what exactly is cos ?

Slide 3-11

Class of Service (CoS) &

Quality of Service (QoS) Sources:

MPLS ForumV. Alwayn, Advanced MPLS Design and Implementation, Cisco Press

E. W. Gray, MPLS Implementing the Technology, Addison WesleyB. Davie and Y. Rekhter, MPLS Technology and Applications, Morgan Kaufmann

E. Osborne and A. Simha, Traffic Engineering with MPLS, CiscoPress

Slide Slide 22

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 Slide 33

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 Slide 44

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 Slide 55

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 Slide 66

No state

Best Effort

Per-flow state

IntServ / R SVP

Aggregatedstate

DiffServ

1. T he orig inal IP service

2. F irst efforts at IP Q oS

3. Seeking simplic ity and scale

4. Bandw idth O ptim ization & e2e SLAs((IntServ +DiffServ+ T raffic Engineering))

Time

The QoS Pendulum

Slide Slide 77

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 3-88

Integrated Services (IntServ)

Slide Slide 99

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 Slide 1010

The IntServ Model

Sender Receiver

Signalling required by end-stationsfor Resource-Reservation (RSVP)

Slide Slide 1111

The IntServ Model – Connection Set-Up

Sender Receiver

Step 1: RSVP PathStep 2: RSVP RESVStep 3: Data

Slide Slide 1212

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 Slide 1313

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 Slide 1414

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 Slide 1515

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 3-1616

Differentiated Services (DiffServ)

Slide Slide 1717

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 Slide 1818

DiffServ Architecture

Each router participates in providing a packet its class ofservice. This is called as “Per Hop Behaviour (PHB)”.

Slide Slide 1919

Classification of Packets

• What parameters can be used for classification? Source/destination IP addresses Incoming/outgoing interface IP precedence values, DSCP value ….

Slide Slide 2020

The DiffServ Model

Differentiated Services Domain(DS Domain)

DS Boundary Nodes(Ingress / Egress)

DS Interior Nodes

Slide Slide 2121

The DiffServ Model

Contiguous DS Domainscan 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 Slide 2222

DiffServ Service Concepts

DS Domain

Conditioning at ingress devices Per-hop behaviour in

transit nodes

Service = Conditioning + Behaviors

Slide Slide 2323

DiffServ Service Classes orPer 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 Slide 2424

DSCP CU

0 1 2 3 4 5 6 7

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 Slide 2525


0 1 2 3 4 5 6 7

0 0 0 0 0 0 unusedBest Effort DSCP

The common best effort forwarding behavior available in all routersNetwork will deliver these packets whenever resources availableNode should make sure that these packets don’t get ‘starved’Packets with an unidentified DSCP should also receives this PHB

Slide Slide 2626


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 – 001AF2 – 010AF3 – 011AF4 – 100

Drop Precedence - marks relative importance of a packet within a given class.010 low100 medium110 high

0 1 2 3 4 5 6 7

Drop Class Precedence unused

Slide Slide 2727


Expedited Forward (EF) DSCP

These packets must be policed at ingressNon conforming packets are discardedThese packets must be shaped on egressThese packets should receive Priority Queuing or LLQ (Premium Service PHB)

0 1 2 3 4 5 6 7

1 0 1 1 1 0 unused

Slide Slide 2828

DiffServ Service ClassesSummary

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 Slide 2929

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 Slide 3030

DS Domain 2

DS Domain 3

DS Domain 1

Source now sends traffic marked for Gold service levelNO SIGNALLING OR STATE IS INVOLVED

How Is A DiffServ Service Used?

Slide Slide 3131

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 Slide 3232

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 Slide 3333

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 3-3434

MPLS and DiffServ

Slide Slide 3535

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 Slide 3636


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 Slide 3737



IWF


MPLS provides Traffic Engineeringin addition to CoS/QoS

Slide Slide 3838

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


DiffServ DSCP

0 1 2 3 4 5

12 possible combinations

Slide Slide 3939


• What to map? DSCP has 6 bits MPLS header?

• How to map?

Slide Slide 4040


• E-LSP – the MPLS ‘shim’ EXP field maps PHBs using only the drop precedence field of the DSCP


DiffServ DSCP

0 1 2 3 4 5

0 1 2

EXP

MPLS Label

Slide Slide 4141

DSCP to MPLS Mapping

• L-LSP – the DSCP is completely used to map LSPs for a single FEC / BA pair


DiffServ DSCP

0 1 2 3 4 5

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

PSC - PHB Scheduling Class

DSCP

Slide Slide 4242

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 Slide 4343

Label Request Message

Label Request Message Length

Message IDLSPID 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 Slide 4444

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 Slide 4545

DiffServ TLV for L-LSP CR-LDP

Diff-Serv (0x901) Length

T Reserved PSC

DSCP0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

PSC

Slide Slide 4646

MPLS – DiffServ Interworking


IWF


Packet classified by Destinationand DiffServ Code Point (i.e., Class of Service)

Behavior Aggregate (BA) get‘s mapped to LSP by LER.

(multiple possible scenarios)

what exactly is cos ?

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