Driving Optical Network Evolution

Driving Optical Network Evolution Overview Over the years, advancement in technologies has improved transmission limitations, the number of wavelengths we can send down a piece of fiber, performance, amplification techniques, and protection and redundancy of the network. When people have described and spoken at length about optical networks, they have typically limited the discussion of optical network technology to providing physical-layer connectivity. When actual network services are discussed, optical transport is augmented through the addition of several protocol layers, each with its own sets of unique requirements, to make up a service-enabling network. Until recently, transport was provided through specific companies that concentrated on the core of the network and provided only pointto-point transport services. A strong shift in revenue opportunities from a service provider and vendor perspective, changing traffic patterns from the enterprise customer, and capabilities to drive optical fiber into metropolitan (metro) areas has opened up the next emerging frontier of networking. Providers are now considering emerging lucrative opportunities in the metro space. Whereas traditional or incumbent vendors have been installing optical equipment in the space for some time, little attention has been paid to the opportunity available through the introduction of new technology advancements and the economic implications these technologies will have. Specifically, the new technologies in the metro space provide better and more profitable economics, scale, and new services and business models. The current metro infrastructure comprises this equipment, which emphasizes voice traffic; is limited in scalability; and was not designed to take advantage of new technologies, topologies, and changing traffic conditions. Next-generation equipment such as next-generation Synchronous Optical Network (SONET), metro core dense wavelength division multiplexing (DWDM), metro-edge DWDM, and advancements in the optical core have taken advantage of these limitations, and they are scalable and data optimized; they include integrated DWDM functionality and new amplification techniques; and they have made improvements in the operational and provisioning cycles. This tutorial provides technical information that can help engineers address numerous Cisco innovations and technologies for Cisco Complete Optical Multiservice Edge and Transport (Cisco COMET). They can be broken down into five key areas: photonics, protection, protocols, packets, and provisioning.

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Network Flexibility Networks today must support a variety of traffic types, including legacy traffic based on regional SONET ring structures that require multiple traffic adds/drops (that is, voice, asynchronous transfer mode [ATM], frame relay) but must also support high-speed Internet backbones that are typically express lanes that require little add/drop multiplexing. Deploying the hybrid Raman amplifier and erbium-doped fiber amplifier (EDFA) amplification application in the L-band enables extended long-haul reach for this express Internet traffic, while still allowing deployment of the C-band as traditional long haul for legacy-type traffic, a deployment that requires multiple traffic add/drop sites. This mix of traditional long haul in the C-band and extended long haul in the L-band allows for better network flexibility.

Amplification Extended to Metro, Long Haul The key drivers for this application include a reduction in the cost of bandwidth (that is, a reduction in price/performance and distance, an increase in network capacity, higher network availability, and better network flexibility).

Reduction in Cost of Bandwidth In conventional long-haul (EDFA) technology, the transmission signals must be regenerated every 500 km or so to overcome signal distortion due to dispersion and nonlinear effects and to overcome the build-up of noise generated within the EDFA amplifiers. This regeneration is accomplished through optical-to-electricalto-optical (O–E–O) conversion, the signal being regenerated during the electrical phase. This regeneration equipment is required on a per-channel basis and is, therefore, very expensive, and it also requires a large equipment footprint and high electrical power consumption and subsequent site climatic control. If a hybrid distributed Raman amplifier plus EDFA technology is used, the regeneration-site spacing can be extended from 500 km to 2,000 km. This extended–long-haul application, therefore, introduces significant cost savings and reduces the dollar cost of transmission capacity for digital signal (DS3) per kilometer.

Network Capacity A limiting factor in DWDM systems that restricts the minimum channel spacing and, therefore, the capacity of the system lies in pulse distortions and interference that arises from nonlinear effects. Four-wave mixing (FWM) and cross-phase modulation (XPM) are two such nonlinear effects that are channelspacing dependent and, therefore, restrict the minimum channel spacing and ultimate fiber capacity. However, the efficiency of these nonlinear effects is Web ProForum Tutorials http://www.iec.org

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dependent on the channel signal power. Using the Raman amplification effectively reduces the "apparent" loss of the transmission fiber that the signal sees. Therefore, the "per-channel" power launched by the EDFA can be reduced, and this reduction in per-channel power reduces nonlinear effects in the fiber and allows closer channel spacing and greater system capacity.

Network Availability The network availability is determined from the failure in time (FIT) rates of the components that make up the network. The regeneration sites that are placed every 500 km in conventional EDFA–based networks are "heavy" in high-speed electronics and optical components and, therefore, have the highest FIT rate and thus the highest failure rate in the network. Using hybrid distributed Raman amplifiers plus EDFA amplification in extended–long-haul systems dramatically reduces the number of regeneration sites, yielding significantly higher network availability.

Channel Spacing With enhancements in demultiplexing technology, it is now possible to deploy DWDM systems with 50-GHz channel spacing at 10-Gbps rates. This scenario allows for greater channel counts and, therefore, higher capacities. Previously in the C-band with 100-GHz spacing, it was possible to deploy 40 channels; with 50-GHz spacing, this figure has been doubled to 80 channels. Improved transmitter wavelength stability is required to achieve 50-GHz channel spacing. "Wavelength locking" of transponder transmitter lasers has been introduced to achieve improved wavelength stability. The local feedback loop ensures long-term accuracy of the transmitter laser wavelength over the operating temperature range of the system. With the closer channel spacing, multichannel, nonlinear effects such as FWM and XPM become more critical. To control these nonlinear effects, automatic power provisioning (APP) of the amplifiers is required to control and maintain channel launch powers below nonlinear thresholds. To maintain span distances with the greater channel counts and with the requirement to maintain perchannel launch power below nonlinear thresholds, greater sensitivity is required in the receivers. This (change increased to greater) increased sensitivity has been achieved through the introduction of out-of-band forward error correction (OOB FEC) transponders. The 7-dB FEC gain, in fact, allows for enhanced span distances, even with this increased capacity. Until recently, the EDFA gain bandwidth was restricted to the so-called C-band, a wavelength band of about 35 nm spanning from just below 1530 nm to just over 1560 nm. However, by optimizing the erbium fiber doping composition and fiber Web ProForum Tutorials http://www.iec.org

