Communications(Networking)

Presented by :

John Simon

Benneth Nwogu

Transmission Medium

Copper Wire

Glass Fiber

Radio

Satellites

RS-232

Popular standard used for asynchronous, serial communication over short distances between a computer and a modem or ASCII terminal

Precedes each character with a start bit, follows each character with an idle period at least one bit long (stop bit), and sends each bit in exactly the same length of time.

Digital Signal

Baud – number of changes in the signal per second that a transmission hardware generates

Bandwidth – maximum rate that a transmission system can change a signal. Measured in cycles per second (Hz)

Carrier Wave

Modulation Techniques

Amplitude Modulation – varies the strength of the outgoing signal in proportion to the info. being sent.

Frequency Modulation – varies the frequency of the underlying carrier in proportion to the info. being sent.

Phase Shift Modulation- changes the timing of the carrier wave abruptly to encode data.

Modem

Hardware circuit that accepts a sequence of data bits and applies modulation for the sender and demodulation for the receiver.

Packet

A small, self contained parcel of data sent across a computer network. Each packet contains a header that identifies the sender and the recipient, and a payload area that contains the data being sent.

Each packet is organized to the specifications of an Ethernet frame.

Ethernet Frame

The basic form of a packet that the underlying hardware sends and receive across a shared medium.

Transmission Error

When packets on a carrier are lost or damaged due to any interference affecting data.

Error Checkinga.Parity Checkb.Checksumc. CRC

Synchronization (cont.)

Token Ring Passing- Computers attached to a token ring network

use a special, short message called token to coordinate use of the ring. One token exists on the ring at any time . To send data, a computer must wait for the token to arrive, transmit exactly one frame, and then transmit the token to the next computer. When the computers have no data to send, the token cycles around the ring at high speeds.

Synchronization

Carrier Sense On Multi-Access Networks and Collision Detection (CSMA/CD)

- a mechanism used to coordinate transmission in an Ethernet network. A computer waits for an idle shared medium before it transmits data. In case of collision, the computers involved will use exponential back-off to choose which computer proceeds. Each computer delays a random time before trying to transmit again , and then doubles the delay for each successive collision.

3 Different Network Technology Categories

Local Area Network Metropolitan Area Network Wide Area Network

Local Area Network

Can span a single building or campus Consists of a single shared medium, usually

a cable, to which many computers attach 3 basic Topologies

a. Star Topology

b. Ring Topology

c. Bus Topology

Bus Topology

Bus Topology (cont.)

Uses a single coaxial cable called a backbone.

Inexpensive for modest-sized Ethernet networks.

While easy to install and add computers, heavy traffic will slow it down and a cable break will shut down the entire network.

Ring Topology

Ring Topology (cont.)

Using token passing, computers are connected to each other in a circle

Although good for high speed networks, it is difficult to expand, and the entire network is vulnerable if one node goes down.

It requires more cabling than a bus, and adding nodes disrupts the entire network.

Star Topology

Star Topology (cont.)

Each computer connects to a central hub with its own cable making it easy to add computers and more reliable than a bus.

It is more expensive than a bus because of more cable requirements.

If the central hub fails, so does the network.

Wide Area Network

A network that can span sites in multiple cities, countries or continents.

WAN Technologies

- ATM

- ISDN

- SMD

Two Service Paradigms

Connection Oriented service

- analogous to telephone communications in which a connection must be established between two computers before any data can be transferred

Connectionless Service

- analogous to a postal mail system. Whenever it has to send data, a computer must place the data in the appropriate frame format, attach the address of the computer to which the data should be delivered and then pass the frame to the network for delivery.

Service Paradigms (cont.)

Network Performance Characteristics

Delay

- specifies how long it takes for a bit of data to travel across the network from one computer to another.

Throughput

- measure of the rate at which data can be sent through the network. Usually specified in bits per second(bps).

Delay-Throughput Product

T x D The product of delay and throughput

measures the volume of data that can be present on the network.

A network with throughput T and delay D has a total of T x D bits in transit at any time.

