CDPD(Cellular digital packet data)

CDPD(Cellular digital packet data)，namely Cellular digital packet data exchange network click here to add pictures shows that people call the real wireless Internet. CDPD nets in digital packet data technology as the foundation, the cellular mobile telecommunication network mode for the mobile wireless data communications network. Used in portable machine CDPD simply connect a special wireless modem, even sit in carriage of 100 kilometers per hour, are not affecting online.

The principle

A special CDPD wireless data networks, signal not easily affected by interference, can any website. Compared with other wireless Internet way, CDPD nets could reach 19.2 1000 bits/SEC, whereas normal GSM mobile network for 9.6 1000 bits/SEC. In data communications security, CDPD in authorized user login with a variety of functions, such as setting allows user login user login frequency range, statistics, To a safe area, a safe user defined, further improve the particular user's special safety; Using 40 key encryption algorithm, and channel each are not identical, automatic check old key replace new keys, data even being stolen, also cannot explain dust-laden. CDPD use still has many characteristics: convenient installation, users need not apply for telephone lines or other route, Communication through quick response to, such as in the business card, and using MODEM connected time 20 to 45 seconds, and CDPD as long as 1 second; Terminal system points mobile, fixed two kinds, can realize local and remote roaming.

introduction

Along with the development of computer and communication technology, wireless data communication in modern society people flow sadly arisen. Modern laptop and personal digital assistant (PDA) machine appear more wireless mobile data of communication provides favorable conditions, so flexible, convenient and efficient wireless data communication in recent years in international obtained a rapid development and application, become the new focus of wireless communication. Among the cellular digital packet data networks (CDPD) is recognized as the best current wireless data formats. It is based on the existing cellular telephone network with digital packet technology as the basis, the cellular mobile telecommunication network mode for the mobile wireless data communication technology. CDPD began in the United States, 1992 start study, 1995 year launched the first commercial CDPD network, to date in the United States has already realized basically the nationwide coverage. Our country 1995 started feasibility study, 1996, Shanghai, has built trial network, the original decision by the end of 1997 and telecommunications construction "China public wireless data communication net". Adopt CDPD technology. This paper will introduce in detail the network structure, agreement CDPD model and frame structure.

CDPD network structure

By following CDPD four components: mobile terminal system (MES), mobile data base station (MDBS), mobile data exchange system (MDIS) and mobile terminal system (MES) : it consists of mobile terminal and CDPD wireless Modem composition, wireless Modem CDPD radio link is responsible for the management and agreement, usually, mobile terminal and wireless Modem communication between the standard serial interface protocols, such as: serial Internet protocol (SLIP or peer-to-peer protocol (PPP), Modem interface has RS? 232, PCMCIA and built-in PCI slots type.

Mobile data base station (MDBS) : most per base can be installed six letters DaoBan, each letter for mobile terminals provide a DaoBan 19.2 KBPS air access, make mobile terminal for full-duplex packet data transmission, at the same time it is also responsible for monitoring and frequency spectrum management. It through a root 64kbps frame relay and switches connected.

Mobile data exchange system (MDIS) : it consists of grouping server and management server component. Responsible for packet switched data packet server. Management server is responsible for user accounts, billing and mobility management, mobility management using Internet standards organization IETF (InternetEngineeringTaskForce) made mobile IP mode.

CDPD backbone: it consists of general intermediate system (IS) composition, it IS actually IP router. IS providing connectionless data submitted to business, according to the destination address of each group and the current network topology for grouping routed. CDPD is based on TCP/IP open systems, convenient access Internet also support the OSI standard difficult agreement CLNP (connectionless networks protocol).

CDPD agreement model

MES and MDIS CDPD layered agreement between the model as figure2shows. Um interface is CDPD air interface. Um interface communication protocol has five layers of bottom-up order physical layer, media access control (MAC) layer, logical link control (LLC) layer, SNDCP (subnet rely on combination protocol) layer and network layer.

