1 2a. Introduction to Data Communications and Networking 1. Communication Link 2. General Definition 3. Example of Computer Communication Systems 4. Networking.

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2a. Introduction to Data Communications and Networking

1. Communication Link

2. General Definition 

3. Example of Computer Communication Systems

4. Networking a. Telephone Network

b. Computer Networks

c. Cable Television

d. Wireless Networks.

5. Communication Standards a. System Interconnection

6. OSI/RM

7. Layer Descriptions

8. The TCP/IP Reference Model a. Protocol Hierarchies

b. Internet Layer

c. Transport Layer

d. Application Layer

e. Host-to-Network Layer

9. Packet Switching and Circuit Switching

10.Connect-oriented and Conn.less Services

(T. pg. 1-84)

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1. Communication Link

Input Device

1 2 3 4 5 6

Input Information

Input Data or Signal

Transmitted Signal

Received Signal

Output Information

Output Data or Signal

Transmitter Transmission

Medium Receiver

Output Device

2 1 3 4 5 6

Source System Destination System

Data Communication Link

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2. General Definitions • Information is the meaning that a human being assigns to

data by means of the conventions applied to those data.

• Data is a representation of facts, concepts, or instructions in a formalized manner suitable for communications.

• Signals are the physical encoding of data, electric, or electromagnetic means.

Signals can be:

• Analog (continuous in time and amplitude),

• Discrete (discrete in time, continuous in amplitude), or

• Digital. A digital signal (discrete in time and amplitude),it is a sequence of digital values which changes once every interval.

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3. Example of a Computer Communication Systems

Message Generator

m

Computer

Message Encoder

gd (t) Error Control Encoder

Sd (t)

Se (t)

Modulator

Sm (t)

Analog Transmission

Line

Demodulator

?e (t)

Error Control Decoder

m

Message Decoder gd (t) Sd (t)

User

Remote Device

?a (t)

?m (t)

Regenerator

Digital Signal

Encoded Digital Signal

Modulated Signal

Noise

Altered Modulated Signal

Analog Signal

Regenerated Encoded Digital Signal (with possible errors)

Regenerated Digital Signal (errors detected and corrected)

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4. Networking • Communication networks enable many users to transfer

information in different form of voice, video, electronic mail, and computer files.

• a. In Telephone Network:

Circuit switching. “Circuit" reefers-one telephone conversation along one link.

• Circuit switching occurs at the beginning of new telephone call.  

• An electronic interface, coder/decoder (codec) in the switch converts the analog signal traveling on the link from the telephone set to the switch into digital signal-a bit stream.  

• Since the 1980s the transmission links of the telephone network have been changing to the SONET, or Synchronous Optical Network, standard. SONET rates are arranged in the Synchronous Transfer Signal (STS).

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Phone connection to digital network

Analog signal

Switch

Codec

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• Carrier Signal Rate in Mbps• OC-1 STS-1 51,840

• OC-3 STS-3 155,520 • OC-9 STS-9 466,560

• OC-12 STS-12 622,080 • OC-18 STS-18 933,120 • OC-24 STS-24 1244,160 • OC-36 STS-36 1866,240 • OC-48 STS-48 2488,320

• OC-192 STS-192 9853,280• OC-768 STS-768 39,413,120

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• b. Computer or Data Communication Networks

• Data packets • Packet switching + Rules of operations (protocols) =The ARPANET -single packet format and addressing scheme.

Through the ARPANET was evolved into the Internet. ARPANET architecture was formalized layered model of OSI

• The packet switching technique in networks is based on Multiplexing and/or Multiple Access methods of computer interconnections.

• Multiplexing: TDM FDM (WDM / DWDM) • Multiple Access: Ethernet Network. Token Ring Network. Fiber Distributed Data Interface - FDDI-Timed-token mechanism-fixed time of the arrivals token

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Model of the information system

Clients

Server

Network

Broadcast links.

Point-to-point (unicast) links

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LANTopology of the:

Ethernet (a) and Token Ring networks (b).

A

Ba

bIEEE 802.3

IEEE 802.5

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Wide Area Network (WAN) Subnet Router (Switch)

Host (Server)

Metropolitan Area Networks (MAN)

MAN represents as a interconnected LANs by point-to-point communication links.

The interconnection is controlled by switches,

ClientLinks

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Sprint US backbone network

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• Cable Television, originally known as Community Antenna Television or CATV. In CATV the signal from one master antenna distributed over a large area using coaxial cable and amplifiers. The key innovations in cable TV are optical fiber links, digital compression techniques, and service integration.

