Basics of Networking and TCP/IP

Old Computing Model

predominant in 1960-1985 utilizes a large mainframe computer connected to a set of terminals (host-terminal setup).

Mainframe (IBM 360)

TC:Terminal Controller

low speed link

shared high speed link

Terminals (IBM 3270)

Characteristics of the Old model

All processing is done at the host A terminal is simply an I/O device (Input: via

keyboard; output: via screen) The host computer is a bottleneck and a

central point of failure

New Computing Model

1985-present; utilizes desktop computers connected by a Local Area Network (LAN).

Router

Network A

Network B

desktop computers

Definition of a Computer Network

A computer network is a collection of autonomous (independent of each other) computers that are connected in such a way that data can be exchanged between any two computers.

an internetwork (or simply internet) is a collection of networks that are connected by routers. A router encompasses only the lowest three layers (physical layer, data link layer and network layer).

The Internet (with capital I) is a specific world wide internetwork that is managed by Internic and uses TCP/IP protocols.

Benefits of Computer Networks Resource Sharing. Resources include hardware

devices such disk storage and printers and software (data + programs).

Higher Reliability. This is obtained by duplicating devices and replicating data.

Incremental and cheaper growth. Distributed processing. This comes about in

the form of client/server applications (e.g. web browser/web server) and clustering.

Promote communication among network users through resource sharing and e-mail.

Design Goals of Networking

have two computers exchange data but account for the following.   The two computers may be located in the same room or separated by thousands of miles. The two computers may have different manufacturers and different operating systems. The two computers may use different byte ordering for multi-byte data and may have different character encoding for text. Design must allow for continuing use of existing technology while embracing new technology

ISO Protocol Layering International Standards Organization (ISO) model

was developed, based on its recommendation, in the form of seven layers.

The principles of layering: Each layer should represent a different abstraction level,

wherever needed Each layer should define well defined functions Information flow between layers should be minimum Number of layers should be optimum, not too many not

too few

Transport Layer

Network Layer

Data Link Layer

Physical Layer

Packet

Frame

Signal (Bits)

Presentation Layer

Session Layer

ISO 7-Layer OSI Model

Application Layer

Computer A

Computer B

Protocol

Transport Layer

Network Layer

Data Link Layer

Physical Layer

Presentation Layer

Session Layer

Application Layer

Interface

Data flow from A (Sender) to B (Receiver)

Standards and Protocols A standard is an agreed-upon specification for some

type of product or service. Examples: A4 paper size, 2-feet florescent light,

PC serial (RS232C) and parallel port interfaces A protocol is an agreement (contract) between two

(or more) parties to conduct a joint task. Examples: two persons handshaking, passing

through traffic light.

Network Communication Protocol

A network communication protocol (at the application or lower layers) specifies the format and meaning of messages that are exchanged between two peer (at the same layer) entities. Roughly a network protocol specifies the control header and its interpretation.

Examples: App. Layer Protocol: HTTP used between web browser and server Network Layer Protocol: Internet Protocol (IP)Data Link Layer Protocol: Point-to-Point Protocol (PPP) - used between two routers connected by phone lines

Layering Principle Layered Protocols are designed so that layer n at the

destination receives exactly the same object sent by the layer n at the source.

Protocols are standards that specify how data is represented when being transferred from one machine to another.

Protocols specify how the transfer occurs, how errors are detected, and how acknowledgements are passed.

Transport Layer

Network Layer

Data Link Layer

Physical LayerSignal (Bits)

Presentation Layer

Session Layer

Layers use Control Headers

Application Layer

Computer A

Computer B

Data flow from A (Sender) to B (Receiver)

Transport Layer

Network Layer

Data Link Layer

Physical Layer

Presentation Layer

Session Layer

Application Layer

Physical Layer Interfaces with the physical medium. Specifies bit to signal encoding such as voltage

levels and duration for 0/1. Transmits a stream of bits without boundaries.

Data Link Layer Transmits frames - a frame is a delimited (has

a start and end markers) block of bits. The frame has a checksum to allow error

detection. Control access to the channel (medium),

especially over a broadcast (shared) channel. Implements flow control.

