Modern Communication Systems -Optical Fibre Networks- EEE440 Modern Communication Systems -Optical Fibre Networks- En. Mohd Nazri Mahmud MPhil (Cambridge, UK) BEng (Essex, UK) nazriee@eng.usm.my Room 2.14

Calculation of OSNR for a point-to-point link A Design Example Design a 4X25 span WDM link with an optical amplifier gain of 22 dB and NF equal to 5 dB. Calculate the final OSNR if the input power in 0 dB. Calculate the signal power at the receiver. Will the system work if the receiver sensitivity is a minimum of –25dB? Will the system work if the input power is 10 dB?

Calculation of OSNR for a point-to-point link A Design Example

Calculation of OSNR for a point-to-point link A Design Exercise 1) Design a 4X25 span WDM link with an optical amplifier gain of 18 dB and NF equal to 6 dB. 2) Calculate the final OSNR if the input power in 0 dB. 3) Calculate the signal power at the receiver. 4) Will the system work if the receiver sensitivity is a minimum of –25dB? 5) Will the system work if the input power is 7 dB and amplifier gain = 22 dB?

Calculation of OSNR for a point-to-point link A Design Exercise 2 Find the number of spans in this link, given Pin = 0 dB; OSNRfinal = 20 dB; total length = 300 km; NF = 5 dB; Fibre loss = 0.2 db/km.

Optical Network Topologies

Network Architecture Standardised optical networks such as SONET and SDH are usually configured as a ring architecture called self-healing ring. There are 3 main features Each feature has 2 alternatives. Either 2 or 4 fibres to link the nodes together Either unidirectional (clockwise only) or bidirectional ring Either line switching or path switching for protection switch. 2 architectures have become popular for SONET and SDH networks. 1. Two-fibre, unidirectional, path-switched ring (UPSR) architecture 2. Two-fibre or four-fibre, bidirectional, line-switched ring (BLSR)

SONET/SDH Two-fibre UPSR

SONET/SDH Two-fibre UPSR

SONET/SDH Four-fibre BLSR

SONET/SDH Four-fibre BLSR

SONET/SDH Four-fibre BLSR - reconfiguration

Commercially available SONET/SDH

WDM In fibre-optic communications, wavelength-division multiplexing (WDM) is a technology which multiplexes multiple optical carrier signals on a single optical fibre by using different wavelengths (colours) of laser light to carry different signals. This allows for a multiplication in capacity, in addition to making it possible to perform bidirectional communications over one strand of fibre.

WDM A WDM system uses a multiplexer at the transmitter to join the signals together, and a demultiplexer at the receiver to split them apart. With the right type of fibre it is possible to have a device that does both simultaneously, and can function as an optical add-drop multiplexer. The concept was first published in 1970, and by 1978 WDM systems were being realized in the laboratory. The first WDM systems only combined two signals. Modern systems can handle up to 160 signals and can thus expand a basic 10 Gbit/s fibre system to a theoretical total capacity of over 1.6 Tbit/s over a single fibre pair.

WDM WDM systems are popular with telecommunications companies because they allow them to expand the capacity of the network without laying more fibre. By using WDM and optical amplifiers, they can accommodate several generations of technology development in their optical infrastructure without having to overhaul the backbone network. Capacity of a given link can be expanded by simply upgrading the multiplexers and demultiplexers at each end.

WDM Most WDM systems operate on single mode fibre optical cables, which have a core diameter of 9 µm. Early WDM systems were expensive and complicated to run. However, recent standardization and better understanding of the dynamics of WDM systems have made WDM much cheaper to deploy..

