lecture a4 network / internet

Lecture A4 Network / Internet

Computing and Art : Nature, Power, and LimitsCC 3.12: Fall 2007

FunctionaliaInstructor

Chipp Jansen, chipp@sci.brooklyn.cuny.edu

Course Web Page

http://www.sci.brooklyn.cuny.edu/~chipp/cc3.12/

Today:

• Network Concepts

• Internet Specifics

• Clients and Servers

• IP Address and Domain Name Servers

What is a network?

• when computers talk to each other, this is called a network

purpose: to share resources, physical (hardware), digital (software and data)

• open system = “a system whose architecture is not a secret”

• Internet is a distributed network

- robust to failure, or attack

ARPAnet

Components of a Network• the network can have different kinds of computers and peripherals attached to it

router

printer

camera

toaster

Toaster?

2001 - British Design - queried the local weather via the network, burned an appropriate symbol on your toast.

WAN vs. LAN

What is a LAN?

What is a WAN?

What kind of network is the internet?

WAN vs. LAN

What is a LAN?

• networks in which computers are physically connected to each other in the close geographical proximity are called local area networks (LANs)

What is a WAN?

• other networks are called wide area networks (WANs)

What kind of network is the internet?

• the internet is a wide area network

Network Topologies

• the way in which the computers are connected to each other is called the network’s topology

Hub - Star

Kinds of Network Topologies

• bus (linear model; inexpensive to run cables, but not robust to node failure) (back-bones of the internet)

Kinds of Network Topologies

• ring (example: IBM token ring)

Kinds of Network Topologies

• star (can be expensive to run cables, but robust to node failure)

Kinds of Network Topologies

• hub (efficient; internet model) (scalable, centralized point of failure)

hub

workstation

workstation

workstation

printer

file-server

Network Architecture

• Open System Interconnection (OSI) reference model or “7-layer” model

1. application layer

2. presentation layer

3. session layer

4. transport layer

5. network layer

6. data link layer

7. physical layer

• “All People Seem To Need Data Processing.”

What is a layer?

• layers allow us to break-down a large task (i.e. communicating over a network) into smaller tasks

• provides abstraction

• a collection of related functions that provides services to the layer above it and receives service from the layer below it

presentation

application

session

providesservice

receivesservice

OSI / “7-layer” model

1. application layer

• displays data, communicates with lower layers via presentation layer

• programmers writing applications (i.e. web-browser) use this layer’s functionality

• end-user’s use the application itself

2. presentation layer

3. session layer

4. transport layer

5. network layer

6. data link layer

7. physical layer

OSI / “7-layer” model

1. application layer

2. presentation layer

• converts application layer data to forms understandable by other layers, and back; translates the “meaning” of the bits

• “special-packaging”

• encryption

3. session layer

4. transport layer

5. network layer

6. data link layer

7. physical layer

OSI / “7-layer” model

1. application layer

2. presentation layer

3. session layer

• exchange of data between applications – “dialog” – and synchronization between applications

• manages and terminates the connections between the local and remote application

4. transport layer

5. network layer

6. data link layer

7. physical layer

OSI / “7-layer” model

1. application layer

2. presentation layer

3. session layer

4. transport layer

• transfer of data through network; effects flow control; provides some error recovery

• TCP (transmission control protocol) and UDP (universal datagram protocol) operate at this layer

• “post-office” - handles / classifies the parcels

5. network layer

6. data link layer

7. physical layer

OSI / “7-layer” model

1. application layer

2. presentation layer

3. session layer

4. transport layer

5. network layer

• physical routing of data from one computer to another; facilitates sender finding receiver

• IP, Internet Protocol - addressing

• Routers operate at the network level

• fragmentation - can break a package up into smaller packages (packets), handles resending (packet switched)

• “shipping network” - sacks of mail, trucks, airplanes

6. data link layer

7. physical layer

Packet-switching

Sending units in smaller chunks:

1. More efficient: line of people at a busy pay-phone

2. React to failure and congestion: avoiding traffic jams

3. Improves reliability: part of message will arrive, and can resend

OSI / “7-layer” model

1. application layer

2. presentation layer

3. session layer

4. transport layer

5. network layer

6. data link layer

• manages transmissions of low-level data; detects and corrects transmission errors

• point-to-point links

7. physical layer

OSI / “7-layer” model

1. application layer

2. presentation layer

3. session layer

4. transport layer

5. network layer

6. data link layer

7. physical layer

• sends electronic signals, or “bits” – 0’s and 1’s)

• (usually linked to above layer)

• wired ethernet network vs. wireless network

network information units and formats

• “information units” are passed from one layer to another

• “headers” are added as information passes from upper to lower layer

• terminology is defined below (it is often not used clearly or precisely):

– frame - information unit whose source and destination are the data link layer

– packet - information unit whose source and destination are the network layer

– segment - information unit whose source and destination are the transport layer

– message - information unit whose source and destination are the application, presentation or session layers

– datagram - information unit in a “connectionless” network

network/internet protocols

• protocol = set of rules for how computers communicate with each other

• IP: internet protocol, i.e., moving data via TCP or UDP

• TCP: transmission control protocol (computer ↔ computer); can re-

transmit if errors

• UDP: user datagram protocol; no error checking, fast messaging

• HTTP: hypertext transfer protocol (computer ↔ browser)

• FTP: file transfer protocol

• SMTP: simple mail transfer protocol

internet addresses

• IP address = Internet Protocol address

• every computer on the internet has a unique address

• dotted quad notation = four numbers separated by dots (.); e.g., 146.245.250.131 (which is the address of the CIS dept web server...)

