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

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. Outline. Introduction Telecommunication Computer and AdvancedTCA

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

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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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