Um interface of the physical layer for rf interface part, and physical link is responsible for providing air interface rf channel. MES and MDBS between 30kHz by a pair of RF channels for communication, from MDBS to MES channel called positive channel, from MES to MDBS channel called reverse channel, a positive and reverse channel forms a CDPD channel flow. Channel flow use modulation method for GMSK (relative bandwidth BT = 0.5), modulation rate for 19.2 KB/s. The physical with wireless resource management entities (RRME) phase interface, through the interface, RRME to RF channel to power level, transmission and physical link the hige control, and to detect the RF signal level and estimation channel of communication skills. It

Media access control layer

MAC for media access control layer. MAC layer's main function is to define and distribution of air interface CDPD logical channel, make these channels can be different mobile platform sharing. The logical channel points CDPD radio channel and peer-to-peer business channel, radio channel were divided into control and manage two kinds, control channel for radio control information, management channel used to broadcast wireless resource management information (e.g. channel flow recognition parameters, the village configuration parameters, channel access parameters and channel quality evaluation parameters). Peer-to-peer business channel for single MES and service MDIS between information transmission. Each logical channel has assigned to a called temporary equipment identification number (TEI) channel number, TEI = 1 for radio control channel, TEI = 0 for radio management channel, TEI = 16 to 227? 1 assigned to point-to-point business channel which in point-to-point data link connection establishes before giving the connecting corresponding distribution of MES, this MES with distribution of sending and receiving TEI value with the specified TEI value frame. MAC layer through a dependent on execution interface and RRME communication, through this interface MAC layer notice, whether it RRME with current selected positive channel synchronized, and give RRME convey information about received bits and pieces of error count state information, therefore, RRME can be assessed a given CDPD channel receiving powers, and provide wireless resource management functions.

The logical link control layer

LLC layer for logical link control layer. It is a kind of based on ITU? T Suggestions and Q Q.. 920 j 921 wireless link protocol, called mobile data link protocol (MDLP), in the MDLP and realization of MES located within its service MDLP communication. The equivalence MDIS LLC layer is responsible for in high-rise SNDCP (subnet rely on combining agreement) layer of SNDC data unit is formed on LLC address, frame field to create complete LLC frame. Another LLC can realize point-to-multipoint addressing and data re-issue control.

The MDBS LLR layer is logical link forwarded layer. This layer is responsible for forwarding MES and MDIS between LLC frame. LLR layer MDLP data unit for it is completely transparent, i.e. not responsible for handling MDIP data.

SNDCP layer for subnet rely on combining layer. Its function is to finish transmits data packet, pack, data compression, determine the TCP/IP address and encryption method, providing SNDCP top-level multiple network layer entities of the complex answered. MES and MDIS between data transmitted is divided into one or more NPDU (network protocol data unit) packet unit. NPDU packet unit generation after being placed in LLC frame.

