Using Fiber with Ethernet – Fundamentals of Ethernet LANs – 200-301 Study Guide

Using Fiber with Ethernet

To use fiber with Ethernet switches, you need to use a switch with either built-in ports that support a particular optical Ethernet standard, or a switch with modular ports that allow you to change the Ethernet standard used on the port. Refer back to Figure 2-8, which shows a photo of a switch with two SFP+ ports, into which you could insert any of the supported SFP+ modules. Those SFP+ ports support a variety of 10-Gbps standards like those listed in Table 2-4.

Table 2-4 ^{A Sampling of IEEE 802.3 10-Gbps Fiber Standards}

* ^{The maximum distances are based on the IEEE standards with no repeaters.}

For instance, to build an Ethernet LAN in an office park, you might need to use some multimode and single-mode fiber links. In fact, many office parks might already have fiber cabling installed for the expected future use by the tenants in the buildings. If each building was within a few hundred meters of at least one other building, you could use multimode fiber between the buildings and connect switches to create your LAN.

Note

Outside of the need to study for CCNA, if you need to look more deeply at fiber Ethernet and SFP/SFP+, check out tmgmatrix.cisco.com as a place to search for and learn about compatible SFP/SFP+ hardware from Cisco.

Although distance might be the first criterion to consider when thinking about whether to use UTP or fiber cabling, a few other tradeoffs exist as well. UTP wins again on cost, because the cost goes up as you move from UTP, to multimode, and then to single-mode, due to the extra cost for the transmitters like the SFP and SFP+ modules. UTP has some negatives, however. First, UTP might work poorly in some electrically noisy environments such as factories, because UTP can be affected by electromagnetic interference (EMI). Also, UTP cables emit a faint signal outside the cable, so highly secure networks may choose to use fiber, which does not create similar emissions, to make the network more secure. Table 2-5 summarizes these tradeoffs.

Table 2-5 ^{Comparisons Between UTP, MM, and SM Ethernet Cabling}

Sending Data in Ethernet Networks

Although physical layer standards vary quite a bit, other parts of the Ethernet standards work the same regardless of the type of physical Ethernet link. Next, this final major section of this chapter looks at several protocols and rules that Ethernet uses regardless of the type of link. In particular, this section examines the details of the Ethernet data-link layer protocol, plus how Ethernet nodes, switches, and hubs forward Ethernet frames through an Ethernet LAN.