hybrid backup resource optimization for vnf placement over … · 2019-05-23 · »modulation...

Hybrid Backup Resource Optimization for VNF Placement over Optical Transport NetworksJoão Pedro, António Eira

2© 2019 Infinera. All rights reserved. Company Confidential.

Outline

• Motivation

• Network Scenario

• Survivability Mechanisms

– Hop Protection

– Chain Protection

– Hybrid Protection

• Optimization Model

• Simulation Results

• Conclusions


Introduction

• Advent of 5G brings increasingly diverse service requirements

– High BW, high-availability, latency-critical

• Edge computing vital to meet these requirements

– Introduce application-awareness in the network

• Carriers re-purposing central offices (COs) as data centers (DCs)

– Opportunity to cost-effectively host computing resources atmetro-aggregation nodes which are closer to end-users

• Converged nodes combining DC/virtualization capabilities with packet/optical transport

– Joint visibility of both IT and networking resources

– Opportunity to exploit more efficient resource dimensioning methods


Network Scenario

• Network Topology

– Metro DWDM ring network

– Each optical node may be co-located with a DC

• Logical Topology

– Service chains deployed between two end nodes byinstantiating the set of required VNFs at one or more DCs

– Logical topology must ensure each set of VNFs in a chaincan be traversed in the target order

– Placement of VNFs across the network determines bothIT requirements and the logical topology to support them

• Survivability to Link Failures: paramount to support critical 5G Services

DC Node

A

B

C

D

E

F

G

H

VNF SetSource

𝑩𝟏

G f1 f2 f3 B𝑩𝟐 𝑩𝟑 𝑩𝟒

Destination

Bandwidth per hop [Gb/s]

Maximum E2E latency [ms]


Survivability Mechanisms: Hop Protection

• Link-failure survivability via protecting each optical hop of the VNF chain

Low transponder count: backup paths only require additional spectrum

Low IT resource usage: no duplication of VNFs to protect against link failures

Reduced lightpath capacity: same channel format in working and backup lightpaths defined by worst performing one (extreme differences in a ring network)

High worst-case latency: single link failure can trigger multiple backup paths

Lightpath rate constrainedby longest path whentransponders are sharedbetween working/backup

Working Path

Backup Path

Transponder *

fiBackup VNF i

fiWorking VNF i

G A BF

f1, f2 f3

Link-disjointness enforced betweenworking/backup links on each chain hop*

*not required when VNFs at same node

16-QAM

16-QAM

QPSK ** * * **


Survivability Mechanisms: Chain Protection

• Link-failure survivability via replicating the VNF chain over a disjoint path


Working Path

Backup Path

Transponder *

fiBackup VNF i

fiWorking VNF i

High lightpath capacity: independent lightpaths, each using the best channel format

Low worst-case latency: bounded by working or backup chain (independent of failed link)

High transponder count: additional transponders required to support backup lightpaths

High IT resource usage: additional storage/compute resources to duplicate VNFs…

… but provides resilience against failures within DCs

G

H

B

A

F E

f3

f364-QAM

64-QAM

64-QAM

16-QAM

Link-disjointness enforced betweenworking/backup links across entire chain

f1, f2

f1, f2* *


Survivability Mechanisms: Hybrid Protection


Working Path

Backup Path

Transponder *

fiBackup VNF i

fiWorking VNF i

Lowest transponder count: by selectively combining the high lightpath capacity of Chain protection with the absence of dedicated backup transponder of Hop protection

Customizable and adaptable to specific network scenario and optimization priorities…

… but at the expense of a more complex design process

• Link-failure survivability via a combination of per hop protection with replicating segments of the VNF chain over disjoint paths

G

A

BE

F

f3

64-QAM 16-QAM

Link-disjointness enforced between working/backup links for all chain hops in the same cycle

