Jukka Lehtniemi 25 March, 2008 Supervisor: Professor Jörg Ott Instructors: LicPhil Stefan Wiklund

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Protection concerns using Switched Ethernet as internal bus for a Telecommunication Network

ElementJukka Lehtniemi

25 March, 2008

Supervisor: Professor Jörg Ott

Instructors: LicPhil Stefan Wiklund

MSc Juha Eloranta

Top right corner for field-mark, customer or partner logotypes. See Best practice for example.

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Master's Thesis Presentation Jukka Lehtniemi 2008-03-252

Outline

Introduction Telecommunication Computer and AdvancedTCA Evolution of Ethernet Technology Spanning Tree Protocol Other Link Protection Technologies Network Element Topology Considerations Link Protection Solutions for Network Element Conclusions


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Introduction

Is a switched Ethernet based internal bus good enough solution in terms of link protection in a telecommunication network element?

Different link protection mechanisms available and the suitability for use as a telecommunication element internal bus

The network node architecture is assumed according to the AdvancedTCA specification

Literature study & comparison


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Telecommunication Computer Multiprocessor computing

cluster Variety of different

processors: general purpose processors, network processors, DSPs etc.

Variety of different network interfaces: TDM, ATM, Ethernet

Redundancy Modular board & subrack

architecture in a server cabinet

Resources connected together by internal (switched) bus

Boards

InterSubrackLink

Subrack

Backplane


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Advanced Telecommunication Computing Architecture Open hardware framework Specified by PCI Industrial Computer Manufacturers Group - a

consortium of over 450 hardware manufacturers Designed for reliability concerned applications Mechanical design, platform management, data transport etc. Flexible and loose specifications: profiled further by SCOPE

Alliance AdvancedTCA specifies two subrack level interconnection busses:

base interface and fabric interface. Ethernet is the selected technology for the base interface. It is

generally also seen as the most promising candidate for the fabric interface


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Ethernet Evolution: Shared Bus

Base-2Base-T

Repeater 1

Collision Domain


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Base-T

Switch 1 Switch 2

Ethernet Evolution: Switched Bus

Collision Domains

Full Duplex – CSMA/CD disabled

Base-T

Switch 1 Switch 2


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Ethernet Evolution

The Ethernet technology has evolved from a simple media sharing LAN solution to a versatile and diverse family of frame based computer networking technologies.

From the user protocol perspective it still provides a transparent and compatible frame transmission service

Key enhancements– Switching– Microsegmentation – Full Duplex– Flow Control– Virtual LANs – Connectivity Fault Management


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B3

B1

B6

B2

B5

B4

RootBridge

RP

RP

RP

RPRP

DP DP

DPDPDP

DP BP

DP

BP

DP

BP

DPBP

DP

BP

Spanning Tree Protocol Topology loops in a switched

Ethernet LAN will cause frame multiplication and thus they are unacceptable

The Spanning Tree Protocol (STP) operated by the switches will eliminate such loops by blocking redundant links in the physical topology and restricting the active topology to a simply and fully connected tree

STP provides topology recovery in the case of link failure. This can be used as a link protection solution


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Spanning Tree Protocol

STP propagates the topology information by continuous transmission of distance vectors

New protocol version called Rapid STP (RSTP) has been standardized

Proposal-agreement based communication of RSTP responds faster to topology changes

Multiple STP (MSTP) protocol defines per VLAN spanning trees


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Link Aggregation

Link Aggregation is defined by IEEE 802.3 Allows bundling multiple physical links to a single logical link Bandwidth extension Redundancy

Switch 1 Switch 2

Link Aggregate


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Resilient Packet Ring

RPR is specified by IEEE 802.17

Dual Ring topology Service priorities and fairness Topology discovery and

continuity check Healing strategies: Steering

and Wrapping 50 ms protection time against

link failure

SpanFailure

Update!

Update!

Update!

Update!

SteeringWrapping


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Ethernet Protection Switching

ITU-T Rec. G.8031 / Y.1342 Linear Protection Switching VLAN based Point-to-Point connections Failure detection by Ethernet CFM


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Ethernet Automatic Protection Switching By Extreame Networks Switched Ethernet, Ring topology One way transmission: primary port transmitting and

secondary port blocking Continuous health check polling by Master Node Recovery based on filtering database flush ordered by

Master Node and standard Ethernet address learning mechanisms


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AdvancedTCA Subrack

Two switch boards (per interface) Dual Star topology BASE-T specified, BASE-KX or BASE-KR likely in future 8 uplink/interconnect ports per switch board defined by SCOPE


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5 Subrack Topology: Bus & Ladder


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5 Subrack Topology: Star


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5 Subrack Topology: Full Mesh


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5 Subrack Topology: Ring


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Link Protection Solutions forMultisubrack AdvancedTCANetwork Element: Requirements

Primary requirement: < 50 ms protection switching time Manageable complexity Reasonable design, manufacturing and maintainance

costs


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Solutions

Link Aggregation Ethernet Protection Switching Ethernet Automatic Protection Switching Redundant Packet Ring Physically Distinct Switching Planes (Rapid) Spanning Tree

•Point-to-point: Too fine grained (complex) total solution

•Master Node is a single point of failure

•No guaranteed switch over time < 50 ms


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Recommended solutions: RPR

Guaranteed switch over time No need for protection switching

supervision clients on the boards: A board may transmit using either of the subrack bridges at any time

Extendibility: no practical restrictions on the amount of subracks to be connected to the ring interconnect

Equipment prices are presumable higher

Additional LAN technology layer and tunnelling of Ethernet frames on the ring


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Recommended solutions: Physically Distinct Switch Planes Pure Ethernet solution Prices of the equipment probably

lower Topology extension by number of

subracks in case of the redundant star topology may require additional interface boards in central subrack

Supervision and switch-over mechanism needs to be in place on each board


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Conclusions

Variety of link protection solutions for Ethernet exists Most of them do not meet the requirements for a

telecommunication network element Recommended solutions identified by the study:

– RPR interconnect – Construct of redundant, distinct, loopfree switching planes

Further analyzing of these alternatives with proper simulations or real hardware testing is suggested


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Jukka Lehtniemi 25 March, 2008 Supervisor: Professor Jörg Ott Instructors: LicPhil Stefan Wiklund

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