It's no secret that wireless LANs have become increasingly popular. Wide area networks (WANs), like GSM/GPRS and 3G, are the other essential part of the overall wireless data equation. WANs provide wide-area coverage to data users on the move, and at lower rates than WLANs. As far as mobile data is concerned, both WLANs and cellular technologies like GPRS/3G are complementary.
While WLANs provide high-speed wireless data in specific locations, WAN technologies provide wide-area mobility not feasible with WLANs. This means that WLAN/WAN integration is necessary to enable users to access wireless data services seamlessly, taking advantage of high-speed wireless LANs where available and falling back to WANs when on the move or in regions without WLAN coverage. Enterprise users, in particular, can benefit from this integration.
In a broad sense, two types of WLAN/WAN integration are possible. We'll look at both in some detail.
Loose integration
Loose integration involves methods that allow users of a particular mobile network to access operator-controlled WLANs. The mobile operator does the billing and the user receives a consolidated bill. The integration here is "loose" because a seamless handover between WLAN and wide area networks like GPRS is not possible with this method.
One form of easily achievable WLAN/WAN integration requires that subscribers have SMS-enabled handsets (apart from laptops or PDAs) that are equipped with a WLAN card. When in a region with WLAN coverage, the user can access the WLAN by entering his or her mobile phone number into a login screen in their laptop browser. The access gateway, connected to the WLAN as well as the WAN, sends an SMS to the mobile via the WAN, which contains a one-time access (OTA) password for accessing the WLAN. This way the subscriber doesn't need to maintain separate accounts for WLAN access.
Ericsson offers this kind of WLAN/WAN integration; however, it isn't very secure. Enterprises may not be comfortable allowing this kind of access to their WLANs. Further, because of SMS's nature, there can be unnecessary delays in accessing the WLAN.
In a variant of this method, the user is provided a static login and password. The static password replaces the OTA password generated using SMS.
Other techniques allow cellular (WAN) users access to WLANs with a high level of security and authentication.
A user's laptop is equipped with a SIM cardholder apart from the WLAN card necessary to access the WLAN. When the user accesses the WLAN, standard cellular network-like authentication is performed by means of middleware platforms that securely transport authentication information from the user's SIM card over any IP network (including Internet) to the operator's cellular network, where the user is authenticated just like any other cell phone user. Billing and access control are done by the mobile network.
Tight integration
Tight, or "seamless," integration is based mostly on a mobile IP implementation. Such integration provides seamless access and handovers from WLANs to WANs, and vice versa.
Devices equipped with dual WAN/WLAN adapters detect network availability for WAN/WLAN. An Authentication, Authorization, and Accounting (AAA) network element interfacing between the WAN and the mobile network performs the access control and accounting functions. The mobile IP actually takes care of handovers from one network to another. However, implementations like this require subscribers to have dual mode devices or interface cards.
Tight integration should be particularly relevant in North America where CDMA2000 is expected to be prevalent. CDMA2000 uses Mobile IP for handovers between subnets, making it relatively easy to apply Mobile IP-based integration with WLANs. Similar GPRS/WLAN adapters, which provide seamless integration between GPRS and WLAN networks, are now available.
WLAN/WAN integration will become more important as WLAN popularity and the demand for mobile data increase. Integration will combine the speed and cost benefits of WLANs with the wide coverage and mobility of mobile networks. For enterprise users wanting to stay in touch with corporate information, this integration will be most useful, indeed.
Puneet Gupta is a wireless and Internet technology writer and independent consultant.
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