Packet- OPtical the transmode WaY

Transcription

1 Packet- Optical THE TRANSMODE WAY

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3 Introduction transmode introduction 3

4 Packet-Optical the Transmode Way, has been written by Transmode to help customers, prospects, partners or anyone else who needs to have a better understanding of the packet-optical world. It is intended to accompany WDM the Transmode Way, which covers all aspects of Layer 1 optical networking. This book focuses on the integration of higher layer functionality into optical systems to create Packet-Optical Transport Systems (P-OTS) i.e. packet-optical networks. Optical fiber provides almost loss-less transmission of signals at an ultra-wide range of frequencies. Packet switching, implemented according to the Ethernet family of protocols, offers one of the most efficient ways for sorting and directing streams of digital data. With packet-optical networking these two outstanding technologies are positioned to dominate the next generation of transport networks. The term P-OTS is widely used within the industry and has been recycled from an earlier definition (Plain Old Telephone Service) to cover a range of solutions and networks with varying degrees of capabilities and functionality. Transmode defines P-OTS devices and networks using the classifications developed by Infonetics Research. We have therefore asked Andrew Schmitt, Principal Analyst at Infonetics Research, to give us a short introduction to packet-optical technology and the specific definitions they use in Chapter 2. Packet-optical integration has some great advantages in terms of cost and service differentiation. Transmode s Native Packet Optical 2.0 architecture takes this one step further and its benefits in terms of reduced equipment and operational cost, key capabilities such as latency and sync and simplified operations are outlined in Chapter 3. Chapter 4 then 4 introduction transmode

5 takes the reader further on into how these values are leveraged by various applications, such as Business Ethernet, Mobile Backhaul and CableTV Backhaul. For those wanting a better understanding of the various Layer 2 Ethernet technologies, Chapter 5 includes a description of how these function and how they are leveraged in wide area networks. Packet-Optical the Transmode Way has been written to enable readers to use the book as needed to research a particular subject or to read the complete volume from end to end. Either way, we hope you find the book informative and useful. details of the TM-Series, the multi-layer management suite Enlighten, or other parts of Transmode s product portfolio are available at: Unique features of Transmode s packet-optical solutions are highlighted with this marker throughout the text. The information included is subject to change without further notice. All statements, information and recommendations are believed to be accurate but are presented without warranty of any kind. As with the accompanying book WDM the Transmode Way, the descriptions in this book are kept as product release independent as possible. Current product transmode introduction 5

6 Content Introduction 3 1. an overview of the packetoptical market by Andrew Schmitt, Infonetics Research 9 2. Packet-optical networking Chapter summary The principles of packet-optical integration Why aggregate traffic at Layer 2? Ethernet transport at Layer 2 versus Layer Native Ethernet and ODU2e framing MPLS-TP for traffic engineering and service scalability A packet-optical architecture optimized for transport The main elements of a Transmode packet-optical transport network Ethernet Demarcation Units (EDU) and Network Interface Devices (NID) Ethernet Muxponders (EMXP) Optical add/drop multiplexors (OADM, ROADM) and other optical elements The multi-layer service management system Advantages of packet-optical transport Benefits of the packet-optical approach Advantages of Transmode s Native Packet Optical 2.0 architecture Migrating legacy TDM services to Ethernet One common infrastructure for Ethernet and legacy TDM services Using the isfp to convert SDH/SONET services for Ethernet transport Multi-layer network management Transmode s multi-layer management suite Enlighten Network management principles A unified information model for multi-layer management Layer 2 Service Provisioning Layer 2 Service Assurance Software Defined Networking (SDN) and Network Virtualization 41 6 transmode

7 3. applications of packetoptical networking Chapter summary ethernet services for enterprises Business Ethernet Serving enterprise customers A network for Business Ethernet Aggregation of IP traffic IP backhaul IP based services over a common infrastructure A lean and transport centric aggregation network The flexible optical network brings scalability Mobile backhaul G and 4G/LTE place new requirements on mobile backhaul A backhaul network optimized for 3G and 4G/LTE Switched video transport Streaming 3D and HD video to the home Transmode s solution for switched video transport Data center interconnect and cloud computing ethernet and Layer 2 technologies Chapter summary Ethernet basics Ethernet mode of operation Virtual LANs Ethernet physical media (PHY) Synchronization and circuit emulation services over Ethernet Synchronous and asynchronous transport Synchronization standards Ethernet protection Link aggregation (LAG) Ethernet ring protection switching (ERPS) Carrier Ethernet architecture and services Carrier Ethernet: Ethernet as a transport service The Carrier Ethernet architecture and terminology Carrier Ethernet 2.0 Services Carrier Ethernet Service Attributes Carrier Ethernet traffic management Bandwidth profiles Class of Service (CoS) and Service Level Agreements (SLA) Traffic shaping Carrier Ethernet Operations, Administration and Maintenance (Ethernet OAM) The management framework Standards for Ethernet OAM The service lifecycle Ethernet Service OAM Performance and fault management 78 Summary 82 index 83 transmode 7

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9 1. An overview of the packetoptical market by Andrew Schmitt, Infonetics Research

