Chapter 1 ISDN's business
First, ISDN's business capabilities and classification
Second, carrying business
Third, user terminal business
Fourth, supplement business
First, ISDN's business capabilities and classification
ISDN has a lot of business, and its business capabilities are developing. The ISDN's business follows the following principles when the classification:
(1) ISDN should be able to continue to provide existing networks, including all services required by the public exchange telephone network, packet data network, user telegraph, etc .;
(2) ISDN's business should take into account interoperability and compatibility of ISDN and existing networks;
(3) ISDN's business needs to fully estimate the new business needs of users, including new communication needs that may occur in the near future.
The ISDN telecom service can be divided into a bearer service and user terminal services that contain terminal functions (TELESERVICES). In addition to these two basic business, supplementary services (Supplementary Services) is changed or supplemented by the basic business. With these supplementary services, you can bring great convenience to users' communications.
The bearer service provides means to deliver information in real time between users, without changing the content included in the information itself, such a service corresponding to the low-level function of the open system interconnect (OSI) reference model. The user terminal service combines the transfer function and the information processing function, not only providing the low 2 function of OSI, but also provides high-level functions (HLF). If the carrier service defines the requirements for the network function, and by the network function, the user terminal service includes both terminal capabilities and network capabilities. Both the carrier business and user terminal services can be provided with the supplemental service to provide users with the user, but the supplementary service can be combined with one or more bearer services or user terminal services, and cannot be used separately.
In order to access different terminal devices, such as digital phones, fax, data, microcomputer, PABX, etc. to provide a variety of telecommunications services. CCITT specifies the ISDN user-network interface and service access point to enable a variety of telecom services to access the ISDN network. ISDN User-Network Interface and Service Access Point Configuration are shown below.
In the figure, TE1 is an ISDN standard terminal with 1 to 7 layers of user terminal services, and an access point is 3. TE2 is an ISDN non-standard terminal with different interfaces and access points. TA is a terminal adapter with adaptation functions that enable ISDN non-standard terminals to access ISDN users - network interface (access point 4). It is the X series, the V series communication terminal passes TA, using ISDN to carry the access point. R, S and T are reference points.
The business access point refers to the location of the user accepts the service. For example, the service access point of the analog telephone network is located between the phone and the user line, that is, the junction box. In ISDN, in order to provide different services with a wide variety of terminals, there are a variety of business access points, and the services corresponding to each business access point are clarified. As mentioned above, in addition to 4 points, 1 to 5 points are ISDN's business access point, where 1 and 2 correspond to the carrier service, 3 and 5 correspond to the user terminal service.
Second, carrying business
1, the concept of carrying business
ISDN is referred to as a bearer service in the business access point 1 (reference point T) and access point 2 (reference point s). In the carrier service, the network provides only a low-level information transfer capability, so that the bearer service can be understood to be seen from the S or T reference point to the network direction, the information transfer capability of the ISDN network. The carrier service only illustrates the communication capability of the communication network, and is independent of the type of the terminal. Therefore, various types of different terminals can use the same bearer service. The bearer service adopts the recommendations of the first to third layers of the seven-layer models related to S or T reference points. 2, hosting the property of the business
You can divide all independent properties of the carrier business into three categories, namely
(1) Information delivery attributes. Indicates an attribute of a network information transfer capability between a S or T reference point to another (or more) S or T reference points, such as information transfer mode, and information transmission rate, and the like.
(2) Service access properties indicate the path rate and protocol attributes on the S or T reference point. It involves the specifications of the S or T reference point at 1 to 3 layers. (3) General attributes, indicating an attribute of the feature of supplementary services and service quality. The following table lists the specific business properties in various properties and their definitions.
The following table lists the specific business properties in various properties and their definitions.
Category Service Attribute and Its Definition Attribute Definition Information Transfer Properties 1, the information transfer method is shown in the exchange mode 2 required to transmit user information, and the information transfer rate is represented as the transfer rate or throughput 3 required to transmit user information. 3, information transfer capability The species 4 of the user information can be transmitted, and the structure represents the structure 5 of the bitstream of the user information, and the establishment of communication is immediately, and the reservation such as communication establishment form 6, the symmetry represents the directionality of user information and the symmetry 7, and the communication configuration representation Point-to-point, point to multi-point communication connection form Access attribute 8, access path and its rate indicate the user information transfer rate and transmission path type 9 on the network interface, the access protocol is indicated in the ISDN user - network Protocol of user information and signaling information on the interface 10, supplementary business details to continue research 11, business quality 12, interoperability 13, business and commercial properties
Information transfer mode: Circuit exchange, packet swap or frame mode can be used.
Information transfer rate: The communication rate of the end to the end. At present, the speed of the user terminal may have standardized 64kbit / s, a plurality of 64kbit / s rates or rates below 64kbit / s.
Information transfer capability: means that the end to the end is transmitted. For example, "Unrestricted Digital Information" means that the bitstream sent by the sender does not change to the trustee, also known as a bit transparent. "Voice" means only used for voice communication.
Structure: Indicates the classification criteria associated with the data structure transmitted or received on the user-network interface. The 8kHz structure is suitable for circuit exchange, which indicates that the data is sent or received in each 125μs timing.
The establishment of communication: indicates the time relationship from the acceptance user request to establish communication. Some users communicate instant connection, subscription connection, and special line connections as needed.
Symmetry: Refers to the attributes related to the sender to establish an exhalation between the encoder. The exact product of the attribute in the outgoing and incoming direction is referred to as "bidirectional symmetry", even if there is a different attribute, it is also calculated as "bidirectional non-true". Only one-way traffic can be established as "one-way business".
Communication configuration: indicates that the location of communication is point-to-point, point to multi-point or multi-point or more points.
Access path and its rate: indicate the properties of the path type on the user-network interface.
Access protocol: Indicates the properties of the protocol type used to implement the service in the user-network interface. I.441 and I.451 in the access protocol, specify the user-network interface second and third layers of the network interface, respectively. X.25 specifies the protocol used in the packet mode.
3. Bearing the classification of business
The carrier business is divided into three categories. The first category is a carrier business of circuit exchange; the second class is a bearer service in group exchange; the third category is a frame manner carrying service.
The carrying business of the first type of circuit switching method has the following:
(1) 3KHz structure, unrestricted 64kbit / s carrying business
Unrestricted 64kbit / s bearer business is the most basic bearer business of ISDN. It provides transparent information transfer capabilities between the S or T reference points on the reception interface. Such services can support users' various businesses, such as: voice, 3.1KHz audio signal, composite low speed digital stream and transparent access X.25 utilities, etc. In addition, communication between a variety of terminals such as the G4-class fax terminal, a PC, and other terminals are utilized. Although the telephone terminal can also communicate with each other, since the unrestricted 64kbit / s bearer service does not provide the functions required for voice communication such as A / μ conversion and echo control, the telephone terminal must be under the conditions of these functions. In order to use this kind of business call.
(2) 8kHz structure, 64kbit / s carrying business for voice transmission
Such services are used for voice information. With such services, the digital signals in the S or T reference point should comply with the recommendations of G.711. Networks can use various processing technologies suitable for voice, such as analog transmission, echo clearance, low bit rate voice coding, and the like. Therefore, bit integrity is not guaranteed when information is transmitted. Therefore, this business cannot be taken when the G4 type fax machine and the visual telephone communicate. All CCITT recommendations relating to voice information in the network are applicable to such services. (3) 8kHz structure, 64kbit / s carrying business for 3.1kHz audio information
Such business corresponds to the business provided by the current public telephone network. The user information it passes is the audio information of speech and 3.1 kHz bandwidth. The information of 3.1KHz bandwidth includes information of the spendle data, G2 or G3 fax machine generated by the modem. Digital information in the S or T reference point also needs to comply with G.711 proposed regulations. In order to meet the requirements of voice conveying, the network must also have the necessary voice processing technology. Among them, some processing techniques such as echo control devices, speech processing devices, etc., for non-voice signals, when they need to transmit these signals, they can be controlled by the 2100 Hz signal tone in the belt, so they do not work .
