energy efficient fragment recovery techniques for low-power and lossy networks

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.


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


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.


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 .


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.


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


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


Fragment Acknowledgement: Dispatch type and Header

A 32 bits uncompressed bitmap is obtained by prepending zeroes tothe XXX in the pattern below.

else,

Figure: Compressed acknowledgement bitmap encoding


Expanded bitmap examples

(a) Expanding 1 octet encoding

(b) Expanding 3 octets encoding

Figure: Expanded bitmap encoding


An SFFR scenario

Sender Receiver

RFRAGRFRAG

.RFRAG-AR

RFRAG-ACK

RFRAG-AR

RFRAG-ACK

Figure: End-to-end simple fragment forwarding and recovery


Parameters

Table: Network parameters.

Parameter ValueHop number 5

Application data size 1048 kbytes

TCP MSS/ UDP payload size 512/1024 bytes

NHC header 1 bytes

TCPHC header 8 bytes

6LoWPAN header 3 bytes

IEEE 802.15.4 header 23 bytes

IEEE 802.15.4 acknowledgment size 10 bytes

Transmit Energy 0.24 µJ/bit

Receive Energy 0.21 µJ/bit


Impact of SFFR on the energy consumption of TCP (1/2)

10−5 10−4 10−3

102

103

BER

Co

nsu

med

ener

gy

(J)

No ARQ, No SFFR

No ARQ, SFFR

ARQ=3, No SFFR

ARQ=3, SFFR

(a) MSS = 1024 bytes

10−5 10−4 10−3

102

103

BER

Co

nsu

med

ener

gy

(J)

No ARQ, No SFFR

No ARQ, SFFR

ARQ=3, No SFFR

ARQ=3, SFFR

(b) MSS = 512 bytes

Figure: Energy Consumption of an TCP data transfer with vs without SFFR(number of hops is equal to five).


Impact of SFFR on the energy consumption of TCP (2/2)

2 4 6 8 10

102

103

Number of hops

Co

nsu

med

En

erg

y(J

)

1024, No SFFR

1024, SFFR

512, No SFFR

512, SFFR

Figure: Energy Consumption of an TCP data transfer with vs without SFFRSFFR (ARQ=3, B = 5 × 10−4).


Impact of SFFR on the energy consumption of UDP (1/2)

control congestion

10−5 10−4 10−310−3

10−2

10−1

BER

En

erg

yE

ffici

ency

No ARQ, No SFFR

No ARQ, SFFR

ARQ=3, No SFFR

ARQ=3, SFFR

(a) UDP payload size = 1024 bytes

10−5 10−4 10−310−3

10−2

10−1

BERE

ner

gy

Effi

cien

cy

No ARQ, No SFFR

No ARQ, SFFR

ARQ=3, No SFFR

ARQ=3, SFFR

(b) UDP payload size = 512 bytes

Figure: Energy Efficiency of an UDP data transfer with vs without SFFR.


Impact of SFFR on the energy consumption of UDP (2/2)

2 4 6 8 10

10−2

10−1

Number of hops

En

erg

yE

ffici

ency

1024, No SFFR

1024, SFFR

512, No SFFR

512, SFFR

Figure: Energy Efficiency of an UDP data trasfer with and without SFFR(ARQ=3, B = 5 × 10−4).


The SFFR rounds improve the Energy Efficiency

10−5 10−4 10−310−3

10−2

10−1

BER

En

erg

yE

ffici

ency

No SFFR

SFFR=1

SFFR=2

SFFR=3

Figure: Energy Efficiency of an UDP data transfer with different SFFR rounds(ARQ=3, 5 hops).


When it is better to used SFFR?

2 4 6 8 1010−4

10−3

MSS=1280

MSS=1024MSS=768

MSS=512

MSS=256

Number of Hops (h)

BE

R

Figure: SFFR in a multi-hop TCP transmission: prefer SFFR above the curves(ARQ=3).


Conclusion and perspectives

Conclusion

SFFR is a new energy-efficient end-to-end fragment recovery,

Simulations results show that SFFR reduces significantly theconsumed energy.

Perspectives

Congestion control due to fragmentation,

Reduces the PER of RFRAG-AR and RFRAG-ACK.


energy efficient fragment recovery techniques for low-power and lossy networks

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