Slide 3-1 Class of Service (CoS) & Quality of Service (QoS) Sources: MPLS Forum V. Alwayn, Advanced MPLS Design and Implementation, Cisco Press E. W. Gray, MPLS Implementing the Technology, Addison Wesley B. Davie and Y. Rekhter, MPLS Technology and Applications, Morgan Kaufmann E. Osborne and A. Simha, Traffic Engineering with MPLS, CiscoPress

Slide 2 What exactly is CoS ? Class of Service (CoS): Groups of flows with same level of treatment Traffic differentiation or the ability to treat packets differently based on the application or packet’s importance or priority Service-level depends on state of the network and relative priority  Example: 802.1p (Ethernet): No resources allocated per call, but differentiation of service level through priority. Relative priority, i.e. If network is congested service WILL degrade. CoS is the ability of network devices to prioritize best-effort traffic No guarantees, highest class traffic get priority over other traffic when congestion happens No connections maintained end-to-end No per-flow state information maintained

Slide 3 Class of Service How many classes? Service provider specific. Example: Sprint has 4 classes (once)  Class A Premium Traffic: reserved for latency-sensitive applications only, e.g., VoIP or Video over IP.  Class B Critical Traffic: highest class for data applications, e.g., financial transactions  Class C Business Traffic: second class for data applications, e.g. database applications.  Class D Standard Traffic: This class is the default class, all traffic not prioritized in the above queues will be serviced in this class. Typical traffic for this queue is web browsing.  Bandwidth allocation recommendations (depends on ISPs): - 35% for VoIP, 25% for class B, 15% for class C, 25% for class D

Slide 4 What exactly is QoS ? Quality of Service (QoS) Mechanisms that allow network managers to contorl the mix of bandwidth, delay, jitter, and packet loss Hard allocation of resources What you pay for is what you get  Example: Connection set-up in an ATM network which allocates a fixed amount of resources QoS is the ability to guarantee transmission characteristics end-to-end, not a device feature Bandwidth, maximum end-to-end delay, maximum delay variation Signaling and end-to-end connections may be required Granularity and state information on a per flow basis Prioritization of service classes, bandwidth allocation, and congestion aviodance Evolution of standards: Best Effort Service: 1981 Integrated Services (IntServ): 1997 Differentiated Services (DiffServ): 1998 DiffServ-Aware TE (DS-TE)

Slide 5 IP QoS – group discussion 2-minute competition Identify types of policies/mechanisms in support of IP QoS Control policies  Admission control, policy control, congestion control, conditioning policy (between networks) Data or packet policies  marking, classification  policing, dropping policy  Queuing / scheduling policy - LLQ, Priority Queuing - WFQ, CBWFQ - Hybrid - Adaptive queuing -…-…

Slide 6 Time The QoS Pendulum

Slide 7 IP QoS over MPLS Service providers that offer IP services over an MPLS backbone must support IP QoS over their MPLS infrastructure – IP QoS over MPLS VPNs or MPLS traffic engineered paths. MPLS can offer IP QoS services more efficiently over a range of platforms, including ATM LSRs. Some useful QoS capabilities such as guaranteed-bandwidth LSPs can be supported over MPLS networks.

Slide 3-8 Integrated Services (IntServ)

Slide 9 What is IntServ ? An architecture allowing the delivery of the required level of QoS to real-time applications Introduces a circuit-switched model to IP A signalling-based system where the endsystem has to request the required service-level RSVP – one of the signaling protocols of choice A way of providing end-to-end QoS, state maintenance (for each RSVP flow and reservation), and admission control at each NE

Slide 10 The IntServ Model Sender Receiver Signalling required by end-stations for Resource-Reservation (RSVP)

Slide 11 The IntServ Model – Connection Set-Up Sender Receiver Step 1: RSVP Path Step 2: RSVP RESV Step 3: Data

Slide 12 IntServ Characteristics Introduces the model of connections or flows Defines a traffic specification called Tspec, which specifies the kind of application traffic that ingresses the network. IntServ also defines a reservation spec called Rspec, which requests specific QoS levels and ther reservation of resources. Requires the following to verify that traffic conform to its Tspec: Known QoS requirements Signalling protocol (i.e., RSVP) Significant enhancements on network element:  Admission control  Policy control  Packet classification and marking  Packet scheduling and queuing  Packet dropping policy

Slide 13 IntServ Summary Provides the means for real-time applications over IP Introduces a connection / flow approach Uses RSVP as signalling mechanism Requires the end-station / application to signal for QoS Requires network elements to maintain connection state

Slide 14 MPLS Implementation of IntServ Path setup, including bandwidth reservation, is the same as before In operational mode, Ingress: associates all packets associated with a FEC and assign them to a particular LSP. Tandom node: when a packet arrives, it looks up the label in its table and recognizes all the QoS-related mechanisms associated with the packet, such as policing and queuing. The IP header needs not be examined.

