1. Introduction to Data Communications
In data communications, we transfer information in analog or digital form between two parties over a distance on networks
The components of a given system are
The message
The sender
The receiver
The medium
The protocol

2. Data Representation Information comes in many forms:
Text may be in ASCII, Extended ASCII, Unicode or ISO
Numbers: integers/fractions/exponentials
Images: GIF or JPEG or other
Audio: raw audio or compressed MP3
Video: AVI, MPEG, Flash or other

3. Structures and Topologies
Connection types may be:
Point-to-Point: 2 devices directly connected
Multipoint: multiple devices sharing links
Topologies may be:
Meshes, partly or fully meshed
Stars, buses or rings

4. Network Categories Personal Area Networks or PANs
Local Area Networks -LANs, usually private
Local (to a floor, a building or a campus)
Metropolitan Area Networks (MANs)
Town or city wide, public or private
Wide Area Networks (WANs)
National and International or Global

5. Internetworks
When 2 or more networks are connected, they become an internetwork (small i)
When many networks are connected to the Global Internet, they become part of the Internet (capital I)
In AIT 235, we will increase our focus on transmission technologies and protocols

6. Protocols and Standards
We will be studying many protocols in use in data communications.
Most of them are issued by Standards Organizations that publish open standards.
The standards documentation may be available on the Web or may be purchased for a fee.

7. Standards Organizations
Many organizations play a part in telecommunications and usually have well-known acronyms associated with them. They include the following:
ISO
ITU-T
ANSI
IEEE
EIA
Frame Relay Forum
ATM Forum
ISOC
IETF
and others

8. Network Models
To give flexibility to networks, tasks are divided or “layered” in a hierarchy
One standard hierarchy is the 7 layer ISO model
A more common hierarchy is the 5 layer TCP/IP
In both models, each layer has a task and two interfaces, one up and one down
We will take a brief look and each layer and its tasks or responsibilities

9. The ISO OSI Model

10. The Internet or TCP/IP Model
Divides networking into five “layers”.
The layers from top to bottom are:
Application - what we actually want to do
Transport - end-to-end responsibility
Network - routing and switching
Data link - framing the bits
Physical - carrying the bits
Let’s look at each layer individually

11. Physical Layer
This layer deals with the electrical and mechanical equipment needed to transmit information over the network
It is concerned with
Physical characteristics of interfaces and media
Representation and the transmission rate of bits
Bit Synchronization and Line Configuration
Physical Topology and Transmission Mode
It carries the Bits across each physical link

12. Data Link Layer
Prepares the data into frames so that they can be transmitted across the network
Specific responsibilities include:
Framing and frame synchronization
Physical Addressing
Flow control and Error control
Access control
It aligns bits and contains them in Frames

13. Network Layer
The network layer is responsible for the delivery of a packetized frame from its source to its destination
The network layer is responsible for
Logical or network-wide addressing
Routing or switching (more on that later)
It creates Packets to contain the frames

14. Transport Layer
The transport layer is responsible for the end to end delivery of the packet from source to destination
The transport layer is responsible for
Service-point addressing
Segmentation and reassembly
Connection, flow and Error control
It creates Segments to contain the packets

15. Application Layer
The application layer deals with interfaces and support for , remote file access and transfer and other services such as the World Wide Web. It is the interface to the user.

16. Remembering the Layers
Transport Layer - Segments
Network Layer - Packets
Data Link Layer - Frames
Physical Layer - Bits
S, P, F, B = Swap Pizza For Beer