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Routing and Wavelength Assignment in Optical Networks. Xavi Masip, Sergi Sánchez, Eva Marín and Josep Solé, UPC {xmasip, sergio, eva, [email protected] Outline. Introduction Routing in OTN Signalling in OTN Wavelength conversion QoS in OTN New routing proposals

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Routing and wavelength assignment in optical networks

Routing and Wavelength Assignment in Optical Networks

Xavi Masip, Sergi Sánchez, Eva Marín and Josep Solé, UPC

{xmasip, sergio, eva, [email protected]


Outline

Outline

  • Introduction

  • Routing in OTN

  • Signalling in OTN

  • Wavelength conversion

  • QoS in OTN

  • New routing proposals

  • The Routing Inaccuracy Problem

  • The Routing Inaccuracy Problem in hierarchical networks

  • Open issues


Introduction

Introduction

  • Control Plane

    • Routing issues: compute the lightpath

    • Signalling issues: establish the lightpath

    • GMPLS1 is a strong candidate

  • Routing protocols

    • Constraint-based routing

  • Signalling protocols

    • RSVP-TE2

    • CR-LDP3

1L.Berger, “Generalized Multi-Protocol Label Switching (GMPLS): Signaling Functional Description”, IETF, RFC3471, Jan., 2003.

2 “GMPLS signalling resources reservation protocol-traffic engineering (RSVP-TE) extensions”, IETF, RFC3473, Jan. 2003.

3 P.Ashwood-Smith et al, “GMPLS signalling constraint-based routed label distribution protocol (CR-LDP) extensions”, IETF, RFC3472, Jan.2003.


Introduction1

Introduction

QoS Routing

  • Routing in IP networks

    • QoS constraints

    • Source routing (CBR)

BW, delay, jitter, loses,…

Network state information

?


Introduction2

Introduction

  • Routing target

    • Establish a lightpath between source-destination node pair

  • Routing open issues

    • Depends on network:

      • Circuit-switched (ASON)

      • Burst-switched (OBS)

      • Packet-switched (OPS)

    • Depends on wavelength conversion capabilities

    • Depends on control plane

      • Centralized lightpath establishment

      • Distributed lightpath establishment (source/destination-based)

    • QoS routing: what does it mean in OTN?

    • Network parameters

    • Update policies


Introduction3

Introduction

Cables

Fibers

Wavelegnths

Bands

Wavelengths

{l..l}1

l

TimeSlots

Packets

t0

t1

t2


Outline1

Outline

  • Introduction

  • Routing in OTN

    • Routing constraints

    • The RWA problem

  • Signalling in OTN

  • Wavelength conversion

  • QoS in OTN

  • New routing proposals

  • The Routing Inaccuracy Problem

  • The Routing Inaccuracy Problem in hierarchical networks

  • Open issues


Routing in otn

Routing in OTN

ASON, OBS, OPS

  • Routing and wavelength assignment problem

    • Determine both: physical route and wavelength/s to be assigned

    • Connection management protocol

Physical path, wavelength assignment


Routing constraints

Routing Constraints

  • Routing depends on connection management

    • In legacy backbone networks traffic is generally static

    • In next-generation optical networks traffic is more dynamic

    • OBS

      • Connection requests arriving at high rates

      • Average duration about several tens or hundreds of milliseconds

  • New dynamic lightpath provisioning schemes

  • Control plane is required: GMPLS


Routing constraints1

Routing Constraints

  • Wavelength continuity-constraint

    • Wavelength converters are expensive (at least for the next 5 years)

    • Wavelength Selective networks (WS):

      • There are not wavelength conversion devices

      • Same wavelength on all the route

    • Wavelength Interchangeable networks (WI):

      • There are wavelength conversion devices

      • Different wavelengths in the end-to-end path


Routing constraints2

Routing Constraints

  • Traffic in a wavelength-routed network

    • Static traffic pattern

      • Lightpaths set up all at once

      • Remain in the network for a long period of time

    • Dynamic traffic pattern

      • Lightpath is set up reacting to an incoming request

      • Lightpaths take down dynamically

  • Dynamic lightpath (on-demand) is foreseen to best accommodate current and future Internet traffic

  • Big challenge

    • Develop efficient algorithms and protocols for establishing lightpaths


The rwa problem

The RWA problem

  • Dynamic lightpath establishment

  • Routing and wavelength assignment problem (RWA)

    • It is NP-complete to find the optimal solution for the two problems1

    • Addressed separately

    • Through heuristic algorithms

  • Routing decomposed into:

    • Routing problem

    • Wavelength assignment problem

1A.Mokhtar, M.Azizoglu, “Adaptive Wavelength Routing in all-optical networks”, IEEE/ACM Trans.Netw., 1998


