Chapter 15: Application Layer

What is a swarm or BiTorrent?

A swarm is when clients ask for pieces from multiple users at the same time.

What does a P2P application allow a device to do?

Allows a device to act as both a client and a server within the same communication.

Client and server processes are considered to be in which layer in the OSI model?

Application

What is the swarm technology called?

BitTorrent

In the client/server model the device requesting the information is called what?

Client

One of primary services offered by and ISP is what?

Email Hosting

True or False? The peer-to-peer networking model requires the implementation of a dedicated server for data access. True False

False

What does HTTPS stand for?

Hypertext Transfer Protocol Secure

File Transfer UDP client 69 A simple, connectionless file transfer protocol with best-effort, unacknowledged file delivery It uses less overhead than FTP

TFTP-Trivial File Transfer protocol

What is the first step that happens when you request a web page?

The browser interprets the three parts of the URL

IMAP is another protocol that describes a method to _______?

retrieve email messages

Many Gnutella client applications are available:

uTorrent BitComet DC++ Deluge emule

After the connection when using SMTP, the client attempts to do what?

Attempts to send the email to the server across the connection.

Host Config UDP Client 68, Server 67 Enables a diskless workstation to discover its own IP address, the IP address of a BOOTP server on the network, and a file to be loaded into memory to boot the machine Is being superseded by DHCP

BOOTP-Bootstrap Protocol

The server starts the POP service by passively listening on which TCP port for client connection request?

110

Common P2P networks include the follwoing:

BitTorrent Direct Connect eDonkey Freenet

Data transfer from a server to a client is referred to as what?

Download

When a client wants to make use of the POP service, it does what?

It sends a request to establish a TCP connection with the server using port 110. When the connection is established, the POP server sends a greeting.

Email clients communicate with who to send and receive email?

Mail Servers

The presentation layer formats data for the application layer, and it sets standards for file formats. What are three well-known standards for video?

Mastroska Video (MKV) Motion Picture Experts Group (MPG) QuickTime Video (MOV)

SMTP message format require what?

Message header and message body Note: Although the message body can contain any amount of text, the message header must have a properly formatted recipient email address and a sender address.

True or False: An email does not communicate directly with another email clients when sending email.

True, Instead, both clients rely on the mail server to transport messages.

True or False: Although HTTP is remarkably flexible, it is not secure a protocol

True, The request messages send information to the server in plaintext that can be intercepted and read. The server responses, typically HTML pages, are also unencrypted.

What does URI stand for?

Uniform Resource Identifier

What does URL stand for?

Uniform Resource Locator (URL)

How is IMAP different form POP?

Unlike POP, when the user connect to an IMAP-capable server, copies of the messages are downloaded to the client application The original messages are kept on the server until manually deleted.

Data transfer from a client to a server is referred to as what?

Upload

P2P Applications require that each device provide what?

User interface Run background service

Which of the following is a feature of Gnutella Protocol? Users can share whole files with other users Users can share pieces of files with other users Users can access an index server to get the location of resources shared by other users.

Users can share whole files with other users

This is a function of the OSI session layer. Compress and decompress data provide an interface between applications format data for the application layer exchange of information to initiate dialog between peers

exchange of information to initiate dialog between peers

These three OSI layers define the same functions as the TCP/IP model application layer. Application Presentation Session Transport Network Data Link

Application Presentation Session

What are Application Layer protocols used for?

Application Layer protocols are used to exchange data between programs running on the source and destination hosts.

What layer protocols describe the format of the requests and the responses between clients and server?

Application layer protocols describe the format of the requests and responses between clients and servers. In addition to the actual data transfer, this exchange may also require user authentication and the identification of a data file to be transferred.

Based on the TCP/IP model what three upper layers of the OSI model define the functions of the TCP/IP Application layer?

Application, Presentation, Session

This layer of the OSI model is concerned with the protocols that exchange data between programs running on hosts. Application Transport Network Physical

Applicaton

What does email require to run on a computer or other end device?

