Transcript IP Traffic Engineering and QoS 홍석원(명지대)/안상현(서울시립대)

IP Traffic Engineering and QoS
2001년 2월 14일
명지대학교 홍 석 원
서울 시립대 안 상 현
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HSN 2001
목차
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IP Traffic Engineering
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IP QoS
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Traffic Engineering 구성 요소
경로 설정과 Constraint-based routing
TE signaling과 MPLS
Motivation
Approach
Intserv
RSVP
Diffserv
Reference
HSN 2001
Traffic Engineering
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“A major goal of Internet Traffic Engineering is to
facilitate efficient and reliable network operations
while simultaneously optimizing network resource
utilization and performance.”
(RFC 2702
Requirement for Traffic Engineering over MPLS)
Intra-domain
unicast traffic
HSN 2001
IP Traffic Engineering 목표
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Efficient network를 위해서,
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Reliable network를 위해서,
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“constraint”를 고려한 경로 설정과 트래픽 할당
load balancing과 congestion 해소
서비스의 질을 높임, 등등
링크/노드 고장 시 이를 검출하고,
대체 경로 설정
트래픽의 rerouting
결국 망 보호/복구
HSN 2001
IP Traffic Engineering의 접근
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Interior Gateway Protocol(IGP)
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Layer 2 switching 망의 virtual circuit을 이용
Constraint-based routing을 이용
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constraint 기반의 routing을 하지 못한다.
MPLS의 신호 프로토콜 사용
HSN 2001
MPLS TE 요소
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경로 설정
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트래픽 할당
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traffic을 경로에 할당
MPLS에 의한 패킷 전달
경로 관리
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경로 정보 관리
link resource 정보 관리
망 상태 정보의 전달: IGP의 Link state packet의 확장
경로 선택
signaling
트래픽을 monitor/measure
망 보호/복구
HSN 2001
경로 설정
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경로 정보 관리
Traffic trunk
 Traffic trunk attributes
 resource attributes
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link resource 정보 관리
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정보의 전달(distribution)
경로 계산
 경로 설정을 위한 signaling
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HSN 2001
Traffic Trunk
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An abstraction of aggregated traffic flow that
follows the same path(s) (within a service provider)
between two end points
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예로서 a POP to another POP
동일한 QoS 요구 사항을 갖는다.
LSP tunnel과 동의어로 사용될 수 있다.
ATM의 VC와 유사한 개념
Traffic trunk
R
R
R
R
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R
R
R
HSN 2001
경로 설정의 과제
Traffic trunk
Traffic Trunk attributes
R
R
destination
source
Physical network
Resource
attributes
R
R
R
R
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R
R
R
HSN 2001
Traffic Trunk Attributes(1)
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Traffic parameter attributes
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priority attribute
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setup priority
holding priority
preemption attribute
resilience attribute
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트래픽 특성: peak, average rates, burst size 등
결국, resource requirements(bandwidth)
장애가 발생했을 때 trunk를 어떻게 조치해야
하는가를 규정한다.
HSN 2001
Traffic Trunk Attributes(2)
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resource class affinity attributes
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administratively specified explicit paths
adaptivity attribute
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특정 resource class(color)를 포함할 것인지를
결정한다.
Affinity attribute는 include/exclude의 두 값을 갖는다.
따라서 <resource class, affinity>의 tuple로서
주어진다.
망의 변화에 따라 re-optimization을 할 것인지를
규정한다.
HSN 2001
Resource Attributes
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모든 link는 resource attributes를 갖는다.
Resource attributes는 다음과 같은 파라메터로
구성된다.
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resource attributes 정보는 모든 라우터들에게
broadcast된다.
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Bandwidth
link attributes
TE-specific link metrics 등
IGP의 LSA로서 전달
따라서 IGP의 LSA의 확장 필요
HSN 2001
Trunk와 link resource attributes예
Priority=3
bandwidth= 50
Traffic trunk
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R
destination
source
Resource
attributes
Physical network
BW(3)=80
BW(3)=100
R
BW(3)=30
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R
R
100
60
R
BW(3)=80
50
R
BW(3)=20
R
70
BW(3)=100
R
BW(3)=40
HSN 2001
Resource Class Affinity
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Resource class
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Affinity
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망 관리자에 의해서 각 link에 설정된 policy를
의미한다.
각 link는 특정 policy attribute를 포함할 수도 있고
무시할 수도 있다. 즉 망의 policy에 의해서
결정된다.
Affinity는 binary variable로서 특정 policy attribute를
포함(1) 혹은 배제(0)를 명시하는 값을 나타낸다.
HSN 2001
Resource Class Affinity 예
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예를 들면, 네 개의 policy attribute가 존재하고 세번째
attribute가 restoration 가능 여부를 나타내는
attribute라고 하자. 그러면 각 link는 다음의 bit
string으로 resource class affinity를 나타낼 수 있다.
