Cables

Multimode, 50- and 62.5-micron cable.
Multimode cable has a large-diameter core and multiple pathways of light. It comes in two core sizes: 50-micron and 62.5-micron.

Multimode fiber optic cable can be used for most general data and voice fiber applications, such as bringing fiber to the desktop, adding segments to an existing network, and in smaller applications such as alarm systems. Both 50- and 62.5-micron cable feature the same cladding diameter of 125 microns, but 50-micron fiber cable features a smaller core (the light-carrying portion of the fiber).

Although both can be used in the same way, 50-micron cable is recommended for premise applications (backbone, horizontal, and intrabuilding connections) and should be considered for any new construction and installations. Both also use either LED or laser light sources. The big difference between the two is that 50-micron cable provides longer link lengths and/or higher speeds, particularly in the 850-nm wavelength.

Single-mode, 8–10-micron cable.
Single-mode cable has a small, 8–10-micron glass core and only one pathway of light. With only a single wavelength of light passing through its core, single-mode cable realigns the light toward the center of the core instead of simply bouncing it off the edge of the core as multimode does.

Single-mode cable provides 50 times more distance than multimode cable. Consequently, single-mode cable is typically used in long-haul network connections spread out over extended areas, including cable television and campus backbone applications. Telcos use it for connections between switching offices. Single-mode cable also provides higher bandwidth, so you can use a pair of single-mode fiber strands full-duplex for up to twice the throughput of multimode fiber.

Specification comparison:

50-/125-Micron Multimode Fiber

850-nm Wavelength:
Bandwidth: 500 MHz/km;
Attenuation: 3.5 dB/km;
Distance: 550 m;

1300-nm Wavelength:
Bandwidth: 500 MHz/km;
Attenuation: 1.5 dB/km;
Distance: 550 m

62.5-/125-Miron Multimode Fiber

850-nm Wavelength:
Bandwidth: 160 MHz/km;
Attenuation: 3.5 dB/km;
Distance: 220 m;

1300-nm Wavelength:
Bandwidth: 500 MHz/km;
Attenuation: 1.5 dB/km;
Distance: 500 m

8–10-Micron Single-Mode Fiber

Premise Application:
Wavelength: 1310 nm and 1550 nm;
Attenuation: 1.0 dB/km;

Outside Plant Application:
Wavelength: 1310 nm and 1550 nm;
Attenuation: 0.1 dB/km

What is Fibre Channel?
Fibre Channel is a set of communication standards designed to provide high-speed data transfer over a duplex, serial interface. It’s an open standard that supports multiple protocols including higher-level protocols, such as FDDI, SCSI, HIPPI, and IPI, to manage data transfer.

Although it operates at a range of 133 Mbps to 4 Gbps, Fibre Channel is most commonly used at speeds of 1 or 2 Gbps. A working standards group recently announced that 10-Gbps speeds are expected in soon.

Why is it called Fibre Channel?
Originally, Fibre Channel was designed to support only fiber. When copper was added, the International Standards Organization (ISO) task force changed the spelling of fiber to fibre instead of renaming the technology.

Fibre Channel history.
Fibre Channel was first developed in 1988, and the American National Standards Institute (ANSI) formed a committee in 1989. To ensure interoperability, IBM®, Hewlett-Packard®, and Sun Microsystems® formed the FCSI (Fibre Channel Systems Initiative), a temporary organization, in 1992. FCSI later dissolved, and development was handed over to the FCA (Fibre Channel Association) in 1994. ANSI accepted Fibre Channel as a standard in 1994.

The best of both worlds.
This hardware-based standard combines the best of both channel and network communication methods into one I/O interface. It takes advantage of hardware-intensive, quicker point-to-point channel links that offer low overhead, such as SCSI bus technology, as well as the broad connectivity and long-distance benefits of software-intensive network technology.

Where Fibre Channel is used.
Fibre Channel is used to transfer large amounts of data quickly between supercomputers, mainframes, workstations, desktop computers, storage devices, displays, and other peripherals.

Fibre Channel offers reliability, scalability, congestion-free data flow, Gigabit bandwidth, compatibility with multiple topologies and protocols, flow control, self management, hot pluggability, speed, cost efficiency, loop resiliency, and distance. This makes it ideal for large data operations such as Internet/intranets, data warehousing, networked storage, integrated audio/video, real-time computing, on-line services, and imaging.

