Transcript September 2004

September 2004
doc.: IEEE 802.11-04/0991r0
W-CHAMB
Wireless CHannel Oriented Ad-hoc Multi-hop Broadband
A new MAC for better support of
Mesh networks with QoS
Rui Zhao, Bernhard Walke, Guido R. Hiertz
ComNets
Chair of Communication Networks
RWTH Aachen University
Aachen
Germany
Submission
Slide 1
Rui Zhao, ComNets, RWTH Aachen University
September 2004
doc.: IEEE 802.11-04/0991r0
Outline
•
•
•
•
•
•
Overview of W-CHAMB
Better Multi-hop Support
QoS Support of W-CHAMB
Synchronization of W-CHAMB
Summary
Simulation Result
Submission
Slide 2
Rui Zhao, ComNets, RWTH Aachen University
September 2004
doc.: IEEE 802.11-04/0991r0
Overview of W-CHAMB
• TDMA based
• Channel-oriented
• Fully distributed MAC
protocol
• Possible PHY
– IEEE 802.11a/g
– OFDMA
– MC-CDMA
• Full scale QoS guarantee
– Prioritized access
(DiffServ)
• Energy (E) signals
– Access-E-Signal
• Prioritized access to wireless
medium
– Busy-E-Signal
• Calm down hidden stations
• Control transmission direction
• Adaptive multi-slot option
– Control of capacity of Traffic
Channel (TCH)
– Increase of channel utilization
• Large-scale ad-hoc Mesh
networks
• Multi-hop operation
Submission
Slide 3
Rui Zhao, ComNets, RWTH Aachen University
September 2004
doc.: IEEE 802.11-04/0991r0
W-CHAMB Protocol Stack
• Radio Resource Control (RRC)
–
–
–
–
Call Admission Control (CAC)
Dynamic Frequency Selection (DFS)
Power Control (PC)
Link Adaptation (LA)
• Media Access Control (MAC)
– Multiple access to wireless medium
– TDMA channels with dynamic TDD
mode
– Hidden station elimination (busy
tone)
– TDMA Traffic Channel (TCH) to
connect neighbored Mesh points
– Priority handling of packet data flows
per Mesh point
– Multiplex packets to TCHs under
DiffServ
Submission
Slide 4
Layer 6
APPLICATION
Layer 5
TCP/UDP
Layer 4
IP
Layer 3
W-CHAMB RRC
(CAC,DFS,PC,LA)
Layer 2
Layer 1
W-CHAMB RLC
W-CHAMB MAC
IEEE802.11 PHY
or other
• Radio Link Control (RLC)
– Un-/acknowledged data
Rui Zhao, ComNets, RWTH Aachen University
September 2004
doc.: IEEE 802.11-04/0991r0
Important Notice!
• All PHY
parameters
are examples
only
• All durations
are example
values
Submission
• No assumption
on PHY to be
used is made
• Here: “.11a”
OFDM like
realistic PHY
assumed
Slide 5
Rui Zhao, ComNets, RWTH Aachen University
September 2004
doc.: IEEE 802.11-04/0991r0
MAC Frame and Energy Signals
ACH
TCH1
…
…
TCHn
ACH1-n
45us x n
ECH 1-n
6us x n
6us
6us
6us
6us x (n +m) + 28us
1us
Tx
On
2us
Signal
2us 1us
Tx
Off
Prioritization
Phase
Contention
Phase
n
m
Transmission
Phase
1us 1us
2us
2us
1us
Guard
Tx
On
2us
2us 1us
28us
Guard
Tx
On
Single Value Busy-ESignal (SVB)
Access-E-signal
• Access Channel (ACH)
• Traffic Channel (TCH)
• Energy signal Channel (ECH)
Signal Tx
Off
Signal
Tx
Off
Guard
Double Value Busy-ESignal (DVB)
• Single Value Busy-E-Signal (SVB)
– Signal “TCH occupied” to hidden
stations
• Double Value Busy-E-Signal (DVB)
– Signal “TCH occupied & Reverse
(TDD) transmission requested”
Submission
Slide 6
Rui Zhao, ComNets, RWTH Aachen University
September 2004
doc.: IEEE 802.11-04/0991r0
Access Channel (ACH)
6us x (n +m) + 28us
Prioritization
Phase
Contention
Phase
Transmission
