This document discusses various network technologies including transmission medium, link configuration, user mobility, area coverage, topology design, and network integration. It describes wired and wireless transmission mediums, point-to-point and point-to-multipoint link configurations, and how networks are designed based on factors like scalability, fault tolerance, and ability of nodes to communicate. It also summarizes common network topologies including bus, star, ring, and their characteristics, and how bridges, routers, gateways, and switches can integrate local and wide area networks.

1. LAN and WAN Technologies
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2. Categorizing Network Technologies
• Transmission Medium
 Wired vs Wireless
• Link Configuration
Point-to-point vs Point-to-multipoint
• User Mobility
 Fixed vs mobile
• Types of Users
Access vs core (backbone)
• Coverage Area
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3. Selecting the Transmission Medium
• Wired
o No interference from others ! high data rates, easy to
o upgrade capacity
o Small, predictable delay
o Expensive to install in hard to access locations
o Device locations are fixed
• Wireless
o No physical connection ! mobility, convenience
o Interference, varying channel conditions ! poor
o performance
o Licenses often required
o Hard to add more capacity
o Physical security is difficult
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4. Access vs Core Network
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5. Area Coverage
 In centimeters; people, objects
– Body Area Network
– Personal Area Network
– Infrared, Bluetooth, ZigBee, IEEE 802.15.4, . . .
 In meters; homes, offices, buildings
– Local Area Network
– Home Area Network
– Storage Area Network
– IEEE 802.3 (Ethernet), IEEE 802.11 (WiFi), Fibre
– Channel . . .
 In kilometers; cities, countries, between countries
– Metropolitan Area Network
– Wide Area Network
– PDH, SDH, ATM, Frame-Relay, WiMax, satellite, . . .
 In megamergers; globe, between planets
– Global Area Network
– The Internet, interplanetary networks
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6. Topology Design Requirements
• Station should be able to communicate with any other
station
• Dedicated point-to-point links are better than shared
multipoint links
• Use as few links as possible
• Scales well: adding a new node requires little effort
• Fault-tolerant: failure of a link still allows other nodes
to communicate; failure of a device doesn't prevent
other nodes from communicating
• Fault-detection: a fault can be automatically detected
by network
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7. Network Topologies Links
• Links: point-to-point, point-to-multipoint
– Mesh: every station has point-to-point link to
every other station
– Bus: every station connected via a multipoint link
– Ring: point-to-point links between pairs of
stations, or via special link, to form ring
– Star: every station has point-to-point link to
central device
– Hybrid: combination of 2 or more of above, e.g.
tree is combination of star and bus topologies
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8. Full Mesh Topology
• Used in small WANs; becomes too complex as
number of nodes increase
• Each pair of nodes have dedicated point-to-
point link
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9. Partial Mesh Topology
• Selection of node pairs have point-to-point link
• Some pairs can not communicate, unless nodes can
forward data.
• Used in WANs
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10. Bus Topology
• Used in early (Ethernet) LANs, but replaced by star
• point to multipoint link(one node transmit the others
receives)
• Transmission propagates throughout medium and is heard
by all stations
• Terminator absorbs frames at end of medium/cable
• Pros: easy installation
• Cons: require protocols to share medium
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11. Ring Topology
• Unidirectional point-to-point links to form loop
• Stations attach to repeaters
• Pros: simple to install and reconfigure; easy to identify
faults
• Cons: require protocols to share medium; traffic flows in
one direction
• Usage: old LANs (e.g. IBM/IEEE 802.5 Token Ring)
• Dual ring is still common in MANs and WANs
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12. Star Topology
• Traffic between stations goes via the central node
• Usually two point-to-point links between station and
central node (or duplex link)
• Pros: easy to install; fault tolerance for links
• Cons: depends on central node
• Usage: Most LANs today
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13. Point-to-Multipoint Links
• Multiple users share a point-to-multipoint link
• Typical for wireless systems (WiFi, mobile phone) and some wired LANs
• Use multiple access schemes to determine who transmits and when
– Fixed Assignment : e.g. FDMA(Frequency Division Multiple Access),
TDMA(Time Division Multiple Access)
• The sub channel assignments are fixed and the same.
• FDMA used in radio systems to share the radio spectrum.
• TDMA used in digital transmission technology
• This techniques is suitable for broadcast satellite communication
– Demand Assignment: Eg. Reservation, polling
• The sub channel allotment depends on user’s demand(use time to divide).
• Ignore idle nodes and consider only nodes that are ready to transmit
• This technique is suitable for point to point communication.
