Tabriz university school of new science and technology Optical switching networks

1. Tabriz university school of new science and technologyOptical switching networks Designed by : N.pasyar

2. Optical switching network optical switching networks refers to all the various types of flexible and reconfigurable optical networks that use any of the multiplexing , tuning , and switching techniques. optical switching networks are single-channel or multichannel (WDM) networks whose configuration can be changed dynamically in response to varying traffic loads and network failures.

3. End-to-end optical networks Optical switching networks have been used in backbone networks in order to cope with the ever-increasing amount of traffic and bandwidth-hungry applications. They are also used in metro(politan), access, and local area networks. Long-haul backbone Networks Wide Area Core Ring Metro Area Edge Ring Edge Ring Access/Local Area Fig 2.1 Hierarchy of optical switching networks.

4. Last/first mile phone companies deploy digital subscriber line (DSL) while cable providers deploy cable modems .so, copper is used on the final network segment to connect subscribers. copper-based network segment forms a bandwidth bottleneck. The bandwidth bottleneck is referred to as the so-called last mile bottleneck, or also as the first mile bottleneckin order to emphasize its importance to the end users.

5. To remove the first/last mile bottleneck, fiber is brought closeor even all the way to the subscribers, who might be either business or residential users. Depending on the demarcation point of fiber, these optical access networks are called fiber to the X (FTTX) networks, where X denotes the various possible demarcation points of fiber.

6. PON To build cost-effective optical access networks FTTX networks are based on passive optical components without using amplifiers or any other powered devices. these FTTX networks are called passive optical networks (PONs). They simplify their operation, administration, and maintenance (OAM) as well as their management due to the completely passive nature of their underlying components. The transport of data traffic over PONs may be based on asynchronous transfer mode (ATM), resulting in the so-called ATM PON (APON). Ethernet frames may be transported in their native format in the so-called Ethernet PON (EPON),

7. whether APON or EPONs are suitable for cost-effective broadband optical access networks ? Given the low costs of Ethernet equipment and by capitalizing on the technology and products of the Ethernet LAN market, EPON appears to be better than ATM-based PONs. the use of WDM on the already installed fiber infrastructure provides an multichannel upgrade path of EPON access networks, leading to WDM EPONs. The 10-Gigabit Ethernet (10GbE) provides an extended maximum transmission range of 40 kilometers, compared to (GbE) 5 kilometers,.

8. Ethernet is the predominant technology in local area networks (LANs).and low-cost solution also for optical high-speed MANs and WANs. • 10GbE equipment costs are about 80% lower than that of SONET equipment and 30–60% lower than other managed network services. • The use of Ethernet technology not only in today’s LANs but also in future access, metropolitan, and wide area networks will potentially lead to end-to-end Ethernet optical networks. • future access networks are likely to be bimodal .So-called radio-over-fiber (RoF) networks may be viewed as the final frontier of optical networks which interface optical access networks with their wireless counterparts

9. Applications Throughput-Critical includes large-size file transfers require much bandwidth Latency-Critical comprises small- to medium size file transfers video & image email attachments backup of files broadcast television interactive games file downloading ebooks video conferencing

10. Depending on the application, traffic loads and throughput-delay performance requirements may change over time. web browsing has led to rather asymmetric network traffic loads. it is based on the client–server paradigm, (each client sends a short request message to a server for downloading data files). In future (optical) networks, the traffic load is expected to become less asymmetric via so-called peer-to-peer (P2P) applications.In p2p each client also acts as a server from which other clients may download files

11. Services Connection-Oriented Services:Connection-oriented services require a connection to be established before any data can be sent by executing a specific handshake procedure between sender and destination. sender and destination and possibly also intermediate nodes need to maintain state information for each established connection. Examples are transmission control protocol (TCP), ATM, and multi protocol label switching (MPLS). By using the state information, connection-oriented services are able to recover from data loss and provide quality of service (QoS) to applications.

12. Services Connectionless Services:Connectionless services do not require the establishment of any connection prior to sending data. Connectionless services are less reliable than their connection-oriented counterparts, but they are well suited for the transfer of best-effort traffic. As an example is the Internet protocol (IP) which provides best-effort service to higher protocol layers and applications.

13. Some of today’s most important services triple-playservices :Triple-play offerings comprise bidirectional voice, bidirectional data, and unidirectional video services. all three services are delivered to the subscriber via FTTX networks . virtual private network (VPN) services:A VPN supports a closed community of authorized users, allowing them to access various network-related services and sources. a VPN is a virtual topology that is built on a physical network infrastructure whose resources may be shared by multiple other VPNs. cost-effective provide privacy by isolating traffic belonging to different VPNs from each other. offer services that enable a mobile to remotely access the intranet and/or extranet of a company.