10 Optical technology has surged forward in recent years with the move to higher speed coherent optics, more optical flexibility with the wide-scale adoption of ROADM technology and the integration of Ethernet functionality from higher layers in the OSI stack into the optical layer, what we refer to as Packet-Optical integration. Of these, the move to packetoptical solutions is perhaps the most confusing, as the phrase means different things to different parties, be they vendors, operators, analysts or the media. The variation stems from individual experiences with the wide range of solutions on the market. Infonetics formed its definition of packet-optical largely through dialogue with service providers from many regions and markets. In a nutshell, packet-optical integration encompasses a range of systems that supports a combination of optical and packet/ethernet technology. After many years of tracking this evolving market, and asking carriers specifically how they define packet-optical, we recently modified and updated our definitions of the P-OTS market to match the latest trends in the industry, and we split the industry into two distinct sub-segments: metro-edge P-OTS and metro-core P-OTS. Metro-edge P-OTS are systems aimed at applications toward the edge of an optical network. These systems are WDM-based optical networking platforms with integrated Ethernet switching. They have varying degrees of support for Layer 1 technologies such as SDH/SONET and OTN, but must also support Layer 2 Ethernet functionality. This Ethernet functionality, which will be explained in full later in this book, includes a minimal level functionality that must be supported to be classified within the metro-edge P-OTS category. This functionality includes provisioning, managing, verifying and protecting Layer 2 Ethernet services using a defined group of standardized protocols and procedures. Of course, many systems in the market will support a much wider level of functionality than this minimum requirement. There are also some systems that do not meet the required level, but still are marketed as packet-optical systems. Metro-core P-OTS are similar systems that support all the functionality required in a metro-edge P-OTS system but also support applications within the core of a network. As such, they are typically physically larger systems that support a larger capacity but must also support switching across the whole chassis or node from any port to any other port, rather than just within ports on a single plug-in unit that is common in metroedge P-OTS platforms. These metro-core P-OTS platforms must therefore support centralized switching fabrics for Ethernet traffic and a centralized SDH/SONET and/or OTN switch. They must also support fully integrated ROADM-based optical switching and a single control plane. These definitions allow us to track the progress of the industry with a clear demarcation between the different systems that are closer to the edge of the network and those deeper in the network and closer to the core. Those at the edge often have features that are very application specific, such as Ethernet synchronization schemes for mobile backhaul 10 An overview of the packet-optical market transmode

11 networks, and can require this functionality in both compact edge nodes and larger aggregation nodes. These metro-edge P-OTS systems need to also pay special attention to the service demarcation and provisioning aspects of running a network and therefore support of standards like those defined by the Metro Ethernet Forum (MEF) are particularly important. Those systems at the core of a network are typically dealing with traffic from many applications and as such require less service awareness but require the capacity to handle more traffic and a higher degree of Layer 1 transport capabilities over Layer 2 Ethernet, as shown below. While Transmode s product portfolio supports some of the metro-core P-OTS functionality such as integrated ROADM technology, the functionality of the company s Native Packet Optical 2.0 architecture currently falls clearly into the metro-edge P-OTS category. The terms Packet- Optical and P-OTS in this book cover both the metro-edge and metrocore P-OTS definitions from Infonetics Research. The use of these terms implies that the strict minimum functionality levels are achieved within the packet-optical transport system. The move to P-OTS networks allows operators to capitalize on Ethernet as a single standard service protocol and to build single networks capable of supporting many parallel applications over the same infrastructure. It has the potential to play a significant role in enabling operators to address the challenges they face as they evolve their networks, particularly as they look to add support for Software Defined Networking (SDN) features. We at Infonetics Research see the evolution of P-OTS systems and networks as a very important aspect of the overall evolution of optical networking. This area is one of the fastest growing segments of the industry and has a large part to play in supporting the networks of today and tomorrow. Exciting times are ahead! Figure 1. The future of transport and switching. Source: Infonetics Research. Andrew Schmitt Principal Analyst, Optical Infonetics Research transmode An overview of the packet-optical market 11

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13 2. Packet-optical networking

14 2.1 Chapter summary Optical fiber provides almost loss-less transmission of signals at an ultra-wide range of frequencies. Packet switching, implemented according to the Ethernet family of protocols, offers one of the most efficient ways ever for sorting and directing streams of digital data. Packet-optical networking fundamentally addresses how to leverage the outstanding characteristics of these two technologies to implement the next generation of telecommunication networks. The scalability and cost effectiveness of Ethernet has made it the unifying service protocol for modern wide area networking. Increasingly the consolidation of the optical and Ethernet/IP transport infrastructure within the same network elements has become the means to drive down both network investment costs and the associated operational costs. The additional support of label switching mechanisms (MPLS-TP 1 ) is an extra tool kit to complement Ethernet and to enhance the transport capabilities and scalability of the network. Supervised by a multi-layer management system, integrating the handling of OSI Layer 1 optical channels and Layer 2 Ethernet services, a flexible, cost efficient and future proof telecommunications infrastructure is here and ready to be deployed. This chapter deals with the principles of transporting Ethernet traffic over WDM networks and describes how these two key technologies are integrated by a unifying architecture Native Packet Optical 2.0. It also highlights the advantages of the architecture, including how traffic is transported with minimal delay and without loss of synchronization. The chapter ends with a section on network management and approaches to Software Defined Networking (SDN). 2.2 The principles of packet-optical integration Why aggregate traffic at Layer 2? The introduction of Layer 2, i.e. Ethernet, aggregation brings several benefits to network operators. Traditionally, metro aggregation networks were implemented by WDM equipment attached to other equipment such as DSLAMs and mobile base stations or to enterprise networks. The traffic from these was transported to an IP core network directly, i.e. at Layer 1, using fibers in ring or star topologies. As the number of end points grew, the central IP core network had to be extended, requiring more IP routers at more sites and with more ports, as indicated on the left side of Figure 2. 1 Multiprotocol Label Switching Transport Profile. 14 Packet-optical networking transmode

