6LoWPAN: The wireless embedded Internet - Part 4: Addressing, etc. & a network example

When connecting a LoWPAN to another IP network or to the Internet, there are several issues to be considered. 6LoWPAN enables IPv6 for simple embedded devices over low-power wireless networks by efficiently compressing headers and simplifying IPv6 requirements. Issues to be considered when integrating LoWPANs with other IP networks include:

• Maximum transmission unit: In order to comply with the 1280 byteMTU size requirement of IPv6, 6LoWPAN performs fragmentation and reassembly. Applications designed for the Wireless Embedded Internet should however try to minimize packet sizes if possible. This is to avoid forcing a LoWPAN to fragment IPv6 packets, as this incurs a performance penalty. Additional considerations on fragmentation avoidance are covered in Section 2.7.2.

• Application protocols: Application protocols on the Web today depend on payloads of HTML, XML or SOAP carried over HTTP and TCP. This results in payloads ranging in size from hundreds of bytes to several kilobytes. This is far too large for use with 6LoWPAN Nodes. End-to-end application protocols should make use of UDP and compact payload formats (preferably binary) wherever possible, as discussed further in Chapter 5. Technologies which are capable of the transparent compression of web services into a format suitable for 6LoWPAN Nodes are especially interesting.

• Firewalls and NATs: In real network deployments firewalls and network address translators (NATs) are a reality. When connecting 6LoWPAN through these there may be several problems that need to be dealt with, for example the blocking of compressed UDP ports and non-standard application protocols used for 6LoWPAN applications, along with the unavailability of static IP addresses.

• IPv4 interconnectivity: 6LoWPAN natively supports only IPv6, however often it will be necessary for 6LoWPAN Nodes to interact with IPv4 nodes or across IPv4 networks. There are several ways to deal with IPv4 interconnectivity, including IPv6-in-IPv4 tunneling and address translation. These mechanisms are typically collocated on LoWPAN Edge Routers, on a local gateway router, or on a node configured for that purpose on the Internet. IPv4 interconnectivity is covered in Section 4.3.

• Security: When connecting embedded devices to the public Internet, security should always be a major concern as embedded devices are limited in resources and are autonomous. This is very much so with 6LoWPAN as node and network limitations prevent the use of the full IPsec suite, transport layer ("socket") security or the use of sophisticated firewalls on each node. Although link-layer security inside a LoWPAN (employing the 128-bit AES encryption in IEEE 802.15.4) provides some protection, communication beyond LoWPAN Routers is still vulnerable. This increases the need for end-to-end security at the application layer. Security is dealt with further in Section 3.3.