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Cisco's Official Stand On Using Cat3 Cable For IPT

Answered Question
Dec 17th, 2009
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Does anyone know what Cisco's official stand is on using Cat3 cable for VoIP in 2009?

Correct Answer by asandborgh about 7 years 8 months ago

er - guys,


while I would never recommend that a client run it - Cisco does support it.  From the CCM 7.X SRND:


Category 3 Cabling

The use of Category 3 cabling is supported for IP Communications under the following conditions:

Phones with a PC port and a PC attached to it (Cisco Unified IP Phones 7975, 7971, 7970, 7965, 7962, 7961, 7960, 7945, 7942, 7941, 7940, 7911, and 7910+SW) should be set to 10 Mb, full-duplex.

This setting requires hard-coding the upstream switch port, the phone switch and PC ports, and the PC NIC port to 10 Mb, full-duplex. No ports should be set to AUTO negotiate. If desired, you can hard-code the phone's PC port to 10 Mb half-duplex, thereby forcing the PC's NIC to negotiate to 10 Mb half-duplex (assuming the PC's NIC is configured to AUTO negotiate). This configuration is acceptable as long as the uplink between the phone and the upstream switch port is set to 10 Mb full-duplex.

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.

Phones with a PC port but no PC attached to it (Cisco Unified IP Phones 7975, 7971, 7970, 7965, 7962, 7961, 7960, 7945, 7942, 7941, 7940, 7912, 7911, and 7910+SW) can be allowed to negotiate to 10 Mb, half-duplex.

If you leave these phones with the default switch port configuration of AUTO negotiate and configure the upstream switch port to 10 Mb, half-duplex, these phones will revert to 10Mb, half-duplex.



Note The Cisco Unified IP Phone 7912 should not be used with Category 3 cable when a PC is attached because the switch and PC ports on this phone cannot be forced to 10 Mb, full duplex.



Correct Answer by Rob Huffman about 7 years 8 months ago

Hey DW,


My friend Paolo is most correct (+5 buddy!)


Here is a clip from an "old" Cisco doc;


There is limited support from Cisco for using Cat3, have a look;


Q What type of Ethernet cables can/must be used?


A We support all standard cable types.


CAT3 Supported for 10Mbps

CAT5 and above Supported for 10/100/1000Mbps


The link between a bus and a drop cable that connects a workstation to the bus.

Category 5 (CAT5) cables support frequencies up to 100 MHz, while Category 3 (CAT3) cables support frequencies no higher than 16 MHz. For this and other reasons, CAT5 is an increasingly popular choice, especially in networks that carry both data and voice traffic.




Hope this helps!

Rob

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paolo bevilacqua Thu, 12/17/2009 - 10:55
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Since 100 mbos ethernet is not supported on cat3, you cannot run ipt on it neither.


There is no need of a official Cisco answer on this well known fact.

Correct Answer
Rob Huffman Thu, 12/17/2009 - 11:24
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Hey DW,


My friend Paolo is most correct (+5 buddy!)


Here is a clip from an "old" Cisco doc;


There is limited support from Cisco for using Cat3, have a look;


Q What type of Ethernet cables can/must be used?


A We support all standard cable types.


CAT3 Supported for 10Mbps

CAT5 and above Supported for 10/100/1000Mbps


The link between a bus and a drop cable that connects a workstation to the bus.

Category 5 (CAT5) cables support frequencies up to 100 MHz, while Category 3 (CAT3) cables support frequencies no higher than 16 MHz. For this and other reasons, CAT5 is an increasingly popular choice, especially in networks that carry both data and voice traffic.




Hope this helps!

Rob

Correct Answer
asandborgh Thu, 12/17/2009 - 13:28
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er - guys,


while I would never recommend that a client run it - Cisco does support it.  From the CCM 7.X SRND:


Category 3 Cabling

The use of Category 3 cabling is supported for IP Communications under the following conditions:

Phones with a PC port and a PC attached to it (Cisco Unified IP Phones 7975, 7971, 7970, 7965, 7962, 7961, 7960, 7945, 7942, 7941, 7940, 7911, and 7910+SW) should be set to 10 Mb, full-duplex.

This setting requires hard-coding the upstream switch port, the phone switch and PC ports, and the PC NIC port to 10 Mb, full-duplex. No ports should be set to AUTO negotiate. If desired, you can hard-code the phone's PC port to 10 Mb half-duplex, thereby forcing the PC's NIC to negotiate to 10 Mb half-duplex (assuming the PC's NIC is configured to AUTO negotiate). This configuration is acceptable as long as the uplink between the phone and the upstream switch port is set to 10 Mb full-duplex.

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.

Phones with a PC port but no PC attached to it (Cisco Unified IP Phones 7975, 7971, 7970, 7965, 7962, 7961, 7960, 7945, 7942, 7941, 7940, 7912, 7911, and 7910+SW) can be allowed to negotiate to 10 Mb, half-duplex.

If you leave these phones with the default switch port configuration of AUTO negotiate and configure the upstream switch port to 10 Mb, half-duplex, these phones will revert to 10Mb, half-duplex.



Note The Cisco Unified IP Phone 7912 should not be used with Category 3 cable when a PC is attached because the switch and PC ports on this phone cannot be forced to 10 Mb, full duplex.



Leo Laohoo Thu, 12/17/2009 - 13:56
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You're right.  VoIP support using Cat3 is still "acceptable" but at 10mb, full duplex and not 100mb, full duplex.


IF the client is acceptable running their network at 10mb, then it should be fine.  Plus looking at the notes, the network admin has to constantly configure each ports to the required settings.  You can get away with this by configuring AutoSmartPorts.


Hmmmmm ... Cat3 in a multi-media environment.  One word:  DON'T.

asandborgh Thu, 12/17/2009 - 14:05
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I agree wholeheartedly but,


The only reason I noted the support in the SRND is that I have had several large clients that would have had to spend many times the cost of the IPT to upgrade their existing Cat3 wiring - one to the tune of over $10M USD - in most cases just to enable single line phones in large manufacturing environments.  I think that is why Cisco finally permitted it, and restricted it down, because back in the CCM 3.0 days it was strictly verbotten.


It's one of those costs that can sink the entire project, even if the user will never do anything beyond getting/making calls.


BTW - we did float putting just analog phones on the cat3 - that does not generally fly either....


Art

Leo Laohoo Thu, 12/17/2009 - 15:23
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Don't get me wrong here but my initial response was not meant to take a dig at you.  It's the idea of using Cat3 and expecting 100/1000mb, full duplex.

asandborgh Thu, 12/17/2009 - 15:44
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Leo,


I appreciate your concern - really do, but LOL here.  I'm too old (cut my teeth on mechanical and tube adders + relay logic) and crusty to take much of anything to heart.  I was almost embarrased to even post the SRND quote - but it has saved a few projects - that in the end worked just fine for the customer's need -  so I figured it was worthy - kinda.


And yes you're absolutely correct - when I tell a client this I give them full disclosure - it is a band-aid.


You're going to have to work a bunch more to offend me!


Happy Trails my friend.


Cheers!


Art

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