Scheduling and Quality of Services (QoS)

Advanced Telecommunication Network(ET5187)

byAris Cahyadi Risdianto

23210016

Review Scheduling

• Scheduling and Qos : Qontrolling input to output• Packet Classification : Same Class (FIFO/LIFO)

or Different Class (Lost/Delay Sensitive, Class)• Queuing System : Scheduling control • Loss Sensitive Scheduling : HoL, PBS, POB,

RED• Buffer size : small assured delay, but loss cell• Delay Sensitive Scheduling : Upper Bound

Method

Review QoS

• QoS as Technological Lever : over installed resources or controlling traffic in the network

• QoS as Commercial Lever : sub-optimal controlling resources = loss revenue

• QoS : performance, availability, reliability and security (L3 QoS inspired by ATM)

• Evolution architecture : Integration IP and ATM (Dual-Mode, I-PNNI, Ipsilon, IETF-MPLS)

• RSVP : IP Signaling Protocol, Path and Reservation Messages

• IntServ : guaranteed and controlled-load service

Upper Bound Method

• Used for solving CAC (Call Admission Control) problem

• Some assumption : o Each arrival process satisfies with certain

business constraino Service time for cell/packet is deterministic and

proportionalo Scheduling rule is used to generate QoS for

class k with minimal μk ("fair" rule to prevent blocking another class getting served)

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

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

Generalized Processor Sharing (GPS)

Differ from fair policy including minimum service rate and excess capacity allocation

Provide inherent fairness (measurable amount resource reserved for each class based on weight

Work-conserving discipline, ideal for small amount of data from I different jobs

Generalized Cμ-rules (Gcμ rules)

Powerful, dynamic scheduling rule which view QoS from different angle such as posses delay function as monetary cost

Founded from 3 fact in the Queuing theory: Total workload invariant for work-conserving scheduling

rules Class workloads “live on the faster time scale” than total

workload process Well behaved heavy traffic limit systems, class workload

process “Converges” Distribute total workload over different class to minimize

delay cost rate at each point

Generalized Cμ-rules (Gcμ rules)

With “lagrange” optimization problem, the solution defines as mapping g intepreted as switching curve of Gcμ-rules parameterized by scalar W

QoS (Quality of Services)

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

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

DS Class: Expedited Forwarding (EF)

• Absolute dedicated BW independent from other • Guaranteed BW for providing low packet loss, low

latency and low jitter• Implement with Priority Queue and Strict Policing• EF behavior : departure rate EF traffic must equal

or exceeded configurable rate• Guaranteed BW means excess traffic must be

discarded (strict policing)

DS Class: Assured Forwarding (AF)

• “No Free Lunch”, better service for one class, expense of other service

• 4 Class with 3 class each based on drop preferences

• Level forwarding assurance based on resource allocation, load offered and drop preference

• Implement with weighted Round-robin (WRR), Weight Fair-Queue (WFQ), and drop technology (RED/WRED)

Shortcut Routing to MPLS

• Traditionally Internet routing create problem, because size of route, per-packet lookup burden network, bottleneck

• Solution : Eliminate L3 processing by L2 packet forwarding (Shortcut Routing)

• IP over ATM : mixed CL(connectionless)/CO (connection oriented) for best effort traffic

• 3 Approach : flow driven, topology driven, and Explicit shortcut

Layered Routing

• Top level routing by IP (OSPF), route between nodes by ATM layer Routing (I-PNNI)

• ATM change the path based on available resources, OSPF rediscover low weight link regularly => Hop-by-hop path different next-hop nodes

• More vulnerable to loop, L2/L3 routing loop is hidden at both L2/L3

• Transient loop for CO/CL environment• I-PNNI the ultimate solution, but the standard never

finished

Flow Driven Shortcut

• Short messages use CL (connectionless) because connection setup costly

• Long duration high-traffic use CO (connection-oriented) for header efficiency

• Pareto Law : 20% flows are long and constitute of 80% bytes

• Decision between router and switch is complicated

• Ipsilon Switching : decision based on Ipv4 header (TCP = switch, UDP = route)

Topology Driven Shortcut

• Special ATM-VC setup to “shortcut” number of router

• Integrated switch & router individually decide to shortcut

• Sources and destination path stored in “shortcut” forwarding table

• CO/CL forward together with QoS differentiation

• The approach is Cisco Tag-Switching

Multiprotocol Label Switching (MPLS)

• TDP (Cisco) & LDP (IETF) : signaling protocol for routing to “shortcut” based on MPLS tag

• Support explicit routing to provide QoS constrain routing

• Based on LDP, construct label forwarding table (LIB), similar to ATM VPI/VCI

• Adopt label stack approach, up to 3 labels including “push”, “pop”, and “swap”

Multiprotocol Label Switching (MPLS) continue..

• Separated control and forwarding with Traffic Engineering (TE) can mapped into label

• Flexible to form FEC to build VPN for any other medium didn't support labelling

• Traffic Engineering : redirect, balance and restoration the path

• “Forwarding with the clue”, the clue give next-hop downstream router, the current router end-up with IP lookup

Generalized MPLS (G-MPLS)

• Extension of MPLS for other packet switched as IP packet

• TDM/Optical Lamda can be formed• Redesign MPLS protocol and optical switching

without optical-electronic conversion• Extend control plane for legacy equipment: Simplification O&M Efficiency and Faster Higher Flexibility

Generalized MPLS (G-MPLS) Summary

• LMP assigned to manage critical network by mapping time slot, lambda, or port into label

• Extension to OSPF for advertising availability of optical resources

• Enhance IP signaling RSVP to setup LSP accross

• Scalability features such as hierarchical LSPs

Generalized MPLS (G-MPLS) Example

IP Network (left) and SDH Network (right)

Each SDH has link capacity of 2 Mbps

Three different configuration originate by GMPLS switching in the SDH nodes

Reference

Piet Van Mieghem, “Data Communication Networking”, Delft University Technology, Amsterdam, 2006.