Hardware Concepts Chapter 4

Contents Explain the different types of network topology Describe the different types of network cabling Describe and distinguish between the 802.2, 802.3, 802.5, and 802.11 IEEE networking standards

Topology

Topology A topology describes how computers connect to each other

Types of Topologies Bus Ring Star Mesh All computers connect via a main line, called a bus cable Ring All computers attach to a central ring of cable Star All computers connect to a central wiring point, usually a hub Mesh Each computer has a dedicated line to every other computer Exam Tip Make sure you know your topologies.

Types of Topologies Tech Tip A mesh topology is very robust but not practical For just 10 computers, it would take 45 cables for every PC to connect to every other PC With a wireless network radio waves are used instead of actual cables A true mesh topology may be used

Network Technologies A network technology is a practical application of a topology to get data from one computer or network to another Ethernet Token Ring FDDI Tech Tip Logical vs. Physical Topology The physical topology describes how the cables are actually connected to the devices on the network The logical topology describes how data actually flows in the network

Bus Topology Ethernet was the first network technology that used the bus topology Each computer on the network is connected to the single cable

Bus Topology If there is a break in the cable, the entire network would stop functioning It has no fault tolerance to survive a problem Fault tolerance refers to a system’s capability to continue functioning even when some part of the system has failed. When bad things happen, a robust or fault tolerant system continues to operate, at least to some degree.

Star Topology Each computer is connected to a central device such as a hub If a cable breaks only the one computer is affected A good way to separate logical from physical is to think about an electronic schematic. The schematic shows how everything connects, but does not represent the way the piece of electronics will actually physically appear.

Star Bus Topology A star bus topology is a hybrid topology Uses a physical star topology Uses a logical bus topology Most common topology used today

Token Ring Topology Token ring uses a star ring topology Uses a physical star topology Uses a logical ring topology Declining in popularity

Cabling

Coax Coaxial cable (or coax) contains a central conductor wire, surrounded by an insulating material, which in turn is surrounded by a braided metal shield The braided metal shield lessens electro-magnetic interference (EMI). EMI will corrupt the signal flowing through the cable causing interference. EMI is caused by things like lights, fans, copy machines, and refrigerators.

EMI Electro-magnetic interference (EMI) is caused by lights, fans, copy machines, and other devices EMI corrupts the signal flowing through the cable The braided shield helps to reduce the effects of EMI

Types of Coax Cable The Ohm rating is a measure of resistance in the cable and differentiates different types of coaxial cable RG-8, RG-62, and RG-58 are used in computer networks Exam Tip Know the Ohm ratings. Tech Tip Ohm Rating and Why It Matters The Ohm rating of a particular piece of cable describes the impedance of that cable. Impedance describes a set of characteristics of that define how much a cable resists the flow of electricity. It’s not simple resistance, though, but also factors in things like how long it takes the wire to get a full charge—the wire’s capacitance—and other things. The most important aspect of Ohms ratings for network technicians is to use the same-rated cables within a network, otherwise you’ll run into data corruption and data loss.

RG-8 RG-8 cable is also called Thick Ethernet Oldest type of coax still in use Rated at 50 ohms Yellow or orange/brown color

RG-62 RG-62 cable is never installed in networks today Was used with ARCnet

RG-58 RG-58 is also called Thin Ethernet Still in widespread use today

Twisted Pair Shielded Twisted Pair (STP) and Unshielded Twisted Pair (UTP) are the most common types of cabling used today Composed of multiple pairs of wires twisted together to reduce interference from adjacent wires, called crosstalk

Shielded Twisted Pair (STP) Twisted pairs of wires surrounded by shielding to protect them from EMI Only used in older Token Ring networks

Unshielded Twisted Pair (UTP) Most common type of cabling used in networks Twisted pairs of wires surrounded by a plastic jacket Inexpensive and flexible

CAT Ratings Twisted pair cabling varies by things like the number of twists per foot Cables are rated in categories or CAT ratings (or levels) Tech Tip Throughput and Bandwidth UTP cables are rated to handle a certain bandwidth, such as 10 MHz or 100 MHz, which originally translated as the maximum throughput for a cable. On a one-for-one basis, for example, a 10 million cycle per second (10 MHz) cable could accommodate 10 million bits per second (10 Mbps)—1 bit per cycle. Through the use of bandwidth efficient encoding schemes, such as MLT-3, manufacturers can squeeze more bits into the same signal as long as the cable can handle it. Thus the CAT 5e cable can handle throughput of up to 1000 Mbps even though it’s rated to handle a bandwidth of only up to 100 MHz.

CAT Ratings CAT Rating Bandwidth Typical Throughput in Networks CAT 1 <1 MHz Analog phone lines – not data CAT 2 4 MHz Speeds up to 4 Mbps CAT 3 16 MHz Speeds up to 16 Mbps CAT 4 20 MHz Speeds up to 20 Mbps CAT 5 100 MHz Speeds up to 100 Mbps CAT 5e Speeds up to 1000 Mbps CAT 6 200-250 MHz Speeds up to 10000 Mbps Tech Tip When network engineers talk about cable, they refer to them using terminology such as CAT-5 or CAT-6. CAT 5e is an enhanced version of CAT 5 that supports higher speeds.

CAT Usage Most new installations use CAT 5e cable since it is cheaper than CAT 6 cable CAT level CAT level

Fiber Optic Fiber optic cabling transmits light rather than electricity Immune to EMI Very long distances Consists of the fiber, cladding, and insulating jacket Defined by fiber and cladding measurements Most common is 62.5/125 µm Fiber generally requires two cables Note: The symbol µ stands for micro, or 1/1000th.

Light Sources Fiber optic cables use two possible light sources Light Emitting Diodes (LEDs) – called multimode Lasers – called single-mode Supports faster speeds and longer lengths Exam Tip Concentrate on UTP—that’s where the hardest Network+ questions lie. Don’t forget to give STP and fiber a quick pass as well to understand why you would pick one type of cabling over another. Even though Network+ doesn’t test too hard on cabling, this is important information that you will use in the real networking world.

Networking Industry Standards

IEEE Institute of Electrical and Electronic Engineers (IEEE) defines industry-wide standards Organized the 802 committee in February of 1980 to define networking standards Split up into smaller subcommittees

IEEE Subcommittees IEEE 802 LAN/MAN Overview & Architecture IEEE 802.2 Logical Link Control (LLC) IEEE 802.3 CSMA/CD access method (Ethernet) IEEE 802.3ae 10 Gigabit Ethernet IEEE 802.5 Token Ring access method and Physical layer specifications IEEE 802.8 Fiber Optic IEEE 802.11 Wireless LAN Medium Access Control (MAC) and Physical layer specifications Exam Tip Memorize the 802.2, 802.3, 802.5, and 802.11 standards. Ignore the rest. There are more subcommittees than listed in this table.