The rwa problem1

The RWA problem

  • Routing subproblem

    • Static approaches

      • Fixed routing

        • A single fixed route is precomputed

        • Ex: Shortest Path

      • Fixed-alternate routing

        • Multiple fixed routes are precomputed

        • Ex: Fixed shortest-path routing1, Least-Loaded Routing 1

    • Adaptive (dynamic) approaches

      • Ex: Link state approach2, distributed routing approach3

      • Adaptive routing based on global information

      • Adaptive routing based on neighbourhood information

      • Adaptive routing based on local information

1 E.Karasan, E.Ayanoglu, “Effects of wavelength routing and selection algorithms on wavelength conversion gain in WDM optical networks”, IEEE/ACM Trans.Netw., 1998

2 B.Muhherjee, “WDM Optical Communication Networks: Progress and Challenges”, IEEE JSAC, 2000

3 H.Zang, et al, “Connection management for wavelength-routed WDM networks”, Globecom 1999


The rwa problem2

The RWA problem

  • Adaptive routing based on global information

    • Routing decisions based on network state information

    • Full information about wavelength availability

    • Implemented in:

      • Centralized manner

      • Distributed manner:

        • Standardized by GMPLS

        • Different implementations

          • Link state approach

          • Distance-vector approach (or distributed routing approach)

          • Least-congested path algorithm


The rwa problem3

The RWA problem

  • Centralized manner

    • A single device maintains complete network state information

    • A single device finds routes and establishes the lightpaths

    • No huge coordination between nodes is required

    • Critical point of failure

  • Distributed manner

    • Decisions are distributed to different network nodes

    • GMPLS-based network:

      • Routes are computed by any routing (RWA) algorithm

      • A signalling (connection management) scheme is responsible for establishing the lightpath

        • Signalling candidates:

          • RSVP-TE

          • CR-LDP

      • There is not any guarantee that the updated global information with respect to wavelength availability on each link will be available in a distributed environment


The rwa problem4

The RWA problem

  • Distributed manner

    • Link state approach:

      • Each node maintains complete network state information

      • Each node finds the route in a distributed manner

      • Network state updating whenever network state changes

      • Signalling overhead vs outdated information

    • Distance-vector approach (or distributed routing approach):

      • Each node does not maintain global network state information

      • Each node maintains a routing table indicating the next hop and the distance to the destination

      • Updating is also required

    • Least-congested path algorithm:

      • Congestion on a link = number of available wavelengths

      • Links with fewer available wavelengths = links more congested

      • Congestion on a path = congestion on the most congested link on the path

      • Selects a set of sequence of routes for each source-destination pair

      • The least congested is selected

      • Using SP + LCP performs better than only using LCP


The rwa problem5

The RWA problem

  • Summary

    • Routing schemes based on global network state information perform better whenever update network state information

      • Suitable for networks where lightpaths do not change much with time

        • Small optical networks

        • Static traffic (not bursty)

      • Good updating procedure (signalling protocol)

      • New routing schemes assuming outdated network state information


The rwa problem6

The RWA problem

  • Adaptive routing based on neighbourhood information

    • In the LCP all links on all paths must be examined in choosing the least congested one

    • Network state information must be either:

      • Maintained by each node

      • Gathered in real time when establishing the lightpath

    • LCP variant:

      • Only examines the first k-links on each path (neighbourhood information)

      • K = 2 behaves similar than fixed-alternate routing


The rwa problem7

The RWA problem

  • Adaptive routing based on local information (deflection routing)

    • Also named alternate link routing

    • Another approach to adaptive routing with limited information

    • Selects from alternate links on a hop-by-hop basis instead of alternate routes on a end-to-end basis

    • Each node maintains a routing table indicating one or more outgoing links to each destination

    • The outgoing links are precomputed and can be properly ordered

    • A link is selected depending on its wavelength availability

    • Each node only maintains information regarding the wavelength availability on its outgoing links

      • No update messages are required


The rwa problem8

The RWA problem

  • Dynamic routing seems better than static routing:

    • Considers network state information when selecting lightpaths

  • BUT

    • Traditional dynamic routing algorithms selects the path maximizing the number of available wavelengths

      • the length of the routes and the wavelength distribution must be jointly considered in the lightpath selection process

    • Dynamic routing + global information = routing inaccuracy

    • Shortest path selects routes only based on hop length

    • Fixed-alternate routing is a trade-off mechanism


  • The rwa problem9

    The RWA problem

    • Wavelength Assignment subproblem

      • Random, First-Fit, Least-Used, Most-Used, Min-Product, Least-Loaded, Max-Sum, Relative Capacity Loss1

