With the ever increasing demand for data services and broadband services, operators are now feeling the heat to upgrade their network to incorporate new services. The 3G applications and growing hunger for bandwidth demands better transmission technologies.

Problems and solutions
• Move towards single NMS: Service providers are deploying different flavors of transmission products. The products deployed are not only different in terms of technology but also with respect to different vendors. So, the option is to opt for a mix-and-match approach and move forward. On technology the focus was earlier on SDH and DWDM but presently it is tilted towards Metro Ethernet, CWDM, AON, MSPP, and others.

Even on vendor selection, service providers are opting for multiple vendors. This makes networks more cumbersome and complicated. So, service providers are now looking for a single network management system that will take care of network management system of all the transmission products deployed in a service provider network. All this is not easy, as service providers are looking for the best-of-breed technologies.

• Performance management, need of the hour: With bandwidth prices dropping every year, and resource cost increasing, service providers have a very difficult task to check opex to retain their competitiveness. To become competitive, service providers are looking at an opportunity to leverage performance management software to reduce operational expenditure thereby increase network reliability. All this is being done through close monitoring of managing fault, performance, and the availability of networks across multi-network technologies.

To be successful, service providers should focus on: proactive performance management for automating threshold behavior and managing network restoration; flexible management of point-to-point architectures for flexibility and resiliency, creating QoS thresholds for premium customers; dynamic bandwidth reporting for event driven service delivery; leveraging open standards and interfaces for maximum interoperability in hybrid network; understanding convergence issues in diverse network topologies; and real time reporting for managing network resources.

• Increased redundancy: Service providers are now looking at increased redundancy as it is a necessity in broadband networks. Redundancy is increased through RPR (resilient packet ring). Earlier it was deployed in datacom but presently it is now also available in SDH also.

• Increased flexibility: Multiservice provisioning platform (MSPP) gives service providers increased flexibility in terms of offering all kinds of services be it basic Ethernet, Fast Ethernet, or Gigabit Ethernet. So all datacomm features which were earlier present in a network are being incorporated in conventional SDH system. Storage solutions are also being incorporated in SDH solutions.

• One-stop solution: Service providers are looking for a single vendor who can take care of core and edge, and also provide infrastructure in different verticals like enterprise, residential and SMB segment. It should also take care of the last mile rollout be it: cable, DSL, wireless, and Ethernet. Vendors should focus from telco's perspective and should also provide infrastructure for the CATV industry.

• Integrating optical technologies: Despite the benefits integrating optical control plane with the existing system is a major challenge for the organizations. Such integration issues are a major roadblock in the older networks, as they had not taken the optical network elements while designing their networks. In any case putting in a new system without disrupting the normal operations is always on top of CIOs/CTOs mind.

There is a need to have some kind of interface or software to communicate the network performance log to the existing network control system and management systems. The idea is to exploit the benefits of new optical technologies as well as keep the inherent qualities of the existing system. Apart from technology integration, people manning these systems have to be educated and trained to absorb the optical components.

Technology
• SDH/SONET: Synchronous digital hierarchy (SDH) and synchronous optical network (SONET) refer to a group of fiber-optic transmission rates that can transport digital signals of different capacities. SDH has provided transmission networks with a vendor-independent and sophisticated signal structure that has a rich feature set. This has resulted in new network applications, the deployment of new equipment in new network topologies, and management by operations systems of much greater power than previously seen in transmission networks.

It was widely accepted that the new multiplexing method should be synchronous and based not on bit interleaving as was the PDH, but on byte interleaving, as are the multiplexing structures from 64 kbps to the primary rates of 1,544 kbps (1.5 Mbps) and 2,048 kbps (2 Mbps). By these means the new multiplexing method was to give a similar level of switching flexibility both above and below the primary rates (though most SDH products do not implement flexibility below primary rate).

MPLS, RPR, ASON-A Unified Future

In brief, SONET defines optical carrier (OC) levels and electrically equivalent synchronous transport signals (STSs) for the fiber-optic–based transmission hierarchy. SONET, a fiber optic transmission system for high-speed digital traffic, is a North American standard. SONET is widely used in carrier networks to aggregate lower speed T1 and T3 lines and transport their traffic on self-healing ring architectures that have advanced network management and restoration capabilities. SONET is an intelligent system that provides advanced network management and a standard optical interface.

