Application Layer in Networking: Principles, Protocols, and Architectures - Prof. Ching Ch, Study notes of Electrical and Electronics Engineering

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(modified by Cheung for EE586;

based on K&R original)

1-

EE 586 Communication and Switching Networks (Fall 2008)

Lecture 7

September 14, 2008

Announcements

Feedback on guest lecture

HW2 due date extended till Friday

Quiz 1 average: 6.3/

2: Application Layer

2: Application Layer

Chapter 2: Application Layer Our goals:
^

conceptual,implementationaspects of networkapplication protocols^

transport-layerservice models
client-serverparadigm
peer-to-peerparadigm

^

learn about protocolsby examining popularapplication-levelprotocols^

HTTP
FTP
SMTP / POP3 / IMAP
DNS
^

programming networkapplications^

socket API

2: Application Layer

Chapter 2: Application layer
^

2.1 Principles ofnetwork applications
^

2.2 Web and HTTP
^

2.3 FTP

^

2.4 Electronic Mail^

SMTP, POP3, IMAP
^

2.5 DNS

^

2.6 P2P applications
^

2.7 Socket programmingwith TCP
^

2.8 Socket programmingwith UDP

2: Application Layer

Chapter 2: Application layer
^

2.1 Principles ofnetwork applications
^

2.2 Web and HTTP
^

2.3 FTP

^

2.4 Electronic Mail^

SMTP, POP3, IMAP
^

2.5 DNS

^

2.6 P2P applications
^

2.7 Socket programmingwith TCP
^

2.8 Socket programmingwith UDP
^

2.9 Building a Webserver

(modified by Cheung for EE586;

based on K&R original)

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Application architectures^ 1.

Client-server

Peer-to-peer (P2P)

Hybrid of client-server and P2P

The application architecture is designed by

the application developer and dictates howthe application is structured over thevarious end systems.

(modified by Cheung for EE586;

based on K&R original)

1- 10

Pure P2P architecture

no

always-on server
^

arbitrary end systemsdirectly communicate
^

peers are intermittentlyconnected and change IPaddresses
^

Self-scalable -> costeffective
^

Difficult to maintain andsecure

peer-peer

2: Application Layer

Hybrid of client-server and P2P Skype

^

voice-over-IP P2P application
^

centralized server: finding address of remoteparty:
^

client-client connection: direct (not throughserver)

Instant messaging

^

chatting between two users is P2P
^

centralized service: client presencedetection/location• user registers its IP address with central

server when it comes online

• user contacts central server to find IP

addresses of buddies

2: Application Layer

Processes communicating Process:

program running

within a host.
^

within same host, twoprocesses communicateusing

inter-process

communication

(defined

by OS).
^

processes in differenthosts communicate byexchanging

messages

^

processes in same hostcan also communicatewith shared memory

Client process:

process

that initiatescommunication Server process:

process

that waits to becontacted
^

Note: applications withP2P architectures haveclient processes &server processes

2: Application Layer

Sockets
^

process sends/receivesmessages to/from its socket
^

socket analogous to door^

sending process shovesmessage out door
sending process relies ontransport infrastructureon other side of door whichbrings message to socketat receiving process

host orserver process^ socket TCP withbuffers,variables

host orserver process^ socket TCP withbuffers,variables

Internet

controlledby OS

controlled byapp developer

^

API: (1) choice of transport protocol; (2) ability to fixa few parameters

(lots more on this later)

2: Application Layer

Addressing processes^

to receive messages,process must have^ identifier
host device has unique32-bit IP address
^ Q:

does IP address of host on which processruns suffice foridentifying theprocess?^

A:

No,

many

processes can berunning on same host

identifier

includes both

IP address

and

port

numbers

associated with

process on host.
^

Example port numbers:^

HTTP server: 80
Mail server: 25
^

to send HTTP messageto gaia.cs.umass.edu webserver:^

IP address:

128.119.245.

^

Port number:

80

^

more shortly…

2: Application Layer

What transport service does an app need? Data loss
^ some apps (e.g., audio) cantolerate some loss
^ other apps (e.g., filetransfer, telnet) require100% reliable datatransfer Timing
^ some apps (e.g.,Internet telephony,interactive games)require low delay to be“effective”

Throughput
^

some apps (e.g.,multimedia) requireminimum amount ofthroughput to be“effective”
^

other apps (“elastic apps”)make use of whateverthroughput they get Security
^

Encryption, dataintegrity, …

2: Application Layer

Internet transport protocols services TCP service:

connection-oriented:

setup

required between client andserver processes

reliable transport

between

sending and receiving process

flow control:

sender won’t

overwhelm receiver

congestion control:

throttle

sender when networkoverloaded

does not provide:

timing,

minimum throughputguarantees, security

UDP service:
^

unreliable data transferbetween sending andreceiving process
^

does not provide:connection setup,reliability, flow control,congestion control, timing,throughput guarantee, orsecurity Q:

why bother?

Why is

there a UDP?

2: Application Layer

Internet apps: application, transport protocols

Application

e-mail

remote terminal access

Web file transfer

streaming multimedia

Internet telephony

Applicationlayer protocol SMTP [RFC 2821]Telnet [RFC 854]HTTP [RFC 2616]FTP [RFC 959]HTTP (eg Youtube),RTP [RFC 1889]SIP, RTP, proprietary(e.g., Skype)

Underlyingtransport protocol TCPTCPTCPTCPTCP or UDPtypically UDP