      • The literature results show that the First-Fit2:

        • Very good performance

        • Is very simple to implement

    • Examples:

      • Fixed-alternate routing and first-fit wavelength assignment (FAR-FF)

      • Least-Loaded routing and first-fit wavelength assignment (LLR-FF)

        • Fixed-alternate vs dynamic

        • LLR-FF performs better

        • LLR-FF longer setup delays and higher control overheads

    1H.Zang, et al., “A Review of Routing and Wavelength Assignment Approaches for Wavelength-Routed Optical WDM Networks”, ONM, 2000

    2 Y.Zhu, et al, “A Comparison of Allocation Policies in Wavelength Routing Networks”, Photon. Net. Commun.J., 20000


    Outline2

    Outline

    • Introduction

    • Routing in OTN

    • Signalling in OTN

      • Signalling schemes

      • Updating procedure

    • Wavelength conversion

    • QoS in OTN

    • New routing proposals

    • The Routing Inaccuracy Problem

    • The Routing Inaccuracy Problem in hierarchical networks

    • Open issues


    Signalling schemes

    Signalling schemes

    • A signalling protocol is required to reserve resources along the selected route

    • Three signalling schemes

      • Source initiated reservation (SIR)

        • Wavelength resources are reserved as the control messages traverses along the forward path to the destination

      • Destination initiated reservation (DIR)

        • Connection request collecting wavelength availability on each link

        • Based on this information the destination node will select an available wavelength along the path

      • Intermediate-node initiated reservation (IIR)

        • Some intermediate nodes can initiate the wavelength reservation


    Signalling schemes1

    Signalling schemes

    • SIR

      • Source routing (IP networks)

      • Wavelength/s are reserved as setup message is forwarded to the end

      • Wavelength number = f (wavelength information accuracy)

        • If source node has complete network state information:

          • May reserve only one wavelength

        • Complete network state information is not usual

          • Reserve all possible or a group of wavelengths

      • SIR problem: OVER-RESERVATION

        • Consequence: blocking of simultaneous connections


    Signalling schemes2

    Signalling schemes

    • SIR


    Signalling schemes3

    Signalling schemes

    • DIR

    • Blocking produced by outdated information

    • DIR outperforms SIR (no wavelength conversion)


    Signalling schmemes

    Signalling schmemes

    • SIR problem

      • Over-reservation (many wavelengths are reserved)

    • DIR problem

      • Outdated information (only one wavelength is reserved)

    • IIR: proposed solution

      • Allows reservations to be initiated by a set of intermediate nodes before connection request arrives at the destination node

      • Reduces the over-reservation

      • Reduces the vulnerable period = outdated information


    Signalling schemes4

    Signalling schemes

    • IIR without last link conflict


    Signalling schemes5

    Signalling schemes

    • IIR with last link conflict


    Updating procedure

    Updating procedure

    • Update in OTN

      • Updating is needed to refresh network changes

      • Information about topology and resource availability

      • Done by LSAs (link state advertisements) based on flooding

      • Dynamic network = huge amount of update messages = congestion

      • Triggering policies:

        • Update reduction

        • Inaccurate network state information

    • Triggering policies

      • Periodical updating

      • Relative change based triggers

        • Current link state – past link state > th (%)

      • Absolute change based triggers

        • Number of changes > th

      • Lazy flooding (not published yet)

        • Threshold, exponential, fibonacci


    Outline3

    Outline

    • Introduction

    • Routing in OTN

    • Signalling in OTN

    • Wavelength conversion

      • Wavelength conversion schemes

      • Wavelength conversion trade-off

      • Wavelength converters placement

      • Signalling schemes and wavelength conversion

    • QoS in OTN

    • New routing proposals

    • The Routing Inaccuracy Problem

    • The Routing Inaccuracy Problem in hierarchical networks

    • Open issues


    Wavelength conversion scheme

    Wavelength Conversion scheme

    • A lightpath connection could be blocked by

      • A route with a free available wavelength from s-d cannot be found

      • A wavelength cannot be found between s-d although there is free capacity on every hop of the path

        • Wavelength continuity constraint (WCC)

    • Blocking due to the WCC is dominant in the global blocking

    • Solution: Remove the WCC

      • Introducing wavelength converters

    • Problem: Wavelengths converters are expensive

      • It is not feasible to include a wavelength converters on all the network nodes

      • Not affordable in the next 5 years (CISCO said)


    Wavelength conversion scheme1

    Wavelength conversion scheme

    l1

    Fiber #1

    Fiber #1

    l100

    lp

    l1

    Fiber #N

    Fiber #N

    l100

    The labels indicate wavelengths (or frequencies)


