Defense data network
DDN (Digital Data Network), with digital cross connection as the core technology, integrates data communication technology, data and communication technology.
Word communication technology, optical fiber communication technology and other technologies, a data access service network that uses digital channels to transmit data.
It mainly only completes the functions of the physical layer and some data link layer protocols in the OSI seven-layer protocol. Client devices (mainly
Gateway router) generally uses local telephone twisted pair to realize network access through baseband modem or DTU. The main advantages of DDN
As follows:
High transmission quality, short delay and high speed.
It can provide users with digital channels with error rate less than 10-6. At the same time, because there is no need for protocol encapsulation of data transmission.
There is no need for packet-switched storage and forwarding, so the network delay is very short-end-to-end data transmission delay generally does not.
More than 40 ms It also provides a wide access rate range, generally 9.6 Kbps~2.048Mbps.
The digital circuit provided is completely transparent and semi-permanently connected.
An important technical advantage of DDN is the transparency of network transmission. The so-called transparent transmission refers to the data ratio after passing through the transmission channel
Telstream's protocol has not changed. In this way, any communication protocol recognized by both sides can be transmitted on DDN network.
Various communication services. Semi-permanent connection means that once the network management generates the circuit, the connection between the two ends of the user is fixed.
No change, until the user puts forward the business change, the network management will change the relevant data.
The security of the network is very high
Because the transmission relay of DDN adopts optical fiber, which is a point-to-point communication mode, the communication security is very good. Additional security
Good integrity also means that there are usually multiple communication routes between nodes in the network. When the current route fails, the network node
This point will automatically switch to the next optional route to ensure normal communication.
It is very convenient to establish a VPN (Virtual Private Network) for users.
This is very suitable for large users such as government, finance and group users to set up a "private network" between local and remote places. user
Based on public DDN, VPN can realize all business functions of private network with relatively small investment, including
Enjoy the same security, priority, reliability and manageability.
The network covers a large area.
Up to now, most places above the county level and some towns in developed areas have opened DDN services. It can be extensive.
Used for large-scale networking across provinces and cities.
Because DDN can provide high-quality digital circuits with the above characteristics, it is often used as other telecommunication service networks, such as 163 networks.
Transmission relay and access circuit of 169 network, frame relay, packet switching network and user private network. For data traffic
Large, long communication time, high real-time communication requirements, cross-city or inter-provincial networking.
Unit users are very suitable for using DDN to carry out various data services. Therefore, DDN has a huge user base.
Users also enjoy a good reputation. For example, the number of DDN users in Beijing has reached nearly 5,000 after several years of development.
Its shortcomings are mainly:
For some users, the cost is relatively high.
Although DDN has the above advantages, for users with short communication time or users who do not make full use of DDN's business characteristics.
Users, the cost is relatively high, such as the local network business area 128Kbps circuit monthly rental fee of 2540 yuan. This point was put forward by d.
Because of the characteristics of DN-the digital circuit it provides is semi-permanent, that is, whether the user is transmitting data or not,
This digital connection has always existed.
Network flexibility is not high enough.
Because of the characteristics of DDN itself-providing semi-permanent connection circuit in digital cross connection mode and not providing switching function, it
It is only suitable for establishing point-to-point and multipoint communication links for users. For some group users, subordinate departments and companies are the same.
Headquarters connection, can use multi-point-to-point DDN private network; However, if subordinate departments also need to communicate frequently,
What shall we do? If point-to-point connection is adopted again to form a mesh network among various departments under the company, obviously, it is necessary to use it.
The family cost is too high.
father
Frame Relay is a data service based on packet-switched network and combined with digital private line technology.
Network. To some extent, it can be considered as a "fast packet-switched network". It is a project in current data communication.
Important commercial network technology. The user's LAN is generally connected to the frame relay network through the gateway router; If the router does not have a label
The quasi-Frame Relay UNI interface stipulates that Frame Relay Disassembly/Assembly Equipment (FRAD) needs to be added between the router and the Frame Relay network.
. Its main advantages are as follows:
Compared with the packet-switched network, it simplifies the related protocols and improves the transmission speed.
It only completes the functions of physical layer and data link layer in OSI seven-layer protocol, leaving the functions of flow control and error correction to wisdom.
It can be done at the terminal. Therefore, its data link layer protocol (LAPD protocol) is relatively simplified on the basis of reliability, thus reducing
Transmission delay improves the transmission speed (the speed range is generally 9.6 Kbps~2.048Mbps). Besides, it passed.
The LAPD link layer protocol used can successfully carry common protocols such as IP, IPX and SNA.
It uses PVC technology.
Frame relay network can provide two basic services, namely PVC (Permanent Virtual Circuit) and SVC(Sw
Itched virtual circuit), but the current frame relay network only provides PVC services. The so-called PVC refers to network management
After the meaning is completed, the circuits of both parties are permanently connected to the user, but actually only when the user is ready to send the number.
According to time, the network really allocates transmission bandwidth to users.
Statistical multiplexing technology is adopted.
It enables each line and network port of Frame Relay to be shared by multiple end users according to the information flow (i.e. PVC).
That is, multiple logical connections can be provided on a single physical connection. Obviously, it greatly improves the utilization rate of network resources.
