7905 go only in 10/half

Unanswered Question
Nov 23rd, 2007
User Badges:

Hi all, we have a problem with ip phones 7905, it seems that they only work in 10/half mode.

We have connected them to different catalyst switch (2950 and 2960), all in auto/auto configuration.

We observe many errors like this:

%ETHCNTR-3-HALF_DUX_COLLISION_EXCEED_THRESHOLD: Half-duplex loopback detected, collision threshold exceeded on FastEthernet0/12.

We have tried to force connection in 100full but into the phone appear a message "ethernet disconnected".

If we configure the port in trunk mode, then the phone work in 100full.

But for another problem (ip phone sw upgrade doesn't work), opening a tac case, a cisco engineer suggest us to not use trunk configuration for ip phones, and now upgrades work...

Any idea/suggestion?



  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
Rob Huffman Sat, 11/24/2007 - 10:26
User Badges:
  • Super Blue, 32500 points or more
  • Hall of Fame,

    Founding Member

  • Cisco Designated VIP,

    2017 IP Telephony, Unified Communications

Hi Daniele,

This is the expected behaviour for the 7905G as it only only has a 10BaseT Ethernet port :)

Phones with no PC ports and with 10 Mb switch ports (Cisco Unified IP Phones 7902, 7905, and 7910) should be allowed to auto-negotiate to 10 Mb, half-duplex.

Because these phones support only 10 Mb Ethernet and their ports cannot be manually configured, the upstream switch port should be set to either AUTO negotiate or 10 Mb, half-duplex. In both cases, these phones will negotiate to 10 Mb, half-duplex.


Cisco Unified IP Phone 7905G

The Cisco Unified IP Phone 7905G supports a single line, and it has a single 10BaseT Ethernet port on the back of the phone. The speaker operates in one-way listen mode only.


Hope this helps!



This Discussion