14. As shown , optical switching networks offer services to applications. Depending on the traffic demands of various clients optical switching networks need to be able to provide different types of connections. Optical switching networks Applications op services Optical switching networks services Applications Fig 2.2 Optical switching networks offering services to applications.

15. Switching granularity connections between source and destination may be switched at different granularities. Major switching granularities, ranging from coarse granularity at the top to fine granularity at the bottom of the table:

16. Switching granularity Fiber switching : is done by switching all data arriving on an incoming fiber to another outgoing fiber without making any difference among the various wavelength channels. • waveband switching : the set of wavelength channels carried on the fiber is divided into multiple adjacent wavebands. Wavebands are switched independently from each other; waveband switching provides a finer switching granularity.

17. Wavelength switching : wavelength switching an input WDM comb signal is first demultiplexed into its individual wavelength channels and each wavelength channel is then switched independently. A given wavelength channel may carry the data of a single client . In OTDM networks, each time slot carries the data of a different client and may be switched individually. OCS: all switching techniques discussed so far are optical circuit switching (OCS) techniques. circuits – fibers, wavebands, wavelengths, or time slots –are dedicated to source–destination node pairs .

18. OPS: OPS networks is an example for subwavelength switching optical networks, where packets on a given wavelength channel are switched independently from each other. packet-switched networks require buffers to resolve contention. Fiber delay lines (FDLs) are used.FDLs are fiber loops where the optical signal continues to circulate until it is forwarded. the reading/writing of the information is restricted to integer multiples of the round-trip time of the loop FDLs must be designed such that the largest packet size can be stored on the loop. OPS networks favor cell switching, where each cell has the same fixed size.

19. OCS networks provide circuits with a high level of QoS. At the downside, they require a two-way reservation to set up optical circuits. OPS networks are connectionless and thus avoid any delay due to circuit set-up. But OPS networks do not necessarily meet QoS requirements. OBS: in OBS networks client data is aggregated at the network ingress and sent as bursts across the network. For each burst a reservation control packet is sent on a dedicated control wavelength channel prior to sending the burst on one of the data Wavelength channels after an offset time.

20. The control packet is used to configure intermediate OBS nodes between the ingress node and egress node of the OBS network. • The offset time is set such that the burst can be all-optically switched at intermediate nodes. so, the burst does not need to be OEO converted, buffered, and processed at intermediate nodes, thus avoiding the need for optical RAM and FDL. • OBS networks deploy a one-way reservation, as is done in OCS networks .Also, by controlling the offset time, service differentiation and various QoS levels can be achieved.

21. Interlayer networking The data plane encompasses all switching mechanisms required to send data from source to destination. the data plane needs to be controlled by means of a control plane. the control plane is responsible for setting up and making the various switching techniques work in a coordinated and efficient manner throughout the optical network. The control plane can be implemented at the medium access control (MAC) layer of optical switching networks to avoid collisions of data frames on each wavelength channel. Also to route and establish optical connections from source to destination.

22. Two approaches for control plane: new control protocols are designed for the optical switching networks, taking their respective properties into account. already existing control protocols which were successfully deployed in electronic data networks ,are used.for example IP centric control plane . interlayer networkingbetween AONs and IP clients became the next evolutionary step in designing flexible optical switching networks, leading to so-called IP/WDM networks. Interlayer networking

23. interconnection models of IP-over-optical networks: Peer Model: IP networks and optical networks are considered an integrated network with a unified control plane .peer model implies that optical network nodes need to provide IP routers with full routing information . Overlay Model:IP networks and optical networks operate completely independently from each other and run their own set of routing and signaling protocols. In order to interconnect geographically distributed IP routers across optical networks appropriate interfaces between both types of network need to be standardized.

24. Interdomain (Augmented) Model: both IP and optical networks have their own routing instances, but reachability information of geographically distributed IP routers is passed by the underlying optical networks onward to IP clients. The standardization will allow end users and network operators to dynamically control end-to-end connections. International Telecommunication Union (ITU-T). ASTN Internet Engineering Task Force (IETF). GMPLS Optical Internet working Forum (OIF).

25. The ASON and GMPLS protocols are well suited for conventional centrally managed optical switching networks . in customer-controlled and optical networks customers acquire their own dark fibers and/or point-to-point wavelengths and are responsible for protection and restoration, without requiring any service from a central management. Buying one’s own optical network may result in significant cost savings since ongoing monthly expenditures are replaced with a one-time initial CAPEX shared by the customers. user-controlled optical networks support wavelength switching and burst switching.