Different Network Equipment

Hubs Switches Routers Bridges Gateway

HUBS

A device that connects multiple Computers to a network.

receives a packet (chunk) of data (a frame in Ethernet lingo) at one of its ports from a PC on the network, it transmits (repeats) the packet to all of its ports and, thus, to all of the other PCs on the network.

Switches

A device that connects multiple Computers to a network.

divides the network into multiple segments, acts as a high-speed, selective bridge between the segments, and supports simultaneous connections of multiple pairs of computers which don't compete with other pairs of computers for network bandwidth.

Routers

is a physical device that joins multiple networks together. Technically, a router is a "layer 3 gateway," meaning that it connects networks (as gateways do), and that it operates at the network layer of the OSI model.

Bridges (Smart Repeaters)

An electronic device that used to extend a LAN.

Connects two cable segments, forwards complete, correct frames from one segment to another.

Does not forward interference

Gateways

can operate at any level of the OSI model from application protocols to low-level signaling.

Acts as an intermediary between domains.

ISO/OSI Layer

Layer Description

Layer 1: Physical Layer deals with the basic network hardware e.g.. Fiber, twisted-

pair copper, coax Layer 2: Data Link layer

specifies how to organize data into frames and to transmit the frames e.g.. CSMA/CD, token passing, checksum, CRC

Layer 3: Network layer protocols specify how address are assigned

and how packets are forwarded from one end of the network to the other end (e.g.. IP, ARP, RARP)

ISO Layer (cont.)

Layer 4:Transport layer protocols specify how to reliably transfer data from

one end to the other (e.g.. TCP, UDP, RIP) Layer 5: Session layer protocols specify how to establish a communication session

with a remote computer (e.g.. Password authentication, RPC)

ISO Layer (cont.)

Layer 6: Presentation layer protocols specify how to represent data. Needed

because different computers may represent data differently (e.g. XDR).

Layer 7: Application layer protocols e.g. Lpr, rcp, rlogin,rsh, ftp, telnet,

smtp, DNS, NFS, NIS, SNMP, bootp, ntp,tftp

Network Protocol Headers

Frame Transmission with ISO frames protocols

TCP/IP Layer

TCP/IP Layer (cont.)

Application Layer

Defines TCP/IP application protocols and how host programs interface with transport layer services to use the network

Protocols:

HTTP, Telnet, FTP, TFTP, SNMP, DNS, SMTP, X Windows, other application protocols

TCP/IP Layer (cont.)

Transport LayerProvides communication

session management between host computers. Defines the level of service and status of the connection used when transporting data. Protocols: TCP, UDP, RTP

TCP/IP Layer (cont.)

Internet LayerPackages data into IP datagrams, which contain source and destination address information that is used to forward the datagrams between hosts and across networks. Performs routing of IP data grams.

Protocols:

IP, ICMP, ARP, RARP

TCP/IP Layer (cont.)

Network Interface LayerSpecifies details of how data is physically sent through the network, including how bits are electrically signaled by hardware devices that interface directly with a network medium, such as coaxial cable, optical fiber, or twisted-pair copper wire.

Protocols:Ethernet, Token Ring, FDDI, X.25, Frame Relay, RS-232, v.35

IP Addresses

32 bit IP address is divided into two parts: suffix and prefix.

The address prefix identifies the physical network to which the computer is attached

The address suffix identifies the individual computer on that network.

IP Address Classes

Special IP address

ARP Messages

IP Datagram

The internet protocol defines an IP datagram to be the basic unit of transfer across a TCP/IP internet

Sources

ONLINE SOURCES:

• http://www.usyd.edu.au/is/comms/networkcourse/

• http://wks.uts.ohio-state.edu/sysadm_course/html/sysadm-326.html

• http://margo.student.utwente.nl/simon/finished/thesis/thesis2/node11.html

• http://www.pku.edu.cn/academic/research/computer-center/tc/html/TC0102.html

• http://www.netbook.cs.purdue.edu/subjindx/indx420.htm

TEXTBOOK SOURCES:

• Computer Networks and Internets with Internet Applications 3rd Edition by Douglas E. Comer