Homework
Assignment 10
ISDN is
developing in CHINA
GANG LIAN
Computer
Science and Engineering Department
Helsinki University of Technology
28/10/1999
ganglian@cc.hut.fi
Abstract
As a young student, I have a great responsibility for my home country,
contribution for my country is my dream in my life, that is the reason
why I come here to study. Although my knowledge is still very basic, I
want try my best to use the knowledge i have learned to explain why
develop ISDN and how to develop, at the same time deal with some practical
problems which is happening in the development of ISDN of my country. Today,
although ISDN has been quite old technology and introduced to CHINA several
years, developing the ISDN Technology is still a hot argument. Some people
say ISDN will be out of date in the very near future, so we should skip
ISDN to develop more advanced technology such as ASDL, BISDN directly.
But from my stand point, considering the advantages of ISDN combined with
the current our situation and market driver, I firmly support we should
strongly push the development of ISDN technology now.
Table of contents:
1. Introduction
2.Introdction to ISDN
2.1 Definition
2.2 Interfaces
2.3 The Hierarchy
of Protocols
2.4 Advantages
3.Why develop ISDN
technology in CHINA today
3.1 The
current situation of ISDN in CHINA4.7 Solution to tele-course
3.2 Positioned market
of ISDN
3.3
Benefits from developing ISDN technology in China.
4.How to use
ISDN technology in different situation.
4.1 Solution
to connect LANs
4.2 Solution to
small Offices
4.3
Solution for SOHO users to connect Internet
4.4 Solution to DDN
backup
4.5 Solution For
Video Conference
4.6 Solution
to Desk Video Conference
4.7 Solution to tele-course
5. Reference
1.Introdction
In this essay, I will present my option and suggestions about why is ISDN
and how to develop. I will begin introduce briefly the ISDN Technology
and related background; after that, I will continue to justify why we should
foster the ISDN Technology currently in CHINA; at last, I will end up with
presenting some practical solution for the different ISDN Application Environment
(ISE). All right, let me start my essay now.
2.Introdction to ISDN
2.1 Definition:
ISDN ( Abbreviation for
Integrated Services Digital Network ), is is a set of CCITT/ITU standards
for digital transmission over ordinary telephone copper wire as well as
over other media, which has been available for over a decade. This
system allows data to be transmitted simultaneously across the world using
end-to-end digital connectivity. The key idea behind ISDN is that of the
digital bit pipe.With ISDN, voice and data are carried by bearer channels
(B channels) occupying a bandwidth of 64 Kbps (bits per second). Some switches
limit B channels to a capacity of 56 Kbps. A data channel (D channel) handles
signaling at 16 Kbpsor 64 Kbps, depending on the service type. There are
two basic types of ISDN service: Basic Rate Interface (BRI) and Primary
Rate Interface (PRI). BRI consists of two 64 kbps B channels and one 16
kbps D channel for a total of 144 kbps. This basic service is intended
to meet the needs of most individual users. PRI is intended for users
with greater capacity requirements. Typically the channel structure is
23 B channels plus one 64 kbps. D channel for a total of 1536 kbps. In
Europe, PRI consists of 30 B channels plus one 64 kbps D channel for a
total of 1984 kbps. H channels provide a way to aggregate B channels.
To access BRI service,
it is necessary to subscribe to an ISDN phone line. Customer must be within
18000 feet (about 3.4 miles or 5.5 km) of the telephone company central
office for BRI service; beyond that, expensive repeater devices are
required, or ISDN service may not be available at all. Customers will
also need special equipment to communicate with the
phone company switch and with other ISDN devices. These devices include
ISDN Terminal Adapters and ISDN Routers.