• Multi-protocol label switching (MPLS): A major thrust area for the service providers has been MPLS as a packet-based technology. It uses label switching to forward data through the network.

MPLS-based networks separate routing and forwarding in IP networks making data transfer easy and fast. The constraint-based routing gives it an edge in terms of traffic engineering and is well suited for VPNs.

• Dense wavelength division multiplexing (DWDM): It enables a single optical fiber to simultaneously carry multiple traffic-bearing signals, thereby increasing the capacity of fiber many times over. DWDM systems can support more than 150 wavelengths, each carrying up to 10 Gbps. Such systems provide more than a terabit per second of transmission on one optical strand. SDH and DWDM are complimentary in nature with DWDM at the backbone and SDH at access.

• Coarse wavelength division multiplexing (CWDM): It's an older WDM technology and is emerging as a low cost alternative to DWDM especially in metro network access and enterprise applications. As they need to serve smaller bandwidth applications than DWDM systems, CWDM systems are characterized by wider channel spacing than DWDM optical networks.

The frequency separation between each individual color of light on the actual fiber is significantly further apart, which allows the system designers to use lasers that have looser tolerances on spectral width and thermal drift, therefore less expensive.

• Optical Ethernet: Two alternative architectures based on the successful fusion of optical and Ethernet technologies-collectively referred to as Optical Ethernet-have recently emerged to address the shortcomings of legacy SONET/SDH in today's metro networks.

Purposely built for data transport, Ethernet over fiber and next generation SONET/SDH-based metropolitan-area networks (MANs) combine the familiarity and ubiquity of Ethernet networking with the speed of optical transport to overcome capacity bottlenecks and alleviate opex and capex constraints.

Optical Ethernet is the technology that extends Ethernet beyond the local-area network (LAN) and into MANs and wide-area networks (WANs). While Ethernet LANs are almost exclusively used within the enterprise, optical Ethernet technology can be used as a service provider offering. Optical Ethernet supports the delivery of a full suite of carrier class Ethernet services up to 1 Gbps. It also provides for integrated optical transport, switching, and statistical multiplexing to help reduce the number of devices and capital expenses in the MAN. Finally, optical Ethernet provides bandwidth-on-demand service-provisioning capabilities.

• Automatically switched optical network/intelligent optical network (ASON/ION): As networks become more data centric and rising volume of traffic forces service providers create high bandwidth networks, there is a need to provide traffic-engineered services to the service platforms. Automatically Switched Optical Networks (ASON) fulfills this requirement of providing fast services to the platforms.

By adding intelligence to the networks, they are being made smarter and various processes being automated. A possible first step is to upgrade the network management systems with more sophisticated provisioning capabilities. Such a centralized approach to intelligent networking, however, has limitations of both functionality and scalability.

The alternative approach, which is being widely endorsed by the industry, is to distribute intelligence to every network element and link the elements at the control plane level so that they communicate and provide bottom-up data and functions for management.

The network becomes the database of record rather than the management system. This is the approach being embodied now in industry standards efforts such as the ITU-T's G.8080 (formerly G.ason) standards, the IETF's GMPLS specifications and the OIF's Optical UNI or user-network interface.

High bandwidth optical networks are being designed by telecommunications providers to provide traffic-engineered services to the service platforms like routers, ATM switches. Automatically Switched Optical Networks (ASON) is a concept that is being discussed to provide quick service activation to the service platforms in a data-centric network reliably.

• Multi-service provisioning platforms (MSPPs): A major problem for the service providers is to provide data and voice services across dissimilar networks. Multi-Service Provisioning Platforms promises to solve this challenge and allows the service provider to consolidate the number of systems required to provide intelligent optical access.

An MSPP enables add-drop multiplexing, digital cross-connecting, voice trunking, Ethernet switching, ATM switching, IP routing, and DWDM transport among other things.

• Reconfigurable optical add/drop multiplexers (ROADM): With reconfigurable optical add/drop multiplexers additional network capacity can be added without going in for any major upgrade. The best part of ROADM is that it works wherever there is additional services are required without interrupting other
services.

The scalability feature of ROADM is expected to assist third generation of WDM systems for metro and long haul networks. ROADM-based WDM equipments are expected to be a serious challenger to SDH/SONET systems.