Simple Link Protocol (SLP)

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1 Simple ink Protocol (SP) zero-overhead packet delineation for 10Gb thernet N-PHY lbuquerque meeting March 6-10, 2000 Kamran zadet, ei-lei Song, om ruman, Mark Yu Paul Bottorff, Norival Figueira, avid Martin... Fred Weniger. Vitesse om Palkert... MCC Jim Yokouchi.Sumitomo on arson riquint ucent echnologies Nortel Networks 1

2 Goals For packet-delineation & line coding scheme (PCS) Zero overhead No packet length required No rate conversion required (10.000Gb/s and GBaud) Serial- and WM-PM agnostic N friendly - simple and low cost Suitable for other non-ethernet packet-based protocols For chip-to-chip interconnect (XU) M mitigation No code conversion required Can work with 8b/10b H or SUP 2

3 3 Key Concepts for SP Standard thernet frames have sufficient information to find packet/byte boundaries Control characters are embedded in nter-packet Gap (PG) ncoding: zero-overhead scrambling ata payload is scrambled bit serialization of thernet packets Control characters: M-reducing scrambling or C-balanced control chars ata Control ata Control O P SYNCHONZON PN O P S O P

4 SP Frame elineation PHY state machine tracks context : {HUN,, CONO} HUN state: unsynchronized, looking for repeated characters Start of Packet ook for SOP byte When found, enter mode ook for frame termination pattern Frame termination pattern: (-FG) ook for {OP, 11 x } nter CONO state ll bytes are control characters until SOP is found etection of error packet (-FG) : rop current packet and nter CONO state 4

5 etection of control sequences here are 2 critical control sequences, each at least 12-byte long nd of normal packet: -FG nd of error packet: -FG Occurrence of these flags inside payload is once every 2,000 billion years (match over 12Bytes is very unlikely) f the end-of-packet sequence, the -FG, is found inside payload (not a lucky day!) ransmitter generates -FG Packet is re-transmitted with a different scrambler state llowing up to 3-bit mismatches for detection of the control sequences to increase the likelihood of matching patterns 5

6 What about false match? Pattern matching with 3 bit error tolerance means = difference between two words is less than 3 bits ikelihood of matching patterns with 3 bit error tolerance is greater than with no error tolerance, but still extremely small Probability of false match: ~ once every 15 million years (see supporting calculations in full presentation) 6

7 Calculating Probability of False Match Chance that a 96-bit segment matches desired pattern B to within 2 bits Pr X = i Bi 3 = * i= = Number of 96-bit patterns per year (@10Gbit/s) = bit/s x 1/8 bits x (3600x24x365) s / year ; 4x10 16 / year hus, frequency of false match is once every 15 million years 7

8 Scrambling Scheme Payload Control Payload Control x x 7 + x Similar to scrambling scheme used in SON (proposed by Bottorff, Martin & Figueira) x is self-synchronous x 7 + x is periodically synchronized ual scrambler nner scrambler prevents malicious attack Outer scrambler defines spectral characteristics Scrambling improves M characteristics 8

Pattern Spectral Measurements at lane ate 10-20 db improvement for scrambling

9 Pattern Spectral Measurements at lane ate db improvement for scrambling relative to 8b/10b Green: PBS @ 2.5gbit/sec ed: ed: 3.125gbit/sec 9

Pattern Spectral Measurements at ine ate Green: PBS 2 7 7-1

10 Pattern Spectral Measurements at ine ate Green: PBS @ Gb/s Gb/s ed: ed: Gb/s Gb/s 10

11 Control characters S: SOP : OP : rror : dle B: Busy dle 4 bit Hamming distance => 1 bit error correction, or 3bit error detection Can have up to 16 control codes with 4b Hamming distance plenty of spares 11

12 Code for Control Characters he following extended Hamming (8,4) code can be used for representing up to 16 control characters: ( , ), ( , ), ( , ), ( , ), ( , ), ( , ), ( , ), ( , ), ( , ), ( , ), ( , ), ( , ), ( , ), ( , ), ( , ), ( , ). Property: -- minimum Hamming distance of 4 he first 14 code words are C-balanced, hence can be used directly for systems without scrambler 12

13 oss of Synchronization oss of synchronization occurs when: PHY control state machine in mode and no PG after timeout period imeout period can be chosen as maximum frame length ( bytes) for thernet For non-thernet applications, other timeout period can be used (e.g., 8 Kbytes) Synchronization is achieved immediately at the next PG (provided that optical link is up) No handshaking required between ransmitter & eceiver Synchronization time < maximum packet length 13

14 pplication of SP to PCS/PM nterface 16-bit Parallel (625MHz) nterface of choice for serial PM 16 bit interface is formed by grouping two bytes at XGM Phase ambiguity in serial PM results in constant bit offset between mux & demux easily resolved by searching for -FG using sliding window to find byte-sync Scrambled 4-bit Serial (2.5GBaud / lane) SP could also be used for transmission over 4-channel WWM esults in 25% lower Baud-rate for only 2.5% penalty due to C wander ach of the 4 bytes of the encoder is directly sent serially on four lanes eskewing can be done using GN control code periodically embedded in PG 14

15 Summary of Simple ink Protocol Zero overhead ( GBaud) No rate conversion, gear box, or elastic buffers SOP is not restricted to ane 0: no impact on PG irect mapping of thernet (N friendly) ata rate does not decrease to 9.29Gb/s (as for 64b/66b) Preserves byte boundaries (WN friendly) Suitable for both serial and WM ow latency (could be used in serial nfiniband) Scrambling allows C balance and is good for M Best performance, at lowest baud-rate Can work with or without H (as serial /O) 15

emonstration System 16-bit VS @ 622 MHz interface into Opto module < 20k gates

16 emonstration System 16-bit 622 MHz interface into Opto module < 20k gates (~3% of FPG logic resources) VH code will be made available to SP supporters 16

17 Bell aboratories Back-up slides 17

18 18 Case of ransmit rror / bort Support of cut-through packet switching rror can occur inside the payload: when error occurs terminate packet, then: insert at least 4 error symbols (desirable in some applications) X SQUNC XGM S O P O P S O P O P PCS OUPU SQUNC

19 Pattern Spectral Measurements ata Pattern 1megabit in length using PBS 8B10B Pattern 8B10B ncode ata Pattern Scrambled Pattern Scrambled ata Pattern based on proposed X^58+X^19+1 Sequence 19

20 Pattern Spectral Measurements est setup used in spectral measurements Pattern Generator coax Spectrum nalyzer Clock Source 20

21 PCS latency ess than XGM clock latency at encoder (direct mapping of XGM) 3 XGM clock cycles at the decoder to detect OP (12Bytes) can be reduced by using less than 12Bytes to detect OP ex: when using 8Bytes pattern matching, latency can be reduced to 2 cycles Probability of false match with 8bytes and 1b error tolerance is 3.52 x10-18 False match over 8bytes with 1b error tolerance occurs ~ once a year n the conservative case (12Bytes) latency is 16 Byte times total PCS latency is = 12.8ns 21

22 Scrambler synchronization uring loss of sync or initialization enter HUN mode ook for sequence of repeated characters Output of descrambled s should give a long chain of 000. nitially open the loop of the side-stream descrambler, and after observing N zeros, enable sync bit (then close the loop of the descrambling shift register) 100BS-X uses a similar scheme... x6 x 7 + sync... x6 x Sync detect sync 22

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