    Wavelength conversion scheme2

    Wavelength conversion scheme

    Fiber #1

    Fiber #1

    Fiber #1

    lp

    {l..l}10

    Fiber #N

    Fiber #N

    {l..l}10

    The labels indicate wavelength bands


    Wavelength conversion scheme3

    Wavelength conversion scheme

    • Solution

      • Sparse wavelength conversion

      • Limited wavelength conversion

    • Sparse wavelength conversion

      • Wavelength conversion is available only on a set of nodes

      • New converters placement schemes must be developed

    • Limited wavelength conversion

      • Limits the range of conversion by a fixed value k

      • Translation degree D

    • Λ is the total number of wavelengths on a link


    Wavelength conversion scheme4

    Wavelength conversion scheme

    • In short

      • In WDM networks with centralized wavelength provisioning, sparse conversion could achieve nearly the same performance as full wavelength conversion

    • The question is:

      • Given a network topology, a certain number of wavelength converters, and traffic statistics

      • How can the wavelength converters be placed into the network in order to minimize the overall blocking probability?


    Wavelength converters placement

    Wavelength converters placement

    • Easy way

      • Analyze nodes more congested

      • These nodes are candidates to get conversion capabilities

    • Best way:

      • There are many converter placement algorithms for simple topologies (bus, ring)

      • The complex the topology the complex the algorithm

      • Many heuristics are currently defined for static routing + random

      • It has been demonstrated that any converter placement algorithm does not work on any RWA1

      • Both issues must be tackled together

    1X.Chu, B.Li, I.Chlamtac, “Wavelength Converter Placement under Different RWA Algorithms in Wavelength-Routed All-Optical Networks”, IEEE ToN, vol51, nº4, April 2003


    Wavelength converters placement1

    Wavelength converters placement

    • Target:

      • Place the wavelength converters in those nodes so that blocking decreases

    • Proposals1

      • Minimum blocking probability first (MBPF)

        • To be applied to the FAR-FF (fixed-alternate routing)

      • Weighted Maximum Segment Length (WMSL)

        • To be applied to the LLC-FF (dynamic routing)

      • Boths solutions assume:

        • Sparse wavelength conversion

        • Full range conversion (not limited)

      • Based on placing converters one by one sequentially

    1X.Chu, B.Li, I.Chlamtac, “Wavelength Converter Placement under Different RWA Algorithms in Wavelength-Routed All-Optical Networks”, IEEE ToN, vol51, nº4, April 2003


    Wavelength converters placement2

    Wavelength converters placement

    • MBPF:

      • Find the N feasible paths according to the FAR

      • Define candidate nodes as those nodes without conversion capabilities

      • Assume a WC on all candidate nodes (one by one)

      • Compute blocking based on a mathematical model

      • Place a WC in that node minimizing the blocking

      • Repeat the process till the M WC are placed

    • WMSL:

      • Assign a weight to each candidate node indicating the impact of this node on the blocking

      • Assume that the hop length significantly contributes to the blocking for WS networks

      • Introduce WC so that the end-to-end paths are divided into several “WS” segments.

      • Blocking is fully dependent on the segment length


    Signalling schemes and wavelength conversion

    Signalling schemes and Wavelength conversion

    • DIR for networks with sparse wavelength conversion


    Signalling schemes and wavelength conversion1

    Signalling schemes and Wavelength conversion

    • IIR for networks with sparse wavelength conversion


    Outline4

    Outline

    • Introduction

    • Routing in OTN

    • Signalling in OTN

    • Wavelength conversion

    • QoS in OTN

    • New routing proposals

    • The Routing Inaccuracy Problem

    • The Routing Inaccuracy Problem in hierarchical networks

    • Open issues


    Qos in otn

    QoS in OTN

    • What does QoS mean in OTN?

      • The answer is not easy at all

    • What we know is how network performance can be evaluated

      • The blocking probability

    • Look at:

      • Customer needs

      • Applications requirements

      • Operator technical requirements

      • Service classes


    Qos in otn1

    Usability Requirements

    blocking probability

    network availability

    application set-up time

    connection set-up time

    network robustness

    throughput

    delay

    jitter

    packet loss rate

    BER (bit error rate)

    bandwidth requirements

    security requirements

    nomadism

    connectivity (number of senders/receivers)

    naming and numbering

    Operator Requirements

    (fulfill user requirements with the lowest possible quantity of resources and in the most efficent way)

    business roles

    elasticity (level of modification of original traffic shape)

    interactivity

    availability

    nature of bidirectional traffic (symmetric or asymmetric)

    provisioning of network resources

    naming and numbering

    supervision of network performance and faults (monitoring)

