Transcript Application Layer - Teknik Elektro UGM

Application Layer
Widyawan
Review…
Layered network model



The concept of layers is used to describe
communication from one computer to another.
A conversation between two people provides a
good opportunity to use a layered approach to
analyze information flow.
It is important that all the devices on the network
speak the same language or protocol.
TCP/IP model

The designers of TCP/IP felt that the application layer
should include the OSI session and presentation layer
details. They created an application layer that handles
issues of representation, encoding, and dialog control.

The transport layer deals with the quality of service issues
of reliability, flow control, and error correction.
 One of its protocols, the transmission control protocol
(TCP), provides excellent and flexible ways to create
reliable, well-flowing, low-error network
communications.
 TCP is a connection-oriented protocolrequire that a
logical connection be established between two devices
before transferring data.

The purpose of the Internet layer is to divide TCP
segments into packets and send them from any network
to their destination. The specific protocol that governs
this layer is called the Internet Protocol (IP). Best path
determination and packet switching occur at this layer.

The network access layer, also known as the host-tonetwork layer, is concerned with all of the components,
both physical and logical, that are required to make a
physical link. It includes the networking technology
details, including all the details in the OSI physical and
data link layers.
Common TCP/IP protocol
Application Layer
Transport layer
Internet layer
Network Access layer
Movie
 PDU in packet tracer

Introduction

Application layer (AL) prepares human communication for transmission over the data
network  it is where the data enters the data network

This layer provides interfaces to the network (interfacing human and data network)

AL software initiates the data transfer process, provides services, and defines the protocols
that are carried out by the applications

Applications are the physical interface with the outside world that allow anyone to initiate
the data transfer process.

Applications provide the means for generating and receiving data that can be transported
on the network.

AL supports applications such as:




Web browser
E-mail
telnet
FTP
Application layer responsible for services to user

Protocols in AL:
 Define
processes on either end of the
communication
 Define the types of messages
 Define the syntax of the messages
 Define the meaning of any informational
fields
 Define how messages are sent and the
expected response
 Define interaction with the next lower layer
Network layer duties
Common network model
Client/server network model
 Peer-to-peer network model (P2P)

Client-server model
Files are download from server to client
A client is a hardware/software
combination that people use
directly
Resources are stored on
the server





Larger organizations may need many servers, each
fulfilling a single task such as file transfer (e.g.FTP), email, and web
Smaller organizations may use a single server to provide
multiple tasks.
A daemon: a background service that listens for traffic of
a specific typea web server will listen for web requests
and ignore FTP requests.
Advantage of client/server network: centralized
management  make administration and security
enforcement much easier compared to P2P network
E.g.: e-mail, http, ftp
Example of a single server with a
single task
Client-server relationship
Telnet client 1
Telnet
Daemon
Telnet client 2
Server processes may support multiple clients.
e.g.:
Telnet
Server
Application
P2P network model




P2P network allow computers to act as both clients and
servers during the same communication.
Each of them is called ‘peer’ because they can perform both
tasks.
Each user is in charge of his own access policies
Disadvantage:



Difficult to manage because management is decentralized
Decentralized management also makes security difficult to enforce
P2P applications allow users to directly share specified file
types across P2P or client/server networks, e.g. Napster
Domain Name System
Domain Name System (DNS) is a system
used on the Internet for translating names
of domains and their publicly advertised
network nodes into IP addresses.
 It follow client/server paradigm

Domain Name Space



DNS uses a hierarchical name space where the
names are defined in an inverted-tree structure
with the root at the top.
* a name space is used to maps each IP
address to a unique name (constructed from
characters).
The tree can have only 128 levels: level 0 (root)
to level 127, see next figure.
Domain name space
Each node in the tree has a different label: which is a string with a max.63 chars.
The root label is a null string (empty string).
Each node in the tree has a domain name (DN).
A full DN is a sequence of labels separated by dots (.), that read from the node
up to the root (null label).
Domain names and labels
Example:
Domains
•A domain is a group of computers that are associated by their geographical
location or their business type.
•It is a sub-tree of the domain name space that also can be divided into subdomains
a. Distribution of Name Spaces
Hierarchy of Name Servers
Zone
Root Server
Primary and Secondary Servers
Hierarchy of name servers
It is inefficient and unreliable to store a huge amount of information
only in one computer and any failures makes the data inaccessible.
DNS servers are computers that are used to distribute the huge amount information
‘primary’ and ‘secondary’ servers.
Note:
A primary server loads all information
from the disk file; the secondary server
loads all information from the primary
server.
b. DNS In The Internet
Generic Domain
Country Domain
Generic domains defines registered hosts according to their generic
behavior.
Country domains section uses 2-character country abbreviation.
Generic domains
Table 1 Generic domain labels
Label
Description
com
Commercial organizations
edu
Educational institutions
gov
Government institutions
int
International organizations
mil
Military groups
net
Network support centers
org
Nonprofit organizations
Table 2 New generic domain labels
Label
Description
aero
Airlines and aerospace companies
biz
Businesses or firms (similar to com)
coop
Cooperative business organizations
info
Information service providers
museum Museums and other nonprofit organizations
name
pro
Personal names (individuals)
Professional individual organizations
Country domains