Phase
n
m
28us
• ACH-Prioritization Phase
• ACH-Transmission Phase
– QoS-related contention
– n binary Access-E-signals
– Transmission of requestpacket
– Network control data
• ACH-Contention Phase
– Contention with m binary
Access-E-signals
– Higher success probability
of an access packet
– m depends on network size
Submission
Slide 7
Rui Zhao, ComNets, RWTH Aachen University
September 2004
doc.: IEEE 802.11-04/0991r0
Access Method
(similar to HiperLAN/1)
• Mesh Points generate
number ∈ [0;2n-1]
Sends
Send E-signal
Prioritized Access Method
– According to QoS requirement
• Check number bit by bit
– If 1, send E-signal
– If 0, listen
– If Mesh point hears E-signal, it
defers from contention
• Winners of prioritization
phase contend again
1 0 0 1 1 0 1 1 1 0 0 1 Req-Packet
listens
listen
1 0 0 1 0 1 1 0 0 1 1 1
0 1 1 1
– Draw random number
from [0;2m-1]
• Winner sends request packet
(or other) via ACH
Submission
Slide 8
Rui Zhao, ComNets, RWTH Aachen University
September 2004
doc.: IEEE 802.11-04/0991r0
Contention Sub-phase in ACH
6us x (n +m) + 28us
• Guarantee single winner
– In almost every contention
– Even in high density mesh
• Failed Mesh Points
– Initiate new contention in
next frame
– Use bigger contention
number
Contention
Phase
Transmission
Phase
n
m
28us
• Support bottle-neck Mesh
Points (Mesh AP, portal)
• Increase chance to win
– Get bigger contention
number
• Achieve fairness among
Mesh points
• Win more access trials
• More transmission chances
– With control algorithms of
TCH
Submission
Prioritizati
on Phase
Slide 9
Rui Zhao, ComNets, RWTH Aachen University
September 2004
doc.: IEEE 802.11-04/0991r0
Transmission
Sender
Receiver
Check available channels
Connection
Setup
Forward
Transmission
Send a request packet on ACH
containing proposed TCHs and
QoS description
Check available channels
Accept the request by signaling SVB on
ECH(s) corresponding to the selected TCH(s)
Send packet data via the reserved TCH(s).
(Data might be station`s own or relay data)
Signal SVB on the corresponding ECH(s)
Send packet data via the reserved TCH(s)
Reverse
Transmission
(On Demand TDD)
Signal DVB on the ECHs to request
reverse TDD transmission
Send packet data via the reserved
TCH(s) in alternate direction
Signal SVB(DVB) on the corresponding ECH(s)
Submission
Slide 10
A TCH is
defined on a per
hop basis only.
Rui Zhao, ComNets, RWTH Aachen University
September 2004
doc.: IEEE 802.11-04/0991r0
Busy-E-Signal to Calm Down
Hidden Stations
• Busy-E-Signal (6μs)
– Does not contain
user related
information
– Preamble not
STA3
needed
• TCHs defined
on disjoint
time slots
Submission
ECH4
STA5
STA4
TCH4
STA6
ECH3
STA8
STA7
TCH3
STA2
Slide 11
STA1
Rui Zhao, ComNets, RWTH Aachen University
September 2004
doc.: IEEE 802.11-04/0991r0
Capacity Increase: Release of a TCH
After Specified Hang-on Time
ACH
• TCH freed by a Mesh
Point
– No packet in TCH buffer
– Hang-on time expired
3
2 1
ECHs
Req
Arrival of packets
1
2
time
• Dependent on type of
service
• Higher service level =
longer hang-on time
• Longer value → lower
transmission delay
4
TCHs
Hang-on
Released
Req
– Packet-oriented behavior
3
Example for hang-on time
equal to 2 MAC frames
