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

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

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

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

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

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.

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

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

The ISO OSI Model

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

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

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

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

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

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

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