    AAA (Authentication, Authorization, Accounting)

    QoS in OTN


    Qos in otn2

    QoS classes

    emergency („strict“ real-time)

    conversational (real-time)

    streaming („almost“ real-time)

    prioritized elastic (business non-real-time)

    best effort (non-real-time)

    Optical network services

    connection-oriented analogue

    connection-oriented with wavelength switching

    connection-oriented burst switching

    connectionless burst switching

    connectionless packet switching

    transparent or opaque lightpaths

    dedicated or shared lightpaths

    Selection of QoS parameters

    required optical network service

    max. and min. holding times

    connection set-up and tear-down time

    blocking probability

    bandwidth requirements

    latency

    BER

    routing stability

    controlling and signalling delay

    load overhead for admin, mgmt etc.

    service availability

    in case of OBS service: burst aggregation mechanism, burst loss and blocking probability

    physical parameters in case of analogue optical network service

    QoS in OTN


    Outline5

    Outline

    • Introduction

    • Routing in OTN

    • Signalling in OTN

    • Wavelength conversion

    • QoS in OTN

    • New routing proposals

      • MICORA (Minimum Coincidence Routing Algorithm)

      • PBR

    • The Routing Inaccuracy Problem

    • The Routing Inaccuracy Problem in hierarchical networks

    • Open issues


    Micora

    MICORA

    • Dynamic routing seems better than static routing: BUT

      • Traditional dynamic routing algorithms selects the path maximizing the number of available wavelengths

        • the length of the routes and the wavelength distribution must be jointly considered in the lightpath selection process

      • Dynamic routing + global information = routing inaccuracy

      • Shortest path selects routes only based on hop length

      • Fixed-alternate routing is a trade-off mechanism

  • New proposal

    • Trade-off between network performance and complexity

    • Fixed-alternate routing + wavelength assignment

    • MICORA (Minimum Coincidence Routing Algorithm)

      • Aims to optimize the physical route selection

      • Aims to reduce effects of selecting paths regardless network state

      • Does not select the k-shortest paths

      • Selects paths with minimum “coincidences”


  • Micora1

    MICORA

    • MICORA1

      • Selects the k-(shortest & minimum coincident) paths

      • Computes the end to end paths considering the routes that have less shared links and minimum number of hops

      • Looks for the k-routes in two iterative basic steps

    • MICORA steps to compute k-routes

      • Selects the shortest path

      • Computes the Minimum Shared Link (MSL)

        MSL =NH * SL

        • NH: number of hops

        • SL: number of links shared between each path and the previous selected path

      • Select the path with minimum MSL

      • Repeat the last two steps (k-2) times

    1S.Sánchez-López, X.Masip-Bruin, J.Solé-Pareta, “The Minimum Coincidence Routing in Optical Networks”, Workshop on G/MPLS, Girona, March 2006


    Micora illustrative example

    Incoming request from node 1 to node 13

    K = 3

    MICORA steps:

    Selects the shortest path as the first path

    MICORA: Illustrative Example

    Shortest paths

    Selected paths

    1-7-12-13

    1-2-8-12-13

    1-7-12-13

    1-6-8-12-13

    1-2-8-5-9-11-14-12-13

    1-6-8-5-9-11-14-12-13


    Micora illustrative example1

    MICORA: Illustrative Example

    Path = 1-7-12-13

    SL

    MSL

    Selected paths

    1-2-8-12-13

    1

    4 * 1 = 4

    1-7-12-13

    1-6-8-12-13

    1

    4 * 1 = 4

    1-2-8-12-13

    1-2-8-5-9-11-14-12-13

    1

    8 * 1 = 8

    1-6-8-5-9-11-14-12-13

    1

    8 * 1 = 8

    • MICORA steps:

      • Computes the MSL parameter

      • Selects the path minimizing the MSL value

      • First iteration to compute the second path

      • Second iteration to compute the third path


    Micora evaluation

    Source nodes: 1, 2, 3, 8

    Destination nodes: 11, 15, 16

    Traffic

    20000 connections (0.25-20 Erlangs)

    Link

    7 unidirectional fibres / 4 wavelengths

    Comparison between

    SPF + First-Fit/random

    MICORA + First-Fit /random

    MICORA: Evaluation


    Prediction based routing

    Prediction-Based Routing

    • Usual routing algorithms need update messages

    • Problems:

      • Signalling overhead

      • Routing under outdated network state information

    • New idea : PBR

      • Source nodes can learn which is the best path and wavelength without update messages

      • Dynamic learning according to the routing information obtained in previous connection set-ups. (Based on branch prediction).

