Chapter 14 Passive Optical Network(PON) Outline • • • • • • Introduction and brief history PON Architecture and Elements Difference b\w Ethernet PON and ATM PON Advantages and Disadvantages Applications of PON Conclusion Introduction • Passive optical networks (PONs) are an optical broadband access technology that provide an optical last-mile solution. • A PON is a point-to multipoint optical network that uses passive optical components such as splitter, coupler, and splicer. • An optical component is said to be passive if it does not require active power to function. History • In 1995, a group of vendors and telecom service providers, in an attempt to standardize PON access networks, formed the Full Service Access Network (FSAN) coalition. • One goal of the FSAN coalition is to develop and standardize a costeffective yet fast solution to create a “full service access network” that would extend emerging high-speed services, such as IP data, video, and 10/100 Ethernet, over fiber optics networks to residential and business customers worldwide (Spears 1999). The FSAN coalition decided to adopt ATM over a passive optical network, known as ATM PON. In 1999, the ITU-T’s Study Group 15 adopted the FSAN coalition’s ATM PON specifications as standards G.983.1 (ITU-T, 1999). Cont…. • An alternative, Ethernet PON technology, emerged while the ATM PON specifications were being finalized. The Ethernet PON efforts have been undertaken mainly by a group of startup companies and research institutes. Ethernet PON is gaining momentum as optical Ethernet (see Chap. 6) such as Gigabit Ethernet and 10 Gigabit Ethernet start taking hold in the metro network marketplace. This chapter discusses both ATM and Ethernet PON. PON Basics PON technology has two essential characteristics that make it a good choice for a broadband access network 1) It supports point-to-multipoint architecture and allows multiple customers to share a single fiber facility. This is an essential requirement of an access network. 2) A PON system does not require much maintenance because of the passive nature of outside plant components of a PON. PON Architecture • A PON network consists of three major components: 1) an optical line terminator (OLT), 2) an optical splitter and a combiner or a cascade of them, and 3) set of optical network units (ONUs) at the customer premises. • This is a passive optical network because there are no active components between the OLT and ONUs. Cont… • This figure for diagram of passive optical network PON Architecture 1) Optical Line Terminal (OLT) • OLT is the headend of an optical cable network • Optical Line Terminal An OLT is a special-purpose switch located either at a service provider’s central office (CO), a service provider’s point of presence, or An OLT connects to one optical splitter and combiner or a cascade of them Main functions of an OLT 1. It broadcasts the downstream data to the connected ONUs over a single fibber and sends traffic to a splitter 2. It aggregates upstream traffic from multiple customer sites. It can use one of several multiplexing techniques such as TDM, CDM, or WDM. 3. It is responsible for interfacing metro backbone networks and performing network protocol conversions such as Ethernet to ATM or IP to ATM, as necessary Passive Optical Splitter and Coupler • The passive splitter and coupler, the only passive components of a PON, are normally placed inside vaults in manholes. Main functions of Passive Optical Splitter and Coupler • To split optical signals going from an OLT to ONUs and combine them in the other direction. • In the downstream direction, as the light broadcast from an OLT hits the splitter, it is deflected onto multiple fiber connections, depending on the splitter used. A splitter may branch from 2 to 32 or 64 branches. Optical Network Unit • Optical Network Unit PON systems terminates at so-called ONUs, also known as optical network terminals (ONTs). • An ONU takes in light that is sent from a passive splitter, converts it to specific types of bandwidth (such as 10/100-Mbit/s Ethernet, ATM, and T1 voice and data), and passes it on to enterprise routers, PBXs, switches, or residential homes. ONUs have an active optical component such as a laser or LED to send optical signals back to the central office at the command of the OLT. Given that the bandwidth allocated to an ONU is merely a branch of that of the OLT, an inexpensive LED can be a good choice. General functions an ONU • It converts optical signals to electrical signals and then to an application bandwidth for a user end terminal such as a PC, a TV, a home hub, enterprise routers, etc. • It generates optical signals for upstream traffic. • It interfaces last-yard access devices like a wireless LAN card or asynchronous digital subscriber loop (ADSL) line at customer premises. ATM PON and Ethernet PON • ATM PON: An ATM PON carries all services in ATM cells, in both upstream and downstream directions. • One main consideration for adopting ATM PON is the guaranteed bandwidth and well-defined QoS provided by ATM technology. • Ethernet PONs: carry all services in variable-length Ethernet frames, each of which has a maximum length of 1518 bytes, in both upstream and downstream directions. ATM PON architecture Hint: the maximum optical signals from a transmitter are passively split into up to 64 ONT. VPI(virtual path identifier b/w ONTs) Ethernet PON architecture Comparison ATM PON and Ethernet PON Comparison ATM PON Ethernet PON Technology complexity more complexity compared Ethernet PON Simple plug and play QoS Excellent No built-in QoS mechanism Data rate Maximum upstream 155 Mpbs ,Downstream 622Mpbs No standard bandwidth defined yet Mechanism distinguishing one ONU from another Uses VPI Uses Mac Addressing Multiple access control TDMA TDMA (proposal only) WAN interface SONET and ATM SONET and DWDM backbound Support service Data,Voice and Video Data, Voice and Video Development Initial field trial stage Very initial trial stage Advantages of PON • Point-to-multipoint fiber-lean architecture instead of running a separate stand of fibber from CO to every customer. Uses a single stand of fiber to serve up to 32 subscribers • it uses optical fibres so that the band with is high, can reach a longer distances • Low cost equipment's per subscriber Advantages of PON • Passive components require a little components, and have a high MTBF (Mean time between Failures) • Additional buildings can be add to the network easily and inexpensively. • Supports a broad range of application icluding Triple play(voice, Video and Data) of a single fibber and FTTB,FTTC,FTTN and FTTH Advantages of PON • Offers a large amount of high speed bandwidth providing greater flexibility for adding future services. • Flexible and scalable bandwidth assignment • Central office (instead of multiple ports) there is only one optical port of the network. Disadvantages of PON 1) Requiring more protection around the fiber cable compared with copper cable 2) Cost Application Of PON • Fiber to the curb (FTTC), where an ONU resides at a roadside wire centre • Fiber to the building (FTTB), where an ONU resides inside a telecommunications closet of a multitenant business or residential building. • Fiber to the floor (FTTF), where an ONU is located at a wire cabinet of a building floor • Fiber to the home (FTTH), where an ONU is located inside a residential customer’s home Conclusion • Passive optical networks (PONs) are an optical broadband access technology that provide an optical last-mile solution. • A PON is a point-to multipoint optical. Main challenges • How the splitter knows the path or which User of this data belongs to, as we know splitter is not intelligent device like router and switch? • How voice video and Data propagate inside a single fiber? END Thanks
