My laptop connects to the ethernet via usb adapter. The adapter has a green LED, and it blinks intermittently all the time when I'm using the internet connection. As I guess, the blinking LED indicates that my PC is sending and receiving data packets.
However, when I turn off the laptop, the LED actually never stops to blink (and there are no other IP hosts on my network). So, my question is - what does this blinking LED actually mean? Are there some kind of communication attempts with my turned-off laptop?
And while speaking about the blinking LED - is it a reliable indicator of data stream intensity? I mean, sometimes (especially when playing online video games) the LED is blinking with higher than usual frequency, while the other times it just stays solid green for tens of seconds, with occasional blinkings. So, 1 LED blink = 1 bunch of data packets sent/received, or what?
Thank you
2 Answers
The Ethernet standards (IEEE 802.3 and related) do not define a standard for activity lights. So the blinking patterns for the light on your adapter are completely up to the manufacturer. In my experience, most manufacturers briefly flash the light every time a packet is sent or received, and leave it off otherwise. They flash it on for quite a bit longer than it actually takes to receive the packet, because otherwise you wouldn’t be able to perceive the flash at all. So when the light seems to be on solid, that doesn’t necessarily indicate 100% load on the network; it could be evenly-spaced 10% load for example.
Even on an idle network with just a switch and a router, there can be a small amount of background multicast/broadcast traffic such as ARP table maintenance, IGMP snooping, and service advertisement (Bonjour/mDNS/ZeroConf, UPnP, LLMNR, NetBIOS Name Service, etc. ). So it’s no surprise to see some activity lights blinking even when all the host devices are switched off.
Usually (but not always) the left LED indicates the connection speed:
- Off: low speed (10Mbps)
- Green: 100Mbps
- Amber: 1Gbs
The right LED blinks to indicate data transfer (but I don't see any connection with actual packets, it seems to be only a fixed blink rate).
The blinking light on your Ethernet connector when your computer is turned off means that the computer is still connected to the network. This is used for Wake-on-LAN (if you computer is pinged by some other computer, it wakes up). This can be disabled in the BIOS. On laptops, Wake-On-LAN is often only enabled when the laptop its connected to its power supply.