15 (time or frequency multiplexing), where the number of users and their data rates are fixed. Statistical multiplexing makes use of the fact that the information rate from each source varies over time and that bandwidth of the optical path only needs to be consumed when there is actual information to send. ysince the traffic is concentrated at Layer 2 in the aggregation network it can be handed over to the IP core routers via a few high speed interfaces rather than over many lower speed interfaces. This simplifies administration and contributes to a lower cost per handled bit. Figure 2. Migrating from Layer 1 to Layer 2 aggregation of traffic. yas an additional benefit the aggregation network itself can be used to offer services within the metro/regional area. For example, point to point Ethernet connections can be provided between offices in a city center without loading any central router nodes. Such direct connectivity gives more rational traffic handling and reduced forwarding delay compared to using the central IP routers. In this situation, there are several reasons to introduce a Layer 2 aggregation network: ythe IP core network can be reduced in size to only a few central routers instead of being spread-out throughout the full metro network area. Layer 2 aggregation equipment is normally less costly 2, consumes less power, has lower latency and requires less expertise to configure than IP routers. This centralization of the IP core network reduces the investment necessary and the operational costs. ylayer 2 aggregation can perform statistical multiplexing of data traffic, and the WDM channels of the underlying optical network can be used much more efficiently than if only Layer 1 aggregation was used. Statistical multiplexing allows the bandwidth to be divided arbitrarily among a variable number of users in contrast to Layer 1 aggregation 2 Analyst estimate that Layer 2 equipment is only between 30 50% the cost of Layer 3 equipment. Figure 3. The statistical multiplexing of Ethernet is leveraged to fill the pipes, a feature which is especially useful in the edge of the network where traffic often is more variable. transmode Packet-optical networking 15

16 2.2.2 Ethernet transport at Layer 2 versus Layer 1 Given the benefits of a Layer 2 aggregation network, it is important to understand how such a network differs from a traditional network with Layer 1 aggregation of Ethernet traffic over WDM. Transporting Ethernet traffic between two remote sites with WDM as the underlying bearer technology can be done in two fundamentally different ways: yusing transparent transport of Ethernet frames over a WDM channel, i.e. Layer 1 (optical) transport yusing an intermediate Carrier Ethernet Network 3 that in turn gets its frames transported over one or more WDM channels, i.e. Layer 2 (Carrier Ethernet) transport. This is the technology used in a Layer 2 aggregation network. Both alternatives have advantages and disadvantages. A basic Layer 1 Ethernet transport solution takes every incoming frame from the sending customer Ethernet network and puts it into a digital wrapper adapted for transmission over the WDM channel. At the receiving end, the wrapper is removed and the original frame is handed over to the customer Ethernet network. In this way, every single frame is forwarded without modification between the two customer networks. The Layer 1 transport solution provides a transparent path between the two customer Ethernet networks, giving the highest possible Quality of Service (QoS) in terms of latency, latency variation and packet loss. A Layer 1 network is also fully deterministic and provides 100% throughput regardless of what services that are carried by the Ethernet traffic. But since a Layer 1 network is totally transparent to the Ethernet traffic it is also unaware of any Ethernet service information and can only manipulate the traffic at Layer 1. Figure 4. Layer 1 transport: Ethernet traffic is carried transparently at Layer 1 over a WDM wavelength. Figure 5. Layer 2 transport: Ethernet traffic is transported via a Service VLAN in a Carrier Ethernet Network extending between operator sites. 3 See section 4.5 for more information about Carrier Ethernet as defined by Metro Ethernet Forum (MEF). 16 Packet-optical networking transmode

