Time Synchronization Over Ethernet Passive Optical Networks

Home , OLT (mobile network), Passive optical network

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ACCEPTED FROM OPEN CALL Time Synchronization over Ethernet Passive Optical Networks

Yuanqiu Luo and Frank J. Effenberger, Huawei Technologies Nirwan Ansari, New Jersey Institute of Technology

ABSTRACT of the emerging applications of fiber optical access. As exemplified in Fig. 1, ONUs can Time synchronization is critical when using either connect to or collocate with base stations Ethernet passive optical networks as a mobile (BSs). The prime motivations of this application backhaul to support time-sensitive services. This include cost saving on backhaul facilities, and article presents an overview of time synchroniza- extended reach and coverage of mobile access tion methods over EPON. It outlines the require- networks. The shared fiber infrastructure of ments and challenges particular to the EPON EPON facilitates the aggregation of multiple link delay asymmetry, and presents the technical BSs to the radio network controller (RNC) in solution recently approved by IEEE. Perfor- the CO. When existing BSs are located in the mance analysis and prototype results demon- areas served with an EPON system, it is highly strate that this technical solution meets various efficient to share the same fiber optical access time synchronization requirements. The article infrastructure with mobile backhaul networks. then reviews the major standard efforts on When there are remote BSs in a wireless net- EPON time synchronization that employ this work, the EPON systems are able to connect solution, IEEE Std 802.1AS™-2011 Clause 13. them to the CO by just extending some of the With this standard in place, EPON can play its distribution fibers. This eliminates the require- part in time distribution networks. ment and effort of deploying a separate fiber network dedicated to mobile backhaul purposes. INTRODUCTION Time synchronization (i.e., distribution of the absolute time, both frequency and phase) is a An Ethernet passive optical network (EPON) crucial issue of using EPON as mobile backhaul. provides broadband access with a shared-fiber Wireless technologies require precise time infor- infrastructure and a maintenance-free optical mation to support various functions. Ordinary distribution network (ODN). As shown in Fig. 1, EPON cannot provide the time synchronization a typical EPON system has an optical reach of service. Therefore, a proper solution is highly about 20 km. The central office (CO) endpoint desired to enable the provisioning of mobile ser- is the optical line terminal (OLT), and the sub- vices over EPON. scriber endpoints are the optical network units This article focuses on the issue of time syn- (ONUs). The OLT is connected to a passive chronization over EPON. We review the time optical splitter by a single feeder fiber. The pas- synchronization requirements of various wireless sive optical splitter fans out signals via multiple technologies, and present the key challenges of distribution fibers to the subscribers. Other than synchronizing time over EPON. We explore the the OLT and ONUs, there are no active ele- technical solution and analyze its achieved per- ments in the EPON system. This enables low formance. We demonstrate a prototype system capital and operational expenditures for high- and report its performance results. Relative speed full-service access. standard trends and efforts are also presented to The IEEE 802.3™-2008 standard [1] specifies conclude this article. the EPON physical layer, data link layer, and other related techniques. EPON features gigabit- level access rates (e.g., 1 Gb/s symmetrical rates). EPON AS MOBILE BACKHAUL: Time-division multiplexing (TDM) and time- REQUIREMENTS AND CHALLENGES division multiple access (TDMA) are employed in the downstream (i.e., from the OLT to the TIME SYNCHRONIZATION REQUIREMENTS OF ONUs) and upstream (i.e., from the ONUs to MOBILE BACKHAUL the OLT), respectively [2, 3]. The EPON system uses a 1490 nm wavelength for the downstream One of the most basic features of wireless is sup- transmission and the wavelength centered in porting mobility. This requires coordinated 1310 nm for the upstream transmission. handoff when a user moves from one BS to the Employing EPON as mobile backhaul is one next. To make the handoff as smooth and loss-

less as possible, precise time information is required to be distributed among a wireless network. Moreover, additional physical layer techniques such as geolocation require exact time OLT Passive optical synchronization to produce accurate results. splitter ONU From the service perspective, when a mobile user accesses the network while he/she is roam- ONU ing among the areas covered by different BSs, the precise time information helps synchronize Central office the services received by the mobile user [4]. Remote node ONU The time synchronization requirements of several typical wireless technologies are listed in Table 1. Time accuracy in microseconds is required for the majority of these wireless net- User premise works. It should be noted that this is the endpoint requirement, and the access network would Figure 1. Ethernet passive optical network (EPON). use only a fraction of this amount. Therefore, a useful time distribution system over EPON should target an inaccuracy of hundreds of nanoseconds. Wireless technology Time requirement

