Optical Storage Networking

Optical Storage Networking
Introduction This lesson describes the applicability of optical networking technologies to storage networking. You will learn how Wave Division Multiplexing (WDM) and Synchronous Optical Networking/Synchronous Digital Hierarchy (SONET/SDH) networks can be used to transport storage protocols. Importance The knowledge gained in this lesson will enable you to identify optical storage networking opportunities for customers. This lesson alone is not sufficient to allow you to design optical networking solutions. Optical networking technologies are complex, and it is beyond the scope of this lesson to provide you with enough knowledge to design an optical networking implementation. However, this lesson will help you identify the Cisco optical networking products that can be used to meet a customer’s storage networking needs.

Objective After you complete this lesson, you will be able to explain how WDM and SONET/SDH technologies apply to storage networking. Performance Objective Upon completion of this lesson you will be able to explain how WDM and SONET/SDH technologies apply to storage networking. Enabling Objectives Explain how a DWDM system transports storage networking protocols Describe the components of a DWDM system Differentiate between DWDM point-to-point, ring, and mesh topologies Describe high-availability DWDM configurations Discuss the performance limitations of DWDM Compare CWDM to DWDM Explain how a SONET/SDH system transports storage networking protocols Identify the components of a SONET/SDH system Identify the general performance limitations of SONET/SDH Identify the factors to consider in selecting the appropriate optical technology for a storage environment Identify Cisco optical storage networking products

Outline Storage Transport Over DWDM DWDM Components DWDM Topologies
DWDM Protection DWDM Performance Limitations CWDM and DWDM Storage Transport Over SONET/SDH SONET/SDH Components SONET/SDH Performance Limitations Storage Applications Cisco Optical Storage Networking Products Prerequisites Curriculum Unit 2, Modules 1 and 2 Module 3, Lesson 6

Storage Transport Over DWDM
Protocol-independent Transparent ESCON ESCON GigE GigE FC 1-2Gb FICON FC 1-2Gb FICON Storage Transport Over DWDM Objective Explain how a DWDM system transports storage networking protocols Introduction This section explains how a DWDM system transports storage networking protocols. Facts A DWDM optical link transports other network protocols (for example, FC, FICON, ESCON, SONET, IP, and ATM) without protocol mapping or translation. The DWDM link overcomes the distance limitations inherent in protocols such as FC. FC-to-DWDM technology is one of the techniques used to extend Fibre Channel over a longer distance. FC-to-DWDM equipment operates by multiplexing FC optical signals onto a higher wavelength fiber medium. Typically, a single E_Port is connected to DWDM equipment, which multiplexes the FC signal to a remote DWDM port. On the receiving side, a DWDM demultiplexer is connected to a remote SAN where the frame is sent out through a single E_Port back into the remote FC SAN. For the FC switch, the existence of a DWDM link is almost transparent—no change occurs to the protocol, the data is received at full speed, and there is no indication that the frame went over a long-distance link. Metro DWDM systems multiply, by a factor of 16 or 32, the amount traffic that can be transported on a single fiber pair. In other words, throughput on a fiber pair, typically on the order of 2.5 or 10 Gb/s, can be increased to 80 Gbps and 320 Gbps, respectively. With DWDM capacity, high volumes of ESCON, FICON, Fibre Channel, ATM, and IP-based storage traffic can be extended transparently across a metropolitan area. Channels (wavelengths) can be added one by one, as required, providing a granular and easily scalable network. By using a DWDM optical network to multiplex data streams across that single pair, a company can save considerable amounts of money over traditional solutions. The Cisco ONS 15540, shown in the preceding graphic, supports 1Gb and 2Gb FC. ONS 15540 ONS 15540 SONET ATM ATM SONET

DWDM Components DWDM Multiplexer DWDM Demultiplexer Router Router
FC switch FC switch DWDM Components Objective Describe the components of a DWDM system Introduction This section describes the components of a Dense Wave Division Multiplexing (DWDM) system. Facts DWDM substantially increases the amount of data that can be carried over a single optical fiber by dividing a single beam of light into discrete wavelengths. This allows a single fiber to operate as if it were multiple fibers. Each signal carried can be at a different rate (typically 2.5Gb/s or 10Gb/s) yet use the same physical fiber optic cable. Carrying each signal on a separate wavelength allows each channel to have its own dedicated bandwidth. The required components of a DWDM system are: Optical transmitters transmit an optical signal using high resolution, precision narrow-band lasers. These lasers allow close channel spacing to increase the number of wavelengths that can be used while minimizing signal impairments such as dispersion. The link consists of optical fiber that exhibits low loss and transmission performance in the relevant wavelength spectra (1550nm for most DWDM applications). Optical receivers detect incoming optical signals and convert them to an appropriate signal for processing by the receiving device. Optical receivers are usually wideband devices that can detect light over a relatively wide range of wavelengths. The ability to detect this wide range of wavelengths allows a single receiver to accept any wavelength in the 1300nm to 1550nm range. Optical DWDM multiplexers combine the transmit signals from different wavelengths onto a single optical fiber. Demultiplexers separate the combined signals into their component wavelengths at the receiving end, using thin film filters or diffractive elements Transmitters/ Receivers Transmitters/ Receivers SONET SONET

DWDM Components (cont.)
DWDM Multiplexer Router FC switch The preceding diagram shows one side of a DWDM connection. Local networking devices, such as GigE routers, FC switches, and SONET multiplexers, are connected to a DWDM multiplexer by way of transmitters and receiver elements. Typically, each local networking device is attached to the transmitter/receiver elements using relatively low-cost multimode or single-mode cables, and using standard broadband wavelengths defined for that networking technology. The transmitter/receiver elements typically contain transponders that convert the incoming broadband optical signal to an electrical signal, and then convert the electrical signal back to an optical signal using precision narrow-band lasers. This is known as O-E-O conversion, and it enables low-cost optical networking devices that are not equipped with precision narrowband lasers to be multiplexed onto a single DWDM fiber. Each narrow-band signal is a different wavelength, or “color.” The narrow-band signals are then fed into a DWDM multiplexer, which combines the wavelengths into a single optical fiber. Most DWDM implementations, including Cisco implementations, use two optical fibers—traffic on each fiber is unidirectional. Note: In DWDM terminology, the term “east-west” refers to the optical signals traveling along the network backbone, while the terms “east-south” and “west-south” refer to the direction of traffic flow as optical signals are routed off of the backbone and into local circuits. SONET Transmitters/ Receivers