namely Cellular digital packet data exchange network click here to add pictures shows that people call the real wireless Internet. CDPD nets in digital packet data technology as the foundation, the cellular mobile telecommunication network mode for the mobile wireless data communications network. Used in portable machine CDPD simply connect a special wireless modem, even sit in carriage of 100 kilometers per hour, are not affecting online.The principleA special CDPD wireless data networks, signal not easily affected by interference, can any website. Compared with other wireless Internet way, CDPD nets could reach 19.2 1000 bits/SEC, whereas normal GSM mobile network for 9.6 1000 bits/SEC. In data communications security, CDPD in authorized user login with a variety of functions, such as setting allows user login user login frequency range, statistics, To a safe area, a safe user defined, further improve the particular user's special safety; Using 40 key encryption algorithm, and channel each are not identical, automatic check old key replace new keys, data even being stolen, also cannot explain dust-laden. CDPD use still has many characteristics: convenient installation, users need not apply for telephone lines or other route, Communication through quick response to, such as in the business card, and using MODEM connected time 20 to 45 seconds, and CDPD as long as 1 second; Terminal system points mobile, fixed two kinds, can realize local and remote roaming.introductionAlong with the development of computer and communication technology, wireless data communication in modern society people flow sadly arisen. Modern laptop and personal digital assistant (PDA) machine appear more wireless mobile data of communication provides favorable conditions, so flexible, convenient and efficient wireless data communication in recent years in international obtained a rapid development and application, become the new focus of wireless communication. Among the cellular digital packet data networks (CDPD) is recognized as the best current wireless data formats. It is based on the existing cellular telephone network with digital packet technology as the basis, the cellular mobile telecommunication network mode for the mobile wireless data communication technology. CDPD began in the United States, 1992 start study, 1995 year launched the first commercial CDPD network, to date in the United States has already realized basically the nationwide coverage. Our country 1995 started feasibility study, 1996, Shanghai, has built trial network, the original decision by the end of 1997 and telecommunications construction "China public wireless data communication net". Adopt CDPD technology. This paper will introduce in detail the network structure, agreement CDPD model and frame structure.CDPD network structureBy following CDPD four components: mobile terminal system (MES), mobile data base station (MDBS), mobile data exchange system (MDIS) and mobile terminal system (MES) : it consists of mobile terminal and CDPD wireless Modem composition, wireless Modem CDPD radio link is responsible for the management and agreement, usually, mobile terminal and wireless Modem communication between the standard serial interface protocols, such as: serial Internet protocol (SLIP or peer-to-peer protocol (PPP), Modem interface has RS? 232, PCMCIA and built-in PCI slots type.Mobile data base station (MDBS) : most per base can be installed six letters DaoBan, each letter for mobile terminals provide a DaoBan 19.2 KBPS air access, make mobile terminal for full-duplex packet data transmission, at the same time it is also responsible for monitoring and frequency spectrum management. It through a root 64kbps frame relay and switches connected.Mobile data exchange system (MDIS) : it consists of grouping server and management server component. Responsible for packet switched data packet server. Management server is responsible for user accounts, billing and mobility management, mobility management using Internet standards organization IETF (InternetEngineeringTaskForce) made mobile IP mode.CDPD backbone: it consists of general intermediate system (IS) composition, it IS actually IP router. IS providing connectionless data submitted to business, according to the destination address of each group and the current network topology for grouping routed. CDPD is based on TCP/IP open systems, convenient access Internet also support the OSI standard difficult agreement CLNP (connectionless networks protocol).CDPD agreement modelMES and MDIS CDPD layered agreement between the model as figure2shows. Um interface is CDPD air interface. Um interface communication protocol has five layers of bottom-up order physical layer, media access control (MAC) layer, logical link control (LLC) layer, SNDCP (subnet rely on combination protocol) layer and network layer.Um interface of the physical layer for rf interface part, and physical link is responsible for providing air interface rf channel. MES and MDBS between 30kHz by a pair of RF channels for communication, from MDBS to MES channel called positive channel, from MES to MDBS channel called reverse channel, a positive and reverse channel forms a CDPD channel flow. Channel flow use modulation method for GMSK (relative bandwidth BT = 0.5), modulation rate for 19.2 KB/s. The physical with wireless resource management entities (RRME) phase interface, through the interface, RRME to RF channel to power level, transmission and physical link the hige control, and to detect the RF signal level and estimation channel of communication skills. ItMedia access control layerMAC for media access control layer. MAC layer's main function is to define and distribution of air interface CDPD logical channel, make these channels can be different mobile platform sharing. The logical channel points CDPD radio channel and peer-to-peer business channel, radio channel were divided into control and manage two kinds, control channel for radio control information, management channel used to broadcast wireless resource management information (e.g. channel flow recognition parameters, the village configuration parameters, channel access parameters and channel quality evaluation parameters). Peer-to-peer business channel for single MES and service MDIS between information transmission. Each logical channel has assigned to a called temporary equipment identification number (TEI) channel number, TEI = 1 for radio control channel, TEI = 0 for radio management channel, TEI = 16 to 227? 1 assigned to point-to-point business channel which in point-to-point data link connection establishes before giving the connecting corresponding distribution of MES, this MES with distribution of sending and receiving TEI value with the specified TEI value frame. MAC layer through a dependent on execution interface and RRME communication, through this interface MAC layer notice, whether it RRME with current selected positive channel synchronized, and give RRME convey information about received bits and pieces of error count state information, therefore, RRME can be assessed a given CDPD channel receiving powers, and provide wireless resource management functions.The logical link control layerLLC layer for logical link control layer. It is a kind of based on ITU? T Suggestions and Q Q.. 920 j 921 wireless link protocol, called mobile data link protocol (MDLP), in the MDLP and realization of MES located within its service MDLP communication. The equivalence MDIS LLC layer is responsible for in high-rise SNDCP (subnet rely on combining agreement) layer of SNDC data unit is formed on LLC address, frame field to create complete LLC frame. Another LLC can realize point-to-multipoint addressing and data re-issue control.The MDBS LLR layer is logical link forwarded layer. This layer is responsible for forwarding MES and MDIS between LLC frame. LLR layer MDLP data unit for it is completely transparent, i.e. not responsible for handling MDIP data.SNDCP layer for subnet rely on combining layer. Its function is to finish transmits data packet, pack, data compression, determine the TCP/IP address and encryption method, provid
ing SNDCP top-level multiple network layer entities of the complex answered. MES and MDIS between data transmitted is divided into one or more NPDU (network protocol data unit) packet unit. NPDU packet unit generation after being placed in LLC frame.