This business is set for the simulation of the telephone network to the ISDN transition, all CCITT recommendations related to voice information in the network apply to such services.
(4) 8kHz structure, can alternately use the 64kbit / s carrying business of speech and unrelated
Such services can provide users with delivery of voice information in the same call, but also provide applications that are not limited to 64kbit / s carrying services. Users can be selected as needed in both. The user must specify the requirements for such services at the time of calling, and proposes the initial working mode is 64kbit / s that is not limited. Such services are generally used to support multi-function user terminals or single function user terminals.
(5) 8kHz structure, unrestricted 2 × 64kbit / s carrying business
Such services provide transparent delivery of two 64kbit / s user information on the user-network interface. This service can make users simultaneously two B pathways. Typical applications are visual calls.
(6) 8kHz structure, unrestricted 384kbit / s carrying business
This type of business transmits user information between the S or T reference points on the user-network interface, transmits user information with a transmission capacity of 384kbit / s, which is called H
0 pathway. Typical applications are information on the conveying conference TV.
(7) 8kHz structure, unlimited 1536kbit / s carrying business
This type of service is transmitted between the S or T reference point on the user-network interface, transmits user information with a transmission capacity of 1536kbit / s, which is called H.
11 pathway. A typical application is to transmit high-speed data and television images.
(8) 8kHz structure, unrestricted 1920kbit / s carrying business
This type of service is transmitted user information between the S or T reference points on the user-network interface, transmits user information with a transmission capacity of 1920kbit / s, which is called H
12 pathway. A group channel is usually used to transmit high-speed data and image services.
(9) 8kHz structure with unrestricted multi-rate
The service allows the user to request and release multiple 64kbit / s circuit switched connections, allowing users to transparently transmit user information. This business expands only 64kbit / s pathonels using only 64kbit / s.
The carrier service of the second type of packet exchange has three types:
(1) Virtual call and permanent virtual circuit bearer
Such services are built in the S or T reference point, and the virtual circuit is created by the B-channel or D path to transmit user information in a packet. The virtual call signaling information and the maintenance operation information of the permanent virtual circuit can be transmitted in a D-channel or B path according to X.31.
(2) Unconnected packet bearer
Such a bearer service is to transmit user information in packet mode using D paths on the network interface. It is suitable for transmitting shorter information because it is not established on the D path. For example, credit card reader confirms the validity of credit card and transmit some telemetry remote control signal.
(3) User - User Signaling Carrier Service
User-User Signaling Carrier Service is transparently transmitted between S or T reference points transmitted and receiving both end interfaces through a signaling pathway, that is, the S or T reference point transmitting and receiving the S or T reference points transmitted and receiving the S or T reference points transmitted and receiving the S or T reference points of the two-end interface through the SFline pathway. User information, that is, the user-ended information can be transparent on the signaling path rather than on the information path. The bearer service of the third type of frame mode is divided into two business of frame relay and frame exchange.
Frame relay services can reduce the system storage and processing procedures of the intermediate node, simplify the processing of protocols to reduce delays, mainly applied to data communication. The procedures in which all the control planes in which the business in the frame are inherited are logically separated. The user plane program of the first layer of physical layer uses I.430 / I.431 Recommendation, the user plane program of the second layer link layer uses the core function of I.441 recommended, and can count the user information traffic, and The order of service data units transmitted two-way transmitted between two S / T reference points can be guaranteed.
The basic feature of the frame exchange service is the same as the frame relay service, but it still uses the ability to confirm the operation, error recovery.
Third, user terminal business
1, the concept of user terminal business
ISDN is referred to as user terminal services in Business Access Points 3 and 5. It includes the communication capabilities of the network and the communication capabilities they have in the terminal itself. The user terminal service can be understood as the service obtained by the user through the communication. Using telephone service calls or fax service delivery characters is an example of user terminal services. The user terminal service is specified by the characteristics of 1 to 7 layers of ISDN. It can be seen that the user terminal service must contain the content of the carrier service.
Point 4, the reference point R is not an access point of the ISDN telecom service. This point is related to the type of terminal adapter TA. Compliance with other series, such as the recommended terminals, such as the V-series, X-Series, etc., can be connected to the R point with the bearer service using the ISDN standard. The bearer service is a telecom service between S or S points, while the user terminal service represents the business between terminals. 2, the properties of user terminal services
The user terminal service is represented by the low-level attributes, high-level properties, and general properties of various services. Low-level properties can be further divided into access attributes of information transmission attributes. They can be represented by the same attribute value as the carrier service. The high-level attribute is related to the specific content of the user terminal business, and its general property needs further research. The following table lists the contents included in each business attribute.
The attribute information transmits attribute low-level property 1, the information transfer mode 2, the information transfer rate 3, the information transfer capability 4, the structure 5, the establishment of communication 6, the symmetry 7, the communication configuration access attribute 8, the access path, and its rate 9, Access Protocol High-level Properties 10, User Information Category 11, Layer 4 Protocol 12, Level 5 Protocol 13, Layer 6 Protocol 14, Layer 7 Protocol General Attributes 15, Supplementary Service 16, Service Quality 17, Interoperable Ability 18, Business and business properties
3. Classification of user terminal services
There are many types of user terminals, such as phones, G4 faxes, views, user telegrams, graphic mixing methods, etc.
Fourth, supplement business
1, supplemental business concept
When the user uses two basic services that carries business and user terminal services, ISDNs can be required to provide additional functions. This additional function provided by the network is referred to as supplemental services. Supplemental services cannot be provided independently, it must be provided with basic communication services. Typically, a supplementary service can be used in combination with one or more basic services. Using supplementary services can bring many convenience to users. 2, ISDN supplementary classification
(1) Number identification class supplement business
1 direct dialing
2 multi-user numbers
3 Call line number display (CLIP: CALLING LINE IDENTIFICATION PRENTATION)
4 Call Number Restriction (CLIR: CALLING LINE IDENTIFICATION RESTRICTION)
5 Displayed by WLP: Connected Line Identification Presentation
6 Limited Limit Restriction (Colr: Connected Line Identification Restriction)
7 sub address (SUB: Subaddressing)
8 Malicious call recognition (MCI: Malicious Call Identification)
(2) Call provides class supplement services
1 Call Conversion (CT: Call Transfer)
2 call forward (CF: Call forward for)
3 log line (LH: line hunting)
(3) Call completion class supplement service 1 Call waiting (CW: Call waiting)
2 Call Keep (HOLD)
3 Complete the call for busy users (CCBS: Completion of Calls to Busy Subscribers)
(4) Multi-communication supplementary business
1 Conference call (conf: conference calling)
2 Tripartite Communication (3pty: Three Party Service)
(5) Community supplementary business
1 Closed User Group (CUG: CLOSED User GROUP)
2 Multi-level priority (mlpp: multi level procedence and preemption)
(6) billing supplementary business
1 Credit Card Call (CRED)
2 Charge Notice (ADC: Advice of Charge)
(7) Additional information transfer business
1 User-User Signaling (UUS: User-User Signalling)
Chapter II ISDN User - Network Interface
I. Function 2, reference configuration three, access configuration four, path type and interface structure 5, protocol 6, ISDN user - network interface hierarchical function seven, ISDN users - network interface physical layer eight, ISDN users - network interface chain Road, ISDN User - Network Interface Network Layer Ten, Interlayer Communication Eleven, Supplementary Business General Protocol I, Function
ISDN User-Network Interface The role of network interface is to enable the user terminal and the ISDN network to exchange information between networks and users, which mainly has the following functions:
(1) With the ability to provide a variety of services using the same interface;
According to user needs, based on the call, select the bit rate, switching method, or encoding method, etc. of the information.
