Transcript Network - CISIVY

Chapter 9 Network Organization
Concepts
CIS106
Microcomputer Operating Systems
Gina Rue
CIS Faculty
Ivy Tech State College Northwest Region 01
Introduction Network Organization Concepts
• Stand-alone computers linked together
through communication systems to form
networks transmit & process data &
information among users in the system
• Goal of networked systems are to provide
a way to share resources:
– hardware: CPU, memory, printers, tape, and
disk drives
– software: programs & data files
See Fig. p.199
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Introduction Network Organization Concepts
OS Types for Networking
• OS built for the network is built on top of
the existing local computer OS is referred
to as a Network Operating System
– users can access resources by:
– logging on to a remote host
– transferring data from the remote computer
to their own
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Introduction Network Organization Concepts
• The Distributed OS provides good control
for distributed computing systems &
allows their resources to be accessed in a
unified way
– advantages: easy & reliable resource
sharing, improved computation performance,
adequate load balancing, dependable
electronic communications among users
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Basic Terminology
• Network is a collection of processors
interconnected by a communication
network
• In a distributed system each processor
classifies the other processors & their
resources as remote & considers its own
resources as local
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Basic Terminology
• Size, type, and identification of
processors varies
• Processors are referred to as sites, hosts,
& nodes
– site is a specific location on the network
containing one or more computers
– host is a specific computer system found at a
site whose services & resources can be used
from remote locations
– node refers to the name assigned to a
computer connected to the
network
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Basic Terminology
• Typically a host at one site is called the
server & has resources that a host at
another site, called the client wants to
use
• Hosts can alternate between being
clients or servers depending on the
requirements
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Network Topologies
– Networks can be physically or logically
connected in a variety of topologies
• Common arrangements are:
– star, ring, bus, tree
– Each topology has tradeoffs
• need for fast communication among all
sites
• tolerance of failure at a site or
communication link
• difficulty of connecting one site to a
large number of other sites
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Network Topologies
– Deciding which configuration to use,
system designers should
consider 3 criteria:
• Basic cost
– expense required to link the various
sites in the system
• Communication cost
– time required to send a message from
one site to another
• Reliability
– assurance that many sites can still
communicate with each other even if a
link or site in the system fails
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Network Topologies
– Star
• sometimes called a “hub” or “centralized”
approach to interconnect devices
• data must pass through a central controller
when going from sender to receiver
• permits easy routing, central station knows
the path to all other sites
• central points makes access to the network
easy to control and priority status
• central site must be extremely reliable & able
to handle heavy network traffic
See Fig. 9.1 p.201
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Network Topologies
– Ring
• all sites are connected in a closed loop
• data is transmitted in packets also contain
source & destination address fields
• a data packet is passed in one direction from
node to node to a local buffer on the
destination node
• a packet will continue to move through the
ring & returns to the source then removed
from the ring
• several variations with more flexibility but at a
cost
See Fig. 9.2 p.202
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Network Topologies
– Bus
• all sites are connected to a single
communication line running the length of the
network
• physically connects the devices by cables that
run between them
• only one node can send a message
successfully at one time
• data may pass directly from one device to
another or may be routed to an end point
controller
See Fig. 9.5 p.206
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Network Topologies
– Tree
• a collection of busses
• communication line is branching cable with no
closed loops
• tree layout begins at the “head end” one or
more cables start
• each cable may have branches that may
additional branches
• bridges are used to translate different
protocols
See Fig. 9.6 p.206
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Network Topologies
– Hybrid
• combination of any of the four topologies
• Objectives
– select among the strong points of each
topology
– combine topologies to meet the that
system’s communication requirements
most cost effectively
See Fig. 9.7 & 9.8 p.207
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Network Types
Often used to group networks
according to the physical distances
they cover
– Local Area Network (LAN)
– Metropolitan Area Network (MAN)
– Wide Area Network (WAN)
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Network Types
Local Area Network (LAN)
– configuration found in a single office
building, warehouse, campus, lab
• generally owned, used, & operated by a
single organization
• LAN can be a component of a larger network
– Bridge is a device & software that
connects two or more LANs that use the
same protocols
– Gateway is a more complex device &
software used to connect two or more
LANs that use different protocols
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Network Types
Local Area Network (LAN)
– operates at speeds from one MB per second
to one GB per second
– bandwidths are available to support highspeed transmission for graphics, video,
digital, & voice
– transmission medium varies from one
topology to another - cable, wire, fiber-optic
– transmission medium considerations are
cost, data rate, reliability, number of devices,
distance, & technical limitations
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Network Types
Metropolitan Area Networks (MAN)
– defines configurations spanning an area
larger than a LAN, ranging from several
blocks to an entire city, not exceeding 100
kilometers
– may be owned & operated by a single or
many individuals & organizations or by public
utilities providing means for connecting LANS
• typically configured as a ring for one direction
transmission or dual ring transmitting in two
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directions
Network Types
Wide Area Network (WAN)
– configuration that interconnects
communication facilities in different parts of
the country or world, or operates as part of a
public utility
– use communication lines of “common
carriers” such as telephone companies
• use broad range of media, satellites,
microwaves & high-speed transmission
• generally slower than LANs
• Internet is the most widely recognized WAN
• ARPnet, Telenet
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Software Designing Issues
Network designers must address four
issues:
– How do sites use addresses at other sites?
