Post on 21-Jan-2016
An SSCOP-based Link Layer Protocol for Wireless LANs
Haoli Wang and Aravind Velayutham
IEEE Global Telecommunications Conference1-5 December, 2003 San Francisco, USA
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Outline Introduction Problems Solutions Proposed Protocol Analysis and Performance Conclusions Q&A
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Introduction
The IEEE 802.11 MAC protocol It’s the standard for medium access
in wireless LANs. It provides fast recovery from frame
losses using a rapid link level positive acknowledgement scheme, generally an ACK frame.
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Positive acknowledgement scheme
Retransmission
Sender Receiver
ACK
DATA
ACK Timeout
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Problems
At a low error rate, the most of the frame transmissions are correct and the positive ACK scheme is inefficient. Since each data frame requires on ACK, the large traffic overhead of ACK transmission wastes the scarce bandwidth.
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Solutions To use the negative ACK scheme, in
order to reduce the amount of ACK traffic by the receiver only requests the retransmission of the lost frames.
The proposed protocol is an adaptation of Service Specific Connection Oriented Protocol (SSCOP) that has already been implemented in ATM networks.
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Proposed Protocol Basic operation
USTAT operation POLL/STAT operation
Timeout mechanisms POLL Timeout Data Timeout
Determination of value Buffer management Modified NAV value Frame formats
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USTAT operation A receiver can detect a frame loss
by checking the sequence number in the frame header.
When a receiver detect a frame loss, it sends an Unsolicited Status (USTAT) control frame to the transmitter
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Example of USTAT operation
Frame loss
Out-of-order frame
Retransmission
USTAT
Sender Receiver
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POLL/STAT operation After a transmitter sends out a
specified number of data frames without acknowledgement, say , a POLL frame is sent out to the receiver.
The receiver will report the status of the last frames to the transmitter using a Status (STAT) frame.
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Example of POLL/STAT operation
STAT
Sender Receiver
POLL
= 3
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Buffer management
STAT
Sender Receiver
POLL
334455
Empty buffer
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8USTAT
Retransmission7
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Remove 8 from buffer
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Analysis and Performance Advantages of the proposed protocol
To reduce the acknowledgement traffic because of is the removal of ACK frame for each data frame transmissions.
To eliminate of ACK timeout from 802.11 Simulation result
To compared the proposed protocol with IEEE 802.11
The overhead The throughput
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To reduce the ACK traffic
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The occurrence of frame loss
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The POLL/STAT overhead with increasing a value
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Total throughput with increase number of flows at frame loss rate = 0
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Total throughput with increase number of flows at frame loss rate = 10%
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Total throughput with increase number of flows at frame loss rate = 20%
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Conclusions The performance improvement of
the proposed protocol increases with increasing bit error rate.
The other issues that will be improved buffer management for more link
between transmitter and receiver
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Q & A