School of Information Technologies IP Quality of Service NETS3303/3603 Weeks 10-11.
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School of Information Technologies IP Quality of Service NETS3303/3603 Weeks 10-11
School of Information Technologies Outcomes Understanding components of IP QoS –What they do –Why they are used or proposed Have knowledge of some case study technologies Understanding the relevance to real-time multimedia delivery
School of Information Technologies What is QoS ? Many definitions in literature Comer’s definition: –Bounds on loss, delay, jitter and minimum throughput that a network guarantees to deliver
School of Information Technologies IP QoS IP provides only Best Effort service: –No guarantees full stop –No guaranteed packet delivery –No guaranteed time –No guaranteed order IP is ignorant of packet content No “Flows” in IP Compare telephony network
School of Information Technologies QoS Internet Network parameters Packet loss Delay Jitter Getting lost is easy here honey. Lost speech: “ing”, “is easy here honey” Get lost
School of Information Technologies QoS Internet Network parameters Packet loss Delay Jitter Getting lost is easy here honey. Delay 1000 ms Where did he go? Silence
School of Information Technologies QoS Internet Network parameters Packet loss Delay Jitter – variability in delay Getting lost is easy here honey. Delay 1000 ms What the G ettinglos tis easyhere h on ey
School of Information Technologies Types of Traffic Different applications generate different types of traffic e.g. –Web pages (delay sensitive) –FTP (BW sensitive) –Streamed Media (BW sensitive) –Conversational Multimedia (delay and BW)
School of Information Technologies Building blocks Networ k Region End host Edge Router Routers End – to – end signalling Routers: Queuing and Scheduling Edge Routers: Add admission control A defined set of rules or classes to request
School of Information Technologies Integrated Services (IntServ) First QoS proposal for IP Offers a set of service classes per flow –Guaranteed Service Hard guarantees (Conversational MM) –Controlled Load Service Same behaviour as lightly loaded BE network (adaptive MM etc.) –Best Effort Service All other types of traffic
School of Information Technologies IntServ Functions Admission control –Check bw availability and make reservation –For specific QoS, reservation required for new flow Resource reSerVation Protocol (RSVP) used Forwarding –Base decision on QoS parameters Queuing and scheduling discipline –Take account of different flow requirements
School of Information Technologies Is there a problem with the per- flow specification?
School of Information Technologies Resource Reservation Protocol (RSVP) Create notion of flow in IP: –E2E Signalling IETF proposal –Resource Reservation Protocol, RSVP Allows applications to make reservations But only keeps soft-state If routing path change, need to re-reserve on new routers!!
School of Information Technologies RSVP Sender announces meta-info of flow Receiver app fills in Traffic specification (T-Spec) Each router: admission control If requirements met: make reservations End Host Router Can I get? OK Flow
School of Information Technologies Queuing Traditional queuing: one queue and FIFO service For QoS, need to separate traffic into classes –So can provide different priority to different classes Need to manage the different queues
School of Information Technologies Priority Queuing K queues –1 ≤ k ≤ K –Queue k+1 higher prio. than queue k –Higher prio. served first Simple implementation Low processing overhead No fairness –low prio. queues can be starved!!
School of Information Technologies QoS Router Standard QoS Router Components –Routing Policy (rules for classification) –Routing table (Where to send packets) –Input Lines (where packets come in, no queue) –Output queues (where packets wait to be sent) –Classifier (puts packets into queues acc. to policy) –Scheduler (decides which queue to empty)
School of Information Technologies Scheduling Generally, the scheduler assigns resources to tasks In a computer: divide CPU time to processes In a router: divide available BW (output queues) to packets –Operates based on router policy
School of Information Technologies Weighted Fair Queuing (WFQ) Involves multiples queues Generalized Round Robin Each class gets weighted amount of service in each cycle => enables prioritisation E.g. 2 queues with weight ratio 1:2 (both queues full) –1 2 2 1 2 2 1 2 2 … Variant implemented by manufacturers
School of Information Technologies Question: Can we do QoS management without Queuing / Scheduling?
School of Information Technologies Differentiated Services (DiffServ) A newer QoS framework for IP IntServ per-flow has scalability problem Solution: aggregate flows –Treat classes not individual flows –Thus, tables kept small IP TOS field becomes DSCP –6 bit identifier of class
School of Information Technologies DiffServ domain Ingress Router Egress Router Core Router Core Router Dimensioned to meet Ingress router admission control PHB
School of Information Technologies DiffServ Architecture Edge/Boundary router: -per-flow traffic management -admission control Core/Interior router: - per class traffic management - queuing and scheduling
School of Information Technologies DiffServ Scales well Provides statistical guarantee only There are also hybrids of IntServ + DiffServ Other popular mechanisms outside IP –Multi-Protocol Label Switching (MPLS) –Better type of tx media such as optical fibre with wavelength division multiplexed (WDM) systems
School of Information Technologies Summary IP, no flows, no traffic separation Different types of traffic, different needs QoS management: –Admission control –Classification –Queuing/scheduling IntServ and DiffServ Supports higher level protocols such as RTP – next!