(2) Has a multi-terminal configuration function;
Multiple terminals can be connected to the same interface, allowing these different terminals simultaneously.
(3) Has a mobility of the terminal;
With standard sockets, the terminal can move and re-recover communication during communication.
(4) Compatibility checking between the calling user and the called user terminal;
In order to verify that the calling and the called terminal can communicate with each other, such as ensuring the consistency of the telephone and the telephone terminal, the fax and the facsimile terminal, etc., the function of having a compatibility verification is required.
Second, the reference configuration
The user-network interface is the interface of the user equipment and the communication network. The reference configuration of the user-network interface is an abstract interface arrangement established by the International Telecommunication Standardization to standardize the above interface. It gives a standardized reference point (R, S, T) and related to it. Various functional communities (NT1, NT2, TE1, TE2, TA). The functional group is a combination and arrangement of various functions that may be needed on the ISDN user access. In practical applications, the user-network interface configuration may be varied according to the requirements of the user, and several functional groups may be implemented by a device.
The reference point is a conceptual reference point for dividing features. It can be a physical interface between each device unit in a user access. When multiple functional groups are implemented in a device, it is only conceptually present, and there is virtually no physical interface exists. R and T reference points are ISDN standardized objects. R Points involve all non-ISDN terminals and adapters, and there is no uniform specification.
Third, access configuration
On the basis of the reference configuration, the actual configuration of the user-network interface may be varied. Five functional groups can be implemented as a device, and three reference points will actually exist as physical interfaces. But this is not necessary, and some or all of the functional groups can be implemented in one device. For example, the NT2 and NT1 can be combined in one device. At this time, the T reference point will physically unseave; or the TA and NT2 can be combined together, then the S-reference point is physically physically. .
NT2 is the user's network facility, not all users need network facilities such as user switches or local area networks. When the user does not need NT2, the user terminal can be directly connected to NT1. In this way, the characteristics of the S interface and T interface operated at the same rate are identical to the specification. The S interface and the T interface will overlap together, called S or T interface.
ISDN User - Network Interface Reference Configuration Map The number of devices has not been restricted. For example, the user can have multiple NT1 and is used together for NT2. As for the number of user terminals, it can be from one to thousands. Fourth, path type and interface structure
ISDN users - There are two important factors in the network interface, namely the path type and interface structure. The passage is the ability to represent interface information transmission. The pathway can be divided into several types based on the rate, the information, and the capacity, referred to as the path type. The combination of path types is called an interface structure, which specifies the maximum digital information transfer capability on this structure.
1, passage type
The path is a transport channel for providing a standard transmission rate for business. While standardizing the bearer service, it is necessary to standardize the path on the user-network interface. There are two main types of pathways. One type is the information path to transmit a variety of information flow for the user; the other is the signaling path, which is to transmit signaling information for call control. According to CCITT, there is the following types of paths provided to users at the user-network interface:
B path: 64kbit / s for delivery of user information.
D passage: 16kbit / s or 64kbit / s for transport signaling and packet data.
Hide
0 passage: 384kbit / s for delivery user information (eg stereo show, image, and data, etc.).
Hide
11 passage: 1536kbit / s for delivery of user information (eg high speed data transfer, conference television, etc.).
Hide
12 passage: 1920kbit / s for delivery of user information (such as telling data transfer, image, and conference television, etc.).
Using the most common obvious B-channel. It can utilize various types of information such as 64kbit / s switching networks that have been formed. It can also be used as an entry channel for users to access grouping data services.
2, interface structure
The ISDN user has been standardized - there are two types of network interfaces, and one is a basic rate interface, and the other is a group rate interface.
(1) Basic interface
The basic interface is the interface specified by the ordinary subscriber line of the existing telephone network as an ISDN subscriber line, which is the most common, most basic user-network interface of ISDN. It consists of two B paths and a D passage (2b D). The rate of B path is 64kbit / s, and the rate of D path is 16kbit / s. So the maximum information transfer rate that the user can utilize is 64 × 2 16 = 144kbit / s.
This interface is designed for the most viable users using ISDN. It cooperates with the user line two-wire two-way transmission system to meet the needs of thousands of households on the ISDN business. Using this interface, users can obtain basic business and supplementary services of various ISDNs.
(2) One group rate interface
The rate of the primary interface transmission is the same as the baseball of the PCM. Due to the international two-specific PCM, ie 1.544Mbit / s and 2.048Mbit / s, ISDN users - network interfaces also have two rates.
A group rate user-network interface structure can have multiple arrangements according to different requirements of communications. A typical structure is NB D. N values correspond to the base group of 2.048 mbit / s and 1.544 Mbit / s, respectively, 30 or 23, respectively. Here, the rate of B pathways and D paths is 64kbit / s. This interface structure is a commonly used option for users of NT2 for integrated business user switches. When the user needs large communication capacity (eg, large enterprise or large company's dedicated communication network), an interface of a group rate may not be used. At this time, you can equip several of the multi-group rate-network interface to increase the number of pathways. When there is a plurality of primary group rate interfaces, there is no need to set a D paths each one-time group interface, which allows N interfaces to use a D-channel.
Users who need to use high-rate paths can adopt interface structures than NB D. For example, MH0 D, H11 D or H12 D can be employed. It is also possible to adopt a structure of both the H0 pathway: Nb MH0 D, where M × 6 n ≤ 30 or 23 here. When the D path on other interfaces can be used, (M × 6 N) may be 31 or 24. User Network Interface Type Physical Interface Speed Interface Structure Structure Name Channel Structure Basic Interface 192kbit / S Basic Interface (Basic Access) 2B D16B = 64kbit / S; D = 16kbit / S Broadcast Speed Interface 1544kbit / S or 2048Kbit / SB Channel interface (multi-channel access) H0 channel interface (high speed access) 23b D64 (D = 64kbit / s) 30b D64 (D = 64kbit / s) 4h or 3H0 D64 (1544kbit / s) 5H0 D64 ( 2048kbit / s) H1 channel interface (high speed access) B / H0 mixed channel interface H11 (1544kbit / s) H12 D64 (2048kbit / s) NB MH0 D64 basic access multiplexing interface 1544kbit / s or 2048kbit / s Basic access multiplex interface 1544kbit / s is studying 12 × (2B D16) (2048kbit / s)
Five, agreement
The call control function of the ISDN standard user-network interface is specified in the form of a user-network protocol. The so-called communication protocol refers to the form of information indicating that the information indicated between the two communication devices and the necessary control procedures.
The communication protocol of ISDN is divided into two categories: one is the communication regulation between the same functional layers, the communication rules between the terminal and the same layer, which is to complete the specific function of the functional layer must comply with the requirements. Another category is a communication status between different functional layers called an interface or service. It specifies the interface relationship between two layers and provides services to the upper layer using the underlying function.