LSP tunnel의 attribute가 0010라면, 빨간 색 link 만이
가능하다.
0010
R
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0010
0100
R
0010
0010
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0000
0010
R
0000
R
R 0010
0000
0010
R
HSN 2001
경로 선택
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constrained-based routing에 의한 경로 선택
Input(constraint)
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결과
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traffic trunk attributes
link resource attributes
topology state information
constraint를 만족하는 explicit path(a list of routers)
HSN 2001
경로 계산
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Constraint를 만족하지 못하는 link는
잘라낸다.(prune)
나머지 link들 중에서 shortest path를 구한다.
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TE-specific metric을 사용한다.
HSN 2001
앞의 예에서,
Priority=3
bandwidth= 50
tunnel attribute=0010
Traffic trunk
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R
BW(3)=80
0000
R
R
BW(3)=100
0010
R
0010
BW(3)=60
BW(3)=80
0010
0010
BW(3)=50
0010
BW(3)=30
R
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R
BW(3)=20
0000
0100
BW(3)=100
0010
BW(3)=70
0000
BW(3)=100
R
R
0010
BW(3)=40
HSN 2001
경로 설정 signaling
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MPLS의 signaling protocol을 사용하여 Explicit
route(ER)을 설정한다.
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CR-LDP (constrained-Based LSP Setup using LDP)
RSVP-TE (RSVP Extension for LSP)
HSN 2001
CR-LDP로 ER-LSP 설정
A
B
C
D
LSR
LSR
LSR
LSR
Explicit Route
Label Request message 전송: ER path <B,C,D>
Label Request message 처리: ER path <C,D>
Label Request message 처리: ER path <D>
Label Mapping message 전송
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HSN 2001
RSVP-TE로 ER-LSP 설정
A
B
C
D
LSR
LSR
LSR
LSR
Explicit Route
Path message 전송 : ERO <B,C,D> RRO <A>
Path message 처리: ERO <C,D> RRO <A,B>
Path message 처리: ERO <D> RRO<A,B,C>
RESV 전송
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HSN 2001
망 상태 정보의 전달
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망 노드 간에 topology state 정보를 전달한다.
이것은 OSPF의 Link State의 전달과 동일하다.
트래픽 엔지니어링을 위해서 현재 IGP Link
State Advertisement(LSA)에 다음과 같은 추가
정보가 필요하다.
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max. link bandwidth
max. reservable link bandwidth
current bandwidth reservation
current bandwidth usage
link coloring 등
HSN 2001
트래픽 할당
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Mapping traffic to paths
load balancing의 과제
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traffic partitioning 혹은 traffic aggregation
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congestion 해소
loss/delay 최소화
1-traffic stream to n-paths
n-traffic streams to 1-path
n-traffic streams to m-paths
HSN 2001
경로 관리
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Traffic monitoring과 measurement
path 상의 고장(failure)의 발견과 이에 대한
대응
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대체 LSP의 선택, rerouting
즉, 망 보호/복구(protection/restoration) 기능
HSN 2001
목차
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IP Traffic Engineering
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IP QoS
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Traffic Engineering 구성 요소
경로 설정과 Constraint-based routing
TE signaling과 MPLS
Motivation
Approach
Intserv
RSVP
Diffserv
Reference
HSN 2001
Motivation
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Characteristics of IP
– Connectionless
– Best-Effort Service = No QoS
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New Internet Applications
– Multimedia Applications with various QoS Requirements
– Bandwidth, Delay, Loss, …
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HSN 2001
Approach
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QoS Service Model
– Extend the Traditional Best-Effort Service Model
– Intserv (Integrated Services),
Diffserv (Differentiated Services)
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QoS Signaling Protocol
– Reserve Resources for QoS-Requiring Flows
– RSVP (Resource ReSerVation Protocol)
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Others
– Admission Control, Queuing Discipline, ...
