Protection Routing in an MPLS Network using Bandwidth Sharing with Primary Paths

Jan 13, 2006 Lahore University of Management Sciences 1

Protection Routing in an MPLS Network

usingBandwidth Sharing with Primary

Paths

Zartash Afzal UzmiComputer Science and Engineering

Lahore University of Management Sciences (LUMS)

Visiting Professor – Chonbuk National University


Outline Background

Network Services and QoS Requirements Protection Routing in MPLS Backup Bandwidth Sharing Sharing with Primary Paths

NPP++ Protection Routing Framework Routing Overhead Path Computation Path Signaling

Simulation Results Evaluation and Experimentation Simulation Parameters Comparative Results


Outline Background





IP versus MPLS

In IP Routing, each router makes its own routing and forwarding decisions

In MPLS: Only one router (source) makes the routing decision Intermediate routers make forwarding decisions A path is computed and a “virtual circuit” is

established from ingress router to egress router

An MPLS path or virtual circuit from source to destination is called an LSP (label switched path)


QoS Requirements Bandwidth Guaranteed Primary Paths

MPLS allows establishing bandwidth-guaranteed paths

Bandwidth Guaranteed Backup Paths BW remains provisioned in case of network failure

Minimal “Recovery Latency” Recovery latency is the time that elapses between:

“the occurrence of a failure”, and “the diversion of network traffic on a new path”

Preset backup paths needed for minimal latency


Types of Backup Paths

Primary PathBackup Path

All links and all nodes are protected!

A B C D E

PLRPLR: Point of Local Repair: Point of Local Repair

nnhop

nhop

LOCAL PROTECTION (showing one LSP only)


Opportunity cost of backup paths

Protection requires that backup paths are setup in advance

Upon failure, traffic is promptly switched onto preset backup paths

Bandwidth must be reserved for all backup paths This results in a reduction in the number of Primary

LSPs that can otherwise be placed on the network

Can we reduce the amount of “backup bandwidth” but still provide guaranteed backups?

YES: Try to share the bandwidth along backup paths


BW Sharing in backup Paths

Example:

max(X, Y)

BW: Y

A B

C D

E F G

LSP1LSP1

LSP2LSP2

BW: XBW: X


XX XXXX

YY YYX+Y

Sharing is possible

IF

Links (A,B) and (C,D) do not simultaneously fail!


Sharing with Primary Paths

Can we do any sharing with primary paths? Normally, the answer is NO because… Traffic is always flowing on the primary paths BUT…

Backup paths protecting a node N may share bandwidth with primary paths that originate or terminate at node N because… Such backup will be active when:

node N fails, and in that condition… No primary originates or terminates at node N

Sharing with (some) primary paths is possible


Outline Background





Protection Routing Framework

Tasks related to backup paths in a protection routing framework: Backup path computation Backup path signaling

Objectives of protection routing framework Incur scalable routing overhead Find optimal backup paths Maximize bandwidth sharing

NPP++ framework achieves all of above


1.Scalable routing overhead

Aggregate Information Scenario (AIS) Fij: Bandwidth reserved on link (i, j) for all

primary LSPs Gij: Bandwidth reserved on link (i, j) for all

backup LSPs Rij: Bandwidth remaining on link (i, j)

Extended NPP (NPP++) relies on AIS Low routing overhead

More Information propagated More potential for BW sharing


2.Optimal backup paths Backup path computation is moved to a node that has

maximal information about the activation set of protected element

Node that computes backup paths maintains two local maps: BFTLIM

How much backup bandwidth will fall on a given link (u,v) if this element fails

PFTLIM How much primary bandwidth will be available on a given link

(u,v) if this element fails FTLIMs keep historical information about bandwidth

reserved for protecting an element Leads to the computation of backup paths that are optimal


Path Computation in NPP++

R1

R2

R3

R4

R5

The backup paths protecting The backup paths protecting against the failure of R2 against the failure of R2 cannot share bandwidth on cannot share bandwidth on any link.any link.

R2 Contains:R2 Contains:

a) BFTLIMa) BFTLIM

b) PFTLIMb) PFTLIM

Path computation is shifted to R2 because…Path computation is shifted to R2 because…

Only R2 has full knowledge of its own Activation setOnly R2 has full knowledge of its own Activation set

But such backup paths But such backup paths may share bandwidth may share bandwidth with primary paths with primary paths originating or originating or terminating at R2.terminating at R2.


3.Maximum Bandwidth Sharing Optimal path is signaled with requirements

for FULL bandwidth All nodes (along the backup path) maintain

two local data structures: BLTFIM

How much backup bandwidth will fall on this link if a given element fails

PLTFIM How much primary bandwidth will be released on

this link if a given element fails LTFIMs help nodes reserve only what is

needed Leading to maximum sharing along backup paths


NPP++ Summary


R1

R2

R3

R4

(2) Path computation is shifted to special (2) Path computation is shifted to special nodesnodes(3) Nodes in primary path maintain “local data (3) Nodes in primary path maintain “local data structures” called BFTLIM/PFTLIMstructures” called BFTLIM/PFTLIM

(4) Nodes in backup paths maintain “local data (4) Nodes in backup paths maintain “local data structures” called BLTFIM/PLTFIMstructures” called BLTFIM/PLTFIM

(1) Advertise aggregate link usage information (1) Advertise aggregate link usage information onlyonly

Results:Results:

•Path computation is Path computation is optimaloptimal

•Bandwidth sharing on backup paths is Bandwidth sharing on backup paths is maximummaximum..

•Advertisement overhead is minimumAdvertisement overhead is minimum

FTLIMsFTLIMs

LTFIMsLTFIMsFTLIMsFTLIMs

FTLIMsFTLIMs

LTFIMsLTFIMs

LTFIMsLTFIMs

Protecting R2


Outline Background





Evaluation & Experimentation

Traffic generation Used existing traffic models

Rejected requests experiments Generate a set of LSP requests Measure the number of rejected requests Simulate on various topologies

Scalability of local state information How do the average number of entries in

locally stored maps grow with the number of requests


Simulation Parameters Simulations performed on two networks Network 1:

15-node heterogeneous topology Core links with capacity 480 units, other links 120

units Network 2:

20-node homogenous topology (metros in the U.S.) Each link with capacity 120 units

LSP requests arrive one-by-one Ingress/Egress pairs chosen randomly

Bandwidth demand for each request is uniformly distributed between 1 and 6

100 experiments with different traffic matrices


Comparative Results: Network 1


Comparative Results: Network 2


Local Storage: Network 1


Local Storage: Network 2


Conclusions: NPP++

Optimal path computation

Maximum sharing along computed path

Scalable routing overhead Practically feasible

15% – 40% improvement over existing protection schemes


Last slide…

Thank you!Questions?

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Protection Routing in an MPLS Network using Bandwidth Sharing with Primary Paths