Transcript Different Network Equipment

Communications
(Networking)
Presented by :
John Simon
Benneth Nwogu
Transmission Medium
 Copper Wire
 Glass Fiber
 Radio
 Satellites
RS-232
 Popular standard used for asynchronous,
serial communication over short distances
between a computer and a modem or ASCII
terminal
 Precedes each character with a start bit,
follows each character with an idle period at
least one bit long (stop bit), and sends each
bit in exactly the same length of time.
Digital Signal
 Baud – number of changes in the signal per
second that a transmission hardware
generates
 Bandwidth – maximum rate that a
transmission system can change a signal.
Measured in cycles per second (Hz)
Carrier Wave
Modulation Techniques
 Amplitude Modulation – varies the strength
of the outgoing signal in proportion to the
info. being sent.
 Frequency Modulation – varies the frequency
of the underlying carrier in proportion to the
info. being sent.
 Phase Shift Modulation- changes the timing
of the carrier wave abruptly to encode data.
Modem
 Hardware circuit that accepts a sequence of
data bits and applies modulation for the
sender and demodulation for the receiver.
Packet
 A small, self contained parcel of data sent
across a computer network. Each packet
contains a header that identifies the sender
and the recipient, and a payload area that
contains the data being sent.
 Each packet is organized to the specifications
of an Ethernet frame.
Ethernet Frame
 The basic form of a packet that the
underlying hardware sends and receive
across a shared medium.
Transmission Error
 When packets on a carrier are lost or
damaged due to any interference affecting
data.
 Error Checking
a.Parity Check
b.Checksum
c. CRC
Synchronization (cont.)
 Token Ring Passing
- Computers attached to a token ring network
use a special, short message called token to
coordinate use of the ring. One token exists on the
ring at any time . To send data, a computer must
wait for the token to arrive, transmit exactly one
frame, and then transmit the token to the next
computer. When the computers have no data to
send, the token cycles around the ring at high
speeds.
Synchronization
 Carrier Sense On Multi-Access Networks and
Collision Detection (CSMA/CD)
- a mechanism used to coordinate transmission
in an Ethernet network. A computer waits for an
idle shared medium before it transmits data. In case
of collision, the computers involved will use
exponential back-off to choose which computer
proceeds. Each computer delays a random time
before trying to transmit again , and then doubles
the delay for each successive collision.
3 Different Network
Technology Categories
 Local Area Network
 Metropolitan Area Network
 Wide Area Network
Local Area Network
 Can span a single building or campus
 Consists of a single shared medium, usually
a cable, to which many computers attach
 3 basic Topologies
a. Star Topology
b. Ring Topology
c. Bus Topology
Bus Topology
Bus Topology (cont.)
 Uses a single coaxial cable called a
backbone.
 Inexpensive for modest-sized Ethernet
networks.
 While easy to install and add computers,
heavy traffic will slow it down and a cable
break will shut down the entire network.
Ring Topology
Ring Topology (cont.)
 Using token passing, computers are
connected to each other in a circle
 Although good for high speed networks, it is
difficult to expand, and the entire network is
vulnerable if one node goes down.
 It requires more cabling than a bus, and
adding nodes disrupts the entire network.
Star Topology
Star Topology (cont.)
 Each computer connects to a central hub with
its own cable making it easy to add
computers and more reliable than a bus.
 It is more expensive than a bus because of
more cable requirements.
 If the central hub fails, so does the network.
Wide Area Network
 A network that can span sites in multiple
cities, countries or continents.
 WAN Technologies
- ATM
- ISDN
- SMD
Two Service Paradigms
 Connection Oriented service
- analogous to telephone communications
in which a connection must be established
between two computers before any data can
be transferred
 Connectionless Service
- analogous to a postal mail system.
Whenever it has to send data, a computer
must place the data in the appropriate frame
format, attach the address of the computer to
which the data should be delivered and then
pass the frame to the network for delivery.
Service Paradigms (cont.)
Network Performance
Characteristics
 Delay
- specifies how long it takes for a bit of data to
travel across the network from one computer to
another.
 Throughput
- measure of the rate at which data can be sent
through the network. Usually specified in bits per
second(bps).
Delay-Throughput Product
T x D
 The product of delay and throughput
measures the volume of data that can be
present on the network.
 A network with throughput T and delay D
has a total of T x D bits in transit at any time.
Different Network Equipment
 Hubs
 Switches
 Routers
 Bridges
 Gateway
HUBS
 A device that connects multiple Computers to
a network.
 receives a packet (chunk) of data (a frame in
Ethernet lingo) at one of its ports from a PC
on the network, it transmits (repeats) the
packet to all of its ports and, thus, to all of
the other PCs on the network.
Switches
 A device that connects multiple Computers
to a network.
 divides the network into multiple segments,
acts as a high-speed, selective bridge
between the segments, and supports
simultaneous connections of multiple pairs
of computers which don't compete with
other pairs of computers for network
bandwidth.
Routers
 is a physical device that joins multiple
networks together. Technically, a router is a
"layer 3 gateway," meaning that it connects
networks (as gateways do), and that it
operates at the network layer of the OSI
model.
Bridges
(Smart Repeaters)
 An electronic device that used to extend a
LAN.
 Connects two cable segments, forwards
complete, correct frames from one segment
to another.
 Does not forward interference
Gateways
 can operate at any level of the OSI model
from application protocols to low-level
signaling.
 Acts as an intermediary between domains.
ISO/OSI Layer
Layer Description
 Layer 1: Physical Layer

