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Using Communications and Network Systems

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Title: Using Communications and Network Systems


1
Unit 24 Using Communications and Network Systems
2
Introduction to Networks
Roger Cain 2000
3
What is a Network
1. A unifying connection of computer, printers,
faxes, modems, servers and sometimes telephones.
2. Connections may be made by cabling of various
kinds or with radio links
3. The network enables computer equipment to
talk to each other and perhaps to connect to
the internet
4
A Typical Network
Server
Laptop
PC
Internet
Router
PC
PC
PC
Printer
5
Some Basics
  • DEFINITION
  • A network is a collection of two or more
    computers connected together.
  • Once computers are joined on a network,
    resources such as files and peripherals can be
    shared
  • When networks at multiple locations are
    connected using services from
    telecommunications companies, people can send
    e-mail, share links to the internet or conduct
    conferences in real time with remote users

6
Packets,Ports and Bandwidth
  • Data is broken up into chunks for
    transmission purposes
  • These chunks are called packets
  • Each packet contains the destination and
    information about the type of data inside
  • this means that an e-mail message, for example
    may be split up and carried in several data
    packets. The computers at either end of a
    communication session put these back together,
    to recreate the message

7
  • A port is a socket on the back of a device to
    allow a cable to be connected.
  • a 12 port switch for example can have 12
    devices connected to it
  • Some devices have additional ports for
    connection to a similar device so that a 12
    port device might be connected to another to
    give 24 ports in total

8
  • Bandwidth is the amount of information that can
    be passed down a wire or through a network
    device in a second
  • It is normally measured in bits per second
    (bps)
  • A typical modem can transmit about 30 -50kbps
  • A typical business LAN would transmit 10Mbps

9
Servers
  • DEFINITION A computer on the network that
    shares resources with other network users. It
    may be dedicated, which means that its purpose
    is to provide service for other network users.
    It may be non dedicated in which case it is
    used as a workstation (client) as well
  • the server acts as a central storage point for
    files or application programs shared on the
    network
  • It will also provide connections to shared
    peripherals such as printers.

10
  • Setting up a dedicated server saves having to
    have every networked computer with large
    storage capacity and duplicate peripherals
  • The computers that connect to the server are
    called clients
  • With a small number of computers in the network
    it is possible to have a peer to peer
    network. In this users can share files, send
    e-mail, and use printers connected to another
    computer
  • But as users are added a dedicated server will
    provide a central point for management duties
    and will improve network performance

11
Client
  • DEFINITION A computer that has access to the
    network but does not share any of its resources
  • Clients are usually cheaper and less powerful
    than servers
  • Most networks have more clients than servers
    (10 clients per server?)

12
Network Cards
  • DEFINITION A Network Interface Card (NIC) An
    adapter card that allows the computer to connect
    to a network
  • Important points about NICs
  • Make sure that the connector on the card
    matches the cabling
  • Thin Ethernet needs BNC, Twisted pair requires
    RJ-45

13
  • 10Mbps 100Mbps and 10/100Mbps cards are all
    available
  • Novell manufactured a card called the NE2000.
    It is no longer made but NE2000 remains the
    standard of compatibility. If a card is
    NE2000 compatible you can use it with almost any
    network.
  • Ensure that the card is compatible with your
    computer. Most computers can use cards
    designed for the standard 16bit ISA bus. Newer
    Pentium based computers can use the 32bit PCI
    bus. PCI cards are faster and easier to
    configure.

14
  • Wherever possible use a plug and play card. It
    saves a lot of configuration time
  • Cards can be tricky to set up. Try not to mix
    cards in a single network.

15
Cabling
  • There are three basic types of cable used for
    networking. Twisted Pair, Coaxial and Fibre
    Optic. Each basic type is further sub-divided

16
Twisted Pair
  • This has become the industry standard in new
    installations
  • It comes in two main forms for networking
  • Unshielded Twisted Pair (UTP) category 3 and
    UTP category 5 are the current standards
  • UTP wire is cheap and easy to install.

