Implementation of QoS mechanisms
in MPLS networks

Avneesh Sachdev(avneesh@procket.com)
2003/09/30

www.procket.com© 2003 Procket Networks, Inc. All rights reserved.

CONFIDENTIAL

Agenda• QoS background• MPLS value addition to QoS• Interaction of MPLS QoS with routing• Procket QoS architecture and implementation• Summary

2003/09/30

2© 2003 Procket Networks, Inc. All rights reserved.

CONFIDENTIALQoS background• Service provided by traditional network varies under congestionor during convergence• Variable delay, jitter, loss, available bandwidth• Traffic has diverse service needs• Voice requires low delay, jitter, loss

• One approach: Avoid congestion by over provisioning• Must guarantee no congestion at all times• May be wasteful to run network at low utilization• Alternative: Make network aware of service needs of traffic• Most effective when there is congestion or you create congestion• Some packets have to lose for others to win

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CONFIDENTIALQoS background

QoS background: Granularity• Fine grained• QoS provided to individual applications or flows (Intservapproach)• Coarse grained• Network aware of large classes of data or aggregated traffic(Diffserv approach)• Coarse grained approach scales better in the core

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CONFIDENTIALMPLS Value Addition to QoS

2003/09/30

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CONFIDENTIALMPLS value addition to QoSMPLS and QoS: Connection oriented• Resource allocation• Route flows (LSPs) through network with admission control• Police and/or monitor traffic at LSP ingress• Bandwidth constraints may be per link (TE) or different fordifferent classes of traffic on a link (DS-TE)• For best results, apply admission control to all traffic that uses
resources in a pool
• Engineer all traffic• Or, use distinct PHB Scheduling Classes (queues) for
engineered and other traffic• Controlled load => less probability of congestion => "better"
service
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CONFIDENTIALMPLS value addition to QoSMPLS and QoS: Connection oriented• Easy identification of flow along LSP path (P2P LSPs)• Enables flexible definition of flow (by ingress)• Allows for more classes -- a flow can be mapped to a trafficclass at signaling time (as in L-LSPs)• Leaves open possibility of QoS guarantees on a finer grainedlevel, as opposed to an aggregate basis• Interoperation with ATM / Frame Relay

2003/09/30

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CONFIDENTIALMPLS value addition to QoSMPLS and QoS: Source routing• Fast Reroute• Minimizes drops in the network due to slow IP convergence• Enables high availability of service• For traffic that requires low loss

• Planned downtime• Traffic can be seamlessly rerouted around an LSR box before
bringing it out of operation• "Costing out" a link in IGP may not be good enough

2003/09/30

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CONFIDENTIALMPLS value addition to QoSMPLS and QoS: Low overhead tunneling• Diffserv transparency• Can use Pipe tunneling model to make transit Diffserv domaintransparent to traffic• Routing table size on transit routers• Allows routing decisions to be made at LSP ingress• QoS-aware routing may require larger routing tables

2003/09/30

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CONFIDENTIAL

Interaction of MPLS QoS with routing

2003/09/30

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CONFIDENTIAL

Interaction of MPLS QoS with routing

Issue: QoS-aware routing• Different paths in the network may be optimal fordifferent services• Control plane decision on path is easy when apredetermined service is required for some traffic• Say, an L2 circuit, or all IP traffic matching a given prefix• Maintaining a routing table per class is expensive forcontrol and forwarding plane

2003/09/30

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Interaction of MPLS QoS with routing

Control time selection of pathTunnel 1/241.
1
10.

PBX

R1

•Tunnel 1 is set up by R1 for carrying real time traffic•Control plane on R1 treats traffic destined to PBX as real time
10.1.1/24 -> Tunnel 1•QoS applied by R1 based on matched prefix, not packet marking

2003/09/30

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Interaction of MPLS QoS with routing

Intra-domain IP routing• Possible extension to IGP shortcuts• Use single topology IGP as today with TE / DS-TE extensions• Run single SPF, modify IGP shortcuts to compute distinct
tunnels as next hop(s) for desired classes• Don't need routing table per service or modification to longest
match lookup• Next hop information more complex, requires sharing acrossprefixes for efficiency• Doesn't require upgrading boxes other than to run TE / DS-TE

2003/09/30

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Interaction of MPLS QoS with routing

IGP shortcuts
Tunnel 2 (Class C2)
R1

R2

R3

R4

Subnet 10/8
Tunnel 1 (Class C1)•R1 signals Tunnel 1 for class C1 and Tunnel 2 for class C2.
•Paths to 10/8 on R1 are as follows

2003/09/30

Prefix

C1 next hop

C2 next hop

Default next hop

10/8

Tunnel 1Tunnel 2R214© 2003 Procket Networks, Inc. All rights reserved.

