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Original question:

DP83848I: Auto-Negotiation Complete Time differs for 10M and 100M

DP83848I: Why Auto-negotiation is long? What factors affect this time?

Hisao Uchikoshi
Genius 14880 points
Part Number: DP83848I

Hi Experts,

Is there any mechanism why auto negotiation compete time is long?

I am using 40cm length Ethernet cable and it seems to take about 500ms to complete Auto-negotiation. What kind of factors affect this time to become long like 2 - 3 seconds? 

Regards,

Uchikoshi

  • 0
    TI__Mastermind 18425 points
    Hi Uchikoshi-san,

    Auto-negotiation process involves two PHYs advertising their capabilities to each other and then linking up with best configuration that is supported by both PHYs. Ethernet PHYs are supposed to keep advertising their capabilities at periodic intervals until a link is successfully established. This process is defined in IEEE standards and involves multipe timers that decided how long to wait for link to be up before auto-negotiation is started again. These timers can add up to several hundreds of milliseconds. Sometimes, the link is not established in the first attempt and multiple autonegotiation attempts are required for link up. In such cases, the link up time can become 2-3 seconds.

    -Regards
    Aniruddha
  • 0 in reply to Aniruddha Khadye
    TI__Genius 14880 points
    Hi Aniruddha,
    Thank you for your detail explanation.
    Do you have any information about the conditions which takes such 2 - 3 seconds?
    Regards,
    Uchikoshi
  • 0 in reply to Hisao Uchikoshi
    TI__Mastermind 18425 points
    Hi Uchikoshi-san,

    It can be due to different factors like timing mismatch between transmit of one PHY and receive of another PHY or some FLPs not being detected by one PHY. It is difficult to list all factors that can affect the link up time.

    -Regards
    Aniruddha