- every number in the address is between 0 and 255(*do you know why?)

• address can be stored in 32 bits; there are four formats, depending on the size of the network (i.e., the size of each of the numbers in the dotted quad notation is defined by the format...)

internet address

• “subnetting” is a standard (defined in 1985) to divide a large network into a number of smaller networks (this is what a router does)

• a computer is assigned one IP address

- assigned statically (manual)

- assigned dynamically (DHCP)

• “subnetting” is a standard (defined in 1985) to divide a large network into anumber of smaller networks (this is what a router does)

• example:network subnet hostprefix number number

IP address 130.5.5.25 → 130.5. .5 .25

domain names

• provides a more convenient way to address a computer on the internet thanthe numeric IP address

• structured hierarchically

• example: www.sci.brooklyn.cuny.edu

• common domain names: com, edu, gov, uk and other country-based domains

• name server : maintains correspondance between numeric IP address and do-main names;

• DNS = internet domain name system = group of domain name servers

clients and servers

• server :

– computer on a network which carries out some service for another com-puter

• client:

– the other computer for whom the server is carrying out the service

• types of servers:

– file servers (provides files for clients)

– database servers (specialized file server: provides databases – structuredfiles – for clients)

∗ what is a database?

∗ key concepts: SQL (structured query language), hierarchy, records,fields

– web servers (specialized file server: provides files that make up the com-ponents of a web site, e.g., html documents, video clips, etc)

– groupware

∗ manages scheduling for individuals and groups of co-workers/collaborators

∗ provides reports (e.g., billing) for collaborators

4

Randall Munroe.

Domain Names

• provides a more convenient way to address a computer on the internet than the numeric IP address (we like naming things)

• structured hierarchically

• example: www.sci.brooklyn.cuny.edu (which is more general?)

• no correspondence between parts of a domain name and numbers in IP

• common domain names : com, edu, gov, uk and other country-based domains (TLDs - top-level domains), (what about .tv? or .fm?)

• name server maintains correspondence between numeric IP address and domain names;

• DNS = internet domain name system = group of domain name servers

URLs

URL - uniform resource locator

- what web-browsers use (not exclusive!)

http://www.sci.brooklyn.cuny.edu/~chipp/cc3.12/syllabus.html

3 Parts

1. Protocol (i.e. telephone vs. fax)

2. DNS name

3. path to a file on the server

clients and servers

• server

– computer on a network which carries out some service for another computer

• client

– the other computer for whom the server is carrying out the service

types of servers

– file servers (provides files for clients)

– database servers (specialized file server: provides databases – structured files – for clients)

• what is a database ?

• key concepts: SQL (structured query language), hierarchy, records, fields

– web servers (specialized file server: provides files that make up the components of a web site, e.g., html documents, video clips, etc)

– groupware

• manages scheduling for individuals and groups of co-workers collaborators

• provides reports (e.g., billing) for collaborators

• supports mailing lists for collaborators

– mail servers (provides mail sending, receiving, storage)

– object servers (provides access to“distributed objects”)

– print servers (manages a print queue)

• adds requests to the queue

• schedules requests

• instructs printer regarding requests

• provides status on requests to clients

– application servers (provides access to particular applications, e.g., game servers)

Client-Server Architecture

• client-server advantages:

– isolates data storage technology

– places more burden on server (instead of client) and distributes tasks amongst server(s)

– follows object-oriented and modular paradigms

∗ supports mailing lists for collaborators

∗ e.g. Lotus Notes

– mail servers (provides mail sending, receiving, storage)

– object servers (provides access to “distributed objects”)

– print servers (manages a print queue)

∗ adds requests to the queue

∗ schedules requests

∗ instructs printer regarding requests

∗ provides status on requests to clients

– application servers (provides access to particular applications, e.g., gameservers)

client-server architectures

internet

and

logic layer

data layer web server

web browser == client

presentation

file server, database server, web server

and

logic layer

data layer

processing

layer

web browser == client

internet

internet

or LAN

application server, web server

presentation

two-tier architecture three-tier architecture

• advantages:

– isolates data storage technology

– places more burden on server (instead of client) and distributes tasksamongst server(s)

– follows object-oriented and modular paradigms

5

Telegarden (1995 - 2004)

Ken Goldberg - UC Berkley Prof.

Tillie, the telerobotic doll (1995 - 1998)

Lynn Hershman (1995 - 1998)

About now in Chicago; about here, now

Michael Rodemer, 1996

Video, wind sensors, fans

Chicago - West Virginia connection.

TO DO

• Homework A (part 1 and 2) DUE Sunday, September 16, 11:59 pm via E-mail as a TEXT FILE attachment.

READ:

• Reed, Chapter 1

• Reed, Chapter 3

• Reed, Chapter 6