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 protocolrequire 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-to-network 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

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

Introduction

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

Resources are stored onthe serverA client is a hardware/software

combination that people use directly

Files are download from server to client

Larger organizations may need many servers, each fulfilling a single task such as file transfer (e.g.FTP), e-mail, 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 typea 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

Server processes may support multiple clients.

e.g.:Telnet ServerApplication

TelnetDaemon

Telnet client 1

Telnet client 2

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 sub-domains

a. Distribution of Name Spacesa. 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.

A primary server loads all information from the disk file; the secondary server loads all information from the primary

server.

NoteNote::

b. DNS In The Internetb. 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 Table 1 Generic domain labelsGeneric 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 Table 2 New generic domain labelsNew 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 Personal names (individuals)

pro 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).

http:// www. ugm.ac.id /teknik/

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 UDPTFTP, 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 TCPPort Protocol Description

   7 Echo Echoes a received datagram back to the sender

    9 Discard Discards any datagram that is received

  11 Users Active users

  13 Daytime Returns the date and the time

  17 Quote Returns a quote of the day

  19 Chargen Returns a string of characters

  20 FTP, Data File Transfer Protocol (data connection)

  21 FTP, Control File Transfer Protocol (control connection)

  23 TELNET Terminal Network

  25 SMTP Simple Mail Transfer Protocol

  53 DNS Domain Name Server

  67 BOOTP Bootstrap Protocol

  79 Finger Finger

  80 HTTP Hypertext Transfer Protocol

111 RPC 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 UDPPort Protocol Description

    7 Echo Echoes a received datagram back to the sender

    9 Discard Discards any datagram that is received

  11 Users Active users

  13 Daytime Returns the date and the time

  17 Quote Returns a quote of the day

  19 Chargen Returns a string of characters

  53 Nameserver Domain Name Service

  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)

Three-step connection establishment

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

A B

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) Hajar Pamungkas (33835)

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, 9, TW 9, Presentasi 9

SMTP Materi: 9, TW 8, Presentasi 8

SNMP Materi: 9, TW 9, Presentasi 8

SSH Materi:9. TW 8. Presentasi 9