1. Presented by Hermes Y.H. Liu
Algorithms for Routing and Centralized Scheduling to Provide QoS in IEEE Mesh Networks
Presented by Hermes Y.H. Liu
2018/12/7

2. Authors Harish Shetiya and Vinod Sharma–
Dept of Electrical Communication Engineering, Indian Institute of Science
ACM conference: WmuNeP’05, Oct 13, 2005 Montreal, Quebec, Canada
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3. Outline Introduction System Model Routing QoS for Real Time Traffic
QoS for TCP Traffic
Joint Scheduling of UDP and TCP Flows
Admission Control
Conclusion
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4. Outline Introduction System Model Routing QoS for Real Time Traffic
QoS for TCP Traffic
Joint Scheduling of UDP and TCP Flows
Admission Control
Conclusion
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5. Introduction 802.16d– Mesh mode Stationary, do not support mobility
Centralized scheduling scheme
Mesh Base Station (MBS)– a node that has a direct connection to backhaul services outside the Mesh network
Mesh Subscriber Station (MSS)
Does not specify an algorithm for scheduling nor any routing algorithm
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6. Introduction
This article provide algorithms for centralized scheduling of real and non real time traffic with QoS in mesh mode
1.Fix the routing within the network, develop scheduling algorithms provide QoS to real time voice and video (UDP)
2.Develop algorithms provide QoS to interactive data uses TCP
3.Combine both real and non real time applications
4.Discuss admission control for sufficient resource concern
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7. Outline Introduction System Model Routing QoS for Real Time Traffic
QoS for TCP Traffic
Joint Scheduling of UDP and TCP Flows
Admission Control
Conclusion
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8. System Model Two physical layers—
WirelessMAN-OFDM in the licensed band and WirelessHUMAN in the unlicensed band, both use 256 point FFT OFDM TDMA/TDM for channel access
Supports only Time Division Duplex (TDD) to share the channel between uplink and downlink
MBS periodically collects channel information and requests of all nodes to make centralized scheduling
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9. System Model M MSSs labeled 1,2,.....M, MBS is labeled 0
is the data rate and is the average data rate of the channel from node i to node j
Real time application: IP telephony and Video conferencing use UDP
Non real time application: Interactive data (ex. Web browsing) use TCP
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10. Outline Introduction System Model Routing QoS for Real Time Traffic
QoS for TCP Traffic
Joint Scheduling of UDP and TCP Flows
Admission Control
Conclusion
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11. Routing Have the same route for all the traffic at a node
Develop algorithm has good performance for UDP and TCP even it is not optimal for either
The route should be fixed:
1.time varying routing can cause loops and may require resequencing at the receiver which cause performance degradation
2.To provide QoS guarantees, resources will be reserved along the route. This is possible only if the route is fixed
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12. Routing Assumptions— 1.The channel states stay same during a frame
2.From frame to frame they change independently forming an i.i.d. sequence (stationary and ergodic)
3.The packets arriving in frame k at a node can be serviced in the next frame only
4.The external arrivals to each node form an i.i.d. sequence
5.Each node has an infinite buffer to store the packets
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13. Routing Assigned transmission rate External arrivals
Arrivals from other nodes to nodes i for output link (i,j) during frame k
queue length at node i for output link (i.j) in the beginning of frame k
time slots assigned in link (i,j)
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14. Routing Where is under the stationary distribution
Where denotes max (0,x)
For the queue to be stable, we need
Where is under the stationary distribution
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15. Routing Let Where are the nodes whose data passes through node i
The entire system is stable if for all i=1...M
Since (total time slots), we get
where are the nodes through which the data of node i is routed
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16. Routing For each node i, if we choose the route that minimizes
, the overall stability region can be maximized and also minimizes the average transmission time to transmit a packet from a node to the MBS
This route can be found by standard shortest path algorithms (Dijkstra’s or Bellman-Ford) by assigning cost to link(i,j)
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17. Outline Introduction System Model Routing QoS for Real Time Traffic
QoS for TCP Traffic
Joint Scheduling of UDP and TCP Flows
Admission Control
Conclusion
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18. QoS for Real Time Traffic
QoS in real time UDP connections like IP telephony and video conferencing
1.End to end delay of a packet should not exceed 150 msec
2.If a packet exceeds this delay, it will be dropped
3.The dropped probability should be less than 2%
We proposed that at the end of a frame we drop the packets which could not be transmitted through the wireless network
Audio encoders (IP telephony) has a constant bit rate (CBR)
