1.3 Network Technologies
Various network technologies can be used to establish network connections, including Ethernet, Fiber Distribution Data Interface (FDDI), Token Ring, and Asynchronous Transfer Mode (ATM). Of these, Ethernet is by far the most popular choice in installed networks because of its low cost, availability, and scalability to higher bandwidths.
1.3.1 Ethernet
Ethernet is based on the Institute of Electrical and Electronics Engineers (IEEE) standard IEEE 802.3 and offers a bandwidth of 10 Mbps between end users. Ethernet is based on the carrier sense multiple access collision detect (CSMA/CD) technology, which requires that transmitting stations back off for a random period of time when a collision occurs.
Coaxial cable was the first media system specified in the Ethernet standard. Coaxial Ethernet cable comes in two major categories: Thicknet (10Base5) and Thinnet (10Base2). These cables differed in their size and their length limitation. Although Ethernet coaxial cable lengths can be quite long, they are susceptible to electromagnetic interference (EMI) and eavesdropping.
Coaxial Cable for Ethernet
|
Cable |
Diameter |
Resistance |
Bandwidth |
Length |
|---|---|---|---|---|
|
Thinnet (10Base2) |
10 mm |
50 ohms |
10 Mbps |
185 m |
|
Thicknet (10Base5) |
5 mm |
50 ohms |
10 Mbps |
500 m |
Most wired networks use twisted-pair media for connections to the desktop. Twisted-pair also comes in two major categories: Unshielded twisted-pair (UTP) and Shielded twisted-pair (STP). One pair of insulated copper wires twisted about each other forms a twisted-pair. The pairs are twisted top reduce interference and crosstalk. Both STP and UTP suffer from high attenuation, therefore these lines are usually restricted to an end-to-end distance of 100 meters between active devices. Furthermore, these cables are sensitive to EMI and eaves dropping. Most networks use 10BaseT UPT cable.
An alternative to twisted-pair cable is fiber optic cable (10BaseFL), which transmits light signals, generated either by light emitting diodes (LEDs) or laser diodes (LDs), instead of electrical signals. These cables support higher transmission speeds and longer distances but are more expensive. Because they do not carry electrical signals, fiber optic cables are immune to EMI and eavesdropping. They also have low attenuation which means they can be used to connect active devices that are up to 2 km apart. However, fiber optic devices are not cost effective while cable installation is complex.
Twisted-Pair and Fiber Optic Cable for Ethernet
|
Cable |
Technology |
Bandwidth |
Cable Length |
|---|---|---|---|
|
Twisted-Pair |
(10BaseT) |
10 Mbps |
100 m |
|
Fiber Optic |
(10BaseFL) |
10 Mbps |
2,000 m |
1.3.2 Fast Ethernet
Fast Ethernet operates at 100 Mbps and is based on the IEEE 802.3u standard. The Ethernet cabling schemes, CSMA/CD operation, and all upper-layer protocol operations have been maintained with Fast Ethernet. Fast Ethernet is also backward compatible with 10 Mbps Ethernet. Compatibility is possible because the two devices at each end of a network connection can automatically negotiate link capabilities so that they both can operate at a common level. This negotiation involves the detection and selection of the highest available bandwidth and half-duplex or full-duplex operation. For this reason, Fast Ethernet is also referred to as 10/100 Mbps Ethernet.
Cabling for Fast Ethernet can be either UTP or fiber optic. Specifications for these cables are shown below
Fast Ethernet Cabling and Distance Limitations
|
Technology |
Wiring Type |
Pairs |
Cable Length |
|---|---|---|---|
|
100BaseTX |
EIA/TIA Category 5 UTP |
2 |
100 m |
|
100BaseT2 |
EIA/TIA Category 3,4,5 UTP |
2 |
100 m |
|
100BaseT4 |
EIA/TIA Category 3,4,5 UTP |
4 |
100 m |
|
100BaseFX |
Multimode fiber (MMF) with 62.5 micron core; 1300 nm laser |
1 |
400 m (half-duplex) 2,000 m (full-duplex) |
|
Single-mode fiber (SMF) with 62.5 micron core; 1300 nm laser |
1 |
10,000 m |
1.3.3 Gigabit Ethernet
Gigabit Ethernet is an escalation of the Fast Ethernet standard using the same IEEE 802.3 Ethernet frame format. Gigabit Ethernet offers a throughput of 1,000 Mbps (1 Gbps). Like Fast Ethernet, Gigabit Ethernet is compatible with earlier Ethernet standards. However, the physical layer has been modified to increase data transmission speeds: The IEEE 802.3 Ethernet standard and the American National Standards Institute (ANSI) X3T11 FibreChannel. IEEE 802.3 provided the foundation of frame format, CSMA/CD, full duplex, and other characteristics of Ethernet. FibreChannel provided a base of high-speed ASICs, optical components, and encoding/decoding and serialization mechanisms. The resulting protocol is termed IEEE 802.3z Gigabit Ethernet.
Gigabit Ethernet supports several cabling types, referred to as 1000BaseX. The table below lists the cabling specifications for each type.
Gigabit Ethernet Cabling and Distance Limitations
Technology |
Wiring Type |
Pairs |
Cable Length |
|---|---|---|---|
|
1000BaseCX |
Shielded Twisted Pair (STP) |
1 |
25 m |
|
1000BaseT |
EIA/TIA Category 5 UTP |
4 |
100 m |
|
1000BaseSX |
Multimode fiber (MMF) with 62.5 micron core; 850 nm laser |
1 |
275 m |
|
Multimode fiber (MMF) with 50 micron core; 1300 nm laser |
1 |
550 m |
|
|
1000BaseLX/LH |
Multimode fiber (MMF) with 62.5 micron core; 1300 nm laser |
1 |
550 m |
|
Single-mode fiber (SMF) with micron core; 1300 nm laser |
1 |
550 m |
|
|
Single-mode fiber (SMF) with micron core; 1300 nm laser |
1 |
10 km |
|
|
1000BaseZX |
Single-mode fiber (SMF) with micron core; 1550 nm laser |
1 |
70 km |
|
Single-mode fiber (SMF) with micron core; 1550 nm laser |
1 |
100 km |