1.2. Specifying the Main Features of Networking Technologies

Whereas the topology of a network is the shape of the network, the technology is the method of putting information onto the network and controlling it based on the physical components that are used and how they operate within the network. Some technologies have evolved over time, some have been all but discontinued, while others have been improved and refined.

In February 1980, the Institute of Electrical and Electronics Engineers (IEEE) developed a set of standards called the 802 project. Each of the standards was given a number beginning with 802 (the 80th year and the second month). These standards have been refined over the last two decades, but (in general) are still used to represent the main networking technologies of the past, present, and future. In this section, we discuss each of these technologies in detail.

1.2.1. Critical Information

Familiarize yourself with the new technologies as well as some of the older, less used technologies. You should be able to specify the main features of each technology, such as speed, access method, topology used, and media used. In the paragraphs that follow, we discuss each of the technologies with which you should be familiar.

1.2.1.1. Ethernet

Ethernet is by far the most common technology in use today. The Internet operates using Ethernet technology. It was first developed by Xerox at the Palo Alto Research Center (PARC) and was defined as 802.3 by the IEEE. Ethernet began production at a speed of only 3Mbps, but common speeds today include 10Mbps, 100Mbps, and 1000Mbps. The speed of the network is dependent on the devices that are used and on the slowest devices in the network. (We will discuss types of network devices later in this chapter.)

Ethernet uses an access method known as Carrier Sense Multiple Access with Collision Detection (CSMA/CD). This method of putting data "on the wire" works by first sensing the wire to determine whether there is currently any data flowing on it, indicated by a fluctuation in electrical current. If no data is flowing on the wire, then the Ethernet device can send its data. Sometimes two devices might try to send data at the same time, resulting in a collision. If this happens, then the network is "stalled" until the devices have sent their data again with no collision. One of the responsibilities of a network designer is to control traffic in order to reduce or eliminate collisions.

Ethernet networks began as bus topologies that used coaxial cable. These networks used a large coaxial cable as a backbone and a smaller coaxial cable to connect the computers and hubs to the backbone. Today, Ethernet networks typically use unshielded twisted-pair (UTP) cable in a star topology. Some networks use wireless connections that require no cable at all. (We will discuss media types in greater detail later in this chapter.) Table 1.1 highlights the main features of the Ethernet topology.

1.2.2. Logical Link Control (LLC)

Logical Link Control (LLC) is a networking technology defined by the IEEE as 802.2. It does not provide a complete networking model, but instead defines the standards for controlling the data sent and received by a system. LLC specifies the protocols, or rules, that perform flow control and error checking. These protocols are the essential foundation for all of the other net-working standards.

1.2.2.1. Token Ring

Token Ring was introduced by IBM in the mid-1980s. Since it virtually eliminated collisions and thereby increased the speed of networks, it became the network topology of choice for those companies who could afford the best and most expensive networks. Defined by the IEEE as 802.5, Token Ring uses a token-passing access method. A token is a unique electronic signal that must be attached to a message in order for the message to enter the network or travel on it. Because there is only one token on each ring, only one message can travel on the network at any given point in time, thereby eliminating the possibility of collisions.

Token Ring uses a physical star topology but the logical topology is a ring. The ring is actually created inside special hubs called multiple-station access units (MSAUs). The media used in Token Ring is twisted-pair cable. Typically, Token Ring networks run at either 4Mbps or 16Mbps. While Token Ring had a huge following in the 1980s, it has been all but eliminated from modern network designs due to advancements in technology that increased the speed and reliability of Ethernet. Table 1.2 highlights the main features of the Token Ring topology.

1.2.2.2. Wireless

Today's networks have the capability to eliminate the cables for many of the computers. The IEEE 802.11 wireless standard was originally defined in the 1980s by the "forward-thinking" representatives of the IEEE. Nowadays, many individuals and companies are adopting the technology for portions of their networks. Because of the conveniences that they offer, wireless networks will likely continue to grow in popularity.

The 802.11 standard has two common levels: 802.11b and 802.11g. The 802.11b standard offers speeds up to 11Mbps, and the 802.11g standard increases the speed to 54Mbps. Both use an access method referred to as Carrier Sense Multiple Access with Collision Avoidance CSMA/CA. This access method is similar to CSMA/CD except that the device that wants to send its message must first send a very small message to make sure that the signal can be received without any collisions or other problems. If the short message is transmitted successfully, then the long message is sent next. The media that 802.11 wireless networks use is the 2.4GHz radio wave band. Table 1.3 highlights the main features of the wireless topology.

1.2.2.3. FDDI

Fiber Distributed Data Interface (FDDI) was developed by the American National Standards Institute (ANSI) in the mid-1980s. It uses a token-passing access method and a dualring topology. Figure 1.6 shows an example of an FDDI topology. The media used by FDDI is typically fiber-optic cable, but it can also use shielded twisted-pair (STP) or unshielded twisted-pair (UTP) cable. (We will discuss cable types in greater detail later in this chapter.) FDDI communicates at a speed of 100 Mbps on copper wire, but can communicate much faster on fiber-optic cable. (FDDI on copper wire is sometimes referred to as CDDI.) Table 1.4 highlights the main features of the FDDI topology.

Figure 1.6. An FDDI topology

1.2.3. Exam Essentials

Know the difference between a topology and a technology. A network's topology represents the way that it is shaped logically and physically, but its technology represents the methods that it uses to introduce data onto the media and transfer it to other computers.

List the characteristics of Ethernet. Ethernet, the most common technology in use today, uses the CSMA/CD access method to put data onto the wire. Ethernet has evolved over time and has many different speeds, including 10Mbps, 100Mbps, 1000Mbps, and 10,000Mbps. Ethernet is defined by the IEEE 802.3 specification.

Describe the characteristics of LLC. LLC is a standard defined by the IEEE 802.2 specification. It is not a complete networking model, but it does define the standards for controlling data sent and received by systems. LLC defines the rules and standard for flow control and error checking.

Know the characteristics of Token Ring. Token Ring is a technology developed by IBM and defined by the 802.5 specification standard. Token Ring uses a token-passing method of carrier access to eliminate the possibility of collisions. The two main speeds of Token Ring are 4Mbps and 16Mbps. Token Ring is used on copper wire for local area networks (LANs).

List the characteristics of the wireless topology. The wireless topology is defined by the 802.11 specification standard. The two most common standards of wireless communication are 802.11b and 802.11g; both use the 2.4GHz radio band. Keep in mind that 802.11b operates at 11Mbps and 802.11g operates at 54Mbps. Wireless communications use a CSMA/CA method of media access, which tests the communication channel before sending data onto it.

Describe the characteristics of FDDI. FDDI is a topology that is used in wide area networks (WANs) rather than LANs. FDDI uses a token-passing method similar to Token Ring, but its method is more advanced. It uses a dualring topology to provide for fault tolerance. The speed of FDDI is generally 100Mbps, but some forms of FDDI can transmit much faster.