Part 1_Network Computing

8/13/2019 Part 1_Network Computing

1/114

Network programming

Lesson 1

HUYNH Cong Phap, [email protected], [email protected]
mailto:[email protected]:[email protected]:[email protected]:[email protected]


2/114

ClientServer Computing


3/114

Client Server Architecture

A networkarchitecture in which

each computer or

process on the

network is either a

clientor a server.


4/114

Components

Clients Servers

Communication Networks

Client

Server


5/114

Applications that run on computers Rely on servers for

Files

Devices

Processing power

Example: E-mail client

An application that enables you to send andreceive e-mail

Clients

Clients are Applications


6/114

Servers

Computers or processes that managenetwork resources

Disk drives (file servers)

Printers (print servers) Network traffic (network servers)

Example: Database Server

A computer system that processes databasequeries

Servers Manage

Resources


7/114

Communication Networks

Networks Connect

Clients and

Servers


8/114

ClientServer Computing

Process takes place on the server and

on the client

Servers Store and protect data

Process requests from clients

Clients

Make requests

Format data on the desktop

Client-Server

Computing Optimizes

Computing Resources


9/114

Application Functions

Software applicationfunctions are separated

into three distinct parts

Client: Presentation & Application Logic

Server:

Data Management


10/114

Application Components

Data Management

Application Logic

Presentation

3 Logical Tiers

1

2

3

Database Applications:

Most common use of client-server architectures

Thin

Client

FatClient

2 Client Types


11/114

Middleware

Software that connects twootherwise separate applications

Example: Middleware product

linking a database system to a

Web server

Client: Requests Data via Web

Database Server:

Manages Data

Web Server:

Presents Dynamic Pages

Middleware Links

Applications


12/114

Types of Servers

Application Servers

Audio/Video Servers

Chat Servers

Fax Servers

FTP Servers

Groupware Servers

IRC Servers

List Servers

Mail Servers

News Servers

Proxy Servers

Telnet Servers

Web Servers

Z39.50 Servers

Source: http://webopedia.lycos.com

From A to Z


13/114

ADVANTAGES OF CLIENT-

SERVERAdvantages often cited include:

Centralization - access, resources, and data

security are controlled through the server

Scalability - any element can be upgradedwhen needed

Flexibility - new technology can be easily

integrated into the system

Interoperability - all components (clients,

network, servers) work together


14/114

DISADVANTAGES OF

CLIENT-SERVER Disadvantages often cited include:

Dependability - when the server goes down,

operations cease

Higher than anticipated costs Can cause network congestion


15/114

CLIENT-SERVER

ARCHITECTURES There are basically two types of client-

server architectures

Two tier architectures

Three tier architectures The choice between the two should be

made based on combination of:

Schedule for project implementation Expected system changes and

enhancements


16/114

TWO-TIER ARCHITECTURES

Application components aredistributed between the

server and client software

In addition to part of the

application software, the

server also stores the data,

and all data accesses are

through the server. The presentation (to the

user) is handled strictly by

the client software.

Server

Network

PC PC PC

Clients


17/114

TWO-TIER ARCHITECTURES

(cont.) The PC clients assume the bulk of the

responsibility for the application logic.

The server assumes the bulk of the

responsibility for data integrity checks,query capabilities, data extraction and

most of the data intensive tasks,

including sending the appropriate data tothe appropriate clients.


18/114

TWO-TIER ARCHITECTURES,

ADVANTAGES The commonly cited advantages of two-

tier systems include:

Fast application development time

Available tools are robust and lendthemselves to fast prototyping to insure user

needs a met accurately and completely.

Conducive to environments with

homogeneous clients, homogeneous

applications, and static business rules.


19/114

TWO-TIER ARCHITECTURES,

DISADVANTAGES The commonly cited disadvantages of

two-tier systems include:

Not suitable for dispersed, heterogeneous

environments with rapidly changing businessrules.

Because the bulk of the application logic is

on the client, there is the problem of client

software version control and new versionredistribution.

Security can be complicated because a user

may require separate passwords for eachSQL server accessed.


20/114


21/114

THREE-TIER

ARCHITECTURES (cont.) When data or processing are required by

the presentation client, a call is made to

the middle-tier functionality server.

This tier performs calculations, doesreports, and makes any needed client

calls to other servers (e.g.. a data base

server).


