Description:
This article describes the process of the PoE negotiation via LLDP between an access point with LCOS LX and a switch from a third party manufacturer with PoE support for 802.3at (max. 30 W).
Depending on the switch manufacturer, the LLDP negotiation may turn out differently.
Requirements:
- LCOS LX as of version 6.14 RU1 (download latest version)
- LLDP dot3 must be active on the switch ports, as LCOS LX only supports tis option. LLDP-Med cannot be used for the negotiation.
PoE negotiation via LLDP with 802.3at support and a maximum power requirement of 30 Watt:
As an example, the PoE negotiation process via LLDP between an LX-6400 (power requirement of 25,5 W) and a Cisco switch with 802.3at Support and a maximum power requirement of 30 W is shown below. Therefore the switch can completely fullfill the power requirement.
1) The switch initially only allocates 13 W to the access point (PSE Allocated Power Value 13.0 Watt).
2) The access point requests 25.5 W, which is required for full operation (PD Requested Power Value 25.5 Watt).
3) The switch allocates the requested 25.5 W to the access point (PSE Allocated Power Value 25.5 Watt) and informs the access point.
4) The access point acknowledges the allocation of 25.5 W (PSE Allocated Power Value 25.5 Watt).
5) Afterwards, the access point and the switch exchange LLDP packets in intervals of two (access point) or three seconds (switch).
PoE negotiation via LLDP with 802.3at support and maximum power requirement of 60 Watt:
As an example, the PoE negotiation process via LLDP between an LX-6500 (power requirement of 51 W) and a Cisco switch with 802.3at support and a maximum power requirement of 60 W is shown below. Therefore, the switch cannot fullfill the power requirement.
1) The switch initially only allocates 13 W to the access point (PSE Allocated Power Value 13.0 Watt).
2) The access point requests 51 W, which is required for full operation (PD Requested Power Value 51.0 Watt). At this point, the access point has not yet adopted the 13 W allocated by the switch (PSE Allocated Power Value).
The 51 W requested by the access point exceeds the maximum allowed value of 30 W supported by the 802.3at standard.
3) The switch still only allocates 13 W to the access point, as the requested value of 51 W is invalid.
In this case, in the webinterface of the Cisco switch the Powerclass is shown as Unknown.
4) The access point still requests 51 W (PD Requested Power Value). It has now adopted the 13 W allocated by the switch.
5) Afterwards, the access point and the switch exchange LLDP packets, where the access point always requests 51 W and the switch allocates 13 W to the access point.
In this case the switch port, the access point is connected to, has to be set to a fixed value of 30 W. Only in doing so, can the access point receive 30 W.
When the access point is operated with 802.3at, its performance will be restricted. The restrictions are described in the following Knowledge Base article:
