Network Design Principles CP3397 Network Design and Security Lecture 2.
Network Design
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Transcript of Network Design
Guide to Novell NetWare 3.x Administration, Enhanced Edition
Chapter 5
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Chapter 3 - Designing the Network
Describe the process of transmitting data on a NetWare LAN
Identify and describe the hardware and software that connect computers to a NetWare LAN
Apply your knowledge of LAN systems to develop a recommendation for a network system
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Computers communicate over LANs by sending blocks of data called packets Each packet contains the data to be transmitted and the
control information that the receiving computer uses to identify and process the packet
Hardware and software perform the complex task of transmitting data packets over a network
LAN communications rely on standards that allow different manufacturers to work together, and several organizations help set and control the standards that provide worldwide interoperability
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The International Standards Organization (ISO) introduced the Open Systems Interconnect (OSI) model to help standardize network implementation The OSI model helps illustrate the basic principles of
network communication This seven layer model acts as a blueprint to help network
designers and developers build reliable network systems that interoperate
Each layer of the OSI model is responsible for a particular function
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The seven layers of the OSI model: The application layer consists of software that users
interact with, enabling them to do their work The presentation layer organizes data to be transmitted
into machine-readable form The session layer initiates and maintains a communication
session with the network system The transport layer manages end-to-end data delivery
using two protocols: TCP and UDP
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The seven layers of the OSI model (cont.): The network layer supplies the information needed to route
packets through the proper network paths to arrive at the destination address
The data link layer is the computer network’s delivery system and is responsible for using the destination address to send the packet through the system
The physical layer consists of the network cable system and connectors, which are responsible for transmitting the packet out as a series of bits
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The first aspect of the physical network system is the media, the transmission system used to send electronic signals Most network media used today are in the form of cables or
wires that run to each network computer Another method used to transmit signals is that of wireless,
involving light and radio waves Three major factors to be considered for medium selection:
bandwidth (transmission capacity), resistance to EMI (susceptibility to outside electrical or magnetic fields), and installation cost
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Physical Layer: Twisted-pair Cable The most common medium for LANs The cable is either unshielded (UTP) and can be affected
by external electrical voltages and magnetic fields, or is shielded (STP) and is protected from these fields by external metal foil
Made of single-strand wire pairs twisted together Twisted-pair cabling comes in six categories Two types of connectors are used on the ends of twisted-
pair cable: RJ-45 (used with UTP) and IBM data connectors (used with STP)
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Physical Layer: Coaxial Cable The name coaxial derives from the two conductors in the
cable sharing the same axis At the center of the cable is a fairly stiff wire encased in
insulating plastic, the plastic is surrounded by the second conductor, which is a wire mesh tube that also serves as a shield, and the outside is a strong insulating plastic tube
Coaxial cable is available in a variety of types and thicknesses for different purposes
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Physical Layer: Fiber-Optic Cable Fiber-optic cable looks similar to coaxial cable, but it
consists of light-conducting glass or plastic fibers at the center of a thick tube of protective cladding surrounded by a tough outer sheath
Pulses of light are transmitted through the cable by lasers or LEDs and received by photo detectors
Fiber-optic is much lighter and smaller than coaxial or twisted-pair, and can support much higher data rates over longer distances
Fiber-optic is used primarily to connect servers
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Physical Layer: Infrared Infrared is wireless medium based on infrared light from
LEDs Infrared signals can be detected by direct line-of-sight
receivers, or by indirect receivers capturing reflected signals off walls or ceilings; they cannot penetrate walls or other opaque objects
Infrared transmissions are cost-efficient and capable of high bandwidths and can be a good way of connecting wireless LANs when all computers are located in a single room or office
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Physical Layer: Narrowband Radio Radio waves are used on a wireless network to transmit
data The line-of-sight focusing that infrared requires is not
needed The workstation must be located within a reasonable
distance from the base station or hub, or the transmission quality can be poor
