In the last week Microsoft have released their Lync Mobile Clients, which support IM, Presence and Call via Work. Competitors have made a lot of noise around the seemingly limited functionality such as not providing Voice over WiFi, Video or Desktop sharing. Like any competitors they will openly pick holes in a product rather than look at why Microsoft may have done this.
Taking a look at the Voice and Video over WiFi aspect of this (and to some extent desktop sharing). Current Wireless Technology is somewhat limited when it comes to Real Time Media and the average Wireless deployment is usually not designed with Real Time Media in mind.
While users can use their Laptop and use real time media within application such as having a Lync call over a wireless connection issues start to occur the moment someone starts to walk around with the laptop. This is because WiFi was never really designed to be used while people are moving, yes it is designed for mobile workers but for them to be stationary while using it.
This changes the moment you start to use a mobile device over WiFi as a user will often walk around with the device, potentially getting further away from an Access Point reducing the signal strength and available bandwidth, moving between access points or even worse outside of coverage completely.
The last two points, moving between access points and leaving the coverage are the ones which really cause issues with real time media over WiFi. Access points do not have the ability to seamlessly handover connections between them; due to this there can be instances where you lose the network connection for a few seconds when moving between them. For real time media this causes major issues and you will lose part of a call for example. This is why technologies such as DECT are still widely used (and seen as the industry standard for wireless telephony devices) as they do offer this functionality and are specifically designed for users moving about while on a call.
Looking at the issue that occurs when leaving the wireless coverage completely, users will be in a position where their call terminates since there is no capability to provide a seamless handover between the WiFi and GSM (this isn't a Lync issue, it is industry wide). Due to this if a user moves out of coverage of the Wireless network then the call will drop and they will have to re-dial causing user frustration along with a bad experience.
This is why Lync Mobile sticks to Voice over GSM as it is the only way to guarantee good quality call and a good experience. This is the “Call via Work” functionality where Lync will place an outbound call to the Mobile Device and then an outbound call to the number dialled, this could be to another Lync user in which case it could be a SIP call or it could be out to the PSTN.
While there is generally a cost to placing these calls it is often the trade-off between having a good call and an alright call which could drop halfway through, personally I know which one I would prefer. There are also ways to mitigate these costs such as using a dedicated “Mobex” connection to your GSM provider or through Mobile Gateways which utilize SIM cards to place calls.
I have worked with several customers who use Mobile Gateways and associated SIM cards they are very easy to set-up and are usually connected to a Lync Certified Gateway, such as NET. On these gateways a static route could route all mobile calls to them or functionality such as LDAP lookups can be used to dynamically route calls for mobile devices owned by the organization to the Mobile Gateway.
Depending on the contracts negotiated with mobile providers it is sometimes possible to provide free calls between the Mobile Gateway (which are effectively mobile phones) and the mobile phones.
Lastly some vendors have stated that they are developing new Wireless Access Points to better support real time media over WiFi, if they do this it should benefit all users who want to run real time media over WiFi, but the very requirement that they need to do this demonstrates that today there are issues.