Algorithms for Routing and Centralized Scheduling to Provide

Algorithms for Routing and Centralized Scheduling to Provide Qo. S in IEEE 802. 16 Mesh Networks Presented by Hermes Y. H. Liu 10/16/2021 1

Authors p Harish Shetiya and Vinod Sharma– Dept of Electrical Communication Engineering, Indian Institute of Science p ACM conference: Wmu. Ne. P’ 05, Oct 13, 2005 Montreal, Quebec, Canada 10/16/2021 2

Outline Introduction p System Model p Routing p Qo. S for Real Time Traffic p Qo. S for TCP Traffic p Joint Scheduling of UDP and TCP Flows p Admission Control p Conclusion p 10/16/2021 3

Outline Introduction p System Model p Routing p Qo. S for Real Time Traffic p Qo. S for TCP Traffic p Joint Scheduling of UDP and TCP Flows p Admission Control p Conclusion p 10/16/2021 4

Introduction • • • 802. 16 d– 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 10/16/2021 5

Introduction p This article provide algorithms for centralized scheduling of real and non real time traffic with Qo. S in 802. 16 mesh mode 1. Fix the routing within the network, develop scheduling algorithms provide Qo. S to real time voice and video (UDP) 2. Develop algorithms provide Qo. S to interactive data uses TCP 3. Combine both real and non real time applications 4. Discuss admission control for sufficient resource concern 10/16/2021 6

Outline Introduction p System Model p Routing p Qo. S for Real Time Traffic p Qo. S for TCP Traffic p Joint Scheduling of UDP and TCP Flows p Admission Control p Conclusion p 10/16/2021 7

System Model p p p Two physical layers— Wireless. MAN-OFDM in the licensed band Wireless. HUMAN 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 10/16/2021 8

System Model p p 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 10/16/2021 9

Outline Introduction p System Model p Routing p Qo. S for Real Time Traffic p Qo. S for TCP Traffic p Joint Scheduling of UDP and TCP Flows p Admission Control p Conclusion p 10/16/2021 10

Routing p p p 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 Qo. S guarantees, resources will be reserved along the route. This is possible only if the route is fixed 10/16/2021 11

Routing p 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 10/16/2021 12

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) 10/16/2021 13

Routing Where denotes max (0, x) For the queue to be stable, we need Where 10/16/2021 is under the stationary distribution 14

Routing p Let p Where through node i The entire system is stable if p Since are the nodes whose data passes for all i=1. . . M (total time slots), we get p where of node i is routed 10/16/2021 are the nodes through which the data 15

Routing p 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 p This route can be found by standard shortest path algorithms (Dijkstra’s or Bellman-Ford) by assigning cost to link(i, j) 10/16/2021 16

Outline Introduction p System Model p Routing p Qo. S for Real Time Traffic p Qo. S for TCP Traffic p Joint Scheduling of UDP and TCP Flows p Admission Control p Conclusion p 10/16/2021 17

Qo. S for Real Time Traffic p Qo. S 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% p 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) p p 10/16/2021 18

Qo. S for Real Time Traffic p p 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 10/16/2021 19

Scheduling of CBR Traffic At node The number of slots required, the drop probability is bounded by has to satisfy This reduces to Rewrite it as 10/16/2021 is the pdf of the link rate which is assumed to be known 20

Scheduling of CBR Traffic p Consider the optimization problem Subject to And Can calculate the scheduling and find the number of slots 10/16/2021 21

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 10/16/2021 22

Simulations p Consider a 10 nodes Mesh network (Fig. 1) 10/16/2021 23

Simulations p Physical layer characteristics (Tab. 1) p Burst profiles and data rates (Tab. 2) 10/16/2021 24

Simulations p Frame duration is 10 ms, scheduling is done over 3 frames p Scenario: 3 CBR flows and 10 VBR flows at each node Desired rate– CBR: 64 kbps, an upper bound of 60 ms and 2% on the delay and drop probability VBR source is characterized by a 4 states Markov chain with the rates 20 kbps, 40 kbps, 60 kbps, 80 kbps. The transition matrix is Each flow requires a delay bound of 60 ms and a drop probability bound of 2% The equivalent bandwidth of the VBR is 66. 9 kbps 10/16/2021 25

Simulations p All the flows get their desired Qo. S 10/16/2021 26

Simulations • The average bandwidth provided is greater than even the maximum Required bandwidth 10/16/2021 27

