, leading to a conflict.

    The upper layer protocol must ensure that each frame's Data field contains at least 46 bytes. Therefore, the Data field with a 14-byte Ethernet frame header and 4-byte check code at the end of the frame equals the minimum frame length of 64 bytes. If the Data field is less than 46 bytes, the upper layer must fill the difference.

    The maximum length of a frame's Data field is 1500 bytes, based on the memory cost and buffer of low-cost LAN controllers in 1979.

  • Maximum transmission distance

    The maximum transmission distance depends on factors such as line quality and signal attenuation.

Ethernet Duplex Modes

The Ethernet physical layer can work in either half- or full-duplex mode.

  • Half-duplex mode

    Half-duplex mode has the following features:

    • Sending and receiving data takes place in one direction at a time.

    • The CSMA/CD mechanism is used.

    • The transmission distance is limited.

    Hubs work in half-duplex mode.

  • Full-duplex mode

    When Layer 2 switches replaced hubs in networking, shared Ethernet changed to switched Ethernet, replacing half-duplex mode with full-duplex mode. As a result, the transmission rate doubled.

    Full-duplex mode solved the problem of conflicts, eliminating the need for CSMA/CD.

    Full-duplex mode has the following features:

    • Transmitting and receiving data can take place simultaneously.

    • The maximum throughput is theoretically twice that of half-duplex mode.

    • This mode extends the transmission distance of half-duplex mode.

    Except for hubs, all network cards, Layer 2 switches, and Routers produced in the past 10 years support full-duplex mode.

    Full-duplex mode has the following requirements:

    • Full-duplex network cards and chips

    • Physical media over which sending and receiving frames are separated

    • Point-to-point connection

Ethernet Auto-Negotiation

  • Purpose of auto-negotiation

    The earlier Ethernet used a 10 Mbit/s half-duplex mode that required CSMA/CD to ensure access by all stations. The introduction of full-duplex mode and 100M Ethernet created a need to achieve compatibility between the earlier and newer Ethernet technologies.

    Auto-negotiation technology achieves this compatibility by enabling the device on either end of a link to choose the operation parameters. By exchanging information, the devices negotiate parameters including half- or full-duplex mode, transmission speed, and flow control. After the negotiation, the devices operate in the negotiated mode and rate.

  • Principle of auto-negotiation

    The auto-negotiation mechanism applies to twisted pair links only.

    When no data is transmitted over a twisted pair link, the link is not idle because the devices on the link transmit pulse signals at low frequency. Each device can identify these Fast Link Pulses (FLPs) and use them to transmit small amounts of data to implement auto-negotiation, as shown in Figure 2-1.

    Figure 2-1 Schematic diagram of pulse insertion

    Auto-negotiation priorities of the Ethernet duplex link are listed as follows in descending order:

    • 1000M full-duplex

    • 1000M half-duplex

    • 100M full-duplex

    • 100M half-duplex

    • 10M full-duplex

    • 10M half-duplex

    If auto-negotiation succeeds, the Ethernet card activates the link. Then, data can be transmitted over it. If auto-negotiation fails, the link is inaccessible.

    Auto-negotiation is implemented at the physical layer and does not require any data packets or have impact on upper-layer protocols.

  • Auto-negotiation rules for interfaces

    Two connected interfaces can communicate with each other only when they are in the same working mode.
    • If both interfaces work in the same non-auto-negotiation mode, the interfaces can communicate.

    • If both interfaces work in auto-negotiation mode, the interfaces can communicate through negotiation. The negotiated working mode depends on the interface with lower capability. Specifically, if one interface works in full-duplex mode and the other interface works in half-duplex mode, the negotiated working mode is half-duplex. The auto-negotiation function also allows the interfaces to negotiate the use of the traffic control function.

    • If a local interface works in auto-negotiation mode and the remote interface works in a non-auto-negotiation mode, the negotiated working mode of the local interface depends on the working mode of the remote interface.

      Table 2-4 describes the auto-negotiation rules for interfaces of the same type.

      Table 2-4 Auto-negotiation rules for interfaces of the same type (local interface working in auto-negotiation mode)
      Interface Type Working Mode of the Remote Interface Auto-negotiation Result Description
      FE electrical interface 10M half-duplex 10M half-duplex

      If the remote interface works in 10M full-duplex or 100M full-duplex mode, the working modes of the two interfaces are different after auto-negotiation, and packets may be dropped. Therefore, if the remote interface works in 10M full-duplex or 100M full-duplex mode, configure the local interface to work in the same mode.