Slide 15 IP Precedence Main problem with IntServ: The IntServ RSVP per-flow approach to QoS is not scalable and adds complexity to implementation. Solution?: IP precedence simplifies it by adopting an aggregate model for flows by classifying various flows into aggregated classes and providing the appropriate QoS for the classified flows.

Slide 3-16 Differentiated Services (DiffServ)

Slide 17 What is DiffServ An architecture for implementing scalable, stateless service differentiation A service defines significant characteristics of packet transmission in one direction across a set of one or more paths in the network Examples of characteristics: Delay Jitter Packet loss

Slide 18 DiffServ Architecture Each router participates in providing a packet its class of service. This is called as “Per Hop Behaviour (PHB)”.

Slide 19 Classification of Packets What parameters can be used for classification? Source/destination IP addresses Incoming/outgoing interface IP precedence values, DSCP value ….

Slide 20 The DiffServ Model Differentiated Services Domain (DS Domain) DS Boundary Nodes (Ingress / Egress) DS Interior Nodes

Slide 21 The DiffServ Model Contiguous DS Domains can be grouped into DS Regions Chacteristics of per-hop-behaviors (PHB) defined per DS Domain Traffic Classification and Conditioning between DS Domains IP packets crossing a link and requiring same DiffServ behavior are referred to as Behavior Aggregate (BA)

Slide 22 DiffServ Service Concepts DS Domain Conditioning at ingress devices Per-hop behaviour in transit nodes Service = Conditioning + Behaviors

Slide 23 DiffServ Service Classes or Per Hop Behaviors (PHB) Describes the forwarding behavior applied to an aggregate of flows The means a network-node allocates resources to meet a behavior aggregate Per Hop Behaviors are implemented (on each router) via: Queue management and scheduling  Buffer size, Queue depth, Over-subscription policy Scheduling  Scheme to determine which queue to service when link is available Congestion management and avoidance  Optimize resource utilization

Slide 24 DSCPCU DiffServ Service Classes Version Hdr Len TOS Total Len more IP Hdr … 4 bit 4bit 1byte 2bytes IP Packet with DiffServ Fields DiffServ Field (DSCP) defines Per-Hop Behavior (PHB) (i.e., marking) The remaining two unused bits in the TOS byte are used for TCP ECN which is defined in RFC3168.

Slide 25 DiffServ Service Classes unused Best Effort DSCP  The common best effort forwarding behavior available in all routers  Network will deliver these packets whenever resources available  Node should make sure that these packets don’t get ‘starved’  Packets with an unidentified DSCP should also receives this PHB

Slide 26 DiffServ Service Classes Assured Forward (AF) DSCP  Class – specifies the PHB that packet is to receive. AF is a method of providing low packet loss, but it makes minimal guarantees about latency.  AF1 – 001  AF2 – 010  AF3 – 011  AF4 – 100  Drop Precedence - marks relative importance of a packet within a given class.  010 low  100 medium  110 high Drop Class Precedence unused

Slide 27 DiffServ Service Classes Expedited Forward (EF) DSCP  These packets must be policed at ingress  Non conforming packets are discarded  These packets must be shaped on egress  These packets should receive Priority Queuing or LLQ (Premium Service PHB) unused

Slide 28 DiffServ Service Classes Summary Expedited Forward (EF) DSCP Priority Delivery Must adhere to “traffic contract” Gold Service Assured Forward (AF) DSCP Specified Forwarding Behavior Specified Drop Precedence Silver Service Best Effort DSCP Best Effort Service Client gets available Resources only Bronze Service

Slide 29 How Is A DiffServ Service Established? DS Domain 2 DS Domain 3 DS Domain 1 DS Administrators set up DS-capable routers within their domain for conditioning and PHB per service class

Slide 30 DS Domain 2 DS Domain 3 DS Domain 1 Source now sends traffic marked for Gold service level NO SIGNALLING OR STATE IS INVOLVED How Is A DiffServ Service Used?