DWDM Transmitter PM SR RCVR LR XMTR DWDM Receiver Terminal/Client Equipment DWDM MUX/DEMUX In standard optical networking technologies like FC and GigE, each optical fiber carries a single traffic channel, so the precision of the optical wavelength is not a concern. Because DWDM carries multiple traffic channels together, it requires each traffic channel to be transmitted on a unique and stable wavelength. To pack many channels into a single fiber, wideband client optical signals are transformed into narrowband signals that contain the exact wavelengths needed for DWDM transmission using a transponder. A transponder is essentially an analog optical receiver/optical transmitter pair that operates at one narrowband wavelength. One transponder is required per wavelength, and each transponder operates at a specific wavelength, or “color.” The key activities of a transponder are reshaping, retiming, and regeneration of the signal. Because the transponder is an analog device, it is transparent to bit rate and format, so a single transponder design can handle multiple types of traffic, including FC traffic, ATM cell streams, high-speed IP packet streams, and multiplexed digital TV channels. The preceding diagram shows a simplified view of a transponder. It contains the following elements: The transmitter module contains a short-reach (SR) receiver, typically operating at 850nm, 1310nm, or 1550nm, to receive wideband signals from the client equipment, and a long-reach (LR) transmitter, operating in the 1500nm range, to send narrowband signals to the DWDM multiplexer. The receiver module contains LR receiver to receive narrowband DWDM signals from the DWDM demultiplexer, and an SR transmitter to pass wideband signals to the client equipment. Both the transmitter and receiver modules contain a performance monitoring (PM) component that enables administrators to detect transponder failure conditions. On the receiver side, wavelength conversion might not be needed. Modern optical receivers are very tolerant to the incoming wavelength, so the demultiplexed traffic channel can often be directly connected to the existing optical networking equipment. Transponder converts wideband client laser input into narrowband DWDM signals: One transponder required per wavelength Signal reshaping, retiming, and regeneration Terminal side is 850/1310/1550 nm, DWDM side is 15xx nm

DWDM Multiplexer OADM Router Optical Amplifier Other DWDM components that might be required are shown in the preceding diagram: For longer distances, flat-gain optical amplifiers can be used to boost the signal on longer spans, or to preamplify the signal before it leaves the local site The most common type of optical amplifier is the erbium doped fiber amplifier (EDFA). Conventional EDFAs operate in the 1530nm to 1560nm range. Optical Add/Drop Multiplexers (OADMs) can be deployed for added signal grooming flexibility. OADMs allow a specific wavelength on the fiber to be demultiplexed (dropped) and remultiplexed (added) while enabling all other wavelengths to pass. The wavelengths that pass through an OADM filter experience a small amount of signal attenuation. Optical cross-connect devices, which are not shown here, act as optical routers, allowing network reconfiguration on a wavelength-by-wavelength basis. These devices can optimize network traffic and enhance network survivability. However, they do cause significant power loss, and introduce cost and complexity to a DWDM network. Variable Optical Attenuator (VOAs) are required for DWDM ring topologies when OADMs are used. When the OADM injects a new wavelength into the ring, the signal strength of that wavelength might be stronger than other wavelengths at that point on the ring. The VOA attenuates (reduces) the strength of the new wavelength so that it matches the strength of the other wavelengths. Dispersion Compensation Units (DCUs) help prevent signal degradation due to dispersion of the optical signals over long distances. DCUs will be required for 10Gb Ethernet and Fibre Channel at distances over 50Km. SONET Transmitters/ Receivers FC switch

FC 1Gb FC 1Gb FC 1Gb 1x 2.5Gb channels FC 1Gb ONS 15530 ONS 15530 Facts With older and low-end DWDM equipment, each protocol channel (such as an FC E_Port-to-E_Port link) can be carried over a separate wavelength. The equipment used for this configuration is typically less expensive, but offers less scalability. More robust DWDM equipment can multiplex multiple protocol channels onto a single wavelength. In the upper diagram, two 1Gb/s FC channels are carried over a single DWDM wavelength via the Cisco ONS that operates at a bit rate of 2.5Gb/s. The ONS also supports 2Gb FC. When 10Gb/s DWDM components are available, the ONS will be able to support up to eight 1Gb FC channels or up to four 2Gb FC channels on a single wavelength, as shown in the lower diagram. FC 2Gb FC 2Gb FC 2Gb FC 2Gb 1x 10Gb channels (Future) FC 2Gb FC 2Gb FC 2Gb ONS 15530 ONS 15530 FC 2Gb

DWDM Point-to-Point Topology
DWDM Topologies DWDM Point-to-Point Topology Point-to-Point DWDM Topologies Objective Differentiate between DWDM point-to-point, ring, and mesh topologies Introduction This section introduces the various DWDM topologies, including point-to-point, ring, and mesh. Definition In its simplest implementation, a point-to-point topology consists of an optical transmitter and an optical receiver, connected by optical fiber. Typically, this topology includes a transponder at each end, to convert broadband optical signals to specific wavelengths using O-E-O conversion. Example The preceding graphics show two examples of a point-to-point topology: The upper diagram shows a simple point-to-point topology that connects two sites. In storage networking, this topology is often used to connect a primary data center to a remote backup center for data mirroring or snapshot applications to support backup and disaster recovery applications. The lower diagram shows a bus configuration in which multiple sites are connected in a linear model. Specific wavelengths (lambdas) are used between the central site and each remote site. This topology might be used to connect multiple campuses in a metropolitan area. Point-to-Point Bus