EPON TIME SYNCHRONIZATION CHALLENGES CDMA2000 3 ms A common approach to transporting time would be to use IEEE 1588™-2008 [6] over EPON. TD-SCDMA 3 ms IEEE 1588™-2008 defines the precision time protocol (PTP) for synchronizing clocks connect- WiMAX TDD 1 ms ed via a packet network. When applying IEEE 1588™-2008 to an EPON system, the time infor- WCDMA (UMTS) TDD 2.5 ms mation is encapsulated into EPON data packets (i.e., either Ethernet frames in EPON). The LTE From 1 ms to 50 ms EPON system distributes those packets in the same way as user data. Table 1. Time synchronization requirements of Unfortunately, this mechanism cannot meet wireless technologies [5]. the mobile backhaul time synchronization requirements. A key assumption of IEEE 1588™- 2008 is link delay symmetry between upstream TIME SYNCHRONIZATION OVER and downstream channels. When calculating the one-way delay from a master clock to a slave EPONS clock, IEEE 1588™-2008 assumes such delay is LOCAL COUNTERS AND equal to that of the reverse link, which is from ROUND-TRIP TIME the slave clock to the master clock. Without the link delay symmetry assumption, IEEE 1588™- While EPON has a special problem of delay 2008 is unable to distribute precise time infor- asymmetry, it also has the special capability of mation. very exact delay measurement. This comes from Such assumption of link delay symmetry, the use of TDMA in the upstream, which however, does not hold in EPON. In EPON, requires very accurately synchronized time. TDM and TDMA are adopted in the down- In an EPON system, both the OLT and stream and upstream for data transmission, ONUs have a local counter. It is represented by respectively. This implies that the upstream 32 bits, and increases by 1 every 16 ns. The delay is different from that of the downstream. EPON Multipoint Control Protocol (MPCP) A typical upstream TDMA cycle is on the order copies the local counter value into the time- of milliseconds; thus, an upstream IEEE 1588™- stamp field of MPCP messages when such mes- 2008 packet can possibly be delayed by millisec- sages are generated in the medium access control onds when the upstream channel is loaded with (MAC) control sublayer (Fig. 2a). The MPCP user data. In contrast, the downstream channel messages enable EPON control functionalities exhibits much lower queuing delays (typically on such as round-trip time (RTT) measurement, the order of microseconds). Moreover, different ONU registration, ranging, and ONU deregistra- wavelengths are used downstream and upstream, tion [1]. and the light propagation delays are asymmetric. Whenever an ONU receives an MPCP mes- Such delay asymmetries impair the time accura- sage from the OLT, the ONU resets its local cy by introducing up to millisecond-scale delay counter by using the timestamp value in the differences. Even worse, the time errors would received MPCP message. In this way, the ONU be dynamically affected by the EPON traffic local counter is locked to the OLT local load in the upstream. counter. The EPON local counter mechanism As tabulated in Table 1, most wireless tech- provides a time granularity of 16 ns. It rolls nologies require microsecond-level time accura- over approximately every 68.72 seconds (i.e., cy. Therefore, employing IEEE 1588™-2008 over 232 . 16 ns). Figure 2b shows the RTT measure- EPON in a transparent way is unable to meet ment in the ranging process. The OLT sends an the mobile backhaul requirements, and a solu- MPCP message with timestamp A. When an tion with higher time accuracy is needed. ONU receives this message, the ONU sets its

