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The Complete One-Week Preparation for the CISCO CCENT/CCNA ICND1 Exam 640-822Second Edition (March 2011)
By Thaar AL_Taiey
iUniverseCopyright © 2011 Thaar AL_Taiey
All right reserved.
Chapter OneINTERNETWORKING ESSENTIALS
In this chapter, some fundamental concepts and terms that can be used in the internetworking are described.
This chapter summarizes some common themes presented throughout the remainder of this book. The chapter focuses mainly on mapping the Open System Interconnection (OSI) model to networking and internetworking functions; OSI model represents the building blocks for internetworks. The advantages of networking models are also stated in this chapter. Understanding the conceptual model helps understanding the complex pieces that make up an internetwork. This chapter also describes in details the concepts of Networking, Internetworking, Physical and Logical Network Topologies, and Ethernet LAN.
The following topics are emphasized in this chapter:
* Networking essentials
* Internetworking essentials
* Internetworking evolving
* Internetworking models
* OSI reference model
* OSI encapsulation and de-encapsulation terminologies
* Ethernet LANs
* Data transmission types
* CSMA/CD algorithm
* Ethernet addressing
* Ethernet connection and cabling
By understanding perfectly the information presented in this chapter and answering the 312 learning questions at the end of this chapter, understanding OSI reference model, understanding Ethernet LAN, and answering the CCNA/CCENT exam related questions will be guaranteed. The main questions herein are intended to reflect the type of questions presented on the CCENT Test.
In this section, networking essentials are presented and the types of networking topologies are described. A network is a collection of connection devices (NICs-Network Interface Cards, routers, switches, firewalls) and end system machines (PCs, servers) interconnected together by some means. Networks carry data in many types of environments, including homes, and up to large enterprises. Networks also carry data in many types of media, including wired and wireless. To accomplish it tasks, network uses many types of connection devices such as NICs, hubs, bridges, switches and routers. These devices will be discussed deeply throughout this book.
Network Functions and Benefits
Today, the main function of computer networks, in addition to share and exchange information between computer machines, it provides communication. In business, networks play a major role. It simplifies and streamlines business processes through the use of data, application and hardware sharing.
Networks make rapidly data and information exchanging. Therefore, business's resources can be used more efficiently. However, several types of resources can be shared by computer networks. This includes but is not limited to: Data and applications, Physical resources, Network storage, Backup devices and of course networking devices and media. Furthermore, users of the network can use many types of networking applications, such as, E-mail, Web browsers, Internet talk, instant messaging, Download application, Broadcasting alerter, RSS feeds, Books reader, Collaboration and Database.
Generally, network applications can be one of the following types; system-to-system batch applications, user interactive applications, and user real-time applications.
Note: The terms above and several other terms in this chapter are given without further discussion because they are out of the scope of CCENT exam and this book does not want to confuse the reader by extra-information. However, more detail can be found from www.google.com.
Networks can be described and compared according to network performance and structured. This includes: Speed, Cost, Security, Availability, Scalability, Reliability, Manageability, and Topology. Today, cost of the network becomes less affecting factor when selecting the network and factors such as speed, security and easily managed network become the main factors for selecting the network. However, this depends on the importance of the network to the business process.
Physical and Logical Network Topologies
Topology defines the interconnection method used between devices, including the layout of the cabling and all paths used in data transmissions. Networks have two types of topologies; the physical and logical topologies. The physical topology is the arrangement of the network (nodes) devices, end systems (laptops, PCs and servers) and the network cables in wired networks. The logical topology, on the other hand, is the mapping of the data flows between the nodes in the network that forming the physical topology.
Physical Network Topology
As stated above, the physical topology is the arrangement of the network devices, end systems (laptops, PCs and servers) and the network cables in wired networks. Some of these topologies depend on the type of cabling that will be installed. Types of cables that are used in the network will be described in the following sections. However, the three basic categories of physical topologies are: Bus, Ring and Star. Figure 1-1 shows the basic physical topologies used in networking.