17
  • When UTP cable is used to construct an Ethernet
    network the computers are all connected to a hub
  • An advantage of this is that if a cable fails
    only the computer attached by that cable is
    affected

Hub
Twisted Pair Cable
18
Useful Information on UTP Cable
  • UTP cable consists of pairs of thin wire
    twisted around each other. Several such pairs
    are set inside an insulating cover. Ethernet
    uses two pairs if wires. The number of pairs in
    UTP wire varies and is often more than two.
  • UTP comes in 5 grades. The higher the grade
    the greater the protection from outside
    electrical interference.
  • Category 3 cable is OK for 10Mbps networks but
    foe 100Mbps you must use category 5. Wherever
    possible use category 5

19
  • 1000Mbps networks require category 5e
    (extended) cable or better ( 6 or 7/2000?)
  • UTP connectors are similar to phone connectors.
    The official name is RJ-45 connectors
  • the maximum allowable cable length between the
    computer and the hub is 100metres

20
Coaxial Cable
  • This comes in two types known as thick Ethernet
    and thin Ethernet
  • Thick Ethernet is now only used in special
    circumstances where a high level of protection
    from outside electrical interference is required

21
  • Thin Ethernet is about 2.5mm in diameter and is
    light and flexible
  • It is connected to the Network Interface Card
    by a twist on BNC connector
  • There is a separate length of cable between
    each computer. At each computer a T- connector
    is used to connect two cables to the NIC

22
  • A terminator is required at each end of the
    series of cables. This kills any signal at
    the end of the segment
  • the total length of all the cables from
    terminator to terminator is called a segment.
    The maximum length of a segment is 185 metres
  • Up to 30 computers can be connected in a
    segment. To connect more than 30 computers or
    to span more than 185 metres a repeater is
    needed

23
Thin Ethernet Cables
24
Fibre-Optic Cable
  • Has a number of advantages over twisted
    pair and coaxial cable
  • (i) Much faster
  • (ii) Immune to electromagnetic or radio
    frequency interference
  • (iii) Can send signals several mile without
    loss
  • (iv) Virtually immune to unauthorised
    reception

25
  • Fibre optic cable is made of pure glass drawn
    into a very thin fibre to form a core
  • These fibres are surrounded by a layer of glass
    with a lower refractive index than the glass in
    the core ( the cladding)
  • The fibre-optic network uses a laser or LED to
    send a signal through the core of the cable
  • Optical repeaters may be used along the path to
    amplify the signal
  • At the receiver the signal is translated back
    into a digital or analogue signal by a
    photo-diode

26
  • the fibre can consist of a single fibre,
    which is known as monomode or several fibres
    (multimode)
  • Monomode fibre has a very wide bandwidth but
    its tiny core makes it extremely difficult to
    splice without specials kits and technical
    expertise
  • Also monomode requires a laser(rather than a
    LED as a signalling source, which is more
    expensive

27
  • Multimode fibre has a smaller bandwidth but is
    much easier to splice
  • Each fibre is unidirectional therefore two way
    communication requires another fibre within
    the cable so that light can also travel in the
    opposite direction

28
  • It is possible to achieve rates of up to 1
    gigabit per second
  • At present fibre optic cabling is still too
    expensive for most installations and its
    technology makes it difficult to add new
    stations after the initial installation
  • It may still be required if a company has
    serious interference problems
  • needs absolute network security
  • or the capability of sending signals several
    miles

29
WIRELESS NETWORKS
  • Some environments are very difficult to cable
  • e.g. Where personnel are frequently relocated
  • PCs can be equipped with small microwave
    transmitter/receivers but the cost is still
    prohibitive when compared to conventional
    cabling systems

30
NETWORK ARCHITECHTURE
  • As there are several different ways to cable a
    LAN there are several different forms a
    network can take
  • these different shapes are known as network
    architecture or topology
  • NB. The form does not limit the medium of
    transmission
  • All methods of transmission lend themselves to
    the different topologies

31
THE STAR
  • This is one of the oldest types of network
    topologies
  • this uses the same approach to receiving and
    sending messages as a telephone system
  • All messages in a STAR topology must go through
    a central computer that controls the flow of
    data
  • This architecture makes it easy to add new
    workstations to the LAN
  • All that is needed is a cable from the central
    computer to the new workstation

32
  • Another advantage is that the network
    administrator can give certain nodes higher
    status than others
  • the central computer will then look for signals
    from these higher priority workstations before
    recognising other nodes
  • this is particularly useful on networks where a
    few key users require immediate response to
    on-line enquiries
  • It also make it easier to have centralised
    diagnostics of all network functions

