Advanced networking - scheduling and QoS part 1
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This document discusses scheduling and quality of service (QoS) in advanced telecommunication networks. It covers several key topics in 3 sentences: It describes different scheduling techniques like FIFO, priority queuing, and weighted fair queuing that can provide class-based differentiation for real-time and non-real-time traffic. Buffer management techniques like head of line blocking, partial buffer sharing, and push out buffer are discussed. The document also covers QoS standards from the IETF like RSVP for signaling, integrated services for per-flow reservations, and differentiated services for class-based forwarding behaviors.
Advanced networking - scheduling and QoS part 1
- 1. Scheduling and Quality of Services (QoS) Advanced Telecommunication Network (ET5187) by Aris Cahyadi Risdianto 23210016
- 2. Scheduling and QoS Input ===> Scheduling and QoS ===> Output (Controller)
- 3. Packet Classification • Same Class / No Class differentiation > FIFO/LIFO > Most Common Used • Different Class > Lost Sensitive and Delay Sensitive > Different rules for different Class
- 4. Queuing System I = class of service of K and J flows Mi(t) = actual service allocated for class i at t time Ni(t) = Buffer size
- 5. Loss Sensitive Scheduling Two different Class (High and Low), for the each same class use FIFO with K buffer • Head of line (HoL) • Partial Buffer Sharing (PBS) • Push Out Buffer (POB) • Random Early Detection (RED)
- 6. Buffer Size Familiar and Famous for ATM network D* = Delay constraint end to end (Based on ITU) -> 10 ms E(H) = average number hops ( <10) M = maximum service rate for STM-1 155 Mbps = 366800 cells K <= M x D*/10 ms K small, assured delay but loss cell
- 7. Head of Line • Known as priority queue for queueu > 2 • Always served High priority cells in the buffer • pre-emptive and non pre-empetive H3 | L5 | L4 | H2 | L3 | H1 | L2 | L1 => HoL Same as : L5 | L4 | L3 | L2 | L1 | H3 | H2 | H1 => FIFO
- 8. Partial Buffer Sharing • The rule specified by threshold T in the queue • Nq(t) is number cells/packet at the time T • Nq(t) < T, high and low enter the queue • Nq(t) > T, only high enter the queue • Nq(t) = K, buffer is full, arriving cells discarded
- 9. Push Out Buffer • Avoid complex determination of best position • Only operates when the buffer is full H3 ==> | L5 | L4 | H2 | L3 | H1 | L2 | L1 LIFO FOB R FOB FIFO FOB
- 10. Random Early Detection (RED) • Like PBS but have 2 threshold Tmin and Tmax • q < Tmin => no packet drop • q > Tmax => all packet are dropped • Tmin < q < Tmax => packet are drop with P = (q- Tmin) * Pmx / Tmax-Tmin • used for TCP flows congestion avoidance • variant of RED is WRED (Weighted RED)
- 11. Delay Sensitive Scheduling • Assumption there is no problem of losing packet and buffer k is long • Consist of processor sharing example WRR has class k with weight Wk • WRR (Processing sharing) inflexible because Wk independent • Processing rule rather than processing sharing
- 12. Upper Bound Method • Used for solving CAC (Call Admission Control) problem • Some assumption : o Each arrival process satisfies with certain business constrain o Service time for cell/packet is deterministic and proportional o Scheduling rule is used to generate QoS for class k with minimal Mk ("fair" rule to prevent blocking another class getting served)
- 13. Upper Bound Method (Cont.) • Queue count is maximum difference between inflow and outflow (λk and μk) • If queue > 0, class served by minimal rate (μk) • Number of queue bounded by burstinest σk provided if λk ≤ μk • Buffer size bounded by sum of burstinest all flows, so loss can be guaranteed • Maximum delay bounded by burstinest divide by inflows, so delay can be guaranteed
- 14. Upper Bound Method (Cont.) • Remarks on upper bound method : • Zero packet loss only guaranteed for admitted packet (satisfied with burstinest constrain), if not packet will be lost • Delay guaranteed are deterministic because all stochastic assumed to be bounded or deterministic • Upper Bound Method more optimal than N*D/D/1 queuing for scenario where N not identical and independent CBR resources
- 15. QoS (Quality of Services)
- 16. Evolution and Importance • Internet and Value Added Services is the main driver • Internet used for e-commerce, self backing and communication • Overall result : people are tolerant about QoS, in certain point some people are frustrated of losing data • Mature Internet need to offer ubiquitous inexpensive, and high quality services
