A study of Cross layer work of
University of Trento folk
A ResiliNet Group Presentation
Sarvesh Kumar Varatharajan
A study of Cross layer work of
University of Trento folk
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Cross-Layer Performance Optimization in wireless
Local Area Network (Kliazovich's PhD Thesis)
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Cross Layer ARQ ( Presented Today)
Cross Layer Congestion Control (Present next week)
The Cross-Layer Paradigm In Next Generation
Internet: Open Issues & Future Perspectives(
Granelli) (Walk through the foils)
Formal Methods in Cross-Layer Modeling and
Optimization of Wireless Networks: State of the
Art and Future Directions (Skip!!!Difficult for me
to understand :-( )
Cross-layer Performance Optimization
in wireless Local Area Network
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Cross-Layer Performance Optimization in wireless
Local Area Network (Kliazovich's PhD Thesis)
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Cross Layer ARQ
Cross-layer Performance Optimization
in wireless Local Area Network
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TCP/IP shows poor performance when extended
to wireless network environment
Limitations in terms of bandwidth,latency,channel
loss and mobility
Available Enhancement Schemes
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Link Layer Solutions
Transport Layer Solutions
Cross-Layer Solutions
Cross-layer Performance Optimization
in wireless Local Area Network
Cross-layer Performance Optimization
in wireless Local Area Network
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Link Layer Solutions
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TCP unaware link layer solution
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TCP unaware protocols optimize performance by hiding the
differences between wired and wireless mediums
Can cause adverse effects eg.) ARQ on TCP RTO
TCP aware link layer solution
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Knowledge of transport layer protocol provides certain
advantages
eg.) Snoop Protocol
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Snoop Agents ( at the BS) caches the TCP packets that are sent to
mobile nodes. Retransmissions occur locally
Disadvantages
 Increases complexity at BS
 No consideration of packet loss delay during hand-off
Cross-layer Performance Optimization
in wireless Local Area Network
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Transport Layer Solutions
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Connection Splitting Solutions
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I-TCP (Indirect TCP)
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Split the connection into two
One between FH and BS and the other between BS and MH
Conceal the wireless link from the FH
Disadvantages:
 End-to-end Schematics lost
 Additional overhead during hand-off
 Can't operate on encrypted packets
TCP Modifications
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eg.) SACK
Disadvantage:
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Modification of the ACK procedure both at sender and reciever
Cross-layer Performance Optimization
in wireless Local Area Network
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Cross-Layer Design
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ILC-TCP (Interlayer Collaboration Protocol)
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State Manager (SM) in parallel to protocol stack
Each layer reports its state to the SM
SM can signal TCP to stop sending packets if conditions not
good
Disadvantage: Additional Layer added to the sender
Cross-layer Performance Optimization
in wireless Local Area Network
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Analysis of existing schemes under 3 different
scenarios
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Single-hop wireless connections
Multi-hop wireless scenario
Wireless-cum-wired scenario
Conclusion from the related work
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No single best solution for all deployment scenario
Cross-layer Performance Optimization
in wireless Local Area Network
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TCP with link level ARQ
Link layer is not the only layer which
acknowledges packet delivery(TCP ACK's)
“A single TCP data packet is acknowledged three
times”( One time at the transport level and two
times at the link level)
This along with the fact that the physical layer
preamble and header are transmitted at the lowest
bit rate penalizes performance at higher bit rate
Cross-layer Performance Optimization
in wireless Local Area Network
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Optimization of the acknowledgement scheme
through interaction between transport and link
layer will bring down the medium busy time and
will improve the performance
A cross layer Link Layer ARQ Exploitation TCP
(LLE-TCP) scheme proposed
The idea is to generate the TCP ACK at the sender
instead of sending it through the channel
Cross-layer Performance Optimization
in wireless Local Area Network
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Cross Layer ARQ Agent
Operates between TCP and MAC
Interfaces both
LLE-TCP is a software module
Goes into the firmware
of the wireless card driver
Cross-layer Performance Optimization
in wireless Local Area Network
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Packet delivery diagram
Cross-layer Performance Optimization
in wireless Local Area Network
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Agent interaction with the Link Layer
