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PNP-MAC: Preemptive slot allocation and Non
Preemptive transmission for Providing QoS in
Body Area NetworksPublished in IEEE CCNC 2010.
Author:
June S. Yoon,
Gahng-Seop Ahn,
Seong-Soon Joo,
Myung J. Lee
Department of Electrical Engineering,
The City University of New York.
Electronics and Telecommunications Research Institute.
Presented by:
Iffat Anjum (Roll: 16)
Nazia Alam (Roll: 28)
Date: 30th May, 2012.
Green Networking Research GroupDept. of Computer Science and Engineering, University of Dhaka
Contents
Contribution.
Problem Definition.
Overview of PNP-MAC.
Features of PNP-MAC.
Priority Classification.
Fast, Preemptive DTS allocation.
Non-Preemptive transmission.
Prioritized CCA in ETS.
Prioritized random back-off in CAP.
Performance Evaluation.
2
Slide 2
Green Networking Research GroupDept. of Computer Science and Engineering, University of Dhaka
Contributions
Proposes a PNP-MAC protocol that can flexibly handle variety of
applications with diverse requirements through,
Fast, preemptive slot allocation,
Non-preemptive transmission in the allocated slots ,and
Flexible super-frame adjustments.
This PNP-MAC protocol can satisfy diverse delay and throughput
requirements of various applications such as,
Continuous streaming,
Routine periodic monitoring, and
Time-critical emergency alarm.
Slide 3
Green Networking Research GroupDept. of Computer Science and Engineering, University of Dhaka
Slide 4 Problem Definition
The BAN applications have diverse QoS requirements in terms of
throughput, latency, and reliability.
Most of the physiological data monitoring applications are periodic
and low rate.
But emergency alarm, the most time-critical data in BAN, requires
instantaneous delivery with the highest reliability.
A BAN should be able to cope with the diverse requirements
simultaneously even when those applications are used together at
the same time.
4Green Networking Research GroupDept. of Computer Science and Engineering, University of Dhaka
Overview of PNP-MAC In order to reflect all design considerations, PNP MAC exploits a
hybrid approach that uses both contention based and time
division-based schemes.
BAN super-frame shows how the two schemes are integrated.
Figure 1: BAN Superframe structure.
5
Slide 5
Green Networking Research GroupDept. of Computer Science and Engineering, University of Dhaka
Overview of PNP-MAC The advertisement informs newly joining nodes and member
nodes of basic information of the BAN coordinator and super-
frame such as,
BAN identifier,
Advertisement interval, and
The length of CAP periods.
Initially the BAN coordinator begins BAN super-frame without
DTS until DTS allocation request is received during CAP.
Then it collects DTS requests embedding the priority of nodes’
data and then allocates DTS slots based on the priorities.
Then announces allocation status through beacon broadcasting.
6
Slide 6
Green Networking Research GroupDept. of Computer Science and Engineering, University of Dhaka
Overview of PNP-MAC
TDMA data transmit period is a contention-free period for time-
critical continuous and periodic data.
It consists of data transmit slot (DTS) and Emergency Data
Transmit slot (ETS).
It allocates time-critical data to DTS.
If all DTSs are exhausted, the BAN coordinator can allocate
time critical data to ETSs.
Emergency Data Transmit Slot (ETS) is a contention access
slot reserved for urgent delivery of unpredictable emergency
data.
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Slide 7
Green Networking Research GroupDept. of Computer Science and Engineering, University of Dhaka
Features of PNP-MAC PNP-MAC provides QoS in accordance with the priority of
traffics.
Back-off in CAP, CCA (Clear Channel assessment) in ETS, and
DTS allocation, all are performed depending on priority.
Priority is determined by the degree of importance and the types
of data.
Generally emergency alarm has the highest priority and medical
data has next highest priority.
The order of importance for data types is:
continuous data, periodic data, and then non-periodic data.
8
Slide 8
Green Networking Research GroupDept. of Computer Science and Engineering, University of Dhaka
Priority Classification
Features of PNP-MAC
9
Slide 9
Green Networking Research GroupDept. of Computer Science and Engineering, University of Dhaka
Table 1: Priority and Back-off class.
Priority Classification
Features of PNP-MAC
A BAN device requests DTS allocation during CAP after it
recognizes the existence of the BAN coordinator from the
advertisement.
Then, the BAN coordinator allocates DTS and notifies it through
the beacon.
And then the devices transmit data in its designated slot.
If the allocation fails due to the lack of remaining DTSs or the
loss of the request packet, the allocation of the slot is not
announced.
The device that has requested DTS allocation can find out the
failure after receiving the beacon, then the device requests DTS
allocation again.
