A Review of 6LoWPAN Routing Protocols

Transcription

1 A Review of 6LoWPAN Routing Protocols Presented by Ee Gee Keng Department of Computer and Communication Systems Faculty of Engineering University Putra Malaysia

2 Introduction 6LoWPAN Overview Outline 6LoWPAN Adaptation Layer Mechanisms And Header Types Existing Routing Protocols in 6LoWPAN Comparison of 6LoWPAN Routing Protocols Conclusion

3 Introduction Personal Area Network (PAN) IEEE (PHY and MAC) Wireless Sensor Network (WSN) IPv6 vs IPv4 6LoWPAN Low power Wireless Personal Area Network (LoWPAN) Ex: ZigBee

4 WSN vs 6LoWPAN NAT devices obviated!

5 6LoWPAN Overview -Provides a WSN node with IP communication capabilities. -RFD (end device) FFD (router) Gateway IP-enabled devices

6 6LoWPAN Protocol Stack Adaptation layer Header compression, fragmentation, reassembly! IPv6 packet (1280 bytes) MAC frame size (25+102= 127 bytes)

7 IEEE PHY and MAC - specifies when the devices may access the channel for communication. - 4 frame structures for MAC layer: beacon frame, data frame, acknowledgement frame and MAC command frame. - A beacon frame - to transmit beacons. - A data frame - data transfers. - Acknowledgement frame - confirm successful frame reception. - MAC command frame - handling all MAC peer entity control transfers. dictates how the IEEE devices may communicate with each other over a wireless channel. - The IEEE standard total 27 channels defined in PHY layer. 868MHz / 915MHz PHY Channel 0 Channels MHz 902 MHz General MAC frame format in PHY frame 2.4 GHz PHY 20Kb/s Channels Kb/s 40Kb/s 5 MHz 2 MHz 928 MHz

8 6LoWPAN Adaptation Layer Mechanisms Header compression, fragmentation and layer-two forwarding. 4 basic 6LoWPAN header types: - HC1 header ( IPv6 Header Compression Header) - Fragmentation header - Mesh header - Dispatch header Header stacking principle is used. First two bits of header are used to identify - Device only uses specific 6LoWPAN defined headers to send its packet.

9 Header Field IPv6 header length 6LoWPAN Adaptation Layer 6LoWPAN HC1 length Mechanisms a) HC1 header - Used to compress those header fields to a few bits while reserving an escape value for the less common ones appear. -> reduce transmission overhead! Explanation Version 4 bits Assuming communicating with IPv6. Traffic class 8 bits 0 = Not compressed. The field is in full size. 1 bit Flow label 20 bits 1 = Compressed. The traffic class and flow label are both zero. Payload length 16 bits Can be derived from MAC frame length or adaptation layer datagram size (6LoWPAN fragmentation header). Next header 8 bits 2 bits Compressed whenever the packet uses UDP, TCP or Internet Control Message Protocol version 6 (ICMPv6). Hop limit 8 bits 8 bits The only field always not compressed. Source address 128 bits 2 bits If Both source and destination IPv6 addresses are in link local, their 64-bit network prefix are compressed into a single bit each with a value of one. Another single bit is Destination address 128 bits 2 bits set to one to indicate that 64-bit interface identifier are elided if the destination can derive them from the corresponding link-layer address in the link-layer frame or mesh addressing header when routing in a mesh. HC2 encoding bit Another compression scheme follows a HC1 header. Total 40 bytes 2 bytes Fully compressed, the HC1 encoding reduces the IPv6 header to two bytes.

10 6LoWPAN Adaptation Layer b) Fragmentation header Mechanisms - Datagram size - specify the size of the entire IP packet before adaptation-layer fragmentation. - Datagram tag - identify all of the fragments of a single original packet. - An extra byte in subsequent fragmentation is used for datagram offset field Datagram size (11 bits) Datagram tag (16 bits) C) Mesh header - Accomplish intra-pan routing. 1 0 O F Hops left (4 bits) Originator address (16-64 bits) Final address (16-64 bits) 1 0 O F 0xF Hops left (8 bits) Originator address (16-64 bits) Final address (16-64 bits)

11 d) Dispatch header 6LoWPAN Adaptation Layer Mechanisms - Used to define the type of header to follow. - Only 5 of the 64 dispatch header types have thus far been defined. 0 1 Dispatch (6 bits) 0 1 0x3F Dispatch (8 bits) The following bits are IPv6 uncompressed header The following bits are IPv6 HC1 compressed encoding The following bits are broadcast header The following 8 bits are an additional field for dispatch value.

12 6LoWPAN Adaptation Layer Mechanisms 6LoWPAN header sequences - Header stacking principle headers present only if needed! IEEE frame Mesh addressing Broadcast header Fragmentation header Dispatch header Compressed IP header Payload 6LoWPAN routing header - To achieve full routing functionality. - Mesh-under (intra-pan) vs route-over (inter-pan). Dispatch Header ( new 6-bit sequence) Routing header Payload

13 Mesh Under - Performs its routing at adaptation layer. - Performs no IP routing within LoWPAN. - Based on MAC address (16-bit or 64-bit). 6LoWPAN Routing classification Route Over -Performs its routing at network layer. -Performs IP routing. -IP address = IPv6 prefix + interface identifier => automatically (stateless auto-configuration) -Each node serves as an IP router. Mesh Under Route Over

14 Existing 6LoWPAN Routing a) 6LoWPAN Ad-hoc On-Demand Distance Vector (LOAD) AODV protocol message exchange LOAD protocol message exchange Modification done in LOAD: - Destination sequence number is not used. - For ensure loop freedom, only destination generates RREP. - new routing metric : link quality indication (LQI) is used. - Link Layer Notification (LLN) instead of Hello message.

15 Existing 6LoWPAN Routing b) Dynamic MANET On-demand for 6LoWPAN Routing (DYMO-low) Differences with LOAD : -16-bit destination sequence number is used. - local repair and route cost accumulation are not used.

16 Existing 6LoWPAN Routing c) Hierarchical Routing (HiLow) PAN coordinator Uses 16-bit short address as interface identifier instead of 64-bit as AODV and LOAD => memory saving and larger scalability. Parent Nodes Child Nodes 17 18

17 AODV (WSN) LOAD DYMOlow HiLow RERR message Use Use Use No use Sequence number Use No use Use No use Precursor list Use No use No use No use Hop count Use Optional Optional Use Hello message Use No use Use No use Local repair Use Use No use No use Energy Usage High Low Low Low Memory usage High Medium Medium Low Mobility Mobile Mobile Mobile Static Scalability Low Low Low High Routing delay High Low High Low Convergence to topology change Comparison of 6LoWPAN Routing Fast Fast Fast Slow

18 Conclusion With the knowledge of the 6LoWPAN header encapsulation, the new routing header can be added in the 6LoWPAN packet to achieve full routing functionality. Existing 6LoWPAN routing protocols such as LOAD, DYMO-low and HiLow are reviewed. There are always some tradeoffs between the routing protocols. A suitable routing protocol only can be chosen based on the application that it involves.

19 Thank You

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