Speed and bandwidth

By convention, network data rates are denoted either in bits (bits per second or bps) or bytes (bytes per second or Bps). In general, parallel interfaces are quoted in bytes and serial in bits.

The numbers below are simplex data rates, which might conflict with the duplex rates that vendors sometimes use in promotional materials. Where two values are listed, the first value is the downstream rate and the second value is the upstream rate.

All quoted figures are in metric decimal units:

򐂰 1 Byte = 8 bits

򐂰 1 Kbps = 1,000 bits per second

򐂰 1 Mbps = 1,000,000 bits per second

򐂰 1 Gbps = 1,000,000,000 bits per second

򐂰 1 KBps = 1,000 bytes per second

򐂰 1 MBps = 1,000,000 bytes per second

򐂰 1 GBps = 1,000,000,000 bytes per second

򐂰 1 TBps = 1,000,000,000,000 bytes per second

These figures go against the traditional use of binary prefixes for memory size. These decimal prefixes are established in data communications.

Table 4-1 lists the technology rates and the medium.

Table 4-1 Technology rates and medium

4.1.5 10 GbE

From its origin more than 25 years ago, Ethernet has evolved to meet the increasing demands of packet-based networks. Ethernet provides the benefits of proven low implementation cost, reliability, and relative simplicity of installation and maintenance. Because of these benefits, the popularity of Ethernet has grown to the point that nearly all of the traffic on the Internet originates or terminates with an Ethernet connection. Furthermore, as the demand for ever-faster network speeds has increased, Ethernet has adapted to handle these higher speeds and the surges in volume demand that accompany them.

The IEEE 802.3ae 2002 (the 10 Gigabit Ethernet (10 GbE) standard) is different in some respects from earlier Ethernet standards in that it operates only in full-duplex mode (collision-detection protocols are unnecessary).

Ethernet can now progress to 10 gigabits per second while retaining its critical Ethernet

Technology Rate (Bit/s) Rate (Byte/s) Media Fast Ethernet (100BASE-X) 100 Mb/s 12.5 MB/s UTP Cat 5 Gigabit Ethernet (1000BASE-X) 1000 Mb/s 125 MB/s UTP Cat 5e / 6 10 Gigabit Ethernet (10GBASE-X)

Chapter 4. Ethernet and system networking concepts 67

4.1.6 10 GbE copper versus fiber

Once the decision is made to implement 10 Gigabit Ethernet (10 GbE) functionality, organizations must consider the data carrying techniques that facilitate such bandwidth. Copper and fiber cabling are the preeminent technologies for data transmission and provide their own unique benefits and drawbacks.

Copper is the default standard for transmitting data between devices because of its low cost, easy installation, and flexibility. It also possesses distinct shortcomings. Copper is best when used in short lengths, typically 100 meters or less. When employed over long distances, electromagnetic signal characteristics hinder performance. In addition, bundling copper cabling can cause interference, making it difficult to employ as a comprehensive backbone. For these reasons, copper cabling is the principal data carrying technique for communication among PCs and LANs, but not campus or long-distance transmission.

Conversely, fiber cabling is typically used for remote campus connectivity, crowded telecommunications closets, long-distance communications, and environments that need protection from interference. An example of such an environment is a manufacturing area. Since it is reliable and less susceptible to attenuation, it is optimum for sending data beyond 100 meters.

However, fiber is also more costly than copper and its use is typically limited to those applications that demand it.

As a result, most organizations use a combination of copper and fiber cabling. As these companies transition to 10 GbE functionality, they must have a solid understanding of the various cabling technologies. Companies must also have a sound migration strategy to ensure that their cabling infrastructure will support their network infrastructure both today and tomorrow.

The IEEE 802.3 Higher Speed Study Group formed in 1998, and the development of

10GigE

began the following year. By 2002, the 10GigE standard was first published as

IEEE Std

802.3ae-2002

. This standard defines a normal data rate of 10 Gigabits, making it 10 times faster than the Gigabit Ethernet.

Subsequent standard updates ensued in relation to the first 10GigE version published in 2002. The IEEE 802.3ae-2002 fiber, followed by 802.3ak-2004 in 2004, were later consolidated into

IEEE 802.3-2005

in the year 2005. In 2006, 802.3an-2006, which is a 10 Gigabit Base-T copper twisted pair, and an enhanced version with fiber-LRM PMD followed, known as

802.3aq-2006

. Finally, in 2007, the

802.3ap-2007

with copper backplane evolved.

As a result of these standards, there are two main types of 10 Gigabit Ethernet cabling: fiber and copper.

The following standards pertain to the 10 Gigabit Ethernet fiber cabling:

򐂰 10GBASE-LX4: It supports ranges of 240 - 300 meters (790 - 980 ft) over traditional multi-mode cabling. This range is achieved by using four separate laser sources that operate at 3.125 Gbit/s in the range of 1300 nm on unique wavelengths. The

10GBASE-LX4 standard also supports 10 kilometers (6.2 mi) over System Management Facilities (SMF).

򐂰 10GBASE-SR: Over obsolete 62.5 micron multi-mode fiber cabling (OM1), it has a maximum range of 26 - 82 meters (85 - 269 ft), depending on the cable type. Over standard 50 µm 2000 MHz·km OM3 multi-mode fiber (MMF), it has a maximum range of 300 meters (980 ft).

򐂰 10GBASE-LR: Has a specified reach of 10 kilometers (6.2 mi), but 10GBASE-LR optical modules can often manage distances of up to 25 kilometers (16 mi) with no data loss.

򐂰 10GBASE-LRM: Supports distances up to 220 meters (720 ft) on FDDI-grade 62.5 µm MMF. This fiber was originally installed in the early 1990s for Fiber Distributed Data Interface (FDDI), 100BaseFX networks, and for 260 meters (850 ft) on OM3. The reach of 10GBASE-LRM is not as far as the older 10GBASE-LX4 standard.

򐂰 10GBASE-ER: This extended range has a reach of 40 kilometers (25 mi).

򐂰 10GBASE-ZR: Several manufacturers introduced 80 km (50 mi) range ER pluggable interfaces under the name

10GBASE-ZR

. This 80 km PHY is not specified within the IEEE 802.3ae standard. Manufacturers created their own specifications that are based upon the 80 km PHY described in the OC-192/STM-64 SDH/SONET specifications. A 10G Ethernet connection can also run over twin-ax cabling and twisted pair cabling. The following standards pertain to the 10 Gigabit Ethernet copper cabling:

򐂰 10GBASE-CX4: This was the first 10G copper standard that was published by 802.3 (as

802.3ak-2004

). It is specified to work up to a distance of 15 m (49 ft). Each lane carries 3.125 gigabaud (Gbaud) of signaling bandwidth.

򐂰 10GBASE-T or IEEE 802.3an-2006: This standard was released in 2006 to provide 10 Gbit/s connections over unshielded or shielded twisted pair cables, over distances up to 100 meters (330 ft).

The following standards pertain to the 10 Gigabit Ethernet copper backplane cabling:

򐂰 10GBASE-X

򐂰 10GBASE-KX4

򐂰 10GBASE-KR

Cables needed to carry 10GBASE-T: Category 6A, or better, of balanced twisted-pair

cables that are specified in ISO 11801 amendment 2 or ANSI/TIA-568-C.2, are needed to carry 10GBASE-T up to distances of 100 m. Category 6 cables can carry 10GBASE-T for shorter distances when qualified, according to the guidelines in ISO TR 24750 or

Chapter 4. Ethernet and system networking concepts 69

In document Introduction to Storage Area Networks (Page 85-89)