The pathway of the user information and signaling information in the ISDN user-network interface is independent, ie call control information such as an outband mode transmission number. This is very different from the way the user signaling in the traditional telephone network is very different. In the telephone network, user information and signaling information are transmitted in the same road. This signal is called inband signaling, that is, what we usually say followed. In contrast, ISDN transmits all call control information, which is transmitted by independent D-channel, is the communication protocol, and the terminal and networks can communicate rich signaling between the terminal and the network and the network and the terminals. Further, since the external manner is used, the signaling information can be transmitted even during communication.
In addition, the agreement between the ISDN user-network interface except for the establishment of the communication required by the basic communication business, it also specifies the control functions of the supplementary service to meet the needs of a large number of supplementary services in ISDN.
Six, ISDN users - hierarchical functionality of network interface
According to the open system interconnect reference model, ISDN user-network interface protocol is divided into three layers: the first layer is a physical layer, which includes a basic access interface and a group rate interface. The second layer is the data link layer. The third layer is a network layer.
The physical layer provides a means of establishing, maintaining and releasing physical connections to ensure information transmission on the physical circuit. The physical layer specification refers to the electrical characteristics, physical properties, including the mechanical characteristics of the interface, and the like.
The link layer provides the establishment, maintenance and release means of the data link on the basis of the physical layer. Data Link Layers Complete link multiplexing, error detection, and recovery traffic control and information transmission.
The network layer completes the function of call control based on the service provided by the second layer, including the control of the circuit switched call and packet switched call.
The second layer and the third layer protocol on the ISDN user-network interface are referred to as 1 No. 1 Digital User Signaling (DSS1).
ISDN User-Network Interface Physical Layer, Link Layer and Network Layer Templary Schematic shown below.
Application layer end-to-end user signaling represents layer session layer transport layer network layer call control I.451X.25 Packet stage to be studied X.25 packet-level data link layer LAP-D (I.441) X.25LAP-B Physics Layer I.430, I.431 Signaling Packet Telemetry Circuit Exchange Rental Circuit Packet Exchange D Channel BT Road Seven, ISDN User - Network Interface Physical Layer
ISDN User-Network Interface Physical Layer is a physical means that guarantees information transfer. The technical requirements of the physical layer are divided into two parts: the basic interface and the primary group rate interface. This section focuses on the application of a wide range of basic interface physical layer requirements, and finally explains the related content of the first layer of the primary rate interface.
1, physical layer function overview
The ISDN physics layer is at the reference point S or T, regardless of the case, including the basic functions of the following physical layer (ISO first layer).
(1) The information that needs to be transmitted is encoded to transmit it through an interface.
(2) Provide B-channel two-way information transmission.
(3) Provide D-channel two-way information transmission.
(4) Complete the path multiplexing function to form a transport structure of the basic access or a group rate access.
(5) Complete the activation and deactivation function of the physical layer.
(6) Provide the power supply function from the network terminal to the user terminal.
(7) With maintenance function, it is possible to isolate the faulty terminal.
(8) The battle of the D pathway, that is, conflict detection.
When the basic access is multi-point configuration, the last function is required, which will be described later.
2, basic interface
The basic interface is an ISDN user access to a wide and flexible interface. Such an interface can be arbitrarily configured according to the actual needs of the user, the most common configuration is that the user can connect the phone, the fax machine, and the data terminal on a pair of user lines, and the user can use a pair of telephone lines at the same time. Or receive fax and data communication. The following is a brief introduction to the work mode, wiring configuration, transmission pattern, frame structure, and interface characteristics of the basic interface.
(1) Working mode and wiring configuration
The basic interface is divided into two categories: one is a point-to-point operation, and the other is a point-to-multipoint operation.
The ISDN basic interface has three basic wiring structures according to different operations:
1 short passive bus
The so-called passive bus is to connect several communication terminals with passive transmission lines (symmetrical line pairs). NT can be placed at one end of the bus, or may be located at the intermediate portion of the bus. According to I.430, the length of such a bus can be as long as 100 to 200m, and the specific length is related to the line quality (propagation time delay and loss). The number of terminals can be subjected to up to 8 terminals.
2 extended passive bus
The extended passive bus is suitable for situations of setting NT and terminal devices. This bus is farthest to the NT distance of 500 m. This configuration requires the location of the terminal relatively concentrated to ensure that the signals between the terminals to NT may not be extended. However, the distance between the farthest terminals should be less than 25 to 50 m.
3 point to point configuration
Point-to-point configuration is simpler. The distance between the terminal device and the NT allows for a maximum of 1000 m. The maximum length of the terminal lead is 25m.
Typically, short passive bus is suitable for small office organizations or home use; extension passive bus and point-to-point mode suitable for large companies, the building extends from user switches to the wiring of various use locations.
(2) Transmission pattern and frame structure
The basic interface of the ISDN physical layer is used in four-wire bidirectional transmission at the basic interface of the S-reference point. The transmission rate is 192kbit / s, where 144kbit / s (2b D) is used at the end of the end, and the remaining bits are used for synchronous and control. The transmission pattern of the ISDN basic interface uses the AMI code. The frame structure employed by the ISDN basic interface is composed of 48bit, where each of the B1, B2 path information accounted for 4bit, F and FA are frame-locating and auxiliary frame positioning. The role of the L bit is to keep the direct current component of the circuit equal to 0. In addition, there is an E bit, which is used for D path competition control.
(3) Interface procedures
There are three interface procedures for the ISDN basic interface physical layer, namely, activation / deactivation procedures, D channel access procedures, and frame positioning procedures.
1 activation / deactivate procedure
Activation and deactivation procedures are specific to the ISDN basic interface. The so-called deactivation means that the system that has entered the working state is transferred to the rest. In the rest, except for a few control circuits, the remaining circuits will stop power to reduce power consumption and extending the service life of the system. In contrast, activation is to transfer the system in the rest state into the working state, and the whole system is powered, and then it operates. This activation and deactivated function is necessary for users with fewer communication services. In the process of system activation, frame positioning is simultaneously performed. 2D channel access procedure
In order to establish communication, users need to take up the D path to exchange control information with the switch. There is only one D path on an interface. When there are multiple terminals on the interface, and when multiple terminals need to establish communication, the D-channel will occur.
D Passage Access Control Procedure Raectors When the access competition occurs, only one terminal signal is perfective. The access of all other terminals is temporarily blocked, and when the D passage is idle, try the access. The D path access control procedure makes signaling better than grouping services, that is, when the battle occurs, the terminal that needs to be sent will give priority to the D-channel. The D path access procedure can be used to provide a service to multiple terminals. This procedure does not allow a single end to occupy a D-channel for a long time.
3 frame positioning procedures
The NT-channel subscriber line extracts the clock from the signal sent by the switch, providing a bit synchronization and frame positioning signal to the interface, and transmits each frame to the TE. TE is acquired by NT to obtain the desired bit synchronization, word synchronization, and frame positioning synchronization signal.
(4) Electrical characteristics and physical properties
CCITT I.430 recommends that the indicators of the electrical characteristics of the basic interface have been detailed.
The physical characteristics of the ISDN basic interface refer to the mechanical part of the connector, connecting cord, cable, etc., physical properties, also known as mechanical properties. ISDN basic interface connectors, namely plugs and sockets use ISO8877 standards. This standard specifies that there are 8 leads, with two pairs of data cables, a pair of power cords and a pair of power load lines. The socket can be fixed on the wall like the city electrical jack. The plug is mounted in TE, as long as the plug is pulled out or insert, you can move the terminal to communicate.
(5) Power supply
In the case of the ISDN basic interface, this power supply mode is used by the NT to TE through the user-network interface, in particular when using digital telephones. Other ISDN terminals are appropriate to determine the use of local power supply or by NT.