    • Main PBR characteristics

      • Prediction based on the history of previous outcomes

      • History = connection request succeeded

      • History is registered in Wavelength registers (WR)

      • The WR values are used to index tables named Prediction Tables

      • The PT content predicts the end-to-end lightpath availability

    Eva Marin, Xavier Masip, Sergio Sánchez, Josep Sole and Jordi Domingo, “The prediction-based routing in optical transport networks”, Computer Communications, 2006


    Pbr evaluation

    PBR: Evaluation

    12000

    10616

    10000

    First-Fit lambda=2

    First-Fit lambda=3

    First-Fit lambda=4

    First-Fit lambda=5

    PBR lambda=2

    PBR lambda=3

    8000

    PBR lambda=4

    PBR lambda=5

    Blocked Requests

    6000

    4000

    3796

    2000

    287

    57

    0

    0

    5

    10

    15

    20

    25

    30

    35

    40

    45

    Cycles N (update)

    • Topology test: 15 nodes (2 sources, 2 destinations) with one-fibre link

    • Connections arrivals (60,000) modelled by Poisson, each one requiring a full wavelength

    • Number of wavelengths variable: 2, 3, 4 and 5


    Outline6

    Outline

    • Introduction

    • Routing in OTN

    • Signalling in OTN

    • Wavelength conversion

    • QoS in OTN

    • New routing proposals

    • The Routing Inaccuracy Problem

      • Problem definition

      • Routing inaccuracy effects

      • BBOR solution

      • Sources of inaccuracy

      • Example for WS networks

      • BBOR and WI networks

      • Performance evaluation

    • The Routing Inaccuracy Problem in hierarchical networks

    • Open issues


    Problem definition

    Problem Definition

    Routing Inaccuracy Problem

    • Problem definition:

      • Signalling overhead

      • Update interval modified by updating Policies

        • Reduce signalling overhead

        • Reduce the network state information reliability

      • Accurate network state information cannot be guaranteed

      • Routing algorithms rely on the routing information accuracy

      • When inaccurate information,

        • Call blocking increase

      • Trade-off

        • Need of having accurate routing information

        • Need of reducing the number of update messages


    Sources of inaccuracy

    Sources of Inaccuracy

    • Triggering policies

      • Reducing the signalling overhead

    • Network state aggregation in hierarchical networks

      • Distributing network state information in a scalable form

    • Protocol convergence time

      • Non-negligible delay

    • Deviation from real parameter values

      • Nominal or sampled values


    Routing inaccuracy effects

    Routing Inaccuracy effects

    b

    a-b

    a

    λ1,λ3

    λ1,λ3

    λ1, λ2, λ3

    λ1,λ3

    λ1, λ2, λ3

    λ1, λ2, λ3

    λ1, λ2, λ3

    λ1, λ2, λ3

    1

    1

    1

    λ1, λ2, λ3

    λ1, λ2

    λ1, λ2

    λ1, λ2

    2

    λ1, λ2, λ3

    λ1, λ2, λ3

    λ1, λ2, λ3

    λ1,λ3

    λ1, λ2, λ3

    λ1, λ2

    λ1, λ2

    λ1, λ2, λ3

    λ1, λ3

    λ1, λ3

    λ1,λ2

    λ1,λ2, λ3

    d

    λ1

    λ1

    λ1

    λ1, λ2, λ3

    3

    Path

    c

    c-d

    Blocked

    Path

    • Routing inaccuracy effects in WS networks

    a, 1, 2, b, (λ1)

    c, 1, 2, d, (λ1)


    Bypass based optical routing bbor solution

    Bypass Based Optical Routing (BBOR) Solution

    • Apply the BBOR to WS networks implies to define:

      • A triggering policy

      • A routing mechanism

    • A triggering policy:

      • Based on a threshold, N

      • Update messages sent after N changes

    • A routing mechanism consists of three steps:

      • Identify the Obstruct-Sensitive Wavelengths (OSWs)

      • Consider these OSWs in the RWA problem

      • Compute optical bypass-paths


    Bbor solution identify the osws step 1

    BBOR Solution: Identify the OSWs (step 1)

    Percentage of N to decide when a λ is OSW

    • Obstruct-Sensitive wavelength (OSW):

      • Due to the inaccuracy potentially a wavelength might not be available in a certain link at the path set-up time

      • This wavelength is defined as OSW and has to be bypassed

    • OSW formal definition:

      • A λi is OSW (λios ) on a certain link if

        R ≤ Tp

        where:

