Data Communication & Network Models TCP/IP Model ( You should - - PowerPoint PPT Presentation

Data Communication & Network Models

TCP/IP Model

(You should know the OSI model already)

Communications Data communications Data communications system Network & its criteria (performance, reliability & security) Physical & Logical Topologies Type of networks (LAN, MAN, WAN) Network Models (TCP/IP & OSI)

Communicate = Share Information.

Locally e.g. face to face OR Remotely (telecommunications)

Data Communications

Exchange of data between two devices via some form of transmission medium such as a wire cable For data communications to occur, the communicating devices must be part of a Communication System CS = Hardware + Software

Data communications system has 5 components

Message: information (data) to be communicated e.g. text, video, audio, pictures Sender: device that sends the data message e.g. computer, workstation, telephone handset, video camera Receiver: device that receives the message e.g. computer, workstation, telephone handset, television Transmission Medium: physical path by which a message travels e.g. twisted-pair wire, coaxial cable, fiber-optic cable, and radio waves. Protocol: set of rules that govern data communications. It represents an agreement between the communicating devices.

Effectiveness of communication system

Delivery: Deliver data to the correct destination. Accuracy: Data that have been altered in transmission and left uncorrected are unusable. Timeliness: Data delivered late are useless e.g. real-time transmission for example video and audio Jitter: variation in the packet arrival time (EMI & crosstalk)

Data Flow

Communication between two devices can be simplex, half-duplex, or full-duplex

Network

Interconnection (via wired or wireless) of a set of devices capable of communication Devices can be host (computer, cellphone, laptop) or connecting device (router, switch, modem)

Transit time (amount of time required for a message to travel from A -B) Response time (elapsed time between an inquiry and a response). Performance: number of users, type of transmission medium and Capabilities of the connected h/w, and efficiency of the s/w Measured by the frequency of failure + Time it takes a link to recover from a failure Protecting data from unauthorized access + Implementing policies and procedures for recovery from breaches/data losses.

Physical Topology

1. Physical layout of devices (routers, switches and hosts) 2. Appearance of the shape or actual layout of the network 3. How the network looks to the naked eye

• Location of power outlets
• Location and Length of cable runs
• Physical device location
• Hardware configuration of end devices such as hosts & servers

Logical Topology

(how data flows within the network)

1. How the systems communicate across the physical topology 2. How the flow of information works its way through the network

• IP addressing scheme
• Naming scheme
• Permissions
• Sharing configuration
• Shows host names and host addresses
• Shows the path the data travels on a network.
• Shows location of broadcast and collision domains.
• Shows size of broadcast domains

Personal Area Network (PAN)

• Personal devices which communicate at a close range
• e.g. cell phone and notebook
• Wireless PAN e.g. Bluetooth, Body Area Network

Local Area Networks (LAN)

• Network that covers a limited distance/area (within 1KM)
• Nodes in close proximity e.g. same building/same campus
• Usually owned by same organization
• Interconnects computers via switches
• Router ensures you reach outside network
• Can be wireless
• Economical way to share printers

Metropolitan Area Networks (LAN)

• Collection of LAN’s joined together
• Might cover a group of nearby corporate offices or a city
• Coverage more than 1KM and < 10KM

Wide Area Networks (WAN)

• Multiple LANs can be connected together using devices such routers, or

gateways, which enable them to share data

• Coverage is more than 10KM
• To cover great distances, WANs may transmit data over leased high-

speed phone lines or wireless links such as satellites

• Internet is the world's largest WAN

It is very rare to see a LAN or a WAN in isolation They are connected to one another. Two or more networks are connected = internetwork, or internet. Company now has an internetwork, or a private internet (lowercase i).

TCP/IP Model/Suite

Two models have been devised to define computer network operations

Models lists the things that need to be done to a piece of information to prepare it to be sent across the network. Lists what needs to be done BUT does not do it Protocols do it (written by programmers) Protocol: set of rules that governs the communications between computers on a network (must be speaking the same language)

When communication is simple, we may need only one simple protocol When communication is complex, we may need to divide the task between different layers A protocol is required at each layer i.e. protocol layering Protocol layering enables us to divide a complex task into several smaller and simpler tasks

Communication does not always use only two end systems There are intermediate systems that need only some layers, but not all layers.

Router is involved in only three layers; there is no transport or application layer in a router

Encapsulation and Decapsulation

(important concepts in protocol layering)

TCP/IP Model

1970’s by Vint Cerf + Bob Kahn Built around the TCP/IP protocol suite Predates ISO/OSI Model (1984) Layered protocol suite used in the Internet today Protocol suite is a large number of related protocols that work together to allow networked computers to communicate

Each layer builds upon the layer below it, adding new functionality Lowest level protocol is concerned purely with the business of sending and receiving data via network hardware Top level protocols designed specifically for tasks like transferring files or delivering email. In between are levels concerned with things like routing and reliability. Benefit that the layered protocol stack If you invent a new n/w application or a new type of hardware You only need to create a protocol for that application or that hardware: you don’t have to rewrite the whole stack.