User fees are relatively economical.
Because the information flow of the network is based on data packets, PVC technology and statistical multiplexing technology are adopted, and its circuit rental cost is low.
Its speed is generally only 40% of that of DDN circuit with the same speed. When the network is idle, it also makes users suddenly surpass themselves.
The applied PVC rate (CIR) occupies dynamic bandwidth. It is very economical for users who often transmit a lot of burst data.
High cost performance.
Promote the transition to a unified ATM platform.
China Telecom built a national frame relay backbone network based on ATM platform at 1997. Frame Relay was built in Beijing in the same year.
The network is also based on ATM platform, the core layer adopts Cisco BPX series ATM switches, and the access layer is IGX series framework.
Relay switch. Frame Relay provides users with communication services by using the high-speed transparent transmission channel provided by ATM. This structure is convenient.
Frame Relay is integrated into a unified ATM network.
However, it does not have enough flow control function. When the data flow of each PVC in the same network port is large at the same time, it can be
Will lead to congestion. The lack of technical support for SVC also makes it lose some advantages in application and affects the progress of business.
One step promotion. Using PVC and statistical multiplexing technology can improve the utilization rate of the network, but at the same time, once the physical lines or things
If the management port fails, multiple PVC will be affected at the same time. In addition, its network scale is generally larger than DDN in China.
Small.
It is not difficult to see that Frame Relay is suitable for data transmission with strong suddenness, high speed, short delay and good economy.
Transportation services, such as network interconnection between companies, multimedia services, such as open telemedicine, e-commerce and VPN group.
Net, etc.
integrated services digital network (ISDN)
Isdn (integrated services digital network) refers to the integrated services digital network. It uses a public telephone.
Network provides users with end-to-end digital channel connection, which is used to carry various telecom industries, including voice and non-voice
Service. Now the generally open ISDN service is N-ISDN, that is, narrowband ISDN, so we only analyze N-ISDN (below).
ISDN means n-isdn).
ISDN service is commonly known as "one-line access", and there are two rate access methods: BRI (basic rate interface), that is, 2.
b+ D； PRI (main rate interface), that is, 30 b+d. BRI interface includes two B letters that can work independently.
Channel (64Kbps) and channel D (16Kbps), in which channel B is generally used to transmit voice, data and images, and channel D.
Channels are used to transmit signaling or packet information (not yet open to business). Both B and D of PRI interface are 64Kbps digital channels.
. User equipment in 2B+D mode is networked through NT 1 or NTI Plus equipment; Connect the user equipment in 30 b+d mode.
Network access is achieved through HDSL equipment (using local twisted pair) or optical modem and optical transceiver (using optical fiber).
Compared with DDN and Frame Relay, its main advantages are as follows:
1. This service is easy to implement and provides various services.
ISDN is based on the existing public telephone network. Anywhere covered by ordinary telephone, as long as the telephone exchange has ISDN function.
Module, which can provide ISDN services for users. For DDN and Frame Relay, you need your own system node machine. ISDN industry
There are many kinds of services, including basic services such as ordinary telephone, networking and videophone, as well as many supplements such as calling number display.
Business.
2. Users are very flexible and convenient to use.
For B2B+D, users can use two mobile phones at the same time, and they can connect to the Internet at 64Kbps, and the other 64Kbps is for general use.
On the phone; You can also network at the rate of 128Kbps as needed. And 30 b+d allows users to flexibly network at high speed.
The price is right.
Because ISDN charges according to the used B channel, and the domestic communication rate of 1B channel is equivalent to the ordinary telephone communication fee.
Rate (according to the most widely used circuit switching mode), it is not difficult to find that for less traffic and shorter communication time,
Users, the cost of choosing ISDN is much lower than the cost of renting DDN private line or frame relay circuit.
For telecom operators, it is also possible to digitally transform the existing analog user external lines with a small investment.
Due to the above advantages of ISDN, China Telecom launched the "ISDN Hurricane Action" nationwide this year. At present,
Telecom departments all over the country are busy promoting this new service to the market. Up to now, hair
The effect of the exhibition is good, far exceeding the original expectation. In addition, China has now completed long-distance ISDN networking in 25 provinces.
, and has achieved ISDN network interconnection with more than a dozen countries and regions, laying the foundation for the further development of ISDN services.
Foundation.
From the analysis of its own characteristics, ISDN is suitable for individual home users or SOHO users to access the Internet, small and medium-sized enterprises and institutions.
LAN networking, chain store sales networking, opening public network videophone, conference TV or being and other value-added services.
Small enterprises and institutions use it as a backup mode for special circuits such as DDN and frame relay.
ISDN is based on the existing telephone switching network, while the traditional telephone network is mainly designed for voice services, that is, according to the general
The average length of a phone call is 3 ~ 5 minutes, and it is designed to be 9 minutes when busy; However, it obviously takes a long time to use ISDN for data communication.
Longer, if you use it to surf the Internet, the average time can reach 30-50 minutes. Therefore, while vigorously developing ISDN services, we must
When considering the transformation of the existing telephone network system, such as realizing voice data service diversion at the local end of ISDN access network.
Wait a minute.