The most popular application for this technology right now is Storage Area Networks (SANs). Independent methods of centralized storage management within a SAN (e.g., RAID, tape backup or library, CD-ROM library) run more efficiently with a Fibre Channel backbone.

Fibre Channel topologies.
Fibre Channel can be connected by three methods. In all cases, the topology of the network is transparent to the attached devices.

Point to point is the simplest topology, which uses simple bidirectional links between two connected devices.

Arbitrated loop is the most common topology and the most complex. It is distributed, connecting up to 126 devices across shared media, and it offers shared bandwidth. Two ports on the loop establish a point-to-point, full-duplex connection through arbitration among all ports.

The cross-point or fabric-switched topology uses 24-bit addressing to connect up to 2 (to the 24th) devices in a cross-point switched configuration. This enables many devices to communicate at the same time and does not require shared media.

Fibre Channel layers.
Fibre Channel protocol is divided into five hierarchical layers: The three bottom layers, FC-0–FC-2, define the physical transmission standard. Layers FC-3 and FC-4 address interfaces with other network protocols.

FC-0: Media and interface layer that defines the physical link.

FC-1: Transmission encode/decode layer. Information is encoded 8 bits at a time into a 10-bit transmission character (8B/10B from IBM).

FC-2: Signaling protocol layer that serves as the transport mechanism performing basic signaling and framing. FC-2 includes the following classes of service:
• Class 1 provides dedicated connections. Intermix is an optional type of Class 1 service in which Class 1 frames are guaranteed a special amount of bandwidth.
• Class 2 is a frame-switched, connectionless service, also known as multiplex. It guarantees delivery and confirms receipt of traffic.
• Class 3 is a one-to-many, connectionless, frame-switched service. It’s similar to Class 2 except it uses buffer-to-buffer flow control and does not confirm frame delivery.

FC-3: Common-services layer that provides common services required for advanced features such as striping, hunt groups, and multicast.

FC-4: Upper layer for protocol mapping of network and channel data transmitting concurrently over the same physical interface.

Fibre Channel media.
Fibre Channel runs at up to 1 Gbps over copper or fiber, but for higher speeds, fiber is required. Copper-wire cable can be video coax, miniature coax, or, most commonly, shielded twisted pair with a DB9 or HSSDC connector. Fiber choices include 62.5- or 50-µm multimode and 7- or 9-µm single-mode fiber, all with an SC connector.

Other Fibre Channel equipment includes disk enclosures, drivers, extenders, hubs, interface converters, host bus adapters, routers, switches, and SCSI bridges.

Smart Serial is the Cisco router interface. It uses a space-saving 26-pin connector that automatically detects RS-232, RS-449, RS-530, X.21, and V.35 interfaces for both DTE and DCE devices based on the type of cable used.

Smart Serial connectors can be found on Smart Serial cables and on the dual-serial-port WAN interface cards used in Cisco 2600 and 1720 series routers. The cables feature a Smart Serial connector on one end and a standard cable connector (such as DB25 or V.35) on the other end. The Smart Serial connector attaches to the dual-serial-port WAN interface card.

Each port on the WAN interface card features a Smart Serial connector. Ports can be configured independently to support two different physical interfaces. For example, you can run RS-232 cable to one port and RS-449 cable to the other port using a single WAN interface card.

What if you need to replace that RS-232 cable with V.35 cable? Just plug a Smart Serial–V.35 cable into the port. Because any Smart Serial connector on the WAN interface card attaches to any Smart Serial cable connector, no additional interface or adapter is necessary. Changing the configuration of your network is literally a snap!

The background
As today’s networks expand, the demand for more bandwidth and greater distances increases. Gigabit Ethernet and the emerging 10 Gigabit Ethernet are becoming the applications of choice for current and future networking needs. Thus, there is a renewed interest in 50-micron fiber optic cable.

First used in 1976, 50-micron cable has not experienced the widespread use in North America that 62.5-micron cable has.

To support campus backbones and horizontal runs over 10-Mbps Ethernet, 62.5 fiber, introduced in 1986, was and still is the predominant fiber optic cable because it offers high bandwidth and long distance.