DWDM Topologies (cont.)
DWDM Ring Topology Corp SAN Definition Rings are the most common DWDM architecture found in metropolitan areas. Rings can span tens of kilometers. Ring topologies can support any-to-any traffic, or they can be configured with a hub and satellite nodes. Traffic can be unidirectional or bidirectional. Example The preceding graphic shows a hubbed ring architecture that connects an enterprise data center to three remote sites using DWDM as the transport. The ONS at the corporate site is the hub, OADMs are used at the remote sites to add and drop specific wavelengths. At the OADM nodes, one or more wavelengths may be dropped off or added, while the others pass through transparently. In this way, ring architectures allow nodes on the ring to provide access to network elements such as routers, switches, or servers by adding or dropping wavelength channels in the optical domain. As the number of OADMs increases, however, the signal is subject to loss and amplification can be required. Ring architecture is subject to noise build-up, which can reach a point where the noise is greater than the signal strength. This problem can be significant when amplifiers are used in the ring. Remote SAN Remote SAN Remote SAN

Corp SAN Example The preceding diagram shows a ring configuration in which each site is connected to a DWDM multiplexer. In this configuration, specific wavelengths (lambdas) are used between each pair of sites. This configuration is referred to as a meshed ring. Remote SAN Remote SAN Remote SAN

DWDM Topology Evolution: Point-to-Point Ring Mesh Ring Definition Mesh architectures provide multiple data paths between network elements. Mesh architectures are the future of optical networks. From a design standpoint, there is a graceful evolutionary path available from point-to-point to mesh topologies. Example By beginning with point-to-point links, equipped with OADM nodes at the outset for flexibility, and subsequently interconnecting them, the network can evolve into a mesh without a complete redesign. Additionally, mesh and ring topologies can be joined by point-to-point links. The preceding graphic depicts this evolution. Facts As networks evolve, rings and point-to-point architectures will still have a place, but mesh promises to be the most robust topology. DWDM mesh networks, consisting of interconnected all-optical nodes, will require more robust protection from link and device failures. Where previous protection schemes relied upon redundancy at the system, card, or fiber level, redundancy in a mesh must migrate to the wavelength level. Mesh networks will therefore require a high degree of intelligence to perform the functions of protection and bandwidth management, including fiber and wavelength switching. In exchange, mesh networks will offer significant improvements in efficient use of fiber. Fiber usage can be low in ring solutions because of the requirement for protection fibers on each ring. In a mesh design, protection and restoration can be based on shared paths, thereby requiring fewer fiber pairs for the same amount of traffic. Finally, mesh networks will be highly dependent upon software for management. A routing protocol for all-optical networks is in development. In addition, network management will require a channel to carry messages among the network elements. Point-to-Point Mesh

DWDM Protection Unprotected Client-Protected Splitter Protected
Y-Cable and Line Card Protected DWDM Protection Objective Describe high-availability DWDM configurations Introduction This section explains how a DWDM system can provide redundancy. Facts In the DWDM market, the term “protection” refers to various schemes for providing redundancy to guard against failure of optical links and devices. In first-generation DWDM equipment, protection is provided at the system level. Parallel links connect redundant systems at either end. Switchover in case of failure is the responsibility of the client equipment (a switch or router, for example), while the DWDM systems themselves just provide capacity. In the preceding diagram, the top two configurations do not involve any optical protection. In the unprotected configuration there is a single link between the client equipment and the DWDM equipment, and in the client-protected configuration there are two links between the client and DWDM equipment. In second-generation DWDM equipment, redundancy is provided at the optical level. Parallel links connect single systems at either end that contain redundant transponders, multiplexers, and CPUs. Optical protection puts redundancy into the DWDM equipment, with switching decisions under local control. The lower two configurations shown in the preceding diagram illustrate two scenarios in which protection is provided at the optical level. In the splitter-protected configuration, the incoming optical signal is split in the DWDM node. In the Y-cable/line-card protected configuration, the incoming optical signal is split prior to entering the DWDM node, and each signal goes to a separate line card in the DWDM node. DWDM Node/Equipment Client Equipment

DWDM Protection (cont.)
Unprotected 1 Client Interface 1 Transponder The preceding diagram illustrates a simple unprotected scenario. Each client has only one interface connected to one transonder. The transponders transmit the DWDM signal in only one direction, so they connect to only one fiber pair. If the fiber is cut or if a transponder fails, there is no protection. Only one transponder needed Only one path available No protection in case of fiber cut, transponder failure, or client failure

Client Protected Mode 2 Client Interfaces 2 Transponders In the preceding diagram, each client has 2 interfaces connected to two separate transponders. One of the transponders transmits towards the east and the other transponder transports to the west direction over two fiber paths. Customers may have already purchased/invested/designed networks to take advantage of redundancy schemes via their routers or switches or SONET/SDH gears (I.e. routing protocols with diverse routes, Hot Standby Routing Protocol (HSRP), port channels, load balancing, etc). Two transponders needed Provides two paths Protection via SONET, Layer 3 routing, Hot Standby Router Protocol, EtherChannel

Optical-Splitter Protection Working Lambda Optical Splitter Switch Protected Lambda The preceding diagram illustrates the optical-splitter protection method. Each client has one interface connected to one transponder, and the transponder splits the laser beam and directs each half of the beam onto a separate fiber. The same data goes both directions around the ring (over two fiber paths) simultaneously. At the remote end, there is a 2x2 switch on the DWDM multiplexer motherboard that listens to both incoming lambdas. One of the lambdas is configured to be the working side, while the other lambda is the protected side. The data coming from the working side is passed through the transponder on the client side. If the 2x2 switch detects a loss of signal on the working side, it switches over and begins transmitting the data that arrives on the protection lambda. The switchover occurs in less than 50ms. This scheme provides protection in the case of a fiber cut, but does not provide protection for a laser failure or a transponder failure. However, this level of protection is sufficient for most enterprise applications. Only one transponder needed Per-fiber switch or per-lambda splitter Does not protect against laser or transponder failure