3, one group rate interface
The first layer of a population rate interface is based on the provisions of the PCM base group. It has many differences from the first layer agreement of the basic excuse. A clutch-point wiring configuration can only be used between the group interface and the terminal, so there is no need to point the access competition control procedure used in multipoint mode. In addition, the network does not supply power to the terminal, and the interface is always in the active state. So do not need to activate / deactivate the procedure. The first layer of the primary rate interface is much simpler than the basic interface, and the following is a summary introduction.
1 electrical characteristics
The electrical characteristics of the 2048kbit / s interface meet the recommendations of G.703, with HDB3 code, and use a balanced 120Ω symmetrical line to interface.
2 frame structure
The frame structure of the 2048kbit / s interface consists of 32 time slots per frame. One time slot contains 8 bits. The number of bits per frame is 256. The repetition rate of the frame is 8000 frames per second. Therefore, the rate of each path is 64kbit / s. A typical application is to support 30 B-channel and one D path, or other applications, including 31 B-channel or various H-channel combinations. ISDN User-Network Interface The frame structure of a group is the same as the frame structure of the PCM base group.
3 timing and synchronization
NT extracts timing synchronization signals from the signal sent from the network. TE extracts the synchronization signal from the signal sent from the NT. If the synchronous signal error is detected in 3 to 4 times, it is considered to be out; synchronization is established when two frame synchronization signals are continuously detected.
Eight, ISDN User - Network Interface Link Layer
ISDN User - Network Interface Link Layer Protocol is called LAPD (Link Access Procedure on The D Channel: D Passage Link Access Protocol). Usually, ISDN's link layer and network layer protocol are typically referred to as D path protocol, and IT is called No. 1 Digital User Signaling (DSS1). The function of the link layer, that is, the second layer is to transmit the third layer or more information through the D paths between the network and the terminal. International Standardization Organization (ISO) specifies the format and control protocol of this layer in Advanced Data Link Control Protocol (HDLC). The second layer LAPB (Link Access ProceFure Balance) of the X.25 protocol used for group exchange is based on HDLC. However, LAPB is a two-layer protocol of group switches, which cannot meet the functional requirements of ISDN, so ISDN's second layer protocol expands some ISDN's functions on the basis of LAPB. 1, LAPD function summary
The main function of the LAPD is to establish a link on the D path of the ISDN basic interface or a group interface, and the information of the third layer is passed in units of frames or the control information of the second layer. When the transmission error is detected, recovery is performed by the retransmission. LAPD also has a function of flow control. Flow control means that when the link is overloaded, the link can be temporarily stopped sending frame information.
The main functions of LAPD are as follows:
(1) One or more data connections are provided on the D channel.
(2) Transfer control information and user information in units, and the boundary and positioning of frames can be performed.
(3) Sequential control can be performed, that is, the transmission and reception order of each frame connected through the data link.
(4) It is capable of detecting transmission errors on a data link connection, format error, and operational error.
(5) Recovery according to the detected transmission error, format error and operational error.
(6) Cannot notify the management entity in an unrecoverable error.
(7) Perform flow control.
2, LAPD operation type
There are two types of LAPD operation types, and one is confirming operation, and the other is no confirmation.
(1) Confirmation
Confirmation operation is the most common way of use. Usually used for information transfer for point-to-point. Confirmation The operation needs to be confirmed for each command. In the ISDN protocol, it is confirmed that the operation is used to pass the call control information of the third layer, while error checksum traffic control is performed. The information transfer form of confirmation operation is called a multi-frame operation.
(2) No confirmation
Unconfirmed operations refers to the transmission process of the confirmed frame. This operation does not guarantee that data sent by one user must be sent to the desired endpoint user. There is no confirming operation to be used for point-to-point connections, or it can be used for broadcast connections. Since the receiving end does not need to be confirmed in this operation, the recovery cannot be recovered when the transmission or format error is detected. There is no function of traffic control without proven operation.
(3) LAPD address and link identification
A data link connection is identified by a data link connection identifier (DLCI) in the address field of each frame. One of the different LAPDs and LAPB is that LAPD can support multiple link connections, which is multiplexed. The implementation of the multiplexing function is done by DLCI.
DLCI consists of two parts: Service Access Point Identification (SAPI) and Terminal Endpoint Identifier (TEI). SAPI is used to identify the network side or user side of the user-network interface. TEI is used to identify a specific connection endpoint within a service access point.
SAPI is an access point that identifies the data link layer entity to provide data link layer services to the third layer management entity. SAPI regulations allow 64 business access points. The assignment of the SAPI value is as follows.
The value of the value of SAPI, the third layer or management entity 0 call control protocol 1 reserves to use the Q.931 Call Management Protocol to group way to communicate with 16-compliant X.25 protocols 63 management protocol Other for future standardization
For point-to-point data link, the TEI value is only related to the terminal device. A terminal device can include a TEI value of one or more transfer points to point data. The TEI value of the broadcast data link is 127. The TEI value of the point-to-point data link is from 0 to 63, and the user equipment is not automatically assigned TEI. The non-automatic TEI value is selected by the user, and the allocation of these values is also completed by the user. 64 to 126 are user equipment that automatically assign TEI. The automatic TEI value is selected by the network, and the allocation of these values is also done by the network.
TEI Value User Terminal Type 0 ~ 6364 ~ 126127 User Device (Manual Assignment) User Equipment (Manual Assignment) Automatic Assignment TEI User Equipment Establishing a SAPI value with a TEI value to constitute a second layer data link together the address of. That is, for a given TEI, there must be an SAPI corresponding to each other, together with a logical connection. The combination of SAPI and TEI is called a Data Link Connection Identifier (DLCI). At any time, LAPD can provide multiple logical connections, each connection has a unique DLCI.
(4) Frame structure of LAPD
The frame structure of the LAPD is constructed based on the frame format of HDLC. The frame check sequence is composed of a logo sequence, an address field, a control field or an information field. Each frame is in units of 8 bit, and the start of one frame begins with a flag sequence indicating the frame head, followed by identifying the address field of the link, and then the control field indicating the frame type. After the control field is followed by the information field and the detected transmission error, the frame test sequence (FCS) is finally the flag sequence indicating the end of the frame. It is not the structure of various types of control frames of the information frame, except for the information field, and other parts are identical to the information frames.
(5) Classification and composition of frames
LAPD has four types of frames, which are information frames for transmitting information, for monitoring status monitoring frames, no sequential numbered format frames and control information exchange frames for connection management.
1 information frame
The function of the information frame is to transmit a number frame including the information field in an orderly manner through the data link connection. Typically information frames are used in multi-frame operations connected to point-to-point data link.
2 monitoring frame
The monitoring frame includes RR (receiving preparation) frame, RNR (received unpredictable) frame and REJ (reject) frame. RR frames and RNR frames are used to monitor the status of the data link connection for flow control. The RR frame represents the buffer idle that stores the receiving frame, and can receive the frame sent by the peer. The RNR indicates that the buffer is fully occupied. Rej indicates that the associated information frame is detected due to the transmission line, and the peer is required to resend the information frame.
3 No numbered frame
There is no order number, there are six kinds of frames. Where SABME is sent when the request is established; the DISC frame is sent when the multi-frame operation is required; the DM frame is to indicate the second layer to the second layer in the unpacking state, and cannot perform multi-frame operation; UA frame is SABME and DISC The response frame of the next frame; the FRMR frame is an abnormal state to the peer; the UI frame is an information frame that is not confirmed in the operation mode for performing signaling transmission that is not numbered.
4 Control Information Exchange Frame
The XID frame is used for the negotiation of the parameters related to the agreement between the two ends.