Email requires several applications and services.

MKV, GIF, and JPG standards are associated with which OSI layer? Application Presentation Session Transport

Presentation

Email is a ____ and ___ method of sending , storing, and retrieving electronic messages across a network.

Store and Forward

Which peer-to-peer application allows users to share pieces of many files with each other at the same time? Hybrid Gnutella BitTorrent

BitTorrent

With P2P applications, each computer in the network that is running the application can act as what?

Client or a server for the other computers in the network that are also running the application.

What doe torrent files contain?

Contains information about tracker computers that keep track of which users have specific pieces of certain files.

What are the Session Layers functions?

Crate and maintain dialogs between source and destination applications Handles the exchange of information to initiate dialogs Keep dialogs active Restart sessions that are disrupted or idle for a long period of time.

Host Config UPD Client 68, Server 67 Dynamically assigns IP address to be re-used when no longer neede

DHCP-Dynamic Host Configuration Protocol

Which two are protocols that belong in the OSI application layer? PNG DNS SMTP QuickTime

DNS SMTP

Name System TCP, UDP client 53 Translates Domain Names, such as cisco.com into IP addresses

DNS -Domain Name System (Service)

File Transfer TCP 20 (data) to 21 (control) Sets rules that enable a user on one host to access and transfer files to and from another host over a network Is reliable, connection-oriented, and acknowledged file delivery protcol

FTP-File Transfer Protocol

What are the Presentation Lyres (Layer 6) three primary functions?

Formatting, or presenting, data at the source device into a compatible format for receipt by the destination device. Compressing data in a way that can be decompressed by the destination device Encrypting data for transmission and decrypting data upon receipt

This client request for data. A client (web browser) sends the GET message to the web server to request HTML pages

GET

The three common message types for HTTP are?

Get POST PUT

The presentation layer formats data for the application layer, and it sets standards for file formats. What are three well-known graphic image formats?

Graphics Interchange Format (GIF) Joint Photographic Experts Group (JPG) Portable Network Graphics (PNG)

This protocol is used by a web browser to establish a connecting to a web server.

HTTP

What are the three parts of the URL example, use the http://www.cisco.com/index.html URL?

HTTP (the protocol or scheme) www.cisco.com (the server name) index.html (The specific filename requested)

Web TCP 80, 8080 A set of rules for exchanging text, graphic images, sound, video, and other multimedia files on the World Wide Web

HTTP-Hyper Text Transfer Protocol

For secure communication across the internet, which HTTP protocol is used?

HTTPS

How does HTTP work?

HTTPS uses authentication and encryption to secure data as it travels between the client and server.

Web TCP, UDP 443 The browser uses encryption to secure HTTP communications Authenticates the website to which you are connecting your browser

HTTPS-Hyper Text Transfer Protocol Secure

What email protocol allows users to view copies of the messages in their email client software?

IMAP

Email TCP 143 Enables clients to access email stored on a mail server Maintains email on the server

IMAP-Internet Message Access Protocol

Where are emails store?

In databases on mail servers

What is the third step that happens when you request a web page?

In response to the request, the server sends the HTML code for this web page to the browser.

What is the Gnutella protocol?

Is a protocol where each user shares whole files with other users. Gnutella-compatible client software allows users to connect to Gnutella services over the internet, and to locate and access resources shared by other Gnutella peers.

When the server receives the message, what will do?

It either places the message in a local account, if the recipient is local Or forward the message to another mail server for delivery.

Periodically, the server checks the queue for messages and attempts to send them again, but what happens if the message is not delivered after a predetermined expiration time?

It is returned to sender as undeliverable

Mail servers communicate with who to transport messages form one domain to another?

Other mail servers

The P2P network model involves two parts:

P2P networks P2P applications Note: Both parts have similar features, but in practice work quite differently.

A client retrieves emails using on of the two Application layer email protocols:

POP IMAP

Which email protocol downloads mail from a mail server to the client and then deletes the email on the server?