10
Slide 10
Green Networking Research GroupDept. of Computer Science and Engineering, University of Dhaka
Fast, Preemptive DTS allocation
Features of PNP-MAC
Unlike 802.15.4, all the stated processes are done in sequence
and within the same superframe interval in PNP-MAC.
Figure 2: Allocation delay comparison.
11
Slide 11
Green Networking Research GroupDept. of Computer Science and Engineering, University of Dhaka
Fast, Preemptive DTS allocation
Features of PNP-MAC
Higher priority data is served first in any case even in heavy
contention.
The BAN coordinator sorts all the requests and allocates higher
priority first from the first available slot.
Figure 3: Priority based DTS allocation.
12
Slide 12
Green Networking Research GroupDept. of Computer Science and Engineering, University of Dhaka
Fast, Preemptive DTS allocation
Features of PNP-MAC
If remaining DTSs are insufficient to admit all requests, higher
priority data preempts lower priority data.
Figure 4: Priority based DTS allocation.
13
Slide 13
Green Networking Research GroupDept. of Computer Science and Engineering, University of Dhaka
Fast, Preemptive DTS allocation
Features of PNP-MAC
Emergency alarms are transmitted using both CAP and ETS
whichever comes first to reduce delay.
The number of ETSs is configurable and ETSs are distributed
within data transmission period (DTP) .
Unlike DTS, preemption of ETS is not allowed.
As emergency alarms rarely occur, dedicating ETS slots may not
be justifiable in view of efficient use of resources.
So, we allow non-emergency alarm data to use ETSs using
prioritized CCA.
14
Slide 14
Green Networking Research GroupDept. of Computer Science and Engineering, University of Dhaka
Non-Preemptive transmission
Features of PNP-MAC
ETS can be assigned to non-emergency data only when available
DTSs are not enough to meet demands from sensor nodes.
The assignee to the ETS must perform CCA first for the
duration specified in Equation below, to avoid collision.
CCA Duration of slot assignee = unitCCAduration × N
N is the number of mini slot for CCA.
15
Slide 15
Green Networking Research GroupDept. of Computer Science and Engineering, University of Dhaka
Prioritized CCA in ETS
Features of PNP-MAC
For the prevention of collision among emergency alarms, they
also need to confirm the availability of the ETS before
transmission.
Emergency alarms also perform CCA for the duration
specified in Equation below,
CCA Duration of alarm = [0, unitCCAdurtion × (N-1)]
The winner is the one who chooses the smallest duration.
16
Slide 16
Green Networking Research GroupDept. of Computer Science and Engineering, University of Dhaka
Prioritized CCA in ETS
Features of PNP-MAC
The figure below is an example of prioritized CCA when N=3.
Figure 4: Prioritized CCA in ETS.
17
Slide 17
Green Networking Research GroupDept. of Computer Science and Engineering, University of Dhaka
Prioritized CCA in ETS
Features of PNP-MAC
Prioritized random back-off is applied during CAP.
All nodes intending to transmit during CAP perform random
backoffs and CCAs.
In Table 1,mentioned before, three back-off classes were listed
based on the priority.
The back-off time is randomly chosen in,
[0, 2BE (Class+1)-1],
where BE denotes the back-off exponent.
18
Slide 18
Green Networking Research GroupDept. of Computer Science and Engineering, University of Dhaka
Prioritized random back-off in CAP
Performance Evaluation
Here star topology has been used, where a BAN coordinator is
centered and sensor devices are placed around it.
The superframe size of PNP-MAC is selected for performance
evaluation is the same as the beacon interval of IEEE 802.15.4
with superframe parameters ,
Beacon Order ,BO=6,
Superframe Order, SO=3,
slot size=7.68ms, and
CAP size=8 slots.
Total number of slots in a BAN superframe of PNP-MAC is 128
slots.
Channel capacity is 250Kb/sec.
19
Slide 19
Green Networking Research GroupDept. of Computer Science and Engineering, University of Dhaka
Performance Evaluation
20
Slide 20
Green Networking Research GroupDept. of Computer Science and Engineering, University of Dhaka
Figure 5: Allocation delay comparison using one node.
Performance Evaluation
21
Slide 21
Green Networking Research GroupDept. of Computer Science and Engineering, University of Dhaka
Figure 6: Emergency alarm delays.
Performance Evaluation
22
Slide 22
Green Networking Research GroupDept. of Computer Science and Engineering, University of Dhaka
Figure 7: Prioritized back-off delays.
Performance Evaluation
23
Slide 23
Green Networking Research GroupDept. of Computer Science and Engineering, University of Dhaka
Figure 8: Allocation delay comparison using seven nodes.