PDF of this tutorialBy leveraging an architecture based on multilayer switching, as shown in Figure 2, service providers can dramatically simplify their networks, offer a richer set of services, and gain flexibility while significantly reducing the cost of infrastructure and operations. A multilayer, multiservice switch combines circuit-switching and DCS functions at Layer 1 with Layer 2 or 3 packet-switching functions in a single device. In addition, the same switch supports multiple types of packet services via an integrated multiprotocol engine. The architectural integration of these key components into a single unified system offers an elegant solution with the simplicity, scalability, and efficiency required to handle many complex functions.
Figure 2. Simplified Network Architecture Using a Multiservice, Multilayer Switch
A multilayer, multiservice switch enables multiservice access to an ATM backbone, including support for frame relay, IP, PPP, and ATM access interfaces. It also supports channelized voice and data streams on an integrated TDM access link and support for voice over an ATM virtual circuit in the backbone using circuit emulation services (CES).
The resulting converged network architecture offers service providers a cost-effective, simple, scalable, and manageable network infrastructure with the following features:
- simplified network design
- unified operations for transport and data layers
- lower cost of equipment and operations
- bandwidth efficiencies of statistical multiplexing in access and backbone network segments
- voice and data integration in access and backbone network segments
- TDM and packet convergence over an ATM network
- single-step, end-to-end provisioning of private lines with automatic rerouting and restoration
Some key aspects of this network architecture include the following:
- raw transport—For an interexchange carrier (IXC) or a competitive local exchange carrier (CLEC) leveraging the access capabilities of an incumbent local exchange carrier (ILEC), the ILEC provides raw transport, aggregated by DCSs, with no awareness of which TDM DS–0 is used for which service or how to groom it. The IXC or CLEC, which provides service to the end user, however, should leverage such intelligence to run a more efficient network and enable service flexibility. Once traffic hits the IXC/CLEC's network, it can go straight into a multilayer, multiservice switch with integrated DCS capabilities. From there, integrated voice and data traffic can be handled in whatever way is necessary.
- voice and data integration on the access link—If the customer integrates voice and data traffic using TDM multiplexing over a DS–1 circuit, the integrated DCS function in a multilayer, multiservice switch can split the voice and data and direct each stream to the appropriate long-haul network. If the voice switch is in the same POP, the voice traffic can be handed off over the TDM interfaces to the voice switch with the appropriate mapping of signaling formats. If the voice switch is at another POP, the groomed voice traffic can be transported over ATM CES to the remote voice switch. If the customer integrates voice and data traffic in the access network using ATM, the ATM switching fabric in a multilayer, multiservice switch can segregate the voice and the data traffic for handoff to the appropriate long-haul network. If the voice switch is in the same POP, the voice traffic must travel across the derived TDM interface to the voice switch. If the voice switch is at another POP, the integrated ATM traffic is switched to that destination, and then voice is split off and delivered to the voice switch.
- the important role of integrated access DCSs—The integrated access (3/1/0) DCS function, with full access to DS–0s within every DS–1/DS–3, enables the integrated access of voice and data on a single DS–1 or fractional DS–1 customer access circuit. The mapping of common channel signaling (CCS) or channel associated signaling (CAS) enables intelligent connectivity to a co-located or remotely located voice switch. These are important functions, once performed by a stand-alone DCS, that are incorporated into a multilayer, multiservice switch at a fraction of the cost and space required for a stand-alone DCS. The integrated DCS function of a multilayer, multiservice switch also takes care of packing partially filled TDM pipes to full density before handing them off to the integrated protocol engines to optimize the performance and cost of a multilayer, multiservice switch.
- cost savings from elimination of stand-alone DCS—The cost savings of convergence are already being designed into the transport backbone, which is migrating from TDM to ATM/SONET, ATM/WDM, or ATM/DWDM and is incorporating the 3/3 DCS functions into the backbone ATM switch. Now this convergence can be extended to the access network.
The network architecture leveraging this integrated DCS function in a multilayer, multiservice switch can eliminate the legacy stand-alone DCS, resulting in savings of $500 to $700 per DS–1 in network equipment. This translates into saving as much as half the cost of overall access equipment, up to a third of the total network equipment cost for data services, and up to 50 percent in the cost of operations.
- service agility—The multiservice protocol engine functionality of a multilayer, multiservice switch supports the full array of data services that customers demand, including frame relay, IP/PPP, ATM DS–1, and IMA. It also supports private lines by circuit emulation and their various service features, such as network and service interworking, switched virtual circuits (SVCs), usage billing, quality of service (QoS), and monitoring and control for service-level agreements (SLAs). The multiprotocol engine supporting these various services has been designed to adaptively incorporate new protocols in the future.
- scaling the network edge and the backbone—The edge of the network can now scale to incorporate more kinds of traffic, a greater number of physical locations, higher density, and increased service bandwidth. At the same time, service providers can scale the backbone bandwidth at the core of their networks. A multilayer, multiservice switch routes traffic from a remote switch through the ATM backbone, which need not deal with the complexity of different services and service intelligence, allowing the ATM backbone to be simple, efficient, and scalable.
- simplified provisioning, rerouting, and restoration for private lines—With the routing and traffic management intelligence of this new converged network, private lines can be provisioned across the network in a single step, rather than using manual or rule-based segment-by-segment provisioning. In the event of any severe network conditions or failures, rerouting or restoration happens automatically.
- operations simplicity and manageability—Thanks to the new multilayer switching architecture, provisioning the TDM access portion and the packet or ATM service portion can all be accomplished using a single network component in a single step. The same is true for ongoing operations, fault isolation, troubleshooting, and all other management functions.
Leveraging the multilayer switching architecture, the service provider can flexibly provide any service (e.g., voice, private line, and advanced data service) at any time to any customer's port. Further, the same customer could use a mix of these services, and the service provider could easily and flexibly alter this mix to meet the customer's needs at different times with just a few simple keystrokes at the management system console. The operations cost savings can easily reach up to 50 percent.
Instead of disparate operations environments for the access and backbone portions of the network, service providers achieve a unified operations environment that is simple and efficient, resulting in enormous savings. Instead of a rigid, fixed service–network infrastructure, the newer, more agile network not only delivers any service that any customer might request today, but enables the service provider to provision new services on the existing infrastructure quickly. Service providers obtain a future-proof network that gives them an unprecedented competitive edge—the edge to race to market leadership.
