Transcript Document

New Distributed QoS Control Scheme for
IEEE 802.16 Wireless Access Networks
Xiaofeng Bai1, Abdallah Shami1, Khalim Amjad Meerja1 and Chadi Assi2
1 The University of Western Ontario, Canada, [email protected],
[email protected], [email protected]
2 Concordia University, Canada, [email protected]
IEEE GLOBECOM 2006 proceedings.
報告者：李宗穎
Outline
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Introduction and motivation
Distributed QoS scheme for IEEE802.16
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Uplink Request Management Agent
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Virtual Clock
Frame generation and scheduling
Simulation experiments
Conclusion
Introduction
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In 802.16, the design of efficient, flexible
and yet bandwidth-saving scheduling
algorithms for such QoS provisioning still
remains an open topic
This paper considers the data control plane
as a collaborative entity and specifies
detailed operations performed at the base
station and each subscriber station
Key QoS parameter
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Real-time Polling Service (rtPS)
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Non-real-time Polling Service (nrtPS)
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minimum reserved traffic rate
maximum sustained traffic rate
maximum latency
minimum reserved traffic rate
maximum sustained traffic rate
Best Effort (BE)
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maximum sustained traffic rate
Motivation (1/2)
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the uplink request/grant scheduling is
crucial for providing service guarantees to
non-UGS connections
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the extra overhead required for connections to
request their real-time bandwidth needs
With the fixed frame duration, the BS’s delayed
perception eventually deteriorates the interconnection statistical bandwidth multiplexing
and potentially leads to bandwidth waste
Motivation (2/2)
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Paper provide Sing-Carrier Scheduling
Algorithm (SCSA) to achieve :
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Guarantee service parameters for each
connection
Minimize the per-connection overhead required
for bandwidth request
Optimize the freshness of BS’s perception on
each connection’s bandwidth need
Distributed QoS Control Scheme
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move some connection level functionalities
performed by the BS to each SS
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Uplink Request Management Agent (SS)
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installed in each SS and processes each connection’s
bandwidth request
the overhead required for bandwidth request is
limited to be only SS-relevant
Frame generation (BS)
Outbound transmission scheduling (BS)
Uplink Request Management Agent
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Service measurement module
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QoS enforcement module
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obtains the instant upper-bound bandwidth request of
each connection
maintains a QoS timer for each rtPS and nrtPS
connection running in the SS
SS request generation module
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generates up to three per-SS bandwidth requests
Virtual Clock Algorithm
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Each switch along the path of a flow uses
two control variables, a Virtual-Clock (VC)
and an auxiliary Virtual-Clock (auxVC), to
monitor and control the flow according to
the specified AR (Average Rate) and AI
(Average Interval) values.
[2] L. Zhang, “Virtual Clock: A New Traffic Control Algorithm for Packet-Switched
Networks,” ACM Transaction on Computer Systems, vol. 9, pp. 101-124, 1991.
Data forwarding
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Upon receiving the first data packet from flowi
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VCi  auxVCi  real time
Upon receiving each packet from flowi
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auxVCi  max(real time, auxVCi)
VCi  (VCi + Vticki), and auxVCi  (auxVCi + Vticki)
(Stamp the packet with the auxVC value)
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Vticki = 1/ARi (packet/sec)
Insert the packet into its outgoing queue. Packets are
queued and served in the order of increasing stamp
values
Flow monitoring
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Upon receiving every set of AIRi (ARi x AIi)
data packets from flowi, the switch checks
the flow in the following way :
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If (VCi – real time) > T
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T is a control threshold, a warning message should
be sent to the flow source
If ( VCi < real time), VCi  real time.
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if doing so does not cause packets from the same
flow from being served out of order:
Real time, Virtual-Clock, and
packet-processing order
Service measurement module
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bandwidth request is upper-bounded by the
connection’s eligible bandwidth request, which is
computed as:
Rimax : maximum sustained traffic rate
t : system time
rie : eligible bandwidth request of connection i
Si(t) : service time
Tick with service timer
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when a connection is established and ticks with
the following value upon the service of each PDU
in the corresponding connection :
Ai : the increment of connection i’s service timer
Bi : the service of a PDU with size (bytes)
ρi : is the measurement rate (in bit/second) for connection I
For the service timer, this value should be Rimax
QoS enforcement module
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For each rtPS or nrtPS connection i, segment its
bandwidth request ri into bandwidth guaranteed (BG)
part and non-bandwidth guaranteed (NBG) part
BG : bandwidth guaranteed
NBG : non- bandwidth guaranteed
Qi(t) : QoS timer
for the QoS timer, the value ρi should be Rimin
Imminent and non-imminent
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For each rtPS connection i, further segment
its riBG into imminent part riBG-im and non imminent part riBG-nim
imminent
N
N+1
N+2
Bandwidth
request
Schedule
transmission
Deadline
SS request generation module
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The per-SS bandwidth requests are prioritized, in
order to enable service differentiation at the BS
im : imminent part
nim : non-imminent part
M : rtPS N : nrtPS L : BE
Frame generation
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Downlink Request Management module
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Resource allocation module
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Similarly to the URMA at a SS, except that the
prioritized bandwidth requests
This module allocates transmission capacity to each
Scheduling Group, according to their prioritized
bandwidth requests
P0 > P1 > P2 (priority)
Frame creation module
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Converts the above symbol assignment result into
timing information in terms of physical slot and
minislot
Outbound transmission
scheduling
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the P0 request
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the P1 request
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the packet with the most imminent maximum
latency deadline is selected and expired
maximum latency deadline will be dropped at
the front of the connection queue
earliest QoS timer is selected
the P2 request
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each connection in a round-robin fashion
Simulation Model
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Simulation environment by NS-2
1-BS 10-SS 2.5km away from the BS
Each SS 1-rtPS 1-nrtPS 1-BE connection
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SS6(3-rtPS 1-BE) SS8(4-nrtPS 1-BE)
Frame Duration : 1ms
We focus on the service provisioning of three uplink connections
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rtPS connection 35 running in SS6, rtPS connection 36 running in SS6
and nrtPS connection 48 running in SS8
QoS Parameter
rtPS
nrtPS
BE
maximum latency
3ms
-
-
maximum sustained traffic rate
1.5Mbps
1.5Mbps
1.5Mbps
minimum reserved traffic rate
1Mbps
1Mbps
-
Offers averagely traffic intensity
1Mbps
1Mbps
1Mbps
Conn.36 (2Mbps)
Scenario one
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referred to as passive
(PASV) scheme, where the
bandwidth allocation is
fixed in every frame and
equally shared by each SS
Drop
Prob.
PASV
SCSA
rtPS(34) 27.04%
0%
rtPS(35) 26.61%
0%
rtPS(36)
30.4%
25.53%
Scenario two
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In PASV, both rtPS
connection 35 and nrtPS
connection 48 were
starved by about 30% of
their minimum reserved
traffic rates
Conclusion
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This proposed Single-Carrier Scheduling
Algorithm (SCSA) scheme guarantees
service parameters for each uplink and
downlink connection and minimizes
signaling overhead in the data control plane