Network Layer Routing of packet over an internetwork. The network

layer examines the network destination address of an incoming packet and re-encapsulates the packet in a new frame that it sends down again through the data link layer of an (outgoing) link.

Provides software abstraction independent of communication hardware (for example, while data link layer addresses are permanently fixed in hardware, network layer address are dynamically configured through software).

TCP/IP 5-Layer Model

Application

Transport

Network

Data Link

Physical

Application

Transport

Network

Data Link

Physical

Network

Data Link

Physical

Computer BComputer A IP Router

IP

TCP

The transport layer is an end-to-end layer. This means that the corresponding stations (hosts) are the actual source and actual destination of the application data.

What is TCP/IP?

TCP/IP: Transmission Control Protocol / Internet Protocol TCP/IP is the name of a protocol suite (protocol stack). Applications interface with TCP layer to communicate with

other peer applications

History of TCP/IP

TCP/IP is the brain child of ARPAnet which was developed by the USA DoD (Department of Defense) supported project (Advanced Research Project Agency).

TCP/IP was first defined in 1974, meant to be used for geographically distant communication. It has evolved with many improvements since then.

The University of Berkeley has incorporated TCP/IP in their BSD Unix. Since than it has been a very good marriage between the two.

The Internet The Internet is a network of networks. Today, the Internet connects tens of thousands of

networks and millions of computer 1990: 3000 networks ( 200,000 users.) 1992: 992,000 hosts. Present: millions of networks, computers, and users.

Why TCP/IP is Popular?

Popularity of TCP/IP simpler than ISO-OSI model provides an elegant solution to world wide data

communication. Open Protocol Standards, freely available, and

independent from any hardware platform.

TCP/IP Features Independence from specific network hardware

Allows TCP/IP to integrate many types of networks (Ethernet, Token Ring, X.25, dial-up)

TCP/IP is used in both LANs and WANs Common addressing scheme

every host on the Internet has a unique address Standardized high-level protocols for world wide

available network services

IP Protocol The primary network layer protocol of TCP/IP stack

Provides basic packet delivery service on which TCP/IP networks are built

Main functions Defines datagram (packet) format, basic unit of

transmission in the Internet Provides Internet addressing Routing of datagrams

TCP Protocol

TCP facilitates process-to-process (i.e. application to application) communication. Any application that needs to send and receive via TCP is assigned an address (i.e. a TCP-port number).

Whereas IP is limited to providing a connectionless service (packets may be dropped at will), TCP provides a connection-oriented service (virtual circuit).

IP

Data Link

Physical

IP

Data Link

Physical

IP

Data Link

Physical

Application

TCP

IP

Data Link

Physical

IP-Layer Operation

XA

B

C

Y

X

A B C

Y

Application

TCP

IP

Data Link

Physical

TCP is an end-to-end layer

Application Layer Includes all software programs that use the Transport

Layer protocols to deliver data messages Examples of protocols:

Telnet: Network Terminal Protocol FTP: File Transfer Protocol SMTP: Simple Mail Transfer Protocol DNS: Domain Name Service WWW: World Wide Web

Layer Decapsulation

Telnet

FTP

SMTP

HTT P

23 21 25 80

TCP Segments

IP Packets

Frames

Bits

Port Number, Destination (Source) Port identifies receiving (sending) application

Type, SAP, or other control info

MAC or WAN addressing

Applications

Transport

Network

Data Link

Physical

LAN Hardware: Ethernet The most widely used LAN hardware. Developed originally in 1980 as 10 Mbps (10 million

bits per second) by Digital, Intel and Xerox Today, the mainstream Ethernet is known as Fast

Ethernet (100 Mbps) which uses HUB and Category 5 UTP wiring

Also Gigabit Ethernet (1000 Mbps) is available but limited in distance.

Ethernet (Cont.)

Ethernet encompasses Data-Link and Physical Layers only

The Ethernet card is responsible for frame generation and reception

An Ethernet frame encapsulates a network layer packet

Fast Ethernet Layout and Components

Fast Ethernet HUB

PC1 PC2 PCn

Category 5 UTP

An ordinary HUB is an active physical-layer device acting as signal repeater

Hubs can be cascaded

Each PC is equipped with Fast Ethernet Card (50 SR)

Hub Cost is proportional to the # of ports (25 SR per port)

Break