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network-programmingbandwidthethernet
MCG
MCG

Reputation: 1031

When we connect an ethernet device on the network,at what speed it starts communication

What steps are performed by ethernet device to connect to a n/w? Does it start communication from it's lowest or highest supported speed?

To make it more clear I have following example

If device A is currently setup at 10Mbps and just connected to N/W router R,which can support both 10Mbps and 100Mbps. Which device(A or R) will communicate first and what speed. If device A, how will router understand the speed of transmission send by device A?

Upvotes: 1

Views: 704

Answers (1)

Mike Pennington
Mike Pennington

Reputation: 43107

You seem to be asking about ethernet autonegotiation - IEEE 802.3ab; Autonegotiation should implement this set of priorities when autonegotiating a 1Gbps link...

  1. 1000BASE-T full duplex
  2. 1000BASE-T half duplex
  3. 100BASE-T2 full duplex
  4. 100BASE-TX full duplex
  5. 100BASE-T2 half duplex
  6. 100BASE-T4
  7. 100BASE-TX half duplex
  8. 10BASE-T full duplex
  9. 10BASE-T half duplex

It doesn't matter which device communicates autonegotiation pulses first; the bottom line is that IEEE defines a very specific time window for both of them to finish autonegotiation.

Whether a device can actually link at these speeds depends on whether both ethernet PHYs support said mode, and whether the channel (i.e. wiring) has sufficient electrical bandwidth capacity... each PHY will conduct a signal to noise ratio test to determine whether the channel supports enough capacity for the desired speed.

Reading this Ethernet PHY application note (National Semiconductor) may be boring, or full of excitement depending on your tolerance for implementation details.

Upvotes: 1

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