Tổng quan về chuẩn 6LoWPAN

1. 
   Features

• 6LoWPAN = IPv6 over Low-Power wireless Area Networks
• Defined by IETF standards( RFC 4919, 4944)
• Stateless header compression
• Enables a standard socket API
• Minimal use of code and memory
• Direct end-to-end Internet integration
  
• support for e.g 64 bit and 16 bit 802.15.4 addressing.
• Useful with low-power link layers such as IEEE 802.15.4, narrowband ISM and power-line commuanication
• Efficient header compression: IPv6 base and extension headeers, UDP header
• Network autoconfiguration using neighbor discovery
• Unicast, multicast and broacast support : Multicast is compressed and mapped to broadcast
• Fragmentation : 1280 byte IPv6 MTU → 127 byte 802.15.4 frames
• Support for IP routing (e.g IETF RPL)
• Support for use of link-layer mesh (e.g. 802.15.5)

2. Architecture

• LoWPAN are stub networks
• Simple LoWPAN (Single Edge Router)
• Extended LoWPAN (Multiple Edge Routers with common backbone link)
• Ad-hoc LoWPAN (No route outside the LoWPAN)
• Internet Integration issues
  • Maximum transmission unit
  • Application protocols
  • IPv4 interconnectivity
  • Firewalls and NATs
  • Security
• 6LoWPAN headers:

2. Link-Layers for 6LoWPAN:

• Sub-GHz industrial, Scientific and Medical band radios
  • Typepically 10-50 kbps data rates,longer range than 2.4 GHz.
  • Usually used CSMA-style medium access control
• Power-Line Communications
  • Some PLC solutions behave like 802.15.4 channel
• Z-Wave
  • A home-automation low-power radio technology

4. The 6LoWPAN Format:

• 6LoWPAN is an adaptation header format:
  • Enables the use of IPv6 over low-power wireless links
  • IPv6 header compression
  • UDP header compression
• Format initially defined in RFC 4944
• Updated by draft-ietf-6lowpan-hc
  

  
  
• 6LoWPAN makes use of IPv6 address compression
• RFC 4944 Features:
  • Basic LoWPAN header format
  • HC1(IPv6 header) and HC2(UDP header)compression formats
  • Fragmentation and reassembly
  • Mesh header feature (depreciation planned)
  • Multicast mapping to 16-bit address space
• draft-ietf-6lowpan-hc Features:
  • New HC (IPv6 header) and NHC (Next-header) compression
  • Support for global address compression (with contexts)
  • Support for IPv6 option header compress
  • Support for compact multicast address compression

5. 6LoWPAN Addressing:

• IPv6 addresses are compressed in 6LoWPAN
• A LoWPAN works on the principle of
  • flat address spaces (wireless network is one IPv6 subnet)
  • with unique MAC addresses (e.g. 64-bit or 16-bit)
• 6LoWPAN compresses IPv6 addresses by
  • Eliding the IPv6 prefix
    • Global prefix known by all nodes in network
    • Link-local prefix indicated by header compression format
  • Compressing the IID
    • Elided for link-local communication
    • Compressed for multihop dst/src addresses
  • Compressing with a well-known “context”
  • Multicast addresses are compressed

5. 6LoWPAN Setup & Operation

• Autoconfiguration is important in embedded networks
• In order for a 6LoWPAN network to start functioning:
  • 1. Link-layer connectivity between nodes (commissioning)
  • 2. Network layer address configuration, discovery of neighbors, registrations (bootstrapping)
  • 3. Routing algorithm sets up paths (route initialization)
  • 4. Continuous maintenance of 1-3

7. 6LoWPAN Neighbor Discorvery:

• Standard ND for IPv6 is not appropriate for 6LoWPAN:
  • Assumption of a single link for an IPv6 subnet prefix
  • Assumption that nodes are always on
  • Heavy use of multicast traffic (broadcast/flood in 6LoWPAN)
  • No efficient multihop support over e.g. 802.15.4
• 6LoWPAN Neighbor Discovery provides:
  • An appropriate link and subnet model for low-power wireless
  • Minimized node-initiated control traffic
  • Node Registration (NR) and Confirmation (NC)
  • Duplicate Address Detection (DAD) and recovery
  • Support for extended Edge Router infrastructures
• ND for 6LoWPAN has been specified in draft-ietf-6lowpan-nd (work in progress)

8. Security for 6LoWPAN :

• Security is important in wireless embedded networks
  • Wireless radios are easily overheard
  • Autonomous devices with limited processing power
• A system usually has three main security goals
  • Confidentiality
  • Integrity
  • Availability
• See the threat model for Internet security in RFC3552