22/114

THREE-TIER

ARCHITECTURES (cont.) Middle tier servers are usually coded in a

highly portable, non-proprietary language

such as C or C++.

Middle tier servers may be multithreadedand can be accessed by multiple clients.

The calling mechanism from client to

server and from server to server is bymeans of RPCs.


23/114

-ARCHITECTURES,

ADVANTAGES (cont.) Commonly cited advantages include: Having separate functionality servers allows

for the parallel development of individual tiers

by application specialists. Provides for more flexible resource

allocation. Can reduce network traffic by

having the functionality servers strip data to

the precise structure needed before sendingit to the clients.


24/114

-ARCHITECTURES,

DISADVANTAGES Often cited disadvantages of 3-tierarchitectures include:

Creates an increased need for network traffic

management, server load balancing, andfault tolerance.

Current tools are relatively immature and are

more complex.

Maintenance tools are currently inadequatefor maintaining server libraries. This is a

potential obstacle for simplifying

maintenance and promoting code reuse

throu hout the or anization.


25/114

Peer to Peer Computing


26/114

What is Peer-to-Peer?

A model of communication where everynode in the network acts alike.

As opposed to the Client-Server model,where one node provides services and

other nodes use the services.


27/114

Advantages of P2P Computing

No central point of failure E.g., the Internet and the Web do not have a central

point of failure.

Most internet and web services use the client-server

model (e.g. HTTP), so a specific service does have acentral point of failure.

Scalability

Since every peer is alike, it is possible to add more

peers to the system and scale to larger networks.


28/114

Disadvantages of P2P

Computing Decentralized coordination

How to keep global state consistent?

Need for distributed coherency protocols.

All nodes are not created equal. Computing power, bandwidth have an impact

on overall performance.

ProgrammabilityAs a corollary of decentralized coordination.


29/114

P2P Computing Applications

File sharing

Process sharing

Collaborative environments


30/114

P2P File Sharing Applications

Improves data availability Replication to compensate for failures.

E.g., Napster, Gnutella, Freenet, KaZaA

(FastTrack), your DFS project.

2 S


31/114

P2P Process Sharing

Applications

For large-scale computations

Data analysis, data mining, scientific

computing E.g., SETI@Home, Folding@Home,

distributed.net, World-Wide Computer
mailto:SETI@Homemailto:Folding@Homemailto:Folding@Homemailto:SETI@Home


32/114

P2P Collaborative Applications

For remote real-time humancollaboration.

Instant messaging, virtual meetings,shared whiteboards, teleconferencing,tele-presence.

E.g., talk, IRC, ICQ, AOL Messenger,

Yahoo! Messenger, Jabber, MSNetmeeting, NCSA Habanero, Games


33/114

Types of P2P

Pure P2P

Hybrid P2P


34/114

Napster


35/114

Gnutella

But introduces a new single point of failure!


36/114

KaZaA/Morpheus


37/114

Distributed systems

Data Networking &Client-Server Communication


38/114

Distributed systems

Independent machines workcooperatively without shared memory

They have to talk somehow

Interconnect is the network


39/114

Modes of connection

Circuit-switched dedicated path

guaranteed (fixed) bandwidth

[almost] constant latencyPacket-switched

shared connection

data is broken into chunks called packets each packet contains destination address

available bandwidth channel capacity

variable latency


40/114

Whats in the data?

For effective communication same language, same conventions

For computers:

electrical encoding of data where is the start of the packet?

which bits contain the length?

is there a checksum? where is it?how is it computed?

what is the format of an address?

byte ordering


41/114

Protocols

These instructions and conventions

are known as protocols


42/114

Protocols

Exist at different levelsunderstand format ofaddress and how tocompute checksum

request web page

humans vs. whalesdifferent wavelengths

French vs. Hungarian

versus


43/114

Layering

To ease software development andmaximize flexibility:

Network protocols are generally organized

in layers Replace one layer without replacing

surrounding layers

Higher-level software does not have toknow how to format an Ethernet packet

or even know that Ethernet is beingused


44/114

Layering

Most popular model of guiding(not specifying) protocol layers is

OSI reference model

Adopted and created by ISO

7 layers of protocols


45/114

OSI Reference Model: Layer 1

Transmits andreceives raw data to

communication

medium.

Does not care about

contents.

voltage levels, speed,

connectors

Physical1Examples: RS-232, 10BaseT


46/114

Data Link


Detects and corrects errors.

