New Distributed QoS Control Scheme for IEEE Wireless Access Networks Xiaofeng Bai 1, Abdallah Shami 1, Khalim Amjad Meerja 1 and Chadi Assi 2 1 The University of Western Ontario, Canada, 2 Concordia University, Canada, 報告者：李宗穎 IEEE GLOBECOM 2006 proceedings.

Outline Introduction and motivation Distributed QoS scheme for IEEE Uplink Request Management Agent Virtual Clock Frame generation and scheduling Simulation experiments Conclusion

Introduction In , 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 Real-time Polling Service (rtPS) minimum reserved traffic rate maximum sustained traffic rate maximum latency Non-real-time Polling Service (nrtPS) minimum reserved traffic rate maximum sustained traffic rate Best Effort (BE) maximum sustained traffic rate

Motivation (1/2) the uplink request/grant scheduling is crucial for providing service guarantees to non-UGS connections 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 inter- connection statistical bandwidth multiplexing and potentially leads to bandwidth waste

Motivation (2/2) Paper provide Sing-Carrier Scheduling Algorithm (SCSA) to achieve : 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 move some connection level functionalities performed by the BS to each SS Uplink Request Management Agent (SS) 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 Service measurement module obtains the instant upper-bound bandwidth request of each connection QoS enforcement module maintains a QoS timer for each rtPS and nrtPS connection running in the SS SS request generation module generates up to three per-SS bandwidth requests

Virtual Clock Algorithm 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 , 1991.

Data forwarding Upon receiving the first data packet from flow i VC i  auxVC i  real time Upon receiving each packet from flow i auxVC i  max(real time, auxVC i ) VC i  (VC i + Vtick i ), and auxVC i  (auxVCi + Vtick i ) (Stamp the packet with the auxVC value) Vtick i = 1/AR i (packet/sec) Insert the packet into its outgoing queue. Packets are queued and served in the order of increasing stamp values

Flow monitoring Upon receiving every set of AIR i (AR i x AI i ) data packets from flow i, the switch checks the flow in the following way : If (VC i – real time) > T T is a control threshold, a warning message should be sent to the flow source If ( VC i < real time), VC i  real time. 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 bandwidth request is upper-bounded by the connection’s eligible bandwidth request, which is computed as: R i max : maximum sustained traffic rate t : system time r i e : eligible bandwidth request of connection i S i (t) : service time

Tick with service timer when a connection is established and ticks with the following value upon the service of each PDU in the corresponding connection : A i : the increment of connection i’s service timer B i : the service of a PDU with size (bytes) ρ i : is the measurement rate (in bit/second) for connection I For the service timer, this value should be R i max

QoS enforcement module For each rtPS or nrtPS connection i, segment its bandwidth request r i into bandwidth guaranteed (BG) part and non-bandwidth guaranteed (NBG) part BG : bandwidth guaranteed NBG : non- bandwidth guaranteed Q i (t) : QoS timer for the QoS timer, the value ρi should be R i min

Imminent and non-imminent For each rtPS connection i, further segment its r i BG into imminent part r i BG-im and non - imminent part r i BG-nim imminent

SS request generation module 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 Downlink Request Management module Similarly to the URMA at a SS, except that the prioritized bandwidth requests Resource allocation module This module allocates transmission capacity to each Scheduling Group, according to their prioritized bandwidth requests P 0 > P 1 > P 2 (priority) Frame creation module Converts the above symbol assignment result into timing information in terms of physical slot and minislot

Outbound transmission scheduling the P0 request 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 the P1 request earliest QoS timer is selected the P2 request each connection in a round-robin fashion

Simulation Model Simulation environment by NS-2 1-BS 10-SS 2.5km away from the BS Each SS 1-rtPS 1-nrtPS 1-BE connection SS6(3-rtPS 1-BE) SS8(4-nrtPS 1-BE) Frame Duration : 1ms We focus on the service provisioning of three uplink connections rtPS connection 35 running in SS6, rtPS connection 36 running in SS6 and nrtPS connection 48 running in SS8 QoS ParameterrtPSnrtPSBE maximum latency3ms-- maximum sustained traffic rate1.5Mbps minimum reserved traffic rate1Mbps - Offers averagely traffic intensity1Mbps Conn.36 (2Mbps) 1Mbps

Scenario one referred to as passive (PASV) scheme, where the bandwidth allocation is fixed in every frame and equally shared by each SS Drop Prob. PASVSCSA rtPS(34)27.04%0% rtPS(35)26.61%0% rtPS(36)30.4%25.53%

Scenario two In PASV, both rtPS connection 35 and nrtPS connection 48 were starved by about 30% of their minimum reserved traffic rates

Conclusion 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