Submission
Hangon
4
Slide 12
Rui Zhao, ComNets, RWTH Aachen University
September 2004
doc.: IEEE 802.11-04/0991r0
Dynamic Adjustment of Number of
TCH for a Connection
Packets in buffer
• Mesh points contend for
more TCHs if QoS
cannot be satisfied
• Release TCH after hangon time
5 4 3 2 1
1
5
1 1
8 7
– Hang-on time = 1 MAC
frame
– Max TCHs = 3 TCHs
 Efficient resource use
even for rt-VBR
Slide 13
1
4
1
6
1
3
1
5
1
8
1
2 3
6 5 4
4 5
1
1
1
2
1
4
1
7
1
0
1
1
1
3
1
6
6
6
8 7
7
9 8
1
0
1
2
1
5
1
8
9
1
1
1
4
1
7
ECH
Req
8
Req
9
1
1
1
4
1
7
1
0
1
2
1
5
1
8
time
• Here
Req
TCH
5 4 3 2
– Service specific
Submission
ACH
1
3
1
6
Rui Zhao, ComNets, RWTH Aachen University
September 2004
doc.: IEEE 802.11-04/0991r0
PDU Trains for better Efficiency
ACH
ACH
TCH
ECHs
TCHs
ECHs
45µs
AS
GY
CN
Tx
power
4.7µs
on
90µs
AS
GY
CN
PDU
36µs
Tx
power
4.3µs
off
Tx
power
4.7µs
on
• PDU trains
PDU
Tx
power
4.3µs
off
27µs
81µs
ACH
– Achieve higher
efficiency
– >2 adjacent TCHs used
from source to same
destination
TCHs
ECHs
135µs
AS
GY
CN
PDU
Tx
power
4.7µs
on
Submission
PDU
PDU
PDU
PDU
Tx
power
4.3µs
off
Rui Zhao, ComNets, RWTH Aachen University
31.5µs
126µs
Slide 14
PDU
September 2004
doc.: IEEE 802.11-04/0991r0
Medium Access Fully Decentralized
• No central control
• Mesh Points connect to
neighbor pico-nets
• Any Mesh point is centre
of a pico-net
• Power control/save mode
depend on Mesh point
• Routing modes:
• Mesh points care for
TCHs to neighbors
– Bridge/router
based
– MANET
Submission
Slide 15
Rui Zhao, ComNets, RWTH Aachen University
September 2004
doc.: IEEE 802.11-04/0991r0
Traffic Schemes for Bottle-necks
Prrmium
• Bottle-necks (BNs), Mesh APs or portals
TCHs
Gold
– More in & out traffic than average
– Powerful computational ability & plenty
power supply & large memory
– In “right” location
Silver
Bronze
• Schemes for transmission between BNs
– Several continuous TCHs reserved
• According to load
• Longer hang-on time values
– Multiplexing of different traffic streams
into reserved TCHs
BN
ACH
TCHs
ECHs
• Expedited forwarding (EF) PHB (Per-Hop
Behaviors) (DiffServ) [6]
10
Submission
Slide 16
8 4
Hang-on times
(unit:
MAC frames)
Rui Zhao, ComNets, RWTH Aachen University
STA
September 2004
doc.: IEEE 802.11-04/0991r0
Better Multi-hop Support
Interference range
Sensing range
Transmission range
RTS
IEEE
802.11
W-CHAMB
Transmitting in
parallel in
different TCHs
1
2
3
4
5
CTS
1
ACH-Req
ECHs
TCHs
2
3
4
TCHs
5
 has knowledge
about existing
transmission
• Ongoing transmission between Mesh point 4 & 5
• Mesh point 1 attempts to initiate a transmission to 2 (Instability, see [4])
Submission
Slide 17
Rui Zhao, ComNets, RWTH Aachen University
September 2004
doc.: IEEE 802.11-04/0991r0
QoS Support
• Efficient prioritized access
– Up to 16 levels
• TCH Valid transmission
time (VTT)
• Multi-slots capability for
higher throughput
• QoS guarantee under heavy
load
– Due to channel-oriented
structure
– Associated with QoS type
– Higher Qos level=higher
value
– Statistical interruption of
lower level transmission
• No probing packets for CAC
(Call Admission Control)
– Observe TCHs & ECHs
• TCH Hangon time
– Depends on priority