17 In a Layer 2 transport network the customer Ethernet networks are interconnected via an intermediate Ethernet, the Carrier Ethernet Network. A Service VLAN (SVLAN) or an MPLS-TP pseudowire in the Carrier Ethernet Network is used to keep traffic from each set of customer Ethernet networks separated, i.e. the SVLAN/pseudowire establishes the connectivity between the involved customer Ethernet networks belonging to the same subscriber. The frames of the Carrier Ethernet SVLAN/pseudowire are transported over channels of the WDM network, just as before. A plain Layer 1 transport solution cannot concentrate the Ethernet traffic being aggregated, which may result in low utilization of the WDM wavelengths. For example, a Layer 1 network collecting Gigabit Ethernet signals that are utilized to a very low extent, will still carry them as if they were 100% loaded. This may lead to unnecessary investment in Layer 1 equipment for additional wavelengths in the transport network. In the Layer 2 transport solution the incoming customer Ethernet frames are analyzed and acted upon by the equipment located at the ingress point of the Carrier Ethernet Network, before being forwarded. It is possible to concentrate the incoming flow of Ethernet frames by statistical multiplexing and applying shaping and policing to the Ethernet traffic. The Layer 2 solution can be made fully Ethernet service aware and analyze and act upon Layer 2 traffic. Multiple Ethernet signals are TDM-multiplexed in a Layer 1 solution. The aggregated signal is not a standard Ethernet signal and consequently de-multiplexing must be done before the original signals are handed over to a switch/router. A Layer 2 solution performs aggregation to a new native Ethernet signal that can be handed over without any need for demultiplexing. A Layer 2 solution will normally require a lower port density on the receiving switch/router, which may have a beneficial impact on the cost of that equipment. Since a Layer 2 network can use policing to separate the effective data rate offered to a subscriber from the actual line rate available on the access line, a Layer 2 network can offer a more flexible and granular set of transport services than a Layer 1 network. While a Layer 1 network typically only provides services at the standard Ethernet line rates, such as 100 Mbit/s or 1 Gbit/s, a Layer 2 network may offer much more flexibility, such as 25 Mbit/s, 200 Mbit/s or 400 Mbit/s transport services over a physical 1 Gbit/s port. The Layer 2 network is intrinsically less deterministic than a Layer 1 transport solution. The throughput of a Layer 2 network may suddenly change due to introduction of a new service or due to changed traffic situations. However, the Layer 2 network can be made to behave in a deterministic way by use of predefined capacity reservations, i.e. by use of traffic engineering. transmode Packet-optical networking 17

18 The following table summarizes some of the differences between a Layer 1 and a Layer 2 network for wide area Ethernet transport. Layer 1 Ethernet transport TDM multiplexing: Collects and delivers traffic at the same format and data rate. Fixed data rates, typically 100 Mbit/s, 1 GbE and 10 GbE. Deterministic. What goes in comes out. Unaware (transparent) of Ethernet service information and can only manipulate traffic at Layer 1 Lowest delay, jitter and packet loss. Layer 2 Ethernet transport Statistical multiplexing: Collects traffic at one data rate and can deliver input from many sources over one interface at a higher rate. Flexible selection of data rates. Allocation of bandwidth by policing and shaping of traffic. Relies on traffic engineering to achieve deterministic behavior. Ethernet service aware. May analyze and act on Layer 2 control information, i.e. can be used to create Ethernet transport services with different characteristics and QoS. Statistical multiplexing implies a risk for delay, jitter and lost packets. Layer 1 Performance Management based on bit errors (CRC). Layer 2 Performance Management based on VLANs and Ethernet Virtual Connections, latency, jitter, frame loss etc. Embedded management channels via overhead bytes in line signal wrapper. Embedded management channels via separate management VLAN at Layer 2. Figure 6. Characteristics of Layer 1 and Layer 2 Ethernet transport. The Transmode packet-optical offering provides the user of the TM-Series with three principal alternatives for transport of Ethernet traffic: yplain Layer 1 transport, i.e. transponders and muxponders that provide 100% transparent Ethernet transport at OSI Layer 1. yethernet-aware Layer 1 transport, i.e. muxponders that provide 100% transparent transport but have Layer 2 features, such as providing information on to what extent a Gigabit Ethernet connection is utilized. This enables the network operator to analyze the wavelength utilization and avoid unnecessary investment in transponders/ muxponders to launch additional wavelengths. Another unique Transmode feature is the ability to inject/extract management VLAN s on a Gigabit Ethernet client port. This enables direct remote management of Layer 2 devices via the same DCN 4 solution as for the optical transport equipment. yfull Layer 2 transport according to the Carrier Ethernet specifications by Metro Ethernet Forum (CE 2.0 from MEF), i.e. equipment providing aggregation and concentration of Ethernet and other traffic with a selected set of Layer 2 functions that support the transport task. Such functions are for example IEEE 802.3ad link aggregation, Traffic Shaping and Policing and Bandwidth Profiles with guaranteed 4 Data Communications Network used for management and control of the network equipment. 18 Packet-optical networking transmode

19 bandwidth allocation. The Transmode Layer 2 network elements the Ethernet Muxponders (EMXP) are also Layer 1 aware, meaning that they can be connected directly to a WDM-link and support features such as Forward Error Correction (FEC) at the optical layer. All the above mentioned units transponders, muxponders and Ethernet Muxponders are plug-in units that can be inserted in any combination in the different chassis options provided by the Transmode TM-Series platform. As an example, Layer 2 capable Ethernet Muxponders can be used at the edge of the network to collect and aggregate Ethernet traffic and hand over to Layer 1 transponders or muxponders that provide continued transport with highest cost-efficiency and Quality of Service Native Ethernet and ODU2e framing The Carrier Ethernet Network of a Layer 2 transport network is built on the WDM optical channels, i.e. the frames of the Carrier Ethernet Network are transported by the underlying WDM optical system. The Ethernet payload data can be packaged in the transport containers of the optical system in several different ways. the standard encapsulation recommended by Transmode for metro/ aggregation networks, since it allows each intermediate node to examine and manipulate the Ethernet control information, i.e. to perform statistical multiplexing and differentiation of services at the Ethernet level. yodu2e framing according to the OTN standard: The frames of the Carrier Ethernet Network are carried over the WDM wavelength by Optical Channel Data Units (ODU) according to the OTN standard. This encapsulation is especially favorable when the Carrier Ethernet extends over longer distances or the data is to be transported via an intermediate core OTN network. Using ODU2e framing between the Ethernet Muxponders allows use of the inherent OTN Forward Error Correction (FEC) mechanisms and optical path monitoring bits, which are of importance for long reach links. And since the encapsulation is in ODU2e format, these data units can also easily traverse any intermediate OTN switches transparently before reaching their final destination. Legacy optical transport systems SDH and SONET incorporate adaption methods such as the Generic Framing Procedure (GFP) to allow for packet data transport. The Optical Transport Network (OTN) standard is a more recent digital wrapper technology that wraps any client signal, including Ethernet frames, in overhead information for operations, administration and management of the optical links. The Transmode Native Packet Optical 2.0 architecture supports two types of encapsulation of the Carrier Ethernet traffic for WDM transport: ynative Ethernet framing: The frames of the Carrier Ethernet Network are transported as is, i.e. using the same framing as on an ordinary LAN, when forwarded over the WDM wavelength. This is Figure 7. ODU2e and native Ethernet framing. The two-colored bars symbolize Ethernet frames with the control information in red. transmode Packet-optical networking 19