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local counter according to the value in the TIME SYNCHRONIZATION MECHANISM timestamp field in the received message (i.e., A). After a certain wait time (e.g., when the The aforementioned discussion of time synchro- ONU local counter reaches B), the ONU sends nization challenges and EPON local counter an MPCP message back to the OLT. This functionalities motivate the following time syn- MPCP message contains timestamp B. The chronization solution. The major steps of this OLT receives this massage when its local solution are illustrated in Fig. 3. The rest of this counter reaches C. The RTT between the OLT subsection describes each step. and the ONU is measured as RTT = tdownstream Step 1: The OLT local clock is compared to a + tupstream = tresponse – twait = (C – A) – (B – A) precise network time. There are different = C – B. Outside the ranging process, the OLT methods to deliver the network time to the is able to measure the RTT drift by comparing OLT. Typical options include GPS and its local counter value to the timestamp of the IEEE 1588™-2008. After synchronization, received MPCP message [1]. the OLT controls the time synchronization Therefore, EPON provides an accurate local over EPON as a clock master, and the distributed time-base. This can be leveraged to ONUs work as clock slaves. provide synchronized time transport in the fol- Step 2: The OLT selects a local counter value, lowing way. First, the OLT obtains an accurate X, as the timing reference, compensates the network time reference, which will be used as link asymmetry by using the one-way down- the reference of the system. Second, the OLT stream transmission delay, and calculates figures out the difference between its local the corresponding network time at ONUi as clock value and the synchronized network time. The downstream propagation delay is also fac- ndown TTxi,,=+ xo RTT i . tored into the clock difference. Third, the nndown+ up (1) adjusted clock difference is transmitted to the ONUs via a control or management message. TX,o is the OLT sending time of a hypotheti- Fourth, the ONU then applies the difference cal MPCP message with the identification to its local clock to produce the precise net- of X. X is the timestamp field value of this work time. hypothetical MPCP message. TX,i is the ONUi receiving time of the hypothetic MPCP message. RTTi is the RTT measured between the OLT and ONUi, ndown is the Destination address index of refraction for the downstream wavelength, and nup is the index of refrac- Source address tion for the upstream wavelength. RTTi consists of two parts: the downstream trans-

Length/type 64 bytes mission time of

Opcode ndown RTTi nn+ C32 C30 ... C2 C1 down uup Timestamp (32 bits) and the upstream transmission time of ... (other info, pad/reserved) EPON local counter ndown RTTi . Frame check sequence nndown+ uup

(a) In Eq. 1, the downstream transmission time is used to compensate for the fiber propa- OLT ONU gation asymmetry. Step 3: The OLT informs ONUi of the association between the local counter value and network time as (X, TX,i). The pair of val- OLT local ues of (X, TX,i) can be transmitted to ONUi counter is A via a Slow Protocol message in EPON [1]. t MPCP message downstream Step 4: When ONUi receives the value pair, (timestamp A) Set ONU local its local clock is adjusted as counter as A t t response wait T = TX,i + (Y – X) * Tgranularit y.(2)

ONU local Y is the ONUi local counter value when the MPCP message counter is B B t clock slave adjustment is performed. Tgranu- (timestamp ) upstream OLT local larity is the local counter time granularity, counter is C which is equal to 16 ns. The timing reference X selected in step 2 is a virtual reference point. The corresponding MPCP message may or may not actually be used (b) to carry the timing message to the ONUs. In other words, X is picked by the OLT only for Figure 2. EPON time measurement: a) 32-bit local counter; b) RTT measure- timing reference purposes. Any value of X can ment. be chosen, as long as it is relative to the current

