The practical application of optical fibers in various optical networks determines the requirements for the technical performance of optical fibers. For short-distance optical transmission networks, the focus is on multimode fibers suitable for laser transmission and wider mode bandwidths to support larger serial signal information transmission capacity. The following is an introduction to the three current network technologies:
1: FDDI/CDDI (fiber/copper wire distributed data interface)
This is a mature, non-carrier sense, 100M bandwidth sharing network technology. The token passing service strategy is adopted, and the main ring and the secondary ring are connected between the network devices, and it has a strong self-reconfiguration capability when the network line or network device fails. At the same time its station management (SMT) function is very powerful, suitable for the backbone network. However, its technical difficulty is high, the price is high, the expansibility is poor, and it is a ring wiring, which is not compatible with ATM.
2: ATM (Asynchronous Transfer Mode)
This is an advanced asynchronous mode based on optical fiber transmission system, applying statistical multiplexing technology and using short cell switching technology. It directly supports multimedia transmission such as data, video, and audio. The rate is quite fast (reaching 155M, 622M). Due to the asynchronous mode, the total efficiency is quite high, and it is more suitable for the backbone grid. But it is still a controversial technology, many standards have yet to be perfected, and the interoperability and commonality between products from different manufacturers needs to be further improved.
3: FASTETHERNET (Fast Ethernet)
Today's high-speed Ethernet technologies generally include two: 100MVG-ANYLAN and 100M-T. The main discussion here is the latter - fast switched Ethernet. Although 100MAG-ANYLAN provides multimedia functions, its poor compatibility, high price and high complexity are not considered here. 100BASE-T is an improved variant of 10BASE-T. On the basis of the original, it divides the grid into several network segments, divides the collision domain, and adopts buffer switching, which greatly improves the transmission rate and transmission efficiency on the grid.
Fast Ethernet is practical (compatible with the original Ethernet, rich in software and hardware), advanced (fast speed - 100MBPS), easy to upgrade (convenient to convert to ATM or faster grid), and good scalability (through interconnecting equipment , switches, routers are easy to expand), good openness (software and hardware protocols are open), cheap (compared to ATM, FDDI), and supported by many manufacturers (supported by Intel, Sun, 3com, Bay, Accton and other big companies) Features. For multimedia grid applications, Fast Ethernet can also meet the requirements very well.
Although the effective distance between the grid devices of Ethernet is short (100 meters), it is suitable for small local area networks at the departmental level, but the transmission distance can be extended by using a fiber optic converter and an optical fiber. Fast Ethernet has excellent extensibility, using switching hubs and common hubs, the expansion of the number of users has no effect on the grid (it can be expanded when in use), which is convenient for future subnet access.
Network Cabling Technology
Based on the above analysis, combined with the main points of the integrated wiring system and grid technology, three integrated wiring schemes are provided here.
1. Adopt the full twisted pair structure wiring scheme (Fast Ethernet technology)
This scheme is that the entire wiring system (vertical subsystem, horizontal subsystem, work area subsystem, equipment room subsystem, wiring room subsystem) all adopts five types of twisted pair, and the network technology adopts Fast Ethernet technology.
Advantages: low cost of wiring, low cost of grid equipment, convenient management, fairly mature Fast Ethernet technology, and its switching is carried out at the second layer without manual intervention.
Disadvantages: If the floor is high, this may cause the wiring length of some residences to exceed 100 meters. As we all know, according to the wiring principle, the twisted pair is generally not allowed to exceed 100 meters, which will cause signal attenuation and even distortion. Secondly, since all the wiring is radiated from the central computer room to other floors through the vertical subsystem, the requirements for the shaft are relatively high. The second is that the full twisted pair structure is difficult to upgrade to ATM technology or Gigabit Ethernet technology. ATM technology and Gigabit Ethernet technology need to use single-mode/multi-mode fiber to connect to form the backbone.
2. Adopt the wiring scheme (ATM technology) with the vertical backbone formed by optical fiber and twisted pair as the edge
The vertical subsystem of this scheme adopts optical fiber structure, and other subsystems adopt five types of twisted pair wiring, and the network technology is ATM technology.
Advantages: First of all, the wiring cost is cheaper (compared with the scheme 1, it is only slightly higher). Secondly, the vertical subsystem is greatly simplified. It only needs to radiate optical fibers from the central computer room to other floors. Each floor is allocated an optical fiber (preferably with a backup line), and five types of twisted pair wiring are used in each floor. The time complexity of wiring And the space complexity is greatly reduced, and the problem of the 100-meter length limit no longer exists, because the fiber is not limited by the short distance (single-mode 15 kilometers, multi-mode 1.5-2 kilometers). The second step is to use the advanced ATM switching technology directly, which will greatly improve the response speed of the network.
Disadvantages: Mainly network equipment and host equipment are quite expensive. Due to the adoption of ATM advanced switching technology, corresponding ATM switches, ATM emulation bridges, and ATM adapters must be configured. These devices are extremely expensive. Moreover, ATM switches need to be managed by special personnel. Based on the current technology, the switching function of ATM cannot be fully automatic, but it needs to work according to the parameters set by people, and the management is subject to certain restrictions.
Considering the advantages and disadvantages of the first and second options, the third option is proposed here.
3. Adopt the cabling scheme with optical fiber as the vertical backbone and twisted pair as the edge (Fast Ethernet technology)
That is, adopt the network technology of scheme one and the wiring method of scheme two. Optical fiber is used in the vertical subsystem, and five types of twisted pairs are used for other subsystems. The network technology uses Fast Switched Ethernet.
Advantages: low cost of wiring; reasonable cost of network equipment; no special configuration for host equipment; easy to upgrade. And Ethernet switching technology does not require human intervention. The automatic exchange is implemented, and the management is convenient. In addition, when it is necessary to upgrade to ATM or Gigabit Ethernet technology, only the network equipment needs to be replaced, and there is no need to replace the wiring equipment, which truly achieves the goal of "one-time wiring, lifetime use". However, when the system needs to be upgraded, some network devices must be replaced.