20 Native Ethernet framing means that standard Ethernet framing is applied to the data payload at the edge of the network, instead of encapsulating it with an OTN or other digital wrapper. By treating the Ethernet packets natively, it is possible to inspect them within the intermediate network nodes and to act upon the Ethernet headers so that the combined benefits of Layer 2 intelligence and efficient Layer 1 transport can be realized. This becomes especially important in the edge of the network where decisions about traffic prioritization are done and where traffic is aggregated to fill the pipes. The wrapping of traffic into full OTN can then be done at the handover to the core network, after aggregated pipes of traffic that are correctly shaped have been created, avoiding wasting bandwidth. Native Ethernet framing uses the VLAN tag or MPLS-TP labels to switch the frames to ports associated with either IP services or with transport services. Each of these service domains is optimized and simplified for the particular service types. For example, frames containing data for high value and high quality IP services (IP-MPLS, IP-VPN or VPLS) can be switched to paths for transport to the necessary IP devices. By contrast, frames that are destined for transport services (Ethernet, MPLS-TP or OTN) can be kept within the optical transport network, with minimal use of expensive Ethernet switching and IP routing resources. The Optical Transport Network (OTN) is a more recent addition to the standards for public telecommunications networks and is sometimes referred to by its ITU-T name G.709. The standard was designed to transport both packet mode traffic such as IP and Ethernet, and legacy SDH/ SONET traffic over fiber optics with DWDM. It supports forward error correction (FEC) and management functions for monitoring a connection end-to-end over multiple optical transport segments. Today OTN has its main application in the long haul network where error correction and interoperability between several operators equipment are important. OTN wraps any client signal in overhead information for operations, administration and management. The client signal to be transported is mapped into an Optical Channel Payload Unit (OPU). The OPU is then encapsulated into the basic unit of information transport by the protocol, the Optical Channel Data Unit (ODU), which is carried within an Optical Channel Transport Unit (OTU) defining the line rate of the connection. Figure 8. Service aware transport enables a differentiated service offering with multiple classes of services having different characteristics. Figure 9. The OTN signal structure and terminology. The Carrier Ethernet frame is carried as the payload of an Optical Channel Payload Unit (OPU). 20 Packet-optical networking transmode

21 Transmode s Ethernet Muxponders, the EMXP family, has the necessary framing capacity for ODU2e 5, including optional G.709 FEC on all 10G ports. The optional ODU2e framing on 10G ports allows the native 10G Ethernet frame to be mapped into an ODU2e data unit ready for transport into the OTN core and large OTN switches. This is most useful once the traffic has been aggregated as much as possible to ensure the best possible utilization of the 10G circuit. An OTN core network can also provide a unified transport layer where core nodes can combine traffic from OTN muxponder based Layer 1 services with EMXP based ODU2e framed Ethernet services from the Native Packet Optical 2.0 architecture. End to end performance monitoring is achievable even over multiple carrier networks through OTN with tandem connection monitoring and Carrier Ethernet s inherent Operations, Administration and Maintenance (OAM) capabilities. In summary: In the access and aggregation part of the transport network where service granularity is required, a service aware packet-optical mechanism is beneficial to support different QoS. Also, access to Ethernet OAM bytes and service tags enable end-to-end management of Ethernet services. Using native Ethernet framing offers benefits from both a revenue generation, investment and an operational perspective in these parts of the network. On the other hand, OTN has all the benefits of a long haul optical transport network once the traffic has been sufficiently aggregated and traverses the core part of the network. ODU2e framing has its main value in long haul and core network parts. Native Ethernet framing Ethernet frames are transported natively over the WDM channels with minimum extra overhead The service information contained in the Ethernet frame can be accessed at every node of the network. This allows for statistical multiplexing and service differentiation at intermediate network nodes No Forward Error Correction without an additional Layer 1 Transponder Traffic carried over OTN is mapped to OTN when it hits a suitably enabled OTN node Especially suited in metro and regional networks were traffic is aggregated and service differentiation is applied ODU2e framing according to OTN Ethernet frames are transported in Optical Channel Payload Units (OPU) within ODU2e frames and OTU containers according to the OTN standard The Ethernet frame is wrapped inside the OPU/ODU and cannot be read and acted upon without de-multiplexing Includes Forward Error Correction and optical path monitoring mechanisms which are important for long distance links Provides direct compatibility with intermediate core OTN networks frames can be forwarded transparently through OTN switches Especially suited in core and long distance networks were traffic has been aggregated into larger streams Figure 10. Some characteristics of native Ethernet framing and ODU2e framing. 5 ODU2e is an OTN Optical Channel Data Unit specifically designed for transport of 10 Gigabit Ethernet and Fiber Channel 10 GFC signals at a data rate of 10.4 Gbit/s. transmode Packet-optical networking 21