Nine, ISDN User - Network Interface Network Layer Agreement
ISDN User-Network Interface Network Layer (Layer 3) The information transfer function of the link layer is transmitted between the user and the network, receives various control information, and controls the establishment, holding and release of the information path according to the user requirements. .
The provisions of the network layer are CCITT I.450 recommendations and I.451 recommendations (or the Q.930 and Q.931 recommendations). It is recommended that the functional summary of the third layer, the call control process should have various status, message type, message constitution, and call control procedures and packet switched programs for the exchange of coding and basic circuits.
1, function summary
The control function of the third layer can be divided into circuit switched call control and packet switching call control. Circuit switched call control means that the terminal and the network exchange signaling information are exchanged by D passage, and transmit user information using the B-channel established circuit switching. The control of the packet call is implemented by the D path, but the packet data information can be transmitted by the D path through the D path.
ISDN User - The function of the third layer protocol of the network interface mainly includes the following:
1 Processing the original language communication with the data link layer.
2 Generate and explain the third layer message for the same communication.
3 Manage timers and logic entities (such as call reference) used in the call control program.
4 Manage various access resources including B-channel and packet layer logic pathways.
5 Check if the service provided meets the requirements, including load capacity, address, and high-level compatibility checking. 2, call control
The basic call control program of the third layer is completed by the migration of multiple states. During the call control, the third layer completes an event, for example, the transmission or reception of a message, the migration of the primary state. The status of the user side and the status of the network side should be corresponding.
The call control information of the third layer is delivered in the form of a message. As an example, the message is divided into four major categories: the first class is a call setup message for starting a new call; the second class is a message in the call information phase, used to pass during a call. Various types of messages; the third category is a call cleaning message for the release of the call; the fourth class is other messages, used to interrogate the call status and transmit some notification information, and the like.
Ten, inter-layer communication
The interlayer communication is to exchange information in the form of an primitive, and the primitives use abstract methods to represent the control of interlayer information. When two homologous entities need to complete a communication process, request, indication, response, and confirm four primitive types.
Request primitives are used for high-level or managed entities request low-level providing services.
Indication primitives for low-level information related to services to high-level or managed entities.
The response primitive is used to manage the entity to confirm the low-level Indication instructions.
Confirm primitives are used to confirm the requested events to the high layer confirmation.
1, third floor and second-level primitive
When using the communication primitive between the second layer and the third layer, it is divided into the following three stages:
(1) Establish multi-frame operation
DL-ESTABLISH-REQUEST
DL-ESTABLISH-INDICATION
DL-ESTABLISH-Confirm
(2) Data transfer
DL-DATA-REQUEST
DL-Data-Indication
DL-Unit-Data-Request
DL-Unit-Data-Indication
If the second layer uses a confirmation mode, when the two third layer entities need to transfer the message with each other, the communication link to the second layer is established using the DL-DATA-Request / Indication primitive. If the second layer adopts an undertaking mode Then use the DL-Unit-Data-Request / Indication primitive.
(3) End multi-frame operation
DL-RELEASE-Request
DL-RELEASE-INDICATION
DL-RELEASE-Confirm
2, the primitive between the second layer and the first layer and the use
There are two main clauses of the second layer and the first layer, and one is a request, and the other is an instruction.
Original language used to activate and deactivate:
Ph-activate-request / indication
Ph-deActivate-indeform
The primitives used to transmit frames are:
PH-DATA-Request / IIDICATION
This summary describes the types of interlayer primitives and use examples. In fact, the three layers of ISDN's three layers need to manage entities to unify coordination, so physical layer and link layers also need to communicate with management entities. Generally, ISDN users-network interface management functions are divided into the following categories: (1) Fault management; (2) Configuration management; (3) Performance management. For details, please refer to the Q.921 recommendation.
XI, the general agreement for supplementing business
Controlling the general protocol for ISDN Supplemental Business Description Universal Process for Applying for and Operation between Users and Networks. The general concept is to refer to the control process of each different supplementary business. Q.932 It is recommended to make a detailed specification for these general protocols, which specifies three general protocols: KeyPad Protocol, Feature Key Management Protocol and Functional Protocol. The keyboard protocol and the feature button management protocol are the STIMULUS protocol, and the function protocol is a functional protocol. The excitation protocol will focus on the control intelligence of the supplementary business in the network, and the user sends a specific character to the network through the terminal. In order to identify and process related supplementary services, you need to identify, translate and issue corresponding instruction information by identifying the received characters. With this agreement, the terminal device does not need to know the application, the operation process, which reduces the complexity of the terminal.
Functional protocol is to focus on the control intelligence of the supplementary business protocol at the terminal, and the terminal device must know the application and operation of the various supplementary services. This protocol is more flexible. You do not need to extend new messages and use a large number of variables to complete the process, easy to standardize. Although different supplementary services can be operated using different protocols, the functional protocol is the basic protocol that controls the ISDN supplement business should be used.
Chapter III ISDN Equipment
First, ISDN Switch II, ISDN User Switch Third, a Class of Network Terminals, Access Unit 5, ISDN Terminal Equipment
ISDN devices refer to ISDN networks to provide all types of devices required by ISDN businesses, including ISDN switches, ISDN user switches, network terminals, access units, and various ISDN terminals and terminal adapters.
First, ISDN switch
The ISDN switch is a switching device in the integrated business digital network. The business characteristics of ISDN are mainly used by ISDN switches. The usual ISDN switch is improved on the basis of the original digital program-controlled switches.
1, the main function of the ISDN switch
(1) Transfer and exchange user information
(2) Signaling function
Since ISDN adopts a DSS1 protocol in the user access system, the ISDN switch must have a function of processing D path protocol and processing public channel signaling.
(3) Timing and synchronization
(4) Talking
(5) Maintenance management function
2, the structure of the ISDN switch
The ISDN switch is evolved on the basis of a program-controlled digital telephone switch. Its structure is very similar to the ordinary program-controlled digital telephone switch, but in order to adapt to the features of the ISDN end-to-end digital connection, all ISDN basic services and supplement services, the software and hardware structures of ISDN switches are complicated than the general program-controlled digital telephone switches. The following figure is a schematic diagram of the ISDN switch structure.
(1) Users and trunk interfaces (L / T)
The user and the trunk interface include interfaces of the user interface switch and other switches through the trunk access to the switch. The user interface of the ISDN switch retains the user-calling of the program-controlled digital telephone switches and converts the analog voice signal into a digital signal in the user circuit. The different point of the ISDN switch and the normal digital program switch in the user interface is the digital user interface, which provides the ISDN basic rate 2b D user access, or user access of the ISDN primary group rate 30b D. The former is the second-wire interface, the same as the user line used by the simulation phone; the latter is the four-wire interface, using the PCM transmission line. In addition, the standardized user access network interface of the Extended ISDN service defined by ITU is called a V5 interface. It provides a standardized unified interface for simulating users, leased line users, and ISDN users, and the rate is extended from a 2048kbit / s to 16 2048kbit / s.
Digital user line terminal LT and switch terminal ET two function blocks, see the figure below. Where lt is responsible for the transmission of the subscriber line; ET is responsible for the access control of digital users, on the one hand, the user information in the B-passage (64kbit / s) is multiplexed to the PCM bus through the PCM interface, and other L / T devices are the same. Way access to the switching network; the other side is handled on the control signaling in the D path, and the user's request and response will be sent to the control section of the switch, and convert the command of the control section into D-channel signaling. user. The trunk interface includes an interface with other ISDN switches and an interface with existing telephone switches. The physical characteristics of the ISDN switch relay interface are the same as the trunk interface of the program-controlled digital switches.
