Chapter Summary

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The following points summarize the key concepts in this chapter:

Access Methods

• Managing data on a network depends on traffic control. The set of rules that governs how network traffic is controlled is called the access method.
• When using the CSMA/CD access method, a computer waits until the network is quiet and then transmits its data. If two computers transmit at the same time, the data will collide and have to be re-sent. If two data packets collide, both will be destroyed.
• When using the CSMA/CA access method, a computer transmits its intent to transmit before actually sending the data.
• When using the token-ring access method, each computer must wait to receive a token before it can transmit data. Only one computer at a time can use the token.
• When using the demand-priority access method, each computer communicates only with a hub. The hub then controls the flow of data.

How Networks Send Data

• Data on a network is not sent in one continuous stream. It is divided up into smaller, more manageable packets.
• All packets include at least the source address, the data, and the destination address.
• Packets are broken into three components:

• A header—Includes an alert signal, source and destination addresses, and clock information
• The data—Contains the content being sent
• A trailer—Contains the error-checking component

Ethernet

• Ethernet is one of the most popular network architectures.
• Ethernet is governed by the specifications found in the OSI reference model physical and data link layers as well as IEEE 802.3.

The following table summarizes the specifications for Ethernet architecture discussed in Lesson 3 of this chapter. It outlines the minimum set of standards required to conform to IEEE specifications. A particular implementation of the network architecture may differ from the information in this table.

Ethernet Specifications (IEEE 802.3)

	10Base2	10Base5	10BaseT
Topology	Bus	Bus	Star bus
Cable type	RG-58 (thinnet coaxial cable)	Thicknet; one-centimeter (3/8-inch) shielded transceiver cable	Category 3, 4, or 5 unshielded twisted-pair cable
Connection to NIC	BNC T connector	DIX or AUI connector	RJ-45
Terminator resistance, Ω (ohms)	50	50	Not applicable
Impedance, Ω	50 ± 2	50 ± 2	85-115 unshielded twisted-pair; 135-165 shielded twisted-pair
Distance	0.5 meters between computers (23 inches)	2.5 meters (8 feet) between taps and maximum of 50 meters (164 feet) between the tap and the computer	100 meters (328 feet) between the transceiver (the computer) and the hub
Maximum cable segment length	185 meters (607 feet)	500 meters (1640 feet)	100 meters (328 feet)
Maximum connected segments	5 (using 4 repeaters); Only 3 segments can have computers connected.	5 (using 4 repeaters). Only 3 segments can have computers connected.	Not applicable
Maximum total network length	925 meters (3035 feet)	2460 meters (8000 feet)	Not applicable
Maximum computers persegment	30 (There can be a maximum of 1024 computers per network.)	100	1 (Each station has its own cable to the hub. There can be a maximum of 12 computers per hub and a maximum of 1024 transceivers per LAN without some type of connectivity.)

Token Ring

The following table summarizes the specifications for Token Ring architecture presented in Lesson 4 of this chapter. It outlines the minimum set of standards required to conform to IEEE specifications. A particular implementation of the network architecture might differ from the information in this table.

Token Ring Specifications

IEEE specification	Token Ring
Topology	Star ring
Cable type	Shielded or unshielded twisted-pair cable
Terminator resistance, Ω (ohms)	Not applicable
Impedance, Ω	100-120 UTP, 150 STP
Maximum cable segment length	From 45 to 200 meters (about 148 to 656 feet), depends on cable type
Minimum length between computers	2.5 meters (about 8 feet)
Maximum connected segments	33 multistation access units (MSAUs)
Maximum computers per segment	Unshielded: 72 computers per hub; Shielded: 260 computers per hub

AppleTalk and ArcNet

• AppleTalk is the network architecture of the Apple (Macintosh) computer environment.
• AppleShare is the operating system used by AppleTalk.
• CSMA/CA is the access method for AppleTalk.
• To use a Macintosh computer on an Ethernet with coaxial cable, you need an EtherTalk card and the EtherTalk software.
• A TokenTalk card and software allow a Macintosh computer to connect to a Token Ring.
• ArcNet is designed for workgroup-size networks.
• ArcNet uses a token-passing bus topology.

The following table summarizes ArcNet specifications.

NOTE

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The following table contains the minimum set of standards required to conform to IEEE specifications. A particular implementation of the ArcNet network architecture might differ from the information in this table.

ArcNet Specifications

IEEE specification	ArcNet
Topology	Series of stars
Cable type	RG-62 or RG-59 (coaxial)
Terminator resistance, Ω (ohms)	Not applicable
Impedance, Ω	RG-62: 93 RG-59: 75
Maximum cable distance with coaxial cable, star topology	610 meters (2000 feet)
Maximum cable distance with coaxial cable, bus topology	305 meters (1000 feet)
Maximum cable distance with twisted-pair cable	244 meters (800 feet)
Minimum length between computers	Depends on cable
Maximum connected segments	Does not support connected segments
Maximum computers per segment	Depends on cable used