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HSN 2001
Intserv
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Characteristics
– Per-Flow based End-to-End QoS Guarantee
– Need Per-Hop Signaling Protocol
– Not Scalable
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QoS Service Type
– Guaranteed Service
• Loss-intolerant and hard real-time service
• Guaranteed delay bound with no queuing loss
– Controlled-Load Service
• Best-effort service under unloaded condition
• No specific delay & loss guarantee
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HSN 2001
RSVP 1/2
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QoS Signaling Protocol
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Heterogeneous Receiver-Controlled Simplex Multipoint
Reservation Request
by Flow Descriptor = (Flowspec, Filterspec)
Soft State in routers to adapt to routing changes
• Need Periodic Refresh  Not Scalable
 RSVP Optimization
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Flexible control over sharing of reservations and
forwarding of subflows
PATH, RESV Messages
HSN 2001
RSVP 2/2
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Optimization
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Bundle Message
• Aggregate multiple RSVP messages in one PDU
• Reduce overall message handling overhead
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MESSAGE_ID Extension
• Shorthand indication of a refresh message
 Allow receiver to readily identify an unchanged message
• Reduce refresh message processing overhead
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Summary Refresh Message
• Send Srefresh message with a list of Msg_ID fields of
corresponding PATH/RESV trigger messages
• Do not need to transmit whole refresh messages
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HSN 2001
Diffserv 1/9
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Characteristics
– No Per-Flow State, No Per-Hop Signaling
– DSCP Marking & Traffic Conditioning at Edge
– Scalable Service Discrimination
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Aggregate QoS Service
– DS Field
DSCP (DS CodePoint; 6 bits)
CU (Currently Unused; 2 bits)
– IPv4 TOS Field, IPv6 Traffic Class Field
– DSCP Mapped to PHB (Per-Hop Behavior)
• PHB : Externally observable forwarding behavior
applied at a DS-compliant node to a DS BA
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HSN 2001
Diffserv 2/9
LSR
LSR
Many flows LSR
Aggregation
of flows
Classification
and
conditioning
(metering, marking,
policing 등)
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LSR
LSR
LSR
LSR
Per Hop Behavior
(scheduling, dropping)
codepoint
PHB
class
HSN 2001
Diffserv 3/9
IPv4 Header
4-bit
version
4-bit
header
length
8-bit type of
service (TOS)
6-bit DS codepoints
PHB
codepoints
Default
000000
class selector xxx000
EF
101110
AF
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16-bit total length (in byte)
Currently
Unused
2-bit
CU
Drop
Class 1
Class 2
Class 3
Class 4
Low
001010
010010
011010
100010
Medium
001100
010100
011100
100100
High
001110
010110
011110
100110
procedence
HSN 2001
Diffserv 4/9
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PHB (Per Hop Behavior)
– Default PHB
• Best-Effort Forwarding
– Class Selector PHB
• Relative Order, Compatible with IP Precedence Field
– EF (Expedited Forwarding) PHB
• (Configured) Min Departure Rate > Max Arrival Rate
 Virtually No Queueing
• Used to Build a Low Loss, Low Latency, Low Jitter, Assured
Bandwidth, End-to-End Service (Virtual Leased Line Service)
– AF (Assured Forwarding) PHB Group
• N AF Classes, M Drop Precedence Levels/Class
• No Quantifiable Timing Requirement
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HSN 2001
Diffserv 5/9
Traffic Conditioning Control Functions Applied to a Behavior Aggregate
To Enforce Agreements between Domains and
To Condition Traffic to Receive a Differenciated Service within a Domain
By Marking packets with the appropriate Codepoint and
By Monitoring and Altering the Temporal Characteristics of the Aggregate
Meter 
Classifier
Marker 
Shaper/
Dropper 
: Components of Traffic Conditioner
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HSN 2001
Diffserv 6/9
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PDB (Per Domain Behavior)
–
–
Expected Treatment that an Identifiable or Target Group of Packets
will receive from “Edge to Edge” of a DS Domain
Associated with PHB (or List of PHBs)
Traffic Conditioning Requirements
–
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PDB Type
• VW (Virtual Wire) PDB
• BH (Bulk Handling) PDB
HSN 2001
Diffserv 7/9
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VW (Virtual Wire) PDB
– Edge-to-Edge Service  Dedicated Wire
• The aggregate input rates are appropriately policed and the EF
service rates on interior links are appropriately configured
• At every transit node, the aggregate’s maximum arrival rate is less
than that aggregate’s minimum departure rate
– Premium Service, or Virtual Leased Line (VLL)
– EF PHB is used
– Concerns : Routing stability, Multipath routing
 5~10% fudge factor in reality
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HSN 2001
Diffserv 8/9
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VW PDB (cont’d)
– Parameterization
• Traffic : packet size, physical wire bandwidth
• Domain : link bandwidth, EF transit bound of a router

• Maximum VW bandwidth allocated between ingress & egress
routers  packet size / EF bound
• When the ingress VW flows are aggregated/policed
appropriately, the EF BA can consist of an arbitrary aggregate of
VW flows
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HSN 2001
Diffserv 9/9
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BH (Bulk Handling) PDB
– For Extremely Non-Critical Traffic
• Packets of BH PDB may be delayed or dropped when any other
traffic is present
• Packets of BH PDB are forwarded onto the node output link when
the link is idle
– Intended as an Additional Tool for Administrators in Engineering
Networks
– No Attributes, No Parameters
– Class Selector (CS1) PHB, AF PHB, or EXP/LU PHB can be used
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HSN 2001
Reference
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Intserv
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RSVP
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RFC 2205, draft-ietf-rsvp-reduct-05
Diffserv
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RFC 1633, 2210, 2211, 2212
RFC 2474, 2475, 2597, 2598
draft-ietf-diffserv-pdb-def-03, draft-ietf-diffserv-pdb-vw-00,
draft-ietf-diffserv-pdb-bh-02
HSN 2001