2.2 Interfaces
SErvice provider provide BRI
customers with a U interface. The U interface is a two-wire (single pair)
interface from the phone switch. It supports full-duplex data transfer
over a single pair of wires, therefore only a single device called Network
Termination 1 (NT1) can be connected to a U interface, and thereby the
customer is given an S/T interface. The NT1 is a relatively simple device
that converts the 2-wire U interface into the 4-wire S/T interface. The
S/T interface supports multiple devices (up to 7 devices can be placed
on the S/T bus) because, while it is still a full-duplex interface, there
is now a pair of wires for receive data, and another for transmit data.
This has the advantage of making the devices less expensive and easier
to install, but often reduces flexibility by preventing additional devices
from being connected. Technically, ISDN devices must go through an Network
Termination 2 (NT2) device also called PBX (private branch exchange) which
converts the T interface into the S interface (Note: the S and T interfaces
are electrically equivalent). The NT-2 communicates with terminal equipment,
and handles the Layer 2 and 3 ISDN protocols. Devices most commonly expect
either a U interface connection or an S/T interface connection, including
ISDN capable telephones and FAX machines, video teleconferencing equipment,
bridge/routers, and terminal adapters.
2.3 The Hierarchy of
Protocols
a. The Physical Layer:
The
U interface provided by the telco for BRI is a 2-wire, 160 kbps digital
connection. Echo cancellation is used to reduce noise, and data encoding
schemes (2B1Q (2 Binary 1 Quaternary) which is the most common signaling
method on U interfaces. Tin North America, 4B3T in Europe) permit this
relatively high data rate over ordinary single-pair local loops.
Frame Format: Each U interface frame is 240 bits long. At the prescribed
data rate of 160 kbps, each frame is therefore 1.5 msec long. Each frame
consists of: Frame overhead-16 kbps, D channel-16 kbps, 2B channels at
64-128 kbps, The Sync field consists of 9 Quaternaries (2 bits each) in
the pattern +3 +3 -3 -3 -3 +3 -3 +3 -3, (B1 + B2 + D) is 18 bits
of data consisting of 8 bits from the first B channel, 8 bits from the
second B channel, and 2 bits of D channel data. , the Maintenance field
contains CRC information, block error detection flags, and "embedded operator
commands used for loopback testing without disrupting user data.
| Sync |
12 * (B1 + B2 + D) |
Maintenance |
| 18 bits |
216 bits |
6 bits |
b. The Data Link
Layer: ISDN use Link Access Protocol - D channel (LAP-D) as the Layer
2 protocol.
LAP-D frame format
| Flag |
Address |
Control |
Information |
CRC |
Flag |
| (1 octet) This is always 7E16 (0111 11102) |
2 octets |
(2 octets) indicates the frame type |
Layer 3 protocol information and User data |
(2 octets) low-level tests for bit errors on the user data. |
(1 octet) This is always 7E16 (0111 11102) |
c. Network Layer:
Layer 3 is used for the establishment, maintenance, and termination of
logical network connections between two devices.
Service Profile IDs (SPIDs) are used to identify what services and features
the telco switch provides to the attached ISDN device. SPIDs are optional;
when they are used, they are only accessed at call setup time.
Layer 3 Call Setup These are the steps that occurs when an ISDN call is
established. Usually, there are three points where messages are sent and
received; 1) the Caller, 2) the ISDN Switch, and 3) the Receiver.
2.4 Advantages
a. Speed: The modem was a big breakthrough in computer communications.
It allowed computers to communicate by converting their digital information
into an analog signal to travel through the public phone network. There
is an upper limit to the amount of information that an analog telephone
line can hold. ISDN allows multiple digital channels to be operated simultaneously
through the same regular phone wiring used for analog lines. The change
comes about when the telephone company's switches can support digital connections.
Therefore, the same physical wiring can be used, but a digital signal,
instead of an analog signal, is transmitted across the line. This scheme
permits a much higher data transfer rate than analog lines. BRI ISDN, using
a channel aggregation protocol such as BONDING orMultilink-PPP, supports
an uncompressed data transfer speed of 128 kbps. In addition, the latency,
or the amount of time it takes for a communication to begin, on an ISDN
line is typically about half that of an analog line. This improves response
for interactive applications, such as games.
b.