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The second aspect of the physical network system is the topology, the physical geometry of the network wiring Choosing the method to connect networked computers is
an important aspect of a network system that uses bounded media
Network administrators must be familiar with a network’s topology in order to attach new computers, or isolate network problems to a faulty segment of the cable
Major LAN topologies: Linear bus, ring, and star
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Physical Layer: Star Topology Derives its name from the fact that the cables radiate from
a central point, usually called the hub The hub device connects the network cables and passes
the signals from one cable to the next The type of hub you need depends on the access system
used by the network cards Star topologies are more reliable and easier to troubleshoot
than other topologies, but they are costlier due to the increased amount of cabling
Star networks are wired with a patch panel
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Physical Layer: Linear Bus Topology Connects computers in series by running a cable from one
computer to the next The method of attaching computers to the bus depends on
the network card and cable system Each end of a linear bus network requires a terminator to
prevent echo signals from interfering Primary advantages: small amount of cable needed, and
the ease of wiring computers Primary disadvantages: adding or removing computers,
and troubleshooting
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Physical Layer: Ring Topology Similar to linear bus, except the ends of the cable are
connected instead of terminated Each computer in the ring receives signals and then
retransmits them to the next computer Advantages: because signals are regenerated at each
device, they can travel longer distances, and ring is easier to troubleshoot than linear bus
Disadvantages: extra cable needed to complete the ring’s circle, difficulty adding/removing devices
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Data Link Layer Components: The data link components control the way the network
cable system transmits and receives signals, and as a result, the components selected for the data link layer determine which topologies and cable types can be used
When using an already existing cable system, select data link products that best support it
The data link layer components consist of the NICs and card driver programs
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Data Link Layer: Network Interface Cards The NIC acts as the interface between the network’s data
link and physical layers Driver software is needed to control the NIC and provide an
interface between the data link layer and network layer software
Novell has developed a set of driver specifications called the Open Data Interface (ODI)
Microsoft’s driver specifications are called the Network Driver Interface Specifications (NDIS)
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Data Link Layer: NICs (cont.) Only one signal can be sent on the network cable at any
one time, and a media access method is necessary to control when computers transmit
In the token passing method, access to the network is controlled by a token, which is a special packet passed from one computer to the next to determine which machine can use the network
In the contention access method, a node transmits a message when it detects an unused channel, this is called CSMA/CD
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Data Link Layer: Token Ring Networks IBM originally designed the token ring system Token ring consists of workstations connected by twisted-
pair cables to a central hub, or MSAU Although it may appear to be a star arrangement, the
network signals actually travel in a ring Token ring is fast, reliable, fault tolerant, and generally
easy to troubleshoot Token ring cards are more expensive than other network
cards, and the star requires extra wiring
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Data Link Layer: Ethernet Networks The members of the Ethernet family are 10Base2,
10BaseT, 100BaseT, and 1000BaseT 10Base2 is based on the linear bus topology on coaxial
cable and uses the CSMA/CD system The term 10Base2 stands for 10 Mbps baseband using
digital baseband signals over two 100-meter coaxial cable segments
10Base2 is often referred to as ThinNet and is not as prevalent today because of better 10BaseT or 100BaseT networks
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Data Link Layer: Ethernet Networks 10BaseT is based on the star topology and uses the
CSMA/CD system The term 10BaseT stands for 10 Mbps baseband using
twisted-pair cable Advantages: 10BaseT network cards are less expensive
than others; network performance is excellent under light-to-medium network loads
Disadvantages: Additional cost for wiring and concentrators, network performance is hampered when many workstations are transmitting
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Data Link Layer: Ethernet Networks 100BaseT is an extension of the 10BaseT system The term 100BaseT stands for 100 Mbps baseband
network using twisted-pair cable Advantages: higher network performance for networks
requiring fast data transmission, such as those using video Disadvantages: shorter maximum cable run lengths in
some cable systems; higher costs for higher speed hubs and NICs
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Data Link Layer: Ethernet Networks 1000BaseT networks allow half and full duplex operation at
