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Implementation of an optimal scheduling algorithmin NCRAWL
Delimpasis Dimosthenis
University of Thessaly
October 14, 2011
Delimpasis Dimosthenis Diploma Thesis Presentation
Click Modular Router
Flexible software architecture for building configurable routers
Written in C++
Belongs to OSI-Layer 3 but it can also give hints toOSI-Layer2
Consists of packet processing modules (elements)
Elements perform simple packet actions (classification,queueing, scheduling, interfacing with network devices)
An individual can write his own elements
Delimpasis Dimosthenis Diploma Thesis Presentation
Click Modular Router (cont.)
Router configurations form an acyclic directed graph
- Written in a declarative language- Describes connectivity between elements- Elements at the vertices- Packets follow along the edges of the graph
Click can be run as:
- A kernel module- A userlevel program- A routing agent withing ns-2 simulator
Delimpasis Dimosthenis Diploma Thesis Presentation
Roofnet
- GoalsOperate without extensive planning or central managementProvide wide coverage and acceptable performance
- Design DecisionsUnconstrained node placementOmni-directional antennasMulti-hop routingOptimization of routing for high throughput
Delimpasis Dimosthenis Diploma Thesis Presentation
Roofnet’s Routing Protocol
- Srcr
Find the highest throughput route between any pair of RoofnetnodesSource-routes data packets like DSRMaintains a partial database of link metrics
Delimpasis Dimosthenis Diploma Thesis Presentation
Contribution #1 (enable Roofnet working using Ath9k)
Roofnet was initially working only with atheros madwifi driver(atheros chipset 5413)
We enable roofnet running with 802.11 n cards drived byath9k
- Raw packet is the packet including all the headers (not justthe payload). The point is that we want to get a raw packet inapplication level without the previous OSI stack layers of theoperating system remove the respective headers
- Roofnet needs the ability of sending and receiving raw packets- Ath9k did not provide raw socket support- We enable the use of raw sockets with Ath9k
Delimpasis Dimosthenis Diploma Thesis Presentation
Wireless Network Coding
In case (a) four transmissions required but in case (b) only three⇒ increased throughput
Cards in monitor mode
PseudoBroadcast
Local intersession NC
Delimpasis Dimosthenis Diploma Thesis Presentation
Usefull Terms
native packet: a non-encoded packet
encoded packet: a packet that is the XOR combination ofmultiple packets
key: the packet needed by a node in order to decode anencoded packet
packet id: a 32-bit hash that identifies a packet uniquely
OutQueue: a FIFO queue in which a node’s packets arestored in order to be transmitted
Delimpasis Dimosthenis Diploma Thesis Presentation
COPE
A network architecture which allows Opportunistic Listening
The first integration of network coding into the network stack
Click+Roofnet
Utilize the broadcast nature of wireless networks
Opportunistic Listening: each node listens to thecommunications over the wireless medium and stores theoverheard packets for a limited period T
Delimpasis Dimosthenis Diploma Thesis Presentation
COPE (cont.)
Learning Neighbor State:
Explicit acking
Probabilistic acking (Fixed Threshold Policy)
Delimpasis Dimosthenis Diploma Thesis Presentation
Network Coding Architecture for Wireless Adaptive Links(NCRAWL)
Modular System
Based on Click+Roofnet
Uses solely statistical information
Enables user to implement his own scheduling algorithms
Experiments with max-weight scheduling (suboptimal)
Delimpasis Dimosthenis Diploma Thesis Presentation
Contribution #2 (porting NCRAWL to the newer click,working with Ath9k)
NCRAWL was written in Click version 1.4
It was based on the old Roofnet setup (supporting only cards5413 drived by old madwifi)
Port NCRAWL in click version 1.8
Now NCRAWL also uses the new roofnet setup (supporting802.11 n cards drived by Ath9k)
Delimpasis Dimosthenis Diploma Thesis Presentation
Description of an Optimal Scheduling Algorithm
Throughput Optimal Algorithm
Aquires knowledge about key ownership by getting feedbackfrom the nodes
A virtual subnetwork for each flow is created
- Each node represents the possible states of a packet(unknown, good, bad)
- Each node is associated with the respective queue (Unknown,Good, Bad)
- The edges of the virtual network represent the state transitionsof a packet and are associated with a transition probability (w)
Delimpasis Dimosthenis Diploma Thesis Presentation
The Virtual Network for the two Flows
Delimpasis Dimosthenis Diploma Thesis Presentation
Getting the Feedback
Delimpasis Dimosthenis Diploma Thesis Presentation
Example
For overhearing probabilities q12 = 0.8 and q21 = 0.5
Delimpasis Dimosthenis Diploma Thesis Presentation
Example (singleton contol)
For I = n1b we have C (I ) = x1b
Delimpasis Dimosthenis Diploma Thesis Presentation
Examle (control pairs)
For I = (n1u, n2u) we have C (I ) = c1(I ) + c2(I ) = 16.2
•c1(I ) = q21x1u +(1−q21)q12(x1u−x1g )+(1−q21)(1−q12)(x1u−x1b ) =
0.5 · 8 + 0.4 · 5 + 0.1 · 6 = 6.6•c2(I ) = q12x
2u +(1−q12)q21(x2u−x2g )+(1−q12)(1−q21)(x1u−x1b ) =
0.8 · 10 + 0.1 · 10 + 0.1 · 6 = 9.6
Delimpasis Dimosthenis Diploma Thesis Presentation
Contribution #3 (Implemantation of the above algorithm)
Based on NCRAWL framework
Implemented as userspace Click module
Additions1 Four new queues added (Good1, Bad1, Good2, Bad2). The
original NCRAWL’s queues were transformed to act asunknown ones.
