kt telecom.network lab. hoon lee 1 traffic engineering over mpls july 23, 1999 kt telecom. network...
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KT Telecom.Network Lab. Hoon Lee
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Traffic Engineering over MPLS
July 23, 1999
KT Telecom. Network Labs. Hoon Lee
KT Telecom.Network Lab. Hoon Lee
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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