33
  • since all messages come through the central
    computer, it is a simple task to analyse all
    workstation messages and to produce reports
    that reveal the files that each node uses
  • This can also be a valuable aid to security
  • the major weakness of this architecture is that
    if anything happens to the central computer the
    entire LAN fails
  • A CLUSTERED STAR topology consists of several
    stars linked together such that the failure of
    any one star does not result in the failure of
    the whole network

34
Star Topology
35
BUS TOPOLOGY
  • A bus topology can best be thought of as a data
    highway that connects several LAN
    workstations
  • Most networks of this type check whether
    anything is coming down the highway before
    sending their messages.
  • Since the workstations all share this bus all
    messages pass other workstations pass other
    workstations on the way to their destinations
  • Each workstation checks the address on the
    message to see if it matches its own address

36
  • If it does it will copy the massage into the
    RAM on its network interface card and then
    process the information as necessary
  • In a star topology the collection of cables at
    the central computer can often create
    logistical problems
  • Bus cabling is much simpler, just like hanging
    washing on the line
  • It requires the least amount of cabling of any
    topology
  • The lowest cost results from a combination of
    bus topology and twisted pair cabling

37
  • Another advantage of the bus topology is that
    the failure of a single workstation will not
    cripple the rest of the network
  • Ethernet is an example of a network that uses
    the bus approach
  • There are however a number of disadvantages to
    the bus topology
  • a) generally a minimum distance is required
    between stations to avoid signal interference
  • b) there is no easy way to run diagnostics on
    the entire network
  • c) the inherent security features of a star
    network are not available (common highway)

38
Bus Topology
File Server
39
Ring Topology
  • A ring topology consists of several nodes
    (workstations) joined together to form a
    circle
  • Messages proceed from workstation to
    workstation, usually in one direction only
    (some networks can work bi- directionally but
    they can only send in one direction at a time)
  • Ring topology permits verification that a
    message has been received
  • When a node receives a message addressed to
    itself it copies the message and then send a
    receipt to the sender

40
  • one of the main issues in a ring topology is
    ensuring that all workstations have equal access
    to the network
  • In a token ring network a data packet known as
    a token is sent from the transmitting station
    throughout the network. This contains the
    address of the sender and the address of the
    node to receive the message
  • When the receiver has copied the message it
    returns the token to the sending station, which
    then passes the token to the next node in the
    ring.
  • If there is nothing to send, the token is
    passed on to the next node

41
  • For system administration purposes one
    workstation is designated as the monitoring
    node
  • this node handles all diagnostic functions
  • Advantages to ring topology
  • a) if the monitoring node fails the network
    still remains operative
  • b) with appropriate by-pass software the network
    can withstand the failure of a number of
    workstations by simply bypassing them
  • Additional ring networks can be linked through
    bridges (more later)

42
  • If several workstations are connected to form a
    ring it can be difficult to add new
    workstations at a later date
  • the network has to be shutdown while the new
    station is installed and the cabling
    reconnected
  • This is why most ring networks now come with
    wire centres
  • these allow workstations to be added and
    removed at the appropriate wire centre
    without disturbing the operation of the
    network

43
Ring Topology
Wire Centres
44
Mesh Topology
  • A mesh network topology has two or more paths
    to any node on the network.
  • It is relatively immune to bottlenecks and
    channel or node failures, because of the several
    paths between nodes
  • It is easy to route traffic around failed or
    busy nodes or cables
  • It is expensive but offers great reliability

45
(No Transcript)
46
Hubs
  • Hubs are simple devices that connect groups of
    users into a local area network (LAN)
  • They forward any data packets they receive over
    one port from a workstation to all of the other
    ports
  • All users connected to a single hub or stack of
    connected hubs are in the same segment
    sharing the hubs bandwidth (data carrying
    capacity)
  • As more users are added to a segment they
    compete for a finite amount of bandwidth
  • This will have an effect on performance

47
Managed Hubs
  • These allow you to monitor and control various
    aspects of the hubs operation from a remote
    computer
  • Benefits
  • they can keep network statistics
  • they can alert you to network errors
  • They can be reconfigured from any computer on
    the network
  • But they cost three times as much

48
Switches
  • Switches are smarter than hubs and offer more
    dedicated bandwidth to each user or group of
    users
  • A switch forwards data packets only to the
    appropriate port that the intended recipient
    is connected to
  • this is based on information in each packets
    header.