WDM WDM systems are divided into different wavelength patterns: Conventional, dense and coarse WDM. WDM, DWDM and CWDM are based on the same concept of using multiple wavelengths of light on a single fibre, but differ in the spacing of the wavelengths, number of channels, and the ability to amplify the multiplexed signals in the optical space

WDM Conventional WDM systems provide up to 16 channels in the 3rd transmission window (C-band) of silica fibres around 1550 nm with a channel spacing of 100 GHz. DWDM uses the same transmission window but with less channel spacing enabling up to 31 channels with 50 GHz spacing, 62 channels with 25 GHz spacing sometimes called ultra dense WDM. CWDM uses increased channel spacing to allow less sophisticated and thus cheaper transceiver designs. To again provide 16 channels on a single fibre CWDM uses the entire frequency band between second and third transmission window (1310/1550 nm respectively)

1

WDM deployment 2

Dense WDM

FTTX FTTX refers to several different optical fiber architectures including: Fiber to the node/neighborhood (FTTN) Fiber to the exchange (FTTEx) Fiber to the cabinet (FTTC) or Fiber to the curb. Fiber to the building (FTTB) or Fiber to the home (FTTH) or Fiber to the premises (FTTP)

FTTX ONT = Optical Network Termination OLT = Optical Line Termination System ONU = Optical Network Unit NT = Networking Termination unit

FTTX ONT – interfaces the system to customers’ home OLT - manages the ONTs, aggregates traffics from multiple services and interface the system to the core transmission networks ONU - multiplex and demultiplex signals to and from a fiber transmission line. An ONU terminates an optical fiber line and converts the signal to a format suitable for distribution to a customer's equipment. NT – provides services to the end user

FTTX

FTTN Fiber to the node (FTTN) is a broadband architecture that provides high speed internet and other services to the home by running fiber to the node and some form of DSL to the end-user. This architecture is lower cost to deploy than the competing fiber to the premises (FTTP) technology because of the ability to use existing copper plant but in turn does not bring the full bandwidth capability of fiber to the home. Data rates are limited by the type of DSL used.

FTTN An integrated platform capable of providing telephony, data and video services to residential customers. One key network element, the FTTN Remote Node (RN). Broadband services are provided to this element from the central Office (CO) by a Gigabit Ethernet Fibre. These are connected to the existing copper line in the service access interface and transported to the customer using DSL technology

FTTC Fiber to the curb or fiber to the cabinet (FTTC) is a telecommunications system based on fiber-optic cables run to a platform that serves several customers. Each of these customers has a connection to this platform via coaxial cable or twisted pair.

FTTCab

FTTEx

FTTH or P Two competing FTTP technologies are Active FTTP, also called Active Ethernet, and passive optical network (PON) architectures. Active FTTP networks utilize powered (i.e. 'active') electronic equipment in neighbourhoods, usually one equipment cabinet for every 400-500 subscribers. The IEEE 802.3ah standard enables service providers to deliver up to 100 Mbit/s full-duplex over one single-mode optical fiber to the premises depending on the provider. A passive optical network (PON) is a point-to-multipoint, fiber to the premises network architecture in which unpowered optical splitters are used to enable a single optical fiber to serve multiple premises, typically 32. A PON consists of an Optical Line Termination (OLT) at the service provider's central office and a number of Optical Network Units (ONUs) near end users.

FTTH (Active Ethernet)

FTTH (PON)

FTTH or P With Passive Optical Networks, all active components between the central office exchange and the customer premises are eliminated, and passive optical components are put into the network to guide traffic based on splitting the power of optical wavelengths to endpoints along the way. This replacement of active with passive components provides a cost-savings to the service provider by eliminating the need to power and service active components in the transmission loop. The passive splitters or couplers are merely devices working to pass or restrict light, and as such, have no power or processing requirements thereby lowering overall maintenance costs for the service provider.   In PON architectures, the switching and routing is done at the carrier's central office.. Optical signals, once received in the home, are processed and routed to the appropriate component in the home (voice, video or data).