• Today cable TV uses frequency-division multiplexing to transmit up to 69 analog TV channels, each 4.5 MHz wide. Transmission is over coaxial cables arranged as a unidirectional tree.

• Amplifiers used to compensate for the attenuation of the cable signal. The number of TV a channels is limited by the bandwidth of coaxial cables.

• Optical fibers are used to transmit the TV signals over longer distance. Transmission over the fiber is still analog. The signal is fed into the coaxial cable network at various points, where the optical signal is converted into electrical signals. This hybrid fiber/coaxial cable distribution system has a longer span and better signal quality than a coaxial cable network. This network called fiber-to-the-curb (FTTC) network.

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• To increase the number of channels, digital transmission technology.

• Before transmitting the TV signals, the CATV company uses a TV codec that converts each signal into a bit stream.• Using Motion Pictures Expert Group (MPEG) algorithms, the codec compresses the bit stream to reduce its rate. • The bit streams are transmitted over fibers to the curb and then

distributed by the neighborhood coaxial network. • The compression gain now allows-transmit about 500 TV

channels. MPEG1 standard, TV signal is encoded-1.5 Mbps bit stream, which can be modulated in a signal that has a bandwidth of about 600 kHz.

• Set-up boxes at the user residence perform the decompression. This CATV network is still unidirectional. Video on demand, Internet access, and telephony, the CATV industry is organizing bidirectional networks. Such a network connects video servers to users by means of control messages.

• The user choices these messages to select the video program, and the video program is sent over the network to the user.

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Residential access: cable modems

Diagram: http://www.cabledatacomnews.com/cmic/diagram.html

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Cable Network Architecture: Overview

home

cable headend

cable distributionnetwork (simplified)

Typically 500 to 5,000 homes

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Cable Network Architecture: Overview

home

cable headend

cable distributionnetwork (simplified)

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Cable Network Architecture: Overview

home

cable headend

cable distributionnetwork

server(s)

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c. Cable Network Architecture: Overview

home

cable headend

cable distributionnetwork

Channels

VIDEO

VIDEO

VIDEO

VIDEO

VIDEO

VIDEO

DATA

DATA

CONTROL

1 2 3 4 5 6 7 8 9

FDM:

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d. Wireless Networks. The first packet-switched wireless network- in 1971- Alohanet,

interconnected computers on four islands in a star topology:

A first approximation wireless network- three main categories:

1. Components interconnection. Short-range radio. Bluetooth network.

2. Wireless LANs. Wireless LAN permitting per-to-per communications networks. LANs called IEEE 802.11, Wireless LAN can operate at bit rates up to about 50 Mbps over distances of tens of meters.

3. Wireless WANs. The radio network used for cellular telephones is an example of a low-bandwidth wireless wide area system. This system has already gone through three generations:

a. The first- analog and voice only.

b. The second- digital and for voice only.

c. The third- digital and is for both voice and data.

Cellular systems operate below 1 Mbps, but the distances between the base station and the computer or telephone is measured in kilometers.

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• Shared wireless access network connects end system to router– via base station “access point”

• wireless LANs:- 802.11b:

- 50 Mbps, tens of meters

• wireless WAN

- Cellular systems

- < 1Mbps, several km

basestation

mobilehosts

router

Wireless access networks

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Telephone Networks

ComputerNetworks

Cable TV Wireless Networks

Circuit switching, separation of call control from voice transfer. ISDN and service integration. Optical links.SONET. ATM.

Packet-switched networks.Multiple-accessNetworks.Layered architecture, ARPANET. Internet. OSI modelIntegrated services. ATM.

Digitization and compression using signal processing techniques. Fiber-to-the-curb network. Two-way links.Service integration.

Radio and TV Broadcast.Cellular. Telephones.Wireless LANs.Voice, data Integration.Bluetooth.

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5. System interconnection

• An important concept in data communications is the interconnections between the communication system components. The interconnection could be done if:

• Physical characteristics of the interconnected equipment are fitted to each other.

• It allows manufacturers of different systems to interconnect their equipment through standard interfaces.

• It also allows software and hardware to integrate well and be portable on differing systems.

• So, standards of hardware and software for interconnections in systems are necessary.

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Communication Standards• Computer communication uses different standard for different

approach. • The RS-232-C standard is used for the serial port of

computer devices. This standard is for low bit rate transmissions (up to 38 Kbps) over short distances (less than 30 m). Transmissions take place over untwisted wires.

• A serial link is often used to attach a computer to a modem. A modem transmits data by converting bits into tones that can be transported by the telephone network. The receiving modem then converts these tones back into bits, thus enabling two computers with compatible modems to communicate over the telephone network as if they were directly connected by a serial link. Modems conforming to new V.90 standard can transmit 56,000 bps.