Line-Card and Y-Cable Protection Working Lambda 2 Transponders Only 1 Tx active “Y” Cable Protected Lambda The preceding diagram shows another method of optical protection called Line-Card and Y-Cable protection. Each client has a single interface connected to two transponders with a Y-cable. The Y-cable is a purely optical device—it contains no electronics. The Y-cable splits the signal to two separate transponders. One of the transponders transmits in east, the other in west. The same data goes both directions around the ring simultaneously. On the receiver side, two transponders receive the data, but they are software-configured to operate in a protection scheme. One of the transponders is configured as working and the other one is configured as protection. The working transponder receives the signal and transmits the signal into the Y-cable. The protection transponder receives the data but throws it away. If the working lambda fails or if the working transponder fails, the CPU turns off the transmitter on the client side of the working transponder, and turns on the transmitter on the client side of the protection transponder. Thus, only one transponder ever transmits data into the Y-cable. This configuration provides more protection than optical splitter because it protects against transponder failure. The increased protection comes at a higher cost because the user must purchase 2 wavelengths for every service channel. This configuration also reduces the number of protected lambdas that can be in a single shelf to 16, but two shelves can be combined into a single system so you can still get 32 protected lambdas. Two transponders needed Increased availability and cost

DWDM Performance Limitations
General DWDM considerations: Topology: Ring is most suitable for metro-area transport Point-to-point spans longer distances Amplification: Extends DWDM point-to-point configurations Can also be used on ring configurations but does not provide the same distance increases Power budget: Node-to-node Network total DWDM Performance Limitations Objective Discuss the performance limitations of DWDM Introduction This section describes key performance issues that apply to DWDM and to FC over DWDM. Facts DWDM technology is capable of spanning great distances between nodes without amplification. For this reason, DWDM technology is used for applications like undersea optical cables. Factors that determine the distance between nodes in a DWDM system include: Topology: Point-to-point topologies can extend over longer distances than ring topologies. This is because ring topologies can build up transmission noise that exceeds the strength of the signal. Amplification: Using optical amplifiers in a point-to-point network greatly increases the distance capability of DWDM. Amplification in a ring topology does not result in the same distance increases, because noise is amplified along with the signal. Power budget: The power budget is a very important part of setting up DWDM links. The overall power budget calculation (both node-to-node and network-wide) ultimately determines the practical distance limitation of a DWDM implementation. Factors that impact the power budget include the inherent device design, type of laser source, type of fiber optic cable used, number of nodes and network topology, and number of wavelengths.

DWDM Performance Limitations (cont.)
Optical signals are attenuated by: Distance (length of the optical fiber) Fiber characteristics Number of access nodes Number of connectors and splices Dirt, flaws, or faults in the cable or connectors Facts When an optical signal reaches a receiving device, it must be strong enough to be detected, but must not overpower the receiver. This requires careful calculation of the “optical power budget” of each span of the network. Optical signals are subject to attenuation caused by: Length of the fiber Attenuation characteristics of the fiber itself (single-mode vs. multimode, quality of optical fiber) Number of access nodes Locations and number of connectors and splices in the cable Dirt, flaws, or faults in the fiber or connectors

S-Band:1460–1530nm Loss (dB)/km vs. Wavelength L-Band:1565–1625nm 2.0 dB/Km C-Band:1530–1565nm OH- Absorption Peaks in Actual Fiber Attenuation Curve Rayleigh Scattering IR Absorption 0.5 dB/Km The preceding diagram shows a spectral attenuation curve that demonstrates the wavelength-dependence of many of the signal attenuation factors. This diagram shows the span of wavelengths used in telecom fiber, from 600nm to 1600nm. The normal operating “bands” of wavelengths, centered around 850nm, 1300nm, and 1550nm, are highlighted. Factors such as Rayleigh Scattering and UV absorption decrease with longer wavelengths. UV absorption also decreases with wavelength. However, IR absorption picks up rapidly at the longer wavelengths and effectively limits the higher wavelength operations. DWDM uses wavelengths in the 1500nm range due to the low loss profile of that range. The “OH” peaks are cause by absorption of light due to OH ions created in the manufacturing process. They are also called “water peaks” because the OH ion is a component of water (H2O). UV Absorption 0.2 dB/Km 800 900 1000 1100 1200 1300 1400 1500 1600 Wavelength in Nanometers (nm)

Amplification is required for long-haul DWDM Considerations include: Link distance Number of nodes Ring vs. point-to-point topology Wavelengths must be power-balanced Network survivability Facts Long-haul point-to-point DWDM topologies require amplifiers due to the inherent signal loss that occurs over the distances involved. For other topologies, and for shorter distances, the question of amplification is more complex. Careful calculation of the total network power budget is required to determine whether amplifiers are necessary. The power budget calculation involves factors that include the characteristics of the hardware and cabling, link distance, number of nodes, and network topology. The decision regarding amplifiers involves several tradeoffs: Limiting the distance of DWDM links, or the number of wavelengths carried, can eliminate the need for amplifiers in the network. Optical amplifiers generate optical noise. This limits the number of nodes that can be deployed to about eight. Closed ring structures are also problematic in amplified networks due to circulating optical noise. In an amplified network, all wavelengths receive equal amplification. Therefore, the wavelengths must be power-balanced before they are amplified. Power balancing involves selective attenuation of individual wavelengths, to equalize the power level of all signals, before amplifying the entire group. A failed optical amplifier will affect multiple wavelengths, and becomes a single point of failure.

Performance issues for FC over DWDM: Link distance increases latency: Delays delivery of R_RDYs and ACKs (round-trip) Requires additional FC BB_credits FC “droop”: Bit errors can destroy R_RDY messages Decreases the number of available credits Link must be reset periodically FC over DWDM typically limited to about km Application-dependent: E.g. synchronous vs. asynchronous mirroring Facts The FC protocol relies on messaging between end stations to confirm data transfer and exchange buffer credits. The greater the distance between end stations, the longer it takes for confirmation messages to travel back and forth. This affects throughput because the originating station cannot send new data until it receives confirmation from the receiving station that previously sent data has safely arrived. This issue can be addressed to some extent by configuring additional FC buffer-to-buffer credits to accommodate the round-trip latency. DWDM networks are also subject to a specific type of performance degradation called Fibre Channel “droop” that affects data throughput. Droop is a result of the impact of bit errors on the FC buffer credit system: In a DWDM network, bit errors can arise from electrical interference in the receive electronics or from the noise inherent in the optical receiver. When a bit error destroys an R_RDY, the number of available credits is reduced. A reduction in the number of credits reduces the utilization of the DWDM link and causes a drop in throughput. The droop continues to worsen until the link is manually reset, or until the number of credits has declined to zero, at which point the fabrics will reset the link and a full complement of credits will be restored. FC droop restricts the ability of most installed FC systems to deliver high throughput over distances greater than kilometers. The requirements of the SAN application help determine the performance requirements and distance limitation. For example, synchronous mirroring requires lower latency than asynchronous mirroring.

