Radio and Networks - Aalto University Wiki

Radio and Networks - Aalto University Wiki
Radio and Networks
Ketan Devadiga
Agenda
• IEEE 802.15.4
• ZigBee
• 6LoWPAN
IEEE 802.15.4
• Physical and Mac layer standard for low-rate
WPANs (LR-WPAN)
• low power consumption, low cost, low data transfer
rate
• Only defines PHY and MAC layer. The above layers
are defined by other specifications: Zigbee,
6LoWPAN, Wireless HART, ISA100
Types of nodes
• FFD: Fully functional device
– all networks have atleast one FFD acting as PAN
coordinator
• RFD: Reduced functional device
– simple end point devices that get information directly from
the environment and send it to the coordinator
Network topologies (contd.)
PHY layer
• Uses Direct Sequence Spread Spectrum (DSSS)
• In 802.15.4-2003
PHY
Frequency
band
No of
channels
Modulation
Bandwidth
Kb/s
Receiver
sensitivity
868 MHz
868.0-868.6
1
BPSK
20
-85dBm
915 MHz
902.0-928.0
10
BPSK
40
-85dBm
2.4 GHz
2.4-2.4835
16
O-QPSK
250
-92dBm
• In 802.15.4-2006
– Data rates of 868/915 improved to 100 and 250 Kb/s
– An alternative 868/915 layer using Parallel Sequence
Spread Spectrum (PSSS)
PHY layer (contd.)
• In 802.15.4a-2007 2 more PHY were added
– Direct Sequence ultra-wideband (UWB)
– Chirp spread spectrum (CSS)
• In 802.15.4c and 802.15.4d, more additions were
made to support bands in China and Japan
PHY Layer Protocol Data Unit
Preamble
Delim
Header
PSDU
4 bytes
1 byte
1 byte <= 127 bytes
• Preamble – Synchronization, chip timing,
frequency adjustment
• Delimiter – End of Preamble
• Header – 1 bit reserved, 7 bits specify SDU length
• PSDU – Physical layer SDU, payload
PHY Layer functions
•
•
•
•
•
Data transfer and reception
Channel selection
Energy detection of current channel (ED)
Link Quality indication (LQI)
Clear channel assessment (CCA)
Logical Link layer (LLC)
•
•
802.15.4 MAC provides services to 802.2 type I
LLC via the service-specific convergence
sublayer
802.15.4 MAC can directly provide services to a
proprietary LLC
MAC Layer
• Two kinds of services through service access
points (SAPs)
– MAC Data services is provided through MAC common part
sublayer SAP (MCPS-SAP)
– MAC Management services is provided through MAC layer
management entity SAP (MLME-SAP)
MAC protocol data unit
2 bytes
1
0-20
Frame control
Seq no
Dest addr
MHR
•
•
•
•
•
•
Src addr
Variable
2
Payload
FCS
MSDU
MFR
FCS – Frame check sequence
MHR – MAC header
MSDU – MAC service data unit
MFR – MAC footer
Total MAC frame size <= 127
Address can be short 16 bit or IEEE 64 bit
Types of MAC Frames
•
•
•
•
Beacon frames
Data frames
Acknowledgement frames
Command frames
Modes of operation
• Beacon mode (slotted CSMA-CA)
• Non-beacon mode (unslotted CSMA-CA)
Superframe mode
• Some networks need dedicated bandwidth to
achieve low latency
• In this mode, PAN coordinators send beacons at
pre-determined interval- 15 ms to 245 ms
• The slot between these beacons is divided into 16
slots
• Dedicated bandwidth is provided via Guaranteed
time slots(GTS)
• Information about superframe, time frame and GTS
is communicated using the beacons
Superframe structure
•
•
•
•
•
CAP – contention access period
CFP – contention free period
GTS – guaranteed time slots
In beacon enabled network, nodes transmit
during CAP using slotted CSMA-CA
In non-beacon networks, it’s standard CSMA-CA
Data transfer
• Device  Coordinator
Listen to beacons, synchronize to superframe, send data
using slotted CSMA-CA
• Coordinator  Device
In beacon, mention data is pending. The device then sends a
request command and the data is sent using slotted
CSMA-CA
Data transfer (contd.)
• Device  Coordinator
Simply transfer using unslotted CSMA-CA
• Coordinator  Device
Store data, whenever device sends a request command,
send data. If no data is available then send a zero-length
payload to indicate no pending data.
Security
Name
Desc
Null
No Security
AES-CTR
Encryption only CTR mode
AES-CBC-MAC-128
128 bit MAC
AES-CBC-MAC-64
64 bit MAC
AES-CBC-MAC-32
32 bit MAC
AES-CCM-MAC-128
Encryption + 128 bit MAC
AES-CCM-MAC-64
Encryption + 64 bit MAC
AES-CCM-MAC-32
Encryption + 32 bit MAC
•
•
•
•
Each device has upto 255 ACLs
Address
Security Suite
Key
Last IV
Replay Ctr
Access List
Integrity
Confidentiality
Replay
Protection
Other functions…
•
•
•
•
Starting and maintaining a PAN
Beacon generation
Association and Disassociation
Synchronization
ZigBee
• ZigBee is a network standard developed using the
IEEE 802.15.4 as the MAC and PHY layers
• Higher layers over MAC- layer 3 and above.