One reason 50-micron cable did not gain widespread use was because of the light source. Both 62.5 and 50-micron fiber cable can use either LED or laser light sources. But in the 1980s and 1990s, LED light sources were common. Since 50-micron cable has a smaller aperture, the lower power of the LED light source caused a reduction in the power budget compared to 62.5-micron cable—thus, the migration to 62.5-micron cable. At that time, laser light sources were not highly developed and were rarely used with 50-micron cable—mostly in research and technological applications.

Common ground
The cables share many characteristics. Although 50-micron fiber cable features a smaller core, which is the light-carrying portion of the fiber, both 50- and 62.5-micron cable use the same glass cladding diameter of 125 microns. Because they have the same outer diameter, they’re equally strong and are handled in the same way. In addition, both types of cable are included in the TIA/EIA 568-B.3 standards for structured cabling and connectivity.

As with 62.5-micron cable, you can use 50-micron fiber in all types of applications: Ethernet, FDDI, 155-Mbps ATM, Token Ring, Fast Ethernet, and Gigabit Ethernet. It is recommended for all premise applications: backbone, horizontal, and intrabuilding connections, and it should be considered especially for any new construction and installations. IT managers looking at the possibility of 10 Gigabit Ethernet and future scalability will get what they need with 50-micron cable.

Gaining ground
The big difference between 50-micron and 62.5-micron cable is in bandwidth. The smaller 50-micron core provides a higher 850-nm bandwidth, making it ideal for inter/intrabuilding connections. 50-micron cable features three times the bandwidth of standard 62.5-micron cable. At 850-nm, 50-micron cable is rated at 500 MHz/km over 500 meters versus 160 MHz/km for 62.5-micron cable over 220 meters.

Fiber Type: 62.5/125 µm
Minimum Bandwidth (MHz-km): 160/500
Distance at 850 nm: 220 m
Distance at 1310 nm: 500 m

Fiber Type: 50/125 µm
Minimum Bandwidth (MHz-km): 500/500
Distance at 850 nm: 500 m
Distance at 1310 nm: 500 m

As we move towards Gigabit Ethernet, the 850-nm wavelength is gaining importance along with the development of improved laser technology. Today, a lower-cost 850-nm laser, the Vertical-Cavity Surface-Emitting Laser (VCSEL), is becoming more available for networking. This is particularly important because Gigabit Ethernet specifies a laser light source.

Other differences between the two types of cable include distance and speed. The bandwidth an application needs depends on the data transmission rate. Usually, data rates are inversely proportional to distance. As the data rate (MHz) goes up, the distance that rate can be sustained goes down. So a higher fiber bandwidth enables you to transmit at a faster rate or for longer distances. In short, 50-micron cable provides longer link lengths and/or higher speeds in the 850-nm wavelength. For example, the proposed link length for 50-micron cable is 500 meters in contrast with 220 meters for 62.5-micron cable.

Migration
Standards now exist that cover the migration of 10-Mbps to 100-Mbps or 1 Gigabit Ethernet at the 850-nm wavelength. The most logical solution for upgrades lies in the connectivity hardware. The easiest way to connect the two types of fiber in a network is through a switch or other networking “box.“ It is not recommended to connect the two types of fiber directly.

There are three main types of digital video interfaces: P&D, DFP, and DVI. P&D (Plug & Display, also known as EVC), the earliest of these technologies, supports both digital and analog RGB connections and is now used primarily on projectors. DFP (Digital Flat-Panel Port) was the first digital-only connector on displays and graphics cards; it’s being phased out.

There are different types of DVI connectors: DVI-D, DVI-I, DVI-A, DFP, and EVC.

DVI-D is a digital-only connector. DVI-I supports both digital and analog RGB connections. Some manufacturers are offering the DVI-I connector type on their products instead of separate analog and digital connectors. DVI-A is used to carry an analog DVI signal to a VGA device, such as a display. DFP, like DVI-D, was an early digital-only connector used on some displays; it’s being phased out. EVC (also known as P&D) is similar to DVI-I only it’s slightly larger in size. It also handles digital and analog connections, and it’s used primarily on projectors.

All these standards are based on transition-minimized differential signaling (TMDS). In a typical single-line digital signal, voltage is raised to a high level and decreased to a low level to create transitions that convey data. TMDS uses a pair of signal wires to minimize the number of transitions needed to transfer data. When one wire goes to a high-voltage state, the other goes to a low-voltage state. This balance increases the data-transfer rate and improves accuracy.