6lowpan Webinar Slides

7/31/2019 6lowpan Webinar Slides

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6LoWPAN

David E. CullerUniversity of California, Berkeley

Jonathan HuiCisco Systems, Inc.

Zach ShelbySensinode

November 30th, 2010


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2

6LoWPAN what it means for smart objects

Low-Power Wireless Embedded devices can now beconnected using familiar networking technology,

like ethernet (but even where wiring is not viable)

and like WiFi (but even where power is not plentiful)

All of these can interoperate in real applications

Interoperate with traditional computing infrastructure

Utilize modern security techniques

Application Requirements and Capacity Planning dictatehow the network is organized,

not artifacts of the underlying technology


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3

Low Power Wireless Internet

IP/LoWPAN Router

IP/LoWPAN Sensor Router

IP Device

IP Network(powered)

LoWPAN -Extended IP Network

IP/LoWPAN Router

IP/LoWPAN Sensor Router

IP Device

IP Network(powered)

LoWPAN -Extended IP Network


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4

Wireless links

802.15.4 802.15.1 802.15.3 802.11 802.3

Class WPAN WPAN WPAN WLAN LAN

Lifetime(days)

100-1000+ 1-7 Powered 0.1-5 Powered

Net Size 65535 7 243 30 1024

BW (kbps) 20-250 720 11,000+ 11,000+ 100,000+

Range (m) 1-75+ 1-10+ 10 1-100 185 (wired)

GoalsLow Power,Large Scale,

Low Cost

CableReplacement

CableReplacement

Throughput Throughput


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6LoWPAN Adaptation Needs

6

Transport Header

(UDP, TCP) Application Payload (HTTP, Modbus, BACnet)

IPv6 Network Payload

Link Header Link Payload

Min MTU Requirement of 1280

40+ bytes

8-20+ bytes

802.15.4 MTU = 127 bytes

Minimum MTU >> 802.15.4 MTU Fragmentation

48+ byte UDP IPv6 Header Header Compression

Defines a Chained Header format via Dispatch Analogous to IPv6 Header stack


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6LoWPAN Fragmentation

802.15.4-2006 has a link MTU of 127 bytes

IPv6 requires a min link MTU of 1280 bytes

6LoWPAN must provide fragmentation

802.15.4 IPv6 Datagram

802.15.4 IPv6 Datagram (Frag 1)Frag


802.15.4 IPv6 Datagram (Frag N)Frag


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6LoWPAN Fragmentation

1 1 0 0 0 dgram_size dgram_tag

1 1 1 0 0 dgram_size dgram_tag

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

0 1 2 3

dgram_offset

2 3 4 5 6 7 8 9

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

0 1 2 3


Size: size of datagram in bytes Included in all fragments to simplify buffer allocation

Tag: identifies all fragments of a datagram

Offset: location of fragment in 8-byte units Elided in first fragment


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6LoWPAN Header Compression

Use little state and do no depend on flows

Common values for header fields => compact forms

Version is always 6 Traffic Class and Flow Label are zero

Payload Length always derived from L2 header

Source and Destination Addrs are link-local and derived from L2 addrs

Ver

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

Traffic Class Flow Label

Payload Length Next Header Hop Limit

Source Address

Destination Address

0

4

8

12

16

24

28

32

3640

IPv6 Header


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IPv6 Header Compression

0 1 1 TF NH HLIM CID SAC SAM M DAMDAC

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5

TF (Traffic Class and Flow Label) 0: Carried Inline (ECN+DSCP+Flow), 1: ECN+Flow, 2: ECN+DSCP, 3: All zero

NH (Next Header compression)

0: Carried Inline, 1: Next Header is compressed

HLIM (Hop Limit = Inline, 1, 64, 255) 0: Carried Inline, 1: 1, 2: 64, 3: 255

CID (Context Identifier Extension) 0: No 1-byte CID identifier, 1: 1-byte identifier follows

SAC/DAC (Source/Destination Address Compression) 0: Stateless, 1: Context-based

SAM/DAM (Source/Destination Address Mode) 0: 16 bytes inline, 1: 8 bytes inline, 2: 2 bytes inline, 3: elided

M (Multicast Destination) 0: Destination is not multicast, 1: Destination is multicast

In-line IPv6 Header Bits


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Traffic Class and Flow Label

11

ECN DSCP rsv Flow Label

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

TF = 00

ECN Flow Label

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3

TF = 01 rsv

TF = 10 ECN DSCP

0 1 2 3 4 5 6 7

TF = 11 [ECN=0, DSCP=0, Flow Label=0]

[DSCP = 0]

[Flow Label = 0]

IPHC

IPHC

IPHC

IPHC

Inline IPv6 Bits

Inline IPv6 Bits

Inline IPv6 Bits

Inline IPv6 Bits


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Next Header

12

IPHCNH = 0 Inline IPv6 Bits Next Header Inline IPv6 Bits Uncompressed Next Header

IPHCNH = 1 Inline IPv6 Bits Inline IPv6 Bits Uncompressed Next HeaderNHC

Hop Limit

HLIM = 00 IPHC Inline IPv6 Bits Hop Limit Inline IPv6 Bits

HLIM = 01 IPHC Inline IPv6 Bits [Hop Limit = 1]