- 17. QoS as Technological Lever • Two Main Approach : o Over Installing resources (less than 30% load) o Controlling Traffic in the network to ensure each flows achieve certain level of QoS • QoS implementation is faster and cost effective than expanding new network (Fiber, equipment, etc)
- 18. QoS as Commercial Lever • Old view: over dimension network without complex network functionality • Notation QoS : demand always beyond supply cause congestion • QoS offer dividing resources, not guarantee quality (lower priority users get less, high priority users get more) • Controlling QoS = Controlling Resources • Sub-optimal controlling resource = loss revenue
- 19. Definition and Property of QoS • In general, QoS express set of service example performance, availability, reliability and security • Network QoS on layer 3 (inspired by ATM network) • Application Layer QoS associate with GoS • QoS provision cause dichotomy “soft” and “hard guarantee” • Perceived QoS (Voice, Streaming, e-games): delay, jitter, echo, packet loss
- 20. Challenges : QoS aware Networking • Main Problem : Stochastic arrival process and deterministic set of traffic or determination • Analysis and computing random variable more complex • Computation level explode state spaces and prevent accurate computations • Inherent problem “connection set-up time” need QoS per flow such as QoS routing, signalling and CAC • Two different future QoS by IETF : IntServ and DiffServ
- 21. Evolution Network Architecture : IP and ATM • Two different approach : IP by IETF and ATM by ATM forum • Layered routing : IP for L3 and ATM for L2 • Integration : • Partially Integrated : Dual-Mode • Fully Integrated : I-PNNI • Ipsilon : ATM for forwarding, IP for control • IETF : MPLS (IP Fast Switching) • ATM goal, reality of IP : Basic Architecture for Broadband Multimedia
- 22. QoS Emerging in the Internet • QoS aware networking including QoS routing, signaling and traffic management • Standardized by IETF but not implemented • QoS aware Internet: • RSVP : signaling • IntServ : end-to-end signaling per flow basis • DiffServ : no end-to-end signaling per flow
- 23. RSVP • RSVP (Resource Reservation Protocol) • IETF signalling protocol based on multicast • Used two types of messages : path and reservation messages • Most of Telecom or connection oriented based on unicast • Continued with SIP protocol as application layer signalling protocol
- 24. RSVP Messages • Path messages : previous hop IP address, sender template and IP address, traffic characteristic, end to end QoS requirement • Teardown Messages : Path Tear and Resv Tear o Path Tear : Iniated by the sender to install reservation state o Reservation Tear : Travels from receiver to the sender to remove reservation state
- 25. RSVP Operations • Sender send path message to receiver of the mcast group, each router install the reservation state and record the hop • Receiver send "Resv Message" to nearest router and ask amount of resources • Nearest Router reserve along the path to the sender • If other receiver joint the mcast group, nearest router ask more resource along the path
- 26. Characteristic of RSVP • Used for unicast and multicast application • Receiver Oriented : flows initiated and resources reservation • Consist of policy control and admission control • MPLS LDP is alternate to RSVP based on explicit routing • QoS state is soft state : messages are flows periodic to adopt the routing changes • reservation for unidirectional data flows
- 27. Integrated Services (IntServ) • Additional component : packet classifier, scheduler and admission control • Required resources reservation for each session/flows using RSVP • If RSVP failed, the session will be best effort (BE) • Two class: o Guaranteed Services : provide services with guaranteed both delay and bandwidth o Controlled-Load Services : provide data flow all same in the unloaded network, and using CAC if network is loaded
- 28. Differentiated Services (DiffServ) • Threat each class differently on per-hop behaviour (PHB) • Class differentiation rather than flow differentiation (more scalable) • Provide QoS more natural than IntServ which inline with Internet • Bandwidth Broker use to managed inter-domain resources for providing end-to-end QoS
- 29. Differentiated Class • IP DSCP format: • Two different PHB Class, except BE (Best Effort) : Expedited Forwarding (EF) = virtual leased line or point-to-point connection Assured Forwarding (AF) = better best efforf
- 30. Next on "Scheduling" • Generalized Processing Sharing (GPS) • Generalized cu-rules (Dynamic Scheduling Rules)
- 31. Next on "Quality of Services" • Shortcut Routing : L2 over L3 (MPLS) • Multiprotocol Label Switching (MPLS) including GMPLS (Generalized MPLS)