Bài giảng Computer Networks 1 (Mạng máy tính 1) - Lecture 10: Application Layer - Phạm Trần Vũ
Lecture 10:
Application Layer
2
Application Layer
ꢀ Where our applications are running
ꢀ Using services provided by layers below
ꢀ We will look at:
ꢁ
ꢁ
ꢁ
ꢁ
Domain Name System
Email
File Transfer Protocol
World Wide Web
3
Domain Name System - DNS
ꢀ
IP addresses can be used to identify a host
machine on the Internet
ꢁ
As people moves around, the addresses need to be
changed accordingly as well
ꢀ
ꢀ
host names into IP addresses
4
The DNS Name Space
A portion of the Internet domain name space.
5
Resource Records
•
•
Every domain has a set of records associated with
The principal DNS resource records types.
6
Resource Records (2)
A portion of a possible DNS database for cs.vu.nl.
7
Resource Records (3)
hcmut.edu.vn. IN SOA hcmut-server.hcmut.edu.vn. webmaster.hcmut.edu.vn. (
2004110800; serial
7200;
3600;
refresh
retry
604800;
86400
expire
hcmut.edu.vn.
hcmut.edu.vn.
hcmut.edu.vn.
hcmut.edu.vn.
86400 IN
NS
NS
MX 0
vnuserv.vnuhcm.edu.vn.
86400 IN
86400 IN
86400 IN
hcmut-server.hcmut.edu.vn. 86400 IN
stu-mailserv.hcmut.edu.vn. 86400 IN
webmailserv.hcmut.e
pop3.student.hcmut.edu.vn. 86400 IN
A
A
28.2.4
CNAME stu-mailserv.hcmut.edu.vn.
CNAME stu-mailserv.hcmut.edu.vn
.
8
Name Servers
•
•
DNS Name Space is organised into nop-overlapping zones
Each zone has Name Servers holding information about it
9
root name server
DNS - Query
iterated query
2
• recursive query
3
– puts burden of name
resolution on contacted
name server.
4
7
– heavy load
local name server
intermediate name server
dns.umass.edu
dns.eurecom.fr
• iterated query
5
6
1
8
– contacted server
replies with name of
server to contact.
authoritative name server
dns.cs.umass.edu
surf.eurecom.fr
– “I don’t know this name,
but ask this server”
gaia.cs.umass.edu
10
Electronic Mail – Email (or E-mail)
ꢀ Has been around since the early days of
Internet
ꢀ Is widely u
ꢀ Informal form of communication
ꢀ Simple and easy to use
11
Electronic Mail (2)
Some smileys :-).
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Architecture and Services
Basic email functions
• Composition
• Transfer
• Reporting
• Displaying
• Dispositio
13
Email Message Structure
14
Envelopes and messages. (a) Paper mail. (b) Electronic mail.
Email Systems
ꢀ Has two basic parts:
ꢁ
User agent: a program that accepts a variety of
commands for composing, receiving, and
replying to messages, as well as for
manipulating mailboxes
ꢁ
from the
15
Reading E-mail
An example display of the contents of a
mailbox.
16
Message Formats
RFC 822 header fields related to message
transport.
17
Message Formats (2)
Some fields used in the RFC 822 message
header.
18
MIME – Multipurpose Internet Mail
Extensions
•
Some problems when using ASCII formatted messages:
•
•
•
•
Languages with accents
(French, German).
Languages in non-Latin alphabets
(Hebrew, Russian).
Languages without alphabets
(Chinese, Japanese).
Messages not containing text at all
(audio or images).
•
MINE adds structure to the message body and defines
encoding rules for non-ASCII messages
19
MIME (2)
RFC 822 headers added by MIME.
20
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