Download Architectures and Topologies

Computer Networks
Week 05
Architectures & Topologies College of Information Science and Engineering
Ritsumeikan University
The Three Basic Types of
Network Architecture
Peer-to-peer networks are decentralized
networks for interactions between similar
software and devices, such as personal
computers
l  In client-server networks, a central computer,
such as a workstation or server, serves as a
source and destination for many different
computers
l  Most networks are a combination of these two
types of architecture and are called hybrids.
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Peer-to-Peer Basics
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Allow resources (files, printers, etc.) to be shared
Best for smaller groups
Allow easy, decentralized communications
Each peer-to-peer network is called a workgroup
Multiple workgroups can be implemented on the
same network
The workgroup name allows users to know
which peer-to-peer network is being used
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Client Server Basics
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Centralized architecture for data storage,
security, applications, network
administration and other services
Also called server-based networks, the
client-server network architecture is highly
scalable
Servers provide central points from which all
services can be provided
Management, administration, and security
can all be controlled centrally by
administrators
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Hybrid Network Architectures
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Many networks employ some characteristics of
both client-server and peer-to-peer
architectures
Central management allows control and
security of client-server architectures
Local resources can be allocated on a peer-topeer basis through workgroups for flexibility
Network access and security measures, such
as password control, can be troublesome for
both administrators and users
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Topologies: Main Points
Topologies show how the network
(usually a LAN) is connected
l  Physical topologies describe how the
lines of a network are connected and
there are several types
l  Logical topologies describe how the
information moves through a network
and there are only a couple of types
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Physical vs. Logical Topologies
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Physical
How the wires are
connected
How different
devices are
physically connected
Several types: bus,
ring, star, mesh, and
several hybrids
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Logical
How the data is
transferred
How media is
accessed and
packets are
transmitted
Two types: bus or
ring
Physical Topologies
Three most common types are bus,
ring, and star
l  Best physical topology is determined
by cost, scalability, bandwidth
capacity, ease of installation and
troubleshooting
l  Most networks use star topology
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Physical Bus Topology
Single central cable (usually coaxial cable) is
the axis of the network
l  Advantages: inexpensive, require less cable,
easy to add on, good for small networks
l  Disadvantages: depends on the backbone,
number of devices limited, difficult to isolate
problems, can have slow access times
l  This legacy topology is important because of
the history of Ethernet
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Physical Bus Topology
terminator
device physical cable
Bus Components
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Terminators were
placed at either end of
the bus
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BNC (Bayonet NeillConcelman) allowed
each device to be
attached to the
network
Bayonet mount
Ethernet as a Physical Bus
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Metcalfe’s original conception of the “Ethernet”
for connecting a desktop computer to a printer 12
Physical Ring Topology
Stations are connected in a circle and
data moves in one direction (single-ring
topology) or in both directions (dual-ring
topology)
l  Advantages: high speeds, no collisions,
easy to find problems, no terminators
l  Disadvantages: more cable, less fault
tolerance, adding requires shutdown,
less common so equipment is scarce
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Single Physical Ring
direction
cable
device
Dual Physical Ring
direction
physical cable
device
Physical Star Topology
All devices are connected by a central device
l  Most Ethernet LANs are star or extended
star systems connected by hubs or switches
l  Advantages: easy to add or remove devices,
good fault tolerance, central management,
easy to troubleshoot, most common
topology, easy to upgrade
l  Disadvantages: requires a lot of cable and
devices, may cost more, depends on the
central hub
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Physical Star
cable
device
hub,
switch,
etc.
Physical Extended Star
Similar to (or the same as) the
topology known as the tree topology
l  Hubs of more than one star topology
are connected
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Physical Mesh and FullyConnected Topologies
All devices may be connected to all
other devices
l  Disadvantages: extremely expensive
and difficult to install, maintain,
troubleshoot, low scalability
l  Advantages: extremely fault tolerant
for reliable connection
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Fully Interconnected
Logical Topologies
Only two basic types need to be studied:
the logical bus and the logical ring
l  Recall the physical bus and the physical
ring
l  The logical topologies describe how the
data moves from device to device: like a
bus or like a ring
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Logical Bus Topology
Ethernet hubs act as buses
l  Data moves out from the source in
both directions on the “bus”
l  Advantages: fault-tolerance, common,
easy to change or add
l  Disadvantages: collisions can occur,
access is one-at-a-time
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Logical Ring Topology
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Token rings pass special data frames called
“tokens” around
When a device has data to transmit, it waits
for an empty token and inserts its data
Multistation Access Units (MAU) act as the
ring in physical star topologies
Advantages: amount of data that can be
transmitted is greater
Disadvantages: not fault tolerant, devices
must wait for empty token
WLAN Topologies
Wireless LANs (WLAN) are not bound by
ordinary topology conventions
l  Transmission is omnidirectional
l  The logical topology is usually a logical
bus, where radio is the medium
l  Wireless peer-to-peer may be a logical
mesh or fully interconnected
l  Wireless access points (WAP) may be
connected to wired topologies
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