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epoch of the OLT local counter. Since the EPON local counter rolls over about every 68.72 RNC OLT ONUi Base station s, a good practice of selecting X is to set it in the near future. This could facilitate an easy imple- Network time mentation of time synchronization by avoiding delivery counter rollover confusion. After receiving the pair of values of (X, TX,i), Step 1: OLT synchronizes to a an ONU could adjust its local time immediately precise network time or afterward. Essentially, Y in Eq. 2 can be either Step 2: One-way transmission the exact local counter value when ONUi delay compensation receives the pair of values, or a later-on local counter value when ONU decides to perform Step 3: Value pair transmission i (X,T ) the adjustment a certain while after the value x,i pair has been received. Again, for the same rea- Step 4: ONU time adjustment son as local counter rollover, the adjustment Network time time should be set in the near future. delivery PERFORMANCE ANALYSIS Performance metrics of time synchronization include local counter inaccuracy, RTT drift, and Figure 3. Time synchronization over EPON. fiber propagation delay difference. The EPON local counter granularity is 16 ns, implying an offset of up to 8 ns. Such an offset to 17 ns. The second order analysis considers the would impact the accuracy of values X and Y in variation of both fibers and wavelengths, and Eq. 2. The EPON TDMA drift tolerance is spec- reveals the fiber dispersion impact. The index ified to be 12 Time_quanta. Each Time_quan- correction factor in the second order analysis tum is defined by the EPON standard as 16 ns. varies from 0.500041 to 0.500090. This intro- Such a drift is equivalent to an RTT drift toler- duces an error of up to 5 ns [7]. Therefore, the ance of up to 192 ns, which corresponds to a error of the first order analysis dominates the one-way delay error of about 96 ns. It should be fiber propagation error. noted that the standard tolerance is the worst The maximum errors introduced by local case value, and that most implementations actu- counter, RTT drift, and fiber propagation are 8 ally achieve far better jitter performance than ns, 96 ns, and 17 ns, respectively. Adding all of this. the three factors together, the maximum error The fiber propagation delay difference is gen- introduced to EPON by the time synchronization erated as a result of the disparity between the mechanism is in the order of 100 nanoseconds. downstream and upstream wavelengths. For a This is in a much smaller order than the wireless typical SMF-28 fiber, the indices of reflection technology time accuracy requirements listed in are ndown = n1490 = 1.4682 and nup = n1310 = Table 1. 1.4677, respectively [7]. The difference between the downstream and upstream wavelengths ROTOTYPE YSTEM AND ESULTS impacts on the index correction factor P S R Figure 4 shows the prototype system design of ndown EPON time synchronization for performance nndown+ up evaluation. The RNC node is configured to distribute two types of time information to the in Eq. 1. Assume N = (nup – ndown)/ndown; the wireless network: IEEE 1588v2 network time impact of the index correction factor can be ana- and local time with 1 pulse/s (PPS). The IEEE lyzed by expanding it into a Taylor series [8] as 1588v2 time input emulates the network time follows.\: source. The local time input emulates other time sources such as GPS. The prototype system is ndown ndown designed to work with either type of the time = information. The time source selection logic on nn+ 2nnn down up down+ () up− down the control card of the OLT chassis selects one 1 1 1 NN2 of the time information to feed into the EPON = = = − ++… OLT card. The selection of time source is for ⎛ nuup− n down ⎞ 2 + N 24 8 the purpose of prototype testing. Two EPON 2 + ⎜ ⎟ ⎝ ndown ⎠ ONUs with BSs are connected to the network via fibers with certain length and a splitter. (3) Mobile users transmit services to and receive services from BSs via the wireless channel. The The zero order analysis essentially assumes other ONU is designed for wired service access. the index is constant over wavelength. This Time synchronization in EPON follows the results in the index correction factor of 0.5. The mechanism described earlier. first order analysis employs nominal fiber but at Tests have been conducted in scenarios with the fixed central wavelengths. This gives an different fiber distance. The received time at the index correction factor of 0.500085. As com- user side is compared with the reference time pared to the zero order result, it implies a fiber from the OLT chassis control card. For illustra- propagation error of 170 ppm in a typical EPON tion purposes, both reference time and received system with 20 km distance, which is equivalent time are converted into 1 PPS with 50 ms width