In this topology, all network devices and automated machines are cabled together in a line. Each machine is connected to the single bus cable through some kind of connector. The main cable segment must end with a terminator that absorbs the electrical signal when it reaches the end of the cable. Since only one cable is utilized, it can be the single point of failure. If the network cable breaks, the entire network will be down, since there is only one cable. This is the main disadvantage of the bus network. Using only one cable, on the other hand, will make the transfer speed between the computers on the network is faster. The bus topology includes both linear bus and distributed bus topologies. An example of this topology is a Thicknet Ethernet cable.
In this topology, all network devices and automated machines are cabled together with the first device connected to the last to form a ring. This means that each machine is connected to the network in a closed loop or ring. In the ring topology, data is transmitted within a "token". Token travels around the ring. If a machine wants to transmit data, it adds that data and the destination address to the token. The token move around the ring until it finds the destination device, which takes the data out of the token. The primary advantage of this topology is that no token collisions occur. On the other hand, the primary disadvantage of ring topology is the failure of one machine will cause the entire network to fail. Two types of ring topology exist: single-ring and dual-ring. As names imply, the first one uses one ring, whereas the second one uses two rings to transmit the token. The dualring uses two rings to allow token to be sent in both directions. This design provides redundancy as compared with the single-ring design, meaning that if one ring fails, token can be transmitted on the second ring.
In this topology, all network devices and automated machines are connected together by a central cabling device. In local area networks where the star topology is used, each machine is connected to a central hub/switch. This will provide each machine on the network a dedicated, point to point connection to the central hub/switch. An advantage of the star topology is the simplicity of adding other machines. Another advantage of using such a topology is that when a cable connected one machine to a central hub/switch is broken, only that one machine is affected and disconnected from the network, and the rest of the network remains operational. This advantage is important and it is the reason why almost every newly designed Ethernet LAN based on a physical star topology. The primary disadvantage of the star topology is the hub/switch represents a single point of failure. If the hub/switch were to fail the entire network would fail as a result of the hub/switch being connected to every machine on the network. The star topology includes both extended-star and distributed-star topologies. When a network is expanded to include an additional network device that is connected to the main network devices, the topology is referred to as an extended-star topology. A common deployment of this topology is in a hierarchical (Tree) design network such as a Campus LAN or an Enterprise or a WAN. Figure 1-2 shows the tree physical topology.
Today, most extended-star networks employ a redundant connection to a separate set of connection devices to prevent isolation in the event of a device failure, especially the central node (core switch, router, and firewall), since if one of these devices fails, a large portion of the network can become isolated. Distributed-star topology is composed of individual networks that are based upon the physical star topology connected together in a linear fashion, i.e., 'daisy-chained'. Therefore, the distributed-star topology has no central connection.
In addition to the basic physical topologies discussed above there is a mesh topology. Mesh topology is similar to star topology. It provides redundancy between machines in a star topology. A network can be fully meshed or partial meshed depending on the level of redundancy required. Figure 1-3 shows these types of physical topology. The mesh topology increases the overall network cost, but it improves network availability and reliability. Full-meshed network connects each machine to all other machines with a point-to-point link for redundancy and fault tolerance– this makes it possible for data to be simultaneously transmitted from any single node to all the other nodes. This topology provides the highest fault tolerant capabilities because the failure of any single link does not affect connectivity in the network. On the other hand, full-meshed network is expensive and complex for practical networks, although the topology is used when there are only a small number of nodes to be interconnected. In a partial-meshed topology, at least one machine maintains to multiply connections to all other machines (meshed) using a point-to-point link. The most important machines should be meshed. This topology trades off the cost of meshing all machines by meshing only the most important machines. By taking some of the advantages of the physical fully mesh topology, such as, the redundancy, the expense and complexity required for a connection between every machine in the network, is not required. All the data that is transmitted between nodes in the partially meshed networks takes the shortest path between nodes, except in the case of a failure in one of the links. When one link is failed, the data must take an alternate path to the destination node.
