Signal Handoff Could Mean Roaming VoIP over WiFi

wassup writes "According to this article in MIT tech review (and here), researchers at University of California San Diego have developed a technology called SyncScan that will reduce handoff delay in WiFi networks to a few milliseconds. VoIP roaming will be here soon!"

Comments

What about TCP/IP handoff?

[hgilde]

Last I checked, VOIP uses TCP sockets. When you move between WiFi base stations, you first must discover your new DHCP server, then get a new local IP address, then reconnect to the VOIP server.

This will definitely be an annoying delay.

Re:What about TCP/IP handoff?

[c_g_hills]

This is why IPv6 is a much better network (layer 3) protocol for VoIP as it supports mobility natively, allowing TCP and UDP sessions to be maintained when roamning from one network to the next.

In fact, the Internet Society point out that IPv6 is necessary for mobile and wireless internet.

Re:What about TCP/IP handoff?

[templeton008]

sip can go over tcp or udp, it's most often used over udp though. The actual rtp audio stream goes exclusively over udp to minimize delay/complexity (it doesn't matter if some packets get dropped).

Re:What about TCP/IP handoff?

[Anonymous Coward]

You are correct about the TCP/IP issues, but the design for multi-AP networks
is to have them all on the same subnet. Then the act of roaming between APs
is scoped to L2.

That leaves a couple different sources for delay/glitch:

One is if the wireless client were to set the WiFi interface "down" upon
dissassociating with the initial AP, then setting the interface back "up"
once it associates with the next AP. This may have the affect of triggering
the IP stack to release it's address information, and then restart a DHCP
transaction when the interface comes up. This sort of thing should be easy
to avoid in a WiFi VoIP client though.

The other stickler is WiFi authentication. Most WiFi users are used to WEP
with Open authentication, which is more or less instant. But a modern,
enterprise-level network with modern authentication features (802.1x/RADIUS)
makes the authentication step not-so-instant. Cisco has some proprietary
features in their APs to make roaming in such an environment a much faster
operation (they basically use an authentication "proxy" of sorts). I follow
this stuff because I'm helping develop a competing AP at the company I work for.

I'm glad to see some new ideas come out, but from looking at the article, it
doesn't look like this new research is taking the full context of the wireless
network - including the authentication scheme - into account.