Transcript A Big Test Result - Knowledge Systems Institute

Introduction to Computer
Networks
Elements of Network
Connectivity
This lesson explores the devices and technologies
available to expand networks beyond the scope of
simple local area networks.
Connectivity Devices
• Devices used to expand LANs include modems,
repeaters, bridges, routers, brouters, and gateways.
• Modem Technology: Modems convert digital signals
to analog waves, and vice versa.
Modem Hardware
• Modems are known as data communications
equipment (DCE) and share the following
characteristics:
• A serial (RS-232)
communications
interface
• An RJ-11
telephone-line
interface (a fourwire telephone
plug)
Modem Standards
• Some of the common industry standards for
modems include:
• Hayes-Compatible: manufacturers currently offer
modems with speeds of 56,600 bps or more.
• International Standards: the International
Telecommunications Union (ITU) has developed
standards for modems.
• These specifications, known as the V series,
include a number that indicates the standard.
ITU Modem Standards
• V.22bis
V.32
14,400
28,800
57,600
56,600
2400
9600
1991
1994
1995
1998
1984
1984
V.34
V.42
V.90
V.32b
• Several of the newer modems feature industry
standards, such as V.42bis/MNP5 data compression,
and have transmission speeds of 57,600 bps; and
some modems go up to 76,800 bps.
Types of Modems
• There are different types of modems because
different types of communication environments
require different methods of sending data.
• These environments can be divided roughly into
two areas related to the timing of
communications:
•
Asynchronous
•
Synchronous
Asynchronous Communication (Async)
• Async was developed in order to make use of
common telephone lines.
• Communication is not synchronized: There is no
clocking method to coordinate the transmission
between the sender and the receiver.
• Speed can be up to 28.8K bps. However, the data
compression can boost the rate to 115.2K.
Synchronous Communication
• Synchronous communication relies on a timing
scheme to transmit bits in block known as frames.
• Special characters are used to synchronize and
check its accuracy periodically.
Synchronous protocols
• Synchronous protocols perform a number of jobs
that asynchronous protocols do not.
• Format data into blocks.
• Add control information.
• Check the information to provide error control.
• The primary protocols in synchronous
communication are:
• Synchronous Data Link Control (SDLC), Highlevel Data Link Control (HDLC), Binary
Synchronous Communications Protocol (bisync).
Asymmetric Digital Subscriber Line
(ADSL)
• This technology converts existing twisted-pair
telephone lines into access paths for multimedia and
high-speed data communications.
• These new connections can transmit more than 8
Mbps to the subscriber and up to 1 Mbps from the
subscriber.
• The technology requires special hardware, including
an ADSL modem on each end of the connection.
• It also requires broadband cabling, which is not
available in every locations, and there is a limit to
the connection length.
Expanding a Network Using
Components
• There are components that can be installed to
increase the size of the network within its existing
environment. These components include:
• Hubs.
• Repeaters.
• Bridges.
• Routers.
• Gateways.
Hubs
• Connecting or adding hubs to a LAN can effectively
increase the number of workstations.
• This method of growing a LAN is popular, but does
come with many design limitations.
• Uplink
crossover
cables are
wired
differently
than standard
patch cables.
Repeaters
• Repeaters regenerate weakened signals
• Repeaters do not translate or filter signals.
• A repeater
cannot
connect
segments
using
different
access
methods.
Implementing a repeater
• Use a repeater to:
• Connect segments of similar or dissimilar media,
• To increase the distance transmitted.
• Pass all traffic in both directions.
• Connect in the most cost-effective manner.
• Do not use a repeater when:
• There is heavy network traffic.
• Segments are using different access methods.
• Data filtering is needed.
Bridges
• Bridges use routing table to segment network
traffics, and make each segment more efficient.
Remote Bridges
• Because bridges can expand and segment
networks, they are often used in large networks tha
have widely dispersed segments.
Spanning tree algorithm (STA)
• Because remote LAN segments can be joined over
telephone lines, it is possible for multiple LANs to
be joined by more than one path.
• In this situation, it is possible that data might get
into a continuous loop. To handle this possibility,
the 802.1 Network Management Committee of
IEEE has implemented the spanning tree algorithm
(STA).
• STA can sense the existence of more than one
route, determine which would be the most efficient,
and then configure the bridge to use that one.
Routers
• Router works in an environment that consists of
several network segments with differing protocols
and architectures
• Router is a device that not only knows the address
of each segment, but can also determine the best
path for sending data and filtering broadcast
traffic.
• Routers work at the network layer of the OSI
reference model, it can exchange protocol-specific
information between separate networks.
Routing Algorithms
• OSPF ("open shortest path first") is a link-state
routing algorithm. Link-state algorithms control the
routing process and allow routers to respond
quickly to changes in the network. NetWare Link
Services Protocol (NLSP) is a link-state algorithm
to be used with IPX.
• RIP (Routing Information Protocol) uses
distance-vector algorithms to determine routes.
Transmission Control Protocol/Internet Protocol
(TCP/IP) and IPX support RIP.
Types of Routers
• Static Routers.
• Static routers require an administrator to
manually set up and configure the routing table
and to specify each route.
• Dynamic Routers.
• Dynamic routers discover routes automatically
and examine information from other routers to
make decisions about how to send data across
the network.
Distinguishing Between Bridges and
Routers
• Bridges work at the data-link layer MAC sublayer,
and routers work at the network layer
Brouters
• A brouter can act as a router for one protocol and
as a bridge for all the others.
• Brouters can:
• Route selected routable protocols.
• Bridge nonroutable protocols.
• Deliver more cost-effective and more manageable
internetworking than separate bridges and
routers.
Gateways
• Gateways enable communication between different
architectures and environments.
• A gateway links two systems that do not use the
same:
• Communication protocols.
• Data-formatting structures.
• Languages.
• Architecture.
How Gateways Work
• Gateways
are taskspecific,
typically
perform
protocol
conversion
at the
application
layer.