– How are messages routed & how are they
sent?
– How do processes communicate with each
other?
– How are conflicting demands for resources
resolved?
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Software Designing Issues
Addressing Conventions
– sites need to be uniquely identified by using
names, addresses & routes
• local name refers a name each unit is known
by on its own system
• global name refers to a name each unit is
known by outside its own system
– Domain Name Service (DNS) protocol a
general purpose distributed data query
service that resolves Internet addresses
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Software Designing Issues
Routing Strategies
– allows data to get from one point on the
network to another
• requires each destination be uniquely identified
• forwards data between networks
– each router records a table of addresses of the
networks that are connected
• variety of message formats
• two most common routing protocols, routing
information protocol & open shortest path first
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Software Designing Issues
Routing Strategies
– Routing Information Protocol (RIP)
• chooses the best path for data transfer with the
smallest number of “hops”
• distance vector algorithm is easy to implement
but may not choose the most reliable path
– Open Shortest Path First (OSPF)
• if an intermediate hop is malfunctioning it is
eliminated from consideration until it is restored
• topological database data structure is maintained
by OSPF & updated when failure occurs
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Software Designing Issues
Connection Models
– not concerned with data content, but with
moving data from one point to another
– network designed to minimize costs
– provides full connectivity among attached
devices
– data entering the network at one point is routed
to its destination by switching from node to
node, whether by
• circuit switching
• packet switching
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Software Designing Issues
Connection Models
– Circuit Switching
• communication model where a dedicated
communication path is established between 2
hosts
• the path is a connected sequence of links
• connection between points only exists until one is
disconnected
• telephone system a good example
• once connection is complete, transparent to users
• information transmitted at a fixed rate
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Software Designing Issues
Connection Models
– Packet Switching
• store-and-forward technique
• message is divided into multiple equal-sized units
called packets
• packets reaching a destination are reassembled
• effective for long-distance transmission
• flexible to different transmission rates
• no guarantee data will arrive in physical
sequential order
• allows users to set priorities to their messages
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Software Designing Issues
Connection Models
– Packet Switching, two methods of selecting a
path
• datagrams
– destination & sequence number of the packet
is added, a route is selected as it is accepted
into the network
• virtual circuit
– destination & packet sequence number are
not added because complete path from sender
to receiver is established before transmission
starts
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Software Designing Issues
Conflict Resolution
– Because networks consist of devices
sharing a common transmission
capability, a method to control access is
necessary to facilitate equal & fair
access to this common resource
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Software Designing Issues
Conflict Resolution
– Access Control Techniques
• Round Robin
– Allows each node to use the communication
medium for a certain amount of time
• Reservation
– Access time on the medium is divided into
slots & nodes can reserve future time
• Contention
– no attempt is made to determine whose turn
it is to transmit so nodes compete for access
to the medium
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Software Designing Issues
Conflict Resolution
– Medium Access Control Procedures
• Carrier Sense Multiple Access (CSMA)
– contention-based protocol
– a node on the network will listen to, or test,
the communication medium before sending a
message
– prevents collision with another node currently
transmitting
• Carrier Sense Multiple Access with Collision
Detection (CSMA/CD)
– Ethernet most widely known
– reduces the number of collisions
See Fig. 9.9 p.216
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Transport Protocol Standards
In the early 1980s network usage grew
& the need to integrate dissimilar
network devices & their complexity
• To allow multi-vendor interoperability,
two standards were developed
– International Organization for
Standardization (ISO)
– Transmission Control Protocol/Internet
Protocol (TCP/IP)
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Transport Protocol Standards
International Organization
Standardization (ISO)
– makes technical recommendations about
data communication interfaces
– Open System Interconnect (OSI) reference
model is the frame work for defining the
services that a network should provide to its
users
– 7 layers are used to group localized functions
so redesigning layers & protocol to take
advantage of changing services
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Transport Protocol Standards
ISO-OSI reference model
Layer 1 - Physical Layer
Layer 2 - Data Link Layer
Layer 3 - Network Layer
Layer 4 - Transport Layer
Layer 5 - Session Layer
Layer 6 - Presentation Layer
Layer 7 - Application Layer
See Fig. 9.10 p.218
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Transport Protocol Standards
Transmission Control Protocol/Internet
Protocol (TCP/IP)
– oldest & most widely used protocol developed by
U.S. Dept. of Defense’s ARPAnet
– provides efficient & error-free transmission
between different systems
– file-transfer protocol (FTP) allows large files to be
sent across unreliable networks error-free
– Three main components:
• processes, hosts, networks
See Fig. 9.11 p.221
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Transport Protocol Standards
Transmission Control Protocol/Internet
Protocol (TCP/IP)
Layer 1 - Network Access
Layer 2 - Internet
Layer 3 - Host-Host
Layer 4 - Process/Application
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Summary
• Network operating systems (NOS)
include functions of the four managers
– memory
– processor
– device
– file
• NOS need to coordinate all functions
among network hardware & software, no
matter where they are physically
located
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Summary
• NOS success must meet reliability
requirements of its owner, NOS must
detect:
– node failure
– changing routing instructions to avoid that
node
– make sure lost messages are retransmitted
until successfully received
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Summary
• Introduced basic network organization
concepts:
– common terminology
– network topologies
– types of networks
– software design issues
– transport protocol standards
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