topologies, backbones, switching, and ethernet itnw 1325, chapter v, part i
TRANSCRIPT
Topologies, Backbones,
Switching, and Ethernet
ITNW 1325, Chapter V, Part I
Physical Topologies
Physical TopologiesOverview: Reflect geometry of physical connections only –
without devices, connectivity methods, or addressing Don’t reflect device types, connectivity methods, or
addressing schemes in use Three fundamental types are bus, ring, and star – can
be mixed to create hybrid topologies Important to understand in order to troubleshoot related
problems or change communications infrastructure Differ from logical topologies – reflect how digital data
propagates between nodes
Physical TopologiesOverview (continued): Physical and logical topologies used within the same
network may be very different The term topology commonly refers to a physical
topology when used alone – with logical used explicitly Too restrictive – rarely seen in their pure form in
medium-sized and large networks
Physical TopologiesBus: Implies nodes connected by a single cable without
employing connectivity devices Provides only one communications channel – baseband
transmission is supported only Enables only one node to transmit at a time – nodes
compete for the right to transmit Requires each node to passively listen for and accept
data directed to it – passive topology Nodes other than sending and receiving ones sense the
transmission but ignore the information sent
Physical TopologiesBus (continued): A broadcast transmission would be processed by all
connected nodes – parts of a single broadcast domain Requires resistors – terminators – at the cable ends to
prevent endless travel of the signal (signal bounce) Without terminators, old signals would keep bouncing
off the wire ends – prevent propagation of new signals Must be grounded at one end – helps to remove static
electricity that could adversely affect the signal Example – nodes connected with a coaxial cable and
sharing the available bandwidth (50-Ohm terminators)
Physical TopologiesBus (continued): Not scalable – performance degrades as more nodes are
added and compete for the right to transmit Hard to troubleshoot – errors are easily detected but
their exact source or location are difficult to locate Not fault tolerant – any single break or defect affects
the entire network disrupting transmissions Lack security – every connected node can read any data
transmission destined to it or to someone else The least expensive topology to set up – rarely used
today due to multiple carried drawbacks
Physical TopologiesBus (continued):
Physical TopologiesBus (continued):
BNC T-Connector BNC Terminator
Physical TopologiesRing: Implies that each node is connected to the two nearest
ones – with the entire topology forming a circle Each node accepts and responds to frames addressed to
it – while forwarding other packets to the next node Implies that each node to participates in delivery acting
as a repeater – active topology Employs twisted pair of fiber optic cable as medium
Physical TopologiesRing (continued): Not scalable – performance degrades as more nodes are
added and introduce additional transmission delays Not fault tolerant – a single malfunctioning node would
break the ring and disable the entire network Used by obsolete Token Ring networks
Physical TopologiesRing (continued):
Physical TopologiesStar: Implies nodes connected through a central connectivity
device – forwards frames to the recipient’s segment Requires more cabling – twisted pair of fiber optic –
and more configuration than bus or star topologies Requires proper configuration and constant availability
of the central device Enables connecting two devices only to each physical
segment – a cabling problem affects two nodes at most Enables many nodes to transmit at a time – depending
on the ability of the central device to handle the load
Physical TopologiesStar (continued): The most scalable topology – can be easily easily
moved, isolated, or interconnected with other networks The most fault tolerant – a malfunctioning node would
not affect any other node or a communication device The easiest to troubleshoot – having one node per
segment makes an error easier to locate Carries single point of failure – a problem with the
central connectivity device affects all connected nodes More expensive to set up and maintain – requires more
cabling and administration than other topologies
Physical TopologiesStar (continued): Limits the number of nodes per segment – may result in
reduced or eliminated competition for the medium Most widely used topology on modern networks
Physical TopologiesStar (continued):
Logical Topologies
Logical TopologiesOverview: Reflect how information propagates between nodes –
may differ from a physical topology used Important to understand when building networks,