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design and implementing an improved pumping scheme, it has been possible to extend the gain bandwidth out past 1600 nm, the L-band. The introduction of amplifiers for the L-band has allowed for increased system capacity over the installed fiber plant. This additional bandwidth allows for growth of up to 80 additional long-haul channels at 50-GHz spacing. Alternatively, this bandwidth can be used with a hybrid of L-band EDFA amplifiers and Raman amplification for extended-long-haul applications, allowing greater reach between costly regeneration sites.

Topics 1. Error Correction, Threshold Control 2. Protection 3. Protocols and Packets 4. Provisioning 5. Provisioning Services 6. Summary Self-Test Correct Answers Glossary

1. Error Correction, Threshold Control Transmission fiber dispersion, fiber nonlinear effects, and amplifier noise limit the number of channels and the unregenerated transmission distance of DWDM systems. These factors can be overcome with OOB FEC transponders to enable a 70 percent increase in the number of channels or a 60 percent increase in the transmission distance. Additionally, the OOB FEC allows an improvement in the quality of service (QoS) by guaranteeing a received data channel bit-error rate (BER) of better than 1.0E—15 OOB FEC coding relies on Reed-Solomon algorithms to add redundancy bits to the data stream, enabling the identification and correction of corrupted data bits. These redundant bits take the optical carrier (OC)–192 data rate from 9.953 Gbps to 10.663 Gbps and yield a 7-dB improvement in optical signal-to-noise ratio (OSNR) margin compared to nonFEC transmission. This 7-dB OSNR improvement allows for the improved channel capacity, transmission distance, and QoS. To further enhance performance, the 10-Gbps OOB FEC transponders utilize optimized threshold crossing control in the receiver side of the transponder to set the decision circuit threshold to the in the received data "eye." When multiple Web ProForum Tutorials http://www.iec.org

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traces of the data stream are superimposed on top of each other, the 0s and 1s form an "eye." The more open the eye, the more reliably the 0s and 1s will be detected and the better the BER. However, amplitude noise from the EDFA amplifiers and electronics, phase noise, dispersion effects, and interference resulting from conversion of phase into amplitude modulation start to close the eye. As the eye closes, the decision circuit that determines if a bit is a 0 or 1 gives fewer bit errors if the decision threshold level can adaptively change to the optimum level. The optical receiver of the OOB FEC line extender modules (LEMs) and receive transponders (RXTs) feature adaptive threshold crossing control driven by the number of errored 0s and 1s determined in the bit stream. The result is improved receiver sensitivity and a resultant improvement in BER performance.

2. Protection As mentioned previously, traditional networks have been optimized for voice traffic, from both transport and protection levels. Many network topologies exist, from point-to-point, ring, and hub-and-spoke to fully meshed networks. Meshed networks fall outside the common Telcordia specified protection schemes of Bidirectional Line-Switched Ring (BLSR) and Universal PathSwitched Ring (UPSR). As a result, legacy SONET equipment manufacturers have not offered viable solutions for meshed networks. With its path-protected meshed network (PPMN) capability, Cisco has extended the simple concept of path protection on a SONET ring to meshed networks, offering service providers a new degree of flexibility in designing their networks.

Meshed Networks "Meshed networks" refers to any number of sites arbitrarily connected together with at least one loop. For this discussion, the connections between sites are SONET, at various line rates. Sites within the meshed network that can be reached from other sites through at least two distinct routes form the mesh, whereas the remaining sites are spurs off of this mesh. Meshed networks are often large rings with numerous sub-rings, as shown in Figure 1. Figure 1. Sample Meshed Network

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With PPMN, a network planner can design the mesh shown in Figure 1 with unprotected spans and various line rates. If a failure occurs on a route, connection is re-established through another path in the mesh within the wellknown SONET restoration time of 50 milliseconds. By designing PPMN consistent with SONET standards, Cisco offers network planners flexibility they can use today.

Practical PPMN Networks Good ideas are usually simple, and this one is no different. By using path protection, PPMN simply extends the UPSR beyond the basic ring topology to the meshed architecture. The software locates two diverse routes in the network between the source and destination of a circuit. These two routes form a logical ring for the path of that circuit, and they behave exactly as UPSR. The source bridges its traffic onto each of the diverse paths, and the destination selects between the two paths. With a failure on the active path, the destination simply switches to the standby path within 50 ms. Again, because of the strict adherence to SONET standards, PPMN applied to the logical ring is no different from the standard, Telcordia-specified UPSR. The real benefit of PPPN, however, lies not in the development of PPMN itself, but in the user interface. Cisco's Java-based graphical user interface (GUI), the Cisco Transport Controller, makes provisioning within a meshed network as simple as clicking a mouse button. All the nodes on the network, as soon as they are turned up, begin the process of autodiscovery. Within minutes, each node has a full description and status of the other nodes and connections throughout the network. (This scenario is possible because Cisco uses Internet protocol [IP] and Open Shortest Path First [OSPF] for SONET Data Country Code [DCC] communications). Creating a circuit is then accomplished by simply specifying the source and destination, another Cisco innovation called A-Z Provisioning. Software then determines the shortest path through the network and establishes all the intermediate cross-connections. A check box determines whether the circuit is to be protected or not. When checked, PPMN is provisioned. A protect circuit is established on the second-shortest path through the network between the source and destination, and a second set of cross-connections is created. With this capability, turn-up and provisioning of circuits can be done in a matter of hours rather than days.

