Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. If you'd prefer to explore, try our test area to get started. And see here for current known issues.

New Member

WS-C3550 POE + Phones

Not sure if this is the correct place to post this ?, does anybody know if the 7942G phone is compatible with the WS-C3550 POE switch ?

We are seeing some rather bizarre behaviour with the phones that would suggest an issue.



New Member

Re: WS-C3550 POE + Phones

Im using 7940 and 7945's on a 3550 on my desk lab right now.  It works great.

Could you elaborate on some of the problems you are having?

This may belong in the voice forums depending on the issue you are having.  But we can continue here and if a moderator wishes to move, they can.

Re: WS-C3550 POE + Phones


The Catalyst 3550 switch supports only Cisco's proprietry version of power over Ethernet as it was released prior to the IEEE 802.3af PoE standard being ratified.

The 7942G Data Sheet and Q&A does state that the 7942G is compatible with Cisco pre-standard switches so in theory you should be ok.

Data Sheet

Supports IEEE 802.3af PoE (Class 2). Also supports  Cisco Prestandard Power over Ethernet (PoE), allowing powering from any  of the Cisco Inline Power-capable blades and boxes, plus Cisco midspan.  48VDC is required; it can be supplied locally at the desktop using an  optional AC-to-DC power supply (part number CP-PWR-CUBE-3=) or power  injector (CP-PWR-INJ=).



Q. Do the Cisco Unified IP Phone 7962G and Cisco Unified IP Phone 7942G support Cisco Inline Power?
A. Yes. Additionally, the phones support IEEE 802.3af Power over Ethernet (PoE) (Class 2) and Cisco Midspan Power.
Q. As Class 2 IEEE devices, do these phones require a continuous draw of 7 watts (standard Class 2 allocation)?
A. No. When Cisco Unified IP Phones are connected to common switches such as the Cisco Catalyst® 3560 Series Switches or Cisco Catalyst 3570 Series Switches, the switch  can automatically detect the phone type and provide the exact amount of  power that the phone needs. The use of Cisco Discovery Protocol  provides this greater granularity to the power classification, allowing  more accurate reporting of power consumption. The Cisco Unified IP Phone  7962G and 7942G models draw a maximum of 6.3W from a switch.
What type of issues are you seeing? - can the switch power a certain number of phones or does it have problems if just one phone is plugged in?

You could try issuing the command below which seems to have solved issues for other users according to this thread

power inline delay shutdown 20 initial 300