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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



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.



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


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):

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



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.



Ramdev Sharma,

product (marketing), Huawei Technologies India

Ravi Sharma, president for South Asia and MD, Alcatel India

Shrikant Shitole,
new business devlp. manager (India) Cisco Systems

Sumita Gupta,
general manager, transmission, ZTE

Challenges for Metro Service Providers

Service breadth where the providers must be able to offer a variety of

offerings like IP, Frame Relay, Ethernet, ATM etc. with flexibility for new

services without heavy additional cost. Service delivery where the network is

optimized for changing access requirements with easy and quick provisioning.

Service awareness where requirements as QoS, class of service, protection

levels take higher precedence. Scalability where the network capacity should be

able to scale much higher than the capital costs for upgrades.

Network reliability where the capability of a SONET network must be

maintained with regard to protection and restoration. Co-existence with existing

infrastructure to carry voice as well as data traffic as well as interfacing

with existing infrastructure.

Topological flexibility where the equipment must be able to support different

physical topologies thereby supporting flexible application traffic flows.

Reduction in operational and network costs since the metro network is driven

by central office access and transmission equipment costs. Newer equipment must

offer increased functionality and performance without proportional cost


(Source: Wipro)