16-QAM

f1, f2

f1, f2* * * *


Optimization Model

• Multifactorial problem structure

– Optimal protection mechanism depends on several factors

» e.g. service BW, possible DC placements, latency constraints

– Protection mechanism impacts lightpath capacity

» e.g. mitigate impact of working/backup ligthpaths with large performance differences via introducing VNF redundancy

• Results in a complex optimization problem

– Routing and spectrum assignment on top of VNF placement, considering specific optical performance constraints associated to each protection mechanism

• Solved via a single ILP model

– Jointly captures all interdependencies

– Applicable to small/medium sized networks,suitable to Metro ring networks

Access

Aggregation

Core Interface

Storage/Compute

Transponder

Bank

Enables fair comparison of the 3 protection mechanisms


Optimization Model

• ILP Objective Function

– Min. total number of transponders required for working and backup chains

• Main ILP Constraints

– Flow conservation; working/backup chain segment disjointness

– Shared vs dedicated backup transponder; lightpath capacity defined by worst-case working/backup in case of shared backup transponders; max. number of optical channels per link

– Max. number of nodes hosting a DC; max. IT resource capacity per node; max. working chain latency

• Chain/Hop protection modelled by manipulating variables and adding constraints

• Number of variables grows with N2 (N – number of nodes)

– Model all candidate paths between arbitrary node pairs (for every chain hop)


Simulation Results: Network Scenario

• Network topology and traffic load

– Ring topologies with {200, 400} km,comprising {5, 10} nodes

– Up to {40, 80} % of nodes host a DC

– 10 Tb/s of traffic (summing over all VNFhops of every chain) generated uniformlybetween all nodes

• Channel formats and optical design

– Flex-rate interfaces with line rates 100-600 Gb/s

» Modulation formats BPSK, QPSK, 8QAM, 16QAM, 32QAM, 64QAM

» Symbol rate of 64 Gbaud; 75 GHz frequency slots

– Reach estimation model accounts for filtering penalties,crosstalk levels and express losses

Virtual Network Functions

1 - Network Address Translation

2 - Firewall

3 - WAN Optimization Controller

4 - Intrusion Detection Prevention System

5 - Video Optimization Controller

6 - Traffic Monitor

Service Type VNF Chain

Web Services 1-2-6-3-4

VoIP 1-2-6-2-1

Video Conferencing 1-2-6-5-4

Cloud Gaming 1-2-5-3-4

5G Service 1-2-6-3-5

From Savi et al., “To distribute or not to distribute? Impact of latency on virtual network function distribution at the edge of FMC networks”, ICTON 2016, We.C3.4

0

100

200

300

400

500

600

1 2 3 4 5 6 7 8 9

Max

imu

m D

ata

Rat

e [

Gb

/s]

Ring Hop Count

10 Nodes - 200 km

10 Nodes - 400 km

5 Nodes - 200 km

5 Nodes - 400 km


Simulation Results: Transponder Count

• Chain protection requires the highest number of transponders

– 23 to 94% more transponders wrt Hop protection

– More inefficient in shorter rings: due to smaller working/backup optical performance differences

• Hybrid protection requires the lowest number of transponders

– 3% reduction wrt Hop protection for 200 km rings: small working/backup performance gap discourages using chain protection

– 9% reduction wrt Hop protection for 400 km rings: uses chain protection in some segments to mitigate working/backup performance gap

0

50

100

150

200

250

300

40% 80% 40% 80% 40% 80% 40% 80%

5 Nodes 10 Nodes 5 Nodes 10 Nodes

200 km 400 km

Nu

mb

er

of T

ran

sp

on

de

rs

Ring Length

Chain ProtectionHop ProtectionHybrid Protection

Max DC

Node %

Results averaged over 10 independent runs


0

500

1000

1500

2000

40% 80% 40% 80% 40% 80% 40% 80%


200 km 400 km

IT C

ap

acity U

nits

Ring Length

Chain ProtectionHop ProtectionHybrid Protection

Max DC

Node %

Simulation Results: IT Resources


• Chain protection requires the highest amount of IT resources

– VNFs duplicated at every node

• Hop protection requires the lowest amount of IT resources

– No VNF duplication

• Hybrid protection only requires slightly more IT resources than Hop protection

– Extent of increase related to transponder savings

– 9% transponder savings obtained at expense of 24% extra IT resources


0

0.5

1

1.5

2

40% 80% 40% 80% 40% 80% 40% 80%


200 km 400 km

La

ten

cy [m

s]

