Đang chuẩn bị nút TẢI XUỐNG, xin hãy chờ
Tải xuống
Practical TCP/IP and Ethernet Networking- P18: The transmitter encodes the information into a suitable form to be transmitted over the communications channel. The communications channel moves this signal as electromagnetic energy from the source to one or more destination receivers. The channel may convert this energy from one form to another, such as electrical to optical signals, whilst maintaining the integrity of the information so the recipient can understand the message sent by the transmitter | Fast and gigabit Ethernet systems 67 4.4 4.4.1 The total one-way delay of 2.445 qs is within the required interval 2.56 qs and allows at least 5 bits safety factor so this connection is permissible. Gigabit Ethernet 1000Base-T Gigabit Ethernet summary Gigabit Ethernet uses the same 802.3 frame format as 10 Mbps and 100 Mbps Ethernet systems. This operates at ten times the clock speed of Fast Ethernet at IGbps. By retaining the same frame format as the earlier versions of Ethernet backward compatibility is assured with earlier versions increasing its attractiveness by offering a high bandwidth connectivity system to the Ethernet family of devices. Gigabit Ethernet is defined by the IEEE 802.3z standard. This defines the gigabit Ethernet media access control MAC layer functionality as well as three different physical layers 1000Base-LX and 1000Base-SX using fiber and 1000Base-CX using copper. These physical layers were originally developed by IBM for the ANSI Fiber channel systems and used 8B 10B encoding to reduce the bandwidth required to send high-speed signals. The IEEE merged the fiber channel to the Ethernet MAC using a gigabit media independent interface GMII which defines an electrical interface enabling existing fiber channel PHY chips to be used and enabling future physical layers to be easily added. 1000Base-T is being developed to provide service over four pairs of category 5 or better copper cable. As discussed earlier this uses the same technology as 100Base-T2. This development is defined by the IEEE 802.3ab standard. These gigabit Ethernet versions are summarized in Figure 4.5. IEEE 802 3z standard IEEE 802 3ab standard Figure 4.5 Gigabit Ethernet versions 4.4.2 Gigabit Ethernet MAC layer Gigabit Ethernet retains the standard 802.3 frame format however the CSMA CD algorithm has had to undergo a small change to enable it to function effectively at 1 Gbps. The slot time of 64 bytes used with both 10 Mbps and 100 Mbps systems has been increased to 512 .