PON A PON consists of a central office node, called an optical line terminal (OLT), one or more user nodes, called optical network units (ONU) or optical network terminals (ONT), and the fibers and splitters between them, called the optical distribution network (ODN). The OLT provides the interface between the PON and the backbone network. These typically include: - standard time division multiplexed (TDM) interfaces such as SONET/SDH or PDH at various rates - Internet Protocol (IP) traffic over Gigabit or 100 Mbit/s Ethernet - ATM UNI at 155-622 Mbit/s

PON A PON is a converged network, in that all of these services are converted and encapsulated in a single packet type for transmission over the PON fiber. A PON is a shared network, in that the OLT sends a single stream of downstream traffic that is seen by all ONTs. Each ONT only reads the content of those packets that are addressed to it. Encryption is used to prevent unauthorized snooping of downstream traffic. The OLT also communicates with each ONT in order to allocate upstream bandwidth to each node. When an ONT has traffic to send, the OLT assigns a timeslot in which the ONT can send its packets. Because bandwidth is not explicitly reserved for each ONT but allocated dynamically, a PON allows statistical multiplexing and over-subscription of both upstream and downstream bandwidth. This gives PON yet another advantage over point-to-point networks, in that not only the fiber but also the bandwidth can be shared across a large group of users, without sacrificing security.

PON standards ITU-T G.983 APON (ATM Passive Optical Network). This was the first Passive optical network standard. It was used primarily for business applications, and was based on ATM. BPON (Broadband PON) is a standard based on APON. It adds support for WDM, dynamic and higher upstream bandwidth allocation, and survivability. The older ITU-T G.983 standard is based on asynchronous transfer mode (ATM), and has therefore been referred to as APON (ATM PON). Further improvements to the original APON standard -- as well as the gradual falling out of favor of ATM as a protocol -- led to the full, final version of ITU-T G.983 being referred to more often as Broadband PON, or BPON. A typical APON/BPON provides 622 Megabits per second (Mbit/s) of downstream bandwidth and 155 Mbit/s of upstream traffic.

PON standards – ATM PON

PON standards – ATM PON The network components supporting ATM PON consist of OLT, ONT, and a passive optical splitter. One fiber is passively split up to 64 times between multiple ONTs that share the capacity of one fiber. The use of the optical splitter in the PON architecture allows users to share bandwidth. The ATM–PON system uses a double-star architecture. The first star is at the OLT, where the wide-area network interface to services is logically split and switched to the ATM–PON interface. The second star occurs at th e splitter where information is passively split and delivered to each ONT. The OLT is typically located in the carrier's CO. The OLT is the interface point between the access system and service points within the carrier's network. When data content from the network reaches the OLT, it is actively switched to the passive splitter using TDM in the downstream. The OLT behaves like an ATM edge switch with ATM–PON interfaces on the subscriber side and ATM–synchronous optical network (SONET) interfaces on the network side.

PON standards ITU-T G.984 GPON (Gigabit PON) is an evolution of the BPON standard. It supports higher rates, enhanced security, and choice of Layer 2 protocol (ATM, GEM, Ethernet). It also created a standard management interface between the OLT and ONU/ONT, enabling mixed-vendor networks. The ITU-T G.984 (GPON) standard represents a boost in both the total bandwidth and bandwidth efficiency through the use of larger, variable-length packets. A GPON network delivers up to 2,488 Mbits per second (Mbit/s) of downstream bandwidth, and 1,244 Mbit/s of upstream bandwidth. GPON Encapsulation Method (GEM) allows very efficient packaging of user traffic, with frame segmentation to allow for higher Quality of Service (QoS) for delay-sensitive traffic such as voice and video communications

PON standards

PON standards IEEE 802.3ah EPON (Ethernet PON) is an IEEE/EFM standard for using Ethernet for packet data. The IEEE 802.3 Ethernet PON (EPON or GEPON) standard was completed in 2004 as part of the Ethernet First Mile project. EPON uses standard 802.3 Ethernet frames with a symmetrical 1 Gbps upstream and downstream rates. EPON is applicable for data-centric networks, as well as full-service voice, data and video networks. Starting in early 2006, work began on a very high-speed 10 Gigabit/second EPON (XEPON or 10-GEPON ) standard

PON standards- GEPON