Roaming back and forth between wireless router and acesss point

[Xavier]

I am using 2 Linksys WRT160N wireless routers: one as my main router, and the second configured as an access point to cover my entire house -my router is in the basement, next to electrical panels and AC duct work

The access point is wired to one of the router ports, they use the same SSID/WAP key, and everything seems to work well -although I struggled several days with the WRT160N firmware DNS bug, but that's another story

I'm curious to understand what happens from a routing standpoint when a wireless device tries to "roam", say from the access point to the router wireless interface? Those IP packets that were coming through the LAN interface of the router -through the wired access point- are now sneaking through its wireless interface... How does the router know that it is not a duplicate IP address, or an intruder stealing an IP/MAC address? Or does the router just not care and quickly update its internal tables according to the new device location in the network map? Are some IP packets lost in the process?

I apologize if this topic has already been covered...

 

[thiggins]

Good question. Wireless roaming is a complicated topic and the exact sequence of events depends on the implementation in the AP and clients involved.

But basically what happens is that at some point, the client makes a decision to start looking for another AP to associate with. It then initiates the same scan process it used to connect to its current AP, i.e. scan for networks, associate, authenticate and connect.

How fast this all happens again depends on the firmware in the AP and drivers in the client. In most consumer wireless gear, things are not optimized to happen quickly and/or seamlessly. So you would probably see the connection drop, then come back. This would take seconds, so, yes, packets would be dropped. So if you were running a VoIP call, you would probably be disconnected.

 

[alevans51]

SEAMLESS ROAMING BETWEEN WI-FI ROUTERS / APs

I am trying to operate equipment with a smartphone from two separate rooms that are divided by a solid steel wall. As I walk from the room with the wireless router (NETGEAR WPN824N), to the room with the extender (NETGEAR WN2000RPT) I find myself having to re-acquire the signal, even though the SSID is the same and the channel is the same between the two devices.

Why can't I get some equipment that works like two cell towers do for a cell phone? Why all the promises of extending but not supporting seamless roaming?

 

[thiggins]

See the answer in my previous post. Consumer gear isn't made to do seamless roaming / fast handoff.

 

[stevech]

Because of the above... it's often best to give the AP a different SSID and let the human choose between the two SSIDs.

 

[sfx2000]

Apple Airport extended networks work just fine in my experience...

I can keep up VOIP and media streaming on iPhone/iPod Touch bouncing between AP's without a glitch.. it's a very fast Layer 2 handoff... not a layer 3, as the IP layer remains the same, it's all at the MAC layer and below...

My install... both the TC and the APExtreme are 3-stream capable.

Cable Modem -- TimeCapsule 4th Gen -- Airport Extreme

The AP extreme is the extended AP, connecting to the TC on 2.4GHz 3 stream - it's dual band as is the TC with common SSID's on both bands. Wide channels on 5GHz, clients include PC's, Mac's, and iOS devices (iPad, iPhone, iPod Touch, and two Apple TV's).

Like I mentioned above - common SSID on both bands, and I let the devices choose which band and AP to attach to - for the most part they make the right choice for Win/Mac - my current Ubuntu box seems to get a bit confused about things, need to dig into that at some point...

Smallish house, 16oo sq ft - the TC is on one side of the house, the APX is in the middle - mostly the APX supports the two streamers (aTV's) and my wife's Macbook air on 5GHz - the TC is mostly GIGe in my office, but devices can hop onto it for WiFi and it also supports dual-band Guest Networking (only on the TC, guest network in Airport speak, cannot be extended).

I get 95Mbps down/70Mbps up on the TC - on the extended network, I get 45Mbps up/45Mbps down on 5Ghz with a Macbook Air 2010 connecting to a Linux host on my 100-Base-T LAN using Speedtest Mini... the TC bandwidth likely would be faster if the Linux box had a GIGe card in it - right now it's using a Intel Pro100 PCI card...

Having a decent performing multiple AP network just comes down to design and hardware - single vendor for the AP's is key - should get similar performance for non-Apple equipment - I'm not an Apple fanboi, but what I can say is that Apple does a decent job with their AP implementations...

I've had up to 30 devices on my WiFi - mixed mode b/g/n and dual band devices - the WiFi network grunts a bit, but everyone has good connectivity and bandwidth.

 

[Mark Uhde]

I am trying to operate equipment with a smartphone from two separate rooms that are divided by a solid steel wall. As I walk from the room with the wireless router (NETGEAR WPN824N), to the room with the extender (NETGEAR WN2000RPT) I find myself having to re-acquire the signal, even though the SSID is the same and the channel is the same between the two devices.

Why can't I get some equipment that works like two cell towers do for a cell phone? Why all the promises of extending but not supporting seamless roaming?

Same channel = bad. But that's what those repeaters do. Don't use a repeater. Use a second AP, with the same SSID and security but on a DIFFERENT, NON-OVERLAPPING channel (stick to all channels 1,6,11 or all channels 1,5,9,11). It'll work much better.

And you absolutely can get equipment that works similar to how cell towers do - Cisco (not Linksys, not Cisco Small Business, but full scale managed Cisco Aironet) is definitely the leader in that space. Their proprietary fast roaming extensions are supported on many, many client devices.

Because of the above... it's often best to give the AP a different SSID and let the human choose between the two SSIDs.

Words cannot express how STRONGLY I disagree. I see this done in offices, malls, everywhere. BAD IDEA. The user probably barely even knows what "north wing" for example is, and almost certainly cannot be trusted to pick the best network. Same SSID and security insures that the client driver (which is MUCH smarter than 99% of users) picks the best AP. This benefits your ENTIRE NETWORK, not just that user, because an edge-of-cell user requires more airtime for a given amount of data transfer, AND increases hidden node problems and interference with adjacent, co-channel, AP's.

