the npp++ framework for protection routing in mpls

1

The NPP++ Framework forProtection Routing in MPLS

Zartash Afzal UzmiComputer Science and Engineering

Lahore University of Management Sciences (LUMS)Pakistan

April 29, 2006Global Internet 2006

Computer Science and EngineeringLahore University of Management Sciences (LUMS) - Pakistan 2

Outline Background and Preview

IP and MPLS Routing 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



IP versus MPLS Routing

IP Routing Destination-based Hop-by-hop

MPLS Routing: An MPLS path or “virtual circuit” from

source to destination (ingress to egress)

A label switched path (LSP) is pre-established



MPLS Flow Progress

LSR1

LSR2

LSR3

LSR5

LSR6

R1 R2LSR4D

Ddestination

D31

D17

D

D11

S

source

LSP

ingress

egress



Protection Routing with MPLS Bandwidth Guaranteed Primary Paths

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

Minimal “Recovery Latency”

Need Preset backup paths with Local Protection



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 of one primary path from A to E



Opportunity cost of backup paths

Backup paths are setup in advance Upon failure, traffic is promptly switched onto preset

backup paths

Bandwidth must be reserved for all backup paths Reduced number of Primary LSPs (that can otherwise

be placed)

Can we reduce the amount of “backup bandwidth”? 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!



Activation SetsA

B

C

D

E

Activation set for node B

Activation set for link (A,B)

A

B

C

D

E

Paths in the same activation set MUST not share bandwidth



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



Protection Routing Framework

Tasks of a protection routing framework: Path computation Path signaling and setup

Objectives of a protection routing framework1. Incur scalable routing overhead2. Find optimal primary paths3. Find optimal backup paths4. Maximize bandwidth sharing

NPP++ framework achieves all of above However, (2) and (3) are not achieved jointly

Primary and Backup



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)

NPP++ relies on AIS Low routing overhead

More Information propagated More potential for BW sharing



2.Optimal backup paths Who computes the backup paths? 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

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

GOAL:GOAL:

Find a backup Find a backup path that path that protects R2protects 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



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 With backup paths and with primary paths

Scalable routing overhead Practically feasible

15% – 40% improvement over existing protection schemes



Last slide…

Thank you!Questions?

the npp++ framework for protection routing in mpls

Documents