Building Broadband Networks by Marlyn Kemper Littman Chapter 4: Ethernet Networks 4.9 Gigabit Ethernet Technical Fundamentals As with its Ethernet and Fast Ethernet predecessors, Gigabit Ethernet technology works in wireless and wireline environments. A multifunctional communications technology, Gigabit Ethernet significantly expands available bandwidth for enabling interactive, high-performance multimedia applications. In comparison to Fast Ethernet, Gigabit Ethernet increases the rates at which data are transmitted by a factor of ten. In contrast to its predecessor, Gigabit Ethernet employs the physical signaling scheme described in the Fibre Channel specification for enabling packet transmission. 4.9.1 Gigabit Ethernet Functions Gigabit Ethernet networks utilize the underlying infrastructure established with Ethernet and Fast Ethernet specifications. As a consequence, Gigabit Ethernet enables a straightforward migration path to higher performance levels without disrupting in-place networking operations. Generally viewed as an extension of Ethernet and Fast Ethernet, Gigabit Ethernet technology ensures seamless interworking with Ethernet and Fast Ethernet services and operations. Gigabit Ethernet also employs the same protocols, transmission schemes, frame size, frame format, flow control procedures, and access methods as Ethernet and Fast Ethernet. Therefore, the need for complex emulation and translation techniques to support migration from Ethernet and Fast Ethernet implementations to Gigabit Ethernet solutions is eliminated. 4.9.2 Gigabit Ethernet Architecture Gigabit Ethernet Physical Layer specifications support half-duplex and full-duplex operations; gigabit transmissions over two strands of optical fiber or two pairs of shielded twisted copper wires; and encoding schemes defined by the ANSI Fibre Channel standard. The network topology for Gigabit Ethernet conforms to the conventional specifications for Ethernet and Fast Ethernet. In conjunction with Ethernet and Fast Ethernet, Gigabit Ethernet employs Layer 1 or the Physical Layer and the Media Access Control (MAC) Sublayer of Layer 2 or the Data-Link Layer for information transport. Additionally, Gigabit Ethernet works in conjunction with upper layer protocols such as IP (Internet Protocol) and TCP (Transmission Control Protocol). In terms of the OSI Reference Model, IP and TCP utilize the Transport Layer or Layer 4 and the Network Layer or Layer 3 for enabling communications services between applications. 4.9.3 Gigabit Ethernet Operations Gigabit Ethernet implementation is basically a replication of deployment procedures associated with its predecessors. Moreover, in-place Ethernet and Fast Ethernet management systems and equipment function in concert with Gigabit Ethernet management systems, services, and applications, thereby enabling cost-effective migration to advanced Gigabit Ethernet solutions. Early Gigabit Ethernet implementations employed optical fiber for supporting full-duplex transmissions and facilitating building-to-building LAN interconnections. As evidenced by the ratification of the Gigabit Ethernet over copper cabling standard by the IEEE, Gigabit Ethernet also works effectively with Unshielded Twisted Pair (UTP) in delivering services to the desktop. As with previous Ethernet generations, Gigabit Ethernet is scalable and extendible, augments functions of in-place networks, and enables a broad array of applications. In the LAN arena, Gigabit Ethernet supports links between servers and switches and interconnects clusters of servers, server farms, and network segments. In addition, Gigabit Ethernet provisions high-speed connections between buildings and supports transmissions ranging from 10 Mbps to 1000 Mbps or 1 Gbps and higher rates. Moreover, Gigabit Ethernet installations are less costly than ATM in terms of implementation, operations, administration, and maintenance. It is important to note that Gigabit Ethernet and its predecessors are subject to distance and signal constraints. Transmission impairments result in attenuation or signal power loss, near-end crosstalk (NEXT), and latencies in signal transport. 4.9.4 IEEE 802.3z or Fiber Optic Gigabit Ethernet Implementations The IEEE 802.3z specification for extending Gigabit Ethernet functions into the optical fiber environment was ratified in 1998. Endorsed by the IEEE 802.3z Gigabit Ethernet Task Force, the Gigabit Ethernet Alliance, and the IEEE Standards Committee, the IEEE 802.3z standard defines Ethernet operations at rates of 1000 Mbps or 1 Gbps for half-duplex transmissions and Ethernet operations at 2000 Mbps or 2 Gbps for full-duplex transmissions. The Gigabit Ethernet IEEE 802.3z standard also clarifies capabilities of transceivers that operate in conjunction with single-mode and multimode optical fiber plants and supports ongoing utilization of in-place optical fiber links that interconnect multiple buildings in campus LANs. The role of optical components such as optical lasers in transporting data-, voice-, and video-over-optical fiber is also indicated. 