(2) Signaling equipment (S)
Signaling equipment is responsible for receiving, sending, and processing of all signaling on the user line and relay lines. According to ISDN's full network, the characteristics of public channel signaling are used, and the main tasks of signaling part are to process common channel signaling, including D-channel signaling and signaling.
Digital program-controlled switches typically have a processing function of signaling, including a message transfer section (MTP), telephone user portion (TUP), and operation maintenance section (OMAP). In order to transmit a local signal in the ISDN, the ISDN switch must increase the ISDN User Section (ISUP) to transmit various parameters and data for the ISDN service, control the establishment, hold and release of the ISDN call. The ISDN switch also needs to increase the Signaling Connection Control section (SCCP), which is used to establish a virtual circuit connection for signaling transmission between the two ISDN switches to facilitate transmission of data and maintenance management.
3, switched network (N)
The switching network is also known as the switch matrix, composed of the time terminal T and the spatial connector S, and the completion of the information on time and space.
4, control section (c)
The program-controlled part consists of a computer and a corresponding control program, and is responsible for the control of each part of the switch. Like the modern program-controlled digital switch, the ISDN switch generally uses the structure of the dispersion control, so that the control function is dispersed into the various parts of the switch, so that both L / T, S, N, pH and O & M have their own processors, the center only retains only Finite features such as resource management, operation and maintenance.
5, packet processor (pH)
The packet processor provides a processing function of packet exchange, so that the group terminal of the ISDN user can communicate with each other, and communicate with the public packet switched network. The protocol of the PH is X.25 proposal, which is consistent with the agreement of the public packet network.
The pH is not a portion of the ISDN switch. When the ISDN switch does not equip pH, ISDN is interoperable in a circuit connection (ie, X.31 recommendation a) and public packet network, and the X.25 terminal within ISDN also needs to communicate with each other. Exchange from a public packet network.
The implementation of the pH can be placed inside the ISDN switch, or it can be placed outside, and when the pH is placed outside the switch, the standard interface PHI of the packet processing access is used.
6, Operation Maintenance Management section (O & M) II, ISDN user switch
The ISDN User Switch (ISPBX) is a dedicated switch to serve a specific agency, such as agency, businesses, mines, schools, and companies, and a public switch, while providing users with a variety of ISDN services. ISPBX is used in a private network, which is not only used for voice communication, but also for data, fax, teletext, and images such as non-talks.
1, ISPBX interface
The ISDN user switch is a category of NT2 in the ISDN user-network interface, and the interface should have.
(1) ISDN user basic interface
(2) ISDN one group interface
(3) Other interfaces connected to existing user terminals and network devices
2, the basic function of ISPBX
The ISDN user switch is generally based on the original telephone subscriber switch, so the basic features of ISPBX include the functionality and ISDN functions of the original telephone subscriber switch, mainly including the following:
(1) Complete 64kbit / s circuit switched function
(2) Provide ISDN interface
(3) Business function
(4) Signaling conversion function
(5) Maintenance and operation
Third, a type of network terminal
A class of network terminals (NT1) is a terminal device of the user transmission line, divided into two types of NT1 and primary group rates of the basic rate. 1, basic function
For NT1 of the basic rate, the following functions are mainly completed:
Transfer function, timing function, D channel access control, activation and deactivation function, maintenance function, and power supply.
For NT1 of a group rate, it is mainly necessary to provide a four-wire two-way transmission capability of 30B D, complete timing and maintenance.
Fourth, access unit
The interconnection between the ISDN and the packet data exchange network is a device that can communicate with the terminal in the grouping terminal in the ISDN and the terminal in the packet data exchange network, also known as the network connector. . The X.25 terminal in the ISDN is connected to the ISDN via the ISDN adapter and then passed through the AU. ISDN accepts a call from TA or AU, establishing a B-channel of a circuit switching method between TA and AU, an ISDN transparently processed packet call. This way to access the packet network in a circuit switching to provide the ISDN to the packet service is the way A.
The ISDN Access Unit is a core device that makes two networks to implement packet services. It is logically belonging to the packet data network, and the AU implements X.25 or X.75 suggests on one side of the connecting packet data network, and implements the open system interconnection (OSI) three-layer protocol to connect the s interface on one side of the ISDN, ie I.430 / I.431, Q.921 and Q.931 recommendations.
V. ISDN terminal equipment
The ISDN terminal refers to a variety of terminal devices having a S interface that can communicate directly into the ISDN network. Among them, an ISDN standard terminal TE1, a non-ISDN terminal TE2, an adapter TA, and a user switch, and the like. Based on its business performance, it can be divided into a multi-function terminal or multimedia terminal such as a voice terminal, an image terminal, a data terminal, and a plurality of functions. The ISDN terminal can also make a combination of various services according to the user's application needs. In addition, ISDN adapters or adapter cards can fit all kinds of devices on existing telephone networks and data online to ISDN.
Typically, the ISDN terminal should have the following basic functions:
(1) The processing function of the D pathway protocol;
(2) S interface physical layer function (see CCITT I.430 / 431 Recommendation)
(3) Terminal selection function
(4) Friendly man-machine interface
(5) User terminal high-level protocol processing
We know that Ta is an interface device or interface card added to an existing non-ISDN terminal (TE2).
The characteristics of TA are basically determined by interface performance on both sides. TA's end of the ISDN is an S interface, which should have all functions required by the S interface technical specification, including the 2nd and three floors of the physical layer, signaling. TA is an R interface at one end of the non-ISDN. The R interface does not refer to an interface of existing terminals that access ISDN for communication. This type of interface is much like, for example, asynchronous data terminals, personal computers, fax machines, and analog phones, etc. TA can be divided into the following categories according to the type of ISDN non-standard terminal:
(1) Suitable for TA of X Series and V Series Terminals
(2) ISDN adapter card suitable for microcomputer
(3) TA suitable for the OSI end
Although ISDN's D-channel protocol is based on an OSI protocol, comply with the OSI protocol cannot be directly connected to ISDN because the signaling of DSS1 is not exactly the same. Therefore, the OSI terminal still needs to access the ISON network through an adapter.
Chapter 4 ISDN Network System
First, ISDN's network constitutes two, ISDN's local signaling three, ISDN's network interoperability
ISDN devices refer to ISDN networks to provide all types of devices required by ISDN businesses, including ISDN switches, ISDN user switches, network terminals, access units, and various ISDN terminals and terminal adapters.
First, ISDN's network composition
Typically, the ISDN network consists of three parts, namely: user network, local network and long-distance network.
The user network refers to the user equipment and wiring of the user. Refers to the wire device included by the user terminal to the T reference point. In the ISDN environment, the user's input method is more complicated than the telephone network user. The general user network can use the following three structures: (1) Bus structure
When the same user has a variety of terminals, a bus structure can be employed. At this time, the plurality of terminals are connected to a passive bus and have the same user number. This mode can be opened at the same time on a 2B D basic rate subscriber line, and eight terminals can be played more and more. Since the user terminal of the passive bus mode can be configured as needed, there is no need to control, so this approach has the shortest connection cable, which can realize a variety of functions.
(2) Star structure
The star structure is one way of accessing multiple ISDN terminals directly through the S-reference point through a user switch, NT2. This approach is suitable for the synthesis of voice and data services, with various user terminals independently, centralized control, maintenance and management, real-time transparency and network extension. Applicable to the group users of the organ, the company and so on.
