[VoiceOps] WiFi SIP phones recommendations

Kristian Kielhofner kris at kriskinc.com
Mon Sep 21 16:05:58 EDT 2015

On Mon, Sep 21, 2015 at 2:40 PM, Robert Johnson <robert.j at bendtel.com> wrote:
> On 09/21/2015 12:32 PM, Aaron Seelye wrote:
>> On 9/19/15 8:42 AM, Jay Ashworth wrote:
>>> ----- Original Message -----
>>>> From: "Alex Balashov" <abalashov at evaristesys.com>
>>>> On 09/08/2015 03:35 PM, Carlos Alvarez wrote:
>>>>> Every Wifi phone I've tried will roam just fine between APs assuming
>>>>> the APs are properly configured.
>>>> Really? Can this take place seamlessly mid-call? With DHCP? What about
>>>> DHCP lease acquisition delay?
>>> An access point is an L1 bridge; everyone on the wireless side of every
>>> AP are all on the same LAN with the same addressing.
>>>> Would such a configuration involve merely bridging all the APs on the
>>>> same LAN segment so that the same DHCP server feeds them? If so, where's
>>>> the guarantee that the DHCP server will lease out the same IP address
>>>> to the client?
>>> Access points.  Not routers.
>> This implies that a level of intelligence/sophistication is (or isn't)
>> in the client unit that when it bounces to a new AP it wouldn't run a
>> refresh on the lease.  It would be very reasonable to think that an AP
>> with the same name might be on a different subnet (different
>> regions/depts of a large building, or whatever), which would then render
>> the call dead.
>> What you're suggesting is intelligent handoffs similar to a cellular
>> network.
>> -Aaron
>> _______________________________________________
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> Correct me if I'm wrong, but doesn't Ubiquiti's UniFi WiFi line do just
> that? Is there something I'm missing when a client moves closer to AP
> "B" and the network dynamically hands off the connection to AP "B"?
> --
> Robert Johnson
> BendTel, Inc.
> (541)389-4020
> Central Oregon's Own Telephone and Internet Service Provider
> http://bendtel.com/about/

Per existing standards the network doesn't decide AP selection, the
client does. The only specific roaming extension I know of is 802.11r
which defines a caching mechanism to reduce the authentication delays
associated with switching access points; the goal being that even
fairly complex 802.1x authenticated networks with RADIUS backends, etc
can provide the same general roaming characteristics and timing of
unauthenticated networks.

I imagine that various AP equipment vendors with controller based
architectures could (and probably do) implement some things to
influence client behavior and/or improve the roaming experience; such
as enforcing some administrator defined or preferred behavior by
having access points trigger client roaming with carefully controlled
output power, selective disassociation frames, AP/BSS specific
association rules/preferences, etc.

Generally speaking 802.1x is used in cases where the backend network
is almost always the same L2 VLAN where DHCP doesn't really enter the
picture although of course the client can certainly do or try all
kinds of strange things. In fact many 802.1x deployments map user
credentials to different L2 VLANs based on provided access credentials
(even over the same SSID). I would hope that in PSK environments this
remains the case, that is "same SSID = same VLAN".

Of course at the end of the day admins can do all kinds of strange
things (and so can equipment/software vendors).

Kristian Kielhofner

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