From Here to Infinity

As the mobile Internet gains momentum, informed industry observers now accept the need for the expanded address capacity available only from the Internet Protocol version 6 (IPv6). But how do we get from the current-generation IPv4 to the protocol of the Web-enabled future?

The Transition

The current IPv4 and the next-generation IPv6 will co-exist for a significant period of time. This will prolong the useful life of existing infrastructure and applications, while amortizing the investment needed to deploy this new protocol over a number of years. At first, isolated IPv6 sites will be connected to one another over the IPv4 network. Then, as the world gradually shifts to the more robust and scalable protocol, this situation will be reversed so that pockets of IPv4 technology will still work in the emerging IPv6 environment.

Due largely to the introduction of wireless Internet services and technologies, mobile communications networks need a logical, cost-effective means to transition between IPv4 and IPv6 standards. Mobility is standardized in the IPv6 protocol. Each mobile node or element identified with a home address is stored by a home agent and is addressable by one or more “care-of” addresses when attached to a foreign link.

The Gateway GPRS Support Node (GGSN) and the mobile terminals themselves will experience the most significant changes as mobile networks move toward IPv6. The three main transition mechanisms are dual protocol stacks in network elements and terminals, tunneling and translators in the network.

Dual Stack

Because a simultaneous, tandem-IP stack strategy delivers comprehensive support for both current- and next-generation protocols, it's the preferred approach by the wireless industry. On the network side, a dual protocol stack is needed in the GGSN to create IPv4 and IPv6 access points and to support the tunneling method. EDGE routers at the border of the carrier's IP network and the public Internet should also feature dual-stack capabilities. And mobile terminals will require dual stacks to function in this transitional environment.

Tunneling

Newly deployed IPv6 sites and hosts can be connected using configured and automatic (for example, “6 to 4”) tunneling. In this approach, IPv6 packets are encapsulated within IPv4 packets, and then decapsulated at the destination end of the tunnel. Tunneling will require dual-stack capabilities in the encapsulating and decapsulating nodes.

Translation

For nodes using different IP versions, Network Address Translator/Protocol Translator (NAT-PT) components also may be used. Header conversion, in which packet headers are converted to and from IPv4/IPv6 with checksum adjustments, is a key mechanism of the translation method.

Translation introduces the problems of end-to-end service breaks and a potential new single point of failure into the mobile network. Although some industry representatives advocate using NAT to prolong the useful life of the IPv4 standards, others believe that NAT simply delays the inevitable, adding unnecessary cost as carriers evolve to IPv6.

What will this transition cost? For most, the IPv4 to IPv6 migration will consist primarily of upgrades in router software and adjustments in network management and DNS functionality. By planning a phased, multiyear evolutionary migration, wireless carriers and service providers can spread the costs, while accelerating the benefits.

What's Next?

There will be three phases in the transition of mobile networks from IPv4 to IPv6.

In the initial phase, widely separated IPv6 islands will be connected using automatically or manually configured tunneling. In the second stage, as IPv6 infrastructure and services become more prevalent, new applications will be deployed on next-generation protocol platforms, and IPv4 tunneling will be used to ensure seamless connectivity. In the third and final phase of implementation, IPv6 will become the dominant protocol standard, and there will be an accelerating disappearance of dual-stack, tunneling and translation methods.

Mobility will place massive new capacity demands on the Internet. Next-generation IPv6 is now widely accepted as the solution to the approaching IP address shortfall. By moving now to begin this evolution, and by understanding the methods and steps needed to complete this migration, carriers can better drive the wireless Internet.

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Suomela is Nokia's technology manager for Internet protocols.