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Path Computation Element (PCE) PCE

PCE · 2013-11-25 · 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

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Text of PCE · 2013-11-25 · 1. Composite PCE: ! PCC and PCE are located in the same node 2. External PCE:...

  • Path Computation Element (PCE)

    PCE

  • 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

  • How PCE works?

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      A single PCE cannot compute a multi-domain path

    PCE

  • 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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  • Path Computation Element (PCE)

    PCE