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Forum Discussion
MS108EUP not supporting LLDP in a good way?
Hi,
I am working quite a bit with hardware and software POE negotiation, and my view of the 802.3 standard is that the switch should announce it's LLDP capabilities and settings (including Power-via-MDI) directly to a connected device that is powered by it.
However, when I take a wireshark trace using the Netgear MS108EUP switch toward an Axis camera, it seems like the switch does not send ANY LLDP packets unless I first send a power request from the camera...
I also logged into the switch and tried to find a way to enable / disable LLDP, but found no such control in the GUI.
What am I doing wrong?
Or is the switch just not working as a 802.3 device should work?
/ Kenneth
5 Replies
Ill add some more:
Why I say this, and why I prefer this is because the PD needs to know if it should start LLDP negotiation or not.
Currently many devices send LLDP power-via-MDI requests blindly, to "wake up" the LLDP protocol in the switch, but that is not how the standard intends switches to work, I think.
It causes a lot of problems for POE negotiation, when devices have to guess whether to request more (or less) power, and a lot of power is wasted on the PSE side, since switches don't know how much PDs really need.
Currently many devices send LLDP power-via-MDI requests blindly, to "wake up" the LLDP protocol in the switch, but that is not how the standard intends switches to work, I think.
Yes, if course. This is the same logic the more common PoE negotiation using pulses works. The PD has to explicitly request power from the PS, typically when the PD ist connected and the PHY link comes up.
The MS108EUP does not come with any explicit LLDP support (or related controls on the Web UI). I guess it's PoE controller does - like on the unmanaged MS108UP - listen to the LLDP power requests.
No "feature" needs to be announced from the PoE capable switch regardless to negotiate PoE power of any type.
It causes a lot of problems for POE negotiation, when devices have to guess whether to request more (or less) power, ... , since switches don't know how much PDs really need.
Very normal, isn't it? The PD devices does request a certain amount of power, being by plusing or LLDP MDI requests on the initializing connection.
Should the PD request more power from the PSE, using pulses it can't.
Using LLDP MDI it can. Permitting the PSE has enough spare power budget available, and the request does not go beyond the port capability (30 or 60 W on the MS108EUP, UP, or TUP), the power will be allocated and granted. However, I can't tell you exactly (as I was never involved in the switch design) under what conditions the switch can and will agree.
Typical design on pulsing type PoE negotiation, on an unmanaged switch: The lower port number has the higher priority.
The MS108EUP does allow setting some kind of priority level per port. I doubt the lower prio PoE port will lowering or stopping the power to the PSE - unclear if the dynamically changed request for more power will be granted.
Based on what standard function, should the PD query the PoE status of the other ports?
and a lot of power is wasted on the PSE side
You talk of the PSE total power budget and it's distribution "schedule" or "priority" here? Have you spotted any clever details in the IEEE standard for a PD device being able to adjust his power request accordingly?
There is a more competent switch called MS108TUP. Might these measurement be supported there?
The MS108TUP does - different from the MS108EUP - support LLDP and it's configurations. So please give it a try, and let the community know.
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