Packet tracer for DNS
FTP Application
FTP is a reliable, connection-oriented service that uses TCP to transfer files between
systems that support FTP.
The main purpose of FTP is to transfer files from one computer to another by copying
and moving files from servers to clients, and from clients to servers.
HTTP






A Web browser is a client-server application, which means that it requires
both a client and a server component in order to function.
A Web browser presents data in multimedia formats on Web pages that
use text, graphics, sound, and video.
The Web pages are created with a format language called Hypertext
Markup Language (HTML).
HTML directs a Web browser on a particular Web page to produce the
appearance of the page in a specific manner.
In addition, HTML specifies locations for the placement of text, files, and
objects that are to be transferred from the Web server to the Web
browser.
The Web page contains, often hidden within its HTML description, an
address location known as a Uniform Resource Locator (URL).
/teknik/
www.
ugm.ac.id
http://
Transport Layer

Fungsi transport layer:
 Segmentation
of upper-layer application data
 Establishment of end-to-end operations
 Transportation of segments from one end host to
another
 Flow control ensures that a source host does not
overflow the buffers in a destination host.
 Reliability provided by sequence numbers and
acknowledgments
TL protocols
TCP used in FTP, HTTP, SMTP, Telnet
 UDPTFTP, SNMP, DHCP, DNS

Field in TCP segment












Source port – Number of the port that sends data
Destination port – Number of the port that receives data
Sequence number – Number used to ensure the data arrives in the correct
order
Acknowledgment number – Next expected TCP octet
HLEN – Number of 32-bit words in the header
Reserved – Set to zero
Code bits – Control functions, such as setup and termination of a session
Window – Number of octets that the sender will accept
Checksum – Calculated checksum of the header and data fields
Urgent pointer – Indicates the end of the urgent data
Option – One option currently defined, maximum TCP segment size
Data – Upper-layer protocol data
Port for TCP
Port
Protocol
Description
7
Echo
Echoes a received datagram back to the sender
9
Discard
11
Users
13
Daytime
17
Quote
19
Chargen
20
FTP, Data
21
FTP, Control
23
TELNET
25
SMTP
53
DNS
67
BOOTP
79
Finger
Finger
80
HTTP
Hypertext Transfer Protocol
111
RPC
Discards any datagram that is received
Active users
Returns the date and the time
Returns a quote of the day
Returns a string of characters
File Transfer Protocol (data connection)
File Transfer Protocol (control connection)
Terminal Network
Simple Mail Transfer Protocol
Domain Name Server
Bootstrap Protocol
Remote Procedure Call
Field in UDP segment
UDP is a connectionless, unreliable protocol that has no flow
and error control. It uses port numbers to multiplex data from
the application layer.
Port number for UDP
Port
Protocol
Description
7
Echo
Echoes a received datagram back to the sender
9
Discard
11
Users
13
Daytime
17
Quote
19
Chargen
53
Nameserver
67
Bootps
Server port to download bootstrap information
68
Bootpc
Client port to download bootstrap information
69
TFTP
Trivial File Transfer Protocol
111
RPC
Remote Procedure Call
123
NTP
Network Time Protocol
161
SNMP
Simple Network Management Protocol
162
SNMP
Simple Network Management Protocol (trap)
Discards any datagram that is received
Active users
Returns the date and the time
Returns a quote of the day
Returns a string of characters
Domain Name Service
Three-step connection
establishment
A
B
Synchronization occurs through an exchange of segments that carry a synchronize (SYN)
control bit and the initial sequence numbers.
1.
The sending host (A) initiates a connection by sending a SYN packet to the receiving
host (B) indicating its INS = X: A - > B SYN, seq of A = X
2.
B receives the packet, records that the seq of A = X, replies with an ACK of X + 1, and
indicates that its INS = Y. The ACK of X + 1 means that host B has received all octets up
to and including X and is expecting X + 1 next: B - > A ACK, seq of A = X, SYN seq of B
= Y, ACK = X + 1
3.
A receives the packet from B, it knows that the seq of B = Y, and responds with an ACK
of Y + 1, which finalizes the connection process: A - > B ACK, seq of B = Y, ACK = Y + 1
Kelompok















SNMP
Dennis Adriansyah G
(34172)
Putu Bagus Susastra W
(34202)
Ferlin Dwi R (33559)
Fery Setiawan (33827)
Agus Joko Sudiarto ( 34213)
FTP +
Vicky Fazlurrahman (33977)
Muhammad Fikri Ali R
(34607)
Fayruz Rahma (34001)
Nurul Qonitah ( 34062)
SMTP
Fikar El Hazmi (33904) Supradi Sitepu (34148)
Pandu Perwira (34304)
DHCP Soimin (6066)
Aji Priatmoko (5890)
Aulia Fajrin (6149)
Dicky Aditya Dharma (5887)
Telnet Manumpak Aguswan Silalahi (5910)
Adit Satria (6134)
Feri Wibowo (6142)
Puthut Punggawasesa (5891)
SSH Dwi Adi Prabawa (31748)
Laksono Kurnianggoro (31820)
Ryan Ramandito (32201)
SNMP,
FTP, SMTP, DHCP, Telnet, SSH, DNS

FTP
 Materi,

SMTP
 Materi:

9, TW 8, Presentasi 8
SNMP
 Materi:

9, TW 9, Presentasi 9
9, TW 9, Presentasi 8
SSH
 Materi:9.
TW 8. Presentasi 9