2 The acknowledgment procedure of NCRAWL was re-designedfrom scratch. In addition now the receivers can not onlypiggy-back acknowledgments, but they are able to send explicitacks (this is usefull in the case of asymmetric flow senarioswhere piggy-backing does not work)
3 A categorizing mechanism has been added. Its purpose is toinsert a packet in the apropropriate queue (Unknown, Good,Bad) based on feedback the router gets via acknowledgements.
4 The scheduling procedure of NCRAWL has been modifiedtowards taking into acount the proposed algorithm’s metrics
Delimpasis Dimosthenis Diploma Thesis Presentation
System Overview (relay side)
Delimpasis Dimosthenis Diploma Thesis Presentation
System Overview (lateral nodes side)
Delimpasis Dimosthenis Diploma Thesis Presentation
Performance Experiments Setup
Rate of each link = 12 Mbps
Delimpasis Dimosthenis Diploma Thesis Presentation
Comparative Results (throughput)
λ1 = λ2
0 . 0 0 . 5 1 . 0 1 . 5 2 . 0 2 . 5 3 . 0 3 . 5 4 . 00 . 0
0 . 5
1 . 0
1 . 5
2 . 0
2 . 5
3 . 0
3 . 5
4 . 0
3 0 . 8 % ( 3 3 % )8 . 5 % ( 9 . 7 5 % )
3 . 1
2 . 5 7
Th
rough
put o
f flow
1 (M
bps)
I n p u t r a t e �� ( M b p s )
N C R A W L + I m p l . A l g o r i t h m p 1 = p 2 = 1 N C R A W L + I m p l . A l g o r i t h m p 1 = 0 . 5 p 2 = 0 . 8 W i F i
2 . 3 7
Delimpasis Dimosthenis Diploma Thesis Presentation
Results for controls selected (case 1)
λ1 = λ2Symmetric case (p12 = 1 and p21 = 1)
1 . 0 1 . 5 2 . 0 2 . 5 3 . 0 3 . 5 4 . 00 . 0
0 . 5
1 . 0
w e a k r e c e i v e r
Pe
rcenta
ge (%
)
A r r i v a l r a t e �� ( M b p s )
s i n g l e x o r s u u u g g u
8 6 . 5 %
s t a b i l i t y
Delimpasis Dimosthenis Diploma Thesis Presentation
Results for controls selected (case 2)
λ1 = λ2Asymmetric case (p12 = 0.5 and p21 = 0.8)
1 . 0 1 . 5 2 . 0 2 . 5 3 . 0 3 . 5 4 . 00 . 0
0 . 2
0 . 4
0 . 6
0 . 8
1 . 0
1 . 2
w e a k r e c e i v e r ( b o t h i n t e r f e r e n c e a n d o v e r h e a r i n g )
7 0 %
s t a b i l i t y
Pe
rcenta
ge (%
)
A r r i v a l r a t e �� ( M b p s )
s i n g l e x o r s u u u g g u
t i m e s h a r i n g g a p
Delimpasis Dimosthenis Diploma Thesis Presentation
Throughput Region
0 . 0 0 . 5 1 . 0 1 . 5 2 . 0 2 . 5 3 . 0 3 . 5 4 . 0 4 . 50 . 0
0 . 5
1 . 0
1 . 5
2 . 0
2 . 5
3 . 0
3 . 5
4 . 0
4 . 5
�����
����������
� �
��
S y m m e t r i c c a s e p 1 = p 2 = 1 ( t h e o r y ) A s s y m e t r i c c a s e p 1 = 0 . 5 , p 2 = 0 . 8 ( t h e o r y ) N C R A W L + I m p l . A l g o r i t h m p 1 = 0 . 5 , p 2 = 0 . 8 W i F i ( t h e o r y ) W i F i
Delimpasis Dimosthenis Diploma Thesis Presentation
Future Work
Software optimizations
Modification in order for the algorithm to run as a kernelmodule
More experiments in various settings
Delay experiments
Delimpasis Dimosthenis Diploma Thesis Presentation
End of presentation
Thanks for listening.Any questions?
Delimpasis Dimosthenis Diploma Thesis Presentation