wrap-up myungchul kim [email protected]. ch 5. mac in wmns myungchul kim [email protected]
TRANSCRIPT
• IEEE 802.11 DCF protocol
Conventional wireless MAC protocols
• IEEE 802.11e MAC protocol– Define the channel access functions and the traffic specification
(TSPEC) management
– Channel access function : hybrid coordination function (HCF)
• A contention-based protocol called enhanced distributed channel access (EDCA)
• A polling mechanism called HCF controlled channel access (HCCA): central control
Conventional wireless MAC protocols
• IEEE 802.11e MAC protocol– EDCA: enhance the original DCF by providing prioritized
medium access based on different traffic classes, access categories (ACs)
– TXOP: a bounded time interval in which a node is allowed to transmit a series of frames.
Conventional wireless MAC protocols
• IEEE 802.11e MAC protocol
Conventional wireless MAC protocols
• IEEE 802.11e MAC protocol
Conventional wireless MAC protocols
• Common channel framework (optional)– Simultaneous transmissions on multiple channels
– Request-to-switch (RTX) and clear-to-switch (CTX)
Advanced MAC features proposed by the 802.11 TDs group
– Generic security services
Security technology overview
Performance of VoIP in a 802.11 Wireless Mesh Networks
by D. Niculescu, S. Ganguly, K. Kim and R. Izmailov Infocom 2006
Myungchul Kim
12
• Fig 1
• With 2Mbps link speed, 8 calls in single hop to one call after 5 hops due to the following:– Decrease in the UDP throughput because of self interference
– Packet loss over multiple hops
– High protocol overhead for small VoIP packets
13
• Aggregation– 802.11 networks incur a high overhead to transfer one packet
– For a 20 byte VoIP payload (43.6 microsec at 11 Mbps)
• RTP/UDP/IP 12+8+20 = 40 bytes
• MAC header + ACK = 38 bytes
• MAC/PHY procedure overhead = 754 microsec– DIFS(50microsec), SIFS(10microsec)
– Preamble + PLCP(192microsec) for data and ACK
– Contention (approx 310microsec)
• 800 microsec at 11 Mbps -> 1250 packets per sec -> G.729a: 12 calls (2Mbps -> 8 calls)
• Throughput: T(x) = 8x / (754 + (78 + x) 8/B)) where x is the payload size in bytes and B is the raw bandwidth of the channel
14
– Reducing the overhead
• Aggregation (Fig 12) -> increase packet delay
• Header compression– Fig 12
Toward an Improvement of H.264 Video Transmission over IEEE 802.11e through a
Cross-Layer Architectureby A. Ksentini, M. Naimi, and A. Gueroui
IEEE Communications Mag. Jan. 2006
Myungchul Kim
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The proposed cross-layer architecture
• Table 1. 802.11 MAC parameters
17
The proposed cross-layer architecture
• Figure 1
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Simulation and results
• Result analysis– Fig 2 IDR loss rate
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Simulation and results
• Result analysis– Fig 4 Partition B loss rate
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Simulation and results
• Result analysis– Fig 5 Partition C loss rate
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Simulation and results
• Result analysis (final decoded frame #76)– Dropped frames: DCF(87), EDCA(41) out of 250 frames
– Fig 8 a) DCF, b) EDCA, c) QoS architecture
Link Layer Assisted Mobility Support Using SIP for Real-time Multimedia
Communications
October 1, 2004
Wooseong Kim, Myungchul Kim, Kyounghee Lee
Information and Communications Univ.{wskim, mckim, leekhe}@icu.ac.kr
Chansu Yu
Cleveland State [email protected]
Ben Lee
Oregon State [email protected]
Mobiwac 04 23
Problem Definition
Handoff delay of SIP mid-call mobility [12]– Handoff Delay = Tn (n=0 to 5)– Link layer handoff delay (T0)– Movement Detection (T1)– DHCP transaction (T2)– Configuration time (T3)– re-INVITE (T4)– RTT/2 (T5)– DHCP [2]: T2 > 1 sec, – DRCP [8]: T2 = 100 ~ 180 ms [7,10] – Total handoff delay of SIP mid-call mobility is not
adoptable to real-time applications
DHCPMN CN
Ha
nd
off D
ela
y
L2 HandoffStart
L2 HandoffFinish
RTP session disconnect
T0
T5
T4
T3
T2
T1
< SIP Mobility Handoff Flow >
Mobiwac 04 24
Proposed scheme: PAR-SIP (cont’d)
Handoff delay of PAR-SIP mid-call mobility
• PAR-SIP handoff delay
= Tn ( n=0,1,3,5) < SIP handoff delay• DHCP transaction time(T2) and SIP re-INVITE
procedure time (T4) are removed • Movement detection time (T1) is diminished• T0,T3 and T5 is same as SIP terminal mobility
L2 HandoffStart
L2 HandoffFinish
RTP sessionAddressReserve
Address Reply
Pre RE-INVITE
200 OK
cBS nBSMN1 MN2
Handoff D
elay
RTP packets
RTP packets
CellPredictionThreshold
DiscoveryOffer
Request
ACK
RTP session disconnect
T0
T3
T1
T5
< PAR-SIP Mobility handoff flow >
Mobiwac 04 25
Experiments (cont’d)
Handoff Delay of Conventional SIP Mobility – SIP_Handoff_Delay = Tn ( n=0 to 5) = 50 ms +5 ms + 1.35 sec + 10 ms + 10 ms +
RTT/2 1.4 s.