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The presented solu- Test reference time EPON tion forms the basis ONU Mobile wireless unit of the relevant stan- BS dards. The standard- IEEE Time ization effort and 1588V2 input time board #1 status in the IEEE Time source EPON have been reviewed. select EPON OLT ONU Given its time accu- logic card Splitter racy performance, Time with Time 1PPS input this solution is able board #1 EPON Control card to tackle the time ONU Mobile wireless unit BS synchronization issue RNC OLT chassis over the 10GE-PON system with minor Figure 4. A prototype system of time synchronization over EPON. updates. The standard trends have to measure the disparity. The reference time is EPON is 10GE-PON [10]. 10GE-PON features represented by a falling-edge 1 PPS signal. The the downstream rate of 10 Gb/s, and the also been highlight- received time is represented by a rising-edge 1 upstream rate of 1 Gb/s or 10 Gb/s. Time syn- ed as a preview of PPS signal. chronization would be updated to align to the this area. Figure 5 shows the worst case results of vari- transmission rate improvement and system speci- ous fiber distances with different time sources. fication enhancement. When the fiber distance between the OLT and When migrating from EPON to 10GE-PON, an ONU in the prototype system is 5 km, the the mechanisms of TDM, TDMA, local counter, received time shows a maximum disparity of 60 and RTT management are well maintained. The ns. The maximum time disparity increases to 65 major changes are the adopted wavelengths. ns when the fiber distance is 10 km. When the This means that the EPON time synchronization fiber distance reaches 15 km, the maximum time mechanism described earlier can be applied to disparity is 70 ns. The maximum time disparity is the 10GE-PON system with the proper update measured as 90 ns when the fiber distance is 20 of the indices of refraction. The aforementioned km. All of the maximum time disparities mea- update has been accommodated in IEEE sured in the prototype system are less than 100 802.1AS Clause 13. ns. Therefore, various wireless services can be delivered to the mobile users. UMMARY In addition to the above measurement, wire- S less voice, data, and video services have been This article has examined the solution of time tested in the prototype. Because the network synchronization over EPON. The primary objec- time is precisely synchronized from the RNC tive is to facilitate the EPON implementation of node to mobile users via EPON, these services mobile backhaul and to support time-sensitive have been provided to the mobile users with sat- broadband access services. Time accuracy isfied quality. Wired services of voice, data, and requirements of various wireless technologies video have also been tested. There was no inter- and challenges of link delay difference have ference between wired and wireless services. been investigated. Based on EPON link asymmetry analysis, the TANDARD TATUS AND RENDS accepted time synchronization solution in stan- S S T dards bodies has been introduced. In the solu- The IEEE 802.1AS standard was published on tion, the existing local timing mechanism of March 30, 2011 [9]. It specifies the protocol and EPON is employed to provide timing reference. procedures for time synchronization across The OLT plays a master role in distributing time bridged and virtual bridged networks. The issue to individual ONUs. After conducting link asym- of EPON time synchronization is addressed by metry compensation and value pair calculation, Clause 13. In particular, the clock master role of the OLT informs an ONU the association the OLT and the slave role of the ONUs are between the accurate time and the ONU local enforced by properly configuring the acceptable counter value. An ONU is able to adjust its local master table feature, which determines the clock time after receiving the value pair via a control priorities and best master selection in an IEEE or management message. 802.1AS network. An Organization-Specific With such procedures defined, the perfor- Slow Protocol (OSSP) message (i.e., mance evaluation has been conducted by ana- TIMESYNC) is employed to transmit the pair lyzing local counter inaccuracy, RTT drift, as of values of (X, TX,i) from the OLT to ONUi. well as fiber propagation difference. Analysis The relevant service primitives, interfaces, and has shown that the maximum error is restrict- station machines are also defined by Clause 13 ed in the 100-nanosecond level. The analysis in this standard. has been verified in a prototype system, which Looking forward, the rate enhanced system of demonstrated nanosecond order accuracy. This

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Reference time Reference time

T T

1→ 1→

2→ 2→ Received time Received time

Ch11.00 VΩ Ch2 1.00 VΩ M 40.0ns Ch1 1.40 V Ch11.00 VΩ Ch2 1.00 VΩ M 40.0ns Ch1 1.40 V (a) (b)

Reference time Reference time

T T

1→ 1→

2→ 2→ Received time Received time

Ch11.00 VΩ Ch2 1.00 VΩ M 40.0ns Ch1 1.40 V Ch11.00 VΩ Ch2 1.00 VΩ M 40.0ns Ch1 1.40 V (c) (d)

Figure 5. Test results (time granularity: 40 ns; Ch1: reference time; Ch2: received time): a) 5 km fiber; b) 10 km fiber; c) 15 km fiber; d) 20 km fiber.

is an order of magnitude better than the [6] IEEE Std 1588TM-2008, A Precision Clock Synchroniza- tion Protocol for Networked Measurement and Control mobile backhaul time synchronization require- Systems, IEEE, 2008. ments. [7] ITU-T Rec. G.984.3 Amend. 2, “Gigabit-Capable Passive The presented solution forms the basis of the Optical Networks (G-PON): Transmission Convergence relevant standards. The standardization effort Layer Specification,” 2009. [8] F. Olver et al., NIST Handbook of Mathematical Func- and status in the IEEE have been reviewed. tions, Cambridge Univ. Press, 2010. Given its time accuracy performance, this solu- [9] IEEE Std 802.1ASTM-2011, “Timing and Synchronization tion is able to tackle the time synchronization for Time-Sensitive Applications in Bridged Local Area issue over the 10GE-PON system with minor Networks,” 2011. [10] IEEE Std 802.3avTM-2009, “Physical Layer Specifica- updates. The standard trends have also been tions and Management Parameters for 10 Gb/s Passive highlighted as a preview of this area. Optical Networks,” 2009.