Organizes data into packets

before passing it down.

Sequences packets (if

necessary).

Accepts acknowledgements

from receiver.

Physical1

2

Examples: Ethernet MAC, PPP


47/114

Network

Data Link


Relay and routeinformation to

destination.

Manage journey ofpackets and figure out

intermediate hops (if

needed).

Physical1

2

3

Examples: IP, X.25


48/114

Transport

Network

Data Link


Provides a consistentinterface for end-to-end(application-to-application)

communication.Manages flow control.

Network interface issimilar to a mailbox.

Physical1

2

3

4

Examples: TCP, UDP


49/114

Session

Transport

Network

Data Link


Services to coordinatedialogue and managedata exchange.

Software implemented

switch.

Manage multiple logicalconnections.

Keep track of who istalking: establish & endcommunications.Physical1

2

3

4

5

Examples: HTTP 1.1, SSL,

NetBIOS


50/114

Presentation

Session

Transport

Network

Data Link


Data representation

Concerned with the

meaning of data bits

Convert between

machine

representations

Physical1

2

3

4

5

6

Examples: XDR, ASN.1,

MIME, MIDI


51/114

Application

Presentation

Session

Transport

Network

Data Link


Collection ofapplication-specificprotocols

Physical1

2

3

4

5

6

7

Examples:email (SMTP, POP, IMAP)file transfer (FTP)

directory services (LDAP)


52/114

Some networkingterminology


53/114

Local Area Network (LAN)

Communications network small area (building, set of buildings)

same, sometimes shared, transmissionmedium

high data rate (often): 1 Mbps1 Gbps

Low latency

devices are peers

any device can initiate a data transfer with anyother device

Most elements on a LAN are workstations endpoints on a LAN are called nodes


54/114

Connecting nodes to LANs

?

network computer


55/114

Connecting nodes to LANsnetwork computer

Adapter expansion slot (PCI, PC Card, USB dongle)

usually integrated onto main board

Network adapters are referred to as

Network Interface Cards(NICs) or

adapters


56/114

Media

Wires (or RF, IR) connecting together thedevices that make up a LAN

Twisted pair Most common:

STP: shielded twisted pair

UTP: unshielded twisted pair(e.g. Telephone cable, Ethernet 10BaseT)

Coaxial cable Thin (similar to TV cable)

Thick (e.g., 10Base5, ThickNet)

Fiber

Wireless


57/114


58/114

Networking Topology

Bus Network


59/114

Networking Topology

Tree Network


60/114

Networking Topology

Star Network


61/114

Networking Topology

Ring Network


62/114

Networking Topology

Mesh Network


63/114

Clients and Servers

Send messages to applications

not just machines

Client must get data to the desiredprocess

server process must get data back to client

process

To offer a service, a server must get a

transport addressfor a particular service

-


64/114

Machine address

versus

Transport address


65/114

Transport provider

Layer of software that accepts a networkmessage and sends it to a remote

machine

Two categories:

connection-oriented protocols

connectionless protocols


66/114

Connection-oriented Protocols

1. establish connection2. [negotiate protocol]3. exchange data4. terminate connection


67/114

Connection-oriented Protocols

virtual circuit service provides illusion of having a dedicated circuit

messages guaranteed to arrive in-order

application does not have to address eachmessage

vs. circuit-switched service

1. establish connection2. [negotiate protocol]3. exchange data4. terminate connection

dial phone number[decide on a language]speakhang up

analogous to phone call

C


68/114

Connectionless Protocols

- no call setup- send/receive data

(each packet addressed)- no termination

C i l P l


69/114

Connectionless Protocols

datagram service

client is not positive whether message arrived

at destination

no state has to be maintained at client orserver

cheaper but less reliable than virtual circuit

service

- no call setup- send/receive data

(each packet addressed)- no termination

drop letter in mailbox(each letter addressed)

analogous to mailbox

Eth t


70/114

Ethernet

Layers 1 & 2 of OSI model Physical (1)

Cables: 10Base-T, 100Base-T, 1000Base-T, etc.

