Energy Efficient Fragment Recovery Techniques for Low-power and Lossy Networks Ahmed Ayadi ? , Pascal Thubert † ? IT/TELECOM Bretagne Rennes, France † Cisco Systems 12 January 2011 Ahmed Ayadi (IT/TELECOM Bretagne) IP and Wireless Sensor Networks’2011 Lyon, 12-13 January 2011 1 / 19
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Energy Efficient Fragment Recovery Techniques for Low-power and Lossy Networks
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Energy Efficient Fragment Recovery Techniques forLow-power and Lossy Networks
Ahmed Ayadi?, Pascal Thubert†
?IT/TELECOM Bretagne Rennes, France†Cisco Systems
12 January 2011
Ahmed Ayadi (IT/TELECOM Bretagne) IP and Wireless Sensor Networks’2011 Lyon, 12-13 January 2011 1 / 19
Motivation
The IETF Working Group 6LoWPAN has recently introduced anadaptation layer that provides header compression andfragmentation/reassembly mechanisms to allow sending/receivingIPv6 packets over LLNs (e.g., IEEE 802.15.4),
The IPv6 length is larger than 1280 bytes while an 802.15.4 framecan have a payload limited to 74 bytes
A IPv6 packet might end up fragmented into as many as 18fragments at the 6LoWPAN layer.
If a single one of those fragments is lost in transmission, all fragmentsmust be resent.
Ahmed Ayadi (IT/TELECOM Bretagne) IP and Wireless Sensor Networks’2011 Lyon, 12-13 January 2011 2 / 19
Outline
1 Link Layer Error Control Mechanisms
2 Simple Fragment Forward and RecoveryFragment Recovery proposalRecoverable Fragment: Dispatch type and HeaderFragment Acknowledgement Dispatch type and HeaderAn SFFR scenario
3 Performance evaluationImpact of SFFR on the energy consumption of TCPImpact of SFFR on the energy consumption of UDPThe SFFR rounds improve the energy efciencyWhen it is better to used SFFR?
4 Conclusion and perspectives
Ahmed Ayadi (IT/TELECOM Bretagne) IP and Wireless Sensor Networks’2011 Lyon, 12-13 January 2011 3 / 19
Link Layer Error Control Mechanisms
Automatic Repeat reQuest (ARQ)I ARQ uses the cyclic redundancy check (CRC) error-detecting code that
is added to the data: the receiver uses the error-detecting code numberto check the integrity of the received data
I After receiving a correct frame, the receiver replies by an ACK.I If the sender does not receive an ACK before the timeout, it
re-transmits the frame/packet until the sender receives anacknowledgment or exceeds a predefined number of re-transmissions.
Forward Error Correction (FEC)I The main idea of FEC is to add redundancy to the original frame, to
allow the destination node to detect and correct some bit errors.I The FEC algorithm adds (α×K) redundancy bits to form a frame of
length D.I FEC can adapt to multihop by adopting more redundancy bits, but.
Ahmed Ayadi (IT/TELECOM Bretagne) IP and Wireless Sensor Networks’2011 Lyon, 12-13 January 2011 4 / 19
Link Layer Error Control Mechanisms
If the wireless network becomes very lossy, ARQ would increase thetransmission delay between the source and the receiver.
Using ARQ, the source continues to send the remaining fragments,even if one fragment is already lost.
The reliable transport layer (e.g., TCP) MUST retransmit thesegment and thus all the fragments.
FEC requires more CPU energy and the amount of overhead is difficultto predict for the rapidly changing conditions of real-world LLNs .
Ahmed Ayadi (IT/TELECOM Bretagne) IP and Wireless Sensor Networks’2011 Lyon, 12-13 January 2011 5 / 19
Simple Fragment Forward and Recovery
SFFR is a new end-to-end recovery algorithm recently proposed byThubert et Hui for 6LoWPANs.
SFFR allows the sender to recover easily and quickly the lostfragments.
SFFR uses the datagram ”tag” as a switchable label.
SFFR minimize the acknowledgement overhead by applying acompressed acknowledgement bitmap
SFFR takes into support the out-of-order fragment delivery.
Ahmed Ayadi (IT/TELECOM Bretagne) IP and Wireless Sensor Networks’2011 Lyon, 12-13 January 2011 6 / 19
Fragment Recovery proposal
SFFR uses 32 bits as SACK Bitmap
SFFR defines 4 new dispatch types:I RFRAG: regular fragments,I RFRAG-AR: the last fragment which request an acknowledgment,I RFRAG-ACK: an new fragment that inform the sender about the
received fragments form the lost one.
Figure: Additional Dispatch Value Bit Patterns
Ahmed Ayadi (IT/TELECOM Bretagne) IP and Wireless Sensor Networks’2011 Lyon, 12-13 January 2011 7 / 19
Recoverable Fragment: Dispatch type and Header
Upon the first fragment, the routers lay an label along the path that isfollowed by that fragment (that is IP routed), and all further fragments arelabel switched along that path.
Figure: Recoverable Fragment Dispatch type and Header
Ahmed Ayadi (IT/TELECOM Bretagne) IP and Wireless Sensor Networks’2011 Lyon, 12-13 January 2011 8 / 19
Fragment Acknowledgement: Dispatch type and Header
A 32 bits uncompressed bitmap is obtained by prepending zeroes tothe XXX in the pattern below.