2. Data Communications, Data
Networks, and the Internet
Thefundamental problem of
communication is that of reproducing at
one point either exactly or approximately a
message selected at another point - The
Mathematical Theory of Communication,
Claude Shannon
3. Contemporary Data Comms
trends
traffic growth at a high & steady rate
development of new services
advances in technology
significant change in requirements
emergence of high-speed LANs
corporate WAN needs
digital electronics
7. Transmission Medium
selection is a basic choice
internal use entirely up to business
long-distance links made by carrier
rapid technology advances change mix
fiber optic
wireless
transmission costs still high
hence interest in efficiency improvements
8. Networking
growth of number & power of computers is
driving need for interconnection
also seeing rapid integration of voice,
data, image & video technologies
two broad categories of communications
networks:
Local Area Network (LAN)
Wide Area Network (WAN)
9. Wide Area Networks
span a large geographical area
cross public rights of way
rely in part on common carrier circuits
alternative technologies used include:
circuit switching
packet switching
frame relay
Asynchronous Transfer Mode (ATM)
10. Circuit Switching
uses a dedicated communications path
established for duration of conversation
comprising a sequence of physical links
with a dedicated logical channel
eg. telephone network
11. Packet Switching
datasent out of sequence
small chunks (packets) of data at a time
packets passed from node to node
between source and destination
used for terminal to computer and
computer to computer communications
12. Frame Relay
packet switching systems have large
overheads to compensate for errors
modern systems are more reliable
errors can be caught in end system
Frame Relay provides higher speeds
with most error control overhead removed
13. Asynchronous Transfer Mode
ATM
evolution of frame relay
fixed packet (called cell) length
with little overhead for error control
anything from 10Mbps to Gbps
constant data rate using packet switching
technique with multiple virtual circuits
14. Local Area Networks
smaller scope
Building or small campus
usually owned by same organization as
attached devices
data rates much higher
switched LANs, eg Ethernet
wireless LANs
15. Metropolitan Area Networks
MAN
middle ground between LAN and WAN
private or public network
high speed
large area
16. The Internet
Internet evolved from ARPANET
first operational packet network
applied to tactical radio & satellite nets also
had a need for interoperability
led to standardized TCP/IP protocols
20. OSI Reference Model &
TCP/IP (Comparison)
How many layers that OSI & TCP/IP
Model?
What are differences between OSI &
TCP/IP Model?
What are similarities among OSI & TCP/IP
Model?
21. Applications – The Interface Between
Human and Data Networks
Most applications such as web browsers or e-mail clients, incorporate
functionality of the OSI layer 5, 6, and 7.
Most TCP/IP applications layer protocols were developed before the
emergence of personal computer, GUIs and multimedia objects.
A comparison of the OSI and TCP/IP model
22. Applications – The Interface Between Human
and Data Networks
There are six steps OSI encapsulation process.
3. Software and hardware convert
comm to a digital format
2. The app layer prepares
human comm for
4. App layer services initiate the data
transmission over the data
transfer 6. The app layer
network
receives data from the
1. People create the network and prepares it
communication for human use.
5. Each layer
plays its role
23. Roles of Transport Layer
Provide services to the adjacent layers
Prepare application data for transport over network
Process network data for use by applications
24. Transport Layer Functions
Primary Functions:
1. Tracking individual
communication between
applications on sender and
receiver
2. Segmenting data and
managing each piece
3. Reassembling segments into
streams of application data
4. Identifying the different
applications
5. Performing flow control
between end users
6. Enabling error recovery
7. Initiating a session
25. OSI network layer
OSImodel layer 3
TCP/IP model Internet layer
Application HTTP, FTP,
Data stream TFTP, SMTP
Presentation etc
Application
Session
Transport Segment TCP, UDP Transport
Network Packet IP Internet
Data link Frame Ethernet,
Network Access
WAN
Physical Bits
technologies
26. Layer 3 protocol
A layer 3 protocol such as IP version 4 must:
Provide an addressing scheme to identify
networks and individual hosts
Encapsulate a segment from layer 4 into a
packet and include addresses
Direct the packet across one or many
networks to the destination host
Decapsulate (remove the packet header)
and give the segment to layer 4.
27. Data Link Layer – Accessing
the Media
It provides a means for exchanging data over a common local media.
Also links many upper layer services responsible for packaging the data
for communication between hosts.
Data Link layer to prepare Network layer packets for transmission and to
control access to the physical media.
28. Physical Layer Protocols &
Servicesthe binary digits that
The role of the OSI Physical layer is to encode
represent Data Link layer frames into signals and to transmit and receive
these signals across the physical media - copper wires, optical fiber, and
wireless - that connect network devices.
29. Physical Layer Protocols &
Services
The delivery of frames across the local media requires the following Physical layer
elements:
a. The physical media and associated connectors
b. A representation of bits on the media
c. Encoding of data and control information
d. Transmitter and receiver circuitry on the network devices
30. Physical Layer Protocols &
Services
There are three basic forms of network media on which data is represented:
- Copper cable
- Fiber
- Wireless
The representation of the bits - that is,
the type of signal - depends on the type
of media.
Copper cable media, the signals are
patterns of electrical pulses.
Fiber, the signals are patterns of
light.
Wireless media, the signals are
patterns of radio transmissions..
31. The TCP/IP Concept
Use existing network hardware
Interconnect networks
Add abstractions to hide heterogeneity
32. TCP/IP
TCP/IP is designed to use all types of
networks
Connection-oriented
Connectionless
Local Area Network (LAN)
Wide Area Network (WAN)
Point-to-point link
Set of bridged networks
33. Examples Of Packet
Switched Networks
Wide Area Nets
ARPANET, NSFNET, ANSNET
Common carrier services
Leased line services
Point-to-point connections
Local Area Nets
Ethernet
Wi-Fi
34. Summary
introduced data communications needs
communications model
defined data communications
overview of networks
introduce Internet
OSI Reference Model & TCP/IP