Logical Network Topology
The logical topology is the mapping of the data flows between the nodes in the network that forming the physical topology-that is, the way in which data accesses the network media and transmits bits across it. Logical topologies are often closely related to media access control (MAC) methods and protocols. The logical topologies are generally determined by the used network protocols, not by the physical layout of the network. Logical topologies can be dynamically reconfigured by special types of equipment such as routers, switches and firewalls.
The physical and logical topologies may or may not be identical in any particular network. For example; in a linear bus physical network topology, the data travels along the length of the bus. Therefore, the network has both a physical bus topology and a logical bus topology. On the other hand; in a star physical topology, the data may travels in a ring logical topology.
The most common implementation of LANs today is a star topology. In either a physical bus or a physical star, Ethernet uses a logical bus topology.
In this section, internetworking history is presented as well as the types of internetworking are described. The CCNA exams, and particularly the CCENT (640-822) exam, focus on the concepts, protocols, and devices of two major networking types: enterprise networking and the Small Office/Home Office or SOHO networking. An enterprise network is a network created by one corporation, or enterprise, for allowing its employees to communicate and to provide services to the outside customers. A SOHO networking allows a user to connect to the Internet using a PC or laptop or mobile and any Internet connection, such as the high-speed cable Internet connection or wireless connection. This type of networking uses the same concepts, protocols, and devices used to create enterprise networks, but both are differing by some features, which are required by that type. Because most enterprise networks also connect to the Internet, the SOHO user can sit at home, or in a small office, and communicate with servers at the enterprise network, as well as with other hosts in the Internet.
In fact, the term "Internet" itself is formed by shortening the phrase "interconnected networks." The Internet consists of most every enterprise network in the world, plus billions of devices connecting to the Internet directly through Internet service providers (ISPs). Basically, The ISP role is to provide internet services to others. Therefore, to create the Internet, ISPs offer Internet access, using a cable TV line, a phone line or a wireless connection. Each enterprise typically connects to at least one ISP, using permanent connections generally called wide-area network (WAN) links. Finally, the ISPs of the world also connect to each other. These interconnected networks—from the smallest PC based home network, to cellular phones and automated devices, to enterprise networks with thousands of devices—all connect to the global Internet.
An internetwork is a collection of individual networks, which function as a single large network, connected by intermediate networking devices (routers, switches, bridges). Internetworking refers to the industry, products, and procedures that meet the challenge of creating and administering internetworks. Figure 1-4 depicts some different kinds of network technologies that can be interconnected by routers and other networking devices to create an internetwork.
The term internetwork is used in this book and in many other resources to refer generally to a network made up of routers, switches, bridges, cables, and other networking equipment, and the word network is used to refer to the more specific concept of an IP network.
History of the Internetworking
The first networks used mainframes and attached dummy terminals. These are time-sharing networks. Such environments were implemented by both IBM's Systems Network Architecture (SNA) and Digital's network architecture. Networks and networking have grown exponentially over the last 20 years.
Local-area networks (LANs) developed around the PC revolution in 1980's. LANs connected multiple users in a relatively small geographical area to exchange files and messages, as well as access shared resources such as file servers and printers.
Wide-area networks (WANs) interconnect LANs with geographically dispersed users to create connectivity. Some of the technologies used for connecting LANs include T1, T3, ATM, ISDN, ADSL, Frame Relay, Radio links, Wireless and others.
Nowadays, high-speed LANs and switched internetworks are becoming widely used, largely because they operate at very high speeds and support high-bandwidth applications such as, multimedia, TV and videoconferencing.
Types of networking
A basic LAN network is shown in Figure 1-5. This LAN connects three PCs together using a simple (now) networking device called a hub. This network is actually one collision domain and one broadcast domain, and these are the major weaknesses of this type of network is growth, the problems such as network speed degradation will appear.
Excerpted from The Complete One-Week Preparation for the CISCO CCENT/CCNA ICND1 Exam 640-822 by Thaar AL_Taiey Copyright © 2011 by Thaar AL_Taiey. Excerpted by permission of iUniverse. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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