(3) Network structure
The mesh ring structure consists of a set of loop digital nodes and loop links, with a network interface, distributed control, and capacity allocation, even if the system functions are more stable. However, when a node is faulty, it will affect the normal operation of the entire system, and even if the system load is lighter, the average delay is also longer. So this is currently only used in LAN and MAN.
The construction of the local ISDN network is based on the ISDN terminal. The ISDN terminal is the most important part of the ISDN service for users. It requires ISDN functionality to use ISDN user signaling between users to the terminal, ie DSS1, between ISDN terminals or terminals and convergence. Signaling.
Long-distance network is a set of devices used to interconnect all local networks. Therefore, the digitalization of the long-distance network, that is, introduces digital long-distance transmission equipment and digital long-distance switching equipment, and the basis for implementing ISDN long-distance transmission and service on long-distance online opening.
Second, ISDN's local signaling
The No. 7 signaling system is an internationally standardized public channel signaling system. The system is designed to meet the requirements of all call control signaling in the telecom service, and is a high flexibility and multi-function signaling.
Structure and function of signaling 1, 7
The functional structure of the X-SLR is shown below. The structure is based on the OSI reference model, and the functions, maintenance, and release of calls are implemented.
(1) Messaging section (MTP) is completed in the signaling network to provide a reliable signaling transmission function. It includes three functional levels of signaling data links, signaling links, and signaling network functions. The lower three layers corresponding to the OSI reference model.
The first stage of MTP is a signaling data link for transmitting a two-way transmission path of signaling, composed of two data paths operating in opposite directions in the opposite direction, complying with the definition requirements of the OSI physical layer by using the same data rate in opposite directions. In the digital data link, 64kbit / s is 4.8kbit / s in the analog data link.
The second stage of the MTP is the function of the signaling link between the two direct connections to provide a reliable signaling link between the two direct connections.
The third level of MTP is a signaling network function. This feature provides the required functions and programs between signaling nodes of signaling networks. In the case of signaling link and signaling transfer point failure, the signal message can be reliably transmitted. The signaling network function includes two parts: signaling message processing and signaling network management functions.
Signaling message processing consists of three partial functions by message selection, message identification, and message allocation. Signaling Network Management refers to the reorganization of the network structure in the case of signaling link or signaling transfer point failure, and controls the functionality of traffic in congestion. Including signaling business management, signaling route management and signaling link management three functions and programs.
(2) Phone User Part (TUP) specifies the functionality and procedures for telephone signals required for international and domestic calls.
TUP can meet the requirements of the telephone service function of the digital telephone network, but not fully meet the business requirements of ISDN, so when the ISDN service is launched, the ISDN User Section (ISUP) should be used instead of TUP.
(3) The ISDN user seques the signaling functions and procedures required to call or all kinds of non-emptying business. It not only provides users' basic business and supplementary business, but also supports 64kbit / s and N × 64kbit / s and other bearer services. ISUP can be used for the continuation requirements of various communication services in international and domestic. (4) Signaling Connection Control section (SCCP) extends the business function of MTP, can transfer circuit related to non-circuit related signal information and other types of information between switching and dedicated centers, establish no connection and connection-oriented Network business. The addressing function using the full site address (GT) and subsystem number (SSN) is added compared to MTP. (5) Interaction capacity (TC) is a communication application protocol of No. 7 letter order. It only specifies the OSI seventh layer (TCAP) of the Layer 7 (Application Layer). TCAP mainly includes mobile application section (MAP) and operations, maintenance, and management part (OMAP). MAP specifies the roaming and channel transitions of mobile services, OMAP only provides MTP routing formal testing and SCCP routing formal test procedures. Third, ISDN's network interworking ISDN is coexisting with existing telecommunications networks, so you must consider interoperability issues with ISDN and other business networks. The interoperability between the network refers to interworking between ISDN and ISDN, as well as interoperability between different ISDN networks. Non-ISDNs interoperable with ISDN include a variety of networks that are providing business, such as business providers other than existing telephone networks, packet data networks, private networks, other ISDNs, and ISDNs.
1, ISDN and telephone network
Since ISDN is developed based on digital telephone network, ISDN and telephone network should be regarded as a whole, but it is only a different function. The telephone network only has the function of transmitting audio signals in the client, while ISDN can process business and capabilities far exceed this range. So when there is a telephone call, the routing can be performed in the ISDN and the telephone network, that is, the voice communication can be freely performed between the terminals in the ISDN and the terminals in the existing telephone network.
In order to complete the communication of ISDN users and existing telephone network users, it is mainly necessary to solve the following technical issues:
(1) Interoperability between signaling system
The local signal of the telephone network may use China No. 1 Signaling or No. 7 Signal Phone User Part (TUP), and the ISDN's inter-signal will use the No. 7 Signaling ISDN User section (ISUP), so you need to complete the local signal. Teamwork.
The user signaling of ISDN is DSS1, so it is also necessary to complete the interoperability of ISDN user signaling and telephone network user access signal.
(2) Interoperability
When the user of the telephone network is called by the ISDN user, it is required that the ISDN local switch can indicate interoperability to the ISDN user, which is convenient for user communication. And require that both telephone networks or ISDN can provide users with various band signal tones.
2, ISDN and Packet Network Interoperability
When a terminal of a packet is required to communicate with another group terminal in ISDN and PSPDN, there are two ways to use: means A-circuit exchange access public packet data network (PSPDN) service; method B - packet exchange Access ISDN virtual circuit service.
The mode A is a transparent circuit exchange access connection to the access unit (Au) between the ISDN and the PSPDN. The AU has interworking, equivalent to IWF (Interworking function). This connection can be created by the user or by AU. Use the D path circuit to exchange call control programs. In this way, only the message of the user communicates only using the B path. Way B is a packet processor (pH) of ISDN to establish a packetized access connection. The implementation of the mode A is relatively easy compared to mode B.
The packet processor access point interface (PHI) is a standard interface between the PH and the switch defined by the European Telecommunications Standard Commission. The interface is based on the CCITT X.31 proposal to specify the technical specifications of the interface, support the various types of services described in X.31 suggestions, and interface signaling based on the ISDN DSS1 protocol, using 30B D structure.
3, common / dedicated ISDN interoperability
ISDN provides users with advanced network technology to provide users with advanced applications with ISDNs gradually expand in public online applications, and some ISDN private networks are also developing. Especially in certain departments and regions, the development of ISDN private networks may exceed public ISDN. At present, CCITT's recommendations for ISDNs can be used for public networks, and can also be used for private networks, so there are some principles to ensure that the utility network and private network provide compatibility function when communicating, so that users provide end-to-end connection capabilities, ie The terminal of the public network and the private network can communicate and interchange, guarantee the quality of the traffic, and ultimately provide the user to provide transparent business. CCITT I.411 recommends describing the functional division and reference configuration of the user-network interface, I.412 recommends the interface structure and reference point of the user-network interface. The figure below is divided into full communication functions through ISDN.
In the figure, the user network refers to the network connected to the public ISDN from the user side. If no user network access, S and T are in a reference point. Sometimes the user network is a dedicated system for an ISDN user switch that provides the same connection type as common ISDN. At this time, the user network in the figure should be replaced by ISPBX / dedicated ISDN.
Public ISDN and dedicated ISDN are used as the interconnect opening in the reference point T, so the protocols related to the T reference point are referred to the Q.920 Series and the Q.930 Series Specification. When public / dedicated ISDN is interoperable, public ISDN is used as the network side, and the dedicated ISDN is used as the user side. It should be noted that the interoperability of the ISDN public network and the private network is in the specific implementation, and the method of interworking is negotiated based on the specific case due to the physical structure of each private network, the signal mode, and the service characteristics.