Data Link (2) Ethernet bridging

Data frame parsing

Data frame transmission

Error detection

Unreliable, connectionless communication

Eth t


71/114

Ethernet

48-byte ethernet address Variable-length packet

1518-byte MTU

18-byte header, 1500 bytes data

Jumbo packets for Gigabit ethernet

9000-byte MTUdest addr src addr

frametype

6 bytes 6 bytes 2

data (payload) CRC

446-1500 bytes

18 bytes + data

IP I t t P t l


72/114

IPInternet Protocol

Born in 1969 as a research network of 4machines

Funded by DoDs ARPA

Goal:build an efficient fault-tolerant networkthat could connect heterogeneous

machines and link separately connectednetworks.

I t t P t l


73/114

Internet Protocol

Connectionless protocol designed to handlethe interconnection of a large number of loc

and wide-area networks that comprise the

internet

IP can route from one physical network to

another


74/114

IP Add


75/114

IP Address space

32-bit addresses>4 billion addresses!

Routers would need a table of 4 billion

entries

Design routing tables so one entry can

match multiple addresses hierarchy: addresses physically close will

share a common prefix

IP Addressing: networks &


76/114


hosts

first 16 bits identify Rutgers

external routers need only one entry

route 128.6.*.* to Rutgers

cs.rutgers.edu

128.6.4.2

80 06 04 02

remus.rutgers.edu

128.6.13.3

80 06 0D 03

network # host #



77/114

g &

hosts

IP address network #:identifies network machine

belongs to

host #:identifies host on the network

use network number to route packet to

correct network

use host number to identify specific

machine

IP Add i


78/114

IP Addressing

Expectation: a few big networks and many small ones

create different classesof networks

use leading bits to identify network

To allow additional networks within an organization:use high bits of host number for anetwork within a network subnet

class leading bits bits for net # bits for host

A 0 7 (128) 24 (16M)

B 10 14 (16K) 16 (64K)

C 110 21 (2M) 8 (256)

IP Add i


79/114

IP Addressing

IBM: 9.0.0.09.255.255.25500001001 xxxxxxxx xxxxxxxx xxxxxxxxx

network #8 bits

host #24 bits

00001001 10101010 11 xxxxxx xxxxxxxxx

network #18 bits

host #14 bits

Subnet within IBM (internal routers only)

R i t f dd


80/114

Running out of addresses

Huge growth

Wasteful allocation of networks

Lots of unused addresses

Every machine connected to the internet

needed a worldwide-unique IP address

Solutions: CIDR, NAT, IPv6

IP Special Addresses


81/114

IP Special Addresses

All bits 0 Valid only as source address

all addresses for this machine

Not valid over network

All host bits 1 Valid only as destination

Broadcast to network

All bits 1 Broadcast to all directly connected networks

Leading bits 1110 Class D network

127.0.0.0: reserved for local traffic 127.0.0.1 usuall assi ned to loo back device

IPv6 vs IPv4


82/114

IPv6 vs. IPv4

IPv4 4 byte (32 bit) addresses

IPv6: 16-byte (128 bit) addresses

3.6 x 1038possible addresses

8 x 1028times more addresses than IPv4

4-bit priority field

Flow label (24-bits)

Network Address Translation


83/114

(NAT)

External IP address24.225.217.243

InternalIP address192.168.1.x

External

addressExt

portInternal

addressInt

port

24.225.217.243 25 192.168.1.1 3455

24.225.217.243 25 192.168.1.2 11231

24.225.217.243 80 192.168.1.1 12482

24.225.217.243 80 192.168.1.3 21908

.1 .2 .3 .4 .5

Getting to the machine


84/114

Getting to the machine

IP is a logical network on top of multiple

physical networks

OS support for IP: IP driver

IP driver

network driver

send data

send packet

to wirefrom wire

receive packet

receive data

IP driver responsibilities


85/114

IP driver responsibilities

Get operating parameters from devicedriver Maximum packet size (MTU)

Functions to initialize HW headers

Length of HW header

Routing packets From one physical network to another

Fragmenting packets Send operations from higher-layers

Receiving data from device driver

Dropping bad/expired data

Device driver responsibilities


86/114

Device driver responsibilities

Controls network interface card Comparable to character driver

Processes interrupts from networkinterface Receive packets

Send them to IP driver

Get packets from IP driver Send them to hardware

Ensure packet goes out without collision

bottomh

alf

tophalf

Network device


87/114

Network device

Network card examines packets on wire Compares destination addresses

Before packet is sent, it must beenvelopedfor the physical network

deviceheader

payload

IP header IP data

Device addressing


88/114

Device addressing

IP addressethernet address

Address Resolution Protocol(ARP)

