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Communicating over the Network

Network Fundamentals – Chapter 2

Dr. C. BouSaba

Objectives

 Describe the structure of a network, including the devices and media that are necessary for successful communications.

 Explain the function of protocols in network communications.

 Explain the advantages of using a layered model to describe network functionality.

 Describe the role of each layer in two recognized network models: The TCP/IP model and the OSI model.

 Describe the importance of addressing and naming schemes in network communications.

Network Structure

 3 Common Elements of communication

1. message source

2. the channel

3. message destination

 Network definition  data or information networks capable of carrying many different

types of communications (including traditional computer data, interactive voice, video, and entertainment products).

 Messages are communicated by dividing the data sent across a network in small manageable “chunks” called segments

Network Structure

Segmentation increases reliability

Network Structure  Segmenting messages has 2 primary benefits:

1. By sending smaller individual pieces from source to destination, many different conversations can be interleaved on the network (multiplexing).

2. Segmentation increases the reliability of network. Segments of each message need not travel same pathway across the network from source to destination.

 If a path becomes congested with data traffic or fails, segments can still be directed to destination using alternate pathways.

 If part of the message fails to make it to the destination, only the missing parts need to be retransmitted.

 Segmenting messages has 1 disadvantage: increases the level of complexity to the process.

Components of a network

 Devices

 Media

 Services

Are the physical elements or hardware

Are the communication programs or software, running on the networked devices

Network Structure  End Devices and their Role in the Network

– Form interface w/ human network & communications network

– Role of end devices depends on software installed on them: a client, a server, or both

 End device, referred to as host, is either the source or destination of a message transmitted over the network, and is identified by an address.

Network Structure  Intermediary devices and their role in the network

– Provide connectivity and ensures data flows across network

– Use destination host address ( + info. about network interconnections), to determine the path that messages should take through the network.

Intermediary network devices functions:

– Regenerate and retransmit data signals

– Maintain info. about existing pathways through network/internetwork

– Notify other devices of errors and communication failures

– Direct data along alternate pathways when there is a link failure

– Classify and direct messages according to QoS priorities

– Permit or deny the flow of data, based on security settings

 Network media is the channel over which a message travels

 Three media types:

1. Metallic wires within cables

2. Glass or plastic fibers (fiber optic cable)

3. Wireless transmission

Network Structure

 Different types of network media have different features and benefits.

Network Structure  The signal encoding that must occur for the message to be

transmitted is different for each media type.

1. On metallic wires, the data is encoded into electrical impulses that match specific patterns.

2. Fiber optic transmissions rely on pulses of light, within either infrared or visible light ranges.

3. In wireless transmission, patterns of electromagnetic waves depict the various bit values.

 Criteria for choosing a network media are:

1. The distance the media can successfully carry a signal.

2. The environment in which the media is to be installed.

3. The amount of data and the transmission speed.

4. The cost of the media and installation

Network Types

 Local Area Networks (LANs)

- A network serving a home, building or campus is considered a (LAN) Local Area Network and is usually administered by a single organization

 Wide Area Networks (WANs)

- Connect LANs that are separated by geographic distance

- Use a telecommunications service provider (TSP) to interconnect the LANs at the different locations.

Network Types

 The Internet is defined as a global mesh of interconnected networks

Network Types

Network Representations

How network devices and media connect to each other?

 Network Interface Card - A NIC, or LAN adapter, provides the physical connection to the network at the PC or other host device. The media connecting the PC to the networking device plugs directly into the NIC.

 Physical Port - A connector or outlet on a networking device where the media is connected to a host or other networking device.

 Interface - Specialized ports on an internetworking device that connect to individual networks. Because routers are used to interconnect networks, the ports on a router are referred to network interfaces.

Function of Protocol in Network Communication

 A protocol is a set of predetermined rules

– facilitate communication over data networks

– is implemented in software and hardware that is loaded on each host and network device.

