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Local Area Networks and Wide Area Networks

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Local Area Networks and Wide Area Networks. Computers in ... Wide Area Networks (WANs) WAN span a large geographic area, often a country or a continent. ... – PowerPoint PPT presentation

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Title: Local Area Networks and Wide Area Networks


1
Local Area Networks and Wide Area Networks
  • Computers in Business
  • Foundation Year

2
Local Area Networks
  • LANs
  • generally privately-owned networks within a
    single building or campus of a few kilometres in
    size.
  • Distinguished from other networks by 3
    characteristics
  • their size
  • transmission technology
  • topology

3
LANs Characteristics
  • Restricted in size
  • worst case transmission time is bounded and known
    in advance.
  • Transmission technology usually consists of a
    single cable
  • Various topologies employed in designing LANs

4
LAN ApplicationsPC Networks
  • Client/Server Communication
  • Shared databases
  • Shared hardware resources
  • Shared Internet access
  • Peer-to-Peer Communication
  • Sharing work and information with colleagues
  • Low cost is high priority
  • Attachment costs in the hundreds of dollars

5
LAN Topologies Bus
  • Multipoint medium
  • Stations attach to linear medium (bus) using tap
  • Full-duplex between station and tap
  • Transmission from any stations travels entire
    medium (both directions)
  • Termination required at ends of bus

6
Bus LAN Diagram
7
LAN Topologies Tree
  • Generalization of bus topology
  • Branching cable with no closed loops
  • Cable(s) begin at headend, travel to branches
    which may have branches of their own
  • Each transmission propagates through network, can
    be received by any station

8
Tree LAN Diagram
9
Bus/Tree Topology Problems
  • How do you identify who the transmission is
    intended for?
  • Data transmitted in frames
  • Each frame has header with addressing info
  • How do you regulate access?
  • Stations take turns sending, by monitoring
    control information in frames

10
LAN Topologies Ring
  • Repeaters are joined by unidirectional
    point-to-point links in a ring
  • As a frame circulates past a receiver, the
    receiver checks its address, and copies those
    intended for it into a local buffer
  • Frame circulates until it returns to source,
    which removes it from network

11
Ring LAN Diagram
12
LAN Topologies Star
  • Each station connected directly to central node,
    usually with two undirectional links
  • Central node can broadcast info, or can switch
    frames among stations

13
Star LAN Diagram
14
Choosing a Topology
  • Factors to consider include reliability,
    flexibility/expandability, and performance
  • Bus/tree is most flexible
  • Tree topology easy to lay out
  • Ring provides high throughput, but reliability
    problems
  • Star can be high speed for short distances, but
    has limited expandability

15
Transmission Media Options
  • Twisted pair--digital signaling
  • Optical fiber--analog signaling
  • Baseband coax--digital signaling
  • Broadband coax--analog signaling
  • Uses FDM to carry multiple channels
  • Can be used over longer distances
  • Inherently unidirectional, due to amplifier
    limitations

16
Selecting Transmission Media
  • Capacity Can it support expected network
    traffic?
  • Reliability Can it meet requirements for
    availability?
  • Types of data supported Is it well-suited to the
    applications involved?
  • Environmental scope Can it provide service in
    the environments required?

17
Ethernet(IEE 802.3)
  • Bus-based broadcast network with decentralised
    control operating at 10 or 100 Mps.
  • Computers on an Ethernet may transmit data
    whenever they want to.
  • If two or more packets collide, each computer
    waits a random time and tries again.

18
Wide Area Networks (WANs)
  • WAN span a large geographic area, often a country
    or a continent.
  • Collection of host computers connected by a
    communication subnet.
  • WANs consist of two distinct components
  • transmission lines (aka circuits, channels or
    trunks)
  • switching elements

19
Switching elements
  • Specialised computers used to connect two or more
    transmission lines.
  • When data arrives on an incoming transmission
    line, the switching element selects an outgoing
    line to forward them on.
  • Routers, aka packet switching nodes or data
    switching exchanges

20
Relation between hosts and subnet
Router
Subnet
Host
LAN
21
WANS communication
  • Most WANs consist of cables or telephone lines
    connecting a pair of routers.
  • If two routers that do not share a connecting
    cable wish to communicate with each other they do
    so through other intermediate routers.
  • Subnets using this principle called
    packet-switching subnet (or point-to-point).

22
WANS topology
  • LANs have a symmetric topology, WANs typically
    have irregular topologies.

Star
Tree
23
LANs and WANs
24
Example networks
  • Novell Netware
  • Most popular network system in the PC world.
  • Based on the Client/Server Model
  • Netware used its own proprietary protocol stack
    based on Xerox Network System XNS.

25
The Novell NetWare reference model
Layer
Application
Transport
Network
Data link
Physical
26
The Internet (history)
  • Predated by the ARPAnet
  • mid 1960s US Department of Defense created a
    command and control network that could survive a
    nuclear war
  • Advanced Research Projects Agency (ARPA) designed
    a packet-switching network consisting of a subnet
    and host computers.
  • 1974 development of TCP/IP model facilitated the
    growth of the ARPAnet, Universities connect to
    the network (TCP/IP established as the official
    internet protocol in 1983)
  • 1980s ARPAnet continued to grow, shut down in 1990

27
The Internet
  • Collection of existing networks
  • ARPAnet, NSFNET, SPAN (NASAs network), HEPNET,
    BITNET, EARN etc.
  • all based on the TCP/IP protocol stack
  • When is a computer on the Internet?
  • Runs the TCP/IP protocol stack
  • has an IP address
  • has the ability to send packets to all the other
    machines on the Internet.

28
TCP/IP
  • Transport layer protocols, basis of the Internet.
  • Transmission Control Protocol/Internet Protocol
  • Allows a byte stream originating on one machine
    to be delivered without error to another machine
    on the Internet.

29
Application Layer
  • Layer on top of the transport layer, containing
    all the higher-level protocols
  • Protocols include
  • TELNET - virtual terminal
  • FTP - file transfer protocol
  • SMTP - simple mail transfer protocol
  • DNS - Domain name server
  • NNTP - network news transfer protocol
  • HTTP - Hyper-text transfer protocol
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