1. Check local ARP cache2. Send broadcast message requesting

ethernet address of machine with certain

IP address

3. Wait for response (with timeout)

Transport-layer protocols over


89/114

y

IP

IP sends packets to machine No mechanism for identifying sending or

receiving application

Transport layer uses a port numberto

identify the application

TCPTransmission Control Protocol

UDPUser Datagram Protocol

TCPTransmission Control


90/114

Protocol

Virtual circuit service(connection-oriented)

Send acknowledgement for each

received packet Checksum to validate data

Data may be transmitted simultaneously

in both directions


91/114


92/114

Headers: TCP & UDP


93/114

Headers: TCP & UDPdevice

headerIP header IP data

TCP/UDP

header

src port dest port

seq number

ack number

hdrlen flags

checksum urgent ptr

options and pad

- window

src port dest port

seg length checksum

TCP header UDP header

20

bytes

8 bytes

payload

Device header (Ethernet II)


94/114

Device header (Ethernet II)device

headerIP header IP data

TCP/UDP

header

dest addr src addr frametype

6 bytes 6 bytes 2

data CRC

446-1500 bytes

18 bytes + data

payload

Quality of Service Problems in


95/114

IP

Too much traffic Congestion

Inefficient packet transmission

59 bytes to send 1 byte in TCP/IP!

20 bytes TCP + 20 bytes IP + 18 bytes

ethernet

Unreliable delivery Software to the rescueTCP/IP

Unpredictable packet delivery


96/114

Sockets


97/114

Sockets

IP lets us send data between machines

TCP & UDP are transport layer protocols

Contain port numberto identify transportendpoint (application)

One popular abstraction for transportlayer connectivity: sockets

Developed at Berkeley

Sockets


98/114

Sockets

Attempt at generalized IPC modelGoals:

communication between processes should

not depend on whether they are on thesame machine

efficiency

compatibility

support different protocols and naming

conventions

Socket


99/114

Socket

Abstract object from which messages aresent and received

Looks like a file descriptor

Application can select particular style ofcommunication

Virtual circuit, datagram, message-based, in-

order delivery

Unrelated processes should be able tolocate communication endpoints

Sockets should be named

Name meaningful in the communications

domain


100/114


101/114

Step 2


102/114

Step 2

Name the socket (assign address, port)int error = bind(s, addr, addrlen)

socket Address structurestruct sockaddr*length ofaddressstructure

Step 3a (server)


103/114

Step 3a (server)

Set socket to be able to accept connectionsint error = listen(s, backlog)

socketqueue length forpending connections

Step 3b (server)


104/114

Step 3b (server)

Wait for a connection from clientint snew = accept(s, clntaddr, &clntalen)

socketpointer to addressstructure

length ofaddressstructurenew socket

for this session

Step 3 (client)


105/114

Step 3 (client)

Connect to serverint error = connect(s, svraddr, svraddrlen)

socket Address structurestruct sockaddr*length ofaddressstructure

Step 4


106/114

Step 4

Exchange dataConnection-oriented

read/writerecv/send (extra flags)

Connectionlesssendto, sendmsg

recvfrom, recvmsg

Step 5


107/114

Step 5

Close connectionshutdown(s, how)

how:0: can send but not receive1: cannot send more data2: cannot send or receive (=0+1)

Sockets in Java


108/114

Sockets in Java

java.net package

Two major classes:

Socket: client-side

ServerSocket: server-side

Step 1a (server)


109/114

Step 1a (server)

Create socket and name itServerSocket svc =

new ServerSocket(port)

Step 1b (server)


110/114

Step 1b (server)

Wait for connection from clientServer req = svc.accept()

new socket for client session

Step 1 (client)


111/114

Step 1 (client)

Create socket and name itSocket s = new Socket(address, port);

obtained from:getLocalHost, getByName,or getAllByName

Socket s =

new Socket(cs.rutgers.edu, 2211);

Step 2


112/114

Step 2

Exchange dataobtain InputStream/OutputStream from

Socket object

BufferedReader in =

new BufferedReader(

new InputStreamReader(

s.getInputStream()));

PrintStream out =new PrintStream(s.getOutputStream());

Step 3


113/114

Step 3

Terminate connectionclose streams, close socket

in.close();

out.close();s.close();


114/114

Part 1_Network Computing

Documents

Transcript of Part 1_Network Computing