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Objectives
This lecture aims to help you:
1. Understand network topologies.
2. Understand network communication basics.
3. Understand packet switching mechanism.
4. Understand addressing/routing methodologies.
5. Understand communication protocols for streaming.
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Computing Network Topology
Definition:
• The way in which the connections within a computing network are
made (e.g., the shape or the layout).
Types:
• Physical refers to the physical design of a network. That is, how
different systems of a network are actually connected with cables
and wires.
• Logical refers to the data communication over the physical network.
That is, how systems communicate across the physical topologies.
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Physical Topologies
Bus
• Each of the systems in the network connects to a “line” (backbone).
Ring
• Each of the systems in the network is connected to its two respective
neighbours forming a ring.
Star
• Each of the systems in the network connects to a “central device” (hub).
Mesh
• Each of the systems in the network has a dedicated point-to-point link to
every other system.
Tree
• Like its name implies, it is a mix use of other types topologies with the
concept of hierarchy (root, nodes, branches, children etc.).
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Bus Topology
Advantages:
• Inexpensive, very low cost
• Easy installation/implementation
(adding/removing)
• Ideal for small networks (netcafe, studios)
Disadvantages:
• Speed/distance limitations.
• Highly depends on the
availability/robustness of the “line”
• Security issues
• Difficulty in troubleshooting
• Unmanageable for large networks
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Ring Topology
Advantages:
• Relatively low cost
• Easy installation
• Token-ring is secure
• Support to form larger network (e.g., small
enterprise intranet)
Disadvantages:
• Speed/distance limitations.
• Difficulties in change (moving, adding,
removing systems) and maintenance.
• One system would fail the entire network!
• Low efficiency
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Star Topology
Advantages:
• Easy installation/upgrading support
• Easy troubleshooting and maintenance
• Simplicities of operation
• Good security
• Ideal for larger networks
Disadvantages:
• Expensive (for long distance)
• Hub dependency – central hub is everything!
• Sometimes not efficient
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Mesh Topology
Advantages:
• Good connection possibility so no traffic
problem
• Security
• Robust
• Fault tolerant
Disadvantages:
• Difficult cabling
• Complex installation
• Connection redundancy
• Cost
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Tree Topology
Advantages:
• Best possible solution for large network
(WAN)
• Point-to-point communication is possible.
• Best topology for branched out networks.
• Each of systems get access to larger
networks in the hierarchy.
Disadvantages:
• Not suitable for smaller networks as it
wastes resources
• Highly depends on the root “backbone”.
• Difficult to configure after a certain point.
Root
Mesh Mesh Mesh
Mesh Star Bus Star Mesh
Star
Bus
Ring
Ring
Ring
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Logical Topology
Shared media (current Ethernet topology)
• Each of systems has the ability to access the physical layout whenever they need it
(unrestricted access).
• However, it could easily cause collisions when two or more systems send information
at the same time. A solution is to add a traffic detection mechanism to monitoring
current traffic.
• It is typically deployed in a bus, star, or hybrid physical topology.
Token based (old-fashioned technology from IBM)
• Use of a token to provide access to the physical media.
• The biggest problem of token is latency as systems have to wait until they get an
available token.
• It is typically deployed in a ring physical topology.
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Network Communication
Network communication
• Communication happens
between different nodes.
• Communication has to be
initialised by a node.
• The node knows which other
nodes it wants to
communicate.
• The node has to let other
nodes aware if they want to
communicate to them (e.g.,
make a link).
Human communication
• Communication happens
between different people.
• Communication has to be
initialised by someone.
• The person knows whom they
want to communicate.
• The person has to let other
people aware if they want to
talk to them (e.g., call their
names).
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Network Communication (cont.)
Network communication
• There are some controls to
make sure only the intended
receiver(s) will receive the
message.
• There are also some
mechanism to ensure the
smooth communication.
• Any of the two sides can end
the communication.
• A communication can not be
forced.
Human communication
• There are some controls to
make sure only the intended
person(s) will receive the
message.
• There are also some
mechanism to ensure the
smooth communication.
• Any of the people can end the
communication.
• A communication cannot be
forced.
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Network Communication (cont.)
Have you realised something important?
• Sender and receiver: important indeed.
• Make connections: switching.
• Know where to go: addressing/routing.
• Smooth communication: protocols.
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Switching
• Switching is the way to create communicational
channel to allow network nodes communicate with
each other in a network.
• In a traditional telephony network, switch
boards/exchanges are used to establish a direct &
physical dedicated connection between two nodes. This
process is normally called circuit switching.
• In a modern digital network (Ethernet or Internet), data
sending from one node are divided into a number of
blocks (packets) which are then transmitted individually
to another node through the network. This process is
normally called packet switching.
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Addressing & Routing
• Routing is a process of selecting paths to send
network traffic.
• Routing is the act of moving information across a
network from a source to a destination.
• The main activities of routing is to 1) determine optimal
(best possible) routing paths and 2) forward packages.
• Routing paths are pre-configured in static routing.
• Routing paths are selected by routing algorithms in non-
static (adaptive or dynamic) routing.
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Addressing/Routing Semantics
Unicast:
• Deliver a message to a single specified node in the network (one to one).
Broadcast:
• Deliver a message to all nodes in the network (one to many).
Multicast:
• Deliver a message to a group of nodes which are receivers (one to many).
Anycast:
• Deliver a message to the topologically nearest node in a group of potential
receivers (one to one of many).
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Network Switches, Hubs & Routers
Switches vs. hubs vs. routers:
• Switches and hubs create a network.
Routers join networks.
• Switches are more intelligent and they
have higher performance than hubs.
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Protocols
What is a communication protocol:
• It is a set of rules for exchanging messages in or
between systems.
• A protocol describes the syntax, semantics, and
synchronisation of communication.
• Protocols can be implemented in hardware or software.
• A data transmission in or between systems normally
requires a set of protocols (for example, Internet Protocol
Suite).
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Common Protocols
TCP (Transmission Control Protocol)
• A reliable but complex data exchange protocol used
for major Internet applications (e.g., emails).
• TCP operation is divided into three handshake
phases, connection establishment, data
transmission & connection termination.
UDP (User Datagram Protocol)
• An unreliable but simple data exchange protocol
commonly used for most contemporary Internet
applications (e.g., online games, streaming etc.).
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TCP
TCP header structure
Source port Destination port
Sequence number
Acknowledge number
Data offset Reserved Flags Window Size
Checksum Urgent pointer
Options
Data
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Research Tasks
• Give real-life examples of network topologies.
• What will be the best Ethernet topology for a small studio
with 20 staff & draw the diagram?
• Give real-life examples of different routing semantics.
• Draw the diagram of how multicast and unicast protocols
are used for video on demand.
• Compare TCP and UDP in terms of streaming.