CWDM and DWDM DWDM: CWDM: Narrower wavelength spacing
C band DWDM: Narrower wavelength spacing Up to 160 wavelengths Can be amplified (EDFA) Optimized for bandwidth EDFA bandwidth 1280nm 1400nm 1500nm 1625nm 1280nm 1400nm 1500nm 1625nm CWDM: Wider wavelength spacing Up to 8 wavelengths Cannot be amplified Optimized for cost CWDM and DWDM Objective Compare CWDM to DWDM Introduction This section compares features of CWDM to those of DWDM. Facts Like DWDM, Coarse Wavelength Division Multiplexing (CWDM) employs multiple light wavelengths to transmit signals over a single optical fiber. The two technologies differ in several respects: Wavelength spacing: CWDM uses significantly wider spacing (20nm as opposed to 1nm for DWDM). The actual frequency grid for DWDM and wavelength grid for CWDM systems are defined by the International Telecommunications Union standards G and G.694.2, respectively. Number of channels: CWDM offers a maximum of 8 wavelengths (lambdas), compared to Metropolitan DWDM systems that support up to 160 wavelengths on a single fiber. Ability to use optical amplifiers: no amplification is possible with CWDM because CWDM uses wavelengths that cannot be amplified with EDFA amplifiers. Taken together, these technological differences result in less complex installation, configuration and operation for a CWDM network. CWDM is optimized for cost, whereas DWDM is optimized for bandwidth.

CWDM and DWDM (cont.) DWDM CWDM Max. Link Speed 2.5–10 Gbps 2.5 Gbps
Link Distance 80km unamplified >80km amplified <80km Cannot amplify Scalability 32–160 lambdas 8 lambdas Cost High initial cost; potential for high ROI 25-35% of DWDM cost Facts Other differences between DWDM and CWDM include: Maximum link speed: Currently deployed DWDM and CDWM components both have a typical bit rate of 2.5Gb/s. However, 10Gb/s components are now available for DWDM. Link distance: CWDM is limited to less than 80 km, due to the inability to use optical amplifiers. Scalability: CWDM is less scalable because it provides fewer wavelengths (lambdas). The Cisco ONS SONET/SDH/DWDM platform supports 160 wavelengths per fiber. The Cisco DWDM products that currently support FC support up to 32 wavelengths. CWDM supports 8 wavelengths. Cost: CWDM components cost a fraction of what DWDM equipment costs, primarily due to lower complexity. Because CWDM offers the same security, reliability, and quality as DWDM, it can be a cost-effective solution where: Dark fiber is already in place The number of applications is limited Data-capacity requirements are lower Fiber spans are less than 80 km Typically, this describes small-to-medium businesses and metropolitan-to-enterprise-edge applications.

SONET Terminal Multiplexer (PTE) SONET Terminal Multiplexer (PTE)
SONET/SDH Components Path Line Line Add/Drop Multiplexer Section Section Section Section Regenerator Regenerator SONET Terminal Multiplexer (PTE) SONET Terminal Multiplexer (PTE) SONET/SDH System Components Objective Identify the components of a SONET/SDH system Introduction This section describes the components of a SONET/SDH system. Facts Synchronous Optical Network (SONET) is a standard for optical transport. SONET is a digital hierarchy interface defined by ANSI for use in North America. Synchronous Digital Hierarchy (SDH) is a standard defined by the International Telecommunications Union (ITU) for worldwide use. SDH is similar to, and partly compatible with, SONET. The components of a SONET/SDH system are shown in the preceding diagram. Components include: Terminating Equipment: Path Terminating Equipment (PTE) terminates each end of a path Line Terminating Equipment (LTE) terminates each end of a line Section Terminating Equipment (STE) terminates each end of a section Add-Drop Multiplexers combine multiple signal inputs into an Optical Carrier (OC-x) signal. At an add/drop site, individual signals are dropped or inserted as required. The remaining traffic is passed through without additional processing. Regenerators are used to maintain sufficient power in the optical signal. Digital Cross-Connect devices (not shown here) are used to multiplex and demultiplex services at the tributary level Service (DS1, DS3… / E1, E3...) Mapping Demapping Service (DS1, DS3… / E1, E3...) Mapping Demapping

Storage Transport Over SONET/SDH
FC FCIP TCP FC IP Storage Transport Over SONET/SDH Objective Explain how a SONET/SDH system transports storage networking protocols Introduction This section explains how a SONET/SDH system transports storage networking protocols. Facts There are four ways to implement multi-site FC SANs over SONET infrastructures: Use FCIP to run FC over IP over packet-over-SONET/SDH (PoS). In this configuration, multiple layers of encapsulation add overhead and latency. This configuration often cannot guarantee sufficient throughput and low latency required for synchronous data replication. Run FC over ATM over SONET/SDH. Encapsulating FC into ATM through an ATM Adaptation Layer (AAL) adds overhead and latency, and adds complexity and cost to network operation and management. This configuration is generally more suitable for asynchronous applications Run FC directly over SONET/SDH. Transporting FC traffic in its native format over SONET requires an intermediate device to connect FC switches to SONET networks. Latency is reduced to the level induced by the SONET protocol overhead. This configuration is can be suitable for synchronous applications. Run FC over SONET/SDH over DWDM. FC traffic is encapsulated as SONET payloads, and the SONET/SDH payloads are then transported over a DWDM network. This configuration provides the bandwidth of DWDM and enables the use of dark fiber while providing the benefits of SONET/SDH’s management capabilities. In addition, if the DWDM equipment does not support multiplexing multiple FC channels on a single wavelength, SONET can perform the multiplexing function. A SONET multiplexer can dedicate the exact amount of bandwidth required for each application on each storage channel. AAL FC Ethernet/PoS ATM FC SONET SONET SONET SONET DWDM FCIP FC over ATM FC over SONET FC over SONET over DWDM

