Faculty of Engineering Computer Engineering Department Islamic University of Gaza Network Lab # 8. Network Design

Transcription

1 Faculty of Engineering Computer Engineering Department Islamic University of Gaza 2012 Network Lab # 8 Network Design

2 Network Lab # 8 Network Design Introduction A computer network is a collection of computers and devices connected to each other. The network allows computers to communicate with each other and share resources and information. The three basic types of networks include: 1. Local Area Network (LAN) A local area network (LAN) is a group of computers and associated devices that share a common communications line or wireless link and typically share the resources of a single processor or server within a small geographic area (for example, within an office building). Usually, the server has applications and data storage that are shared in common by multiple computer users. A local area network may serve as few as two or three users (for example, in a home network) or as many as thousands of users (for example, in an FDDI network). 2. Wide Area Network (WAN) Wide Area Networks (WANs) connect larger geographic areas, such as Florida, the United States, or the world. Dedicated transoceanic cabling or satellite uplinks may be used to connect this type of network. Using a WAN, schools in Florida can communicate with places like Tokyo in a matter of minutes, without paying enormous phone bills. A WAN is complicated. It uses multiplexers to connect local and metropolitan networks to global communications networks like the Internet. To users, however, a WAN will not appear to be much different than a LAN or a MAN. 3. Metropolitan Area Network (MAN) A Metropolitan Area Network (MAN) covers larger geographic areas, such as cities or university districts. Network Cabling: Cable is the medium through which information usually moves from one network device to another. There are several types of cable which are commonly used with LANs. In some cases, a network will utilize only one type of cable, other networks will use a variety of cable types. The type of cable chosen for a network is related to the network's topology, protocol, and size. Understanding the characteristics of different types of cable and how they relate to other aspects of a network is necessary for the development of a successful network. The types of cables used in networks: Unshielded Twisted Pair (UTP) Cable Shielded Twisted Pair (STP) Cable Coaxial Cable Fiber Optic Cable Wireless LANs ٢

3 Installing Cable - Some Guidelines: When running cable, it is best to follow a few simple rules: Always use more cable than you need. Leave plenty of slack. Test every part of a network as you install it. Even if it is brand new, it may have problems that will be difficult to isolate later. Stay at least 3 feet away from fluorescent light boxes and other sources of electrical interference. If it is necessary to run cable across the floor, cover the cable with cable protectors. Label both ends of each cable. Use cable ties (not tape) to keep cables in the same location together. Networking Hardware: Networking hardware includes all computers, peripherals, interface cards and other equipment needed to perform data-processing and communications within the network. Types of the hardware components: File Servers Workstations Network Interface Cards Switches Repeaters Bridges Routers File Servers A file server stands at the heart of most networks. It is a very fast computer with a large amount of RAM and storage space, along with a fast network interface card. The network operating system software resides on this computer, along with any software applications and data files that need to be shared. ٣

4 The file server controls the communication of information between the nodes on a network. For example, it may be asked to send a word processor program to one workstation, receive a database file from another workstation, and store an message during the same time period. This requires a computer that can store a lot of information and share it very quickly. File servers should have at least the following characteristics: 800 megahertz or faster microprocessor (Pentium 3 or 4, G4 or G5) A fast hard drive with at least 120 gigabytes of storage A RAID (Redundant Array of Inexpensive Disks) to preserve data after a disk casualty A tape back-up unit (i.e. DAT, JAZ, Zip, or CD-RW drive) Numerous expansion slots Fast network interface card At least of 512 MB of RAM Workstations All of the user computers connected to a network are called workstations. A typical workstation is a computer that is configured with a network interface card, networking software, and the appropriate cables. Workstations do not necessarily need floppy disk drives because files can be saved on the file server. Almost any computer can serve as a network workstation. Network Interface Cards A network card, network adapter or NIC (network interface card) is a piece of computer hardware designed to allow computers to communicate over a computer network. It provides physical access to a networking medium and often provides a low-level addressing system through the use of MAC addresses. Hubs A hub contains multiple ports. When a packet arrives at one port, it is copied unmodified to all ports of the hub for transmission. The destination address in the frame is not changed to a broadcast address. Switch A switch is a device that forwards and filters OSI layer 2 datagrams (chunk of data communication) between ports (connected cables) based on the MAC addresses in the packets. This is distinct from a hub in that it only forwards the packets to the ports involved in the communications rather than all ports connected. Strictly speaking, a switch is not capable of routing traffic based on IP address (OSI Layer 3) which is necessary for communicating between network segments or within a large or complex LAN. A switch normally has numerous ports, with the intention being that most or all of the network is connected directly to the switch, or another switch that is in turn connected to a switch. Routers A router translates information from one network to another; it is similar to a super intelligent bridge. Routers select the best path to route a message, based on the destination address and origin. The router can direct traffic to prevent head-on collisions, and is smart enough to know when to direct traffic along back roads and shortcuts. Routers work at the network layer. If you have a school LAN that you want to connect to the Internet, you will need to purchase a router. In this case, the router serves as the translator between the information on your LAN and the Internet. It also determines the best route to send the data over the Internet. ٤