Ring Length

Chain Protection

Hop Protection

Hybrid Protection

Max DC

Node %

Simulation Results: Latency


• Working chain latency

– Only depends on path selected

– Chain protection tends to increase latency:VNF replication can result in higher spread of functions across DCs => higher hop count per chain

• Backup chain latency

– Requires simulating every link failure to determine worst-case value

– Slightly higher latency with hop protection:extra latency from rerouting around the ring between end nodes of failed hop

• Hybrid protection exhibits smoother fluctuations in working & backup latency

Working

Backup (worst-case)


Conclusions

• Metro networks with optical nodes co-located with DCs

• 3 mechanisms for VNF chains to survive link failures

– Hop, chain and hybrid protection

• ILP model to evaluate and compare the effectiveness of the 3 strategies

• Simulation results highlight the merits of hybrid protection

– Requires lowest number of transponders by selectively using VNF replication in cases where there are significant performance differences between working and backup paths…

– …effectively trading-off IT resources for transponders…

– ….and without compromising latency

Thank [email protected]

mailto:[email protected]


• Rational re-use of the existing fiber layout Often ring topologies interconnecting aggregation sites

One node interfaces with the core network

• Basic requirements Capacity: support very high BW towards the core

Flexibility: support reconfiguration of existing servicesin response to traffic dynamics and VNF re-optimization

Resiliency: services should survive failures while meetingtheir requirements with minimal resource overprovisioning

• Evaluate optical node architectures for Metro rings Broadcast-and-Select (B&S), i.e., ROADM node

Drop-and-Waste (D&W) , i.e., Filterless node

Fixed Filter, i.e. FOADM node

Motivation


Metro Transport Architectures

ROADM Node

1 … N

SC

Drop stage Add stage

1 … N

WSS

Flexible use/re-use of frequencies between different node pairs

Noise bandwidth filtered at each node

Easier upgrade to higher nodal degrees (i.e., from ring/chain to mesh)

WSS at the add stage increases cost

Susceptible to cascaded filtering penalties

Drop stage: power splitterAdd stage: low-port count pluggable WSS


SC

Drop stage

SC

Add stage

1 … N1 … N


Filterless Node

Lowest cost realization of add and drop stages

Not susceptible to cascaded filtering penalties (natively gridless)

Any frequency can be used between any node pair…

…but frequency re-use is not possible (each frequency used for a single node pair)

Core facing node still requires a WSS to avoid lasing loop

Drop stage: power splitterAdd stage: power combiner


FF FF

Drop stage Add stage

l1 l2 l3 l4 l1 l2 l3 l4


FOADM Node

Drop stage: fixed filterAdd stage: fixed filter

Low cost fixed filters at the add and drop stages

Frequency re-use by different node pairs is possible…

…but only according to the installed filter configurations

Colored ports further limit dynamic resource allocation

Requires reserving spectrum bands for hub-tributary and single-hop connections


• 1+1 protection at the optical layer

Every lightpath replicated in the opposite ring direction

Line-side protection enables to use the same transponderfor working/backup paths

• Impact in latency

Latency constraints are imposed on the working servicechain end-to-end

Additional latency due to failures evaluated as the highestlatency added over the whole chain given any single link failure

• Filterless nodes impose additional requirement Working/protection signals are split between the fiber pairs