Cisco COMET Applications in Meshed Topologies The following is an example of PPMN in the meshed network shown in Figure 1. Suppose a protected circuit is specified between nodes C and J. The PPMN software will determine that the shortest route between the two end nodes passes through node H and node G. Cross-connections at each of the four nodes (C, H, G, and J) are then automatically created, and working traffic is initially carried on Web ProForum Tutorials http://www.iec.org

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this route. Concurrently, cross-connections are created for the protected traffic on the second-shortest unique route between nodes C and J, C – B – A – L – J. If a fiber is cut or other failure occurs on the primary route, node J immediately switches to the traffic coming in from node L (instead of node G), and service resumes. Figures 2 and 3 offer graphical descriptions of this scenario and also show how the ring formed by A – B – C – H – G – J – L is a UPSR ring for this circuit. Figure 2. Working and Protecting Traffic Routed through a Meshed Network

Figure 3. Failure on Primary Path in Meshed Network

Another application for PPMN in meshed Cisco COMET networks is building what is commonly called "virtual rings." Figure 4 shows nodes A, B, C, and D forming an existing OC–192 backbone ring. Nodes E, F, G, and H are then added with OC–48 links to the backbone. The ring formed by E – F – G – H, which uses some of the bandwidth on the OC–192 backbone, is termed a "virtual ring." Protecting circuits created in this network topology is no different from the aforementioned example. Furthermore, PPMN does not care if the OC–192 backbone is UPSR or BLSR, as long as there is protected path from source to destination.

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Figure 4. Example of a Virtual Ring

Protection for Ethernet MANs With Ethernet the accepted Local-Area Network (LAN) standard, many organizations are looking to extend Ethernet into the metropolitan-area network (MAN). This in turn provides numerous consequences with regard to how the network will handle this type of traffic from both QoS and protection levels. Although Ethernet provides a tremendous foundation on which to build this next-generation network, fully realizing this end-to-end solution requires an Ethernet with carrier-class robustness. New capabilities are necessary to provide comprehensive Operations, Administration, Maintenance, and Provisioning (OAM&P) in a unified Ethernet optical environment. Ethernet must provide optical performance monitoring to help carriers deliver quality services meeting committed service-level agreements (SLAs). If an optical failure occurs, Ethernet must provide alarm indications and failure-protection mechanisms and help with fiber-failure isolation. QoS and class-of-service (CoS) capabilities are required to segregate and differentiate applications in a public services environment. Ethernet must continue to efficiently transport IP traffic while meeting the additional delaysensitive requirements of certain applications. Optimizing this data traffic requires integrated routing and control for both IP and optical layers to build an optimal Cisco COMET network.

3. Protocols and Packets Resilient Packet Ring Technology As service providers struggle to keep up with the demands of their customer base in the MAN, packet-based technologies are migrating from the traditional LAN to the MAN. Enterprise application growth is driving the increased bandwidth requirements and exceeding the existing capacity limits of the transport architectures in most provider networks. Until now, providers have generally deployed TDM technologies such as SONET/Synchronous Digital Hierarchy (SONET/SDH) for their offerings in this space. Inherent to Time Division Multiplexing (TDM) architectures, bandwidth is allocated in fixed amounts on point-to-point style circuits. This technology was successful for transporting Web ProForum Tutorials http://www.iec.org

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traditional voice, circuit-switched links, but the growth of pure data transport has exceeded the capacity in many networks. In addition, providers are finding it very difficult to provision new services quickly and expensive to upgrade to meet the demands of their customers. Therefore, providers have been forced to look to packet-based technologies to scale these needs. When reviewing the options available to scale this need, one immediately thinks of Ethernet as the leader for the inexpensive and flexible transport of packetbased topologies. However, Ethernet relies on the Spanning-Tree Protocol (802.1d) to provide for loop detection and elimination, generally recovering from a fault in 5 to 30 seconds. SONET offers the ability to provide protection from physical and logical failures in the ring in 50 ms based on the automatic protection switching (APS) standard. Whereas some proprietary technologies exist for recovery in shorter periods, the 50 ms recovery time was needed for many of the voice services carried over these networks. In addition to recovery issues, Ethernet is based on point-to-point, non-meshed physical layouts not conducive to deployment over the existing ringbased architectures of SONET. These two keys issues left providers with few options for solving the bandwidth needs of their customers. Enter packet-ring technologies. Cisco introduced Dynamic Packet Transport (DPT) in early 1999 based on a new concept called Spatial Reuse Protocol (SRP). This protocol takes advantage of both the ring-based architecture of SONET and the packet characteristics of Ethernet. DPT emerged as a new standard for deployment of these services for many providers seeking a solution without requiring the replacement of their existing fiber infrastructures. The Institute of Electrical and Electronics Engineers (IEEE) standards body quickly embraced this technology; subsequently, a new group was formed to advance the standardization of the technology. Many participate in this group, and they all work to make Resilient Packet Ring (RPR) technology more robust and interoperable. The working group rapidly adopted numerous objectives set forth to drive the use of RPR technology into the service-provider market: •

Distributed Access—There is no "master node" required in an RPR ring, allowing for the loss of any node in the ring without affecting ring operation.

•

Destination Stripping for Unicast Frames—In other packet-ring technologies, such as token ring, unicast frames must transit the entire ring to be removed only by the sending node after the intended receiver (802.5, Frame Copy Indication [FCI]) copies them. In RPR, the destination node removes unicast frames as they arrive, thereby freeing the bandwidth for downstream nodes.

