How to access the WAN

How to access the WAN

Its deficiencies are mainly as follows:

For some users, the cost is relatively high.

Although DDN has the above advantages, but for short communications users, or not fully utilize the DDN business characteristics of users, relatively high costs, such as the local network operating area 128Kbps circuit monthly rental fee of 2540 yuan. This is caused by the characteristics of the DDN-the digital circuitry it provides is a semi-permanent connection, that is, whether the user is transmitting data or not, the digital connection persists.

Network flexibility is not high enough.

Because of the characteristic of DDN itself-to provide a semi permanent connection circuit in digital cross connection, it does not provide switching function, it is only suitable for the user to establish point-to-point and multiple point-to-point communication links. For some groups of users, subordinate departments with the company headquarters, you can use a point-to-point approach to the DDN line network; But what if the subordinate departments also need to communicate with each other frequently? If you take a point-to-point connection, the company's various departments to form a mesh network, it is clear that the cost of users is too high.

Frame Relay

Frame Relay (Relay) is a data service network which is based on packet switching network and combined with digital special-line technology. To some extent it can be considered as a "fast packet switching network". It is an important business network technology in the current data communication. The user's LAN generally accesses the frame relay network through the gateway router, if the router does not have the standard Frame Relay Uni interface procedure, then will need to increase the frame relay dismantling/loading equipment (FRAD) between the router and the Frame relay network. Its main advantages are:

Compared with packet switched networks, it simplifies the related protocols and improves the transmission speed.

It only completes the function of the physical layer and the data link layer in the OSI Seven layer protocol, and leaves the function of flow control and error correction to the intelligent terminal. Therefore, the Data Link layer Protocol (LAPD protocol) is relatively simplified on a reliable basis, thus reducing the transmission delay and increasing the transmission speed (the rate range is generally also 9.6 kbps~2.048mbps). In addition, it adopts the LAPD Link layer protocol, which can carry out common protocols such as IP, IPX and SNA smoothly.

It uses the PVC technology.

There are two basic services available in the Frame relay network, namely, PVC (permanent virtual circuit) and SVC (Switched virtual circuit), but the current frame relay network only provides PVC business. The so-called PVC refers to the completion of the network management definition, the communication between the two sides of the circuit in the user appears to be a permanent connection, but in fact only when the user is ready to send data, the network will really transfer bandwidth allocated to the user.

Statistical multiplexing techniques are used.

It enables each line of frame relay and network port to be shared by multiple end users on the basis of information flow (i.e., PVC), which provides multiple logical connections on a single physical connection. Obviously, it has greatly improved the utilization of network resources.

User costs are relative to the economy.

Because the information flow of network is based on data packet, PVC technology and statistic multiplexing technology are used, and the cost of the circuit renting is low. The rate is generally only 40% of the same rate DDN circuit. And when the network is idle, it also allows the user to burst over the dynamic bandwidth of the PVC rate (CIR) that they are applying for. For users who often deliver large bursts of data, it is very cost-effective.

Facilitates transition to a unified ATM platform.

China Telecom built a national frame Relay backbone network based on ATM platform in 1997. The Frame Relay network built in Beijing was also based on ATM platform, and the core layer adopted Cisco's BPX series ATM switch, and the access Layer was IGX Series Frame Relay switch. Frame Relay provides communication services to users using high-speed transparent transmission channels provided by ATM. This structure facilitates the integration of frame relay into a unified ATM network.

But it itself does not have enough flow control function, when the same network port of the PVC at the same time data flow is very large, may cause congestion. Technical lack of support for SVC also makes it lose some of the advantages of the application, affecting the further promotion of the business. The use of PVC and statistical multiplexing technology can improve the utilization of the network, but at the same time, once the physical line or physical port failure, there will be more than one PVC is affected. In addition, its network scale is generally smaller than DDN in our country.

It is not difficult to see, Frame Relay is suitable for sudden strong, high speed, short time delay and better economic data transmission business, such as network interconnection between companies, open telemedicine and other multimedia services, E-commerce and VPN networking.

Isdn

ISDN (integrated service Digital Network), Integrated Services Digital network. It uses the public telephone network to provide end-to-end digital channel connectivity to the user to host a variety of telecommunications services, including voice and non voice. Now the generally open ISDN business is N-ISDN, or narrowband ISDN, so we only analyze n-isdn (ISDN below refers to N-ISDN).

ISDN business is commonly known as "first-line", it has two types of speed access: BRI (Basic Rate Interface), that is, 2b+d; PRI (Primary Rate Interface), i.e. 30b+d. The BRI interface consists of two independently working B channels (64Kbps) and a D channel (16Kbps), where B channels are typically used to transmit voice, data, and images, and D channels are used to transmit signaling or packet information (which is not yet open to business). Both B and D of the PRI interface are 64Kbps digital channels. 2b+d user devices are networked through NT1 or NTI plus devices, and the user devices in the 30b+d mode are connected through HDSL equipment (using the local twisted pair) or optical modem and optical transceiver (optical fiber).

Compared with DDN and Frame relay, its main advantages are as follows:

1. Business implementation convenience, the provision of a wide range of business.

ISDN is based on the existing public telephone network, where ordinary telephone coverage is provided, as long as the telephone exchange has an ISDN function module to provide users with ISDN business. For DDN and Frame relay, you need your own system node machine. ISDN business of a wide range, including ordinary telephone, networking, videophone and other basic business and the main call number display, and many other supplementary services.

2. Users are very flexible and convenient to use.

For 2b+d, the user can be used as two telephones at the same time, can 64Kbps network, another 64Kbps for ordinary telephone, but also according to the needs of the 128Kbps rate network. And 30b+d can make users flexible, high-speed networking.

Appropriate price/performance.

Since ISDN is billed as a B-channel for use, and the domestic communication rate for the 1B channel is equivalent to the ordinary telephone rate (by the most widely used circuit-switching mode), it is not difficult to find that for users with less traffic and shorter communication time, The cost of using ISDN is much lower than the cost of renting DDN or Frame relay circuits.

For telecom operators, it is also possible to make small investments in the digital transformation of the existing analog user perimeter.

Due to the above advantages of ISDN, China Telecom launched a nationwide "hurricane operation of ISDN" this year. At present, the telecommunications sector across the country are in full swing to the market to promote this morning should be launched new business. So far, the development effect is good, far beyond the original expectations. In addition, our country has now completed long-distance ISDN networking in 25 provinces and ISDN network interconnection with more than 10 countries and regions, which lays the groundwork for further development of the ISDN business.

From its own characteristics analysis, ISDN is suitable for personal home users or Soho users access to the Internet, small and medium-sized enterprises LAN networking, chain store sales network and open the public network of Videophone, conference TV and other value-added services, or by the small and medium-sized enterprises for DDN, Frame Relay and other special-line circuit standby way.

Because ISDN is based on an existing telephone exchange network, the traditional telephone network is mainly designed for voice service, that is, the average length of 3-5 minutes by ordinary telephone calls, busy 9 minutes of design, but the use of ISDN for data communication is obviously longer, such as the average time spent on the internet can reach 30-50 minutes. Therefore, in the development of ISDN business, we must consider the existing telephone network system transformation, such as in the ISDN access network at the Office of the implementation of voice data traffic streaming.