26. security Many of the security mechanisms used in electronic networks can also be applied in optical networks. Differences: for high-speed data rates on multiple WDM channels infrequent attacks may lead to large amounts of lost information. eavesdropping by means of tapping may comprise the privacy of optical communications. malicious signals are harder to detect in transparent optical networks than in opaque ones with OEO conversion.

27. In (EDFAs), a malicious high-power optical signal uses more of the upper-state photons and reduces the gain of the other user signals. the limited crosstalk of optical devices ,(OXCs) and (OADMs), can lead to a reduced QoS on one or more wavelength channels if the power of a malicious optical signal is sufficiently high. the security of optical networks can be improved by means of preventive measures. bandlimiting optical filters discard optical signals outside the operational spectrum and mitigate the gain competition of EDFAs.

28. Traffic grooming • Traffic grooming:is the process of grouping many small telecomunications flows into larger units, which can be processed as single entities. • In anetworkusing bothTDMandWDM , two flows which are destined for a common node can be placed on the same wavelength, allowing them to be dropped by a singleOADM. • traffic grooming was done in the area of SONET/ (SDH) ring networks. it can be extended to optical mesh WDM networks, where low-rate circuits and data flows are assigned to wavelength channels which optically bypass OADMs.

29. objective of grooming • Often the objective of grooming is minimizing the cost of the network and line terminating equipment (LTE). • Thus grooming typically involves minimizing the usage of ADMs.This is similar to the use ofvirtual networking andvirtual paths inATMnetworks. • Effective grooming requires consideration of thetopologyof the network and the different routes in use. This is especially useful when dealing withmesh networkes

30. Building blocks

31. Components Combiner:It collects wavelength channels from all S input ports and combines them onto the common output port. Splitter: It equally distributes all incoming wavelength channels to all S output ports. λ λ λ λ S x 1 1XS λ λ λ Combiner Splitter λ

32. Waveband partitioner: It partitions an incoming set of contiguous wavelength channels into two wavebands A and B, where 1 ≤ΛA, ΛB≤ Λ− 1, and Λ= ΛA + ΛB. Waveband departitioner:It collects two different wavebands consisting of ΛA and ΛB contiguous wavelength channels from the upper and lower input port, respectively. ΛA ΛA Λ Λ λ λ ΛB Π Σ ΛB λ λ λ λ

33. Passive star coupler (PSC): . it collects wavelength channels from all D input ports and equally distributes them to all D output ports. Arrayed waveguide grating (AWG):The AWG routes every second wavelength to the same output port. This period of the wavelength response is called free spectral range (FSR). the FSR of a D × D AWG consists of D contiguous wavelengths, the physical degree of an AWG is identical to the number of wavelengths per FSR. FSR FSR λ λ λ λ DxD psc DxD AWG λ λ λ

34. In put / out put waveguides N input ports N output ports Slab waveguide Array of M waveguides Waveplate The arrayed waveguides introduce wavelength-dependent phase delays such that only frequencies with a phase difference of integer times2πinterfere constructively in the output slab waveguide. Thus, each output port carries periodic pass frequencies. The spacing of these periodic pass frequencies is called FSR. Schematic layout of an NxN AWG

35. λ8 1 1 λ1…λ4 …λ8 2 λ1 2 λ1…λ4 …λ8 3 λ1 3 λ1…λ4 …λ8 λ4 4 4 OUTPUT 5 λ4 5 INPUT 6 6 λ8 7 7 8 λ8 8 Fig. 3.3 In Fig. 3.3 the routing connectivity of an 8 × 8 AWG is illustrated. λk ’s routing information is to exit the output port that is (k − 1) ports below the corresponding input port; that is, λ1 goes from input port 1 to exit port 1 and from input port 5 to exit port 5.

36. Transmitters A transmitter comprises a light source, a modulator ,and supporting electronics. Broadband light sources: broad spectrum in the range of 10-100 nm. small bandwidth-distance product LEDs are mainly applied for low data rates and/or short distances. output powers −10 dBm. superluminescent diodes with an output power of 18.0 dBm and a 3-dB bandwidth of 35 nm . Lasers: To achieve a significantly increased bandwidth-distance product lasers are deployed. laser is an optical amplifier enclosed within a reflective cavity that causes the light to oscillate via positive feedback. output powers, between 0 and 10 dBm.

37. Lasers can be either fixed tuned or tunable. a laser can be tuned by controlling the cavity length and/or the refractive index of the lasing medium. instead of tunable lasers one might use an array of fixed-tuned lasers, or multi frequency lasers

38. Receivers (optical filters) A receiver is composed of an optical filter, a photodetector, a demodulator, and supporting electronics. Optical filters :are used to select a slice of a broadband signal or one wavelength out of the (WDM) comb. The selected wavelength is subsequently optoelectrically converted by a photodetector.