Outline Introduction p System Model p Routing p Qo. S for Real Time Traffic p Qo. S for TCP Traffic p Joint Scheduling of UDP and TCP Flows p Admission Control p Conclusion p 10/16/2021 28

Qo. S for TCP Traffic p p p Emails do not require any Qo. S, 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 Qo. S to two different TCPs: n n Persistent TCP: long lived connections need to send a large file, Qo. S 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. Qo. S requirement is the mean file download time 10/16/2021 29

Qo. S for TCP Traffic p p p 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) 10/16/2021 30

Fixed Allocation Scheme p Notation 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 Allocate a fixed number of slots per frame to each node depending upon The average data arrival rate and the estimate average channel rate 10/16/2021 31

Fixed Allocation Scheme Constraint– (C 1) (C 2, end to end throughput is is the same) , i = 1, . . . M (C 3, proportional fairness) Combining (C 1), (C 2), (C 3), With , it is a proportionally fair allocation provide the maximum 10/16/2021 throughput to different nodes 32

Fixed Allocation Scheme p p p 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. p In Adaptive Fixed Allocation Scheme use the instantaneous 10/16/2021 33 channel state and queue length information to adapt p

Adaptive Fixed Allocation Scheme p 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 p If p , then , else If If Then the number of slots to node i in frame k in the first round is If otherwise where 10/16/2021 is the smallest integer greater than x 34

Adaptive Fixed Allocation Scheme The first round , the remaining are allotted in the second round p 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 slot at a time, recalculating the credits and remaining data to transmit after each slot p Credit update: 10/16/2021 35

Adaptive Fixed Allocation Scheme p p p 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 10/16/2021 36

Simulations p p p p 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 40 kbps, 80 kbps, 120 kbps) 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 Class 1 T(on)=3 s T(off)=4 s D=25 packets Class 2 T(on)=3 s T(off)=5 s D=50 packets Mean packet size is 1000 bytes Delays in the external network are arbitrarily fixed {0, 60} 10/16/2021 37

Simulations (Percentage difference) All the fixed schemes satisfy Qo. S 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 10/16/2021 38

Outline Introduction p System Model p Routing p Qo. S for Real Time Traffic p Qo. S for TCP Traffic p Joint Scheduling of UDP and TCP Flows p Admission Control p Conclusion p 10/16/2021 39

Joint Scheduling of UDP and TCP Flows p UDP consider the worst case channel condition TCP consider the average channel rate p The difference between average bandwidth requested and the average bandwidth provided will be utilized for TCP flows p 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 10/16/2021 40

Joint Scheduling of UDP and TCP Flows p p p Let denote the total number of slots to node i to meet the Qo. S requirements of UDP flows Let be the average throughput required by all UDP Let be the total throughput required by TCP flows p To provide a mean throughput , the calculated by the Fixed Allocation Scheme p Ensure Qo. S to all UDP connections while TCP get their average throughput p In Channel Adaptive, considering the channel conditions we can defer the allocation of the other slots 10/16/2021 can be 41

Simulations p p Mesh network in Fig. 1 and characteristics 3 CBR, 3 VBR, (UDP) 12 TCP (6 uplink, 6 downlink) 10/16/2021 42

Simulations Compare to Fig. 2 the available resources are almost fully utilized 10/16/2021 43

Outline Introduction p System Model p Routing p Qo. S for Real Time Traffic p Qo. S for TCP Traffic p Joint Scheduling of UDP and TCP Flows p Admission Control p Conclusion p 10/16/2021 44

Admission Control p The number of slots allotted for node i at node j is p 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: p p The connection is accepted if If the above condition is not met, then the Adaptive Allocation Scheme is used p If there is no additional resource after these algorithms, the new request is rejected 10/16/2021 45 p

Admission Control p 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. p If the required slots is less than the number of slots available then the connection is accepted; otherwise not 10/16/2021 46

Outline Introduction p System Model p Routing p Qo. S for Real Time Traffic p Qo. S for TCP Traffic p Joint Scheduling of UDP and TCP Flows p Admission Control p Conclusion p 10/16/2021 47

Conclusion p p Designed algorithms for routing and centralized scheduling in IEEE 802. 16 mesh networks. Considered end to end Qo. S Handled UDP TCP traffic separately and considered them jointly Provided admission control policy 10/16/2021 48

Thanks for your listening Hermes Y. H. Liu 10/16/2021 49