Slide 31 Service Classes Are Locally Significant DS Domain 2 DS Domain 3 DS Domain 1 Service for a given DiffServ category (e.g., Gold) is not necessarily the same in Domain 2 as in Domain 1 Interdomain agreements must be brokered to ensure E2E QoS Policy-driven approach is seen as a good mechanism to achieve end to end consistency

Slide 32 DiffServ Characteristics DiffServ is a relatively simple and coarse method to provide differentiated Classes of Service. Offers a small well defined set of building blocks from which several services may be built. Flows (stream of packets with a common observable characteristics) are conditioned at the network ingress and receive a certain forwarding treatment per hop behavior within the network. Multiple queuing mechanisms offer differentiated forwarding treatments.

Slide 33 DiffServ Summary Model consists of a set of Differentiated Services Domains (Policy / Management Domain) Interconnections of DS Domains require Traffic Classification and Conditioning DiffServ deals with aggregates of flows assigned to a PHB DiffServ operates stateless and does not require signalling DiffServ is a refined CoS mechanism

Slide 3-34 MPLS and DiffServ

Slide 35 MPLS and DiffServ – Basic Operation DiffServ enabled Network MPLS enabled Network with DIffServ capabilities IWF Packet‘s forwarded according to Destination Address (DA) and DiffServ Control Point (DSCP)

Slide 36 MPLS and DiffServ – Basic Operation DiffServ enabled Network IWF MPLS enabled Network with DIffServ capabilities Packet‘s forwarded along an LSP based on Label that identfies a specific FEC

Slide 37 MPLS and DiffServ – Basic Operation DiffServ enabled Network IWF MPLS enabled Network with DIffServ capabilities MPLS provides Traffic Engineering in addition to CoS/QoS

Slide 38 DSCP to MPLS Mapping (1) Class – specifies the PHB that packet is to receive AF1 – 001 AF2 – 010 AF3 – 011 AF4 – 100 Drop Precedence - marks relative importance of a packet within a given class 001 low 010 medium 011 high Drop Class Precedence unused DiffServ DSCP possible combinations

Slide 39 DSCP to MPLS Mapping (2) What to map? DSCP has 6 bits MPLS header? How to map?

Slide 40 DSCP to MPLS Mapping (3) E-LSP – the MPLS ‘shim’ EXP field maps PHBs using only the drop precedence field of the DSCP Drop Class Precedence unused DiffServ DSCP EXP MPLS Label

Slide 41 DSCP to MPLS Mapping L-LSP – the DSCP is completely used to map LSPs for a single FEC / BA pair Drop Class Precedence unused DiffServ DSCP PSC - PHB Scheduling Class DSCP

Slide 42 E-LSP and L-LSP PSC = PHB Scheduling Class (PSC) E-LSP (<= 8 PHB) EXP-Inferred-PSC LSP A single LSP can support up to eight BA’s EXP (3-bits) maps LSP using drop precedence (3-bits) L-LSP (<= 64 PHB ) Label-Only-Inferred-PSC LSP A separate LSP for a single FEC / BA (OA) pair Label maps LSP using DSCP (6-bits) Defined for both CR-LDP and RSVP-TE

Slide 43 Label Request Message Label Request Message Length Message ID LSPID TLV Explicit Route TLV (optional) Traffic Parameters TLV (optional) Pinning TLV (optional) Resource Class TLV (optional) Pre-emption TLV (optional) Diff-Serv TLV (optional)

Slide 44 DiffServ TLV for E-LSP CR-LDP Diff-Serv (0x901) Length T Reserved Mapnb(4) Map 1. Mapnb Reserved (13) EXP (3) PHBID (16) Map Entry Format

Slide 45 DiffServ TLV for L-LSP CR-LDP Diff-Serv (0x901) Length T Reserved PSC DSCP PSC

Slide 46 MPLS – DiffServ Interworking DiffServ enabled Network IWF MPLS enabled Network with DIffServ capabilities Packet classified by Destination and DiffServ Code Point (i.e., Class of Service) Behavior Aggregate (BA) get‘s mapped to LSP by LER. (multiple possible scenarios)