Download Transporting the broadband surge TextStart The explosive growth of

Transporting the broadband surge
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The explosive growth of IP and video services, like the P2P and IPTV, are causing a
dramatic spike in demand for high bandwidth in metro transport networks. OVUM
RHK forecasted a CAGR of 18% and 33% respectively for the DSL market and FTTx
market in the upcoming five years; while traffic in the metro transport networks would
increase by 30 times. Operators now have both a challenge and a great opportunity.
Making the right choice is crucial to success in maintaining customer satisfaction.
Metro transport for broadband wave
Suddenly, transport of mass IP services has become a priority and poses an
unprecedented challenge to existing networks. A traditional metro transport network
(also called a narrowband transport network) is a ring network based on the
synchronous digital hierarchy (SDH), bearing voice services and small-granularity
private line services. With the development of high bandwidth services, the traditional
transport network is moving towards a broadband transport network that can bear IPTV
and various large-granularity private line services.
WDM: an essential choice
In South Korea, the broadband penetration rate is 93% with an average speed of
49.5Mbps. Japan has 55% with 63.6Mbps and the USA clocks in with a 57% rate and a
speed of 4.9Mbps. The Information Technology and Innovation Foundation (ITIF)
published a report in May 2008 that showed a brisk worldwide broadband market
fueled by the rapid growth of video services requiring higher bandwidth.
Family broadband access is graduating from 2M to 30M or even 100M, and evolving
into ultra broadband. Suppose there are 500,000 family broadband subscribers in a
metropolitan area network (MAN), and the access bandwidth for each family is 30M,
equaling 40×10G wavelengths converged at the network core. If the access bandwidth
for each family is 100M, then more than 120×10G wavelengths converge at the core of
the MAN.
To alleviate potential bottlenecks, a wavelength division multiplexing (WDM)
technology is applied to make full use of the tremendous bandwidth resources of fiber
lines. In an MAN that adopts WDM technology, signals with different characteristics
are transmitted transparently, and the MAN can easily bear service signals of various
formats, plus save expansion costs. This had made WDM an indispensable technology
for the MAN.
To meet the bandwidth demands of broadband services, 40×10G wavelengths need to
be planned for the core exchange layer of a small and medium-sized MAN; 80×10G or
even 160×10G wavelengths for the core exchange layer of a large MAN. The 40G
transmission technology can be adopted when necessary to prevent the wavelengths
from being used up.
OTN: the networking WDM
In a traditional MAN, SDH is adopted for interoffice service scheduling, monitoring
and protection. However, the SDH cannot be used for broadband service bearing
because of its limited bandwidth and transport efficiency. Currently, interoffice service
scheduling, monitoring and protection are still required in a MAN, so optical transport
network (OTN) is used to satisfy scheduling and protection of large-granularity
services.
In a traditional WDM network, services are transported point to point and the network
does not support capacity and distance expansion functions or end-to-end connection
and protection functions, whereas the OTN network supports both functions.
The traditional WDM network with P2P links can be developed into a highly efficient
OTN network with end-to-end connection, monitoring and protection functions. This is
why OTN is regarded as a networking WDM system. If WDM links are compared to
information expressways where broadband services travel, then the OTN network is an
overpass that joins the information expressways together into a highly efficient
information expressway where the bandwidth is high and the transport is flexible.
According to Zhang Chengliang, Deputy Chief Engineer of the China Telecom Beijing
Research Institute, OTN technology is introduced into a WDM system in two phases. In
Phase 1, OTN interfaces are introduced into the WDM system, including the line
interfaces and tributary interfaces (also called inter-domain interfaces or service
interfaces). After OTN interfaces are introduced into the WDM system, the
performance and faults of wavelength channels in the system can be monitored end to
end. With OTN technology, various client signals are transparently transported within
the system, enabling the router to use 10GE LAN interfaces.
In Phase 2, the OTN-based cross-connected T-bit capacity equipment is introduced into
the WDM system. The equipment enhances the transport reliability of the system,
achieving the quick commissioning and scheduling of large-granularity services, and
optimizes the IP network structure.
OTN has become the only approach for managing the system resources in the optical
and electrical domains in a unified manner. With the development of broadband,
tremendous wavelengths are surging over MANs. The Gigabit Ethernet (GE) and
10-Gigabit Ethernet (10GE) interfaces for large-granularity services have become
mainstream network interfaces. Neither the traditional WDM technology nor the
reconfigurable optical add/drop multiplexing (ROADM) technology can solve
problems in the complex operation, administration and maintenance (OAM) of a
multiple-granularity and multilayer network. The OTN, however, can be used for
managing the services in the optical and electrical layers in a unified manner.
