Leading Huawei networking products distributor-huanetwork.com The Detailed Process of Auto-negotiation on Ethernet

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
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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.
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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.
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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.
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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
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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
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