In other words, except in very limited circumstances, NO, use THE SAME SSID. The computer is much smarter about these decisions than your users!

 

[sfx2000]

Same channel = bad. But that's what those repeaters do. Don't use a repeater. Use a second AP, with the same SSID and security but on a DIFFERENT, NON-OVERLAPPING channel (stick to all channels 1,6,11 or all channels 1,5,9,11). It'll work much better.

Same channel, different channel - lot depends on how the 2nd AP is connected to the first AP, and OEM implementation - one key thing to take into consideration though - the 2nd AP should only be in AP mode, not as a router - SNB has a good article there - disable the DHCP server and connect to a LAN port if you're going wired to the second AP...

Repeaters can work well for low-bandwidth devices like handhelds (smartphones/tablets) - but placing the repeater is critical...

 

[stevech]

Professional WiFi uses non-IEEE methods to improve fast handoffs in WiFi. Usually though, it requires cooperating software in the PC / handheld device.

Fact: The speed and efficiency of the change-of-AP is dependent on what the client PC/handheld does, not the infrastructure device, in IEEE standards based systems (versus proprietary as in the preceding paragraph). IEEE 802.11 b/g/n lacks any infrastructure-directed handoff mechanism like cellular has.

 

[Mark Uhde]

Professional WiFi uses non-IEEE methods to improve fast handoffs in WiFi. Usually though, it requires cooperating software in the PC / handheld device.

Fact: The speed and efficiency of the change-of-AP is dependent on what the client PC/handheld does, not the infrastructure device, in IEEE standards based systems (versus proprietary as in the preceding paragraph). IEEE 802.11 b/g/n lacks any infrastructure-directed handoff mechanism like cellular has.

Correct, I believe I stated if you're referring to me - "And you absolutely can get equipment that works similar to how cell towers do - Cisco (not Linksys, not Cisco Small Business, but full scale managed Cisco Aironet) is definitely the leader in that space. Their proprietary fast roaming extensions are supported on many, many client devices." Sorry if you weren't referring to me, but it sounded like a response to what I said, and I was pretty clear (I think) that I was referring to to Cisco's proprietary fast roaming. Yes, it requires clients to support Cisco Compatible Extensions, but many do. Cisco is not the best performer out there under load (that goes to Ruckus) but between their very good airtime fairness and their fast roaming extensions that are widely supported, Cisco is the way to go for a VoIP network.

By no means does all professional Wi-Fi use proprietary fast roaming though. If you don't need VoIP it's unnecessary. There's a lot of good, managed even, Wi-Fi without fast roaming. Ubiquiti UniFi is a nice managed system. EnGenius EAP's work great for the money was well, and while not managed, have EnGenius' "zone controller" software that gives you some of the benefits of a managed system. Plenty of professional networks are not using fast roaming in any form. Most clients, and, as you note - it's very dependent on the client - can roam fairly seamlessly in a properly setup network.

sfx2000, your points are good, that's what I guess I was trying to say. Except my opinion on repeaters is harsher - avoid at all costs. If you need wireless backhaul, use a separate WDS infrastructure network dedicated just to backhaul. The exception to this is some managed systems like Ruckus, that are optimized for mesh deployment with minimal performance impact.

 

[stevech]

WDS repeaters.. major PITA.

 

[sfx2000]

Professional WiFi uses non-IEEE methods to improve fast handoffs in WiFi. Usually though, it requires cooperating software in the PC / handheld device.

Fact: The speed and efficiency of the change-of-AP is dependent on what the client PC/handheld does, not the infrastructure device, in IEEE standards based systems (versus proprietary as in the preceding paragraph). IEEE 802.11 b/g/n lacks any infrastructure-directed handoff mechanism like cellular has.

Some do, some don't - what I've seen from first hand experience - Cisco does a great job of layer 2 fast handovers with their enterprise gear, even the older Aeronet's on 802.11a/g - upside I suppose of having thin AP's with a central controller... worked fine with devices even without the Cisco client software installed.

At my current workplace, we have Aruba, and to be honest, they don't even do Layer 3 handover...

 

[stevech]

Cisco Aironet has an option called Cisco Certified Extensions or some such. If the client PC/handheld has this support installed, the client can detect what APs exist near the currently chosen AP. This is a "neighbor list" sent by the chosen access point, usually as data content in the 802.11 SSID broadcast frames. The client can use the list to be "ready" to change to a neighbor given its "pre-discovered" as to what channel to use. And moreover, the fast reassociation for enterprise users is improved by passing the authentication (RADIUS) credentials to avoid repeating that. And so on.

I assume that Cisco continued this when they bought AirEspace to get a thin-AP capability to compete with the likes of Aruba.

None of this exists in the Linksys consumer gear, as I understand.

 

[Mark Uhde]

None of this exists in the Linksys consumer gear, as I understand.

Or in Cisco Small Business gear. Cisco Certified Extensions for fast handovers is the biggest selling point for Cisco managed networks. But how many of us really need fast handovers? They're only needed for VoIP, and only then if you're using VoIP mobiles and the like.

Most client cards make the handover process very quick even on standard equipments IFF your network is setup properly (all the same SSID, etc). The reason using the same SSID and security is critical is because if you don't, most clients won't switch until they completely and totally lose the first SSID. At which point it'll have long been unusable, and your handovers will be messy as heck, take forever, and you'll have a slower network (lower data rates, more hidden nodes).