Beta and Epsilon Point Update Adam Healey Mark Marlett August 8, 2007 Contributors and Supporters • Dean Wallace, QLogic • Pravin Patel, IBM • Eric Kvamme, LSI • Tae-Kwang Jeon, LSI • Bill Fulmer, LSI • Max Olsen, LSI T11/07-399v1 2 Executive summary • Proposal defines the operation of 8.5 Gb/s Fibre Channel in the server blade environment • [Enhanced] TWDP-based transmitter device compliance methodology • [Enhanced] WDP-based receiver device signal tolerance input • Reference receiver with 1 feed-forward, 3 feedback taps • Comprehensive channel analysis, loss and jitter budgets presented to support proposed specifications • Relevant test procedures from SFF-8431, tailored to 8.5 Gb/s Fibre Channel applications, to be included in Annex A – Described in detail in companion document T11/07-398v1 • Additional detailed modifications to the FC-PI-4 draft also described in companion document T11/07-399v1 3 August 8, 2007 Updates • Corrected Epsilon point reference model • Added Beta point requirements to the specification tables • Introduced transmitter minimum output rise/fall times as a crosstalk control measure • Increased the VMA (min), which yielded a corresponding increase in T the minimum receiver VMA (min) R – Influences TWDP targets for the transmitter • Updated transmitter TWDP requirements to include an allowance for transmitter duty cycle distortion • Defined a new interference source for receiver signal tolerance test T11/07-399v1 4 Assumptions • Epsilon point specifications describe point-to-point links traversing a passive electrical backplane in a modular platform environment • The Epsilon point differs from the Beta point in that: – It considers only fabric topologies (not arbitrated loop) – It has more aggressive performance targets (links span longer distances, include more connectors, higher density, e.g. higher loss and crosstalk) – Blade server versus JBOD and RAID • It is desirable to leverage IEEE 802.3apTM-2007 (Backplane Ethernet) and OIF Common Electrical Interface – However, these are serdes (Alpha point) specifications – Work is required to project the methodologies and requirements to Epsilon point T11/07-399v1 5 Epsilon Point Reference Model ε ε T R Serdes Serdes ε ε R T Mezzanine card Switch Backplane Server blade • Links spans up to 33” of differential trace on FR-4 printed circuit boards with up to three connectors [1] – It is an objective to support up to 20 dB of loss, at 4.25 GHz, between ε and ε [2] T R • Interoperability points are the separable connectors closest to the serdes – A variety of connectors are currently employed at the mezzanine card and backplane interfaces, so a specific connector is not defined • The link is assumed to be AC-coupled (may be implemented in the serdes, or on the mezzanine/switch card) T11/07-399v1 6 Channel considerations – fitted attenuation Fitted Attenuation 0.00 -5.00 -10.00 ) B d -15.00 ( e d u -20.00 t i n g a -25.00 M -30.00 A(f ) = a +a f +a f +a f 2 0 1 2 3 -35.00 -40.00 0.000 1.000 2.000 3.000 4.000 5.000 6.000 7.000 Frequency (GHz) • The fitted attenuation, A( f ), is the least mean squares fit of the insertion loss, expressed in dB, to a polynomial function • The fit is limited to the frequency range DC to 6.375 GHz T11/07-399v1 7 Channel considerations – insertion loss deviation Insertion loss deviation 6.00 4.00 2.00 ) B d 0.00 ( ILD(1) e d u -2.00 ILD(2) t i n ILD(3) g a -4.00 M -6.00 -8.00 -10.00 0.000 1.000 2.000 3.000 4.000 5.000 6.000 7.000 Frequency (GHz) • Insertion loss deviation (ILD) is the error relative to the polynomial fit • ILD corresponds to tail ripple in the channel impulse response • The terminations presented by the transmitter and receiver devices will modify ILD T11/07-399v1 8 Channel considerations – step response Step response • A comparison of the step response 1 generated from the fitted attenuation 0.9 and the original step response 0.8 illustrates the impact of ILD 0.7 • Much of ripple in the step response UI)0.6 can not be compensated by the e ( ud0.5 reference receiver, e.g. more than 3 plit m0.4 UI away A 0.3 • Such ripple is empirical in nature, e.g. variation in the path delay alters 0.2 TCTF(1) the arrival time of reflections and 0.1 TCTF(2) impacts the performance TCTF(3) 0 0 5 10 15 20 • Stressors will be based on the fitted Time (UI) attenuation and the impact of ILD will be rendered as a term in the loss budget T11/07-399v1 9 Channel Considerations – crosstalk -3 Step response • Examination of the crosstalk step x 10 4 FEXT (high loss) responses reveal resonances that FEXT (low loss) 3 NEXT span 10’s of symbols • Since the crosstalk is the weighted 2 sum of many symbol amplitudes, it 1 V) tends toward a Gaussian distribution e ( d u 0 • The addition of more aggressors plit m reinforces this trend A-1 -2 -3 -4 0 10 20 30 40 50 60 Time (UI) T11/07-399v1 10