Original TCP/IP Network Model started with 4 Layers Second version of TCP/IP became 5 layers

• Layer that actually interacts with the transmission media
• Contains protocols relating to the physical medium on which TCP/IP

will be communicating

• Electrical Protocols: line voltage, bit timing, encoding, signal

shape

• Functional Protocols: what something does e.g. ‘Request to

Send’ is functional description of PIN 4 of EIA-232-D

• Mechanical Protocols: e.g. dimensions of a connector or metallic

makeup of a wire (Pin 1 is for shield, pin 2 is for transmit data, pin 3 for receive data etc.)

• Procedural Protocols: how something is done (sequence of
• perations to be carried out for specific applications) e.g. if a PC is

connected to the modem using RS232, the procedure is as follows When modem (DCE) is ready, it gives the DCE ready signal etc.

• Involved in physically carrying information from one node in the

network to the next

• Provide services for the data link layer
• Encode the binary digits that represent Data Link layer frames into

signals (electrical pulses = copper media, optical (patterns of light) = fiber, or radio waves = wireless) and to transmit and receive these signals across the physical media

• Upstream: retrieve those individual signals from the media restore

them to their bit representation, and pass the bits up to the Data Link Layer as a complete frame.

• Downstream: creates an electrical, optical, or radiowave signals that

represents the bits in each frame. These signals are then sent on the media one at a time.

• Bits are just bits. With only a physical layer, System A has no

way to tell System B, “Get ready for some bits,” “Here are the bits,” and “Did you get those bits okay?”

• Data link layer solves this problem by organizing the bit

stream into a data unit called a frame

• Data in the data link layer consists of 0s and 1s organized

into frames that are ready to be sent across the transmission medium

• Protocols that control the physical layer i.e. how the medium

is accessed/shared, how devices on the medium are identified and how data is framed before been transmitted on the medium

• Performs framing, physical addressing, and error detection
• Frame header typically contains a source and destination

address (known as the “physical address”)

• Body of the frame contains the sequence of bits being

transferred across the network.

• Trailer usually contains information used in detecting bit

errors (such as cyclical redundancy check [CRC]).

• Responsible for addressing, packaging, and routing

functions

• Accepts and delivers packets for the network.
• Performs the responsibilities as same like the Network layer
• f the OSI reference model

• Typically related directly with the same named layer in the

OSI model.

• Establishes the connection between applications running on

different hosts via TCP & UDP

• Responsible for application-to-application data delivery.
• Functions include message segmentation,

acknowledgement, traffic control, error detection and correction, and message reordering.

• Data Link & Transport Layer (Host-to-Host layer) both define

flow and error control. Data link controls traffic on data link (physical medium connecting 2 devices) while Transport controls traffic on logical link end to end connection of two devices (whose logical link traverses a series of data links).

• Maps to the OSI application, presentation and session

layers, it is also responsible for details such as character formats and basic encryption

• Applications gain access to the network through this layer,

via protocols e.g. HTTP, FTP, SMTP, POP3. Provides network services to applications.

• e.g. HTTP defines how web browsers can pull the contents
• f a web page from a web server, so the application layer

provides an interface between a browser running on a PC and a web services running on a web server.

• Some routing protocols (BGP & RIP) reside on this layer as

they use TCP (BGP) and UDP (RIP) to transport its messages.

Data has been segmented by the Transport Layer using destination and source TCP Port Numbers Placed into an IP packet by Network Layer using a destination and source IP address Encapsulated as Ethernet Header/Trailer, forming a frame with destination and source MAC addresses.

• Adds the TCP or UDP header which includes the source and destination port addresses.
• Additional information like the packet sequence number used for TCP will also be added to the header.
• Segment is then sent to the Network Layer.
• Generates a Message.
• In this case the specific application is a web browser requesting a web page download.
• Message is then sent to the Transport Layer
• Adds a header including the source and destination IP address to generate a packet.
• Packet is then sent to the Data Link Layer.
• Adds a header containing the MAC address information to create a frame.
• Frame is then sent it to the Physical Layer to transmit the bits.

Since each layer of the TCP/IP model and OSI model do a unique task separate of the other layers We refer to the data package at each layer with different names i.e. PDU Unit The image on the left refers to the OSI (with the PDU Units)while the image on the right refers to the PDU Units on the TCP/IP Model.

Notice that the Transport Layer may have one of tw o names: segment or datagram. If the TCP protocol is being used = Segment. If the UDP protocol is being used = Datagram