troubleshooting them, or optimizing their performance Represented by two fundamental types – bus and ring
Logical TopologiesBus (“Local Broadcast”): Data travels from one network device to all other ones
on the segment – each connected node can access data Commonly supported by networks that use a bus, a star,
or a star-wired bus physical topology
Ring: Data follows a circular path between sender and
receiver – even in case physical connections form a star Supported by networks that use a ring or a star-wired
ring physical topology
Logical TopologiesBus (continued):
Logical TopologiesRing (continued):
Hybrid Physical Topologies
Hybrid Physical TopologiesOverview: Complex combinations of fundamental physical
topologies – more suitable for modern networks Minimize weaknesses and increase scalability of
networks – better fit large and growing networks Two primary kinds – star-wired ring and star-wired bus
Hybrid Physical TopologiesStar-Wired Bus: Implies groups of nodes that are star-connected to
connectivity devices that are connected via a bus Enables covering longer distances and interconnecting
or isolating different network segments Inherits fault-tolerance, scalability, and manageability
from a star topology Requires more cabling and more connectivity devices
than a star or a bus – more expensive than basic ones A basis for modern midsize and large Ethernet
networks
Hybrid Physical TopologiesStar-Wired Bus (continued):
Hybrid Physical TopologiesStar-Wired Ring: Implies groups of nodes that are star-connected to
connectivity devices – and the ring logical topology Data flows in a circular pattern over the star-like wiring Inherits fault-tolerance, scalability, and manageability
from a star topology A basis for obsolete Token Ring networks
Hybrid Physical TopologiesStar-Wired Ring (continued):
Backbone Networks
Backbone NetworksOverview: Cabling that interconnects various parts of enterprise –
local and remote offices, departments, and computers Commonly carry substantially more traffic than cables
connecting to workstations – possess increased capacity Designed for continuous high throughput to avoid
congestion – complex and require careful planning Four fundamental types – serial, distributed, collapsed,
and parallel
Backbone NetworksSerial: Implies two or more internetworking devices connected
to each other in a daisy-chain fashion (linked series) Used for extending networks and adding device ports to
connect more user workstations Requires to observe the maximum number of connected
devices and segments – depends on the network type Not scalable – delays in information delivery increase
as more devices are added to the backbone Not fault tolerant – any single break or defect affects
the entire backbone disrupting transmissions
Backbone NetworksSerial (continued): The simplest logically, the least expensive, and the
easiest to implement backbone type
Backbone NetworksDistributed: Consists of a number of connectivity devices connected
to multiple central devices in a hierarchy More devices can be added to existing layers – allows
for simple expansion at lower costs of adding networks Can employ advanced devices for connecting LAN
segments – raise effectiveness of data transmissions Maps onto the structure of a building – with some
devices serving floors and/or departments and other ones connecting these segments together
Enables segregation and easy management of networks
Backbone NetworksDistributed (continued): May include a daisy-chain linked bus – inherits its
limitations requiring to place it thoughtfully Device at the upper layers represent potential single
points of failure – can damage the entire network Brings relatively simple, quick, and inexpensive
implementation – popular on today’s LANs and MANs
Backbone NetworksDistributed (continued):
Backbone NetworksCollapsed: Implies having the single central connection point for
multiple networks – connects multiple LANs together Makes the central device the highest level of the
backbone – must be able to handle heavy traffic loads Scalable – makes addition of new segments easy, with
potential necessity to upgrade the central device only The central network device represents single point of
failure for the entire network – must be available Fault tolerant – a failed segment does not affect others
Backbone NetworksCollapsed (continued): Centralizes maintenance and troubleshooting and
enables interconnecting networks of different types
Backbone NetworksCollapsed (continued):
Backbone NetworksParallel: Resembles other backbone types – implies duplicate
connections between connectivity devices Doubles the amount of cable needed and physical ports
used on network devices – can be quite expensive Provides network load balancing, redundancy, and
increased performance Most robust backbone type – commonly implemented
within critical segments of the network