OTN on the rise
Mick Reeve, the former CTO of BT, once said: "OTN will be more and more popular
with operators because of the limitations of SDH and traditional WDM technologies."
Mainstream operators all over the world are now highly focused on the development
and application of OTN, and WDM transmission interfaces in most networks support
the OTN function. As a result, OTN has become a mainstream support technology for
the backbone transport network and the metropolitan core transport layer.
Development in three phases
As early as in 2006, OVUM RHK accurately forecasted the development of OTN
markets with the following statement: About USD3 billion of the roughly USD11
billion spent on optical networks was addressable by OTN-capable products; the
opportunity will increase substantially over the next five years. Even in modest
implementations, OTN offers an opportunity for network operators to capture its
benefits to increase the utility and lower the cost of their evolving unified packet optical
infrastructure, which is steadily outstripping the ability of SONET/SDH to efficiently
manage high-bandwidth pipes.
The OTN will basically develop in three phases. Phase 1: Introduction of the OTN (or
Pre-OTN) with compatible interfaces. In this phase, different equipment from different
suppliers supports OTN capsulation, mapping, overhead management, and forward
error correction (FEC) functions as defined in ITU-T G.709. This phase began in 2005
and is largely completed.
Phase 2: Introduction of cross-connect capability. This phase started in 2006 and is still
underway. At the ITU Telecom World 2006 in Hong Kong, Huawei demonstrated the
first WDM-based OTN system in the world: a next-generation (NG) intelligent optical
transport system, called the OptiX OSN 6800/3800.
By the end of May 2008, more than 5000 sets of OTN equipment have been put into
stable and mature operation in networks around the world by leading operators like
Vodafone, Telefonica, China Mobile, and China Telecom.
Phase 3: Introduction of automatically switched optical network (ASON) and
generalized multi-protocol label switching (GMPLS) to support the intelligent
networking capability. As early as 2006, some leading equipment suppliers claimed
that OTN would support ASON and GMPLS, and some ASON OTN networks have
been put into actual operation.
Broadband bears future
Equipment that supports the ASON/GMPLS control at both the optical and electrical
layers has been launched on the market. ASON technology used in the WDM system is
able to support higher service bearing efficiency in a more robust and reliable network.
This kind of intelligent and automatic networking brings a remarkable reduction in
capital expenditure (CAPEX) and operational expenditure (OPEX).
Most experts in the industry believe that the metropolitan core transport network in the
future will be a two-layer network formed by the IP and OTN layers. The GMPLS
control plane will enable unified management of data and optical transport equipment.
At the Beijing high-end transport network exhibition in May 2008, Huawei
demonstrated OTN equipment with T-bit cross-connect capabilities. The equipment
supports the mix of ODU1, ODU2, and ODU3 and the unified GMPLS control plane
for wavelengths and ODUs. Statistics from OVUM RHK showed that the Huawei
Metro WDM equipment had the highest global market share in 2007 4Q and 2008 1Q.
The rapid growth of OTN is a stepping stone for operators to expand their
future-oriented services. For instance, a well-known fixed network operator in Europe
started constructing an NG WDM network in 2007 to shorten the development time for
network broadband services. When finished, the network will be flexible and reliable
enough to bear both broadband services and mass private line (including GE, 10GE,
and wavelength private line) services.
Because the OTN network is an open network based on end-to-end connections, the
operator has deployed an integrated WDM/OTN network that stretches from the
national backbone to the metro core layer and the metro edge access layer.
On the strength of the powerful OAM capabilities of OTN, unified management of
ROADMs and large-granularity electrical-layer services was achieved in the
WDM/OTN network. Compared with the months of service provisioning time for the
traditional WDM network, the service provisioning time of the WDM/OTN network
was shortened to minutes, achieving the initial goal of constructing a flexible and
dynamic WDM network.
The next step is to enhance network resource utilization and service protection
efficiency. OTN-based ASON/GMPLS networks will become the new focus of
network planning, and equipment in the existing networks can support the
ASON/GMPLS capability by software upgrades. Looking ahead, operators who can
quickly expand their networks with high-bandwidth services now, will have more
opportunities, seize more market share and beat the fierce competition in the future.
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