Passive Optical Network & EPON 1 Dr. Monir Hossen ECE, KUET

Outlines of the Class  Introduction of Passive Optical Network ( PON)  Properties of PON System  PON Topologies  Advantage & Disadvantage of E-PON  EPON Downstream and upstream  MPCP (Multi Point Control Protocol)  Bandwidth Allocation of EPON 2

3 Why Fiber Based Network? Today’s high datarate networks are all based on optical fiber the reason is simple Twisted copper pair(s) –8 3 km, km (ADSL) –1 100 meters (802.3ab) Microwave –70 30 km (WiMax) Coax – km –30 30 km (cable modem) Optical fiber –1GB to km

4 Why is fiber better ? Attenuation per unit length Reasons for energy loss – copper: resistance, skin effect, radiation, coupling – fiber: internal scattering, imperfect total internal reflection So fiber beats coax by about 2 orders of magnitude – e.g. 10 dB/km for thin coax at 50MHz, 0.15 dB/km for 1550 nm fiber Noise entrance and cross-talk copper couples to all nearby conductors no similar entrance mechanism for fiber Ground-potential, galvanic isolation, lightning protection copper can be hard to handle and dangerous no concerns for fiber

5 Access network bottleneck Hard for end users to get high data rates because of the access bottleneck local area networks use copper cable get high data rates over short distances core networks use fiber optics get high data rate over long distances small number of active network elements access networks (first/last mile) long distances –so fiber would be the best choice many network elements and large number of endpoints –if fiber is used then need multiple optical transceivers –so copper is the best choice –this severely limits the datarates coreaccess LAN

6 Fiber To The Curb Hybrid Fiber Coax and VDSL switch/transceiver/miniDSLAM located at curb or in basement need only 2 optical transceivers but not pure optical solution lower BW from transceiver to end users need complex converter in constrained environment N end users core access network feeder fiber copper

7 Fiber To The Premises we can implement point-to-multipoint topology purely in optic s but we need a fiber (pair) to each end user requires 2 N optical transceivers complex and costly to maintain N end users core access network

8 An obvious solution deploy intermediate switches (active) switch located at curb or in basement saves space at central office need 2 N + 2 optical transceivers core access network feeder fiber fiber

Introduction of Passive Optical Network (PON) 9  PON:  Contains only passive components from Optical Line Terminal (OLT) to Optical Network Units (ONUs)  Provide huge bandwidth Upstream(US): Multi-point to point ONU1 ONUN ONU2 1: N Optical Splitter OLT User 1 User 2 User N Downstream(DS): Point to multi-point OLT acts as a central office (CO) ONUs store the data packet s from users and also act as transceivers

10 Properties of PON System  Point to Point –N fibers, 2N optical transceivers –High Bandwidth –High Fiber Plant cost because of PTP configuration of fiber pairs.  Active Star (Curve Switched) –1 fiber, 2N+2 optical transceivers –Minimum fiber/space in CO –Electrical power in the filed –High Operations & maintenance c ost  PON (Passive Optical Network) –1 fiber, N+1 optical transceivers –Minimum fiber/space in CO –No electrical power in the field –Low Operations cost

11 Properties of PON System  PON –No Power between CO & ONU –No active processing (routing, switching) –Only signal power split  Tree Topology –Downstream: Broadcasting and Selection –Upstream: Multiplexing –TDM-PON EPON, BPON, GPON Requires Control Protocol for Upstream Requires Encryption for Downstream –WDM-PON DWDM-PON, CWDM-PON

12 PON Topologies

PON Types 13 Many types of PONs have been defined: APONATM PON BPONBroadband PON GPONGigabit PON EPONEthernet PON GEPONGigabit Ethernet PON CPONCDMA PON WPONWDM PON

14 Types of TDM-PON B-PONGE-PONG-PON MACATMEthernet ATM, Ethernet, SONET/SDH Data Rate Down622 Mbps1.25G / 10G1.2G / 2.4G Up155 Mbps1.25G / 10G 155M/622M /1.2G/2.4G Max. distance20 km

Importance of E-PON  IEEE 802.3ah standard by IEEE EFM(Ethernet on the First Mile) in 2001  Influences large installed base of Ethernet ports  Eliminates unnecessary protocol conversion  Allows for future low-cost, high volume & high speed optical & hybrid architecture  Does not limit to certain applications, but rather enables a host of applications: Voice, Video & Data  Participants include a host of industry representatives –Customers: Service Providers –Vendors: System, Silicon and Optical vendors –Diversity in participants allows the standard to address a diversity of issues 15

Comparison of EPON with Ethernet 16

Advantage & Disadvantage of E-PON  Advantages –Easy integration of existing IP-based service –Interface to low-price Ethernet equipments –High-speed data rate (1Gbps) –Less overhead compared to B-PON  Disadvantages –less sufficient OAM –not enough adaptation to versatile transmission service Ethernet-based –QoS Problem –Protection/Restoration problem 17

18 EPON Downstream  Downstream uses broadcast  Variable length packet (IEEE frame) –Max. : 1,518 bytes –Min. : 64 bytes

19 EPON Upstream  Upstream time slicing  Burst mode  No collision  No packet fragmentation

Operation of OLT  OLT (Optical Line Terminal) Operation –Generates time stamped messages to be used as global time reference –Generates discovery windows for new ONUs –Performs ranging operation –Controls ONU registration process –Assigns bandwidth to each ONU 20

21 Operation of ONU  ONU (Optical Network Unit) Operation  Waits for discovery gate  Performs discovery process  Synchronization to OLT via timestamps  Request for additional bandwidth in report frames  Waits for grants from OLT

MPCP (Multi Point Control Protocol)  Control mechanism between OLT & ONUs  Defined within the MAC control layer  GATE sent by the OLT –Request that the ONU allow transmission of frames at a time, and for a period of time  REPORT sent by the ONU –Notify the OLT of pending transmission requests –Reports are used to send ONU state to OLT –Requests for additional bandwidth  REGISTER_REQ sent by the ONU –Request that the station be recognized by the protocol as participating in a gated transmission procedure  REGISTER sent by the OLT –Notify the ONU that the station is recognized by the protocol as participating in a gated transmission procedure  REGISTER_ACK sent by the ONU –Notify the OLT that the station acknowledges participation in a gated transmission procedure 22

23 MPCP – RTT measurement  OLT sends GATE at absolute T1  ONU receives GATE at T2 and reset local counter to show T1  ONU sends REPORT at time T3, showing timestamp T4  OLT receives REPORT at absoute T5 RTT = (T2 – T1) + (T5-T3) = (T5-T1) – (T3 – T2)

24 PON has a unique architecture  (broadcast) point-to-multipoint in DS direction  (multiple access) multipoint-to-point in US direction contrast that with, for example  Ethernet - multipoint-to-multipoint  ATM - point-to-point This means that existing protocols - do not provide all the needed functionalities e.g. receive filtering, ranging, security, BW allocation downstream upstream Why a New Protocol or Algorithm?

25 Bandwidth Allocation of EPON  What is bandwidth allocation? –Permission of transmission slot to each ONU –Required to increase the upstream transmission efficiency  Static Bandwidth Allocation (SBA) –Unsolicited permit –Provisioning by OLT  Dynamic Bandwidth Allocation (DBA) –Request- and-permit –Changing bandwidth sharing among ONUs –Multiplexing gain for each ONU –Can consider the priority of ONUs or Packet types

26 Bandwidth Allocation Schemes

27 Thank You Very Much for Your Kind Attention Department of Electronics and Communication Engineering, KUET