SONET/SDH Performance Limitations
Network management features introduce latency Electronic components limit transmission speeds Pre-defined bandwidth increments result in unused capacity Voice traffic optimization means less efficient bandwidth allocation SONET/SDH Performance Limitations Objective Identify the general performance limitations of SONET/SDH Introduction This section describes the performance limitations of SONET/SDH. Facts The SONET/SDH protocol provides for administration and monitoring functions, security, Quality of Service, and troubleshooting tools. These advantages come at the expense of some latency. The electronic components in a SONET/SDH network impact total throughput. The typical long distance bandwidth available in a standard single-mode optical fiber is GHz. SONET and SDH systems are limited in their exploitation of this bandwidth by electronic component speeds, which currently limit transmission to bit rates of a few tens of Gbps. When bandwidth requirements increase, additional capacity is only available in pre-defined increments. These increments may exceed the additional requirements, resulting in significant unused capacity. This rigid hierarchy, along with the practical upper bandwidth limit of OC-768, limits the scalability of SONET/SDH networks. SONET/SDH technology is optimized for time-division multiplexing (TDM) applications, such as voice transmission, rather than data transmission. As a result, SONET/SDH allocates the available bandwidth less efficiently than DWDM.

Storage Applications Considerations for selecting an optical storage networking solution: Data rate requirements Distance requirements Protocol support Scalability (number of applications/channels) High availability and redundancy Network management required Existing infrastructure Cost Storage Applications Objective Identify the factors to consider in selecting the appropriate optical technology for a storage environment Introduction This section identifies the factors to consider in selecting optical technologies. Guidelines To select an appropriate technology for a particular storage application, consider the following factors: Data rate requirements—what level of throughput does the application require? Distance requirements—how far does the data have to travel from source to destination? Protocol support—are required storage protocols (e.g. FC, ESCON, FICON, GigE) supported? Scalability—how many channels are required, and what is the expected growth in demand? High availability—what levels of redundancy do the customer’s applications require? Network management—what network insight and troubleshooting capability is required? Existing infrastructure—does the customer already have an optical infrastructure or dark fiber? Cost—what is the budget for the solution? Example 1 An e-commerce company wants to mirror all its daily transactions to a remote data center 150 miles from the primary processing center. Their current fiber network is experiencing congestion from the steadily increasing volume of database updates. They are planning to introduce two major new product lines, and need a solution that will scale with their business. Based on their requirements for throughput, number of applications, link distance, and scalability, DWDM might be the best solution.

Storage Applications (cont.)
SONET/SDH offers: Robust network management and troubleshooting Significant installed infrastructure Support for longer distances Scalability issues (bandwidth) DWDM offers: Highest performance and scalability, but highest cost Less widely available Use of dark fiber Limited management capability CWDM offers: Lower cost than DWDM, but lower performance and scalability Guidelines SONET/SDH, DWDM, and CWDM have different strengths and limitations: SONET/SDH offers robust network management and troubleshooting capabilities and a significant installed infrastructure. SONET/SDH services are readily available in many areas, and can support longer distances than DWDM and CWDM. However, SONET/SDH can suffer from scalability issues. Only OC-192 provides enough bandwidth (9.952Gb/s) to support more than one 2Gb/s FC or FICON channel, and OC-192 is not as widely available. The more widely available SONET/SDH service levels (such as OC-3) provide less than 1Gb/s of bandwidth. DWDM offers ample bandwidth, performance, and scalability, but also costs more. DWDM services are not as widely available as SONET/SDH, so companies might need to implement and manage their own DWDM solutions. However, DWDM allows the use of dark fiber, so companies that already have access to dark fiber might find DWDM attractive. DWDM does not have the same robust management capabilities as SONET/SDH, so management can be more costly. CWDM offers levels of performance and scalability that are greater than SONET/SDH, but less than DWDM. Accordingly, the cost of CWDM is likely to fall between the cost of SONET/SDH and DWDM. Example 2 A global financial services firm is generating an increasing volume of transaction and collaborative data. The resulting storage requirements and network traffic were degrading network performance, causing delayed or failed transactions. Their current infrastructure consisted of DWDM components, carrying ESCON, Gigabit Ethernet, and Fibre Channel. However, insufficient network monitoring capability has contributed to the ongoing network performance problems. Their goals are to increase network capacity and improve network performance monitoring capability. A SONET solution will work with their existing infrastructure, scale to meet their increasing volume, support the protocols they deploy, and provide detailed network management capability.

Large Enterprise – Multiple Data Centers Synchronous Replication Asynchronous Replication Remote Vaulting BC/DR Applications Optical FCIP Network Infrastructure Guidelines Business continuance and disaster recovery (BC/DR) applications are the most common applications for optical storage networking. Large enterprises that have the resources to implement optical solutions like CWDM, DWDM, and SONET, and that may already have dark fiber in place, can leverage any of these technologies depending on the specific BC/DR application: Synchronous replication requires high bandwidth and low latency, and is therefore well-suited for optical CWDM and DWDM infrastructures in which FC is channeled directly over an optical network. For longer distances—where the cost of leasing or maintaining a CWDM or DWDM infrastructure is higher—FCIP over SONET can also be used for synchronous replication if the SONET infrastructure provides the needed bandwidth and low latency. Asynchronous replication consumes less bandwidth and can tolerate more latency, so FCIP over SONET can provide a more cost-effective solution in addition to supporting longer distances. Remote vaulting applications—which resemble standard backup applications, but where the backup device is located at a remote location, such as at an SSP—can require longer distances, but do not have stringent latency requirements. For these solutions, FCIP over SONET can be the most cost-effective solution. If the remote vault is hosted by an SSP, establishing a SONET link to an SSP is generally simpler than establishing a CWDM or DWDM link. CWDM • Campus DWDM • Campus • Metro SONET/SDH • Metro Ethernet Services • WAN Services Long Distance Short Distance

