pce · 2013-11-25 · 1. composite pce: ! pcc and pce are located in the same node 2. external pce:...
TRANSCRIPT
Index 1. What is QoS? 2. Why it’s necessary in networks? 3. Qualities of traffic
1. An example of IGP Cost, OSPF
4. Adding QoS in OSPF 1. Problem: Adding QoS in IGP(OSPF)
5. Solution: PCE 6. How PCE works? 7. PCE and TED 8. PCE and Multi-Domains 9. PCE Architecture 10. PCECP Protocol
1. PCRequest & PCReply
11. Multi-Domain Path computation 1. Per-Domain Path Computation 2. Cooperating PCEs 3. Backward Recursive Path Computation 4. BRPC: Mesh Domain Problems
12. Conclusions
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What is QoS? � QoS(Quality of Service): is the collective effect of service
performance which determines the degree of satisfaction of a user of the service
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Why it’s necessary in networks? � Sometimes there is stricter service demands that can’t be
provided by the default systems
� For example: o Video Streaming o VoIP o Cloud Computing
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Qualities of traffic
� Low throughput � Dropped Packets � Errors � Latency � Jitter � Out-of-order delivery � Green Routing
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An example of IGP Cost, OSPF � The cost of an interface in OSPF is an indication of the
overhead required to send packets across a certain interface � The cost of an interface is inversely proportional to the
bandwidth of that interface
� Cost= 10↑8 /𝑏𝑎𝑛𝑑𝑤𝑖𝑑𝑡ℎ in bps
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Adding QoS in OSPF � In practice, this OSPF routing cost is not enough
� It’s necessary improve a new next-hope calculation
� Cost = α BW + β Delay + χ Jitter + … + ζ Losses
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Problem: Adding QoS in IGP(OSPF) � Adding new parameters, seriously complicates the dynamics
of flooding because the flooding convergence time can be longer than the change rate of some metrics like available bandwidth
� Adding new parameters increments the network overhead � Creates inaccuracy
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Solution: PCE � Definition: An entity (component, application, or
network node) that is capable of computing a network path or route based on a network graph and applying computational constrains (RFC4655)
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How PCE works?
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� PCC-PCE communication protocol (PCEP) � PCE
� The remote server that provides path computation � Path computation capabilities
� PCE Responds with a path (or failure)
� PCC � The network element that request computation services
� PCC Requests a computation � From where to where � Type of path? (Constraints)
PCE and TED
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� Path computation requires knowledge of available network resources
� TED: Traffic Engineering Database � The TED may be built from
� Information distributed by a routing protocol (OSPF-TE) � Information configured directly
PCE and Multi-Domains
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� A PCE only see inside its domain then � Computation of a multi-domain path may use cooperating
PCEs � Communication between PCEs � This communication is exactly as PCE-PCC communication
How PCE works?
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� A single PC cannot compute a multi-domain path
PCE
PCE PCE
PCE
Domain 1
Domain 2 Domain 3
Domain 4
PCE Architecture
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1. Composite PCE: � PCC and PCE are located in the same node
2. External PCE: � PCC and PCE are located in different nodes
3. Management-based PCE: � PCC is a NMS
4. Multiple PCE Path Computation: � Multiple PCEs are used to compute the path � No inter PCE communication
5. Multiple PCE Path Computation with Inter-PCE communication:
� Multiple PCEs collaborate to compute the path � Inter PCE communication
PCE Architecture
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PCE
TED NMS
LSR
Signalling Engine
LSR
Signalling Engine
LSR
Signalling Engine
LSR
Signalling Engine
LSR
Signalling Engine
LSR
Signalling Engine
LSR
Signalling Engine
LSR
Signalling Engine
PCE
TED
PCE
TED
Server
PCE
TED
Server
Type 3 Type 1 Type 2 & 5
PCEP Protocol
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� Operates over TCP � Session-based protocol � Seven messages
� Open � Keepalive � Request � Response � Notify � Error � Close
PCRequest & PCReply
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� PCReq message asks for a path computation � From and To � Constraints (bandwidth, etc…) � Metric to optimize
� IGP metric (ospf) � TE metric � Hop count
� PCRep reports the computed path (or failure) � Explicit route � Failure
Multi-Domain Path computation
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� Three main methods have already been defined 1. Per-domain path computation 2. Simple cooperating PCEs 3. Backward Recursive Path Computation
Per-Domain Path Computation
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� PCE calculates the path for it’s own domain. � Pro:
� Simple � Cont:
� It’s not the optimal path route, because you can’t see all the domains.
PCE1
PCE2
1 2
3
4
Cooperating PCEs
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Ingress
Egress
PCE
A
D
C
B
2. Thinks… “A looks best”
PCE
4. Thinks… “D would be best”
6. Route thru’ X and B
1. I want to reach the Egress
3. How should I reach the Egress?
X
5. Route thru’ B
Y
7. I want to reach the Egress
8. Route thru’ Y
Backward Recursive Path Computation
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� PCE calculates the path for all domains. � Pass the set of paths to the neighboring PCEs � Pro:
� Compute the optimal global path � Cont:
� It’s slow and expensive. � It’s a point of failures. � The destination must be known.
A
TQ
L
M
J I
GEC
B VSD
PCE1 PCE2
PCE3
BRPC: Mesh Domain Problems
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� BRPC uses recursive backward algorithm � The root it’s the destination � That means every PCE-AS calculates it’s own domain part of
path and then delegates route tree to the backward crossed AS to find the optimum path
� This algorithm generates death loops
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A UT
Q
R
L
M
N
K
J
I H
GE
FC
B
SP
DPCE1
PCE2
PCE3
PCE4
Conclusions
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� PCE is a logical functional component � May be centralized within a domain or distributed � It is not an all-seeing oracle
� PCEs may cooperate to determine end-to-end multidomain path
� It may too complex for large multidomain paths � Loops, erased by knowing sequences of domains
Bibliography � http://people.ac.upc.edu/careglio/teaching/XC2/XCII-Tema2e.pdf
� http://en.wikipedia.org/wiki/Quality_of_service � http://tools.ietf.org/html/rfc5088
� http://docwiki.cisco.com/wiki/Main_Page
� http://www.cisco.com/en/US/docs/ios_xr_sw/iosxr_r3.7/routing/configuration/guide/rc37ospf.html
� http://es.scribd.com/yerenial/d/89531987-Cisco-PCE
� http://www.itg523.de/oeffentlich/07maerz/PCE-Concept.pdf � http://www.rfc-editor.org/rfc/rfc4655.txt
� http://www.olddog.co.uk/Farrel_PCE_Tutorial.ppt
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