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•

"Plug-and-Play" Support—This operation allows new nodes to be easily added to a ring without manual configuration or reconfiguration of other nodes in that ring.

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Bandwidth Distribution—Bandwidth is dynamically allocated to competing flows on demand as they enter the ring. Theories specific to this area abound. Currently, Cisco's DPT technology protects traffic already on the ring and queues traffic bound for the ring. The standards body has not reached an agreement on how this area should be handled in the draft specification.

•

Dual-Ring Topology—Unlike SONET, which uses one ring to transmit live traffic and the other for protection, RPR utilizes both directions. By using both rings, transmitting data in opposite directions at the same time, RPR substantially increases fiber utilization.

•

Rapid Protection Switching—RPR offers restoration from ring interruption in less than 50 ms. This restoration feature is very important for providers looking to maintain ring stability if a fiber is cut. In many voice networks, it is critical to the support of circuit-switched traffic. Also, as more IP traffic is deployed carrying loss-sensitive data, protection switching will help guarantee that traffic is not lost.

•

Multicast Traffic Support—Multicast traffic travels around the entire ring one time. This topology is very different from mesh-based topologies where multicast traffic must be replicated by each device in the network in order to reach all destinations.

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Universal Physical-Layer (PHY) Support—RPR is a Media Access Control (MAC)–layer specification and, therefore, allows the use of existing PHYs already available.

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Multi-Gigabit Ethernet Transport—RPR can carry 10/100-Mbps Ethernet as well as 1 Gbps and 10 Gbps.

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QoS Support—The goal of RPR is to deliver TDM–like QoS offerings to enable service providers to offer many varying services while maintaining customer SLA requirements for jitter and guaranteed-bandwidth services.

Structured Design and Architecture for Cisco COMET Metro Ethernet Networks Regardless of whether a pure, switched Layer-2 network or an Ethernet-overmultiprotocol label switching (EoMPLS) network is utilized, careful consideration of numerous parameters must be made. The following sections Web ProForum Tutorials http://www.iec.org

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provide some general guidelines that must be considered before designing and deploying a metro network.

Failure Domain A Layer-2 switched domain is considered to be a failure domain because a misconfigured or malfunctioning workstation can introduce errors that impact or disable the entire domain. For example, a jabbering network interface card (NIC) might flood the entire domain with broadcasts or undesirable frames at a very high rate. A protocol malfunction (for example, spanning-tree error or misconfiguration) can inhibit a large part of the network. Problems of this nature can be very difficult to localize in a flat, switched Ethernet environment. Therefore, care must be taken in terms of how this type of network is deployed. In this model, it is strongly recommended that each enterprise customer be mapped to a virtual LAN (VLAN). This set-up affords the service provider the ability to segment the network by customer. Although it could be possible to have multiple enterprise customers per VLAN, this set-up is considered undesirable for numerous reasons. First, an unexpected broadcast storm in one customer's network could affect the performance of the other customers on that VLAN. Second, and perhaps more important, the customers will have the ability to "sniff" the other customers' traffic, providing for massive security breaches. Finally, because of the inherent ability to sniff Ethernet traffic on the wire, a malicious individual could cause significant damage to multiple customers' networks. This scenario could potentially leave the service provider open to violations in its SLAs to its customers, to say nothing of a poor customer-service situation. Service providers can take many steps to limit the failure domain per VLAN. First, service providers can limit the number of switches that are participating in that VLAN. Cisco's VLAN trunking protocol (VTP) can enable every switch in the network to be aware of a new VLAN in the network and to autoconfigure trunk ports and spanning trees. In an enterprise network, this feature can be very helpful, but it can be highly detrimental in a service provider's Layer-2 network. Therefore, VTP should be disabled and VLANs manually configured as needed per switch. Secondly, Cisco technology can specify VLANs that are enabled on the 802.1Q trunk links. Only the VLANs of interest should be configured on a trunk link. Finally, the topology of the network should be well known and mapped out, both generally and specifically, per VLAN. This scenario allows the service provider to better isolate potential network faults.

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Topology and Spanning-Tree Protocol Considerations The topology of the network refers to the way in which the network is physically connected. It is very important for the service provider to understand the layout of the network and how to plan for its interconnection. If a service provider is implementing an Ethernet service over a SONET or Wavelength Division Multiplexing (WDM) network, then the Ethernet topology is more straightforward. In this case, the Ethernet network does not need to account for redundancy because redundancy can (and should) be accounted for at the transport layer by SONET or WDM. After all, SONET and WDM have significantly faster convergence times than spanning tree (50 milliseconds versus 50 seconds), meaning that spanning tree may not be necessary and Ethernet can be run in a simple point-to-point configuration with no loops. However, if the service provider is building the network based on pure Ethernet transport, then the Ethernet topology becomes critically important. The first thing to account for is summarized by the rule: "If some redundancy is good, more redundancy is not better!" This mistake is one of the major ones made by network architects utilizing spanning tree and Ethernet. Spanning tree requires control packets (called bridge protocol data units, or BPDUs) to be sent out and processed by each switch in the broadcast domain to stabilize the topology and reroute around failures. The more complicated the network, the more time it will take for the network to converge. In addition, a large Layer-2 switched network may enter a state in which the central processing unit (CPU) is so busy processing BPDUs that some are missed, preventing the spanning tree from ever recovering. It was not uncommon in the early days of VLANs to have a network in such a state that all redundancy had to be removed just to stabilize the network. The network should be designed in such a way that the primary and secondary root bridges of the spanning tree can be easily and readily identified. These switches should be located in a central point of presence (POP).

