1st International Workshop on Community Networks and FTTH/P/x Importance of last mile interoperability Eric Lynskey October 16, 2003
Outline Conformance and interoperability Ethernet experiences Ethernet in the First Mile strategies Conclusions
What is conformance? Implement all mandatory portions of a standard IEEE 802.3 shall and shall not mandatory should and should not recommendations may and may not options State diagrams and associated variables, functions, etc Protocol Implementation Conformance Statement (PICS)
Verification of conformance PICS and spec. sheets Not a guarantee of conformance Spec sheet Independent testing Independent report Third party independent testing Testing before and after system integration Agreed upon test methodologies
Test methodologies Different test tools provide different answers Oscilloscopes, network analyzers, power meters Accuracy and repeatability of equipment Testing algorithms can vary between vendors More than one way to make a measurement Possible solution is to strictly define: Test boards (probing problem) Minimum requirements for test equipment Test conditions
What is interoperability? Two or more devices can establish, maintain, and tear down a connection under a given set of conditions while maintaining a certain level of performance. Interoperability at different layers Protocol Physical Common and agreed upon set of guidelines
10 GbE interoperability 10 Gigabit Attachment Unit Interface (XAUI) 4 lanes at 3.125 Gb/s with 8B/10B encoding Up to 50cm on standard FR-4 PCB Development of XAUI interoperability document Joint effort between 10GEA and UNH IOL Defined test channel, traffic, pass/fail condition Basis for technical feasibility study of XAUI Industry standard methodology for proof of interoperability
Verification of interoperability Public demonstrations Trade shows, conferences Private demonstrations Corporate laboratories, potential customers Third party independent testing Full and partial mesh interoperability Plugfests
Interoperability and conformance Standard defines interfaces and behaviors Must conform to these requirements Not always clear what standards meant to say Necessary to understand the importance of what standards do not say Multiple implementations can and will exist Different interpretations of standard Similar interpretations but different implementations Interoperability is related to both the standard and its implementation
Conformance Interoperability Conform to multiple options EPON forward error correction XAUI channel definition System vs. component conformance Conformant components can be integrated into nonconformant systems, thus creating interoperability problems Different features may not be interoperable
Interoperability Conformance Multiple devices wrongly implement same feature Not all mandatory features affect interoperability Do all mandatory parts of standard need to be treated equally?
Options inhibit interoperability Certain options are only useful if both ends of the link support it Flow control, FEC Users must be aware of options in order to take advantage of them An increase in options leads to an increase in implementations, and therefore an increase in interoperability problems
Standards not the final answer Standards don t define everything DBA, security, QoS Standards don t always specify how/what to test Documented and agreed upon test metrics are necessary for agreed upon conditions for claims of interoperability and conformance Industry needs to pull together to create this documentation
Why do we need it? A one word description of Ethernet is simple Interoperability has contributed to the success of Ethernet As Ethernet moves into the access space, this trend of simplicity and interoperability must continue for the technology to be successful
How do we get it? Clearly document test plans that have achieved industry acceptance Test, test, and test again Publicly demonstrate real interoperability and conformance Walk into Best Buy, buy an EFM modem, plug it in, and it works!
Gigabit Ethernet example Borrowed heavily from Fibre Channel Defined new Auto-Negotiation protocol Handshaking protocol to determine HCD link Minor modifications to existing MAC (FD only) Conformance and interoperability issues
Gigabit Ethernet conformance Observed interoperability problem On average, packet loss between two devices transmitting randomly sized frames over low attenuation optical channel approaches 50% Cause is a conformance problem Preamble defined as 7 bytes transmitted by the MAC PCS allows for reduction of preamble to 6 bytes Some devices do not accept 6 bytes of preamble
Interoperability case study 25 Gigabit Ethernet Interoperability failures Percent failures 20 15 10 5 0 Dec-97 Apr-98 Aug-98 Dec-98 Apr-99 Aug-99 Dec-99 Apr-00 Aug-00 Time Dec-00 Apr-01 Aug-01 Dec-01 Apr-02
EFM Example Borrowing heavily from existing Ethernets PCS, MAC, MAC Control New single fiber solutions New MPCP sublayer Requires (de)registration, GATE and REPORT, timing New OAM sublayer Requires handshaking New forward error correction New Reconciliation Sublayer (preamble)
EFM preamble modifications 55 55 SPD 55 55 LLID LLID CRC8 Preamble DA SA Length/ Type Data/Pad FCS 8-bytes 6-bytes 6-bytes 2-bytes 46-1500 bytes 4-bytes
EPON Conformance test tool PC or equivalent Programmable hardware and test equipment Database of Results Report Generator User-defined test scripts Processing Engine Transmit Emulator Intelligent Analysis Complex Triggering Capability Receive Emulator Device Under Test
EPON Conformance test tool 2 OLT Functions Test vector generator Out to DUT OAM/ MAC Client MAC Functions 8B/10B Encoder 10B/8B Decoder FEC 8B/10B Encoder SERDES/ PMD ONU Functions FEC block (optional)
EFM OAM Interoperability Frame based protocol Optical channel not really an issue Potential issues Discovery process Critical events Vendor extensions
EFM P2P Interoperability Auto-Negotiation DONE MAC, PCS, MAC Control, RS DONE Potential issues Distance Temperature Single fiber Need to define interoperability channel
EFM EPON Interoperability MPCP Registration of ONU onto EPON P2P Emulation GATE and REPORT messages Optical channel Single fiber Lengths, number of splits Topology (tree, bus, hybrid) FEC for operating at high BER with MPN penalty
Conclusions EFM community has a lot of work to do even after the standard is complete Prove the unproven technologies defined by EFM Develop test methodologies for interoperability Document what is not written in the standard Test Development of interoperability group Where is it placed Combine multiple technologies (EPON, GPON )