HP ProLiant DL185 10 Gigabit Ethernet technology for industry-standard servers - Page 5

Latency Transmission latency within networks typically has three components - time of flight, data rate, and queuing or buffer delays. Time of flight is the propagation delay across the cable, and that delay increases in a linear fashion with distance. The data rate affects how long a packet takes to complete transmission, from first bit sent to last bit received. Queuing or buffer delays increase with congestion and are an issue for all network cards, switches and routers. Older NICs and switches stored a complete packet then forwarded it to the destination port after checking the integrity. Newer 1GbE, and most 10GbE, NICs and switches now employ cut-through packet forwarding techniques which allow the beginning of the packet to be forwarded to a destination port before the remainder of the packet has been completely received by the NIC or switch. This significantly reduces latency and makes 10GbE more attractive for HPC environments. HP supported 10GbE media standards All HP supported media specifications for cable, connections, and connection modules employed in the design and construction of 10GbE networks are standards certified by IEEE. Physical medium dependent connections for 10GbE The 10GbE standard specifies various physical medium dependent (PMD) connections to different transmission media. Several versions of the10GbE standard exist, with each version specifying a different medium, media connection (PMD type), and 10GbE Transmit/Receive range for the medium. Table 1 lists the key versions of the 10GbE standard and their distinguishing attributes, summarizes the options supported, and indicates distances achieved, depending on the grade of fiber. Table 1. Cable media specification Protocol 10GBASE-SR 10GBASE-LR 10GBASE-LRM 10GBASE-KX4 10GBASE-KR 10GBASE-CX4 10GBASE-T IEEE STD 802.3ae 802.3ae 802.3aq 802.3ap 802.3ap 802.3ak 802.3an Distance 26, 33, 82, 300m 10km Media fiber fiber 220m fiber 1m 15m 15m 55m on Cat6 100m on Cat6A, 7 backplane backplane copper copper Media Specification FDDI, OM1, OM2, OM3 Single-mode fiber (SMF), 10um Multi-mode fiber (MMF), 50-62um 4-Lane Backplane 1-Lane Backplane Twinax ( IBx4 Cable ) Cat6, Cat6A UTP, Cat6-FTP, or Cat7 The physical media supported includes both copper and fiber cabling. For copper, the twin-axial copper cabling (10GBASE-CX4) specification supports a maximum of 15m (49 feet). Fiber cabling, on the other hand, supports multiple derivatives of the standard related to the different optical types required for the various WAN and LAN applications. 5