Overview
This section of the training is based on related topics in the Network Fundamentals section of the CCNA 200-301 exam blueprint from Cisco, which focuses on physical media trough which data moves through from source to destination. As in all other areas of information technology, there has been many advancements on the media through which data is moved and our networks over the years have had to deal with more and more data and because of these , there has been a need for faster and faster physical solutions to move the data.
Single Mode
Single mode fiber is a very thin strand of fiber glass, Single-mode fiber has a much smaller diameter core for the network cable. Single mode means, the fiber enables one type of light mode to be propagated at a time. To use this much smaller fiber-optic strand, a laser-based transmitter sends the light at a single angle through the core. The fiber small light-carrying core is about 9 micrometers (µm) in diameter. So, to better understand how thin the fiber glass is, a human hair is closer to 100 µm. The core is surrounded by a cladding that brings the overall diameter of the optical fiber to 125 µm.
Multimode Fiber
Multimode fiber permits multiple angles of light waves, called modes, to propagate through the core. multimode means the fiber can propagate multiple modes. A larger core means multiple modes or multiple rays of light can travel down the core simultaneously. The core is also surrounded by a cladding just like the single mode and that brings the overall diameter of the optical fiber to 125 µm as shown above.
The differences between single mode and multimode fiber mainly lies in;
- fiber core diameter,
- wavelength & light source,
- bandwidth,
- color sheath,
- distance and cost.
Wavelength & Light Source : Due to the large core size of multimode fiber, some low-cost light sources like LEDs and VCSELs are used in multimode fiber cables, while the single mode fiber often uses a laser or laser diodes to produce light injected into the cable.
Bandwidth: Multimode fiber bandwidth is limited at present to 28000MHz*km of OM5 fiber, while single mode fiber bandwidth is unlimited theoretically because it allows only one light mode to pass through at a time.
Color Sheath: According to the TIA-598C standard definition, for non-military applications, single mode cable is coated with yellow outer sheath, and multimode fiber is coated with orange or aqua jacket.
Single Mode vs Multimode Fiber Distance
| Fiber Optic Cable Type | Fiber Cable Distance | |||||||
|---|---|---|---|---|---|---|---|---|
| Fast Ethernet 100BA SE-FX | 1Gb Ethernet 1000BASE-SX | 1Gb Ethernet 1000BA SE-LX | 10Gb Base SE-SR | 25Gb Base SR-S | 40Gb Base SR4 | 100Gb Base SR10 | ||
| Single mode fiber | OS2 | 200m | 5,000m | 5,000m | 10km | / | / | / |
| Multimode fiber | OM1 | 200m | 275m | 550m (mode conditioning patch cable required) | / | / | / | / |
| OM2 | 200m | 550m | / | / | / | / | ||
| OM3 | 200m | 550m | 300m | 70m | 100m | 100m | ||
| OM4 | 200m | 550m | 400m | 100m | 150m | 150m | ||
| OM5 | 200m | 550m | 300m | 100m | 400m | 400m | ||
From the chart, we can see that single mode fiber distance is much longer than that of multimode fiber cables at the data rate from 1G to 10G, but OM3/OM4/OM5 multimode fiber supports a higher data rate. Because multimode optical fiber has a large core size and supports more than one light mode, its fiber distance is limited by modal dispersion which is a common phenomenon in multimode step-index fiber. While single mode fiber is not. That’s the essential difference between them. In addition, OS2 single mode fiber could support longer distances in 40G and 100G links, which is not listed in the table.
Single Mode vs Multimode Fiber Cost
“Single mode vs multimode fiber cost” is usually focused on the optical transceiver cost, system cost and installation cost. In summary, we can conclude that both single-mode optics and multimode optics have their own features. Single-mode fiber cabling system is suitable for long-reach data transmission applications and widely deployed in carrier networks, MANs while Multimode fiber cabling system has a shorter reach and is widely deployed in enterprise, data centers and LANs.
No matter which one you choose, choosing the one that best suits your network demands is an important task for every network designer.
Standards
IEEE 802 is a collection of networking standards that cover the physical and data-link layer specifications for technologies such as Ethernet and wireless. These specifications apply to local area networks (LAN) and metropolitan area networks (MAN). These days, Ethernet is NOT just made up of copper at its core, but Fiber options also now exist within the standards and this brought the advent of blazing speeds over relatively long distances. The 802 specifications Provides asynchronous networking using “carrier sense, multiple access with collision detect” (CSMA/CD) over coax, twisted-pair copper and optical fiber media.
Early Ethernet (802.3 Standard)
IEEE 802.3 family of standards defines physical interface specifications for the wired Ethernet.
IEEE 802.3z standard is called Ethernet over Fiber-Optic at 1Gbit/s and references multiple other standards. Example are 1000Base-SX (multi-mode fiber) and 1000Base-LX (multi-mode/single-mode fiber). The most commonly used standard options are 10GBase-SR, 10GBase-LR.
The first versions of Ethernet used coaxial cable to connect computers in a bus topology. Each computer was directly connected to the backbone. The early implementations of Ethernet were deployed in a low-bandwidth LAN environment where access to the shared media was managed by CSMA, and later CSMA/CD. These early versions of Ethernet were known as Thicknet, (10BASE5) and Thinnet (10BASE2). Thicknet, used a thick coaxial that allowed for cabling distances of up to 500 meters before the signal required a repeater. In addition to the Ethernet being a logical bus topology at the Data Link layer, it also used a physical bus topology as shown here. This topology became problematic as the LANs grew larger.
COAX Cables
COAX Cables —-> UTP Cables
The original thick coaxial physical media were replaced by early categories of UTP cables. Compared to the coaxial cables, the UTP cables were easier to work with, lightweight, and less expensive.
The physical topology was also changed to a star topology using hubs.
Hubs concentrate connections. In other words, they take a group of nodes and allow the network to see them as a single unit, so that, when a frame arrives at one port, it is copied to the other ports so that all the segments on the LAN receive the frame. Using the hub in this star topology increased network reliability by allowing any single cable to fail without disrupting the entire network. However, repeating the frame to all other ports did not solve the issue of collisions. Hence, the reason for the introduction of a switch which came as a replacement for the hub.