4.9.4.1 Gigabit Media Independent Interface (GMII) The IEEE 802.3z specification also describes Gigabit Media Independent Interface (GMII) services. The GMII enables interconnectivity of MAC Sublayer protocol devices with the Physical Layer or Layer 1 of the OSI Reference Model. Furthermore, the GMII supports half-duplex and full-duplex transmissions, multivendor interoperability, and backward compatibility with Ethernet and Fast Ethernet installations. In addition, the GMII enables virtual independent pathways or channels for data transmission and reception. 4.10 Gigabit Ethernet Solutions Based on the work of the IEEE 802.3z Gigabit Ethernet Task Force and the Gigabit Ethernet Alliance and ratified by the IEEE, the Gigabit Ethernet standard defines network interfaces, repeater operations, topologies, and capabilities of 1000BASE-SX and 1000BASE-LX configurations. The IEEE 802.3z Gigabit Ethernet Task Force and the Gigabit Ethernet Alliance also clarify features and functions of 1000BASE-LH and 1000BASE-CX networks. 4.10.1 1000BASE-SX Based on the Fibre Channel signaling standard, 1000BASE-SX describes Gigabit Ethernet short wavelength solutions. In supporting full-duplex mode transmissions, each 1000BASE-SX network segment enables transmission via multimode optical fiber at distances that extend to 275 meters. In addition, each 1000BASE-SX network segment supports full-duplex information transport over single-mode optical fiber at distances that extend to 550 meters. 4.10.2 1000BASE-LX 1000BASE-LX describes long wavelength Gigabit Ethernet solutions. With full-duplex mode operations, each 1000BASE-LX network segment facilitates transmissions via single-mode optical fiber at distances that reach 5000 meters. In enabling full-duplex operations over multimode optical fiber, each 1000BASE-LX network segment enables voice, video, and data transport at distances that extend to 550 meters. 4.10.2.1 Differential Mode Delay (DMD) The IEEE 802.3z Gigabit Ethernet Task Force also developed a solution for reducing the adverse impact of Differential Mode Delay (DMD), a condition that generates jitter in LED (Light Emitting Diode) installations supporting transmissions via multimode optical fiber. According to this Task Force, the utilization of conditioners with 1000BASE-LX and 1000BASE-SX configurations and dispersal of light pulses evenly through every lightpath or channel in each network segment resolves DMD transmission disruptions. 4.10.3 1000BASE-LH Supported by the IEEE 802.3z Gigabit Ethernet Task Force and the Gigabit Ethernet Alliance, 1000BASE-LH defines long-haul fiber optic Gigabit Ethernet Metropolitan Area Network (MAN) solutions that operate in multivendor urban environments. 4.10.4 1000BASE-CX Developed by the IEEE 802.3z Gigabit Ethernet Task Force and the Gigabit Ethernet Alliance, 1000BASE-CX refers to Gigabit Ethernet transmission over Category 5 Unshielded Twisted Pair (UTP). Each 1000BASE-CX network segment enables full-duplex operations at distances that extend to 25 meters. 4.10.5 IEEE 802.3ab or 1000BASE-T The IEEE ratified the IEEE 802.3ab standard, also known as 1000BASE-T, in 1999. This standard is based on research efforts sponsored by the Gigabit Ethernet Alliance. To verify 1000BASE-T capabilities, tests benchmarking the performance of Gigabit Ethernet over copper wiring were conducted by Gigabit Ethernet Alliance participants, including Alteon Web System, Extreme Networks, 3Com, and Sun Microsystems, at the Silicon Valley Networking Lab (SVNL). These tests evaluated Gigabit Ethernet performance in seamlessly enabling interoperability, full-motion video, groupware applications, and remote file transfers over Category 5 UTP (Unshielded Twisted Pair). Findings contributed to IEEE endorsement of the 1000BASE-T Giga-bit Ethernet-over- copper wire specification. 1000BASE-T solutions utilize four pairs of Category 5 UTP copper wires for enabling transmissions up to 100 meters over a single network segment. Each copper pair supports throughput at 250 Mbps for enabling a total transmission of 1000 Mbps or 1 Gbps in half-duplex mode and 2000 Mbps or 2 Gbps in full-duplex mode. Because 1000BASE-T installations work in conjunction with the installed Category 5 wireline infrastructure, the need to rewire ceilings, walls, or raised floors is eliminated. 1000BASE-T is compatible with Ethernet and Fast Ethernet technologies and works in concert with 56 Kbps (Kilobits per second) modems. A high-performance networking