I. Current Status

The third-level and fourth-level communication networks of the XX Province Public Security Bureau have undergone multiple upgrades, from leased DDN channels and leased E1 channels from county bureaus to police stations, to a PDH 100M fiber optic communication network. With the construction of the Tianwang Project, increasing transmission bandwidth is required. The fiber optic transmission bandwidth is now being upgraded again to achieve multiple line-rate Gigabit Ethernet transmissions. Due to the confidentiality requirements of the public security private network, several Ethernet networks with different functions are required to be physically isolated and achieve line-rate 100M or 1000M.

Among the public, procuratorial, judicial, and justice organs of the political-legal system, only the Public Security Bureau has its own technical capabilities to establish its own communication system in its own equipment room. In other provinces, relying on the basic infrastructure of the Public Security Bureau, a dedicated communication network for the public, procuratorial, judicial, and justice systems is built, providing each system with its own physically isolated Ethernet system, while sharing the Ministry of Public Security internal telephone system of the political-legal system. Currently, in XX Province, apart from the public security system, other political-legal systems generally use operator VPN private networks for data transmission, which is relatively single-purpose, has weak confidentiality, and is not conducive to business expansion.

Building several systems together not only saves communication equipment rooms, communication equipment, and reduces maintenance personnel, but also enables the use of the same fiber core, saving fiber line rental costs. Generally, public, procuratorial, judicial, and justice organs at the township level are usually located in the same compound or not far apart. In 2010, the Hebei Province political-legal network organized a provincial bidding to uniformly procure equipment for municipal political-legal networks. It provided Ministry of Public Security internal telephones and telephone number resources for township judicial units, using the same exchange number for the political-legal system's local telephone service, which not only unified the external image but also facilitated centralized management. As this system was built relatively early, the transmission bandwidth generally uses a 155M SDH ring network system, leaving limited reserved bandwidth for video transmission of the Tianwang Project. Later bidding regions adopted a 622M SDH ring network system.

II. Recommended Structure for the Fourth-Level Network

In this fourth-level network upgrade, the central end is equipped with SDH ring network protection interface aggregation, and can access the public security telephone switching network and the local telephone switching network through No.1, No.7, and PRI signaling. Point-to-multipoint multi-Gigabit fiber optic access equipment is adopted for each township.

Since video big data storage, processing, and processing servers can be placed at the county bureau, and township technical capabilities are weak with limited equipment room conditions, only the county bureau to township links require multiple line-rate Gigabit network transmissions. The county bureau to city bureau uses 622M SDH ring transmission for processed video big data, as well as the public security internal network, video conferencing, etc.

The fiber optic transmission system upgraded in this XX Province Public Security fourth-level network adopts a 2.5G or 5G transmission rate, providing 2 or 4 line-rate 1000M physically isolated Ethernet channels on the fiber, meeting the high-bandwidth requirements from county bureaus to townships. This large-capacity bandwidth also provides sufficient channels for video transmission including video conferencing and video surveillance.

2.5G optical transmission has a longer transmission distance compared to 5G optical transmission. Typically, transmission distances above 5G are generally less than 10KM, and expensive optical amplifiers are required for longer distances. 2.5G, however, can typically transmit 20KM, 40KM, 60KM, etc.

Currently, each county conducts its own bidding with inconsistent technical requirements. Telephone access still uses FXO and FXS distribution frame access methods, which have high costs, multiple failure points, and low telephone switching efficiency. For example, in the Hebei Province political-legal network bidding, it was required that remote telephones be aggregated and uniformly accessed into the public security telephone access system via China No.1 signaling, and into the local operator telephone network via China No.7 signaling and PRI signaling.

Additionally, standard SDH technology can directly access the operator's telephone switching system.

In some important locations, fiber optic loop protection is also required, meaning that when one fiber break occurs on the fiber loop, all equipment can still continue communicating in a chain network. Although some locations do not use ring networks, dual optical port mutual backup is required on the fiber interface.

Providing high-definition video interfaces in fiber optic equipment is very convenient.

III. Public Security Checkpoint System

Nowadays, public security agencies across various regions have established public security convenience kiosks. These kiosks should be connected to the public security internal information network and the public security internal telephone. At the same time, to facilitate service to the public, Internet access and local telephone services should also be provided. That is, 2 physically isolated Ethernet channels and at least 2 telephone lines should be provided; some require two networks: the road surveillance network and the public security internal office network. Typically, 1 bidirectional video channel is also required for simple video conferencing.

Our company's NTD421 is a data terminal with a fiber line rate of 250M, capable of providing the above services. It can be used in point-to-point pairs, or can access the upper-level network through the GP_MPconv device. The GP_MPconv is a device that can be used standalone or inserted into our company's G3CP integrated service platform. It also provides 2 telephone line accesses and 1 RS485 channel access.

When the number of remote NTD421 units is small, access can also be achieved by inserting the GPuser card on the G3CP into the MP200 optical interface card.

Additionally, our company's GTD441 is a 2.5G fiber line device that can output two groups of line-rate Gigabit interfaces (each Gigabit group consists of 1 optical port and 1 electrical port, which can be switched), with dual optical ports supporting mutual backup; it can also form a chain network or ring network. In this case, the 2 Gigabit electrical ports and the optical port are on the same Gigabit channel and can switch with each other, while the other Gigabit channel is directly connected between the optical ports. The GTD441 also provides 4 telephone line accesses and 1 RS485 channel access.

The GTD441 can be accessed by inserting the GPuser card on the G3CP into the GP2000 optical interface card.