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Success
Failure
Agent interaction with the transport layer
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Sender side
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ARQ Agent sniffs the packet generated by the higher layer
Access the TCP headers
On successful reception of the link layer ACK, it prepares
the TCP ACK
Upon SUCCESS TCP ACK is released to the Transport layer
On FAILURE three duplicate ACK's are generated triggering
the fast retransmit
Cross-layer Performance Optimization
in wireless Local Area Network
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Agent interaction with the transport layer
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Receiver side
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Silently drops all the standalone non-duplicate TCP ACK
packets
Advantages
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Does not interfere with the flow control mechanisms
Reduces the Round Trip Time(RTT)
Cross-layer Performance Optimization
in wireless Local Area Network
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TCP Connection Phases
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Connection Establishment (Three Way handshake)
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Data Exchange
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Full ACK suppression
Connection Termination
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ACK suppression is done only for the third handshake as
sequence number synchronization,negotiation of the size of
the contention window takes place
Full ACK suppression
Bidirectional data exchange
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If the incoming packet acknowledges a segment
number lower or equal to the already acknowledged
one,the ACK flag is cleared
Cross-layer Performance Optimization
in wireless Local Area Network
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Infrastructure Network Scenario
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TCP performs poorly in such environments due to
completely different characteristics between fixed and
wireless parts
Cross-layer Performance Optimization
in wireless Local Area Network
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TCP ACK's generated at the BS is delivered to the
fixed host
TCP ACK's avoided in the wireless
part(bottleneck)
LLE-TCP at BS accesses the rwnd of the ACK
header and replaces it with empty buffer space left
at the BS. Improves Congestion control
Drawback: Complexity at the BS
Mobile station switches off its LLE-TCP if the BS
does not support it
Cross-layer Performance Optimization
in wireless Local Area Network
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Multi hop Networks
Cross-layer Performance Optimization
in wireless Local Area Network
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Congestion Control at the sender side
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LLE-TCP congestion control module (LLE-TCP_CC)
LLE-TCP_CC buffer stores the packet till it gets the
ACK from LHR
rwnd set to 1 packet if LLE-TCP buffer not full
rwnd set to 0 packets if LLE-TCP buffer is full
Send a duplicate ACK for the last transmitted data
packet with positive value for the advertised window
Cross-layer Performance Optimization
in wireless Local Area Network
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Experimental Results
Simulation in ns-2
Implementation of single-hop scenario in 802.11b
testbed( Fedora Core Linux with 802.11b Orinoco
Silver Cards)
TCP Reno is chosen for comparison
Cross-layer Performance Optimization
in wireless Local Area Network
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Single-hop Network (Simulation Results)
Cross-layer Performance Optimization
in wireless Local Area Network
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Single-hop Network ( Implementation Results)
These results are 3% less than simulation results??
Cross-layer Performance Optimization
in wireless Local Area Network
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Multi hop Scenario (Simulation Results)
TCP Segment size=1000 bytes
10 % to 20 % improvement for small # of hops
Cross-layer Performance Optimization
in wireless Local Area Network
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Multi hop Scenario (Simulation Results)
Three hops, static environment
Cross-layer Performance Optimization
in wireless Local Area Network
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Multi hop Scenario (Simulation Results)
30 nodes placed randomly in 100*100 m
With node mobility ,AODV,RTS/CTS ON
1000s simulation
Fewer route errors
Fewer route discovery
messages
Reduced RTT
Cross-layer Performance Optimization
in wireless Local Area Network
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Infrastructure Network Scenario (Simulation
Results)
IEEE 802.11b
Wired link 100Mbps,2ms
Results close to single hop
This is bec ACK is sent
on wired link
Congestion control at BS
A study of Cross layer work of
University of Trento folk

Cross-Layer Performance Optimization in wireless
Local Area Network (Kliazovich's PhD Thesis)




Cross Layer ARQ ( Presented Today)
Cross Layer Congestion Control (Present next week)
The Cross-Layer Paradigm In Next Generation
Internet: Open Issues & Future Perspectives(
Granelli) (Walk through the foils)
Formal Methods in Cross-Layer Modeling and
Optimization of Wireless Networks: State of the
Art and Future Directions (Skip!!!Difficult for me
to understand :-( )