Tx/Rx signals must use different frequencies to avoidinterference

Protection in Service Chains

VNF 1VNF 2

VNF 3

Source

Destination

Working

Protection

SC

Drop stage

SC

Add stage

1 … N1 … N

SC

Drop stage

SC

Add stage

1 … N1 … N

Tx Rx

Working

Protectionλ1 λ2

λ1 , λ2

λ2

λ2

λ1 , λ2


Simulation Results

Network Scenario

• Network topology and traffic Ring topology with 100 km and containing 5, 10 or 15 evenly spaced aggregation nodes

2.5 to 7.5 Tb/s of total traffic load, with varying shares of locally processed traffic (25-75%)

• Each scenario is re-optimized four times Changing traffic patterns and re-configuring VNF instantiation

• Channel formats and optical design Flex-rate interfaces with line rates between 100-600 Gb/s

Symbol rates between 32 and 64 Gbaud

Modulation formats between QPSK and 64-QAM

Full C-band (4.8 THz), flexible grid (12.5 GHz granularity)

Pre-amplifiers only deployed when attenuation exceeds 20dB

Reach estimation model for the different architectures accounts for filtering penalties, crosstalk levels and express losses


Simulation Results

Number of Transponders & Average Lightpath Spectral Efficiency

• Filterless viability hampered by (1) number of nodes, (2) total traffic load, (3) share of locally processed traffic

Any of which leads to faster spectrum exhaustion

• ROADM requires less transponders in the majority of cases, being the most robust architecture

• In some cases, FOADM and even Filterless benefit from slightly better optical performance than ROADM

More spectral efficient formats occasionally possible due to lower express losses and reduced filtering penalties

0

40

80

120

160

200

5 10 15 5 10 15 5 10 15 5 10 15 5 10 15 5 10 15

2.5 5.0 7.5 2.5 5.0 7.5

25% 75%

Tota

l Tra

nsp

on

der

Co

un

t

ROADM Filterless FOADM

OfferedLoad [Tb/s]% of Service-Chaining Traffic

Ring Nodes

0

2

4

6

8

5 10 15 5 10 15 5 10 15 5 10 15 5 10 15 5 10 15

2.5 5.0 7.5 2.5 5.0 7.5

25% 75%

Ave

rage

Lig

htp

ath

SE

[b/s

/Hz]

ROADM Filterless FOADM

% of Service-Chaining Traffic


Simulation Results

Latency

• Filterless and ROADM outperform FOADM with respect to latency performance

No clear advantage of one architecture over the other

• FOADM can introduce significantly more latency

Higher number of lightpath hops per chain, in order to escape connectivity restrictions imposed by the fixed filters

Further aggravated in case of single link failure

0

1

2

3

RO

AD

M

Filt

erle

ss

FOA

DM

RO

AD

M

Filt

erle

ss

FOA

DM

RO

AD

M

Filt

erle

ss

FOA

DM

RO

AD

M

Filt

erle

ss

FOA

DM

RO

AD

M

Filt

erle

ss

FOA

DM

RO

AD

M

Filt

erle

ss

FOA

DM

5 10 15 5 10 15

2.5 7.5

Late

ncy

[m

s]

PropagationO/E/OProtection

Offered Load [Tb/s] (25% service-chained traffic)Ring

Nodes


Evaluated the capacity and scalability of 3 possible Metro optical transport architectures for supporting 5G services with survivability constraints

– Coexistence of Metro-Core traffic with service chained traffic within the Metro network

– Vary network node count, total traffic load and share of service chained traffic

– Optimize VNF placement (IT resources) and transponder count (transport resources)

Conclusions

ROADM

Deployment “sweet spot”: small node count, highly dominant hub traffic (ill-suited when increasing the amount of IT resource sharing within the Metro network)

FOADM

Filterless

Most robust and scalable architecture: any network size, any traffic pattern, with possible upgrade of nodal degree (WSS still implies a premium)

Reasonably scalable but with substantial trade-offs: increase of transponder count and worst-case latency and demanding careful fixed frequency allocation

hybrid backup resource optimization for vnf placement over … · 2019-05-23 · »modulation...

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