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Abstract: the transmission network is a foundation for constructing
various service networks. A study of the technical development of
the transmission network is of great significance in senses of building
and managing a robust transmission network. This article discusses
the structural characteristics of the transmission network, elaborates
the architecture adoptable on the network and describes the features
and development of the Next Generation Transmission Network, i.e.,
the Intelligent Optical Network (ION).
The digital transmission network is basic network platform for constructing
and developing various telecommunications services, and has played
a pivotal role in each and every period of time leading to the fledged
communications world nowadays. The digital transmission equipment
underwent a development process of from PDH to SDH. So far, BeijingCom's
transmission network has grown into a fully digitized SDH backbone
of a considerable scale.
1. The Architecture of the Transmission Network
BeijingCom's SDH network adopted two kinds of architectures in
different construction period, namely, hierarchical architecture
and ring architecture. The former features clear-cut network structure,
flexible circuit deployment, high path utilization ratio, ease of
capacity upgrading and optimization as well as a strong adaptability
to changing demand. The latter better suits the need of relatively
static demand scenario, with a low starting cost. It is also fit
for conditions where more internal circuit deployment is required
compared to the outgoing transit need. Complicated and inflexible
in circuit organization, this sort of network architecture is not
geared for easy capacity upgrading. It has been proved through the
practice that a metropolis like Beijing should apply a hierarchical
architecture on its transmission network.
The hierarchical transmission network comprises three layers: the
backbone layer, the convergence layer and the access layer. The
backbone layer is composed of backbone nodes; the convergence layer
is composed of convergence nodes; and the access layer is composed
of access nodes. The network architecture is shown in Figure 1.
Figure 1
The concept of transmission network is based on the SDH technology.
The selection of network equipment is determined in conformity with
backbone nodes, convergence nodes and access nodes respectively.
The transmission backbone node refers to the node where traffic
converges. Such nodes feature enormous requirements for the transmission
bandwidth, such as the tandem office and service convergence office
in the local switching network, the long-distance hub office, the
telegraph office and the service interconnection gateway office,
etc.
The transmission convergence node refers to nodes where the switching
capacity is handsome or data traffic converges. Such nodes are characteristic
of enormous requirements for the transmission bandwidth so as to
connect to a multitude of access nodes. Examples of such nodes are
end offices with multiple module offices, an end office with multiple
switching systems and central offices in counties or prefectures,
etc.
The transmission access nodes refer to sundry nodes of small traffic
flows, such as module offices, big mansions and office towers, etc.
The transmission backbone node should adopt bandwidth management
equipment with multiple 10Gbit/s optical ports, large capacity 4/4
cross-connect capability and multi-service support. The transmission
convergence node normally adopts 10Gbit/s multi-optical port ADM
equipment. Based on service demand, the transmission access node
normally adopts the ordinary 2.5Gbit/s or lower than 2.5Gbit/s ADM
equipment. The equipment for the convergence layer and the access
layer tends to be combined with the Multi-service Transmission Platform
(MSTP) technology and the Optical Ethernet technology and so on.
The equipment for the convergence node should provide STM-64, STM-16,
STM-4, STM-1, GE, E3, ATM Switch Card, 10/100M Ethernet interfaces.
The equipment for the access node should provide STM-16, STM-4,
STM-1, GE, E3, ATM Switch Card, E1, 10/100M Ethernet interfaces.
2. Functional Requirements of the Transmission Backbone Node Equipment
As stated above, the transmission backbone node should adopt multi-optical
port bandwidth management equipment to support ultra-large capacity
cross connection. Optical interfaces of a wide array of rates play
a key role in large transport networks. Specific functions are illustrated
as follows:
， Flexible traffic deployment and diversion. Flexible service creation
and deletion features especially in the case of emergency conditions;
， Traffic diversion, merging, distribution and assembling, to improve
the network utilization ratio and form an explicit organization
of communications channels;
， Traffic recovery of the entire network according to certain network
viability algorithm to make the operating to protection capacity
ratio of the network hit N:1, so as to boost the network operating
capacity by a big margin;
， Protection of various mechanisms thanks to its integration of
the ADM feature;
， An organic connection to all network levels to present a clear-cut
and orderly network structure;
， Gradual construction of network paths according to requirement
to ensure a rapid and handy capacity upgrading process, without
any side effect on the existing network architecture and services;
， As a result of its integrated design, the equipment and network
organization expenses are slashed to save footprints and eliminate
failures caused by too many interconnection cables between equipment;
， Driven by the development of optoelectronic technologies and market
demands, the multi-optical port bandwidth management equipment is
going towards large capacity, due intelligence and full services;
，The large capacity is reflected in the cross-connect capacity that
would skyrocket to several or dozens of Tb/s from the present several
hundred Gb/s. Meanwhile, with the progress of chip technology, the
equipment is more and more integrated and presenting increasingly
smaller form factor;
， The intelligence is reflected in the application of smart control
technologies to realize distributed network management and dynamic
configuration of network nodes and transmission paths, so as to
improve the operating speed and efficiency of the network;
， Full services are reflected in a fusion of optical cross-connect,
ATM/ IP and Terabit processing capabilities. In so doing, real time
and broadband data traffic can be linked together in an organic
manner for processing of full services.