Video encoder (MPEG) has a variable bit rate (VBR)
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19. QoS for Real Time Traffic
4.1 Scheduling of CBR traffic
The scheduling problem for CBR-UDP is to calculate the number of slots required at node , such that units of data can be transmitted to the MBR and the end to end drop probability is bounded by
Constant, the amount of traffic generated by users at node i during a frame
The upper bound of the drop probability at node i
Nodes through which the data of node i traverses
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20. Scheduling of CBR Traffic
At node the drop probability is bounded by
The number of slots required, has to satisfy
This reduces to
Rewrite it as
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is the pdf of the link rate which is assumed to be known

21. Scheduling of CBR Traffic
Consider the optimization problem
Subject to
And
Can calculate the scheduling and find the number of slots
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22. Scheduling of VBR Traffic
Be the amount of data generated by flow j (VBR flows) in frame k
Assume the arrival process for each J is
stationary and ergodic with known statistics
Also assume the arrival process from various sources are
mutually independent
Find such that
is called the equivalent bandwidth of the VBR source, the MBS
can treat VBR as a CBR flow generating units of data per frame and calculate the number of slots required
In practice, the exact statistics of a VBR arrival process may not be
available, we calculate the value of by using a source model has
all the known characteristics but has the worst case behavior
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23. Simulations
Consider a 10 nodes Mesh network (Fig. 1)
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24. Simulations Physical layer characteristics (Tab. 1)
Burst profiles and data rates (Tab. 2)
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25. Simulations Scenario: 3 CBR flows and 10 VBR flows at each node
Frame duration is 10 ms, scheduling is done over 3 frames
Scenario: 3 CBR flows and 10 VBR flows at each node
Desired rate– CBR: 64 kbps, an upper bound of 60ms and 2% on the delay and drop probability
VBR source is characterized by a 4 states Markov chain with the rates 20kbps, 40kbps, 60kbps, 80kbps. The transition matrix is
Each flow requires a delay bound of 60ms and a drop probability bound of 2%
The equivalent bandwidth of the VBR is 66.9 kbps
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26. Simulations
All the flows get their desired QoS
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27. Simulations
The average bandwidth provided is greater than even the maximum
Required bandwidth
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28. Outline Introduction System Model Routing QoS for Real Time Traffic
QoS for TCP Traffic
Joint Scheduling of UDP and TCP Flows
Admission Control
Conclusion
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29. QoS for TCP Traffic
s do not require any QoS, but web traffic and file transfer may require certain minimum throughput
In addition to ensuring the minimum throughout requested, we need to allocate excess bandwidth fairly to different TCP connections
QoS to two different TCPs:
Persistent TCP: long lived connections need to send a large file, QoS requirement is the minimum mean throughput
TCP-ON-OFF: A TCP connection transfers multiple files. Between transfer of two files, a TCP connection may not have a file to transfer (OFF period) for sometime. QoS requirement is the mean file download time
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30. QoS for TCP Traffic
Let be the minimum throughput of all TCP connections at node i
Fairness issues will be considered
When the route is fixed via the shortest path routing, we compute the total number of slots to be allocated (Fixed Allocation Scheme) and use the channel conditions to adapt it (Adaptive Fixed Allocation Scheme)
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31. Fixed Allocation Scheme
Notation
Allocate a fixed number of slots per frame to each node depending upon The average data arrival rate and the estimate average channel rate
Minimum throughput (in bytes per frame) required by TCP traffic generated at node i
Mean rate of link i
Number of slots to be allocated at node j
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32. Fixed Allocation Scheme
Constraint–
(C1)
(C2, end to end throughput is
is the same)
,i = 1,...M
(C3, proportional fairness)
C2: the flows from a node at nodes along the route to the destination is the same, can avoid wastage of resources
C3:the throughput provided to the traffic of node I is proportional to its minimum requirement lemda
Combining (C1), (C2), (C3),
With , it is a proportionally fair allocation provide the maximum
throughput to different nodes
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33. Fixed Allocation Scheme
Let This is the number of slots allocated by the node j for the total TCP traffic passing through it
will not ensure the TCP traffic generated at node i will get its share of slots at node j
For TCP traffic originating at node i, we form a separate queue at each node of its route. Via WRR (Weighted Round Robin) out of the total allocation of slots, we provide slots to this queue at node j
Problem:
1.Links can be in bad state or
2.nodes do not have enough data to transmit at a given time.
