What are the connection technologies of common WANs?

The Wide Area Network (WAN) is a cross-regional data communication network that uses infrastructure provided by telecom operators as the underlying platform for information transmission. Compared to the OSI reference model, WAN technology primarily operates at the lower three layers: the physical layer, the data link layer, and the network layer. This means it focuses on the actual transmission of data across long distances, rather than handling higher-level functions like application or session management. **First, PSTN (Dial-Up Internet)** PSTN, or the Public Switched Telephone Network, provides an analog private channel that connects various telephone exchanges. When two devices—such as hosts or routers—need to communicate through PSTN, they must both have a modem connected to the network on the user side. The PSTN modem performs analog-to-digital and digital-to-analog signal conversion. From the perspective of the OSI model, PSTN acts as an extension of the physical layer, offering no flow control, error control, or other advanced features. Additionally, since PSTN is circuit-switched, a dedicated path is reserved between the two ends for the entire duration of the connection, even if no data is being transmitted. This results in inefficient use of bandwidth. An example of network interconnection via PSTN involves connecting two LANs using the public phone network. Each local area network has a router with a serial port connected to a modem, which then links to the PSTN. This setup allows the two LANs to communicate over long distances through the PSTN infrastructure.  **Second, ISDN (Integrated Services Digital Network)** ISDN evolved from the Integrated Digital Network to offer end-to-end digital connectivity, supporting a wide range of services including voice, fax, and data. It provides users with a standardized interface to access the network, enabling multiple services such as telephone, video conferencing, and data transfer over a single line. Unlike traditional analog lines, ISDN supports digital transmission, allowing for faster and more reliable communication. It can carry voice and data simultaneously, making it ideal for applications like video calls and high-quality data transfers. ISDN also offers better call quality and stability compared to regular phone lines, especially when used for VoIP or other digital services. One of the key advantages of ISDN is its speed. At 128 kbps, it is significantly faster than dial-up modems, though slower than modern broadband technologies. However, for users who don’t need constant high-speed access, ISDN can be more cost-effective than ADSL, especially for those with limited monthly usage. It also allows for multiple simultaneous connections, making it a versatile option for small businesses or remote offices. ISDN requires a fully digital infrastructure to transmit signals composed solely of binary data (0s and 1s). This makes it more suitable for advanced digital services, such as video streaming, image transfer, and secure data communications. In Europe, ISDN was once a popular choice for both residential and business users due to its reliability and flexibility.  In addition to its primary use in telecommunications, ISDN can also refer to a set of protocols used for managing circuit-switched connections. It is also an abbreviation for a medical drug, but that’s not relevant in the context of networking. Key benefits of ISDN include: 1. **High Reliability and Quality**: Since the communication path is fully digital, noise, crosstalk, and signal distortion are minimized, leading to clearer and more stable connections. 2. **Ease of Use**: ISDN separates the information and signaling channels, allowing multiple devices to operate simultaneously over a single line. 3. **Cost-Effective for Specific Users**: For low-volume users, ISDN can be cheaper than broadband options, especially when considering usage limits and billing structures. Overall, while newer technologies like DSL and fiber have largely replaced ISDN in many regions, it played a crucial role in the transition from analog to digital communication, paving the way for modern high-speed internet services.

Schuko Surge Protector Power Strips

Schuko Surge Protector Power Strips, schuko power strip with surge protection,EU Schuko Power Strip

Yang Guang Auli Electronic Appliances Co., Ltd. , https://www.ygpowerstrips.com