49
  • the switch establishes individual, temporary
    connections between the sources and
    destinations of particular transmissions.
  • the connection is terminated once the
    conversation is finished
  • A switch is a cost effective solution if the
    aim is to optimise internal network performance
  • A switch may consist of ports of different
    speeds e.g 10Mbps Ethernet ports, with 100Mbps
    ports for fast connection to other switches or
    servers

50
Bridges
  • A device to connect two networks so that they
    act as if they are one
  • Used to partition one large network in to a
    series of smaller ones for performance reasons
  • A bridge can be thought of as a smart repeater.

51
  • A repeater listens to a signal coming down a
    cable amplifies it and sends it down another
    cable
  • they do not consider the content of the signals
    at all
  • A bridge however can work out the address of
    each computer on either side of the bridge ie.
    It can inspect each message that comes from one
    side and only broadcast it to the other side if
    it is intended for a computer on the other side

52
  • Some bridges have the capability to translate
    messages from one format to another e.g.
    Ethernet to Token Ring
  • They can increase the efficiency of one large
    network by dividing it into two smaller more
    efficient networks
  • They work best in networks which are highly
    segregated ie. Where the sections do not talk
    much to each other but there is a large amount
    of traffic within each segment

53
Routers
  • Routers are even smarter than switches . A
    router is a node on the network, which means
    that messages can be directed to a router,
    bridges are invisible
  • They use a more complete packet address to
    determine which router or workstation should
    receive each packet next
  • Based on a routing table routers can help
    ensure that packets are travelling by the most
    efficient paths to their destinations

54
  • If a link between two routers fails, the
    sending router can determine an alternative
    route in order to keep the traffic moving
  • Routers also provide links between networks
    that speak different languages (protocols)
  • Because of their built in intelligence they can
    also provide basic levels of security by
    preventing certain traffic from accessing
    certain parts of the network

55
  • Routers can connect networks in a single
    location or set of buildings
  • They also provide interfaces for connecting
    LANs to Wide Area Network (WAN) services, such
    as connecting several branches together, or to
    the Internet
  • These WAN services are provided by
    telecommunications companies to connect
    geographically dispersed networks

56
  • They are not cheap but are essential for large
    networks
  • Some routers are computers with several network
    cards and special software to perform the
    router functions. NetWare and NT come with
    programs that allow a server to act as a router

57
Firewalls
  • A firewall is may be a router or a piece of
    software that sits between the outside world and
    the LAN. All traffic into and out of the LAN
    must travel through the firewall, which prevents
    unauthorised access to the LAN.
  • If you host a web-site on a server that is
    connected to your LAN a firewall is essential.
    Otherwise any one who visits the web-site can
    break into the LAN.

58
Gateways
  • Definition A device that connects dissimilar
    networks. They are used to connect Ethernet
    networks to mainframes and to the Internet
  • They translate messages from one networks
    format to anothers.
  • They are only necessary because there is no
    single standard for networks

59
Raid
  • In most networks a failed disk drive is a
    disaster.
  • A RAID system is a number of disk drives linked
    together, which are treated as if they are on
    large drive. If one of the drives in the system
    fails no data will be lost
  • Any drive that fails can be removed and
    replaced and the data that was on it can be
    reconstructed from the other drives

60
  • RAID stands for Redundant Array of Inexpensive
    Disks
  • These systems are usually held in a separate
    cabinet, which includes its own disk controller
  • The most advanced systems have hot swappable
    drives i.e. one of the disks can be shut down
    and removed while the system continues to
    operate. After the failed disk is replaced, the
    new disk just comes back on line without problems

61
Gigabit Ethernet
  • This is a relatively new version of Ethernet,
    which runs at 1000mbps instead of 10 or 100mbps.
  • It is also known as 1000baseX. It was design
    to operate over fibre-optic cabling but will
    eventually be able to work over high quality
    category 5 and upwards cable. Provided that the
    cable lengths are not too long (over 100 metres)
  • It is expensive and switches can cost several
    thousand pounds and one is needed at each end of
    the backbone

62
  • Useful web sites
  • www.cisco.com
  • www.techtutorials.com
  • www.zdnet.com
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