In Adaptive Fixed Allocation Scheme use the instantaneous channel state and queue length information to adapt
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34. Adaptive Fixed Allocation Scheme
If , we declare the link to be bad
where is the link rate and is the predefined threshold rate
Let G, B denote the set of good and bad links
If , then , else If If
The idea is
1.To differ the allocation of slots to links which are bad or which do not have enough data to fully utilize the slots
2.Ensure the node gets the required throughput in the long term
C(i) is the number of slots in order to compensate for the missed slots (the credit of node i)
An upper bound Clim(i) 要是超過,就給他slots,不管channel 狀況
n(i) be the total number of slots allocated to node i by the Fixed Allocation Scheme
Then the number of slots to node i in frame k in the first round is If
otherwise
where is the smallest integer greater than x
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35. Adaptive Fixed Allocation Scheme
The first round , the remaining are allotted in the second round
Second round preference:
1.nodes with good links, positive credits and MAX data
2.good links with MAX data
3.bad links with MAX data
The allocation is done one slot at a time, recalculating the credits and remaining data to transmit after each slot
Credit update:
與第一輪的差異: not consider the queue length and to set n to n(bar)
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36. Adaptive Fixed Allocation Scheme
In second round keep the same order of preference without the MAX data transmission condition which is so called Channel Adaptive Fixed Allocation Scheme
We can optimize the parameters ( ) to utilize some system performance (e.g. maximizing overall TCP throughput in the system)
Once we get the slot allocation for each node j via fix or adaptive algorithms, we provide the slots to node i via WRR
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37. Simulations In Mesh network Fig. 1
12 TCP persistent flows originating at each node, 6 in uplink and 6 in downlink
3 classes of traffic (throughput requirement 40kbps, 80kbps, 120kbps) with 2 flows each at a node
10 TCP-ON-OFF flows originating at each node, all in uplink
2 classes of TCP-ON-OFF flows with 5 flows in each class
Mean packet size is 1000 bytes
Delays in the external network are arbitrarily fixed {0, 60}
Class 1
T(on)=3s
T(off)=4s
D=25 packets
Class 2
T(off)=5s
D=50 packets
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38. Simulations
(Percentage difference)
All the fixed schemes satisfy QoS of most of the users. The Adaptive
fixed allocation scheme provide more than the min required throughput
to most of the flows. So more flows can be supported with this scheme
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39. Outline Introduction System Model Routing QoS for Real Time Traffic
QoS for TCP Traffic
Joint Scheduling of UDP and TCP Flows
Admission Control
Conclusion
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40. Joint Scheduling of UDP and TCP Flows
UDP consider the worst case channel condition
TCP consider the average channel rate
The difference between average bandwidth requested and the average bandwidth provided will be utilized for TCP flows
UDP has higher priority than TCP. In that case, the delays experienced by UDP can be drastically reduced without affecting the throughput of TCP flows. Also it will save resources
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41. Joint Scheduling of UDP and TCP Flows
Let denote the total number of slots to node i to meet the QoS requirements of UDP flows
Let be the average throughput required by all UDP
Let be the total throughput required by TCP flows
To provide a mean throughput ,the can be calculated by the Fixed Allocation Scheme
Ensure QoS to all UDP connections while TCP get their average throughput
In Channel Adaptive, considering the channel conditions we can defer the allocation of the other slots
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42. Simulations Mesh network in Fig. 1 and characteristics
3 CBR, 3VBR, (UDP) 12 TCP (6 uplink, 6 downlink)
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43. Simulations Compare to Fig. 2 the available resources
are almost fully utilized
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44. Outline Introduction System Model Routing QoS for Real Time Traffic
QoS for TCP Traffic
Joint Scheduling of UDP and TCP Flows
Admission Control
Conclusion
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45. Admission Control The number of slots allotted for node i at node j is
Suppose now a new TCP connection request for a bandwidth of arrives. MBS applies Fixed Allocation Scheme first.
The number of slots required at the node for the new request is:
The connection is accepted if
If the above condition is not met, then the Adaptive Allocation Scheme is used
If there is no additional resource after these algorithms, the new request is rejected
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46. Admission Control
The arrival of a new UDP connection, if VBR traffic, the MSS determines the class to which it belongs, recomputes the effective bandwidth and MBS calculates the number of slots in methods above.
If the required slots is less than the number of slots available then the connection is accepted; otherwise not
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47. Outline Introduction System Model Routing QoS for Real Time Traffic
QoS for TCP Traffic
Joint Scheduling of UDP and TCP Flows
Admission Control
Conclusion
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48. Conclusion
Designed algorithms for routing and centralized scheduling in IEEE mesh networks.
Considered end to end QoS
Handled UDP TCP traffic separately and considered them jointly
Provided admission control policy
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49. Thanks for your listening
Hermes Y.H. Liu
2018/12/7