      • B: total number of a certain λi on a link

      • N: threshold value

      • R: current number of available λi on this link

      • Tp: threshold percentage


    Bbor solution consider the osws in the rwa problem step 2

    BBOR Solution: Consider the OSWs in the RWA problem (step 2)

    Degree of obstruction

    • New parameter OSWi (L,F):

      • i: colour

      • L: number of links where λi is OSW

      • F: minimum number of λi‘s available along the selected lightpath

    • Two routing algorithms:

      • ALG1

        • Prioritizes to minimize the obstruction

      • ALG2

        • Prioritizes to minimize the congestion

    Degree of congestion

    λi with min L among those with max F

    λi with max F among those with min L


    Bbor solution compute the optical bypass paths step 3

    BBOR Solution: Compute the optical bypass-paths (step 3)

    • A bypass-path is computed for all the OSWs

      • Bypass the links where the selected wavelength is OSW

      • Cost:

        • minimum number of hops

        • minimum number of OSW

        • minimize congestion

      • Used depending on the real wavelength availability at the lightpath set-up time


    Example for ws networks

    Example for WS networks

    1

    5

    6

    2

    1

    2

    3

    4

    7

    8

    1-4

    • B = 10 fibres per link (4 wavelengths per fibre)

    • N = 6 and Tp = 50% (R ≤ 3)


    Example for ws networks1

    Example for WS networks

    Path

    (5,3,4)

    Path

    (3,4)

    5

    5

    6

    6

    1-4

    λ1

    λ2

    λ2

    Path

    (2-2,5,3-,3,4)

    Path

    (3,4)

    Path

    (4)

    1

    1

    2

    2

    3

    3

    4

    4

    7

    7

    8

    8

    1-4

    Path

    (4)

    Path

    (7,8,4)

    Path

    (8,4)

    Blocked

    Blocked

    • ALG1

    1-2-3-4 (λ1)

    2-5-3 (λ1)

    λ1?

    • ALG2

    1-7-8-4 (λ2)

    1-7-8

    λ2?

    λ2?


    Bbor and wi networks

    BBOR and WI Networks

    • Conversion capabilities

      • How many nodes are conversion capable?

      • Which is the wavelength conversion range?

    • Optimal situation

      • Conversion on every node

      • Unlimited range of conversion

      • Not affordable

    • Limitation

      • Sparse Conversion

        • q = conversion density

      • Limited range of wavelength conversion

        • D = degree of conversion

      • Substantial improvement for D = 25%1

    Full wavelength conversion capability

    1J.Yates et al, “Limited-range Wavelength Translation in ALL-Optical Networks”, IEEE INFOCOM 1996


    Bbor and wi networks1

    BBOR and WI Networks

    hopcount

    • Three main differences:

      • Select K-shortest paths

      • New weight factor, Fp

        • Balance the number of potentially obstructed wavelengths and the real congestion

      • Bypass-path computation:

        • Wavelength conversion: in a conversion capable node

        • Bypass-path computation: in a non-conversion capable node

    • New algorithm ALG31

    Degree of obstruction

    Degree of congestion

    1X.Masip, et al., “Routing and Wavelength Assignment under Inaccurate Routing Information in Networks with Sparse and Limited Wavelength Conversion”, IEEE GLOBECOM 2003


    Bbor algorithms

    BBOR Algorithms

    Shortest paths

    K-Shortest paths

    Mark λios

    ALG1

    ALG2

    ALG3

    λi | min {L}, OSWi(L,F)

    λi | max {F}, OSWi(L,F)

    λi | min {Fp},

    λi | max {F}, OSWi(L,F)

    λi | min {L}, OSWi(L,F)

    F

    Conversion

    T

    Compute bypas-paths

    Wavelength Conversion


    Performance evaluation

    Performance Evaluation

    • Simulation scenario:

      • Source-destination pairs randomly selected

      • B = 5 fibres with 10 wavelengths on all fibres

      • Traffic characteristics:

        • Connection arrivals modelled by a Poisson distribution

        • Holding time exponentially distributed

        • Every connection requires a full wavelength

      • Adaptive routing:

        • Shortest Path, First-Fit

        • ALG1, ALG2 and ALG3


    Performance evaluation1

    Performance Evaluation

    4000

    N=1

    3500

    N=6

    3000

    54%

    N=10

    2500

    Number of update messages

    2000

    76.41%

    1500

    1000

    500

    0

    0

    0,2

    0,4

    0,6

    0,8

    1

    Erlangs

    • Signaling overhead

    • Achieves a reduction in the number of update messages

    • The larger the N the lower the signalling messages


    Performance evaluation2

    Performance Evaluation

    200

    180

    N=6

    160

    N=10

    46%

    140

    120

    Number of OSW

    100

    80

    60

    40

    20

    0

    0

    25

    50

    75

    100

    Tp (%)

