PDF of this tutorial- interoperability
- access flexibility
- transport efficiency
- provisioning simplicity and flexibility
- network management and operations support systems (OSSs)
Interoperability
With over 150,000 SONET systems in the United States and over 150,000 SDH systems in the rest of the world, SONET/SDH is the dominant metro access and transport technology. The economics are simple: existing SONET/SDH infrastructures must be leveraged, and current services and revenues based on SONET/SDH must be protected. While many vendors claim SONET/SDH interoperability, most are in fact incapable. An access device may collapse many of the current devices needed to provide multiple services, but in many cases, these devices will only talk with peers of like type on the SONET/SDH ring, as in the case of virtual path ATM solutions. True SONET/SDH interoperability mandates that the device must communicate with existing SONET/SDH ADMs at not only the physical layer, but at the control and signaling layers as well. True interoperability gives carriers the ability to replace legacy equipment in their network over time with next-generation equipment that is more flexible, scalable, and efficient. Given today’s requirements for rapid return on investment (ROI), full interoperability assures lower risk and faster payback migration strategy.
Access Flexibility
To provide bundled services based on both voice and data, these devices will terminate, switch, and route a vast array of traffic types and services. Today this requires the purchase of optical access equipment such as ADMs, multiplexers (MUXs), and DCS switches, in addition to Layer-2 and 3 switching and routing equipment. The price tag of this equipment is high, not including the costs to install, manage, and maintain it. Next-generation metro optical access devices will collapse the functionality of many of these traditional devices, aggregating, switching, and transporting TDM, frame, IP, and ATM–based traffic from DS0 all the way up to OC–48 and beyond.
Transport Efficiency
By incorporating the functionality of 3/1/0 DCS switches, these devices are able to distribute core DS0–level switching decisions at the edge of the metro network, significantly increasing SONET/SDH transport efficiency and increasing central office (CO) port efficiency as well.
Consider the task of switching DS0–level services in a traditional network. Traffic originating from the user side of the network must traverse the entire transport network and enter the CO (where the DCS switches traditionally reside) to be processed and switched. This not only wastes a tremendous amount of transport bandwidth but precious CO ports. By pushing DCS functionality and intelligence to the network edge, these devices tremendously increase bandwidth utilization in the transport network and increase port efficiency in the core. A classic application utilizing fractional T1 circuits is that of branch office interconnect to corporate frame-relay VPNs.
Application: Optimizing SONET for Fractional T1
Typical Fractional T1 Deployment
At a remote site, 12 fractional T1s are connected to a SONET ADM, as depicted in Figure 3. These 12 T1s are carried around the ring in 12 separate VT1.5s, where they are then connected to 12 T1 ports on a frame-relay switch. If we assume that the fractional T1s are 128–kbps services, the actual used bandwidth is approximately 1.54 Mbps. This represents a bandwidth efficiency of approximately 8 percent (1.54 Mb of data carried over 18 Mb of transport). This grossly inefficient transport not only wastes ring bandwidth, but quickly exhausts switching ports in the CO.
Figure 3. Typical Fractional T1 Deployment
Optimized Fractional T1 Deployment
When a next-generation optical metro access device is placed at the remote location, as depicted in Figure 4, ring bandwidth efficiency and port efficiency can be dramatically enhanced. The new device, with its built-in 3/1/0 DCS capabilities, will take the same 12 fractional T1 frame-relay circuits and combine them into one DS1 for transport in a single VT1.5 on the SONET ring. When the traditional SONET ADM at the CO drops the DS–1 signal out of the ring, the result is a completely standard T1 frame-relay signal that uses only one port on the frame-relay switch. While typical frame-relay services are data-only, these devices can effectively aggregate, groom, and switch voice traffic at a DS0 level, as well.
Figure 4. Optimized Fractional T1 Deployment
Provisioning Simplicity and Flexibility
Voice and data services of the past were based on fairly standardized technologies, and demand was fairly easy to predict. Today, the traffic mix is more heterogeneous in nature and not as predictable. The challenge is to innovate new ways to address multiple types of traffic with new, scalable, bundled service offerings that are easy to provision, manage, and scale.
By decoupling physical interfaces from protocol processing, these new devices allow fast turnup of new services, easy service migration, and the ability to add capacity on a port basis quickly. With these devices, a service provider can migrate from simple voice and data services to more advanced ATM and IP services within minutes versus weeks. For example, the service provider may want to incorporate only traditional Layer-1 functions such as circuit switching, multiplexing, and cross-connecting at initial deployment. Then, when demand warrants, they may gracefully migrate to more advanced Layer-2 and Layer-3 services such as ATM and frame relay VPNs, packet over SONET, and even IP over DWDM.
In addition to provisioning local services over individual network elements, next-generation access and transport devices will be able to provision end-to-end services fully over a multitude of network elements, including integrated access devices (IADs), other ADMs, and fast data switches and routers.
Network Management and OSSs
To deliver a multiplicity of voice and data services capably, carriers of all types must integrate the management of a variety of network technologies and platforms. Today’s emerging optical metro access platforms offer service providers the management and operations integration support and capabilities that are required to offer next-generation voice and data services from existing SONET/SDH architectures. Key enabling management technologies that are delivered in emerging optical metro access platforms include the following:
- point-and-click provisioning—equipment, facilities, cross-connects, protocols, service-level agreements (SLAs), static routing, VPNs
- fault management—alarm notification and propagation, root-cause correlation, and reporting
- performance management—performance monitoring of all access and SONET/SDH facilities as well as traffic management
- security management—IP– and UNIX–based security
- accounting management—call and traffic detail reports
- protocols—full SONET DCC mess transport, Web-based user interface, command line interface, transaction language 1 (TL1), signaling network management protocol version 2 (SNMP v2), common object request broker architecture (CORBA), common management information protocol (CMIP) Q3
Utilization of these robust management and OSS technologies allow service providers to consolidate services and therefore realize significant savings in capital investment, operations management support systems, and personnel, while delivering the high availability and robust services that enterprise customers demand.
