BUDAPEST UNIVERSITY OF TECHNOLOGY AND ECONOMICS DEPARTMENT OF TELECOMMUNICATIONS AND MEDIA...

BUDAPEST UNIVERSITY OF TECHNOLOGY AND ECONOMICSDEPARTMENT OF TELECOMMUNICATIONS AND MEDIA INFORMATICS


TRAFFIC-DRIVEN OPTIMIZATION OF ROUTING FOR METROPOLITAN ETHERNET NETWORKS

András Kern, Tibor Cinkler, István Moldován

World Telecommunications Congress 2006 2

BME - TMIT BUDAPEST UNIVERSITY OF TECHNOLOGY AND ECONOMICSDEPARTMENT OF TELECOMMUNICATIONS AND MEDIA INFORMATICS

» Ethernet is the most dominating LAN technology» Cheap equipment + high speed (up to 10 Gbps)

Ethernet in Metro Access Networks

Switch Edge nodeAccess Multiplexer Switch SwitchSwitch

Metro Core

RS CS TR RD TD CDTALK / DATA

TALK

CableModem1 2 3

4 5 6

7 8 9

* 8 #

Metro Access

First MileHome Network CoreMetro Network

» Introduce Ethernet into the Metro network (Metro Ethernet Forum): » consistent network platform

» Ethernet should be Carrier Grade:» Traffic separation» QoS» Operation, Administration Management» Reliability» Scalability



Routing in Ethernet: Spanning Trees Protocols (STP)

» MORE VLAN based spanning trees» Multiple spanning tree

instances» Each tree runs a separate

Rapid STP instance» 1 VLAN 1 tree

Bridge D

Bridge A

Bridge B

Bridge

Bridge

Bridge

Bridge

Bridge

Bridge C

Root II.Root I.

» By default tree spanning is “Topology-Driven”:» Port costs based on topology and link capacities

» Costs can be set manually (to obtain desired trees)

» Spanning Trees form loop-free logical topologies » Their shape influenced by Port Costs» Provide restoration



Resilience

» MSTP supports restoration» Does NOT consider either QoS or bandwidth reqs. may

harm them.

» Protection at Ethernet level

» Ethernet Protection Switch (EPS)

» VLAN switching » 2 VLANs: one for working one for backup » After link failure switch to backup VLAN» Supports QoS and bandwidth reqs.!!!!



Quality of Service

» Priority based scheduling:» Lower priority traffic is not served until there is higher priority

traffic in the queue.

» To ensure low delay for each QoS class:amount of higher priority traffic should be limited for each link

» For each QoS class » Global» Static» Predefined

limit is given.

» The method of how to determine these limits is out of scope.



Traffic Driven Optimization Method



Traffic Driven Optimization of Metro Ethernet

» Layer 2 TE» optimal network utilization, allowing high bandwidth but no

protection, » good throughput with dedicated protection switching

» To reach it:» Span more tree instances, and » Assign the VLANs (traffic demands) to these trees

» Optimization aim is to:» Minimize the network usage to maximize the throughput while» Neither QoS nor bandwidth are violated

» We proposed ILP based method to solve this problem



Resilience in Traffic Driven Metro Ethernet

» Alternatives:» Counting on the repairing capability of RSTP

» Protection based on VLAN switching» Two link disjoint VLANs for each demands» same capacity is dedicated at both VLANs

» Only prioritized traffic is protected with VLAN switching» Backup capacity is dedicated for them» It can be shared with BE traffic!



Performance of Traffic Driven Optimization



Assumed Topology

» The traffic flows from the ANs to the ENs» Root of Tree instances at ENs.

Core

Aggregation

EN EN

AN

AN AN AN

AN

AN

ANAggregation

TrafficSource

TrafficDestinatio

n



Traffic model

» 3 QoS + 1 best effort traffic class.» Between every access-edge node pair one aggregated

demand for each TC» Throughput estimator parameter (Global traffic level)

Class name Traffic Class Ratio

Platinum 3%

Gold 13%

Silver 30%

BE 54%

Demand sizes are based on:» Traffic Class Ratio» Global Traffic Level



Achieved Throughput

1,257679251,1991485

0,44973883 0,59942125

0

0,5

1

1,5

2

2,5

3

3,5

4

4,5

Spanning Tree Protocol Multiple Spanning TreeProtocol

MSTP optimizing MSTP opt with two treesper roots

Methods

Rel

ativ

e G

amm

a

0

1

2

3

4

5

6

7

8

9

10

Use

d C

apac

ity

[Gb

ps]

Relative Gamma Used Capacity

The throughput significantly increased! But why?



Balancing the trees

AN

EN EN

AN

AN AN AN

AN

AN

AN

AN

EN EN

AN

AN AN AN

AN

AN

AN

Topology Driven MSTP Optimized Tree instance

Bottleneck!!!



Resilience

» Topology driven:» 100% resilience» Low throughput

» Optimizing MSTP:» Using redundant links» Higher throughput but

lower resilience» VLAN protection:

» Decreased throughput» Higher resilience

0

50000

100000

150000

200000

250000

300000

350000

400000

450000

Selective Full MSTPopt MSTP STP

VLAN Switching (MSTPopt) RSTP Restoration

Av

ail

ab

le T

hro

ug

hp

ut

in K

bp

s

Achievable Throughput Throughput after link failure [Worst Case]



Conclusion

» QoS + Protection + TE » Can be realized using MSTP» But tree optimization is required

» We presented an ILP model for» Optimization» QoS, capacity and protection constraints are fulfilled

» Significantly increased throughput is realized

» RSTP Restoration does not consider

» VLAN switch based protection is proposed» Halves the throughput but considers QoS!

» Selective protection is proposed» Tradeoff between throughput and protection



Thank You

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