Virtual LANs A VLAN is essentially an extended Layer-2 switched domain—that is, a broadcast domain that extends as far as the VLAN reaches. If several VLANs coexist across a set of Layer-2 switches, each individual VLAN has the same characteristics of a failure domain, broadcast domain, and spanning-tree domain, as described previously. Therefore, although customers can use VLANs to segment the metro network, deploying pervasive VLANs throughout the metro introduces complexity and reduces the deterministic behavior of the network. Avoiding loops and restricting VLANs to the specific Layer-2 switch where they have a presence minimizes the complexity. Web ProForum Tutorials http://www.iec.org

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802.1Q Encapsulation 802.1Q encapsulation, often referred to as QinQ, provides a VLAN tunneling mechanism by encapsulating a frame tagged with an 802.1Q header with another 802.1Q header. (Extreme Networks has similar functionality; its solution is called Virtual MAN, or VMAN.) This means that an enterprise could transport multiple VLANs across the service provider's network without interfering with the service provider's VLAN identifications. For example, Acme, Inc. could send 10 VLANs, with IDs 1 through 10, into the service-provider cloud. The service provider would encapsulate those frames with another 802.1Q header with its own VLAN, let's say VLAN 100. The service provider would transport VLAN 100 across its own network and, wherever VLAN 100 terminated, out would come the 10 customer VLANs. In theory, this means that a service provider could support 4,096 VLANs, with each VLAN containing 4,096 customer VLANs. Some practical issues must be considered when implementing a QinQ encapsulation. First, QinQ assumes that customers want to transport their VLANs and spanning trees across a MAN or WAN, and, as discussed previously, this assumption is not true for most enterprise customers. This assumption has led to the failure of many previous transparent LAN services (TLSs). Second, one of the main benefits of QinQ is that, in theory, it scales the number of VLANs in the network from 4,096 to 40,962, or 16,777,216 VLANs. In reality, however, it is unlikely that an enterprise customer would be willing to put its VLANs in a service provider's "super-VLAN" with numerous other customers. The risk for security breaches and spanning-tree events damaging their network is far too great. Keep in mind that the service provider will still switch frames based on only the "outer" tag, not both tags.

Ethernet over Multiprotocol Label Switching Many service providers are looking to expand their metro networks to very large scales or perhaps to inter-metro areas. A pure Layer-2 solution is limited by the IEEE 802.1Q specification to 4,096 VLANs. Therefore, a service provider would be able to support only 4,096 customers within the metropolitan area. To scale beyond the 4,096 VLAN limit, EoMPLS can be utilized. Using this technology, a particular VLAN can be mapped to an EoMPLS tunnel. The provider-edge router will then transport that tunnel through the MPLS network. It is important to note a few points here regarding MPLS and its Ethernet type. First, MPLS resides on top of an IP network backbone. This set-up inherently allows the network to scale as well as provides the mapping between the MPLS label and some underlying intelligence. Therefore, it is strongly recommended that the network architect understand the best practices and guidelines for IP routing deployment on such protocols as OSPF, Intermediate System-to-Intermediate System (IS-IS) or Border Gateway Protocol (BGP). Web ProForum Tutorials http://www.iec.org

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Secondly, EoMPLS is a point-to-point solution only (based on the Martini draft; there is a follow-up draft that has not been readily adopted called Kompella, which allows for an Ethernet point-to-multipoint broadcast domain). For example, if the service provider wants to transport VLAN 100 across an EoMPLS network, the other side of the MPLS cloud can have only a single exit point. This issue, however, is not important in network design, because the enterprise will utilize multiple VLANs, one per destination site exiting the MPLS cloud. Examples of how to set up this scenario are discussed later in this tutorial.

Cisco COMET UCP Protocols Perhaps more important than the technology differences between each protocol is how customers intend to apply each of the protocols. The way service providers apply unified control plane (UCP) protocols is important later in this section, where both the specific feature requirements and platforms and relevant protocols for different opportunity areas are discussed. Figure 5. O–ONI and GMPLS Protocols

Figure 5 illustrates the basic aspects of both Generalized Multiprotocol Label Switching (GMPLS) and Optical User-to-Network Interface (O–UNI) protocols and how the protocols apply to routing both within a domain and between a user(or client)-side interface and that domain. O–UNI is illustrated on the right side of the network, emphasizing that there is a clearly delineated boundary between which a client-side UNI device (O–UNI–C) communicates with a network-side UNI device (O–UNI–N). The differences between the function of the O–UNI–C and the O–UNI–N is that the O–UNI–C provides a signaling termination function, whereas O–UNI–N provides a signaling pass-through and interworking function, circuit routing, and reachability information. Between the nodes on this interface, information about light paths available on the network is presented. Light paths are illustrated in Figure 5 by the lines above the O–UNI interface. If O–UNI is employed, the optical transport network (OTN) can run any kind of routing, including GMPLS, other standards such as Private Network-to-Network

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Interface (PNNI) or OSPF, or even a proprietary routing protocol can be employed. The interface between an edge GMPLS node and a GMPLS label-switched router (LSR) on the network side can also be referred to as a User Network Interface (UNI), whereas the interface between two network-side LSRs may be referred to as a Network-to-Network Interface (NNI). Nonetheless, GMPLS does not specify separately a UNI and a NNI protocol, an important point to understand when looking at the requirements. In GMPLS, edge nodes are simply connected to LSRs on the network side, and these LSRs are in turn connected between them. There is no delineated boundary over which a distinct protocol function is introduced such as with O–UNI. Of course, the lack of defined boundary and distinct protocol set does not mean the behavior of an edge node needs to be exactly the same as the behavior of an LSR on the network side. Specifically, in the aforementioned case, the edge node might be responsible for signaling paths across the network. If GMPLS is used, however, the edge node needs to communicate as a peer to the network-side device. Specifically, the two network elements will share topology, addressing, and other types of routing information. In fact, the boundaries between devices are not only divided along protocol layers, but they are also divided between different operations management groups. Indeed, service providers typically have two or more distinct operations groups specific to either data service or transport layers. Typically one group owns the provisioning, operations, and management of the transport and another is responsible for the functions for data services. Communications between the data-services and transport organizations are defined by a workflow process whereby orders are submitted by the data-services group and then subsequently filled by the transport group. This group distinction has a major impact on the choice of protocols. Service providers with distinct groups where one supports data services and the other supports transport services are more inclined to desire strict adherence to a non-routing–enabled boundary between the two administrative functions of these groups. Here O–UNI is a preferred method because it separates the roles of each operations department.

