IOS and Ethernet vs. Fast Ethernet

Posted on 2004-10-13
Last Modified: 2008-01-09
Dear Experts,

I have been going back and forth with different techs both with NEC and Cisco on the correct IOS to use for VOIP.  I have Cisco's 2620 and several 2611's.  They have 64 and 16, memory and flash.  Cisco says that the IOS c2600-is-mz.122-11.T11.bin should work.  NEC is telling me to use c2600-is-mz.122-15.T14.bin.  The second IOS is too large and requires more flash and a ROM upgrade.  Also NEC is saying they have doubts about my equipment.

The 2611 which has two 10 base T ethernet ports.  I was told by NEC that this would cause a problem with VOIP because it is "Half Duplex" vs. Full Duplex like the fast Ethernet port.

Is this correct and have you found this port speed or processor of the 2611/2620 causes issues with VOIP?

I am hoping to not have to replace several of my 2611's and my 2620.

If anyone knows or has been in this situation and can give me some good advice I would be very appreciative.


Question by:ReggieM
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LVL 13

Accepted Solution

Dr-IP earned 500 total points
ID: 12304236
It sounds like NEC is getting involved in nitpicking every little thing, but let’s address the supposed issues.

The difference between those two ISO’s are minimal, mostly minor code changes and bug fixes, but nothing major, so I’d say chances are good that won’t be an issue.

As for the 10 Meg port, theoretically it could be an issue, that is if you ran two T1’s ones of G711 VOIP traffic through it (G711 has no compression and uses 64K per call), which could overload the interface. Now you’re not gong to do that, are you? Beside that, are not the calls going to be sent out the serial interface, which is full duplex anyway?

By the way I have an AS5300 where the fast Ethernet port is dead, and I am having no issues even with running 4 T1’s of calls using the G729 codec through it's 10 Meg Ethernet port. So I think it’s safe to say you won’t have an issue with the 10 Meg Ethernet port so long as you don’t plug it into an overloaded hub, but big bother NEC will make sure you don’t  contemplate something even remotely as awful as that.




Author Comment

ID: 12309409
Thank you for the feedback.

Which routers and IOS images are you using or have seen in use for VOIP?

I am going to buy the upgraded Flash/ROM to accomidate the new IOS he is recomending but the NEC tech keeps pointing out my equipment.  Now he has hinted at the possibitliy of having to replace my 1721's with 1760's as well as the few 2611's I have!

Well I appreciate any information you can provide, and I am gratefull for the dialog.

LVL 13

Expert Comment

ID: 12313544
Why don’t you describe the bigger picture in greater detail? Like, what is the maximum number of calls each router is going to handle simultaneously? Are the routers going to have VOIP modules installed in them and if they are, are they going to be used as dedicated VOIP gateways, and if the routers are going to be used for routing too, how big is the internet circuit?  
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Expert Comment

ID: 12344109
You might be able to set your 10Mbps ports on your 2610 to full duplex to alleviate NEC's concerns about collisions.

Depending on what your 2610 is doing (i.e. T1, PRI, FXS, FXO, etc.) it might be fine.

-Eric, who used to work for NEC BNS

Expert Comment

ID: 12345947
What role is NEC playing in this solution?  Are you connecting to one of their PBXs?  Or are they simply trying to provide network engineering support?

Author Comment

ID: 12374624

Thank you for the support.  I have been so busy and I now have Cisco involved. To answer your question the NEC fellow is working for the Vendor we purchased the phone system from.  Some of the offices have the CTX/PBX NEC system in them some of the small offices are going to just have the IP phones in them.  The NEC tech is trying to figure out what configuration/Hardware/IOS is needed to pass voice traffice across our WAN links.  I have a 2620 with 32MB flash and 64MB NVRAM.  I have several 1720's and 2611's and one 1721.  I have been told by the NEC Rep that the 2611's are "half Duplex" and therfore will cause an issue with the VOIP.

So the 2611 is half duplex?  Does anyone know how you set it for full duplex?

The office I am trying to connect now is just calling other extensions meaning people in the other offices and checking voice mail accross the WAN.  All calls to the outside will go through the PBX.  I have a small office of three people that I put IP phones in that offices calls all come accross the WAN to the PBX at our hub office.  I have a hub and spoke network with all data traffic coming to the hub on dedicated Frame connections of varying speeds.  The smallest bandwidth is 512K.  I am just right now trying to eliminate the hardware as a source of my problems. If I can do that then I can concentrate on the configuration.

If I did not answer all of your questions, let me know.  I thank you deeply for all of the communication and help!!

Expert Comment

ID: 12376541
Some of the 10Mbps ports on the 2600 series can do full duplex. The way to check is to go to the interface config and try "full-duplex" or "duplex full" and see if it works.

LVL 13

Expert Comment

ID: 12386988
Actually if the routers are only going to pass the VOIP packets for the IP phones, the only import thing for the version of ISO is that it supports QOS or CAR so that you can make sure that the other network traffic doesn’t interfere with the VOIP calls.

As for the half duplex garbage for VOIP, I wouldn’t worry about it, especially for the smaller offices. Just make sure the routers are connected to switch’s, not hubs and all should be well so long as you are not pounding the WAN links with more traffic than they can handle.

As I said before, I have an AS5300 access server with a dead fast Ethernet port on it working happily on the 10 Meg port running half duplex with almost a hundred calls on it, and the voice quality is just as good as the rest of my gateways running on their fast Ethernet ports. I doubt you are gong to have anywhere close to the hundred calls I know can work just fine on a 10 Meg Ethernet, so I wouldn’t worry about it. And instead concentrate on configuring QOS, or CAR on the routers so VOIP packets get the preferential preference they need.      

Author Comment

ID: 12399552
Thank you for all of the information it helped out a ton!!

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