PMD Burst Mode Dynamic Performance Requirement

Transcription

1 PMD Burst Mode Dynamic Performance Requirement List of Supporters: Eyal Shraga Frank Effenberger Glen Koziuk Hernando Valencia Meir Bartur Raanan Ivry Rob Carlisle Ron Rundquist Tony Anderson Walt Soto Wenjia Wang Yusuke Ota 10/15/2001 EFM Los Angeles October 17-19th 1

2 Outline What is Burst Mode? Definition of relevant Burst Mode Terms Optical Extinction Ratio Optical Off-State Power Optical Dynamic Range Benefit of Burst Mode (BM)? Why do we need short Burst? Upstream Burst Efficiency Tradeoff Assumptions & Definitions Burst Efficiency as a function of transmission burst size PMD Upstream Dynamics for OLT Rx Path Upstream Guard Time Requirement Upstream Delimiter Requirement Upstream Overhead Byte Requirement PMD P2MP System CDR Synchronization 10/15/2001 EFM Los Angeles October 17-19th 2

3 PMD s Burst Mode Analog ICs What is Burst Mode? P2MP PONs employ short bursts of data packets upstream instead of continuous data packets used in Continuous Mode (CM) P2P applications. Hence the term Burst Mode (BM). Typical Headend Typical Client GMII MDIO OLT 1.25Gbps PON-PHY Digital IC PECL OLT Transceiver TxRx Module Bidi BM CDR CM LD BM LA Laser Diode WDM BM TIA Photo Diode ONU/T Transceiver TxRx Module Bidi Photo Diode WDM CM TIA Laser Diode CM LA BM LD CM CDR PECL ONU/T 1.25Gbps PON-PHY Digital IC GMII MDIO OLT s Burst Mode Guard Time Constraint Dynamics occurs here and affected by ONU/T s laser on/off performance. <20km Point-to-Multipoint w/ Passive Splitters enabling <32 End Users Key: CDR - Clock & Data Recovery LA - Limiting Amp TIA - Transimpedance Amp LD - Laser Driver 10/15/2001 EFM Los Angeles October 17-19th 3

4 What is ER & Off-State Power? ER refers to the Extinction Ratio, which is the ratio of Optical Power transmitted by ONU for logic one & zero levels during an upstream packet burst. (ER > 10dB per ITU-T G.983.1) Off-State Power refers to how much the ONU is polluting Upstream when Laser is powered off. (Off-State Power < -45dBm) ER & Off-State Power numbers as seen by OLT. ER=10Log(P L1 /P L0 ) 10/15/2001 EFM Los Angeles October 17-19th 4

5 Why do we care about ER & Off-State Power? Helps to define performance for transition region between burst. Tradeoffs are captured within Guard Time bits fields. Upstream aggregated throughput performance impacted. 10/15/2001 EFM Los Angeles October 17-19th 5

6 What is the PMD s Optical System Dynamic Range? Dynamic Rage is related to ratio of Strongest to Weakest Optical Signal seen by OLT. 10Log(Strong/Weak) = System Dynamic Range > 23dB example. Strong Weak 10/15/2001 EFM Los Angeles October 17-19th 6

7 PMD s Burst Mode Benefits Why we need Burst Mode? Improves the efficiency of PON s upstream data bit stream. Cost comparable with Continuous Mode (CM) ICs Saves ONU power by allowing ONU to power off TX path. Typical saving range between 50% to 90% compared to CM. What are the Dynamic relationships within BM ICs? Clock synchronization and clock recovery. Proper delineation of received data called Delimiter. Time between data packets is called Guard time. Guard time is strongly dependent on Power Ratio of back-toback data packet bursts. Photodiodes can be designed to minimize residual carrier effects without adding cost Doping or masking the fringing field solves this problem 10/15/2001 EFM Los Angeles October 17-19th 7

8 Upstream Burst Efficiency Typical Bit-Stream Usage: Upstream (US) transmission burst is divided into slots, Each ONU/T is granted a group of consecutive slots for US burst of data, Each ONT transmission burst is lead by the Overhead Bytes. Small slot size enables high US grant granularity and is desirable for overall US throughput efficiency. Most US bursts are relatively small due to nature of access networks (Examples are small 64 byte US Ethernet packets ACK s for DS data). ONT K Transmission Burst (Burst_size) ONT L Transmission Burst OLT RX n n+1 n+2 n+3 n+4 n+5 m m+1 m+2 m+3 _size Burst Overhead Control Header Upstream Payload Overhead 10/15/2001 EFM Los Angeles October 17-19th 8

