IP mobility to run seamless course

he slow data rates of current cellular networks combined with the rapid deployment of high-speed wireless local-area networks (WLANs) is creating a demand for Internet Protocol (IP) mobility solutions to allow seamless roaming between the two heterogeneous systems.

"The marriage of these two networks can greatly increase applications and the productivity to the end user," said Ali Tabissi, chief technology and development officer at Mobilestar Network Corp., which is busy wiring public areas with high-speed broadband wireless connectivity. "We’ll continue to deploy WLANs in hot spots," he said, "but at the same time, we’ve been in discussion with cellular and PCS providers as we do see the need for convergence between these two."

While the market opportunities may be clear, service providers offering both wide-area and local-area options face a daunting task, as that connection must be made seamless if users are to truly benefit. Seamless can be defined as the ability to migrate from subnet to subnet and network to network without loss of connectivity and without applications timing out–all done transparently to the user.

"In addition," said Tabissi, "billing is a major issue. Clearly, if the two networks are capable of doing real-time billing, this isn’t too much of a challenge–but those who don’t have real-time billing and providing customer data in real-time will have a problem." Cellular networks already have this scheme in place, he said, as does Mobilestar. "Nonetheless," said Tabissi, "I don’t see this [convergence] as a short-term thing - it’s nine to 12 months before we see this being implemented."

And the reasons are manifold. Along with IP mobility requirements and customer billing, the design of a physical layer that caters to all the potential air interfaces remains elusive, though startups are wrestling with 802.11b (WLAN)/general packet radio service (GPRS) solutions out the door. Other combination radios include 802.11b/Bluetooth, 802.11b/802.11a, and even claims of software-defined radios that cover the whole spectrum from 300 MHz to 5 GHz. All have yet to be proven.

In the meantime, the common link that will maximize the use of all the networks as they migrate toward all IP resides in the concept of IP mobility. Not a new concept, IP mobility ranges in form from standards-based solutions based on Mobile IP, as defined by the Internet Engineering Task Force (IETF) in 1996, to a plethora of relatively new proprietary solutions from companies such as Columbitech, NetMotion, PacketAir, and Vernier.

Though not new, IP mobility has been slow to catch on, but that is changing. Thanks to WLAN developments, in both the enterprise and the public space, as well as the realization that the long-awaited third-generation (3G) networks, with their promise of 2-Mbit/s connectivity, may take some time to materialize, operators are seeing the need to maximize use of current networks.

Current data-enabled wide-area networks (WANs) have achieved anywhere from 9,600 bits/s to 144 kbits/s, compared with 11 Mbits/s for WLANs (actual payload and data rates vary). In addition, as 802.11a-compliant networks in the 5-GHz range start to emerge, and Intel is promising product this month, the WLAN data rate will jump to 54 Mbits/s. Hence the drive to devise a scheme whereby a user can migrate between cellular and WLAN networks.

All the schemes offered to date have their relative advantages and disadvantages. Scalability marred by slow adoption typifies standards-compliant Mobile IP-based solutions, while speedy rollout hampered by limited adoption has been the signature of proprietary solutions.

"The IETF gets a bunch of new [IP mobility] proposals every year," said Basavaraj Patil, senior systems engineer at Nokia (Irving, Texas), and co-chair of the Mobile IP Working Group within the IETF. "There’s a lot of momentum behind Mobile IP, so it’s going to be a matter of numbers," he said, pointing to the cdma2000 networks now ramping up, namely from Qualcomm and Nortel Networks. They recently announced the first Mobile IP connection over a 3G network (cdma2000 1x). The connection was made using the Qualcomm MSM5105 Mobile Station Modem and Nortel’s Shasta wireless Internet infrastructure equipment. The call was made using the IS-835 codification of Mobile IP for cdma2000 networks.