• The Synchronous Transmission Standard increases the transmission rate. These standards are known as Synchronous Data Link Control (SDLC). The main idea of SDLC is to avoid the time wasting by RS-232-C.

• SDLC groups many data bits into packets.

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• With an open system of standards any company can manufacture equipment or write software. Companies must cooperate on standards.

• Standard organizations create and administer standards. Often competing companies will form a committee to create a standard acceptable to all interested parties. Then the companies will ask a standard organization for formal recognition of that standard.

• An example: Ethernet, a Local Area Network (LAN) system created by Xerox, Intel, and Digital Equipment Corporation. These companies asked the Institute of Electrical and Electronics Engineers (IEEE) to formalize Ethernet, and this becomes standard IEEE 802.3.

• United States major standards from industry are: The American National Standard Institute (ANSI), the IEEE,

and the Electronic Industries Association (EIA). The major governmental standards organization is the National institute of Standards and Technology (NIST).

NIST major standards concerns are the standard Volt, standard Ampere, time, and dimensions for manufactures.

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Application Presentation Session Transport Network Data Link Physical

Application Presentation Session Transport Network Data Link Physical

Data Data

User application, process And management functions Data interpretation, format And control transformation Administration and control Of session between two nodes Network transparent data trans- fer and transmission control Routing, switching and flow Control over a network Maintain and release data: Link, error and flow control Electrical and mechanical characteristics

Actual Data Flow

Open System Interconnection Reference Model

Communication subnet

Each layer is a kind of virtual machine, offering certain services to the

layer above

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Protocol Hierarchies

• The philosopher-translator-secretary architecture.

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• Each layer is a kind of virtual machine, offering certain services to the layer above it.

• Layer n on one machine carries on a conversation with layer n on another machine. The rules and conversations are known as the layer n protocol.

• A protocol is an agreement between the communicating parties on how communication is to proceed.

Dealing with complex systems:• Clear structure allows identification, relationship of complex

system’s pieces• modularization eases maintenance, updating of system

change of implementation of layer’s service transparent to rest of system

Why layering?

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• The function of layer: what task the layer is perform, but not how the layer performs its task.• The function of interface: how a layer will communicate with the layer above it and the layer below it. • For software interfaces, information may be passed in a

manner similar to parameter passing. The information must be in a particular format (a. length, b. the order in which individual fields appear within a frame, c. the bit order within individual frames).

• The hardware interfaces (physical level) may be: a. voltages, b. impedance, and c. mechanical dimensions.

• Bottom three layers - Communications Subnet. They are: 1. the Physical Layer, (is hardware) 2. the Data Link Layer (DLL), (can be a mixture of hardware and software). 3. the Network Layer.The Communication Subnet is one of the major subjects of CS 117 and CS M 171L classes to study.

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Communications Subnet.1. the Physical Layer, is hardware The

Physical is the actual medium that conveys the bit stream. This connects the networks together and carries the "ones" and "zeros" (voltage or light pulses). Typical questions here are how many volts should be used to represent a “1” and how many for “0”. How many nanoseconds a bit lists,

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• Layer 1: Physical Layer. Transmitted signals are modulated electromagnetic waves that propagate through medium.

• The medium can be fiber optics, twisted pair copper wire, coaxial cable, microwaves, satellite, laser beams, or radio waves. Layer 1 also includes the antennas, cables, satellites, and connectors.

• The transmitter converts the bits into signals, and the physical layer in the receiver converts the signals back into bits. The receiver must be synchronized to be able to recover the arrival bits. To assist the synchronization, the transmitter inserts a specific bit pattern, called a preamble, at the beginning of the packet.

• The physical layer transmits bits by converting them into electrical, electromagnetic waves, or optical signal.

• Generally, wireless links are slower than copper links, and copper links are slower than optical links.

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Coaxial cable:• copper conductors

• bidirectional

• baseband:– single channel on

cable

• broadband:– multiple channel on

cable

Fiber optic cable:• glass fiber carrying light

pulses, each pulse a bit• high-speed operation:

– high-speed point-to-point transmission (e.g., 5 Gps)

• low error rate: repeaters spaced far apart ; immune to electromagnetic noise

Physical Media: coax, fiber

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• signal carried in electromagnetic spectrum

• no physical “wire”

• bidirectional

• propagation environment effects:– reflection – obstruction by objects– interference

Radio link types:• terrestrial microwave:

– e.g. up to 45 Mbps channels

• LAN (e.g., WaveLAN)– 2Mbps, 11Mbps

• wide-area (e.g., cellular)– e.g. 3G: hundreds of kbps

• Satellite:– up to 50Mbps channel (or

multiple smaller channels)– 270 msec end-end dela

Physical media: radio

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Communications Subnet (cont)

2. the Data Link Layer (DLL): 1. Error control; 2. Flow control; 3 Synchronizes the receiver to the incoming bit stream; 4. Decodes the bit stream.

