Chapter 9

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Oct 24, 2013 (3 years and 5 months ago)

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Chapter 9


Computer Networks


Chapter Outline


Network Topology

Addressing and Routing

Media Access Control

Network Hardware

OSI Network Layers

TCP/IP

Focus



Voice over IP

Network Standards

Focus

-

Ethernet

Focus

-

Upgrading Network Capacity (Part II)


Chapter 9

Computer Networks

Chapter Goals


Compare and contrast

bus, ring, and star
network topologies


Describe

packet routing across local and
wide area networks


Describe

the CSMA/CD media access control
protocol


Describe

network hardware devices, including
network interface units, routers, and
switches


Describe

the OSI network model, the
TCP/IP protocol suite, and IEEE network
standards


Chapter 9

Computer Networks

Network Topology


Spatial organization of network devices,
physical routing of network cabling, and flow
of messages from one network node to
another



Can be physical or logical



Three types


star
,
bus
,
ring



differentiated by


Length and routing of network cable


Type of node connections


Data transfer performance


Susceptibility of network to failure

Point
-
to
-
Point Network Topology

Impractical for all but very small networks

Point
-
to
-
Point Network Topology

Impractical for all but very small networks

Point
-
to
-
Point Network Topology

Impractical for all but very small networks

Advanced Network Topologies

Improve practicality for most networks

Store and Forward System

Centralizes the work of networking

Network Topologies

Star


Uses a central node to which all end nodes
are connected


Relatively simple wiring

Bus


Connects each end node to a common
transmission line


Relatively simple wiring


Low susceptibility to failure

Ring


Connects each end node to two other end
nodes


Long maximum network length


Low susceptibility to noise and distortion


Susceptible to failure and difficulty in
adding, removing, or moving nodes

Star Topology

Uses a central node

to which all end nodes

are connected

Relatively

simple

wiring

Bus Topology

Connects each

end node

to a common
transmission
line

Low
susceptibility

to failure

Relatively

simple

wiring

Ring Topology

Connects each

end node

to two other
end nodes

Susceptible to failure
and difficulty in
adding, removing, or
moving nodes

Long maximum
network length

Low susceptibility
to noise

and distortion

The strengths of two different topologies can be combined
by using one topology for physical layout

and another for message routing.

Physical Star / Logical Bus
Topology

Addressing and Routing


How messages sent by end nodes find their
way through transmission lines and central
nodes to their ultimate destination



Local area networks (LANs)


Interconnected to form WANs



Wide area networks (WANs)

Local Area Network Routing


Each central node maintains and uses a
routing table to make routing decisions



LAN hub or switch usually handles packet
routing



Logical network topology determines exact
procedure for routing a message between
two end nodes in the same LAN

Includes



end nodes



LANs



zone


networks



backbone


network



central


nodes

Example

of a
WAN

LAN Central Node

Routing Decisions

Wide Area Network Routing


Packet routing uses a store and forward
approach



Forwarding stations can be implemented using


Bridges


Routers


Switches

Media Access Control


Uses a protocol that specifies rules for
accessing a shared transmission medium



Carrier Sense Multiple Access/Collision
Detection (
CSMA/CD
)



Commonly used in bus networks to
detect and recover from collisions



Token passing MAC protocol



Used by ring network topologies

CSMA/CD Protocol


Process


Listen and wait for an idle state


Transmit a packet


Listen for a collision


If a collision is detected


First wait for a random period of time


Then retransmit the same packet



Primary Advantage


Simplicity



Primary Disadvantage


Potentially inefficient use of data transfer
capacity

Token Passing MAC Protocol


Token passes from node to node



in a predetermined order


includes all nodes on network


in a specified time interval



Only the node that “possesses” the token is
allowed to transmit messages


All others can only receive and repeat
messages



No longer used in LANs; rarely in WANs

Effect of
CSMA
/CD

Protocol

on Network Throughput

Network Hardware Devices

Network Interface Units

(NIUs)


Interface between network node and network
transmission medium



Scan destination address of all packets



In bus network


ignores packets not addressed to it



In ring network


retransmits all packets not addressed to it



Implement media access control functions

Hubs


Connect nodes to form a LAN



Most are Ethernet devices



Combine separate point
-
to
-
point connections
between nodes and the hub into a single
shared transmission medium by repeating all
incoming packets to every connection point



Low
-
cost alternative for home and small
office networks

Bridges


Connect two networks or network segments
and copy packets between them



Look at source addresses and update internal
tables of node addresses on each network
segment



Common uses



Construct a virtual LAN from two separate
LANs



Divide a network into segments in order to
minimize congestion

Routers


Intelligently route and forward packets
among two or more networks



Forward packets based on information other
than destination address



Build internal “map” of the network


constantly scan the netework to monitor
traffic patterns and network node
changes

