A standard is expected to be approved soon that will enable
seamless handoffs between multiple radio access networks.
As WiMAX networks start to proliferate around the world this year, it may seem that wireless telecommunications keeps becoming more complex and fragmented. WiMAX becomes another access technology to go alongside 2G and 3G networks and even Wi-Fi.
Even as the level of complexity increases, though, companies and organizations are working to make it easier for Joe Consumer to connect to these different networks. And not even knowing when he’s doing it.
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The chart shows the IEEE’s vision of how 802.21 can bring together
various air interfaceand signaling protocols, both wide area and local area. |
Source: IEEE |
That’s the vision of Qualcomm’s engineers in developing its Gobi and Snapdragon chipsets, both of which started shipping in late 2007. The former marries CDMA EV-DO Rev. A and W-CDMA/HSPA for notebook access. The latter supports HSPA and EV-DO Rev. B, Wi-Fi and Bluetooth, as well as multimedia services like broadcast TV, and high-definition video.
At a higher, organizational level, several computing and engineering groups are getting close to a standard allowing devices to seamlessly connect to a variety of access networks. These include WiMAX, Wi-Fi, Bluetooth, 3G cellular and even Ethernet.
The Institute of Electrical and Electronics Engineers (IEEE) is the principal organization working on this standard, which it has put under the 802.21 umbrella. Numerous company members are involved. And so is the Internet Engineering Task Force (IETF). The work has been mostly undercover, even though work on the standard has been going on since 2002.
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Converged mobile and fixed networks of the future will require seamless handoffs
between wireless networks (shown at the bottom of this illustration)
while always being connected to IMS and web services.
Connectivity will be through IP core networks.
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Source: InterDigital Communications |
The IEEE 802.21 work group is getting close to a final standard, which could be approved in the weeks before the IEEE’s 802 plenary session in Orlando, Fla., the week of March 16.
Ulises Olivera-Hernandez, who heads the standards effort at InterDigital Communications, says the idea for 802.21 came together in late 2002 as Wi-Fi was starting to take off. Engineers from Intel and InterDigital saw a need to have a standard to provide internetworking involving the 802 technology family. Initially the idea was to provide a framework for handoffs between 802.11 and Ethernet, which falls under 802.3.
Several proposals were made for a standard during 2003 and 2004, coming from Intel, InterDigital and Lucent, as well as others. As the work continued, other access technologies such as WiMAX and 3G were brought on. All along, according to Jack Indekeu, corporate marketing director for InterDigital, the idea was to have seamless handoffs between networks using multiple radios on the device.
Indekeu says 802.21 will provide handoffs for any IP-based services, including IMS services, instant messaging, VoIP, online gaming and others.
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InterDigital built a converged solution for Korea’s SK Telecom,
providing seamless handoffs between the carrier’s WiBro and W-CDMA networks.
The solution uses an 802.21 server and Mobile IP. |
Source: InterDigital Communications |
PRE-STANDARD SOLUTIONS
Using a working text of a proposed standard that was completed in 2005, the IEEE work group completed a draft standard in early 2007. Olivera-Hernandez says that draft was shared with other standards bodies like the IETF and 3GPP. It also meant that companies could use the draft standard as a template to start implementing pre-standard solutions.
“There is a good degree of stability” in the draft standard, he says. “Because the standard is still in the works it could change, but at this level it can be shared with others. Companies at this stage can implement it with pre-standard solutions.”
Other standards groups will have to modify or enhance their protocols to enable 802.21. In the case of the Wi-Fi family, that standard is 802.11u. The 3GPP has accepted portions of 802.21, enough so that the 3GPP’s Long Term Evolution can include 802.21 handoffs.
Olivera-Hernandez says the CDMA community, under the 3GPP2 standards body, has not yet developed protocols to enable 802.21.
The handoffs using 802.21 likely would be controlled by a server in each network, using a transport protocol being defined by the IETF. There also would be software on the handset to handle the client end of the handoffs. But Indekeu says 802.21 also would make it possible to have only a client on the handset, without a separate server. That kind of solution likely would not make all the services available for handoffs, especially information services.
Indekeu also says 802.21 will not mean any modification to the radio access network itself, so that legacy base stations and network controllers can be used. That’s because the basic approach is at the IP network level.
InterDigital is working with SK Telecom in Korea to implement a pre-standard 802.21 solution that will allow handoffs between SKT’s W-CDMA and WiBro (WiMAX) networks. SKT is using servers, which detect signal strength for dual-mode handsets and switches the access to the strongest.
Indekeu says SKT is deploying the 802.21 solution at its campus and in downtown Seoul, where it initially sees the greatest demand. The carrier initially is using a USB terminal for laptops but expects to have the solution on smartphones.
The main drawback for the use of 802.21 is that it does not support handoffs between circuit-switched and packet-switched networks, which could be a big stumbling block until carriers have an all-IP core. But Indekeu says carriers could use 802.21 in conjunction with another technology like Unlicensed Mobile Access that does support circuit-switched handoffs.
With networks heading toward an all-IP world anyway, 802.21 should be ready when carriers want to enable that kind of smooth handoff between multiple access technologies.