– Both nodes can not receive packets for 1.5 seconds. Rx delay of a MN is a little longer than that of a CN due to re-INVITE delay
< MN transmission rate during Handoff > < CN transmission rate during Handoff >
0
5
10
15
20
25
30
0 1 2 3 4
second
kbps
SIP_MN_RX
SIP_MN_TX
0
5
10
15
20
0 0.5 1 1.5 2second
kbps
SIP_CN_RXSIP_CN_TX
Mobiwac 04 26
Experiments (cont’d)
Handoff Delay of PAR-SIP Mobility – PAR-SIP_Handoff_Delay = Tn ( n=0,1,3,5) = T0+T1+T3+T5 = 50 ms +1 ms + 7 ms
+ RTT/2 60ms.
– A MN transmission rate is a little shorter than a CN because a CN keeps bi-casting for a MN during handoff
< MN transmission rate during Handoff >
< CN transmission rate during Handoff >
0
5
10
15
20
25
30
0 0.1 0.2 0.3 0.4 0.5 0.6second
kbps
PARSIP_MN_RX
PARSIP_MN_TX
0
5
10
15
20
25
30
0 0.1 0.2 0.3 0.4 0.5 0.6
second
kbps
PARSIP_CN_RX
PARSIP_CN_TX
Mobiwac 04 27
Experiments (cont’d)
Average transmission rate variation during handoff• PAR-SIP Mobility shows better transmission rate due to handoff than existing SIP mobility while receiving
2500 packets.• PAR-SIP only drops by 2 kbps during handoff
< Average transmission rate during handoff >
0
2
4
6
8
10
12
14
16
0 500 1000 1500 2000 2500
packets
kbps
PARSIP_MN_RXSIP_MN_RX
Mobiwac 04 28
Experiments (cont’d)
Packet loss• Low latency handoff and bi-casting can reduce the number of lost packets• Packet loss of PAR-SIP mobility using all kinds of codecs shows about 1% of total packets comparing to 5%
in conventional SIP mobility (handoff :4 times/sec)
< Packet loss rate Comparison>
0
1
2
3
4
5
6
7
GSM LPC10 MULAW ALAW SPEEX
codec
rate
(%)
PARSIP_MN_RX PARSIP_CN_RX
SIP_CN_RX SIP_MN_RX
The Symbiosis of Cognitive Radio and WMNs
from “Guide to WMNs” by Sudip Misra and et al, 2009
Myungchul Kim
• Spectrum usage
– new spectrum increasingly scarce
– Spectrum is vastly under-used: 5.2% usage
• Change
– “command and control” approach to spectrum regulation
Background
• Static core topology– For CR, the fixed network changes the problem of
collecting awareness of the network’s surroundings
• Spectrum information collection– The WMN presents a distributed infrastructure to collect
spectrum data at a large number of locations
– CR devices act as sensors to gauge interference levels
• Traffic awareness– Fairly easy to obtain from the gateway
Directions for future research
• Data distribution and decision making– Within the mesh itself
• Spectrum monitoring and policing– Primary spectrum rights should be protected
– The WMN may be able to collaborate to detect users and determine the location of illegal transmissions
Directions for future research
Construction and Evaluation of a WMN Testbed
from “Guide to WMNs” by Sudip Misra and et al, 2009
Myungchul Kim
• OLSR– Link-state routing protocol
– MPR
• Methodology
Performance evaluation
• Measurement discussion
Performance evaluation
• Measurement discussion
Performance evaluation
• Existing testbeds
Related work