4. Provisioning One new technology that will simplify provisioning is called the unified control plane, or UCP. UCP represents a common set of control functions and interconnection mechanisms that allow unified communication, routing, and control across disparate types of underlying transport technologies (for example, IP, ATM, SONET/SDH, and DWDM). Traditionally, each specific technology has its own control protocols and, as a result, cannot communicate directly with the others. Networks are layered one on top of the other, creating overlays at each layer to collectively provide end-user services. Obviously, this process requires

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knowledge of each technology domain, provisioning of each layer, and separate management of per-domain operations functions. Cisco's UCP uses a set of industry-standard common addressing, routing, and signaling protocols that uniformly communicate and control across different transport technologies. Quick deployment of IP applications and services results from flow-through provisioning of services at single touch points of service access. No longer will providers need to configure connectivity over each technology domain separately and manually correlate cross-layer connectivity as they do today. Figure 6 depicts an abstraction of the IP–based control plane over different types of transport networks. Figure 6. Unified Control Plane

To address the determination of the appropriate control-plane architecture, the industry has embraced extending MPLS for integrating data and optical network technologies. MPLS provides an attractive foundation for the optical controlplane architecture, because MPLS has natural separation between its data and control planes. Hence, the Internet Engineering Task Force (IETF) has extended the MPLS label-switching concept to include other types of forwarding planes. For example, if we extend the definition of a label, MPLS can be applied to wavelengths, and the wavelength acts as its own label. The extended MPLS protocols considered a superset of MPLS are called Generalized MPLS, or GMPLS. It is important to note that GMPLS does not define separately edge nodes connected to the network that imply boundaries between user and network planes. The interface between an edge GMPLS node and a GMPLS LSR on the network side is often referred to as a user-to-network interface, or UNI. To support the UNI case specifically, the Optical Internetworking Forum has extended several GMPLS components and defined a set of UNI protocols explicitly. The protocols are known as Optical User-to-Network Interface, or O– UNI, whereby the client-side device runs O–UNI–C protocols and the networkside device runs O–UNI–N protocols. O–UNI provides a user-to-network bidirectional signaling interface between the service requester and serviceprovider control-plane entry point and does not share routing information across these domains. Web ProForum Tutorials http://www.iec.org

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UCP will include both O–UNI and GMPLS protocols under the Cisco UCP umbrella to provide essential flexibility in addressing a variety of service and network models. Providers can select, apply, and deploy the UCP protocol that best meets their situation, given their own specific organizational, architectural, or other requirements or constraints.

5. Provisioning Services The historical context around how optical networks have been designed and deployed provides much appreciation for why new requirements (for example, efficient and timely provisioning and management) and services (for example, on-demand services, CoS, communities of interest) are prevailing challenges today. New network requirements invalidate the assumptions upon which legacy networks were founded. Indeed, the communications networks that exist today were designed primarily for private-line and voice service using circuit switching. Capacity was portioned out in 64-kbps pieces (the size of an uncompressed voice channel) using multiple layers of hierarchy. Typically these networks required several months to deploy a service. This time frame met requirements then because the traffic demand was quite predictable and assumed to remain static for years at a time. As the business case for providing data services became attractive, service providers retrofitted their network typically by yet another layering of protocols to support multiple data-service interfaces and networks, including ATM, Frame Relay, and IP. Layering became an issue as data services became the predominant service relative to voice and private-line services. The unpredictable nature of data traffic as well as its flow-direction uncertainty and continual changes invalidated initial assumptions for voice networks. Procedures to provision services, reserve new bandwidth, or change network parameters to address growing traffic volumes or meet customer demands across the network over multiple protocol layers are time consuming, administratively difficult, and workforce intensive. Overlay networks require management of their different layers, such as the IP and ATM layers, as though they are separate networks. Intelligence can be implemented for some layers but is limited to the specific layers where it is implemented. Layers do not communicate with each other, so management and scalability of the network are compromised. Disparate technology layers also limit the ability to engineer traffic to maximize network and resource efficiency and avoid points of congestion. Functions are often duplicated, and network management and control algorithms can even work against each other in a layered protocol network, creating conflicts and oscillations. And restoration, performed in varying time scales across multiple layers, is uncoordinated and in most cases resource inefficient. Additionally, complications of tunneling the protocols of one technology over another results in inefficiencies due to framing and packet overhead, multiple instances of sometimes-conflicting functions, and the inability to optimize based on desired service granularity. Web ProForum Tutorials http://www.iec.org