POP Note: This is the default operation of POP

Which version of POP is the most commonly used version?

POP3

Email TCP 110 Enables clients to retrieve email form a mail server Downloads the email to the local mail application of the client

POP3-Post Office Protocol 3

This message type is used when uploading data files to a web server. GET POST PUT

POST

This uploads data files to the web server, such as form data.

POST

This uploads resources or content to the web server, such as an image

PUT

What type of protocol is a HTTP?

Request/response protocol

What does it mean if a P2P application uses a hybrid system?

Resource sharing is decentralized, but the indexes that point to resource locations are stored in a centralized directory. In a hybrid system, each peer accesses an index server to get the location of a resource stored on another peer.

The application layer process that sends mail uses which email protocol?

SMTP

This protocol is used by a client to send email to a mail server. POP SMTP IMAP HTTP

SMTP

Email TCP 25 Enables clients to send email to a mail server Enables servers to send email to other servers

SMTP-Simple Mail Transfer protocol

In the client /server model the device responding to the request is call what?

Server

Email supports three separate protocols for operation:

Simple Mail Transfer Protocol (SMTP) Post Office Protocol version 3 (POP3) Internet Message Access Protocol (IMAP)

What does the Application Layer provide?

The Application layer provides the interface between the applications used to communicate, and the underlying network over which messages are transmitted.

What is the fourth step that happens when you request a web page?

The browser deciphers the HTML code and formats the page for the browser window.

What is the second step that happens when you request a web page?

The browser then checks with a name server to convert www.cisco.com into a numeric IP address, which it uses to connect to the server. The client initiates an Http request to a server by sending a GET request to the server and asks for the index.html file.

When a clients sends email, how does the client SMTP process connect with the server SMTP process?

The client SMTP process connects with a server SMTP process on well-known port 25.

When a client, typically a web browser, sends a request to a web server, HTTP specifies what?

The message types used for that communication.

What happens when you type a URL into a web browser?

The web browser establishes a connection to the web service. The web service is running on the server that is using the HTTP protocol.

The destination email server may no be online, or may be busy, when email messages are sent. Therefore what happens to the email?

Therefore, SMTP spools messages to be sent at a later time.

What do the TCP/IP Application Layer protocols specify?

They specify the formats and control information necessary for many common internet communication functions.

With POP email messages downloaded and removed from the mail server, what does this mean?

This means there is no centralized location where email messages are kept.

POP is used by an application to do what?

To retrieve mail from a mail server.

What doe clients use to locate other users who have pieces that they need so that they can then connect directly to them?

Torrent File

HTTPS uses the same client request-server response process as HTTP, but the data stream is encrypted by what two possible cryptographic protocol?

Transport Layer Security - TLS Secure Socket Layer - SSL

True or False: Any type of file can be shared between users. Many of these files are copyrighted, meaning that only the creator has the right to use and distribute them. It is against the law to download or distribute copyrighted files without permission from the copyright holder. Copyright violation can result in criminal charges and civil lawsuits.

True

True or False: Application layer protocols are used by both the source and destination devices during a communication session. For the communications to be successful, the application layer protocols that are implemented on the source and destination host must be compatible.

True

True or False: Because POP does not store messages, it is not recommended for a small business that needs a centralized backup solution.

True

True or False: In the peer-to-peer (P2P) networking model, the data is accessed form a peer device without the use of dedicated server.

True

True or False: Many P2P applications allow users to share pieces of many files with each other at the same time.

True

True or False: The client and POP server exchange commands and responses until the connection is closed or aborted.

True

True or False? In a peer-to-peer network environment every peer can function as both client and server. True

True

True or False: BitTorrent has its own client

True, But there are many other BitTorrent clients including uTorrent, Deluge, and qBittorren

Users using IMAP-capable servers can create a file hierarchy on the server to organize and store mail. That file structure is duplicated on the email client as well. So what happens when you delete a message using the client email software?

When a user decides to delete a message, the server synchronizes that action and deletes the message form the server.