REFERENCES BIOGRAPHIES

[1] IEEE Std 802.3TM-2008, Carrier Sense Multiple Access YUANQIU LUO [S’02, M’06, SM’11] (Yuanqiu.luo@huawei. with Collision Detection (CSMA/CD) access method and com) is a staff engineer in the Advanced Technology Physical Layer specifications, IEEE, 2008. Department of Futurewei (Huawei) Technologies, Bridgewa- [2] Y. Luo et al., “Resource Management for Broadband ter, New Jersey. Her research interests are in the areas of Access over Time-Division Multiplexed Passive Optical broadband access networks, network modeling, and inte- Networks,” IEEE Network, vol. 21, no. 5, Sept.–Oct. grated optical and wireless networks. She has been heavily 2007, pp. 20–27. involved in the pioneering R&D effort of optical access net- [3] J. Zheng and H. T. Mouftah, “A Survey of Dynamic works, such as the first XG-PON1 trial, time synchroniza- Bandwidth Allocation Algorithm for Ethernet Passive tion over PON, and the first 40G-PON prototype system. Optical Networks,” Elsevier Optical Switching and Net- She is a coeditor of ITU-T Recommendations G.987 and working, vol. 6, no. 3, July 2009, pp. 151–62. G.987.3, and a clause editor of IEEE Standard 802.1AS. [4] F. Ren, C. Lin, and F. Liu, “ Self-Correcting Time Syn- Currently she is leading the contribution to the FSAN NG- chronization Using Reference Broadcast in Wireless Sen- PON2 white paper TWDM-PON section. In 2011, she was sor Network,” IEEE Wireless Commun., vol. 15, no. 4, honored with an IEEE Standards Award. She received both Aug. 2008 , pp. 79–85. her Bachelor degree in electronics and information systems [5] ITU-T Rec. G.987.1,” 10-Gigabit-Capable Passive Optical and her Master degree in electrical engineering from Shan- Networks (XG-PON): General Requirements,” ITU-T, 2009. dong University, China. Her Ph.D. degree in electrical engi-

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neering was received from New Jersey Institute of Technol- world’s first field trial of XG-PON. In 2011 he was named a ogy, Newark. She is an author of more than 40 publica- Huawei Fellow. tions and holds two patents. Before joining Huawei she was with NEC Laboratories America, Princeton, New Jersey, NIRWAN ANSARI [S’78, M’83, SM’94, F’09] received his where she received a SEEDS award for innovation. B.S.E.E. (summa cum laude with a perfect GPA) from the New Jersey Institute of Technology (NJIT), Newark, in 1982, FRANK J. EFFENBERGER completed his doctoral work in 1995. his M.S.E.E. degree from the University of Michigan, Ann He then took a position with Bellcore (now Telcordia) Arbor, in 1983, and his Ph.D. degree from Purdue Universi- where he analyzed all types of access network technolo- ty, West Lafayette, Indiana, in 1988. He joined NJIT’s gies, focusing on those that employed passive optical net- Department of Electrical and Computer Engineering as an works. He witnessed the early development of the FSAN assistant professor in 1988, and has been a full professor initiative and the development of the APON standard. In since 1997. He has also assumed various administrative 2000 he moved to Quantum Bridge Communications (now positions at NJIT. He authored Computational Intelligence a part of Motorola), where he managed system engineer- for Optimization (Springer, 1997) with E.S.H. Hou, and ing in their PON division. This work supported the develop- edited Neural Networks in Telecommunications (Springer, ment and standardization of advanced optical access 1994) with B. Yuhas. His research focuses on various systems based on B-PON and G-PON technologies. In 2006 aspects of broadband networks and multimedia communi- he became director of FTTx in the Advanced Technology cations. He has also contributed over 400 technical papers, Department of Huawei Technologies USA. He remains over one third of which were published in widely cited ref- heavily involved in standards work, and has been the lead- ereed journals/magazines. He has also guest edited a num- ing contributor and editor of the major PON standards in ber of special issues, covering various emerging topics in the ITU. In 2008 he became chairman of ITU-T Q2/15 — communications and networking. He was/is serving on the the group that creates standards for optical access sys- Advisory Boards and Editorial Boards of eight journals, tems. He and his team work on forward-looking fiber including as a Senior Technical Editor of IEEE Communica- access technologies, including the 802.3av 10G EPON and tions Magazine (2006–2009). He has served or is serving ITU XG-PON topics. Notably, his team supported the the IEEE in various capacities.

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