    • Number of OSW as a function of N and Tp

    • The larger the N the larger the OSWs

    • Simulations with N=6 and Tp=50%


    Performance evaluation3

    Performance Evaluation

    8.8%

    • Blocking probability in WS networks (N=6 and Tp=50%)

    • ALG3 exhibits lower blocking probability due to the weight factor

    • ALG2 performs better than ALG1

      • Minimize the congestion instead of obstruction


    Performance evaluation4

    Performance Evaluation

    • Blocking probability in WI networks (D=25%)

    • ALG3 performs better even when increasing the number of conversion capable nodes

    • q>25% does not imply a significant blocking reduction

    q = conversion density (sparse conversion)


    Performance evaluation5

    Performance Evaluation

    • WS and WI analysis

    • ALG2 (WS) ≈ SP (q=25%, D=25%)


    Performance evaluation6

    Performance Evaluation

    0.005%

    0.003%

    • WS and WI analysis

    • ALG2 (WS) ≈ SP (q=25%, D=25%)

    • ALG3 (WS) <SP (q=25%, D=25%)


    Outline7

    Outline

    • Introduction

    • Routing in OTN

    • Signalling in OTN

    • Wavelength conversion

    • QoS in OTN

    • New routing proposals

    • The Routing Inaccuracy Problem

    • The Routing Inaccuracy Problem in hierarchical networks

      • Aggregation schemes

      • Hierarchical issues

      • Routing algorithm

      • Evaluation

    • Open issues


    Hierarchical issues

    Hierarchical Issues

    • ASON (Automatically Switched Optical network )

      • Hierarchical routing, so scalability

        • Network information dissemination

        • Constraint-base path computation

    • Main hierarchical routing issues

      • Aggregation process (reduce disseminated information)

      • Update policy (accurate network state information)

      • Lightpath selection process


    Hierarchical issues1

    Hierarchical Issues

    • Topology example

      • Global information requires an efficient update mechanism


    Aggregation schemes

    Aggregation Schemes

    • Many possible aggregation schemes:

      • Full Mesh Aggregation Scheme

      • Both consider QoS parameters

      • Asymmetric Simple Aggregation Scheme

        • Delay, capacity and cost

        • Not suitable for OTN

      • “QoS” parameters in OTN

        • Propagation delay, number of wavelengths per link,…

    • The RIP contribution to the overall blocking is quite significant

    • New proposal1 consists in:

      • A new aggregation scheme (Node Aggregation Scheme, NAS)

      • A new Routing Algorithm (BHOR)

    1E.Marín-Tordera, X.Masip-Bruin, S.Sánchez-López, J.Solé-Pareta, J.Domingo-Pascual, “A hierarchical routing approach for optical transport networks”, Computer Networks journal, Elsevier, vol.5, issue 2, pp.251-267, February 2006


    Aggregation schemes1

    Aggregation Schemes

    • The NAS works as follows:

      • Aggregated Delay (Di):

        1. Compute all the lightpaths from node i to all border nodes.

        2. Add the propagation delay of each link for each lightpath.

        • Select the minimum value among the values computed in the step 2

      • Aggregated number of available wavelength (Wip):

        1. Compute all the lightpaths from node i to all border nodes.

        2. Select the minimum number of wavelength per color that is available on each path.

        • Select the maximum value among the values computed in the step 2

    • Formally:

      • Aggregated Delay (Di):

      • Available Wavelength (Wip):


    Routing algorithm

    Routing Algorithm

    • BBOR routing algorithm:

      • Extending ALG_3 to be applied to hierarchical networks, BHOR

      • n is the number of hierarchical levels

      • Bypass-paths are computed on each hierarchical level


    Evaluation

    Blocking with/without aggregation

    Blocking for the FF and the BHOR

    Evaluation


    Outline8

    Outline

    • Introduction

    • Routing in OTN

    • Signalling in OTN

    • Wavelength conversion

    • QoS in OTN

    • New routing proposals

    • The Routing Inaccuracy Problem

    • The Routing Inaccuracy Problem in hierarchical networks

    • Some open issues


    Some open issues

    Some open issues

    • Inter-domain

    • QOS definition

    • Class of services definition

    • Multilayer Traffic Engineering

    • OBS

    • OPS

    • Resilience, fault protection

    • Wavelength conversion

    • Improve RWA algorithms

    • All-optical network

    • Wavelength converters placement schemes

    • Should QoS routing is still an open issue in traditional IP/MPLS networks it is actually an “unknown” issue in OTN


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