39. Fixed tuned filters Dielectric thin film filters Diffraction gratings Fiber bragg gratings(FBGS)

40. tunable optical filters Mach-Zehnder interferometer (MZI) acousto-optic tunable filters (AOTFs) Electro-optic tunable filters (EOTFs)

41. Transmission impairments Attenuation. Dispersion Nonlinearities Attenuation: The peak in loss in the 1400-nm region is due to hydroxyl ion (OH−) impurities in the fiber. this peak is reduced In Lucent’s AllWave fiber. among 0.85, 1.3, and 1.55 µm, the latter band provides the smallest attenuation of ∼0.25 dB/km.

42. dispersion different components of the transmitted signal travel at different velocities in the fiber, arriving at different times at the receiver. As a result, the pulse widens and causes inter symbol interference (ISI). dispersion limits the minimum bit spacing (maximum transmission rate). Modal dispersion: arises only in multimode fiber where different modes travel at different velocities. Clearly, in single-mode fibers (SMFs) modal dispersion is not a problem.

43. Waveguide dispersion :After entering an SMF, major portion of an information-carrying light pulse travels within the core, the rest within the cladding. Both portions propagate at different velocities since the core and the cladding have different refractive indices. Chromatic (material) dispersion:different frequency components of a pulse travel at different velocities due to the fact that the refractive index of the fiber is a function of the wavelength. Standard (SMFs) have a chromatic dispersion of 17 ps/(nm·km) at 1550 nm.

44. By controlling the waveguide dispersion accordingly, NZ-DSFs have a chromatic dispersion between 1 and 8 ps/(nm·km). Alcatel’s TeraLight Metro Fiber has a dispersion of 8 ps/(nm·km). low negative dispersion of Corning’s MetroCor fiber enables the use of low-cost directly modulated DFB lasers. Polarization mode dispersion (PMD) :PMD arises because the fiber core is not perfectly circular, particularly in older installations.Thus, different polarizations of the signal travel at different velocities. PMD is proving to be a serious impediment in very-high-speed systems operating at 10 Gb/s and beyond.

45. Nonlinearities when the power levels get fairly high the nonlinearities can place significant limitations on high-speed systems as well as WDM systems. Nonlinearities owing to the dependence of refractive index on the optical power : (SPM), (XPM), and four-wave mixing (FWM). Nonlinearities owing to scattering effects in the fiber medium due to the interaction of light waves with phonons (molecular vibrations) in the silica medium. stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS).

46. Self-phase modulation :variations in the power of an optical signal changes the phase of the signal. It leads to spectral broadening. instantaneous variations of the frequency around the signal’s central frequency. Cross-phase modulation :XPM is a shift in the phase of a signal caused by the change in intensity of a signal propagating at a different wavelength. XPM can lead to asymmetric spectral broadening. Four-wave mixing :FWM occurs when two wavelengths, operating at frequencies f1 and f2, respectively ,mix to cause signals at frequencies such as 2 f1 − f2 and 2 f2 − f1. These extra signals can cause interference if they overlap with frequencies used for data transmission.

47. Stimulated Raman scattering :SRS is caused by the interaction of light with molecular vibrations. Light incident on the molecules creates scattered light at a longer wavelength than that of the incident light. The light generated at the lower frequencies is called the Stokes wave. To reduce the amount of loss, the power on each channel needs to be below a certain level. Stimulated Brillouin scattering :SBS is similar to SRS, except that the frequency shift is caused by sound waves rather than molecular vibrations .in SBS the Stokes wave propagates in the opposite direction of the input light.

48. Crosstalk Crosstalk decreases the signal-to-noise ratio (SNR) leading to an increased BER. interchannel crosstalk : is caused by signals on different wavelengths . It may be removed through the use of appropriate narrowband filters. intrachannel crosstalk: is caused by signals on the same wavelength on another fiber due to imperfect transmission characteristics of components (AWG). it occurs in switching/routing nodes and it cannot be removed through filtering.

49. Noise Amplified spontaneous emission (ASE) :In optical EDFA the spontaneous emission is amplified in addition to the incident light signal. Shot noise :Is the main complication in recovering the transmitted bit of photodetector. Shot noise current occurs due to the random distribution of the electrons generated by the photodetection even when the input light intensity is constant. Thermal noise :the photocurrent is amplified by an electrical amplifier. The electrical amplifier introduces thermal noise current due to the random motion of electrons at typical temperatures.

50. TheEnd Thank you for your attention