ATM network structure and Interface

I. ATM Network Structure
The ATM network can be divided into three parts: Public ATM network, private ATM network, and ATM access network.
A Public ATM network is an ATM network operated and managed by the Telecommunications Management Department. It connects to a dedicated ATM network and an ATM terminal through a public user network interface. As a backbone network, the Public ATM network should be able to ensure communication with various existing networks, and should be able to support various existing services, including general telephones, A complete set of maintenance, management, and billing functions are also required. Currently, there is no commercial public ATM network, and the Protocols for Public ATM networks are constantly being improved.
A dedicated ATM network refers to an ATM network within a unit or department. Because its network size is smaller than that of a public network, it does not need to charge fees or other management procedures, therefore, the dedicated ATM network is the first practical ATM network, and new ATM devices and technologies are often used in the dedicated ATM network. At present, a private network is mainly used for LAN interconnection or directly forming an atm lan to provide high-quality multimedia services and high-speed data transmission on the LAN.
Access to the ATM network refers to the use of the ATM technology in various access networks to transmit ATM cells, such as ATM-based Passive Optical fiber networks (APON) and hybrid optical fiber coaxial (HFCs) asymmetric Digital loop (ADSL) and wireless access technology using ATM.
Ii. Main ATM Interfaces
1. UNI (User-Network Interface)
UNI is the user network interface in the ATM network. It is the interface between the user device and the network and is directly oriented to the user. The UNI interface defines the interface standard of the physical transmission line, that is, the physical line and interface that the user can use to connect to the ATM network, the ATM layer standard, UNI signaling, OAM functions, and management functions are also defined. The UNI interface can be divided into the UNI of the public network and the UNI (PUNI) of the private network according to the location of the UNI interface. The definitions of these two UNI interfaces are basically the same, but since PUNI does not have to consider strict consistency as many interfaces on the public network, PUNI has more interface forms, more flexibility, and faster development.
2. NNI (Network to Network/Network Node Interface)
NNI can be understood as a network node interface or an interface between networks or networks. It is generally an interface between two switches, just like UNI, the NNI interface also defines specifications for the physical layer and ATM layer, as well as signaling and other functions. However, because the NNI interface is related to the routing of connections in the network, therefore, the routing selection method is particularly described. Similarly, NNI interfaces are divided into public network NNI and private network NNI (PNNI). The difference between public network NNI and PNNI is quite large, for example, the public network NNI signaling is 3, 7 signaling system broadband ISDN User Part Of The B-ISUP, while PNNI is completely based on UNI interface, still using UNI signaling structure.
3. B-ICI (BISDN Inter-Carrier Interface)
The B-ICI is defined as the interface between two Public ATM networks and provides a connection for the UNI interface of the two operators respectively. Its definition is based on the NNI interface, it supports transmission of multiple services across different networks, including cell-based PVC, PVC-based frame relay, circuit simulation, SMDS, and SVC.
4. DXI (Data Exchange Interface)
DXI is defined between the digital terminal device DTE and the digital connection device DCE. DTE is connected to the DCE through DXI, and then connected to the ATM network through the atm uni interface, DCE completes the adaptation process from a data terminal that does not conform to the ATM standard to an ATM, which is equivalent to a terminal adapter.
5. FUNI (Frame Based UNI Interface)
The significance of FUNI is similar to that of DXI. FUNI completely migrates the ATM adaptation function to the switch, and transfers FUNI frames between the terminal and the ATM switch. Therefore, compared with the cell-based DXI interface, FUNI has higher efficiency on the Access Line.