– Random Access : eg. CSMA
• unpredictable performance
– Demand Assignment and Random access called Medium Access Control (MAC)
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14. Medium Access Control
• In a shared medium, if two (or more) stations transmit at the same
time, there is a chance the two transmissions will interfere with
each other
• Collision of frames: receiver receives two or more frames partially
overlapping in time; assume all frames are corrupted/lost
• Medium Access Control: allow one station to use the shared
medium at a time (avoiding collisions)
• MAC techniques must give stations opportunities to transmit: fair
and efficient
Demand Assignment reservation, polling, round-robin
– Stations are coordinated by a schedule
Random Access Aloha, CSMA
– Stations wait a random time and transmit if no-one else is currently
transmitting
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15. WANs and LANs
• Wide Area Networks(WAN)
– Connect devices/networks over large geographical area
– Between campuses, offices buildings, cities, countries
– Owned and operated by organizations on behalf of
– users, e.g. TOT, CAT, TT&T
– Leased to users, e.g. unis, companies, smaller ISPs
• Local Area Networks(LAN)
– Connect end-user devices over small area
– Within campuses, buildings, homes
– Owned and operated by organization using the network
– Typically support higher data rates than WANs (internal
– communications, multiplexing)
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16. Selecting the Link Configuration
• Point-to-point
– Dedicated link for users ! high, predictable
– Performance
– Need many links, planning of end-points (Topology)
– Wired links, wireless links with directional antennas
• Point-to-multipoint
– Cover multiple users with single link
– Requires sharing of medium: multiple access, Medium
– Access Control protocol
– Wireless links with omnidirectional antennas, shared
– wired links
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17. Identifying a Network Type
• Communications medium
– Wire cable, fiber-optic cable, radio waves, microwaves
• Protocol
– How networked data is formatted into discrete units
– How each unit is transmitted and interpreted
• Topology
– Physical layout of cable and logical path
• Network type
– Private versus public
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18. LAN/WAN Integration
• Becoming more advanced through networking
devices
– Bridges
– Routers
– Gateways
– Switches
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19. Bridges
• Connect different LANs or LAN segments using
the same access method
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20. Routers
• Connect networks having the same or
different access methods and media
• Forward packets and frames to networks by
using a decision-making process based on:
– Routing table data
– Discovery of most efficient routes
– Preprogrammed information from network
administrator
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21. Routers
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22. Gateways
• Enable communications between two
different types of networked systems
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23. Switches
• Link network
segments
• Forward and filter
frames between
segments
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24. Integrating Data Between LANs and
WANs
• Translation(Gateway)
• Encapsulation(Data PDU)
• LAN emulation (LANE): Local Area Network
Emulation (LANE) enables local area network
(LAN) data bridging and routing over an
Asynchronous Transfer Mode (ATM) network
and facilitates the exchange of Ethernet and
token ring network data.
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25. Media Access
• Perhaps the most important part of data link
protocols. This part determines the way a
particular device gains the right to transmit
data on the medium
• There are two main standards that are
adhered to—contention and token passing.
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26. Contention
• Each station has equal access to the medium.
– Each node monitors the medium to see if a
message is being transmitted.
– If no message is detected then any node can
transmit.
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27. Collision
• One of the challenges with contention is the
possibility that two stations will transmit at
the same time.
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28. CSMA/CD
• An alternative format to straight contention
• Known as a fair protocol
– All nodes listen to the medium to see whether a message
is being transmitted
– If medium is quiet, transmit message. If medium is busy,
wait for the signal to clear then transmit.
– If a collision occurs, wait for the signal to clear, then wait
for a random interval, and then retransmit
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29. Token Passing Media Access Protocol
– Nodes wait to transmit token
– If transmit token is received and there is no message to
send, send the token to the next node.
– If token is received and there is a message to send, then:
• Transmit message
• Wait for acknowledgement
• When acknowledgement is received, pass the token to the next
mode.
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30. Token Ring versus Ethernet (CSMA/CD)
• Token Ring networks are deterministic in nature -nodes may only transmit at certain well
defined times. Result is high bandwidth efficiency. Up to 90% in Token Ring, 40% in Ethernet.
• Guaranteed sequential access to network eliminates fluctuating response times experienced
on other network topologies.
• Token Ring performance does not deteriorate to the same extent as Ethernet when network
traffic increases. This means that at high loads, the presence of collisions of data frames on
Ethernet networks becomes a major problem and can seriously affect the throughput.
• By its nature Token Ring has a higher reliability, the ring can continue normal operation in
most cases despite any single fault.
• Ethernet has an advantage over Token Ring in that the cost of network equipment is lower
for Ethernet. Token Ring networks tend to be more expensive to set up and maintain than
Ethernet, although hardware costs for Token Ring are decreasing.
• Advances in Ethernet technology have tended to be much more rapid than Token Ring.
Gigabit Ethernet being an example of this. Token Ring technologies are being developed
however to allow data transfer rates of 100Mbps using technologies such as Token Ring
Switching.
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