22 2.2.4 MPLS-TP for traffic engineering and service scalability While Carrier Ethernet Networks and the use of Service VLANs (SVLAN) bring great advantages to the packet-optical network, there are some limitations in terms of protection options, traffic engineering and service scalability. These can be addressed by the use of MPLS-TP, which is the Transport Profile of Multiprotocol Label Switching (MPLS). MPLS-TP is a way to simplify Carrier Ethernet services by pre-defining connection oriented services over packet-based networking technologies in a way that gives support for traditional transport operational models. It takes the advantages of MPLS concepts by adding more flexibility and network manageability than the basic Ethernet SVLAN architecture. Figure 12. MPLS-TP Framework. Figure 11. Using MPLS-TP to define label switched paths within the Carrier Ethernet Network. Principles of MPLS-TP Multiprotocol Label Switching (MPLS) is a technique that forwards packets based on labels as opposed to a standard Carrier Ethernet network where the frames are switched based on their SVLAN tags and MAC addresses. A Label Switched Path (LSP) is defined between nodes were traffic enters and leaves the MPLS-TP network. Using MPLS-TP terminology, the entry and exit nodes are referred to as MPLS-TP Provider Edge (PE) nodes and any intermediate nodes being passed by the LSP are referred to as MPLS-TP Provider (P). Often the physical node performing the PE function is called a Label Edge Router 6 (LER) and the intermediate transit node is called a Label Switching Router (LSR). Transmode s Ethernet Muxponders can act as both an LER and an LSR, and also combine these roles. 6 Note that the use of the term router is historic and neither requires nor precludes the ability to perform IP forwarding. It is sometimes used instead of node in MPLS context. 22 Packet-optical networking transmode

23 Figure 13. MPLS-TP Tunnel. Figure 14. Data is carried by a pseudowire defined within the MPSL-TP Tunnel and Label Switched Path (LSP). An MPLS-TP tunnel is a pre-defined MPLS-TP transport path from the source LER to the destination LER. The MPLS-TP tunnel always has an active LSP that defines the primary and working path. It may also have a protect LSP which define a recovery path. Both the tunnel and the LSP can be envisaged as pre-defined circuits for information to follow through the network, and consequently tunnels and LSPs are configured in advance from the network management system. A key feature of MPLS-TP, which distinguishes it from classic IP MPLS, is in fact that management and protection are designed to operate without a dynamic control plane, i.e. similar to a traditional SDH/SONET network, where circuits are set up by the management system. A pseudowire is an emulation of a Layer 2, point-to-point, connectionoriented service over a packet-switching network (PSN), from Attachment Circuit (AC) to AC. The pseudowire used in MPLS-TP is a connection established between two MPLS-TP Label Edge Routers (LER) across the MPLS-TP tunnel/lsp with the Attachment Circuit frames encapsulated as MPLS data. The actual data traffic is carried by a pseudowire (PW) inside the LSP/ tunnel. One MPLS-TP LSP may carry one or more pseudowires, i.e. the pseudowires offer a means for multiplexing of traffic. transmode Packet-optical networking 23

24 Figure 15. Ethernet over MPLS encapsulation. Figure 17. MPLS-TP OSI network layers. The two variants of the physical layer correspond to native Ethernet framing and ODU2e framing respectively. A Layer 2 transport service is established between two Attachment Circuits and the service is carried by a pseudowire. The pseudowire travels through the network in an MPLS-TP tunnel. The MPLS-TP tunnel is in its turn mapped to at least one LSP, the active LSP. Figure 16. Relation between pseudowire, tunnel and Label Switched Path (LSP). The following diagram summarizes how transport in an MPLS-TP network relates to the OSI model. Note that Ethernet framing is present both at the link layer and the client service layer. Both Ethernet SVLAN and MPLS-TP forwarding techniques have their own benefits and it is often advantageous to be able to offer services based on both technologies. For example multicast services are generally more suited for deployment directly over SVLANs on Ethernet, whereas pointto-point trunks requiring protection benefits more from the MPLS-TP features. MPLS-TP is fully supported by Transmode s Native Packet Optical 2.0 architecture and the EMXP family of muxponders. Any physical port on an Ethernet Muxponder can support both native Ethernet and MPLS-TP, allowing operators to deploy MPLS-TP where and when it makes sense for them. It is possible to run MPLS selective per port or separate MPLS traffic based on MAC address and VLAN within the same port. This allows seamless migration and co-existence with the two protocols running independently side by side. 24 Packet-optical networking transmode