      10M full-duplex 10M half-duplex
      100M half-duplex 100M half-duplex
      100M full-duplex 100M half-duplex
      GE electrical interface FE auto-negotiation 100M full-duplex

      If the remote interface works in 10M full-duplex or 100M full-duplex mode, the working modes of the two interfaces are different after auto-negotiation, and packets may be dropped. Therefore, if the remote interface works in 10M full-duplex or 100M full-duplex mode, configure the local interface to work in the same mode.

      10M half-duplex 10M half-duplex
      10M full-duplex 10M half-duplex
      100M half-duplex 100M half-duplex
      100M full-duplex 100M half-duplex
      1000M full-duplex 1000M full-duplex

      Table 2-5 describes the auto-negotiation rules for interfaces of different types.

      Table 2-5 Auto-negotiation rules for interfaces of different types
      Interface Type Working Mode of an FE Electrical Interface Working Mode of a GE Electrical Interface Auto-negotiation Result Description
      An FE electrical interface connecting to a GE electrical interface 10M half-duplex Auto-negotiation 10M half-duplex

      If the FE electrical interface works in 10M full-duplex or 100M full-duplex mode and the GE electrical interface works in auto-negotiation mode, the working modes of the two interfaces are different after auto-negotiation and packets may be dropped. Therefore, if the FE electrical interface works in 10M full-duplex or 100M full-duplex mode, configure the GE electrical interface to work in the same mode.

      10M full-duplex 10M half-duplex
      100M half-duplex 100M half-duplex
      100M full-duplex 100M half-duplex
      Auto-negotiation 10M half-duplex 10M half-duplex

      If the FE electrical interface works in auto-negotiation mode and the GE electrical interface works in 10M full-duplex or 100M full-duplex mode, the working modes of the two interfaces are different after auto-negotiation, and packets may be dropped. Therefore, if the GE electrical interface works in 10M full-duplex or 100M full-duplex mode, configure the FE electrical interface to work in the same mode.

      If you configure the GE electrical interface to work in 1000M full-duplex mode, auto-negotiation fails.

      10M full-duplex 10M half-duplex
      100M half-duplex 100M half-duplex
      100M full-duplex 100M half-duplex
      1000M full-duplex Failure

      According to the auto-negotiation rules described in Table 2-4 and Table 2-5, if an interface works in auto-negotiation mode and the connected interface works in a non-auto-negotiation mode, packets may be dropped or auto-negotiation may fail. It is recommended that you configure two connected interfaces to work in the same mode to ensure that they can communicate properly.

      FE and higher-rate optical interfaces only support full-duplex mode. Auto-negotiation is enabled on GE interfaces for the negotiation of traffic control. When devices are directly connected using GE optical interfaces, auto-negotiation is enabled on the optical interfaces to detect unidirectional optical fiber faults. If one of two optical fibers is faulty, the fault information is synchronized on both ends through auto-negotiation. As a result, interfaces on both ends go Down. After the fault is rectified, the interfaces go Up again through auto-negotiation.

Hub

  • Hub principle

    When terminals are connected through twisted pair cables, a convergence device called a hub is required. Hubs operate at the physical layer. Figure 2-2 shows a hub operation model.

    Figure 2-2 Hub operation model

    A hub is configured as a box with multiple interfaces, each of which can connect to a terminal. Therefore, multiple devices can be connected through a hub to form a star topology.

    Note that although the physical topology is a star, the hub uses bus and CSMA/CD technologies.

    Figure 2-3 Hub operation principle

  • Two types of hubs are possible, distinguished by their interfaces:

    • − Category-I hub: provides a single type of physical interfaces.

      For example, a Category-I hub can accommodate either Category-5 twisted pair interfaces, Category-3 twisted pair interfaces, or optical fiber interfaces.

    • − Category-II hub: provides interfaces of different types. For example, a Category-II hub can provide both Category-5 twisted pair interfaces and optical fiber interfaces.

      Aside from the interface provision, these hub types have no differences in their internal operation. In practice, Category-I hubs are commonly used.

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Updated: 2019-01-02

Document ID: EDOC1100058405

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