Simplifying the TDM to packet transition

By Frank Wiener

Overview

New platforms enable service providers to continue to leverage TDM services using established methods, while migrating to the new generation of Ethernet services in a phased, controlled, and more cost-efficient manner.

Service providers globally have a common goal of a network that delivers an expanding array of packet-based services in a capital and operationally efficient manner. The challenge for most providers is the amount of TDM-based infrastructure remaining in their network and how to transition this infrastructure to achieve that goal. Up until now carriers have lacked a compelling option to exploit this installed infrastructure and associated human capital while scaling and optimizing the network for packet transmission.

Many providers have taken an overlay strategy where all new network scale is addressed with a parallel overlay packet network. Unfortunately, this approach actually increases the costs and headaches for service providers as it results in two networks to plan, maintain, and operate. Others have taken a protocol convergence approach, translating TDM services into packet transports with pseudowire in a quest to evolve to an all-packet switching and transport infrastructure. However, the cost and complexity of translating TDM services to packet for transport and then back to TDM for handoff at the other end of the network adds cost and complexity—with no additional revenue.

FIGURE 1. Multilayer management provides a converged view of the network or per-layer and interlayer perspectives.

Until recently, there were limited alternatives to these two approaches. Fortunately, new packet optical networking platforms (PONPs) provide the ability to natively support any mix of both TDM and packet capabilities in one homogeneous network. This enables service providers to continue to leverage TDM services using established methods, while migrating to the new generation of Ethernet services in a phased, controlled, and more cost-efficient manner.

Multilayer PONPs enabling new options

New PONPs are modular and leverage the latest component technologies to integrate scalable, next-generation packet transport switch functions and DWDM/ROADMs with SONET/SDH multiservice provisioning platforms (MSPPs). Any mix of packet, TDM, and DWDM transport modules can be deployed on an as-needed basis. Packet modules support both wholesale and retail Ethernet transport services. MSPP modules support native SONET and SDH transport functions. DWDM modules support expansion of capacity for all service types. ITU G.709 Optical Transport Network (OTN) technology provides a common digital wrapper for both packet and TDM services and is ideal for transport over DWDM fiber links.

New innovations in packet optical transport technologies support multilayer management to enable a unified management view of the multiple technology and operational layers that exist in virtually every large network (see Fig. 1). These systems visually display the layers and relationships between conduits, fibers, wavelengths, OTN, SONET/SDH, connection-oriented Ethernet transport, and service layers of the network to enable management optimization across all layers of the network.

The ability to natively groom packet, TDM, and optical services in one integrated platform and then transport these services over a common fiber-based network enables the efficiency and operational benefits of one fully converged network. These systems operate seamlessly alongside the installed base of SONET or SDH equipment. Transparency ensures that both TDM and packet services are transported predictably and reliably. The payload data is simply encapsulated and transported. There is no TDM-to-packet processing-related jitter or latency. The costly, complex, and risky circuit emulation techniques required to transport high-bandwidth SONET/SDH payloads over packet are unnecessary and can be avoided entirely in the transport network.

This packet optical transport approach offloads transport traffic from routers, which are often used to provide Layer 2 switching and transport. Offloading transit traffic unclogs expensive router ports, freeing this capacity for network services expansion. Packet optical networking platforms can now provide lower latency with these services for a fraction of the cost of using routers for transport. The platforms also provide higher capacity, lower latency and jitter, and native support for established SONET/SDH services on a lower-cost network that scales better and is simpler and cheaper to operate.

Achieving network and operational convergence and making more efficient use of network resources, while TDM and packet technologies natively coexist in one physically converged network, sets the stage for a simplified and cost-optimized network transition from TDM to packet.

Multilayer transport network transformation strategies

Modular PONPs integrate into existing networks to provide incremental service capacity and facilitate network transformation to a packet-services-optimized network. Multiple strategies coexist during the transition—as determined by the existing and emerging network and business constraints that vary across the network.

While sequencing can vary, the basic elements of the network transformation strategy will likely consist of the following benefits for service providers:

deploying Metro Ethernet Forum (MEF) services us ing connection-oriented Ethernet (COE) transport
consolidating and further scaling SONET with OC- 192 or SDH with STM-64
providing gateway functions to bridge services be- tween TDM and packet transports
using OTN as the common high-bandwidth transparent transport technology for its forward error correction; consistent robust operations, administration, and maintenance (OAM); and its high-capacity optical services channel for manage ment connectivity
expanding fiber capacity with DWDM
leveraging next-generation node architectures to scale services and transport capacity
optimizing and simplifying with multilayer management

Scale MEF services with COE transport for efficiency

Ethernet has become the de facto interface for both retail and wholesale packet transport services. Multiservice provisioning platforms introduced multiservice transport by supporting encapsulation of packet services for grooming using SONET. Grooming is a term associated with transport networks and supports aggregation of traffic over shared high-capacity links. Grooming of packet services using SONET/SDH is complex and suboptimal. Next-generation PONPs support grooming of conventional and advanced packet services such as Ethernet Private Line, Ethernet Virtual Private Line, and Ethernet LAN over a native packet transport technology.