 Successful communication between hosts on a network requires the interaction of many different protocols.

 A protocol suite is a group of inter-related protocols that are necessary to perform a communication function.

 Network protocols

Network protocols are used

to allow devices to

Communicate successfully

Function of Protocol in Network Communication

 Protocol suites and industry standards

A standard is

a process or protocol that has been endorsed by the networking industry and ratified by a standards organization

Function of Protocol in Network Communication

 Application Protocol:

–HTTP governs the interaction between a web server and a web client.

–HTTP defines the content and formatting of the requests and responses

 Transport Protocol:

–TCP manages the conversations between web servers and web clients.

–TCP divides HTTP messages into smaller pieces, segments, to be sent to client.

–TCP controls the size and rate of exchanged messages between client/server.

 Internetwork Protocol:

–IP is responsible for taking the formatted segments from TCP, encapsulating them into packets, assigning the appropriate addresses, and selecting the best path to the destination host.

 Network Access Protocols: describe 2 primary functions, data link management and the physical transmission of data on the media.

–Data-link management protocols take the packets from IP and format them to be transmitted over the media.

–Physical media protocols govern how the signals are sent and how they are interpreted. Transceivers on the network interface cards implement the appropriate standards for the media that is being used.

Function of Protocol in Network Communication

 Technology independent Protocols

-Many diverse types of devices can communicate using the same sets of protocols. This is because protocols specify network functionality, not the underlying technology to support this functionality.

Function of Protocol in Network Communication

Benefits of using a layered model  Assists in protocol design

 Fosters competition

 Changes in one layer do not affect other layers

 Provides a common language

Layers with TCP/IP and OSI Model  A protocol model provides

a model that closely matches the structure of a particular protocol suite.

– TCP/IP

 A reference model provides a common reference for maintaining consistency within all types of network protocols and services.

– OSI (Open System Interconnection)

TCP/IP Model

TCP/IP Communication Process

1. Creation of data at the Application layer of the originating source end device

2. Segmentation and encapsulation of data as it passes down the protocol stack in the source end device

3. Generation of data onto the media at the Network Access layer of the stack

4. Transportation of the data through the internetwork, which consists of media and any intermediary devices

5. Reception of data at the Network Access layer of the destination end device

6. Decapsulation and reassembly of the data as it passes up the stack in the destination device

7. Passing this data to the destination application at the Application layer of the destination end device

Protocol data units (PDU) and encapsulation

Process of sending and receiving messages

The OSI Model

Layers with TCP/IP and OSI Model

 Compare OSI and TCP/IP model

 Transport layer – responsible for low-level network access and for message transfer between clients, including partitioning messages into packets, maintaining packet order, controlling flow, and generating physical addresses

 Session layer – implements sessions, or process-to-process communications protocols

 Presentation layer – resolves the differences in formats among the various sites in the network, including character conversions, and half duplex/full duplex (echoing)

 Application layer – interacts directly with the users: deals with file transfer, remote-login protocols & email, as well as schemas for distributed databases

Communication Protocol  Physical layer – handles the mechanical and electrical details of the physical

transmission of a bit stream

 Data-link layer – handles the frames, or fixed-length parts of packets, including any error detection and recovery that occurred in the physical layer

 Network layer –provides connections & routes packets in the communication network, including handling the address of outgoing packets, decoding the address of incoming packets, & maintaining routing information for proper response to changing load levels

Communication Via ISO Network Model

The ISO Protocol

Layer

The ISO Network Message

Addressing and Naming Schemes

 Labels in encapsulation headers are used to manage communication in data networks

Addressing and Naming Schemes

 Examples of Ethernet MAC Addresses, IP Addresses, and TCP/UDP Port numbers

Addressing and Naming Schemes  How labels in encapsulation headers are used to

manage communication in data networks

Addressing and Naming Schemes  Information in the encapsulation header is used to

identify the source and destination processes for data communication

Summary