On any network there are two types of computers present servers
and clients. By definition Client-Server architecture refers to
Client server architecture is servers providing requests for
clients. Clients request a service and wait for a response.
Slide 4
For example when a web server retrieves and transmits web pages
OR a database server retrieving and transmitting records. A client
is: a computer that requests a service. A Server is: a computer on
a network dedicated to providing clients with a service. Eg. Web,
Email or Print.
Slide 5
This definition seems to imply that servers are a special type
of dedicated computer on a network and on a large LAN this might be
the case. For a home network this is not the case. A computer in a
small office that connects to the internet could act as a web
server or similarly a print server.
Slide 6
Regarding client machines there are two types Fat clients and
Thin clients. A Fat client is a client that has applications
installed that are executed by the client CPU. A thin client is a
basic computer terminal that is involved in simple tasks such as
displaying data.
Slide 7
Slide 8
The topology of a network describes the way in which the
devices (nodes) are connected. A node is any device connected to a
network including computers, printers, hubs, switches and routers.
All nodes must be able to communicate using the suite of protocols
defined for the particular networks. Nodes are connected to each
other via transmission media, either wired or wireless.
Slide 9
The topology of a network describes these connections in terms
of their physical layout and also in terms of how data is
transferred between nodes. We call this Physical and Logical
Topologies. The Physical Topology determines how the devices are
physically connected. The Logical Topology describes how nodes
communicate with each other rather than how they are physically
connected.
Slide 10
There are three basic topologies the bus, the star and the
ring. In addition there are two other topologies common on larger
networks hybrid and mesh. We will look at these in terms of the
Physical and Logical Topologies which are often different.
Slide 11
Physical Bus Topology All nodes are connected to a single
backbone also known as a trunk or bus. The backbone is a single
cable that carries data packets to all nodes. Each node attaches
and listens for data present on the backbone. A single break in the
cable deactivates the entire network.
Slide 12
Physical Bus Topology
Slide 13
Physical Star Topology All nodes connect to a central node via
their own dedicated cable. Mostly used for LANs. Central node is
usually a switch containing multiple ports. Advantages: if one node
goes down, others dont and nodes can be added or removed without
the network being deactivated. Wired routers use star.
Slide 14
Physical Star Topology
Slide 15
Physical Ring Topology Similar to BUS except the cable makes a
complete ring. Nodes are connected in series which means that if
one is deactivated, all others suffer because the series is broken.
Similarly adding or removing a node requires the network to be
stopped.
Slide 16
Physical Ring Topology
Slide 17
Physical Hybrid Topology Hybrid networks use a combination of
bus, star and ring topologies. Commonly a bus is the start, or
backbone, of the network with a series of physical star networks
branching off. All hybrid topologies have a single transmission
between each node which is why they can often be called a
tree.
Slide 18
Physical Hybrid Topology
Slide 19
Physical Mesh Topology A physical mesh topology means that
there are more than one physical path between each pair of nodes.
This is the primary topology of the internet where IP datagrams can
travel different paths from the transmitter to the reciever.
Commonly the nodes on a network are all routers and each router
connects to further routers or a LAN.
Slide 20
Physical Mesh Topology
Slide 21
As a reminder The logical topology of a network describes how
data is transmitted and received on a network regardless of the
physical connections.
Slide 22
Logical Bus Topology Logical Topology (or Flow of data) in BUS
makes use of CSMA/CD Carrier Sense Multiple Access with Collision
Detection. This means a node will send data if transmission medium
is available (BUS is clear). IF a collision occurs, the node waits
and sends again.
Slide 23
Logical Ring Topology Data, in packets or frames, circulate the
ring one at a time through each node in the network. As a result
there cannot be data collisions. Ring networks use either Ethernet
or token ring protocols. Token ring is a token that continually
circles around the network.
Slide 24
Logical Star Topology The logical flow of data matches the
physical star layout. Nodes are attached to a central switch which
sends information back and forth to each node along its own network
segment.