UMA vs IMS

Inmoving beyond superficial services bundling in pursuit of truly integrated FMC services,carriers are proceesing down two distinct main technology paths:unlicensed mobile access (UMA) and IP multimedia system (IMS)

UMA is preferred primarily by mobile carriers,as it operates effectively as an extention of the mobile network,keeping all control in the hands of the mobile carrier.When a mobile subscriber with a UMA-enabled,dual mode handset moves within range of a WLAN access point, it can attemp to roam onto WLAN.The handset contacts a UMA network controller via the IP access network, and if authenticated and authorized,has it current location information registered by the mobile network,which routes further calls via the WLAN

Most industry analysts view UMA as tactical,intermediary step on the part of mobile carriers who are not yet ready to convert their extensive global system for mobile communication (GSM) and general packet radio service (GPRS) core networks to IP, an IMS prerequisite

The UMA functional architecture are:

1. mobile station
2. WLAN access point
3. Broadband IP network
4. UMA network controller (UNA)
5. UNC security gateway
6. Public land mobile network (PLMN) : mobile switching center, serving GPRS support node, AAA proxy server, HLR
7. Home PLMN (roaming case) : AAA server, HLR

IMS is prefered primarily by carriers (typically fixed) that already have extensive IP backbones in place, as it keeps call control in their hands and runs VOIP and SIP without major impact on their networks.

Its primary advantages over UMA are its scalability and applicability to a much broader range of underlying access technologies.Its basis in IP yields an ability to leverage the much wider range of applications that already exploit IP based services and interfaces.Its reliance on SIP based signalling simplifies the introduction of multiservice combinations,e.g, instant messaging plus voice

Perhaps most important,it provides a basis for more sophisticated billing of new services,allowing carriers to more quickly monetize the considerable investments they will have to make in network infrastucture, OSS upgrades and system integration services to migrate to IMS

The three layer architecture of IMS are:

1. Transport layer : core network
2. Control layer : home subscriber service and call session control function
3. Service layer : application servers

What FMC means to enterprises today

Many enterprises may look at the timeline for the arrival of true FMC services and conclude that it can be safetly ignored for now. To the extent that FMC is in the hands of carriers, this is largely true.But enterprises do have one critical element of FMC in their control today: their WLANs. Furthure, most market researchers are forecasting rapid growth over the next few years in enterprise spending on WLAN equipment.

A majority of network managers expect to voice enable their WLANs in that timeframe.Even if enterprises discount the possible arrival of FMC service, they should be scrutinizing how well ther WLAN build outs can accomodate high quality mobile voice service

As it happens,the key WLAN capabilities required to deliver mobile voice over WLAN services - granular control of QoS and security,fast voice call handoffs when raoming,zero configuration access from a wide range of devices,graceful capacity scaling,tighter integration with wired LAN infrastructure and improved WLAN security - are perfectly congruent with those needed to facilitate FMC services.Thus investments in voice grade WLAN infrastructure today can yield a second payoff if enterprise eventually migrates to FMC services