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Prefix

Addrs within 6LoWPAN typically contain common prefix

Nodes typically communicate with one or few central devices

Establish state (contexts) for such prefixes only state maintenance

Support for up to 16 contexts

Interface Identifier

Typically derived from L2 addr during autoconfiguration

Elide when Interface Identifier can be derived from L2 header

Prefix Interface IdentifierIPv6 Addr

128 bits

IPv6 Unicast Address


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14


128 bits

Source/Destination Address Mode

SAM/DAM = 00 IPv6 Address Bits [0,127]

SAM/DAM = 01 IPv6 Address Bits [64,127]

SAM/DAM = 10Bits

[112,127]

SAM/DAM = 11

[64-bit prefix elided]

[112-bit prefix elided]

[Full 128-bit address elided, IID derived from link-layer]


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15


128 bits

IPv6 Prefix

Stateless Mode (SAC/DAC=0)

Prefix is link-local (fe80::/10)

Context-based Mode (SAC/DAC=1)

Prefix taken from stored contexts (up to 16 contexts)

CID = 0, use ContextID = 0

CID = 1, include 4-bit ContextID for source & destination


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0xFFDAM = 00 Flags Group Identifier Bits [0,111]Scope

DAM = 01 Flags Group Identifier Bits [64,111]Scope

DAM = 10 Flags Group Identifier Bits [80,111]Scope

DAM = 11Group ID

Bits [104,112]

IPv6 Multicast Address

GroupIDs typically consume a small number of bits

(Solicited Node Mcast)

[Flags = 0, Scope = 2] (Link-local All-Nodes, All-

Routers)

(All DHCP Servers/Relays)


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Each compressed header indicates if the next header is alsocompressed

Following control byte(s) include next header identifier

Framework for defining arbitrary Next Header compression methods

802.15.4 Compressed IPv6 Hdr

Com

presse

dIP

v6

How

IPv6

iscomp

ressed

How

UDP

iscomp

ressed

Compressed UDP Hdr


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UDP Header


0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

0

4

Source Port Destination Port

Length Checksum

Assume common values for header fields and define compact forms

Ports within 61616 to 61632 (4 bits)

Length derived from IPv6 Length

Checksum may be elided if other integrity checks are in use (e.g. Ipsec)

No definition for TCP or ICMPv6

1 1 1 1 0 C P

0 1 2 3 4 5 6 7

C (Checksum): 0: Inline, 1: Elide P (Ports):

0: Inline

1: Elide first 8 bits of Dest Port

2: Elide first 8 bits of Source Port

3: Elide first 12 bits of Source and Dest Ports


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Example: Link-Local Unicast

Ver = 6 Traffic Class = 0 Flow Label = 0

Payload Length Next Header = UDP Hop Limit = 1

Source Prefix = fe80::/64

Len = 50 FCF DSN DSTPAN

DST = 00-17-3B-00-AA-BB-CC-DD

SRC = 00-17-3B-00-11-22-33-44

802.15.4

Source IID = 0217:3B00:AABB:CCDD

Dest Prefix = fe80::/64

Dest IID = 0217:3B00:1122:3344

Link Hdr

IPv6 Hdr

Derived from link hdr

Compact forms


Length Checksum

UDP Hdr

1 1 12 2

48-byte UDP/IPv6 Hdr 7 bytes


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Example: Global Unicast



Source Prefix = 2001:5a8:4:3721::/64



SRC = 00-17-3B-00-11-22-33-44

802.15.4

Source IID = ::1234

Dest Prefix = 2001:5a8:4:3721::/64

Dest IID = ::ABCD

Link Hdr

IPv6 Hdr


Compact forms


Length Checksum

UDP Hdr

1 1 12 2


1 2 2

Derived from context


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Example: Link-Local Multicast



Source Prefix = fe80::/64



SRC = 00-17-3B-00-11-22-33-44

802.15.4

Source IID = 0217:3B00:AABB:CCDD

Dest Prefix = ff02::1

Link Hdr

IPv6 Hdr


Compact forms


Length Checksum

UDP Hdr

1 1 12 2


1


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Neighbor Discovery in 6LoWPAN

IPv6 Neighbor Discovery defines [RFC4861]

How hosts discover routers and prefixes How nodes resolve L2 addresses from IP addresses

How nodes perform unreachability detection

But ND was originally designed for LAN (e.g. Ethernet) connected interfaces

Always-on equipment such as PCs 6LoWPAN has unique requirements

Both single-hop mesh and multi-hop IP routed networks

Lossy and asymmetric radio environment

Frequent multicast traffic is expensive

Address resolution is not required Unique EUI-64 addresses

Hosts may be sleeping to preserve energy


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6LoWPAN ND at a Glance


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24

LoWPAN in an IP Stack

802.15.4, 802.11Ethernet Sonet

XML / RPC / REST / SOAP / OSGI

IP

IETF 6lowpan

Web Services

TCP / UDP

HTTP / FTP / SNMP Pro

xy/G

ateway

LoWPAN 802.15.4

1% of 802.11 power, easier toembed, as easy to use.

8-16 bit MCUs with KBs, notMBs.

Off 99% of the time


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Conclusion

6LoWPAN turns IEEE 802.15.4 into the next IP-enabled link

Provides open-systems based interoperability among low-power devices over IEEE 802.15.4

Provides interoperability between low-power devices andexisting IP devices, using standard routing techniques

Paves the way for further standardization of communication

functions among low-power IEEE 802.15.4 devices Offers watershed leverage of a huge body of IP-based

operations, management and communication services andtools

Great ability to work within the resource constraints of low-

power, low-memory, low-bandwidth devices like WSN

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