5 Repeaters Since a signal loses strength as it passes along a cable, it is often necessary to boost the signal with a device called a repeater. The repeater electrically amplifies the signal it receives and rebroadcasts it. They are used when the total length of your network cable exceeds the standards set for the type of cable being used. What is a Topology? Network topology is the study of the arrangement or mapping of the elements (links, nodes, etc.) of a network, especially the physical (real) and logical (virtual) interconnections between nodes. A local area network (LAN) is one example of a network that exhibits both a physical topology and a logical topology. Any given node in the LAN will have one or more links to one or more other nodes in the network and the mapping of these links and nodes onto a graph results in a geometrical shape that determines the physical topology of the network. Likewise, the mapping of the flow of data between the nodes in the network determines the logical topology of the network. The physical and logical topologies might be identical in any particular network but they also may be different. Any particular network topology is determined only by the graphical mapping of the configuration of physical and/or logical connections between nodes. LAN Network Topology is, therefore, technically a part of graph theory. Distances between nodes, physical interconnections, transmission rates, and/or signal types may differ in two networks and yet their topologies may be identical. The following are the types of the physical topologies used in networks. Bus Star Ring Tree Mesh LAN Design Goals: The first step in designing a LAN is to establish and document the goals of the design. These goals are particular to each organization or situation. However, the following requirements tend to show up in most network designs: Functionality-the network must work. That is, it must allow users to meet their job requirements. The network must provide user-to-user and user-to-application connectivity with reasonable speed and reliability. Scalability-the network must be able to grow. Adaptability-the network must be designed with an eye toward future technologies, and it should include no element that would limit implementation of new technologies as they become available. Manageability-the network should be designed to facilitate network monitoring and management. ٥

6 Network Design Methodology: For a LAN to be effective and serve the needs of its users, it should be designed and implemented according to a planned series of systematic steps, which include the following: Gathering the users' requirements and expectations: Gather data about the organizational structure, history and current status, projected growth, operating policies and management procedures, office systems and procedures, and the viewpoints of the people who will be using the LAN. Analyzing requirements: The next step in designing a network is to analyze the requirements of the network and its users that were gathered in the last step. Design the layer 1, 2, and 3 LAN structure (that is, topology): After determining the overall requirements for the network, the next step is to decide on an overall LAN topology that will satisfy the user requirements. The major pieces of a LAN topology design can be broken into three unique categories of the OSI model the network layer, the data link layer, and the physical layer. Documenting the logical and physical network implementation: An organization's existing computer hardware and software must be documented, and projected hardware and software needs identified. Notes: The physical cabling is one of the most important components to consider when designing a network. Routers can be used to create unique LAN segments and allow communication between segments based on layer 3 addressing, such as IP addressing. They also allow for connectivity to (WANs), such as the internet. They forward data packets based on destination addresses. If the destination address is local, the sending host can encapsulate the packet in a data-link header and send a unicast frame directly to the station. The sending host might have to use ARP. If the destination is not local, then the sending station transmits the packet to the router. The router sends the frame to the destination or to the next hop, based on its routing table. Simple Network Diagram: ٦

7 Broadcast and Collision domains: With hub networks, When any one pc places data on the wire it is automatically sent to all other ports (pc's) on that hub and any other hubs daisy chained to it. This is a collision domain because another PC could place data on the wire at the same time as another and thus cause a collision. It doesn't matter if either pc is sending unicast or broadcast packets everything gets sent to all ports because that is all a hub does. Hubs are also half duplex devices which means data can only from in one direction at a time. A switch on the other hand can tell the difference between a broadcast and a unicast packet it receives. If an 8 port switch receives a packet from one PC destined for another PC (unicast) it only sends that data down the wire the destination PC resides. This is why it's called a switch. It creates a virtual path between two devices. When a switch receives a broadcast it will forward out all ports except the port it received the broadcast on (no point in echoing back what you were just told) Now the reason this does not cause collisions is because switches are full duplex. They send and receive at the same time so it doesn't matter if a pc receives a broadcast at the same time they are sending data. Hubs don t break collision and broadcast domains. So any packet will be forwarded to all ports. switch can divide collision domain but not broadcast domain. Routers divide both broadcast and collision domains. how many broadcast and collision domain in this network? ٧

8 Unicast, Multicast, Broadcast Unicast : one device calls another. Multicast : one device calls a group of the network. Broadcast : one Device calls all the network. The OSI Model: Open Systems Interconnection (OSI) consists of seven separate but related layers. The purpose of the OSI model is to show how to facilitate communication between different systems without requiring changes to the logic of the underlying hardware and software. ٨

9 TCP/IP Model: The TCP/IP model (Transmission Control Protocol/Internet Protocol) is a descriptive framework for the Internet Protocol Suite of computer network protocols created in the 1970s by the United States Department of Defense. The TCP/IP Protocol Suite: ٩