deals with the basic network hardware e.g.. Fiber,
twisted-pair copper, coax
 Layer 2: Data Link layer

specifies how to organize data into frames and to
transmit the frames e.g.. CSMA/CD, token passing,
checksum, CRC
 Layer 3:

Network layer protocols specify how address are
assigned and how packets are forwarded from one end of
the network to the other end (e.g.. IP, ARP, RARP)
ISO Layer (cont.)
 Layer 4:Transport layer



protocols specify how to reliably transfer data from
one end to the other (e.g.. TCP, UDP, RIP)
Layer 5: Session layer protocols
specify how to establish a communication session
with a remote computer (e.g.. Password
authentication, RPC)
ISO Layer (cont.)
 Layer 6: Presentation layer

protocols specify how to represent data. Needed
because different computers may represent data
differently (e.g. XDR).
 Layer 7: Application layer

protocols e.g. Lpr, rcp, rlogin,rsh, ftp, telnet,
smtp, DNS, NFS, NIS, SNMP, bootp, ntp,tftp
Network Protocol Headers
Frame Transmission with ISO
frames protocols
TCP/IP Layer
TCP/IP Layer (cont.)
 Application Layer
Defines TCP/IP application protocols and how host
programs interface with transport layer services to use
the network
Protocols:
HTTP, Telnet, FTP, TFTP, SNMP, DNS, SMTP,
X Windows, other application protocols
TCP/IP Layer (cont.)
 Transport Layer
Provides communication session
management between host
computers. Defines the level of
service and status of the connection
used when transporting data.
Protocols:
TCP, UDP, RTP
TCP/IP Layer (cont.)
 Internet Layer
Packages data into IP datagrams, which
contain source and destination address
information that is used to forward the
datagrams between hosts and across
networks. Performs routing of IP data grams.
Protocols:
IP, ICMP, ARP, RARP
TCP/IP Layer (cont.)
 Network Interface Layer
Specifies details of how data is physically
sent through the network, including how
bits are electrically signaled by hardware
devices that interface directly with a
network medium, such as coaxial cable,
optical fiber, or twisted-pair copper wire.
Protocols:Ethernet, Token Ring, FDDI, X.25,
Frame Relay, RS-232, v.35
IP Addresses
 32 bit IP address is divided into two parts:
suffix and prefix.
 The address prefix identifies the physical
network to which the computer is attached
 The address suffix identifies the individual
computer on that network.
IP Address Classes
Special IP address
ARP Messages
IP Datagram
 The internet protocol defines an IP datagram
to be the basic unit of transfer across a
TCP/IP internet
Sources
ONLINE SOURCES:
•
http://www.usyd.edu.au/is/comms/networkcourse/
•
http://wks.uts.ohio-state.edu/sysadm_course/html/sysadm-326.html
•
http://margo.student.utwente.nl/simon/finished/thesis/thesis2/node11.html
•
http://www.pku.edu.cn/academic/research/computer-center/tc/html/TC0102.html
•
http://www.netbook.cs.purdue.edu/subjindx/indx420.htm
TEXTBOOK SOURCES:
•
Computer Networks and Internets with Internet Applications 3rd Edition by
Douglas E. Comer