Một ví dụ của một giao thức kiểm soát liên kết dữ liệu có thể cư trú ở lớp này là các cấp cao của ITU Data Link Control (HDLC). Bởi vì sự phát triển của các lớp OSI ban đầu được nhắm mục tiêu hướng tới kết nối mạng diện rộng, ứng dụng của nó với các mạng khu vực địa phương yêu cầu một mức độ thay đổi. | ethernet networks 105 used at both ends of the segment. Otherwise the mixing of 10BASE-FL and FOIRL equipment reduces the maximum length of the optical segment to 1000 meters. The development of the 10BASE-FL standard was intended as a replacement for the older FOIRL specification. Unlike FOIRL that was restricted to providing an optical connection between repeaters 10BASE-FL enables an optical segment to be routed between two workstations two repeaters or between a workstation and a repeater port. The actual connection of a copper-based network node to a 10BASE-FL segment can be accomplished in one of two ways. First a stand-alone fiber-optic MAU FOMAU can be connected via the 15-pin AUI connector on a network adapter to provide an electrical-to-optical conversion capability. A second method is to use a 10BASE-T FL converter. The latter is used when only a 10BASE-T port is available on a NIC. Both the 10BASE-FL FOMAU and the 10BASE-T FL converter include two fiber-optic connectors one for transmitting and one for receiving data. Some 10BASE-T FL converters include two RJ-45 connectors that provide a high degree of cabling flexibility. One RJ-45 connector functions as a crossover cable and allows hub-to-hub communications via optical media while the second connector is for workstations that use a straight-through connection. The top portion of Figure illustrates the connection of a workstation to a 10BASE-FL FOMAU via a 15-pin AUI connector. The lower portion of that illustration shows the use of a 10BASE-T FL converter. Both devices provide you with the ability to transmit up to 2000 meters via a fiber link when a 10BASE-F-compliant optical device is at the other end of the optical link. In addition to the use of a 10BASE-FL FOMAU and 10BASE-T FL converter other types of converters have been developed to extend a fiber-optic transmission capability to other types of Ethernet networks. For example a 10BASE-2 FL converter enables you to extend the transmission
