60 Seconds with Akbar Rahman
Principal Engineer, InterDigital

Akbar Rahman has 15 years of experience researching and developing wireless systems. He's Principal Engineer at InterDigital (www. interdigital.com), where he leads the 802.21 initiative, an upcoming IEEE standard that will govern the handover of mobile services, transitioning wireless signals from one type of network to another. It's a perfect project for InterDigital, which for more than 35 years has developed advanced wireless technologies and products that drive voice and data communications, such as their SlimChip family of high performance mobile broadband modem solutions.

Richard "Zippy" Grigonis recently spoke with Rahman about IEEE 802.21 and UC.

RG: What's the theory behind IEE 802.21?

AR: Our main model is a packet-switched IP world. The key requirement is our desire for mobility among different access networks so we can plug in as a sort of subnet into this environment. The traditional wireless interfaces we're talking about here are wireless LANs, different versions of cellular [UMTS, CDMA 2000, etc.], WiMAX and its variation, WiBro. Until now, handover has been achieved in limited scenarios and has been something of a patchwork. The vision of IEEE is that, as we move into the future, more and more devices will be equipped with multiuple radios, primarly cellular and WLAN. But, going forward, there will also be WiMAX and the choice of docking the device into an Ethernet network. In the wired world, providers have achieved some limited mobility and nomadic support. But in the wireless world we want more capabilities. We want to stay connected as we move between these different technologies, so we have a good experience.

That leads us to IEEE 802.21. About five years ago, the IEEE recognized the need for a standard supporting mobility across various IEEE standards technologies, and for the mobile user to experience handover exhibiting very small or even no interruption times. Also, it should provide QoS continuity across the different technologies as you handover the signal. In terms of the actual implementation, it had to follow an IP model. So its simplest manifestation would be a thin client on the terminal and some type of server in the network. Everything between is IP. So you only have to alter the end nodes to achieve seamless handover.

You can do a network-controlled handover - let's say an operator in a given city owns a cellular network, plus a wireless WLAN hotspot network. Owning both networks, it might feel that it's best able to make the decision about the handover in the network, and this new standard will allow them to do that. Or, if the wireless hotspots are independent or owned by a different operator, the client could make the decision about handover, because there's no obvious "central" place in the network where it could be done, since the networks are owned by different operators. That's why the standard allows both models.

IEEE mandates 802.3 Ethernet, 802.11 Wireless LANs, 802.16 WiMAX, and now the new 802.21 protocol so you can do handovers, for example, between Ethernet and Wireless LANs such as WiFi, or Wireless LANS and WiMAX, or between any new IEEE standard that will ever appear.

However, the 3G cellular standards are formulated by different standards bodies, the 3GPP and 3GPP2, but the IEEE is trying to get them to support this model for handover between, say, WiMAX and cellular. That's the main target. WiMAX and 3GPP/2 handovers should be 802.21-based. We'll see how those discussions turn out.

In the upper layers, the IEEE has been working with IETF to work with the main protocols such as SIP (Session Initiation Protocol), Mobile IP or the new variation, Proxy Mobile IP, also known as Proxy MIP or PMIP. IEEE 802.21 assumes that the upper-layer mobility for IP address changes are handled by an IETF protocol, and it will occur in the lower wireless layers, such as Layer 1 and 2.

RG: What about IMS compatibility?

AR: The basic concept is compatible with IMS [IP Multimedia Subsystem] though IMS' VCC [Voice Call Continuity] actually handles circuit switch-topacket switch handovers, which is complementary to 802.21's packet switch-to-packet switch handovers. But all of these protocols can work together.

Assuming that IP stacks remain popular, 802.21 will make handover among all wireless technologies quite seamless. You'll be able to roam anywhere, with any mobile device in any network being able to handover to anything else.