– Controls traffic performance
(longer value → lower
transmission delay)
Submission
Slide 18
Rui Zhao, ComNets, RWTH Aachen University
September 2004
doc.: IEEE 802.11-04/0991r0
Synchronization of W-CHAMB [5]
• Periodic Beacons
–
–
–
–
–
–
Every Mesh Point participates in generation
Analysis by recipients
In full ad-hoc operations mode
Able to support large scale networks
Support multi-hop operation
Support Mesh Point mobility
Beacon
• Clock shift compensation
algorithm
– Combat clock
drifts
Every Mesh Point
– Accuracy for
can send Beacon
one-hop
network = 0.4±0.1 µs
Submission
Slide 19
Higher priority in Beacon
generation to bottle necks
Rui Zhao, ComNets, RWTH Aachen University
September 2004
doc.: IEEE 802.11-04/0991r0
W-CHAMB Summary
• Channel-Oriented
• On top of any
existent or future
PHY layer
• Decentral Control
Scheme
• Flexible Multi-Hop
(Mesh) Support
Submission
• Perfect Ad-Hoc
Mesh Networking
• Sophisticated QoS
Guarantee
• Support of large
number of Mesh
points in ad-hoc
Mesh
Slide 20
Rui Zhao, ComNets, RWTH Aachen University
September 2004
doc.: IEEE 802.11-04/0991r0
References
•
•
•
•
•
•
[1]. B. Xu, B. Walke, W-CHAMB: A Wireless Channel-oriented Ad-hoc
Multihop Broadband Network – Comparison with IEEE 802.11. In Proc.
European Wireless’99, Munich, Germany, October 1999. pp. 79-84
[2]. B. Xu, B. Walke, Protocols and Algorithms supporting QoS in an Ad-hoc
Wireless ATM Multihop Network, in Proc. EPMCC’99, pp. 79-84, Paris,
France, Mar. 1999.
[3]. M. Lott and B. Walke, Performance of theWireless Ad hoc Network WCHAMB, in Proc. European Wireless (EW’99), (Munich, Germany), Oct.
1999.
[4]. S. Xu and T. Saadawi – “Does the IEEE 802.11 MAC Protocol Work Well
in Multihop Wireless Ad Hoc Networks?” IEEE Communications Magazine,
June 2001, pp 130-137.
[5]. R. Zhao, and B. Walke: A Synchronization Scheme for the Wireless
Channel-oriented Ad-hoc Multi-hop Broadband System (W-CHAMB). In
Wireless World Research Forum, Zurich, Switzerland, July 2003
[6]. RFC 2598, An Expedited Forwarding PHB, June 1999
Submission
Slide 21
Rui Zhao, ComNets, RWTH Aachen University
September 2004
doc.: IEEE 802.11-04/0991r0
Simulation
• Comparing maximum throughput, 802.11 & W-CHAMB
STA2
STA1
– PHY: 802.11a (OFDM)
– Packet size = 9 symbols
2 hop2
• W-CHAMB
MAP1
– 81B @ QPSK¾,
162B @ 16QAM¾,
243B @ 64QAM¾
• 802.11
MAP2
1 hop
STA6
– 115B @ QPSK¾ ,
192B @ 16QAM¾,
277B @ 64QAM¾
STA3
MAP3
MAP6
MAP
MAP5
• W-CHAMB MAC
MAP4
– Number of TCH & ECH
• 16
STA4
STA5
– TCH
• 45µs
– Energy signal
A two hop scenario
• 6µs
– ACH
• (6*4+8*4+28)µs = 100µs
Submission
Slide 22
MAP:
Mesh AP
STA:
Station
Rui Zhao, ComNets, RWTH Aachen University
September 2004
doc.: IEEE 802.11-04/0991r0
Maximum Throughput
25
IEEE 802.11a 18Mbps
IEEE 802.11a 36Mbps
IEEE 802.11a 54Mbps
W-CHAMB 18 Mbps
W-CHAMB 36 Mbps
W-CHAMB 54 Mbps
Maximum Throughput (Mbps)
20
15
10
5
0
Submission
1
2
3
4
5
Number of MAP/STA
Slide 23
6
7
8
9
Rui Zhao, ComNets, RWTH Aachen University
September 2004
doc.: IEEE 802.11-04/0991r0
Thanks for your attention
[email protected]
[email protected]
[email protected]
http://www.comnets.rwth-aachen.de
Submission
Slide 24
Rui Zhao, ComNets, RWTH Aachen University