• Sublayer 2a: Media Access Control (MAC). regulate the access to that shared link

• Sublayer 2b: Logical Link Control (LLC). Implement error detection or reliable packet

transmission between computers attached to a shared link.• The MAC and LLC together constitute the data link

layer to implement a packet transmission service with error detection or a reliable packet transmission service

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Communications Subnet (cont)• Layer 3: Network Layer is concerned with routing

the frame. The three steps of routing are: 1. Establishing the connection, 2. Maintaining the connection, 3. Terminating the connection after the data transfer is complete.

• Routing is the function to find the path the packets must follow.

• The network layer appends unique network addresses of the source and destination computers.

• Addressing scheme in packet-switched networks is that used by the Internet.

• Circuit-switch networks, like the telephone network, use different addressing schemes.

• The network layer uses the transmission over point-to-point links provided by the data link layer to transmit packets between any two computers attached in a network.

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• End systems (hosts):– Run application programs

– Web, email

– at “edge of network”

• Client/server model– Client host requests, receives

service from always-on server

– Web browser/server; email client/server

The network edge:

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The Network Core

• Mesh of interconnected routers

• the fundamental question: how is data transferred through network?

• --circuit switching: dedicated circuit per call: telephone net– packet-switching:

data sent thru net in packets

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Circuit SwitchingEnd-to-end

resources reserved for “call”

• link bandwidth, switch capacity

• dedicated resources: no sharing

• circuit-like (guaranteed) performance

• call setup required

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Packet Switching

Each end-end data stream divided into packets

• users share network resources dynamically

• each packet uses full link bandwidth

• resources used as needed

Resource contention: • aggregate resource

demand can exceed amount available bandwidth

• congestion: packets queue, wait for link use

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Packet Switching: Statistical Multiplexing

Sequence of A & B packets does not have fixed pattern statistical multiplexing.

A

B

C10 MbsEthernet

1.5 Mbs

D E

statistical multiplexing

queue of packetswaiting for output

link

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What’s the Internet:

• Millions of connected computing devices: hosts, end-systems– PCs workstations, servers;

running network applcts• communication links

– fiber, copper, radio, satellite

– transmission rate = bandwidth

• Routers (gateways): forward packets (chunks of data)

local ISP

companynetwork

regional ISP

router workstation

servermobile

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What’s a protocol?

Hi

Hi

Got thetime?

2:00

TCP connection req

TCP connectionresponse

<file>time

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human protocols:• “what’s the time?”• “I have a question”• introductions

… specific msgs sent

… specific actions taken when msgs received, or other events

network protocols:• machines rather than

humans• all communication

activity in Internet governed by protocols

protocols define format, order of msgs sent and

received among network entities, and actions

taken on msg transmission, receipt

What’s a protocol?

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Protocol “Layers”Networks are

complex! • many “pieces”:

– hosts– routers– links of various

media– applications– protocols– hardware,

software

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• Network edge: applications and hosts

• Network core: – routers– network of networks

• Access networks, Physical media: communication links

A closer look at network structure:

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Internet protocol stack• application: supporting network

applications– FTP, SMTP, STTP

• transport: host-host data transfer -TCP, UDP (user datagram protocol)

• Network: routing of datagrams from source to destination– IP, routing protocols

• Data link: data transfer between neighboring network elements– PPP, Ethernet

• Physical: bits “on the wire”

application

transport

network

link

physical

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Network SoftwareProtocol Hierarchies

• Layers, protocols, and interface services.

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The relationship between a service and a protocol

Layer k Layer k

Layer k+1 Layer k+1

Layer k-1 Layer k-1

Service provided by layer k

Protocol

A set of layers and protocols is called network architecture. A list of protocols used by a certain system, one protocol per layer, is called a protocol stack.

