|
In 1994, the United States launched the Internet, setting off a
new upsurge in the information industry in the last decade of the
20th century. Shortly after, the Chinese Academy of Sciences got
access to the Internet, introducing on-line information from the
United Sates and other developed nations. The year 1993 witnessed
the setting up of the first ISP node on China's interconnection
network, thus placing CHINANET into commercial use. However, it
is not until the second half of 1995 that the country started large-scale
construction of CHINANET, because the government was not well prepared.
After that, all of a sudden, various types of ISPs and ICPs emerged
in large numbers throughout the country. In contrast with the crisis
of the global information industry, the IP-based Internet still
enjoys rapid development in China and various software and applications
of Chinese information have come to the fore.
IP broadband, low cost IP telephony, the establishment of 3G standards
and the application IPv6 together have greatly impacted against
the traditional telecommunications operators. Apart from stimulating
competition in the industry, the privatization carried out in the
Northern American and European telecommunications industries brought
the pleasure of using the Internet to their people and in turn upgraded
their requirements for the information network. Manufacturers of
traditional network equipment embarked on researches on new products.
Those manufacturers who emerged in the 1990s also rolled out a series
of brand-new network products, such as SoftSwitches, Ethernet-based
route managers, intelligent optical networks (notably, time division
networks), wireless broadband access networks and 3G products. This
tends to give rise to the misconception that the NGN means the interconnection
and interworking between the traditional and IP networks.
However, when you take a closer look at the goal the NGN pursues,
you will find that the interconnection between the traditional and
IP networks is only part of the goal. The NGN should include a basic
network composed of wave division multiplex (WDM) and an all intelligent
optical network. The intelligent optical network is a super-large
node (module) that integrates optical and electrical switching.
It has signaling and routing functions and can be formed into a
core network through realtime and dynamic connection. The intelligent
access network is the edge layer of the network. The last one is
the intelligent terminal which adapts to a certain bandwidth granularity
and has signaling function. All this make automatic end-to-end connection
possible.
No matter whether all optical technology or optical/electrical
combined time division technology or optical/electrical combined
IP technology or Wireless time division or IP technology is used,
all of them should perform full automatic switching, transmit unified
standard signaling between nodes and perform safe connection between
customers. That is the basic concept of the NGN, not to mention
safety, protection, maintainability, billing, network management,
etc.
No matter how the NGN will evolve, it will be an all round evolution
based a modern network. Now, let's discuss the NGN from the perspective
of evolution.
The main characteristic of a modern network is one service network
for one service. This means that an independent network only provides
a single service. For instance, a telephone network is composed
of telephone exchanges, a No. 7 signaling network, inter-exchange
trunk networks and copper access networks, thus incurring large
investment and high cost and leading to the complexity of the network.
Figure 1 shows the structure of a modern telecommunications network.
In the 1990s, thanks to the progress of electronic and optical
technologies, innovative products emerged one after another, such
as DWDM, single optical wave time division, and optical wave division
switches, etc.
With the advance of high-speed I/O chips, the transmission capacity
of a single optical wavelength has increased from 2.5 Gbit/s up
to 10 Gbit/s and 40 Gbit/s.
With the emergence of high capacity DXCs, signaling and routing
are introduced into transfer networks. Hence, the brand-new "intelligent
optical network" came up. AT&T's CINA CDR and Cisco Systems'
ONS-15454 intelligent optical network equipment have realized ASTN
function using OSRP signaling, while Alcatel's transfer network
adopts the ITU-T's UNI, which has also realized automatic end-to-end
dispatch function (Articles concerning the related standards of
intelligent optical and transfer networks are contained in this
journal).
Currently the application of intelligent networks is limited to
node to node and mostly to long distance networks due to their high
cost. The key to the realization of the NGN lies in the metropolitan
area network. However, the focus of researches and trials both at
home and abroad is gradually moving to its localization and the
ITU is making a study of standards in this regard. As for the core
layer, the all optical switching network is at the trial stage.
Since optical switching with the mechanical low light mirror cannot
convert wavelengths, the increase of switching capacity is problematic.
Therefore, O-E-O switching units are currently used to increase
unit switching capacity. The basic structure of these units are
shown in Figure 2.
To provide services, the backbone core network composed of O-E-O
switching units need the support of an intelligent edge network
using standard interfaces and signaling. See Figure 3.
Now we need to implement the ITU-T's O-UNI and P-UNI at the down
end of the access (edge) layer. When the intelligent terminal is
equipped with the customer network interface and the unified signaling
software, the NGN is implemented.
It should be noted that all the standards needed have been established
and it is not far from the realization of the NGN.
For the basic structure of the NGN, see Figure 4.
With the MPLS VPN mode adopted, the public IP network, or the Internet,
can provide the customers with end-to-end service with a high QoS
class to ensure sufficient network bandwidth and information safety.
The most important advantage of the IP network is bandwidth readjustibility
and multicast. As is well known, if the information it transfers
requires high confidentiality, this does not comply with its inherent
"best efforts" protocol. However, as a common network
that ordinal people draw public information and receive entertainment
and educational content, the IP network is a favorite network to
all walks of life.
As for Softswitch, it integrates the trunk signaling of the telephone
network with the IP network and enables multicast of voice and other
media, which is out of the question in the telephone network. It
also enables direct calls between the telephone and the IP networks.
Notwithstanding, it is not NGN itself.
The NGN means the realization of a full intelligent network from
the terminals at the bottom to the core network at the top. When
the user terminals and the network signaling are standardized, a
new user can call from the terminal to any terminal in the network.
That is the NGN.
|