25 In order to deploy MPLS in a production network, MPLS can be introduced either as an overlay to the existing Ethernet or incremental as an evolutionary build-out in parallel on the same networking hardware. Transmode believes in a smooth evolution, provided by Ships in the Night capability with Ethernet and MPLS in parallel as independent non-interfering protocols in the same system. MPLS-TP in Flexible Optical Networks Packet-optical networks are often deployed today over a ROADM based Flexible Optical Network and this brings a mesh based structure to the wavelength routing and the paths available through the physical network for any services. One previous drawback with Ethernet was that it wasn t well suited for protection and restoration over mesh based networks as the available protection schemes were largely based on point to point or ring architectures. MPLS-TP is highly suited for a mesh based environment and allows network operators to design network resilience strategies that are closely aligned to the physical structure of the network, ensuring the best possible resilience and service up time. MPLS-TP Easy service creation Another advantage of MPLS-TP is that it breaks the service creation into two steps. Firstly, tunnels are created between end points within the network for service and protection paths for the MPLS-TP based services. Then, the network administrator simply creates new services by adding the new services to the tunnel end points as pseudowires, safe in the knowledge that all routing aspects of the service have already been handled. This brings two distinct advantages. First, it makes the solution more scalable and it is simpler to add a large number of services to the network. Second, it brings a very familiar look and feel to service creation to the network, as it is similar to the processes involved in traditional transport networks. This helps operators migrate from traditional transport networks to packet-optical networks. MPLS-TP resolves the MAC scalability problem In an SVLAN based Carrier Ethernet Network all MAC addresses of the attached Customer Ethernet networks are visible to every switch within the Carrier Ethernet Network. Since each customer network may include an extensive number of devices and MAC addresses, this result in a need for large MAC address tables in each network node, creating various problems and extra equipment cost. Using MPLS-TP, the customer MAC addresses are encapsulated within the pseudowire payload and not seen by the intermediate switches of the Carrier Ethernet Network. The switches of the Carrier Ethernet Network do not have to be designed with the number of Customer Ethernet MAC addresses in mind. MPLS-TP allows for virtually unlimited number of customers The IEEE 802.1Q standard allows for a maximum of 4094 SVLANs in a Carrier Ethernet Network and one SVLAN is normally required per subscribing customer. Since MPLS-TP uses tunnels and label switched paths to define the connectivity within the network, there is no such upper limit for the number of customers that can be handled by a network using MPLS-TP. Of course, as the MPLS-TP services in Transmode s Native Packet Optical 2.0 architecture are delivered over the same hardware platform as native Ethernet services, they also benefit from the same transport-like performance with extremely low latency and almost zero jitter and can be combined with synchronization schemes such as SyncE when required, e.g. in mobile backhaul networks. transmode Packet-optical networking 25

26 2.3 A packet-optical architecture optimized for transport Transmode s Native Packet Optical 2.0 architecture is the base for Transmode s packet-optical networks. The architecture builds on Transmode s long and recognized experience in optical networking combined with the Ethernet, MPLS-TP and OTN transport capabilities outlined in section 2.2. The architecture supports the delivery of fully MEF compliant Carrier Ethernet 2.0 services and other Layer 2 services in combination with the flexibility of a wide choice of underlying transport technology alternatives. A key objective in the development of the architecture has been to expand the number of services that can be provided by and over an optical infrastructure: More services over the same network means more revenues and less cost for the operator. By integrating a selected set of Layer 2 functions with the optical layer, the network becomes much more potent in terms of service offering and can be made more scalable. The tight integration between Layer 1 and Layer 2 also makes it possible to increase resilience and improve traffic management in ways not possible with less integrated approaches. One major advantage of the Native Packet Optical 2.0 architecture is that it is agnostic to the chosen transport network technology. The traffic may flow over a ROADM-based, flexible optical network which provides the underlying connectivity and can be used for transparent Layer 1 services. In addition, a Transmode packet-optical network can seamlessly interoperate with its transport network over MPLS-TP tunnels, Ethernet SVLANs or OTN switches and any combination of these. Figure 18. Key features of Transmode s Native Packet Optical 2.0 architecture. 26 Packet-optical networking transmode

27 Figure 19. Transmode s Native Packet Optical 2.0 architecture offers a wide range of Layer 2 services and the selection of multiple underlying transport technologies. Furthermore, together with the management suite Enlighten, the Native Packet-Optical 2.0 architecture provides multi-layer traffic and service management. Depending on traffic load or link degradation, the packetoptical network can switch between different transport alternatives, ensuring the highest possible quality of service for the subscribers. The tight integration between Layer 2 and Layer 1 functionality in the architecture also opens up for advanced management of the traffic. For example, the optical channel quality information detected at Layer 1 may be used for automated decisions on how a particular SVLAN or MPLS-TP tunnel is set up and handled at Layer 2. Native Packet Optical is implemented through the family of optimized Ethernet Muxponders (EMXP) within the widely deployed TM-Series networking platform. transmode Packet-optical networking 27