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Correspondence of OSI and TCP/IP Reference models

7 6 5 4 3 2 1

Application

Presentation

Session

Transport

Network

Data link

Physical

Application

Transport

Internet

Host-to-network

Not presented in the model

OSI TCP/IP

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Protocols and networks in the TCP/IP model initially

TELNET FTP SMTP DNS

TCP UDP

ARPANET

IP

SATNET Packet radio

LAN

Protocols

Networks

Application

Transport

Network

Physical+ data link

Layer (OSI) names

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Mixed OSI and TCP/IP layers

Each layer takes data from above• adds header information to create new data unit• passes new data unit to layer below

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

source destination

M

M

M

M

Ht

HtHn

HtHnHl

M

M

M

M

Ht

HtHn

HtHnHl

message

segment

datagram

frame

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Layering: physical communication

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

networklink

physical

data

data

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• The Internet Layer is the glue that holds the whole architecture together. Its job is to permit hosts to inject packets into any network and have them travel independently to the destination (potentially on a different network). They may even arrive in different order than they were sent, in which case it is the job of higher layers to rearrange them, if in-order delivery is desired.

• The internet layer defines an official packet format and protocol called IP (Internet Protocol). The job of the internet layer is to deliver IP packets where they are supposed to go. Packet routing is clearly the major issue here, as is avoiding congestion. For these reason, it is possible to say that:

the internet layer is similar in functionality to the OSI network layer.

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• The Transport Layer is designed to allow the source and destination hosts to carry on a conversation, just as in the OSI transport layer.

• Two end-to-end transport protocols are: • 1. TCP (Transport Control Protocol), is a reliable

connection-oriented protocol that allows a byte stream originating on one machine to be delivered within error on any other machine in the Internet. It fragments the incoming byte stream into discrete messages and passes each one on the internet layer. At the destination, the receiving TCP process reassembles the received messages into the output. TCP also handles flow control.

• 2. UDP (User Datagram Protocol), is an unreliable, connectionless protocol for application that do not want TCP’s sequencing or flow control and wish to provide their own. It is also widely used for one-shot, client-server-type request-reply queries and applications in which prompt delivery is more important than accurate delivery, such as transmitting speech or video.

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Connectionless and Connection-Oriented Services

• Internet, generally TCP/IP network provide two types of services to its applications:

1. connectionless services;

2. connection-oriented services

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Goal: data transfer between end systems

• handshaking: setup (prepare for) data transfer ahead of time– Hello, hello back

human protocol

– set up “state” in two communicating hosts

• TCP - Transmission Control Protocol – Internet’s connection-

oriented service

TCP service [RFC 793]

• reliable, in-order byte-stream data transfer– loss: acknowledgements

and retransmissions

• flow control: – sender won’t overwhelm

receiver

• congestion control: – senders “slow down

sending rate” when network congested

Connection-oriented service

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Goal: data transfer between end systems– same as before!

• UDP - User Datagram Protocol:

• Internet’s connectionless service– unreliable data

transfer– no flow control– no congestion control

App’s using TCP: • HTTP (Web), FTP (file

transfer), Telnet (remote login), SMTP (email)

App’s using UDP:• streaming media,

teleconferencing, Internet telephony

Connectionless service

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• The Application Layer• The TCP/IP model does not have session or presentation

layers. • On top of the transport layer is the application layer. It contains

all the higher-level protocols. The early ones included virtual terminal (TELNET), file transfer (FTP), and electronic mail (SMTP). The virtual terminal protocol allows a user on one machine to log onto a distant machine and. Electronic mail was originally just a kind of file transfer, but later a specialized protocol (SMTP) was developed for it. Many other protocols have been added to these over the years, the Domain Name System (DNS) for mapping host names onto their network addresses, NNTP, the protocol for moving USENET news articles around, and HTTP, the protocol for fetching pages on the World Wide Web, and many others.

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Networking Technologies

Circuit Switching Packet Switching

Static Dynamic Connection- Oriented

Connection- Less

SDH/SONET DTM ATM

Gigabit Ethernet

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FDMA

frequency

time

4 users

Example:

frequency

time

TDMA

Circuit Switching: FDMA and TDMA

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each end-end data stream divided into packets

• user A, B packets share network resources

• each packet uses full link bandwidth

• resources used as needed

resource contention: • aggregate resource

demand can exceed amount available

• congestion: packets queue, wait for link use

• store and forward: packets move one hop at a time– transmit over link– wait turn at next

link

Bandwidth division into “pieces”

Dedicated allocation

Resource reservation

Packet Switching

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Layering: logical communication

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

networklink

physical

data

datatransport• take data from

application layer• add addressing,

reliability check info to form “datagram”

• send datagram to peer

• wait for peer to ack receipt

• analogy: post office

data

transport

transport

ack

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Layering: logical communication

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

networklink

physical

Each layer:• distributed• “entities”

implement layer functions at each node

• entities perform actions, exchange messages with peers