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Network Element Link Protection Using Switched Ethernet in Telecommunication

Explore the use of switched Ethernet as an internal bus for link protection in telecommunication network elements. Learn about Ethernet evolution, spanning tree protocol, and other link protection technologies. Discuss network element topology considerations and available protection solutions.

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Network Element Link Protection Using Switched Ethernet in Telecommunication

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  1. Protection concerns using Switched Ethernet as internal bus for a Telecommunication Network Element Jukka Lehtniemi 25 March, 2008 Supervisor: Professor Jörg Ott Instructors: LicPhil Stefan Wiklund MSc Juha Eloranta

  2. 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

  3. 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

  4. Boards Backplane Inter Subrack Link Subrack 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

  5. 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

  6. Collision Domain Ethernet Evolution: Shared Bus

  7. Collision Domains Ethernet Evolution: Switched Bus Full Duplex – CSMA/CD disabled

  8. 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

  9. 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

  10. 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

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

  12. Steering Span Failure Update! Update! Update! Update! Resilient Packet Ring Wrapping • 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

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

  14. 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

  15. 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

  16. 5 Subrack Topology: Bus & Ladder

  17. 5 Subrack Topology: Star

  18. 5 Subrack Topology: Full Mesh

  19. 5 Subrack Topology: Ring

  20. Link Protection Solutions forMultisubrack AdvancedTCANetwork Element: Requirements • Primary requirement: < 50 ms protection switching time • Manageable complexity • Reasonable design, manufacturing and maintainance costs

  21. Solutions • Point-to-point: Too fine grained (complex) total solution • Link Aggregation • Ethernet Protection Switching • Ethernet Automatic Protection Switching • Redundant Packet Ring • Physically Distinct Switching Planes • (Rapid) Spanning Tree • Master Node is • a single point of failure • No guaranteed switch over time < 50 ms

  22. 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

  23. 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

  24. 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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