Wireless and Emergency Responder

[mightyking]

Hello All,

I need someone who is patient enough to explain this to me. I tried to read through the threads before posting my question but it looks like I don't seem to find an answer for my question. Could someone please explain to me how CER is going to work with 7925 Wireless phone. I know the only way is the IP subnet tracking but don't understand how it works. Let's say someone is on the phone(7925) and walking from building-A to building-B. He moves from one AP to another AP. If we use the AP's IP address for ERL, does that person lose connection everytime he/she crosses the bundery of an AP? He was reginstered with AP in building-A and now he is in building-B and he calls 911, what's the location that CER reports to the secuirty? I am hoping that it reports building-B but it looks like it's not the case.  Could you please shad some lights on this and help me to understand? I really need your help to understand this because I am going to present this solution to some high level managment poeple tomorrow.

Regards,

MK

[Joseph Martini]

For the first question about whether or not the user loses connection when roaming between AP's that depends on the wireless/AP configuration.  If they're on the same layer 2 network no, and it might be possible now to roam between AP's on different layer 3 networks but I'm not that familiar with how that works, maybe someone else can elaborate on that part.  If the user moves from building A to building B and is not using an AP in building B that provides IP addresses in a different subnet, say subnet B, then based on subnet based phone tracking CER would report the location as building B.  As long as the IP subnet changes between building A and building B subnet based phone tracking will report building B instead of A.

[srsivara]

http://www.cisco.com/en/US/docs/voice_ip_comm/cer/8_0/English/administration/guide/e911conf.html#wp1050258

If you use Layer 3 (IP) roaming for wireless IP  phones and/or wireless phones register using their Wireless Access  Point's IP address, then Cisco ER will not be able to automatically  track movement of these phones. This is because Cisco ER uses the IP  address of the phone to determine the phone's location. Do not use Layer  3 roaming if you need Cisco ER to automatically track movement of  wireless phones in your network

So, the IP address of the phone should change when moving from one subnet to another, so that CER can track which subnet the wireless phone is in.

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The IP Subnets configured on CER should be granular enough to identify which subnet your IP phone is in (and thus the correct ERL information is conveyed)

The incremental phone tracking on CER is 30 minutes by default - so if you roam from one subnet (A) to another (B) with the wireless phone and make a 911 call before the CER did the incremental phone tracking, the ERL information reported will be that of subnet A.

It is not recommended to lower the incremental phone tracking on the CER, as the CER resource utilization will spike up to do the incremental phone discovery ever so often.

- Sriram

[mightyking]

Thanks Guys,

If I understand well, everytime a wireless phone changes a subnet it will be forced to reset ,am I mistaken?

Thanks,

MK

[srsivara]

I believe so. However, I would suggest you quickly test it out in your lab and check the behavior.

- Sriram

[mightyking]

This is really not good. I am defining two zones per floor like, Floor1 East wing and Floor1 West wing. Does it means everytime I walk from east to west in the same floor the wireless phone will reset? This is really funny. I think the phone will reset at lease 100 times per day and we will spend more time for the phone to reboot than talking with that phone. What's the utility of a wirless phone then? Is there any work around? Please advice.

Thanks,

MK

[srsivara]

I am not sure of the interactions of a Cisco Wireless phone with an AP - so I can't pinpoint the sequence of steps that occurs when a wireless phone moves from one subnet to another.

Configuring a Layer 3 IP address would not help in terms of tracking the correct location of the phone, wrt CER.

I would recommend looking into Cisco documentation, or opening a case with the Wireless TAC team to understand the scenario.

- Sriram