At present, there are a host of vendors offering multi-optical
port bandwidth management equipment, such as LUCENTs Lambda-UNITE,
with up to 32 10G optical ports on one single unit and providing
a cross-connect capability of 320 Gbit/s; SIEMENS's SXD (integrated
type), with up to 32 10G optical ports and a host cross-connect
capability of 320 Gbit/s; ALCATEL's 1674SXs (integrated type), with
up to 128 10G optical ports and a host cross-connect capability
of 1280Gbit/s; NORTEL's HDX (integrated type), with up to 96 10G
optical ports and a host cross-connect capability of 960Gbit/s;
CIENA's Core Director, with up to 64 10 G optical ports and a cross-connect
capability of 640Gbit/s. All such multi-optical port bandwidth management
equipment can provide STM-64, STM-16, STM-4, STM-1 and GE interfaces.
Although the above products are already designed with a certain
degree of cross-connect capability, the vendors have all tried to
increase the equipment capacity by adding the capacity of the equipment
cross-connect matrix of through concatenation methods with a view
to satisfying the fast growth of service transmission in the future.
3. The Intelligentized Development of the Transmission Network
As the information process is accelerated, the demand for data
traffic is on the rise. So is the case with the IP traffic. Given
that the dynamic and bursty IP traffic is not distributed as evenly
as the plain POTS traffic, it would be difficult for network operators
to make appropriate evaluations of the instantaneous traffic. To
improve the quality of service and respond to subscriber demands
in a rapid way, operators must set up dynamic transmission routes
to adapt bursty traffic to the establishment of optical links.
As the network grows, the capacity requirement is gradually shifting
from the core to the edge, i.e., from the initial transport connection
to an end-to-end connectivity service. So it is necessary for the
optical transport network to evolve from providing the present capacity
transport to end-to-end connectivity. That is why the concept of
Intelligent Optical Network (ION) has emerged.
ION integrated the advantages of ATM and IP technologies, and for
the first time introduced Dynamic Route and Signaling into the transmission
network. It is able to connect seamlessly with service networks
like ATM, IP and the like to satisfy dynamic bandwidth demand in
a holistic way, thus providing QoS guarantee and becoming a real
integrated intelligent transport network in all senses. Therefore,
ION is highly valued by all communications standardization bodies
and equipment vendors. For the time being, there are primarily two
kinds of intelligent control methods on the ION. One is called Distributed
Control Mode as advocated by CIENA, which features the Optical Switching
Routing Protocol (OSRP). The other is proposed by NORTEL and ALCATEL
and features a standard control plane to enable the transport layer
to offer dynamic routes. The control plane may be realized through
UNI/NNI interfaces or Management System Interfaces. To that end,
General Multi-protocol Label Switching (GMPLS) is adopted. On the
ION, the intelligent control technology is leveraged to realize
the dynamic allocation of bandwidth, end-to-end protection &
recovery and the collaboration between data NEs and optical NEs.
Intelligent features include resource discovery, status information
announcement, connection management and network management. The
adoption of intelligent control technology has enabled the optical
network to evolve and provide not only the fixed static connectivity,
but also dynamic switching connectivity as well.
4. Management Features of the Intelligent Optical Network
On the whole, the Intelligent Optical Network provides the following
management features:
4.1 Support to Event & Performance Management
The event management features the following:
i. Continuous supervision of the network from one single location,
e.g., a central office or Network Operation Center (NOC);
ii. Report of any status change by any NE in the operation;
iii. Dynamic convergence of correct configurations in the network
and the network event generated by them;
iv. Archiving of all historical events and auditing logs;
v. Status information of the NE layer;
vi. Permission of alarm response to indicate that a reported problem
is known.
The performance management features the following:
i. Reception and display of all key operation attributes of NEs;
ii. Reception and display of standard performance measurement methods.
4.2 Management Planning System (MPS)
MPS is a network modeling and planning tool and features the following
capabilities:
i. NE resource planning and network dimensioning;
ii. Configuration of nodes, links, lines and protection plans;
iii. Simulated transmission for network performance evaluation and
invalid model analysis;
iv. Route and QoS planning based on the simulation result;
v. Offline modeling of the network capacity;
vi. Identification of reasons for invalidated simulations;
vii. Execution of protected switching analysis;
viii. Execution of trend line and projection simulations.
4.3 Subscriber Network Management
Subscriber Network Management is a robust carrier-class software
package to provide service creation, real-time end-to-end configuration
and service management. Service providers may extend this kind of
capability to their subscribers. The Service Management Suite consists
of two applications: Service Layer Management (SLM) and Subscriber
Network Management (SNM).
i. SLM allows service providers to create, configure and supervise
services, service layer management protocols, pre-maintenance services
and service suspension prevention. In the meantime, it is also able
to identify reasons for QoS problems on the ION. SLM also provides
the following services:
， Support of multi-sellers;
， Surfing of service topologies;
， Extension of report capability, e.g., traffic flow statistics
and analysis.
ii. SNM enables service providers to define secure, real-time and
web-based service management capability and information, such as
the availability, performance, SLA status, etc. Service providers
may provide this additional functional module as an extra service
to its subscribers.
As stated above, the Intelligent Optical Network represents a irreversible
trend in the development of the transmission network. Operators
should proactively study the ION technology, select mature ION products
and set up intelligent transmission networks as soon as possible.
Only by doing so can they enhance their network capability, honor
their QoS level, cut their maintenance cost and improve their corporate
competitiveness.
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