The equipment used to form the connection comprised a Qualcomm Surfboard terminal connected into a PC, and through that a data session was initiated. The connection was made "not as a dial-up mode but as a true wireless RTT connection into the PDSN [packet data service node]," said Chuck Bradshaw, senior product manager of CDMA solutions at Nortel. "The PDSN then connected into the external network (through firewalls), FTP’d onto corporate servers and showed the hand-off of data."

An enabling factor for the Qualcomm/Nortel connection, along with the extensive network support, was the development of a Mobile IP client on the Qualcomm terminal. "While IS-835 has been defined for a while," said Bradshaw, "in reality, vendors are just now getting to the point where they’re interoperable."

Mobile IP has also been deployed on Nextel’s iDEN network and SK Telecom’s cdma2000 network in Korea.

Ecutel (Alexandria, Va.) is promoting its own Viatores Mobile IP solution, and through Hewlett-Packard has allowed Telenor, the Norwegian carrier, to seamlessly roam from a LAN, to a WAN, to a GPRS network–"and in some cases even a high-speed GSM network," said John Harrison, co-founder of Ecutel. Here in the United States, the company "has some Phase 1 deployments," said Harrison, "but we can’t say who with."

While Mobile IP is the mobility path for cdma2000 networks, GPRS networks have chosen to go the GPRS Mobility Manager (GMM) route, though GMM does allow for the inclusion of Mobile IP foreign agents.

"Though both are going their own Mobile IP way," said Patil, "three or four years down the road, when Mobile Ipv6 comes about, there might be some convergence on the type of mobility they choose."

Unfortunately, time is something mobile network operators don’t have, say proponents of proprietary routes to mobility. Recognizing the need for IP mobility between networks, and the lack of interoperable Mobile IP solutions available, companies such as Columbitech and NetMotion have introduced their own proprietary solutions.

"There are two paths to solving the problem of roaming between different types of networks and to combine that with security," said Pontus Bergdahl, founder and chief executive officer of Columbitech. "There’s Mobile IP combined with IP security (IPSec), the other is the session mobililty, which puts the roaming and security function at Level 5 on the stack. That’s what Columbitech is doing–so we’re completely independent of Mobile IP."

The problem with Mobile IP networks is that each operator or enterprise has to ensure that their home agent works with the foreign agents of networks into which subscribers may want to roam–"and that’s a major issue for that system," Bergdahl said.

The user advantage of Columbitech’s approach, Bergdahl said, is that if there’s a lapse in data transfer, the application won’t time out. At the same time–and contrary to the Mobile IP approach–a session-level approach is not dependent upon providing a constant IP address.

"Mobile IP has to constantly ping the basestations and also if you roam from a CDPD network to a WLAN network to a Bluetooth network or a GPRS network," Bergdahl said, "you are still changing IP addresses."

With the session-layer approach, when a user roams, rather than protecting the transport session, Columbitech will actually break it at the time of roaming between networks. "We cache the session," said Bergdahl, "and when the client reestablishes a connection with the corporate server, which has also cached the session, the application continues where it left off." In the meantime, a new IP session is being established underneath.

Columbitech uses wireless transport-layer security to secure the connection.

Other companies have taken the session-layer route, including NetMotion (Seattle, Wash.). "We wanted a way to enable mobility with the existing infrastructure without having to modify your system, unlike Mobile IP," said Emil Sturniolo, chief technology officer of NetMotion. "All we need is for the device to have DHCP [Dynamic Host Configuration Protocol], which is very pervasive in business and home."

Sturniolo also pointed to the fact that Mobile IP is simply a packet-forwarding algorithm, so all it can do is forward the packet to the address of where the device happens to be. "But what happens at the transport layer if the device is out of range or has been suspended for conservation of battery? There’s no way to handle that," he said.

Other paths to mobility include PacketAir’s router-based option. "But that only solves the problem on that particular network," said Sturniolo. "If I go off that network, it doesn’t work as it needs to be deployed across the entire infrastructure–we want mobility today, and then add standards as they evolve." NetMotion and others can add Mobile IP capability as it gels as a standard.