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Obviously, a more dynamic and cost-effective network model that provides ondemand set-up of a wide range of differentiated Cisco COMET services and the ability for each class of traffic to be defined and treated appropriately is needed. To help service providers sustain profitability though automated provisioning and optimized delivery of optical services, Cisco UCP technology offers a means to address this overarching need for a more dynamic and cost-effective networkcontrol model. UCP can help carriers to increase profitability by specifically addressing the operational expenditures (OPEX) associated with the deployment and management of services over multiple technology networks. Not only will UCP technologies help carriers reduce their OPEX cost, but UCP will also enhance profitability for high-capacity traffic transport by enabling carriers to deploy new, value-added Cisco COMET services and do so very quickly to market. The new UCP–enabled optical network needs to provide the foundation for delivering an emerging, yet-to-be-defined portfolio of optical services. On the transport side of providers, UCP is seen initially as a means to tie together multivendor domains through the use of O–UNI. Desired here is one method of access to provision across the entire optical transport network, despite having multiple domains of different vendor equipment. Figure 7 illustrates this concept of provisioning across multiple-vendor domains within the transport network. Longer-term, transport architects realize that UCP has a broader and more significant meaning to service providers. Here, GMPLS represents a standard protocol for optical transport network elements. Providers welcome the move from proprietary protocols to open, standards-based protocols. Standards-based protocols will allow providers substantial cost savings by enabling them to introduce any vendor equipment into any given domain. A best-of-breed strategy traditionally has not been available and has been denied by those trying to "lock in" the provider in using its equipment at great cost to the provider. GMPLS is also sought in the transport because of its IP–like features, such as self-discovery and dynamic optimization and provisioning. Transport providers see the combination of the O–UNI and GMPLS protocols as a way to facilitate a seamless evolution to next-generation technologies without having to upgrade or replace network equipment. Service providers understand that GMPLS may not exist in all Cisco SONET/SDH products from the start. They are, however, interested in seeing the path toward GMPLS, because this represents to them Cisco's commitment toward standardsbased technologies.

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Figure 7. Provisioning Across OTN with Multiple Vendor Domains

6. Summary This document has discussed how photonics, protection, protocols, packets, and provisioning insert into the metro edge, metro core, and long-haul and extendedlong-haul segments. It is important to remember that the Cisco innovations are ongoing and that legacy equipment will not disappear over night. The enterprise and service providers still need to protect and provide existing services when migrating or evolving their current architecture offerings. In addition, service providers will need to take advantage of the existing infrastructure. The focus on network evolution is paramount to profitability of providers with existing network and operations management infrastructure. Figure 8. Cisco's Coment Technical Innovations

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Self-Test 1. In conventional long-haul (EDFA) technology, the transmission signals must be regenerated every ______ or so to overcome signal distortion due to dispersion and nonlinear effects. a. 2 km b. 10 km c. 100 km d. 500 km e. 5,000 km 2. In DWDM systems, channel spacing is limited by nonlinear effects such as four-wave mixing (FWM) and ____________. a. Attenuation b. Cross-phase modulation (CPM) c. Bit-error rate (BER) d. Failure in time (FIT) e. Wavelength division multiplexing (WDM) 3. The network availability is determined from the _____________ rates of the components that make up the network. a. Attenuation b. Cross-phase modulation (CPM) c. Bit-error rate (BER) d. Failure in time (FIT) e. Wavelength division multiplexing (WDM) 4. With its __________________ capability, Cisco has extended the simple concept of path protection on a SONET ring to meshed networks, offering service providers a new degree of flexibility in designing their networks.

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a. Bidirectional line-switched ring (BLSR) b. Unidirectional path-swtiched ring (UPSR) c. Sub-network connections protection (SNCP) d. Path-protected meshed network (PPMN) e. Optical signal-to-noise ratio (OSNR) 5. Cisco uses IP and _______________ for SONET data communications channel (DCC) communications. a. RIP b. EIGRP c. BGP d. IS–IS e. OSPF 6. ________ application growth is driving the increased bandwidth requirements and exceeding the existing capacity limits of the transport architectures in most provider networks. a. Enterprise b. Service provider c. Home user d. Government e. Small office

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7. A jabbering network interface card (NIC) might flood the entire domain with __________ or undesirable frames at a very high rate. a. Unicast b. Mulitcast c. Broadcast d. Simulcast e. Duocast 8. 802.1Q encapsulation, often referred to as _____, provides a VLAN tunneling mechanism by encapsulating a frame tagged with an 802.1Q header with another 802.1Q header. a. VLAN b. MPLS c. LRE d. QinQ e. O–E–O 9. Cisco introduced dynamic packet transport (DPT) in early 1999 based on a new concept called spatial reuse protocol (SRP). This protocol takes advantage of both the ring-based architecture of SONET and the packet characteristics of ________. a. ATM b. Frame relay c. Ethernet d. X.25 e. Appletalk

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10. The interface between an edge GMPLS node and a GMPLS label-switched router (LSR) on the network side can also be referred to as a _________, whereas the interface between two network-side LSRs may be referred to as a __________. a. OPEX, CAPEX b. UNI, NNI c. LSR–NS, LSR–NBS d. EGMPLS, NGMPLS e. NE, FE 11. Transport providers see the combination of the O–UNI and GMPLS protocols as a way to facilitate a seamless evolution to next-generation technologies without having to upgrade or replace network equipment. Service providers understand that GMPLS may not exist in all. a. true b. false 12. GMPLS defines separately edge nodes connected to the network that imply boundaries between user and network planes. a. true b. false 13. UCP will include both O–UNI and GMPLS protocols under the Cisco UCP umbrella to prov ide essential flexibility in addressing a variety of service and network models. a. true b. false 14. A VLAN is essentially an extended Layer-2 collision domain. a. true b. false

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15. Ethernet relies on the spanning-tree protocol (802.1d) to provide for loop detection and elimination, generally recovering from a fault in five to 30 seconds. SONET offers the ability to provide protection from physical and logical failures in the ring in 50 ms based on the automatic protection switching (APS) standard. a. true b. false

Correct Answers 1. In conventional long-haul (EDFA) technology, the transmission signals must be regenerated every ______ or so to overcome signal distortion due to dispersion and nonlinear effects. a. 2 km b. 10 km c. 100 km d. 500 km e. 5,000 km 2. In DWDM systems, channel spacing is limited by nonlinear effects such as four-wave mixing (FWM) and ____________. a. Attenuation b. Cross-phase modulation (CPM) c. Bit-error rate (BER) d. Failure in time (FIT) e. Wavelength division multiplexing (WDM)