CONFIDENTIAL

Interaction of MPLS QoS with routing

Inter-domain routing considerations• Routing per service in BGP would be expensive• Existing BGP infrastructure should be okay if desiredservices are supported by selected paths• Desirable for SPs to agree on standard service
definitions for easy translation at border routers• Domains that do not support QoS will increasingly not
be used for transit• Inter-AS TE could be used on a tactical basis to source
route traffic

2003/09/30

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Interaction of MPLS QoS with routing

Inter-domain routing
AS 200(Best effort)
AS 100(QoS)

Tra

fficto A

AS 400(QoS)

S400

AS 300(QoS)•AS 300 has QoS enabled, AS 200 does not•BGP policies avoid paths across AS 200
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CONFIDENTIAL

Procket QoS architecture and implementation

2003/09/30

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CONFIDENTIAL

Procket QoS

Procket Logical Architecture
Route Processor
SCiAPP
IM

TSE
oAPP

MediaAdapters

Line Cards

MSU
MSU
MSU
MSU
MSU
MSU

Switch Cards

IM: Interface Multiplexer
iAPP: Input Adaptive Packet ProcessoroAPP: Output Adaptive Packet Processor
2003/09/30

oAPP
IMiAPPLine Cards

MediaAdapters

TSE: Terabit Switch Engine
MSU: Memory Switch Units
SC: System Controller
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CONFIDENTIAL

Procket QoS

Procket Architecture• Distributed processing on line cards• 40 Gbps processors• Input Adaptive Packet Processor (iAPP): Fully programmable forwarding,accounting• Output Adaptive Packet Processor (oAPP): Fully programmableencapsulation, queuing discipline, accounting• Centralized shared memory switch fabric• 200 ms buffer• Up to 32 queues per physical interface. At least 4 queues per DS-3
• 36K queues per chassis• Packets read in and out of memory once. No separate input/output buffers• 480 Gbps full duplex line rate processing with 40 byte packets• Fully non-blocking, any DS3 to any DS3
2003/09/30

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Procket QoS

Procket Architecture/Packet Flow: QoS
iAPP
IM

TSE
oAPP

MediaAdapters

Line Cards•Packet Classification•Modify DSCP/EXP/Precedence•Policing•RED profile selection•Queue selection

2003/09/30

MSU
MSU
MSU
MSU
MSU
MSU

Switch Cards•RED, WRED
•Report queue fullness to TSE (RED)•Queue lengths

oAPP
IMiAPPLine Cards

MediaAdapters•Programmablequeuing discipline•PQ, DWRR•PQ(DWRR)•DWRR(PQ)•Rate shaping

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CONFIDENTIAL

Procket QoS

Procket QoS Implementation• Provides QoS in hardware without impact to systemthroughput• UI designed so you can focus on delivering services
and not on turning knobs.
• System intelligently maps service requirements to hardware• Classification on EXP, DSCP, Precedence• Programmable RED, WRED
• Input policing, metering & marking• Output marking• Output rate shaping per queue
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Procket QoS

Procket QoS Implementation• Queuing algorithms implemented in microcode• PQ and DWRR currently, set up in two levels of hierarchy• PQ for low latency, DWRR to distribute bandwidth• E-LSPs with uniform tunneling model• Extensive statistics per interface• Packet drops per class• Current and average queue depth• In-spec and out-of-spec packets per class

2003/09/30

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Procket QoS

Example: Service requirements• Real time
• Small packets, delay and jitter sensitive. Low loss.
• Interactive voice and video• Possibly Call signaling• Premium• Low loss

• Streaming media• Less strict delay, jitter requirements• Best effort• Everything else
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Procket QoS

Example: Configuration
qosclass premium
exp internetwork-control
class realtime
exp critical
dscp CS5
class streaming-media
exp flash-override
dscp CS4
output-behavior low-latency
meter rate 3000 burst 100
depth 50
service-profile backbone
class default
class premiumclass realtime
output-behavior low-latencyclass streaming-media
queuing-discipline priority (realtime, dwrr (premium [45], default [20],streaming-media [35]))

2003/09/30

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Procket QoS

Procket QoS Futures• Classification enhancements• Based on policies• 802.1p• More queuing disciplines• WFQ• MDRR?

• Interface rate shaping• Remapping of traffic between services• More MPLS support• DS-TE• L-LSPs

2003/09/30

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CONFIDENTIAL

Summary• QoS allows you to control treatment of packets by network• Most useful when there is congestion• MPLS is a useful technology for QoS• Enables better resource allocation, high availability, easier management,
Diffserv transparency, smaller table sizes...

• Incremental approach to intra-domain QoS-aware routing using
TE and IGP shortcuts• Common service definitions desirable for easier inter-domain
operation• Procket architecture and QoS implementation deliver easily
manageable QoS without comprise on performance

2003/09/30

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CONFIDENTIAL

2003/09/30

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CONFIDENTIAL