Internet Quality of Service: an Overview

Transcription

1 Internet Quality of Service: an Overview W. Zhao and et al, Columbia University presented by 리준걸 INC Lab, Seoul Nat l University

2 Outline Introduce QoS framework IntServ DiffServ Detailed mechanism Queueing Scheduling Control Non-traditional QoS skills Coming issues Summary SNU INC lab. 2

3 Introduce why QoS? Only best effort service provided, before Assured service: audio, video Services with different requirements audio: delay-sensitive UDP: loss rather than delay sensitive Example: Voice calls, only 16 voice calls could be supported, then the 17 th one request for admission. at 1Mbps, 800 byte/s for audio, 100 for UDP, left for others SNU INC lab. 3

4 Introduce definition QoS: providing service differentiation and performance assurance for Internet applications Ingress: differentiate service Core network: admission control, bandwidth control Router: scheduling, queue management end-to-end QoS SNU INC lab. 4

5 QoS architecture a general view per-flow based IntServ (Integrated Service) Characterized by resource reservation per-class class DiffServ (Differentiated Service) Traffic classification SNU INC lab. 5

6 QoS architecture IntServ Router reserve resource to provide special QoS for specific traffic flow RSVP (Resource Reservation Protocol) signaling protocol Sender sends a PATH msg Receiver responds with a RESV message Intermediate router reject or accept the request Allocation of link bandwidth and buffer space for the flow Soft state SNU INC lab. 6

7 QoS architecture IntServ(Cont.) Characteristic Per-flow service Resource reservation Guaranteed service Fine-grained Intra-domain / high-bandwidth flow audio, video Huge amount of queue for flows and overhead for setup path and states stored in router SNU INC lab. 7

8 QoS architecture DiffServ IPv4 TOS (type-of-service) byte field IPv6 DSCP (Diff-Serv CodePoint) field 6 bits PHB (Per-Hop Behaviors) 64 types, only used a few implemented on DSCP Traffic with a certain PHB on DSCP enters DiffServ domain, (classification) Mapping, router decision by profile Forwarding, or dropping SNU INC lab. 8

9 QoS architecture DiffServ(Cont.) Characteristic Per-aggregate class of packets Coarse-grained Simple operation, boundary classification, Separation of policy and supporting mechanism stable PHB, dynamic policy end-to-end behavior may not be predictable Inter-domain policy may be different IntServ in edge network, and DiffServ in core network SNU INC lab. 9

10 Detailed mechanisms packet loss bit error (trivial), drop as congestion packet delay solve the above problem are important goals of QoS Queue management packet loss control length of packet queue (buffer) drop packet Scheduling packet delay reorder the output queue Controls SNU INC lab. 10

11 Detailed - queueing 2 problems lock-out : flows monopolize queue, unfair full queue : queue size close to maximum, long delay RED (Random Early Detection) algorithm queueavg < minth : no packet drop queueavg > maxth : every packet drop else : packet drop with prob Pa (Pa is function of queueavg) Pa [0, Pmax] P (drops) 1 Pmax minth maxth queueavg SNU INC lab. 11

12 Detailed - scheduling propagation (5 us/km), transmission (fragment), queueing FCFS (First Come First Serve) QoS meaningless Priority scheduling DiffServ FCFS high priority queue served first WFQ (Weighted Fair Queueing) flow-based queueing by weight of flows EDF (Earliest Deadline First) dynamic priority scheduling deadline of packet = arrival + delay guarantee need simplicity, i.e. at OC-48(1.2Gbps) rate scheduler has 100ns decision time SNU INC lab. 12

13 Detailed Controls Admission Control resource management (link bandwidth, router buffer space) Router control for flow of IntServ Policy Control Administrative control for access resources policy infrastructure (Policy Server = CPC+PDP, PEP in router) Policy server -> policy DB or AAAC PDP <-> PEP via Common Open Policy Service (COPS) Bandwidth brokers (infrastructure) Manage intra, inter-domain resource Admission control, policy control SNU INC lab. 13

14 QoS innovative MPLS (MultiProtocol Layer Switching) IP level QoS merge routing with QoS, COS (Class of Service) field MPLS domain, using label field, between IP layer and link layer QoS provided by end host Application level QoS (Application Adaptation) careless app at edge node, deadly, break down QoS made by network / efficient retransmission (UDP) audio codec SNU INC lab. 14

15 Coming Issues QoS happened in next generation network i.e. cellular network connect to legacy network (domain to-domain) IntServ? DiffServ? Multi-domain Admission control Policy control - AAAC Handover intra- as well as inter- Cross-layer QoS SNU INC lab. 15

16 Summary IntServ resource reservation flow-based service DiffServ mark on DS field to classify packet group behavior-aggregate-class-based service Router scheduling, queue management Control admission control, policy control Non-traditional MPLS, end-host application adaptation SNU INC lab. 16