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Slide 3-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 / RSVP
Aggregatedstate
DiffServ
1. T he orig inal IP service
2. F irst efforts at IP Q oS
3. Seeking simplicity 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-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)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-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)
Differentiated Services Domain(DS Domain)
DS Boundary Nodes(Ingress / Egress)
DS Boundary Nodes(Ingress / Egress)
DS Interior NodesDS Interior Nodes
Slide Slide 2121
The DiffServ Model
Contiguous DS Domainscan be grouped into DS Regions
Contiguous DS Domainscan be grouped into DS Regions
Chacteristics of per-hop-behaviors (PHB) defined per DS Domain
Chacteristics of per-hop-behaviors (PHB) defined per DS Domain
Traffic Classification and Conditioning between DS Domains
Traffic Classification and Conditioning between DS Domains
IP packets crossing a link and requiring same DiffServ behavior are referred to
as Behavior Aggregate (BA)
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
DS Domain
Conditioning at ingress devicesConditioning at ingress devices Per-hop behaviour in
transit nodesPer-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 FieldsIP Packet with DiffServ Fields
DiffServ Field (DSCP) defines Per-Hop Behavior (PHB) (i.e., marking)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
DiffServ Service Classes
0 1 2 3 4 5 6 7
0 0 0 0 0 0 unusedBest Effort DSCPBest 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
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
DiffServ Service Classes
Assured Forward (AF) DSCP
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
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
DiffServ Service Classes
Expedited Forward (EF) DSCP
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)
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
Expedited Forward (EF) DSCP
•Priority Delivery•Must adhere to “traffic contract”•Priority Delivery•Must adhere to “traffic contract”
Gold Service
Assured Forward (AF) DSCP
Assured Forward (AF) DSCP
•Specified Forwarding Behavior•Specified Drop Precedence•Specified Forwarding Behavior•Specified Drop Precedence
Silver Service
Best Effort DSCPBest Effort DSCP •Best Effort Service•Client gets available Resources only•Best Effort Service•Client gets available Resources only
Bronze Service
Slide Slide 2929
How Is A DiffServ Service Established?
DS Domain 2
DS Domain 2
DS Domain 3
DS Domain 3
DS Domain 1
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 2
DS Domain 3
DS Domain 3
DS Domain 1
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 2
DS Domain 3
DS Domain 3
DS Domain 1
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-Slide 3-3434
MPLS and DiffServ
Slide Slide 3535
MPLS and DiffServ – Basic Operation
DiffServ enabled NetworkDiffServ enabled Network MPLS enabled Network with DIffServ capabilitiesMPLS enabled Network with DIffServ capabilities
IWFIWF
Packet‘s forwarded according to Destination Address (DA) and DiffServ Control Point (DSCP)
Packet‘s forwarded according to Destination Address (DA) and DiffServ Control Point (DSCP)
Slide Slide 3636
MPLS and DiffServ – Basic Operation
DiffServ enabled NetworkDiffServ enabled Network
IWFIWF
MPLS enabled Network with DIffServ capabilitiesMPLS enabled Network with DIffServ capabilities
Packet‘s forwarded along an LSP based on Label that identfies a specific FEC
Packet‘s forwarded along an LSP based on Label that identfies a specific FEC
Slide Slide 3737
MPLS and DiffServ – Basic Operation
DiffServ enabled NetworkDiffServ enabled Network
IWFIWF
MPLS enabled Network with DIffServ capabilitiesMPLS enabled Network with DIffServ capabilities
MPLS provides Traffic Engineeringin addition to CoS/QoS
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
Drop Class Precedence unused
DiffServ DSCP
0 1 2 3 4 5
12 possible combinations
Slide Slide 3939
DSCP to MPLS Mapping (2)
• What to map? DSCP has 6 bits MPLS header?
• How to map?
Slide Slide 4040
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
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
Drop Class Precedence unused
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 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 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
DiffServ enabled NetworkDiffServ enabled Network
IWFIWF
MPLS enabled Network with DIffServ capabilitiesMPLS enabled Network with DIffServ capabilities
Packet classified by Destinationand DiffServ Code Point (i.e., Class of Service)
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)
Behavior Aggregate (BA) get‘s mapped to LSP by LER.
(multiple possible scenarios)