Multiple Devices: Previously, it was necessary to have a phone line
for each device you wished to use simultaneously. Transferring a file to
someone while talking on the phone or seeing their live picture on a video
screen would require several potentially expensive phone lines. It is possible
to combine many different digital data sources and have the information
routed to the proper destination. Since the line is digital, it is easier
to keep the noise and interference out while combining these signals. ISDN
technically refers to specific set of digital services provided through
a single, standard interface. Without ISDN, distinct interfaces are required
instead.
c.
Signaling: Instead of the phone company sending a ring voltage signal
to ring the bell in your phone, it sends a digital packet on a separate
channel. The signal does not disturb established connections, and call
setup time is very fast. For example, a V.34 modem typically takes 30-60
seconds to establish a connection; an ISDN call usually takes less than
2 seconds. The signaling also indicates who is calling, what type of call
it is (data/voice), and what number was dialed. Available ISDN phone equipment
is then capable of making intelligent decisions on how to direct the call.
3.Why develop ISDN
technology in CHINA today
3.1 The current
situation of ISDN in CHINA
Since China
Telecom began to actively develop ISDN and prompt the application os ISDN
technology in 1996, today Beijing, Shanghai and Guangzhou Telecom have
been equipped with the switchs which can support ISDN business, and Shanghai
is the best one. Due to the limitation of existent Telephone Exchange network
and management rules, many developed provinces and center cities haven't
been provided with this kind of ISDN service, but currently all of those
areas are actively construct the upgraded network infrastructure. According
to the plan of China Telecom, in the near future, we will build the network
based on ISDN, which will cover all of center cities and developed areas
in China.
The main
object users of ISDN is SOHO (Small Office, Home Office) users in China.
According to the survey of China Telecom., today, in China, 75 percent
of travel organizations, 83 percent of R&D departments, 86 percent
trading oriented companies, 100 percent finance organizations, government
and large enterprises often need to exchange date information with others
everyday. The research also show the distribution of the potential users
who accept ISDN service as the following table:
| Finance |
Commercial |
R&D Department |
Travels |
Traffic |
Manufacturing |
Others |
| 25.2% |
16.9% |
16.8% |
13.8% |
11.5% |
10.4% |
15.4% |
Moreover, with a
lot of large product material markets, trading centers, stock agents,
subsidiary company of many global companies, various domestic and foreign
multiple shops increasing. All of factors have created a demand a powerful
telecommunication network which can promise to support at least 64Kpbs
data transmission business. Currently, the existent PSTN ( Public Switched
Telecommunications/Telephone Network) can not satisfy this urgent demand.
In the current situation, based on the existent network infrastructure
considering the Performance/Cost, I believed ISDN is the best way to cater
to this need. As a result, there are a huge market space waiting for ISDN,
inversely the application of ISDN technology must prompt greatly the progress
of social digitalization process of China.
3.2 Positioned market of
ISDN
Based o the existent network infrastructure of China Telecom, the main
destination users of ISDN service is the SOHO (Small Office,
Home Office) users. In this case, the ISDN service include Internet Connection,
Video Conference, DDN backup, Interconnections among LANs (Local
Area Network), Two-way Data Transmission and so on. ISDN provide 64Kbps-2Mbps
bandwidth which is thought as the most economical bandwidth based on performance/cost.
ISDN promise to provide the terminal users traditional voice transmission
service, 64-126Kbps Internet connection service, 384Kbit Video Conference,
and 128Kpbs Multimedia business.
3.3 Benefits from developing ISDN technology in China.
a. Best using existent network resources ( including Local Loop resources
)
The current development of ISDN is based on the existent PSTN controlled
by China Telecom, and modification for existent ISDN will help to realize
the digitalization of Local Loop which is helpful to the ATM technology
based BISDN.China Telecom's PSTN is the network which covers widest areas
and have the most terminal users. By motivating ISDN service, China Telecom
can launch new value-added services which make the traditional PSTN
provide multimedia connection except the traditional voice transmission.