speeds of 1000 Mbps Use the 802.3 Ethernet frame formats Use the CSMA/CD access method with support for one
repeater per collision domain Address backward-compatibility with 10BaseT and
100BaseT technologies Gigabit Ethernet products have become reliable to where
they are now used in production networks
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Data Link Layer: Bridges & Switches Bridges connect same topology networks During network operation, the bridge watches packets on
both networks and builds a table of workstation node addresses. When it sees packets destined for MAC addresses on the other network, it sends the packet out on that network
A switch can be thought of as a mulitport bridge, with each port behaving like a miniature bridge
Workstations can connect to a switch instead of a hub and have their own dedicated bandwidth
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Network Layer: Routers Routers are used to create internetworks by connecting
different topology networks Routers access datagram information containing the logical
network address and control data The router information in the datagram packet allows
allows a router to find the correct path and, if necessary, break up the datagram for transmission on a different network system
Because of this, routers require more processing time than bridges
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Protocol Stacks The network’s protocol stack is responsible for formatting
requests to access network services and to transmit data Delivering data packets throughout a network system is the
responsibility of its data link and physical layer components; the functions of the network, transport and session layers are built into a network operating system protocol stack
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Protocol Stacks: IPX/SPX IPX/SPX is Novell’s system that implements the session,
transport, and network layers Internetwork Packet eXchange (IPX) manages packet
routing and formatting at the network layer The key advantage of IPX is that it offers automatic
addressing for network nodes Sequential Packet eXchange (SPX) operates at the
transport layer and guarantees delivery of packets by receiving acknowledgements for each sent
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Protocol Stacks: NetBEUI and AppleTalk NetBEUI is Microsoft’s own protocol stack and is
integrated into Windows for Workgroups, Windows 95/98 and Windows NT products
NetBEUI is one of the easiest protocols to use, but cannot be used in large internetwork environments
The AppleTalk protocol suite was originally developed so that Macintosh computers could communicate in peer-to-peer networks, and it currently provides connectivity for a variety of computer systems
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Chapter Summary
Network communication depends on packets of information being passed from one computer to another. Understanding how information packets flow through a network system means knowing the functions of the seven layers of the OSI model. Each layer of the OSI model is responsible for a particular function, and the modular approach makes it easier to understand and work with network components
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Chapter Summary
Cable types used with today’s LANs include shielded and unshielded twisted-pair, coaxial, and fiber-optic. Infrared and narrowband radio transmission are used in wireless networks. The physical geometry of a bounded medium is called its topology. Major physical topologies include ring, linear bus, and star
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Chapter Summary
Regardless of the topology used, only one machine can transmit on a network at any given time, and with some, a method of access control must be used to avoid data collisions. Access control methods can be contention or token based. Ethernet 10Base2, 10BaseT, 100BaseT, and 1000BaseT networks use a contention system, in which computers attempt to transmit whenever they sense an open period on the network. On busy networks, however, when two or more machines sense an open period and try to transmit at the same time, a collision occurs. With the CSMA/CD system, each machine waits a random time period before retrying its transmission
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Chapter Summary
Token ring networks use the token passing system. A token is passed around the network when no data packet is being transmitted. A machine needing to transmit must wait for the token. When received, it transmits its token without any collisions. Collisions cause CSMA/CD systems to slow under heavy network transmission loads, but token passing systems offer more uniform, predictable performance. Repeaters, bridges, switches, routers are devices that enable administrators to expand networks and reduce collisions or broadcast traffic
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Chapter Summary
Protocols are the languages used to implement the OSI layers. Popular protocols encountered as a network administrator are Novell NetWare’s IPX/ SPX; TCP/IP, used by UNIX and the Internet; NetBEUI, used in Windows-based networks; and AppleTalk, for Macintosh computers. NetWare 6 servers use the IP protocol by default. Earlier versions used IPX/SPX by default, but could be configured to handle TCP/IP and AppleTalk. TCP/IP is popular in UNIX environments and international WANs, such as the Internet