• Maintained by the ZigBee alliance: a group of
companies
• Home automation, industrial control, intruder
warning etc...
ZigBee Node Types
• ZigBee coordinator (ZBC)
– Initiates network connection, stores network tables
– Routing capability, bridge to other networks
– All devices talk to ZBC
• ZigBee Router (ZBR)
– Optional, also has routing capability
– Local address allocation/de-allocation
• ZigBee End Device (ZBE)
– Cheapest device, talks only to coordinator
– Sensor is present in this
ZigBee stack
Source: http://www.meshnetics.com/zigbee-faq/
Network Layer (NWK)
• Routing capabilities
• End devices
– Joining and leaving the network
• Router device
– Forward messages
– Discover neighbors
– Find routes to the devices
• Coordinators
– Start a new network
– Assign address to new devices joining the network
Application layer
•
•
•
•
•
Devices are defined by profiles
Implemented as application objects
Each application object has an endpoint
Binding between end points of devices
Messages between devices are cluster
Application Support Layer (APS)
• Binding between end points
• Discovery of other neighboring devices
Application layer (contd.)
• ZigBee device object (ZDO)
–
–
–
–
–
–
Another application object with end point zero
Has its own profile- ZigBee device profile
Overall device management
Define roles and responsibilties
Initializing APS and NWK
Security policies
Security
• Security services provider
• Three kinds of keys
– Master key- Long term used in exchange of link keys
– Link key – unique between 2 devices
– Network key – shared among the network
• Trust center
– Can be coordinator or dedicated device
– Authenticate new devices
– Update network key
– Helps setup of link keys
• Network and Link key can be updated regularly
6LoWPAN
• Defines how to layer IPv6 over 802.15.4
• Why new protocol for low rate, low power PANs
when we have IPv6
– Already tools available to configure, test IP networks
– Admins need not study a new paradigm
– Many protocols available that work with IPv6 which can be
explored with 6LoWPAN: SNMP, SLP, ICMP etc…
– Also higher level services such as load balancing, caching
etc… can be explored.
6LoWPAN
• IEEE 802.15.4 MAC = 127 Octets
• MAC Header =46 (AES-CCM-128) or 21 (Null
security)
• = 102 Octets or 81 Octets for IPv6
• IPv6 header itself is 40 Octets
• = just 62 or 41 bytes for UDP
• UDP is 8 Bytes
• = 54 or 33 Bytes for application data
6LoWPAN layers
•
•
•
Adaption Layer
Has to support 1280 MTU of IPv6
Employs header compression and stacked
headers
6LoWPAN Headers
Dispatch type header
01
000001
IPv6 uncompressed header
01
000010
IPv6 HC1 compressed header
01
111111
Additional Dispatch types
• The first 2 bits = 00 indicates non-LoWPAN packet
• Only 5 of the header types are define for now
Mesh header type
10 V
F
Hops left
Originator address
Destination address
• 10 indicates Mesh header type
• V = 1 if originator address is short 16-bit
• F = 1 if destination address is short 16-bit
• Hops left is number of hops left to destination
(max15)
Fragmentation header
11
000
Datagram size
Datagram tag
First fragment header
11
100
Datagram size
Datagram tag
Datagram offset
Subsequent fragment header
• 11 bit datagram size
• 16 bit datagram tag
• 8 bit databit offset
Header Compression
• HC1 for IPv6 header compression
–
–
–
–
–
–
Version,
64 bit IPv6 interface identifiers
packet length
traffic class and flow label
next header is TCP/UDP/ICMP
Hop limit shouldn’t be compressed
• HC2 for UDP header compression
– source port
– Destination port
– length
Some notes on security
• Maybe threats because of neighbor discovery and
adhoc routing in case of mesh routing
• RFC suggests to use link-layer security provided by
IEEE 802.15.4
• In case of RFDs link layer security can be used
• In case of FFDs if data has to be sent to off-link IPv6
hosts use usual mechanisms like IPsec, TLS...
References
•
•
•
•
•
•
•
“Home networking with IEEE 802.15.4: a developing standard for low-rate
wireless personal area networks”, IEEE Communication Magazine, Aug
2002
D L Nardis and D Benedetto. “Overview of the IEEE 802.15.4/4a standards
for low data rate Wireless Personal Data Networks”. 4th workshop on
Positioning, Navigation and Communication, March 2007.
Patrick Kinney. "ZigBee Technology: Wireless Control that Simply Works“
http://www.sensor-networks.org/index.php?page=0903503549
G. Montenegro, N. Kushalnagar, J. Hui, and D. Culler. ”Transmission of IPv6
Packets over IEEE 802.15.4 Networks”. RFC 4944, Sept 2007
N. Kushalnagar, G. Montenegro, and C. Schumacher. “IPv6 over LowPower Wireless Personal Area Networks (6LoWPANs): Overview,
Assumptions, Problem Statement, and Goals”. RFC 4919, Aug 2007
http://www.ipso-alliance.org/wp-content/uploads/6lowpan.pdf
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