On the other hand, from the user's stand point, since ISDN has SB+D connection
ability, the terminal users can save an half of investment to get new services.
b. Matured technology: ISDN technology has
been tested and put into practical use since 1980's, The formal stand was
specified in 1984, ISDN became a matured technology in 1988. Today, the
networking and various terminal products designed for ISDN are very popular,
the price of ISDN products are decreasing gradually. Service provider have
accumulate much successful experience about how to prompt application
and market of ISDN technology. In the current situation, we have a strong
basis on ISDN technology.
c. Convenience for both Internet and voice.
ISDN deal with the
problem created by modems that people can not surf Internet and have a
call at the same time successfully.
d. Support for multimedia telecommunication
ISDN promise user
64Kbps digitalized connection, that means, users can transfer voice data,
pictures and other multimedia data. As a result, various application can
be developed and used at this integrated platform
4. How to use
ISDN technology in different situation.
4.1 Solution to connect LANs
Description:
With business competition increasing, more and more small companies
which have several subsidiary companies or offices allocated in the different
areas demand for interconnection within the whole company with a high speed,
but at a low cost. ISDN is the most suitable solution for this kind of
companies. In this figure,by using ISDN, every subsidiary companies or
offices apply for an 64/128kbps ISDN BRI telephone lines, and install an
ISDN router. On the other side, the headquarter side can use several ISDN
BRI telephone lines or an ISDN PRI telephone line, and setup an ISDN router
or a connecting HUB. Then we can construct a company LAN which cross different
areas. In this system, a subsidiary company or office can access the maim
LAN which allocate in the headquarter at with an 64/128Kbps bandwidth,
what is more, can also interconnect with other subsidiary companies' LAN
with the same speed.
4.2 Solution to small Offices
Description:
Using ISDN to serve for small offices, service providers can cater
to the needs of small offices such as file transmission, G3 and G4 fax,
telephones etc. ISDN telephone lines and the device designed for ISDN can
make all of needs easy to realize at a low cost.
4.3 Solution for SOHO
users to connect Internet
Description:
For private family users they can connect personal computers telephone,
Fax etc. through ISDN terminal network adapter. As a result, users can
use personal computers to access Internet at a 64Kbps/128Kbps, and have
a call at the same time. From small company users point of view, they can
integrate LAN, telephone, Fax etc. by ISDN routers, and connect all of
those to the Internet by one or more ISDN lines.
4.4 Solution to DDN backup:
Description:
DDN leased line is very popular among the company users in China. Since
it is a kind of leased line, the cost is far higher than ISDN, in the usual
case, we can use DDN with high efficiency, but if we want to ensure safety
and apply for a backup DDN, it is unworthy. ISDN makes a good answer for
this problem.Using ISDN replacing DDN as backup can prevent the accidence
at a low cost.
4.5 Solution For Video Conference
Description:
In the company intranet, Using multicast video server as a center and
LAN video conference terminal, can provide personal visual work platform
in the Intranet, consequently, can make personnel of company more direct
exchange information. In order to enhance communication among video conference
terminal on the WAN, we can use Gateway equipment which provide transparent
transfer between H.323 and H.320, this Gateway also is applied to connect
multicast video servers of showing room, as aresult, integrate showing
room with intranet of the company as a whole. In the whole solution for
video conference, since the transmission is based on ISDN technology, terminal
application is convenient. We can not only connect to showing system by
dial_up, but also can connect to the other video conference system at any
corner of the world.
4.6 Solution to Desk Video Conference
Description:
By using 128Kbps-512Kbps bandwidth promised by ISDN technology, we
can safely realize Desk Video COnference, at the same time, also provide
private users services such as sharing files, data and applications.
4.7 Solution to tele-course
5. Reference
Details in Homework1
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