FIGURE 2. Packet optical networking platforms support MEF services with COE transport

Transport grooming supports the sharing of capacity, while providing total independence of the different customer payloads, with strong service-level agreement (SLA) guarantees. As a result, transport switches have distinct and critical requirements not found in enterprise or even carrier-class service switches. Connection-oriented Ethernet transport combines packet grooming capability with the transport attributes of SONET and SDH, and is enabled by Ethernet standards such as 802.1Qay (PBB-TE) and the evolving transport-focused MPLS variants such as T-MPLS and MPLS-TP (see Fig. 2).

Grooming of multiple lightly loaded Gigabit Ethernet (GbE) and 10GbE services onto aggregated transports improves efficiency and reduces cost. Packet transport OAM, combined with OTN overhead, actually improves the quality of the product by improving optical performance, reducing jitter and latency, and supporting superior visibility and control of the network for increased availability and reduced time-to-repair.

Consolidate SONET with OC-192 (SDH with STM-64)

While COE is expected to rapidly rise as the preferred Ethernet transport standard, installed infrastructure, existing contracts, and customer agreements will continue to drive demand for SONET/SDH-based transport services. In addition, legacy subrate services often consume valuable fiber resources. Many service providers consider the option of upgrading legacy MSPPs to OC-192/STM-64 or introducing new MSPPs. However, these upgrades are often costly and further proliferate network complexity with multiple separate systems with limited long-term Ethernet potential.

New PONPs use the latest integrated circuit designs that provide the functionality of historic MSPPs on a blade—with disruptive low cost. These integrated SONET/SDH MSPP modules set the stage for a seamless migration to packet by sharing a common management infrastructure and the ability to map Ethernet-over-SONET/SDH to transport Ethernet services over existing SONET/SDH infrastructure.

FIGURE 3. Packet optical networking platforms provide the gateway between packet and TDM.

Bridge MEF services across COE and SONET with gateways

Packet optical networking platforms now provide the ability to transport MEF services, SONET/SDH, OTN, and COE services. Because multiservice and multitechnology support are not sufficient, PONPs must also support concurrent nonblocking grooming of these different services and technologies.

These platforms should also provide multiplexing and adaptation functions to support interlayer functions. For example, gateway network elements will be required between parts of the network that use Ethernet-over-SONET transport and other parts that support COE (see Fig. 3). The gateway nodes may be required to groom in both the TDM and packet domains at the same time. This functionality provides new levels of flexibility to provision services across multiple transport technologies and to seamlessly facilitate the eventual transition of services from one transport technology to another.

Expand fiber capacity with DWDM

Packet optical networking platforms provide several options to multiplex optical channels over shared fibers. Fixed and tunable transceivers, pluggable and nonpluggable optics, and fixed and tunable multiplexing and demultiplexing methods together support both colored and colorless DWDM grooming and both directional and nondirectional transceiver deployments. No single combination of these technologies can target all of the applications. And the technology will continue to evolve.

Through innovative design, new developments in PONPs support four or eight 10-Gbps optical channel DWDM configurations to provide simple and cost-effective capacity expansions. As services scale, modular upgrades to 40-channel configurations with wavelength-selectable switching enable scale with unrivaled operational simplicity.

Optimize and simplify with multilayer management

As we explore the transformation from TDM to packet and even post-transition packet networks, it becomes clear that networks will consist of multiple layers. At a minimum, these networks will consist of:

service layers
transport multiplex layers
OTN layers
optical wavelength layers
fibers and conduits

Historically, these separate layers have been planned and managed independently, often by different dedicated resources. As PONPs provide the ability to interface with networks across these layers, innovative multilayer management systems provide the traditional fault, configuration, accounting, performance, and security (FCAPS) functions for these layers to simplify operations.

Integrating these layers in multitechnology node hardware has significant economic advantages. These advantages are even more dramatic when the node and network software are also multilayer aware. Software can also provide the ability to model the network, cluster demands, and analyze resource assignments across each layer and between the layers of the network. Grooming and multiplexing optimize the economics of all services and all layers of the network.

Network operators are tasked with configuring and maintaining these networks. What-you-see-is-what-you-get, three-dimensional visual-display technology helps network operators understand the network environment and the new technologies. Clarity reduces error, increases confidence, and empowers people to do their jobs.

The transformation to come

The network transformation from TDM to packet will happen at different rates across different parts of the network. Innovations with PONPs present new opportunities to accelerate directly to advanced packet services using packet transport. These systems may also provide the gateway functions to bridge Ethernet services across a mix of TDM and COE transports to facilitate a more evolutionary approach to network transformation.

As network capacities continue to scale, support for an easy expansion to DWDM provides a scalable approach that can extend across the network. Finally, integrated multilayer management systems round out the process with the ability to manage and provision services across both TDM and packet transport with one integrated operational view of the network, enabling a flexible and more holistic approach to network transformation.

Frank Wiener is the vice president of marketing and business development for Cyan. He has a diverse background ranging from engineering to product management, marketing, sales, business development, general management, and executive management for Nortel, AT&T/Paradyne, Calix, and Cyan. Wiener also has authored three telecom books.