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3. The network availability is determined from the _____________ rates of the components that make up the network. a. Attenuation b. Cross-phase modulation (CPM) c. Bit-error rate (BER) d. Failure in time (FIT) e. Wavelength division multiplexing (WDM) 4. With its __________________ capability, Cisco has extended the simple concept of path protection on a SONET ring to meshed networks, offering service providers a new degree of flexibility in designing their networks. a. Bidirectional line-switched ring (BLSR) b. Unidirectional path-swtiched ring (UPSR) c. Sub-network connections protection (SNCP) d. Path-protected meshed network (PPMN) e. Optical signal-to-noise ratio (OSNR) 5. Cisco uses IP and _______________ for SONET data communications channel (DCC) communications. a. RIP b. EIGRP c. BGP d. IS–IS e. OSPF

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6. ________ application growth is driving the increased bandwidth requirements and exceeding the existing capacity limits of the transport architectures in most provider networks. a. Enterprise b. Service provider c. Home user d. Government e. Small office 7. A jabbering network interface card (NIC) might flood the entire domain with __________ or undesirable frames at a very high rate. a. Unicast b. Mulitcast c. Broadcast d. Simulcast e. Duocast 8. 802.1Q encapsulation, often referred to as _____, provides a VLAN tunneling mechanism by encapsulating a frame tagged with an 802.1Q header with another 802.1Q header. a. VLAN b. MPLS c. LRE d. QinQ e. O–E–O

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9. Cisco introduced dynamic packet transport (DPT) in early 1999 based on a new concept called spatial reuse protocol (SRP). This protocol takes advantage of both the ring-based architecture of SONET and the packet characteristics of ________. a. ATM b. Frame relay c. Ethernet d. X.25 e. Appletalk 10. The interface between an edge GMPLS node and a GMPLS label-switched router (LSR) on the network side can also be referred to as a _________, whereas the interface between two network-side LSRs may be referred to as a __________. a. OPEX, CAPEX b. UNI, NNI c. LSR–NS, LSR–NBS d. EGMPLS, NGMPLS e. NE, FE 11. Transport providers see the combination of the O–UNI and GMPLS protocols as a way to facilitate a seamless evolution to next-generation technologies without having to upgrade or replace network equipment. Service providers understand that GMPLS may not exist in all. a. true b. false 12. GMPLS defines separately edge nodes connected to the network that imply boundaries between user and network planes. a. true b. false

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13. UCP will include both O–UNI and GMPLS protocols under the Cisco UCP umbrella to provide essential flexibility in addressing a variety of service and network models. a. true b. false 14. A VLAN is essentially an extended Layer-2 collision domain. a. true b. false 15. Ethernet relies on the spanning-tree protocol (802.1d) to provide for loop detection and elimination, generally recovering from a fault in five to 30 seconds. SONET offers the ability to provide protection from physical and logical failures in the ring in 50 ms based on the automatic protection switching (APS) standard. a. true b. false

Glossary APP Automatic Power Provisioning APS Automatic Protection Switching ATM Asynchronous Transfer Mode BER Bit-Error Rate BGP Border Gateway Protocol BLSR Bidirectional Line-Switched Ring BTDU Bridge Protocol Data Units Web ProForum Tutorials http://www.iec.org

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COMET Complete Optical Multiservice Edge and Transport CoS Class of Service CPU Central Processing Unit DCC Data Communications Channel DPT Dynamic Packet Transport DS Digital Signal DWDM Dense Wavelength Division Multiplexing EDFA Erbium-Doped Fiber Amplifier EoMPLS Ethernet-over–MPLS FCI Frame Copy Indication FEC Forward Error Correction FIT Failure In Time FWM Four-Wave Mixing GHz Gigahertz GMPLS Generalized Multiprotocol Label Switching GUI Graphical User Interface Web ProForum Tutorials http://www.iec.org

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IEEE Institute of Electrical and Electronic Engineers IETF Internet Engineering Task Force IP Internet Protocol IS–IS Intermediate System–to–Intermediate System LAN Local-Area Network LEM Line Extender Module LSR Label-Switched Router MAC Media Access Control MAN Metro-Area Network MPLS Multiprotocol Label Switching NIC Network Interface Card NNI Network-to-Network Interface O–E–O Optical-to-Electrical-to-Optical O–UNI Optical User-to-Network Interface O–UNI–C Optical User-to-Network Interface Client O–UNI–N Optical User-to-Network Interface Network Web ProForum Tutorials http://www.iec.org

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OAM&P Operations, Administration, Maintenance, and Provisioning OC Optical Carrier OOB FEC Out-of-Band Forward Error Correction OSNR Optical Signal-to-Noise Ratio OSPF Open Shortest Path First OTN Optical Transport Network PHY Universal Physical-Layer PNNI Private Network-to-Network Interface POP Point of Presence PPMN Path Protected Meshed Network QoS Quality of Service RPR Resilient Packet Ring RXT Receive Transponders SDCC SONET Data Communications Channel SDH Synchronous Digital Hierarchy SLA Service-Level Agreement Web ProForum Tutorials http://www.iec.org

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SONET Synchronous Optical Network SRP Spatial Reuse Protocol TDM Time Division Multiplexing (T1, T3, E1, etc.) TLS Transparent LAN Services UCP Universal Control Plane UNI User-to-Network Interface UPSR Unidirectional Path-Switched Ring VLAN Virtual LAN VTP VLAN Trunking Protocol WAN Wide-Area Network WDM Wavelength Division Multiplexing XPM Cross-Phase Modulation

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