Switches


High
-
speed devices that create virtual LANs
on a per
-
packet basis



Each input connection is treated as a
separate LAN



Dramatically increase network performance



Connection decisions made by hardware
are based only on destination address



Each virtual LAN has only one sending and
one receiving node


eliminates congestion

OSI Network Layers

Open System Interconnection (OSI) model



ISO conceptual model that divides network
architecture into seven layers



Each layer uses services of layer below and
is unaware of other layer’s implementations



Uses:


General model of networks


Framework for comparing networks


Architectural roadmap that enhances
interoperability among network
architectures and products

OSI

Network Model

Application Layer


Network service request and response



Contains programs that make and respond to
high
-
level requests for network services



End
-
user network utilities



Network services embedded in the OS



Network service providers

Presentation Layer


Converts and formats data



Ensures correct interpretation of
transmitted data



Encryption and decryption


Compression and decompression


Converting data between EBCDIC and
ASCII


Font substitution



Primarily used by applications that format
data for user display

Session Layer


Negotiates and implements high
-
level
protocol parameters



timeout


half or full duplex


synchronization


quality of service



Establishes and manages communication
sessions



Monitors communication to detect and
resolve problems that arise once protocol has
been established

Transport Layer


Formats messages into packets suitable for
transmission over the network



Places messages within a packet data area
and adds header/trailer information (network
addresses, error detection data, packet
sequencing data)



Gives packets to network layer for delivery



Examines packets for errors; requests
retransmission if necessary (when receiving
packets)

Network Layer


Routes packets to their proper destination



Those within central node interact with one
another to exchange routing information and
update internal routing tables

Data Link Layer


Transmits packets and bits



Interface between network software and
hardware

Physical Layer


Transmits bit streams



Where communication between devices
actually takes place



Includes hardware devices that encode and
decode bit streams and the transmission
lines that transport them

OSI Network Model

TCP/IP


The core Internet protocol suite



Delivers most services associated with the
Internet



File transfer via FTP


Remote login via Telnet protocol


Electronic mail distribution via SMTP


Access to Web pages via HTTP



Predates and corresponds poorly to OSI
model

IP

Internet Protocol


Provides connectionless packet transport
across LANs and WANs



Translates datagrams into format suitable
for transport by physical network



IP layer can divide datagram into smaller
units and transmit them individually


Attaches header information to each unit,
including its sequence in the datagram


Assumes datagram will traverse multiple
networks via nodes called gateways



Determines transmission routes via related
protocols (ICMP, RIP)



IP nodes



Identified by unique 32
-
bit address
(nnn.nnn.nnn.nnn)



Periodically exchange routing information
to keep tables current

IP

Internet Protocol

Only the IP layer is
implemented within the gateways

TCP

Transmission Control Protocol


Provides connection
-
oriented packet
transport to higher
-
level Internet service
protocols, including HTTP, FTP, and Telnet



Provides framework to check for lost
messages; explicitly establishes connection
with intended recipient before
transmitting messages



Performs connection management functions
(verifying receipt, verifying data integrity,
controlling message flow, securing message
content)


Sender and recipient TCP layers maintain
information about one another (message
routes, errors encountered, transmission
delays, status of ongoing data transfers)



Uses positive acknowledgment protocol to
ensure data delivery



Establishes connections through a port and
an socket

TCP

Transmission Control Protocol

VoIP

Voice over IP


Technologies/standards that carry voice
messages and data over single packet
-
switched network



Lower cost than traditional public switched
telephone network (PSTN)



Complex and competing standards



Transmission quality problems


packet loss


latency


jitter

H.323

is an umbrella

for many component protocols

Network Standards


IEEE 802 standards



Describe network hardware, transmission
media, transmission methods, and
protocols



Help ensure compatibility among products
from competing vendors



Developed by committees whose
membership is drawn from industry,
government, and academia



Ethernet standard (802.3)
-

very successful

IEEE 802

Network
Standards

Ethernet

No provision for packet priorities

or guarantees of quality of service

10 Gigabit Ethernet

Business Focus


Upgrading
Network and Storage Capacity

Bradley Advertising Agency


The trade
-
off between short and long
-
range
benefits of copper and fiber optic wiring


Copper is installed in most buildings, works
well for current needs, and can be upgraded


Current technology pushes copper to its
maximum


Fiber optic cable has far greater theoretical
capacity than copper


Current optical products are expensive
and not yet perfected


Fiber optic cable is the future


But when is it cost effective for a
particular organization or need?

Summary


Network topology



Addressing and routing



Media access control



Network hardware



OSI network layers



Network standards

Chapter Goals


Compare and contrast

bus, ring, and star
network topologies


Describe

packet routing across local and
wide area networks


Describe

the CSMA/CD media access control
protocol


Describe

network hardware devices, including
network interface units, routers, and
switches


Describe

the OSI network model, the
TCP/IP protocol suite, and IEEE network
standards