9 Upstream Burst Efficiency Equation Based on 3 variables: _count, _size & Overhead. _count is data dependent, but the Overhead to _size ratio R, can be bounded to a small set of values. We cannot find the optimal Overhead or _size, but graphing Efficiency based on several carefully chosen values for R should yield some insight. US Burst Efficiency Equation Efficiency = Burst_size - Overhead Burst_size (1) Since Burst_size = _count * _size Efficiency = _count * _size - Overhead _count * _size (2) Rearrange Efficiency = Overhead _count - _size _count (3) Let SC = _count and R = Overhead _size Efficiency = SC - R SC (4) 10/15/2001 EFM Los Angeles October 17-19th 9

10 From EFM s July Meeting in Portland, we can see the US Packet Distribution. Downstream Upstream ~45% of US Packets are very small (ACKs for Ethernet DS packets) 10/15/2001 EFM Los Angeles October 17-19th 10

11 Upstream Burst Efficiency Results Efficiency US Burst Utilization > 90% efficiency & small bursts Log10(SC) R=0.1 R=0.25 R=0.5 R=1 R=2 R=5 R=10 Plot of Burst Efficiency for several reasonable R value (Overhead/_Size) Results Assumptions: 1. Upstream bursts tend to be small in size with typical _Count < > 90% efficiency desired. Graph suggests R 0.5 Scenario Example If ~45% of US packets are ~64bytes, then to obtain ~94% efficiency: Burst_Size = 72 bytes, _Count = 9 & _size = 8, means Overhead 4 bytes Conclusion Hence small Sizes are desirable, and Overhead should also be small. 10/15/2001 EFM Los Angeles October 17-19th 11

12 Guard Time Dynamics Guard Time Constraints are: Strongly dependent on both Optical Power P1 and P1/P2 Strong to weak Optical Power (>23dB dynamic range) Independent of the bit rate. When P1/P2 < 3db, Guard Time 0(regardless of P1) P is the Optical Power of each Packet P1/P2 is the Ratio of the Optical Power Tmin is called the Guard Time between packets and is the minimum packet spacing required to properly recover the first bit in the second packet Definition of Guard Time Dynamic Terms Example 1.25G Burst Mode Rx Path Trace Diagram 10/15/2001 EFM Los Angeles October 17-19th 12

13 Why do we need Delimiter or Preamble? Start of each Upstream Burst Packet must include known pattern to recover both clock and data correctly, which are referred to as Delimiter & Preamble bits. Delimiter bits are used to delineate the start of a valid burst. Preamble bits are used for phase locking and may not be required. Bit values for Delimiter & Preamble bits vary per implementation and are captured within ITU-T G Overhead Bytes field. > Definition of Guard Time Dynamic Terms 10/15/2001 EFM Los Angeles October 17-19th 13

14 PMD Upstream Overhead Byte Requirement Overhead Bytes are used at the beginning of every packet burst. ITU-T G Defines: Overhead Bytes (OH) = Guard Time + Preamble + Delimiter = 3 bytes 1.25G Prototypes show 3 Bytes of Overhead is possible. RESET signal prior to packet acquisition provided by OLT PHY is implementation specific. Example Lab Trace for 1.25Gbps CDR 10/15/2001 EFM Los Angeles October 17-19th 14

15 System CDR Synchronization Clock and Data Recovery (CDR) performed using bits within the Overhead Byte field. First n-bits may be lost in this process ONU CDR synchronizes frequency/phase and bit alignment to the continuos downstream data from OLT. OLT BM CDR reacquires lock, phase and bit alignment between each upstream burst (i.e. new phase acquired for each burst.). 10/15/2001 EFM Los Angeles October 17-19th 15

16 System CDR Synchronization Upstream transfer clock is derived from Downstream transfer, which means PON system synchronized to OLT transmitter. OLT PON IC (MAC) XTL DATA DATA D M U X Headend CMU BM CDR M U X BM TIA BM LA CM LD BM LD CM TIA CM LA PON splitter not shown M U X CM CDR CMU D M U X Client DATA DATA Sync CLK ONU/T PON IC (MAC) 10/15/2001 EFM Los Angeles October 17-19th 16

17 Thank You 10/15/2001 EFM Los Angeles October 17-19th 17