Mid-Tier Enterprise Host-Based Mirroring Remote Vaulting BC/DR Applications iSCSI FCIP Network Infrastructure For mid-tier enterprises, the cost of implementing an optical CWDM or DWDM solution can be prohibitive. SONET can often provide a more cost-effective solution for these enterprises. Mid-tier enterprises can also lease SONET services from a WAN service provider, which offers more flexibility and is also typically more cost-effective for implementations that involve fewer data centers. The BC/DR applications that are most common in mid-tier enterprises are: Host-based mirroring solutions are generally most suitable for applications with less stringent bandwidth and performance requirements, so either iSCSI over SONET or FCIP over SONET might be suitable infrastructures. Remote vaulting applications are more commonly associated with FCIP over SONET, as is the case with larger enterprises. SONET/SDH • Metro Ethernet Services • WAN Services Long Distance Short Distance

Cisco WDM Products ONS 15200 Family
ONS Multichannel Multiplexer ONS and (DWDM): Supports 1Gb FC only Supports ESCON, FICON, GigE, FDDI, POS No multiplexing of channels Limited certification for storage No roadmap to 2Gb or 10Gb Cisco Optical Storage Networking Products Objective Identify Cisco optical storage networking products Introduction This section describes the Cisco optical networking products that support storage applications. Facts The Cisco ONS Metro DWDM Solution includes the ONS 15252, ONS 15201, and ONS platforms. The Cisco ONS 15252/15201 Optical Network System platform is a modular and scalable dense wavelength division multiplexer (DWDM) platform. The Cisco ONS Single Channel Unit (SCU) terminates a single channel. The Cisco ONS Multichannel Unit (MCU) can terminate up to 48 channels. The Cisco 15252/15201 support: Fibre Channel (1Gb only), ESCON, and FICON. Fast Ethernet and Gigabit Ethernet Fiber Distributed Data Interface (FDDI) SONET/SDH and ATM (Packet over SONET [POS]) at OC-3/STM-1, OC-12/STM-4, and OC-48/STM-16 Client interface 100 Mbps to 1.25 Gbps at 1310 to 1550 nm The ONS15200 does not support channel multiplexing. This means that, for example, a 2.5Gb/s DWDM wavelength can support only a single 1Gb/s FC, FICON, or ESCON channel. Cisco does not currently have a roadmap for further development of the ONS15200 platform. Cisco does not plan to provide 2Gb Fibre Channel or 10Gb Ethernet support for this platform. ONS Single Channel Multiplexer

Cisco WDM Products ONS 15530/15540
ONS (DWDM): 4 wavelengths per chassis 32 wavelengths per fiber 1Gb and 2Gb FC ESCON, FICON, GigE, FDDI, SONET/SDH, and ATM (POS) Multiple protection options Multiplexes up to 8 FC channels into a single wavelength ONS 15530 The Cisco ONS is a DWDM services platform that supports: 4 wavelengths at 10Gb/s on a single chassis Up to 32 wavelengths per fiber pair 1Gb and 2Gb Fibre Channel ESCON and FICON Fast Ethernet, Gigabit Ethernet, and 10 Gigabit Ethernet FDDI SONET/SDH and ATM (POS) at OC-3/STM-1, OC-12/STM-4, and OC-48/STM-16 Disparate traffic types on a single fiber pair Numerous protection options Multiplexing multiple application channels into a single wavelength (up to 8 FC/FICON/GigE or 40 ESCON) The ONS goes beyond the capabilities of today’s DWDM platforms with integrated switching and aggregation capabilities. The typical network paradigm today is to have a single service per wavelength, adding expense to the network and very inefficiently using precious fiber resources. By aggregating multiple interfaces onto a single wavelength and then launching into a common, intelligent optical transmission network, the customer can see dramatic reductions in both cost and complexity of the network. Each wavelength supports 8 ports of Fibre Channel/FICON/Gigabit Ethernet or 40 ports of ESCON. Each Cisco ONS can add/drop 4 protected wavelengths or 8 unprotected wavelengths.

Cisco WDM Products ONS 15530/15540 (cont.)
ONS (DWDM): 32 wavelengths per fiber 1Gb and 2Gb FC ESCON, FICON, GigE, FDDI, SONET/SDH, and ATM (POS) APS Optical, service, and application-level monitoring (Application-Aware DWDM) Does not support channel multiplexing ONS 15540 The ONS is a DWDM platform that integrates data networking, SAN, SONET, and SDH technologies. ONS features include: 32-channel Array Wave Guide (AWG) optical multiplexer module 1Gb and 2Gb Fibre Channel ESCON and FICON Fast Ethernet, Gigabit Ethernet, and 10 Gigabit Ethernet FDDI SONET/SDH and ATM (POS) at OC-3/STM-1, OC-12/STM-4, and OC-48/STM-16 Disparate traffic types on a single fiber pair—but no channel multiplexing Automatic Protection Switching (APS) Optical, service, and application level performance monitoring (per-fiber and per-wavelength) The ONS supports an innovative feature called Application-Aware DWDM. This feature enables non-intrusive application performance monitoring on a per wavelength basis. With this feature, administrators can ensure service levels (for example, providing a bit error rate below 10-15) in addition to protecting against failures. Other vendors’ DWDM platforms do not provide this feature. Unlike the ONS 15530, the ONS does not support channel multiplexing.

Cisco WDM Products ONS 15530/15540 (cont.)
The Cisco ONS and ONS platforms are certified for remote synchronous mirroring solutions offered by IBM, EMC, HDS, and HP/Compaq. The ONS and ONS are also certified by AT&T Solutions, Metromedia, and Brocade.