28 2.4 The main elements of a Transmode packet-optical transport network Having looked at the principles of packet-optical networking, it is time to discuss how these functions are distributed in a complete network. Figure 20 illustrates the general architecture of a packet-optical network. As usual the network may be divided into an access, an aggregation, a regional/metro core and a core segment, each having their optimal technology implementation and architecture Ethernet Demarcation Units (EDU) and Network Interface Devices (NID) Demarcation of the provided service is a key function of the packetoptical access network as it enables the service provider to extend his control over the entire service path, starting from the customer hand off points. The customer s equipment is connected to the Carrier Ethernet network via a provider-owned demarcation device (Ethernet Demarcation Unit (EDU) or Network Interface Device (NID)) deployed at the customer location. The unit enables a clear separation between the user and the provider Ethernet networks. Transmode s Ethernet Demarcation Unit is an independent unit that supports Service Level Agreement (SLA) management capabilities, including sophisticated traffic management and hierarchical Quality of Service (QoS) mechanisms, standard end-to-end Operations, Administration and Maintenance (OAM) and performance monitoring, extensive fault management and diagnostics, all to reduce service provider operating costs and capital expenses. The same set of demarcation functionality is also available via Transmode s Network Interface Device, which is a port device, supported by its parent Ethernet Muxponder. The NID performs service OAM but leaves the service policing and tagging to be done by the Ethernet Muxponder, reducing cost and complexity of the customer located equipment. Figure 2O. The overall architecture of the packet-optical transport network. Figure 21. Transmode s Network Interface Device (NID). 28 Packet-optical networking transmode

29 2.4.2 Ethernet Muxponders (EMXP) In the aggregation network, traffic ingresses via an Ethernet Muxponder (EMXP) in the first node. The very same node may also include muxponders/transponders using additional WDM channels for fully transparent Layer 1 transport and use Layer 2 transport only where inspection and OAM information is required at intermediate points, and where traffic needs to be aggregated by statistical multiplexing. Finally, the core network is typically implemented by a set of IP routers using full IP-MPLS 8 for traffic engineering purposes. Normally operators prefer to have a clear demarcation point towards the aggregation network at the edge of the core network, often referred to as a provider edge (PE) router. The routers of the core network have a broad functionality and very high capacity; they are normally interconnected via a strict Layer 1 WDM network, since the main objective is to provide fat pipes without any need for Ethernet aggregation. Figure 22. Two of the units in Transmode s Ethernet Muxponder (EMXP) family. The aggregation and the metro core networks are interconnected via a packet-optical platform that can provide switching at OSI Layers 1, and 2. In the metro core, Ethernet SVLANs and MPLS-TP enables detailed handling of the Layer 2 services while WDM keeps legacy transport services at Layer 1. A ROADM 7 enabled Layer 1 provides flexible wavelength switching capabilities, while a unified control plane provides management capabilities across the aggregation and metro core networks. 7 Reconfigurable Optical Add/Drop Multiplexor Optical add/drop multiplexors (OADM, ROADM) and other optical elements The Layer 2 specific elements of the aggregation and metro core networks use Layer 1 optical WDM channels for the transport of Ethernet frames between network nodes as described in section All the above Layer 2 specific network elements interwork seamlessly with the flexible optical networking elements at Layer 1, when present in a truly integrated packetoptical platform, such as Transmode s TM-Series. A TM-Series node may include Layer 1 transponders and muxponders, Ethernet Muxponders, ROADMs and other optical network elements 9. The optical layer is indicated by the multicolored ring and links in Figure The multi-layer service management system The chosen network architecture has a profound influence on the degree of operational simplicity that is possible to achieve when it comes to network management. The real benefits of packet-optical networking can only be realized with a truly integrated Layer 1 and Layer 2 transport platform and a unified Layer 1 and Layer 2 management system. 8 MPLS used in conjunction with IP and its routing protocols. 9 For a description of how the optical elements work and are used in a flexible optical network, refer to the book WDM the Transmode Way from Transmode. transmode Packet-optical networking 29

30 A network for Carrier Ethernet services may be implemented as a separate Layer 1 optical network with Layer 2 Ethernet switches attached externally over standard interfaces, as depicted in Figure 23. Although conceptually simple, such a configuration results in a complex hierarchy of management systems. These systems must be carefully integrated in order to provide a useful Ethernet service provisioning and assurance environment. Figure 23. Ethernet services provided by separate Ethernet switches attached to an optical network results in a complex hierarchy of management systems. A multi-layer management system has access to both Layer 1 and Layer 2 network status information and can manage both optical and packet mode equipment. Since Layer 1 and Layer 2 functions are handled by one single system, provisioning of Ethernet services affecting both Layer 2 and Layer 1 can be done by simple point-and-click commands from the management system. Furthermore, Layer 2 services are monitored end-to-end and adequate Layer 1 resources can be allocated directly, should optical paths be broken or changes in the traffic pattern occur. The multi-layer management approach brings further benefits in terms of lower cost for management hardware, less training, less integration and simpler administration and maintenance of the entire network. Especially for network operators not already having an extensive Operations Support System (OSS) in place, the unified packet-optical management system offers significant advantages over the integration of multiple separate management systems. Using a true packet-optical network and an integrated multi-layer management suite, such as Transmode s Enlighten, which includes the Transmode Network Manager, improves this situation drastically. Figure 24. Ethernet services provided by an integrated packet-optical platform and managed from a multi-layer management suite such as Enlighten to simplify operations and reduce cost. 30 Packet-optical networking transmode