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The Detailed Process of Auto-negotiation on Ethernet

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The Detailed Process of Auto-negotiation on Ethernet

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The Detailed Process of Auto-negotiation on Ethernet

  1. 1. The Detailed Process of Auto-negotiation on Ethernet There are two types of auto-negotiation mechanisms: Autonegotiation and Autosensing/Speed Detection. Autonegotiation is a handshake mechanism of the standard negotiation speed. It can be automatically configured to the most possible connection (such as 100M full-duplex) and be connected to old devices or the devices that do not support auto-negotiation. Autosensing/Speed Detection can be automatically configured to only 10M or 100M and does not support the setting of duplex. The 10BASE-T Ethernet interface that supports 10M rather than auto-negotiation sends LTPs before the link is Up. The LTP is used to check whether the link is Up. The 100BASE-T Ethernet interface that supports 100M rather than auto-negotiation sends FAST ETHERNET IDLE flows to check whether the link is Up. The Ethernet interface that supports Autonegotiation sends FLPs before the link is Up. The FLP is actually a group of LTPs and data pulses, indicating a certain meaning. For example, the 100M full-duplex is supported. The old device such as the 10BASE-T device still regards such FLPs as LTPs. The auto-negotiation device, however, can identify the meaning of the FLPs and configure the optimal link by exchanging such handshake messages. The auto-negotiation device sets the local end to 10M half-duplex if common LTPs (not FLPs of specific meanings) enter the device. The auto-negotiation device set the local end to 100M half-duplex if FAST ETHERNET IDLE flows enter the device. The preceding auto-negotiation mechanisms are applicable to only 10/100M copper wire interfaces or 1000M optical/electrical interfaces. The 100BASE-FX device does not support auto-negotiation. The following takes an example to describe the process of 10/100M auto-negotiation: As shown in Figure 1, the two devices that support auto-negotiation are connected. Figure 1 Connection between the two devices that support auto-negotiation Both device A and device B send FLPs. Each device confirms the BIT position in its own FLPs after receiving the FLPs from the peer device. Then each device sets its rate and duplex to the best modes supported by both devices and starts sending FAST 1
  2. 2. ETHERNET IDLE flows. Thus, the link is Up. As shown in Figure 2, an auto-negotiation device is connected to a 10BASE-T device. Device A sends FLPs but device B sends common LTPs. Device A sets the local end to 10M half-duplex after detecting the LTPs of the peer end in a parallel way. This may bring risks. That is, when device B is set to 10M full-duplex, the negotiation result of device A is also 10M halfduplex. As shown in Figure 3, an auto-negotiation device is connected to a 100BASE-T device. Figure 3 Connection between an auto-negotiation device and a 100BASE-T device Device A sends FLPs but device B sends FAST ETHERNET IDLE flows. Device A sets the local end to 100M half-duplex and starts sending FAST ETHERNET IDLE flows after detecting the IDLE flows of the peer end in a parallel way. This may bring risks. That is, when device B is set to 100M full-duplex, the negotiation result of device A is also 100M half-duplex. As shown in Figure 4, the duplexes caused by two auto-negotiation devices are inconsistent. 2
  3. 3. Device A is in auto-negotiation state. Device B is set to 100M full-duplex and autonegotiation is disabled although it supports auto-negotiation. As a result, device A sends FLPs but device B sends FAST ETHERNET IDLE flows. Device A sets the local end to 100M half-duplex after receiving the IDLE flows from device B. Device B, however, is set to 100M full-duplex forcibly, causing the following problem: If device A and device B send a frame at the same time, device A regards that the sending conflicts. It destroys the frame sent by itself, discards the frame of device B, and tries to send the frame of its own again. Device B regards the frame of device A as a corrupted frame without sending the frame again. As a result, many late collisions are recorded on device A and many CRC error frames are recorded on device B. As shown in Figure 5, the link is not Up because of incorrect configurations. FLPs and device B sends FAST ETHERNET IDLE flows. Device A sets the local end to 100M half-duplex and starts sending FAST ETHERNET IDLE flows after receiving the IDLE flows; device B identifies the FLPs received from device A as LTPs, sets the local end to 10M halfduplex, and then sends LTPs. As a result, the link is Up. The FAST ETHERNET IDLE flows sent by device A after the link is Up are regarded as trash data by device B. Or device A may not process the LTPs from device B. Therefore, one end is set to 10M and the other is set to 100M. 3
  4. 4. Or device A sends FLPs and device B sends FAST ETHERNET IDLE flows during initialization. Device B identifies the FLPs received from device A as LTPs, sets the local end to 10M halfduplex, and sends LTPs; device A sets the local end to 10M half-duplex after receiving the LTPs from device B. Thus, the link is Up. The process of 1000M auto-negotiation is as follows: The same mechanism is adopted for 1000M auto-negotiation and 10/100M autonegotiation. The 1000BASE-LX and 1000BASE-SX devices use the auto-negotiation mechanism to negotiate duplexes and flow control. The auto-negotiation on the 1000BASE-T device also includes the negotiation of the additional region (master or slave region). Half-duplex rarely exists (although can be negotiated) on 1000M devices. Thus, many duplex problems do not exist. As shown in Figure 8, the 1000BASE-LX and 1000BASE-SX devices in auto-negotiation and non-auto-negotiation are connected. and the other Down, or neither end is Up. As shown in Figure 9, the 1000BASE-T devices in auto-negotiation and non-autonegotiation are connected. 4
  5. 5. Auto-negotiation is enabled on device A and disabled on device B. As a result, one end is Up and the other Down, or neither end is Up. In this case, the ends can be Up with Huawei devices. More related: Huawei PING command Summary of switch configurations Huawei S5700 basic configuration command Huawei switch restores factory settings More Huawei products and Reviews you can visit: http://www.huanetwork.com/blog Huanetwork.com is a world leading Huawei networking products distributor, we wholesale original new Huawei networking equipments, including Huawei switches, Huawei routers, Huaweisymantec security products, Huawei IAD, Huawei SFP and other Huawei networking products. Our customers include telecom operators, Huawei resellers, ISP and system integrators. Right now most of our sales are contributed by regular customers Our website: http://www.huanetwork.com Telephone: +852-30501940 Email: sales@huanetwork.com Address: 23/F Lucky Plaza, 315-321 Lockhart Road, Wanchai, Hongkong 5
  6. 6. Auto-negotiation is enabled on device A and disabled on device B. As a result, one end is Up and the other Down, or neither end is Up. In this case, the ends can be Up with Huawei devices. More related: Huawei PING command Summary of switch configurations Huawei S5700 basic configuration command Huawei switch restores factory settings More Huawei products and Reviews you can visit: http://www.huanetwork.com/blog Huanetwork.com is a world leading Huawei networking products distributor, we wholesale original new Huawei networking equipments, including Huawei switches, Huawei routers, Huaweisymantec security products, Huawei IAD, Huawei SFP and other Huawei networking products. Our customers include telecom operators, Huawei resellers, ISP and system integrators. Right now most of our sales are contributed by regular customers Our website: http://www.huanetwork.com Telephone: +852-30501940 Email: sales@huanetwork.com Address: 23/F Lucky Plaza, 315-321 Lockhart Road, Wanchai, Hongkong 5

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