Cisco WDM Products CWDM SFPs and OADMs
Cisco CWDM SFPs supported for MDS switches: SAN extension into the MAN—up to 120 Km Multi-rate support (GbE, 1G FC, 2G FC) 8 colored SFPs LC connector Cisco CWDM Optical Add/Drop Modules (OADMs) Facts Cisco CWDM products include the following: Cisco CWDM Chassis Cisco CWDM Optical Add/Drop Modules (OADMs) Cisco CWDM GBICs and SFPs Duplex single-mode patch cable to connect GBICs and OADMs Attenuators for short links (5dB or 10dB loss) so as not to exceed the maximum recommended optical power at receiver Cisco CWDM SFPs are used to connect MDS 9000 Family switches to the DWDM OADM, supporting SAN extension into the MAN at up to 120 Km, depending on the class of DWDM fiber used. The Cisco CWDM solution supports GbE, 1G FC, and 2G FC. There are 8 “colored” types of CWDM SPFs, where each “color” corresponds to a different CWDM wavelength. This allows up to 8 channels per CWDM fiber pair. The Cisco CWDM SFPs use the LC connector type. Cisco CWDM GBICs are used to connect Catalyst switches to the CWDM OADM modules. Cisco CWDM Chassis Cisco CWDM SFPs Cisco CWDM GBICs

Cisco SONET/SDH Products ONS 15454/15327
ONS (SONET/SDH): Carrier-class Multiservice Provisioning Platform (MSPP) Supports TDM, GigE, OC-192 Ring, point-to-point, add drop, star Multiple protection schemes (including ring and mesh) Robust management and monitoring Facts The ONS SONET/SDH Multiservice Provisioning Platform (MSPP) is part of Cisco’s Complete Optical Multiservice, Edge and Transport (COMET) product line. The carrier-class ONS provides the functions of multiple network elements in a single platform. The ONS SDH supports the following capabilities: Aggregation and transport of services including TDM (DS1, DS3, DS3 transmux, EC1/STS-1), data (10/100/1000Mbps Ethernet), and optical (OC-3/OC-3c, OC-12/OC-12c, OC-48/OC-48c, OC-192) Flexible networking support including rings, linear point-to point, linear add/drop, star, and hybrid topologies Multiple protection mechanisms support rings with single and multiple fiber pairs, as well as mesh topologies Robust management capabilities, including integrated node and subnetwork GUI craft interface, automatic inter-node cross-connect provisioning, detailed circuit map, traffic balancing, and node auto-discovery with provisionable subnetwork domain control. Performance monitoring features include near- and far-end reporting, provisionable threshold crossing alerts, intermediate path performance monitoring (IPPM), and SNMP Remote monitoring (RMON). ONS 15454

Cisco SONET/SDH Products ONS 15454/15327 (cont.)
ONS (SONET/SDH): Optical Edge Transport Platform Small, cost-effective platform DS1, DS3, OC-12, OC-48, GigE Ring and mesh protection schemes Deployment with the ONS using any of the 15327's supported configurations Where the full capabilities of the ONS are not required, the Cisco ONS SONET/SDH Optical Edge Transport Platform is a smaller, cost-effective platform for managed services and high-speed bandwidth aggregation for multiple services. The ONS supports: DS1, DS3, OC-12, OC-48, and Gigabit Ethernet services Ring and mesh protection schemes The ONS does not support as wide of a range of configurations as the ONS 15454; for example, the ONS does not support OC-192. However, the ONS can be deployed in a core-edge configuration with the ONS using any of the 15327's supported configurations. ONS 15327

Cisco SONET/SDH Products ONS 15454/15327 (cont.)
Support for FC-over-SONET: ONS and ONS 15327 Planned for late 2003 First release will support only OC-48 (2.488Gb/s) First release will not support subrate SONET FC Cisco plans to offer support for FC on the ONS and ONS later in The first release of the Cisco FC-over-SONET product will only support OC-48. This first release will not support subrate, which means that the entire OC-48 must be dedicated to a single FC channel.

Lesson Review In a DWDM network, what topology gives the best redundancy and future growth? Which of the following architectures can be used to provide more effective use of bandwidth on a DWDM network? What is the key disadvantage of CWDM as a metro-area solution, as compared to DWDM? Practice In a DWDM network, what topology gives the best redundancy and future growth? Ring Point-to-point Unidirectional Path Switched Ring (UPSR) Star Topology Mesh Topology Which of the following architectures can be used to provide more effective use of bandwidth on a DWDM network? FC over IP over DWDM FC over ATM over DWDM FC over DWDM over SONET/SDH FC over SONET/SDH over DWDM What is the key disadvantage of CWDM as a metro-area solution, as compared to DWDM? Distance Performance Reliability Scalability

Lesson Review (cont.) For synchronous data mirroring, how can you compensate for the effects of FC droop? What are the considerations for selecting an optical storage networking solution? For synchronous data mirroring, how can you compensate for the effects of FC droop? (Choose two) Aggregate multiple FC channels over one DWDM channel Increase the number of buffer credits at the FC switches Limit the distance between the primary and mirror sites Transport FC over SONET/SDH What are the considerations for selecting an optical storage networking solution?

Summary DWDM provides transparent transport of FC and other protocols over metro-area distances DWDM required components: Optical transmitters and receivers Optical fiber link DWDM multiplexers / demultiplexers DWDM optional components include: Optical amplifiers OADMs Optical Cross Connects Variable optical attenuators Dispersion compensation units Summary: Optical Storage Networking In this lesson you learned about optical networking technologies and their applicability for transporting storage protocols, and you learned to identify the Cisco optical networking products designed for storage applications.

Summary (cont.) DWDM networks can be configured as:
Point-to-point Ring Meshed DWDM protection schemes use redundant equipment to assure continuity in case of catastrophic failure, or redundant wavelengths for less robust protection DWDM performance is limited by the factors that are used to calculate the optical power budget For FC storage applications, FC “droop” is a key performance concern CWDM offers fewer wavelengths, no amplification, and lower cost

Summary (cont.) Storage network designers can choose from at least four different SONET/SDH architectures, depending on the complexity, latency, and management requirements SONET / SDH components include: Path, line, and section terminating equipment Add/Drop multiplexers Regenerators Digital cross-connect equipment SONET / SDH network performance is impacted by: Management overhead (induces latency) Electronic components (reduce speed) Pre-defined bandwidth increments (less efficient allocation) Voice optimization (less efficient allocation)

Summary (cont.) Evaluating optical systems for storage involves locating the appropriate trade-offs between cost, performance, and scalability Cisco offers DWDM, CWDM, and SONET/SDH multiplexers certified by third-party vendors: ONS DWDM (not recommended) ONS 15530/15540 DWDM CWDM SFPs for the MDS ONS 15454/15327 SONET/SDH (late 2003)

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