traffic engineering over mpls

KT Telecom.Network Lab. Hoon Lee

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Traffic Engineering over MPLS

July 23, 1999

KT Telecom. Network Labs. Hoon Lee


2

Contents

• Brief introduction to MPLS• MPLS and traffic engineering• Summary


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Introduction to MPLS

• MPLS = L2 Label swapping + L3 routing

• Assign short fixed length labels to packets at the ingress to an MPLS cloud, which is used to make forwarding decisions inside the MPLS domain.


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MPLS - Basic Concepts• Switching by fixed length Label

– Edge: Assign label for dest. addr. based on COS via ToS and place information with the same output queue, and forward along the same path

– Core: Label-based switch– Applied to : ATM(VPI/VCI), FR(DLCI), Ethernet(MAC addr)

– MPLS is a class based packet forwarding scheme

• Advantages of MPLS– High speed IP forwarding by switch– Vendor independent– Support IP multicasting– Multiple-QoS support– Protocol expandability

– Independent switching and routing functions


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LER LSR LSR LER

ATM ATM ATM ATM ATM ATM

IProuting

IProuting

IProuting

IProuting

IProuting

IProuting

End System End System

MPLS Operation• Layer 3 routing + layer 2 forwarding

MPLS Domain

LER: Label Edge Router LSR: Label Switched Router


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MPLS Network Architecture

Label Edge Router (LER)

Label Edge Router (LER) MPLS Control Component MPLS Control Component

Label Switch Router (LSR)

Label Switch Router (LSR)

ATM Switch Fabric ATM Switch Fabric • Full-function Layer 3 routers• Label Binding based on FIB

• Switching on Label• Label swapping

LER+LSR

MPLS Domain

LER+LSR

A

C

B

dest QoS labelc gold 1

1

c bronze 2

2

1goldb

3

4

dest QoS labelc gold 3c bronze 4

3goldb


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Router versus MPLS

Packet Forwarding

OSPF

RoutingTable

Packet Forwarding

OSPF

Packet Forwarding

OSPF

Packet Forwarding

LDP/OSPF

RoutingTable

Label Switch

LDP/OSPF

LIB

Packet Forwarding

LDP/OSPF

RoutingTable

RoutingTable

RoutingTable

DA Next hop DA Next hop DA Next hop

IP Packet

IP Packet

LIB

Next hop/LabelDA DA Next hop

ATM Switch

Router-based Internet

MPLS-basedInternet

LER LSR LER

Router Router Router


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IPoA versus MPLS

Signaling Signaling

ATM

IP

Upper

IPOAMPOA

UNI 3.1 PNNI/B-ISUP

ATM

IP

Upper

IPOAMPOA

UNI 3.1

LDP LDP

ATM

IP MPLS

ATM

IPMPLS

IP over ATM

MPLSLDP/OSPFLDP/OSPF LDP/OSPF

Traffic-based routing (Signaling)

Topology-based routing (LDP)

LER

LSR LSR

LER

Upper Upper


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Scope and Objectives

• Goal: To investigate the issues and requirements for traffic engineering over MPLS in a large Internet backbone

• Application areas: To provide scalable differentiated services in the Internet and enterprise networks in combination with RSVP


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MPLS and Internet• Suited to Internet backbone

– Easy to construct the VPN by ATM VC• Lower processing OH compared with router based

VPN

• CoS provision• Guaranteed service via ATM’s QoS capabilities• Differentiated Service capabilities

– Favorable to Internet Traffic engineering

• Adaptable BW• Per path traffic monitoring


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Traffic Engineering in Internet

• TE includes the measurement, modeling, characterization, and control of traffic for performance optimization of networks and user satisfaction

• Esp. over MPLS in Internet, the measurement and control are of most interested


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MPLS and Traffic Engineering

• DiffServ treats traffic with similar characteristics and QoS supports in aggregation

• In MPLS, traffic trunk is an aggregation of traffic flows of the same class which are placed inside a label switched path

• Traffic trunks can be viewed as objects to be routed, so they are similar to VCs in ATM


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Attractiveness of MPLS for TE

• Explicit label switched paths can be easily created

• MPLS allows for both traffic aggregation and disaggregation

• Easy integration with constraint-based routing

• MPLS lowers overhead significantly


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TE Performance Objectives (PO)1. Traffic oriented:

-Aspects that enhance the QoS of traffic streams - In a single class BE Internet, minimization of packet loss & delay and maximization of throughput are key measures - In a DiffServ Internet, Statistically bounded POs ( PDV, PLR, PTD) might become useful

2. Resource oriented: -Aspects pertaining to the optimization of resource utilization: Subsets of network resources do not become over utilized & congested while other subsets along alternate feasible paths remain under utilized

3. Common objectives: Minimizing the congestion, esp., a prolonged congestion period


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Congestion Control: Cause

• Congestion occurs: 1. When network resources are insufficient or inadequate to accommodate offered load (generic cause) 2. When traffic streams are unevenly distributed to available resources (unbalanced engineering) <- caused by the dynamic routing protocols such as RIP, OSPF, etc., because they select the shortest-path to forward packets


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Congestion Control: Counter attacks

• For case 1: (i) Expand capacity by providing more resources ; (ii) Apply classical CC techniques (rate limiting, window flow control, queue management, scheduling, etc) ; (iii) Both

• For case 2: Adopt load balancing through efficient resource allocation: Constraint-based routing (CR), an important tool for TE in MPLS


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Constraint-based Routing(CR) as TE

• CR = QoS-routing + policy of network

Given the QoS request of a flow or an aggregated flow, it returns a route that is most likely to be able to meet the requirements

(QoS guarantee) (Increase network utilization)

CR considers (1) network topology, (2) requirements of the flow, (3) resource availability of the links, etc

In the end, CR may find a longer but lightly loaded path. So, traffic is evenly distributed


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MPLS and Internet QoS• Extending RSVP into WAN

environment has failed (Limited scalability)

• To force to cooperate all the points and reserve BW p2p is not practical

• Set ToS field and indicate the QoS level, and aggregate the pakcet with the same class

• Pass them along the same route (traffic trunk) with simple path finding


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DiffServe and MPLS• DS is based on the concept of PHB• Main objectives of DS: -

Scalability (Millions of networks) - Full speed (Gbps)

• DS’s strategy: - Flow aggregation - Push all the state and control to the edges

• DS’s class: Premium, Assured, and BE


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Traffic & Resource Control Architecture

Performance Monitoring

Performance Monitoring

ControlControlNetwork

managementNetwork

management

Observe the state of the network

Characterize the traffic

Determine the control policy

Modify the TM parameter

Modify the routing parameter

Modify the resource attributes

Control action

Modify bandwidth

Modify routing


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Traffic management in MPLS

UPC: ATM Forum’s GCRA / Worse Best Effort from PS or AS rather than tagging & dropping

Congestion control and load balancing via CR

QoS guarantee in combination with DS

CAC


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Summary• Single paradigm does not care all: We have

to know the pros and cons concerning the selection of paradigm

ATM network Router network

특정 VC 에 특정량의 BW 를 할당 -> QoS 보장 / 트래픽 제어 가능

Data forward 속도가 빠름

Per-VC 트래픽 통계치 보유

ATM Cell Overhead 과다

망 경계에 Router 필요

Double configuration 필요

DS 와 MPLS 로써 Router망도 고속화 , QoS 보장 및 TE 이 가능

Data Overhead 적음

Single configuration 으로 충분

traffic engineering over mpls

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