full duplex simultaneously. That is the transmission and reception of data happens in both directions on the same wire at the same time. As might be expected, this results in a permanent collision on the wire pairs. These collisions result in complex voltage patterns. With the complex integrated circuits using techniques such as echo cancellation, Layer 1 Forward Error Correction (FEC), and prudent selection of voltage levels, the system achieves the 1Gigabit throughput. In idle periods there are nine voltage levels found on the cable, and during data transmission periods there are 17 voltage levels found on the cable. With this large number of states and the effects of noise, the signal on the wire looks more analog than digital. Like analog, the system is more susceptible to noise due to cable and termination problems. The data from the sending station is carefully divided into four parallel streams, encoded, transmitted and detected in parallel, and then reassembled into one received bit stream. Figure represents of the simultaneous full duplex on four-wire pairs. 1000BASE-T supports both half-duplex as well as full-duplex operation. The use of full-duplex 1000BASE-T is widespread. Web Links 1000BASE-T Delivering Gigabit Intelligence on Copper Infrastructure http://www.cisco.com/en/US/tech/tk389/ tk214/ tech_ digest09186a0080091a86.html
Content 7.2 Gigabit and 10-Gigabit Ethernet 7.2.3 1000BASE-SX and LX The IEEE 802.3 standard recommends that Gigabit Ethernet over fiber be the preferred backbone technology. The timing, frame format, and transmission are common to all versions of 1000 Mbps. Two signal-encoding schemes are defined at the physical layer. The 8B/ 10B scheme is used for optical fiber and shielded copper media, and the pulse amplitude modulation 5 (PAM5) is used for UTP. 1000BASE-X uses 8B/10B encoding converted to non-return to zero (NRZ) line encoding. NRZ encoding relies on the signal level found in the timing window to determine the binary value for that bit period. Unlike most of the other encoding schemes described, this encoding system is level driven instead of edge driven. That is the determination of whether a bit is a zero or a one is made by the level of the signal rather than when the signal changes levels. The NRZ signals are then pulsed into the fiber using either short-wavelength or long-wavelength light sources. The short-wavelength uses an 850 nm laser or LED source in multimode optical fiber (1000BASE-SX). It is the lower-cost of the options but has shorter distances. The long-wavelength 1310 nm laser source uses either single-mode or multimode optical fiber (1000BASE-LX). Laser sources used with single-mode fiber can achieve distances of up to 5000 meters. Because of the length of time to completely turn the LED or laser on and off each time, the light is pulsed using low and high power. A logic zero is represented by low power, and a logic one by high power. The Media Access Control method treats the link as point-to-point. Since separate fibers are used for transmitting (Tx) and receiving (Rx) the connection is inherently full duplex. Gigabit Ethernet permits only a single repeater between two stations. Figure is a 1000BASE Ethernet media comparison chart. Interactive Media Activity Drag and Drop: Comparison of Gigabit Ethernet Media After completing this activity, the student will be able to identify the differences in gigabit Ethernet media. Interactive Media Activity Checkbox: Fiber Versions of Gigabit Ethernet After completing this activity, the student will be able to identify Gigabit Ethernet on Fiber. Web Links Introduction to Gigabit Ethernet http://www.cisco.com/en/US/tech/tk389/ tk214/tech_brief09186a0080091a8a.html
Content 7.2 Gigabit and 10-Gigabit Ethernet 7.2.4 Gigabit Ethernet architecture The distance limitations of full-duplex links are only limited by the medium, and not the round-trip delay. Since most Gigabit Ethernet is switched, the values in Figures and are the practical limits between devices. Daisy-chaining, star, and extended star topologies are all allowed. The issue then becomes one of logical topology and data flow, not timing or distance limitations. A 1000BASE-T UTP cable is the same as 10BASE-T and 100BASE-TX cable, except that link performance must meet the higher quality Category 5e or ISO Class D (2000) requirements. Modification of the architecture rules is strongly discouraged for 1000BASE-T. At 100 meters, 1000BASE-T is operating close to the edge of the ability of the hardware to recover the transmitted signal. Any cabling problems or environmental noise could render an otherwise compliant cable inoperable even at distances that are within the specification. It is recommended that all links between a station and a hub or switch be configured for Auto-Negotiation to permit the highest common performance. This will avoid accidental misconfiguration of the other required parameters for proper Gigabit Ethernet operation. Web Links Gigabit Networking Gigabit Ethernet Solutions http://www.cisco.com/en/US/tech/tk389/ tk214/ technologies_white_ paper09186a0080092951.shtml
Content 7.2 Gigabit and 10-Gigabit Ethernet 7.2.5 10-Gigabit Ethernet IEEE 802.3ae was adapted to include 10 Gbps full-duplex transmission over fiber optic cable. The basic similarities between 802.3ae and 802.3, the original Ethernet are remarkable. This 10-Gigabit Ethernet (10GbE) is evolving for not only LANs, but also MANs, and WANs. With the frame format and other Ethernet Layer 2 specifications compatible with previous standards, 10GbE can provide increased bandwidth needs that are interoperable with existing network infrastructure. A major conceptual change for Ethernet is emerging with 10GbE. Ethernet is traditionally thought of as a LAN technology, but 10GbE physical layer standards allow both an extension in distance to 40 km over single-mode fiber and compatibility with synchronous optical network (SONET) and synchronous digital hierarchy (SDH) networks. Operation at 40 km distance makes 10GbE a viable MAN technology. Compatibility with SONET/SDH networks operating up to OC-192 speeds (9.584640 Gbps) make 10GbE a viable WAN technology. 10GbE may also compete with ATM for certain applications. To summarize, how does 10GbE compare to other varieties of Ethernet? The basic standard governing CSMA/CD is IEEE 802.3. An IEEE 802.3 supplement, entitled 802.3ae, governs the 10GbE family. As is typical for new technologies, a variety of implementations are being considered, including: The IEEE 802.3ae Task force and the 10-Gigabit Ethernet Alliance (10 GEA) are working to standardize these emerging technologies. 10-Gbps Ethernet (IEEE 802.3ae) was standardized in June 2002. It is a full-duplex