ITE PC v4.0 Chapter 1 - CCRI Faculty Web

ITE PC v4.0 Chapter 1 - CCRI Faculty Web

Chapter 10: Application Layer Network Basics Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 1 Chapter 10 Objectives Explain how the functions of the application layer, session layer, and presentation layer work together to provide network services to end user applications. Describe how common application layer protocols interact with end user applications. Describe, at a high level, common application layer protocols that provide

Internet services to end-users, including WWW services and email. Describe application layer protocols that provide IP addressing services, including DNS and DHCP. Describe the features and operation of well-known application layer protocols that allow for file sharing services, including: FTP, File Sharing Services, SMB protocol. Explain how data is moved across the network, from opening an application to receiving data. Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 2 Chapter 10 10.1 10.2

10.3 10.4 Presentation_ID Application Layer Protocols Well-Known Application Layer Protocols and Service The Message Heard Around the World Summary 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 3 10.1 Application Layer Protocols The Application Layer provides the interface to the network.

Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 4 Application, Session and Presentation OSI and TCP/IP Models Revisited The OSI model Layers 5, 6, and 7 are used as references for application software developers and vendors to produce products, such as web browsers that need to access networks. The TCP/IP application layer

includes a number of protocols that provide specific functionality to a variety of end-user applications. The key parallels are in the transport and network layer. Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 5 Application Session and Presentation Application Layer

The application layer is closest to the end user. It is the layer that provides the interface between the applications we use to communicate and the underlying network Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 6 Application, Session and Presentation Presentation and Session Layers Presentation layer has three primary functions: Coding and conversion of application layer data Compression of the data (tiff, jpeg, mpeg, etc) Encryption of the data for transmission and the decryption of data upon receipt by the destination

Session Layer Functions create and maintain dialogs between source and destination applications Handles the exchange of information to initiate dialogs, keep them active, and to restart sessions Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 7 Application, Session and Presentation Presentation and Session Layers Presentation_ID

2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 8 Application, Session and Presentation TCP/IP Application Layer Protocols Domain Name Service Protocol (DNS) - used to resolve Internet names to IP addresses Telnet - a terminal emulation protocol used to provide remote access to servers and networking devices Bootstrap Protocol (BOOTP) - a precursor to the DHCP protocol, a network protocol used to obtain IP address information during bootup Dynamic Host Control Protocol (DHCP) - used to assign an IP address, subnet mask, default gateway and DNS

server to a host Hypertext Transfer Protocol (HTTP) - used to transfer files that make up the Web pages of the World Wide Web Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 9 Application, Session and Presentation TCP/IP Application Layer Protocols File Transfer Protocol (FTP) - used for interactive file transfer between systems Trivial File Transfer Protocol (TFTP) - used for connectionless active file transfer Simple Mail Transfer Protocol (SMTP) - used for the

transfer of mail messages and attachments Post Office Protocol (POP) - used by email clients to retrieve email from a remote server Internet Message Access Protocol (IMAP) another protocol for email retrieval Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 10 How Application Protocols Interact with End-User Applications Peer-to-Peer Networks When accessing information on a networking device connected to a network, the data may not be physically stored on the

device. In this case, a request to access that information must be made to the device where the data resides. The P2P network model involves two parts: P2P networks P2P applications. Both parts have similar features, but in practice work quite differently. Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 11

How Application Protocols Interact with End-User Applications Peer-to-Peer Networks Both devices are considered equal in the communication The roles of client and server are set on a per request basis. P2P networks decentralize the resources on a network Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 12 How Application Protocols Interact with End-User Applications

Peer-to-Peer Applications Client and server in the same communication Both can initiate a communication and are considered equal in the communication process Peer-to-peer applications can be used on peer-to-peer networks, clientserver networks, and across the Internet. Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 13 How Application Protocols Interact with End-User Applications Common P2P Applications

With P2P applications, each computer in the network running the application can act as a client or a server for the other computers in the network running the application Common P2P applications include: eDonkey eMule Shareaza BitTorrent Bitcoin LionShare Some P2P applications are based on the Gnutella protocol which enables people to share files on their hard disks with others Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

14 How Application Protocols Interact with End-User Applications Client-Server Model Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 15 How Application Protocols Interact with End-User Applications Client-Server Model Presentation_ID

2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 16 10.2 Well-Known Application Layer Protocols and Services Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 17 Common Application Layer Protocols

Application Layer Protocols Revisited Three application layer protocols that are involved in everyday work or play are: Hypertext Transfer Protocol (HTTP) browse the web Simple Mail Transfer Protocol (SMTP) used to enable users to send email Post Office Protocol (POP) Presentation_ID

used to enable users to receive email 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 18 Common Application Layer Protocols Hypertext Transfer Protocol / Markup Language Example URL: http://www.cisco.com/index.html First, the browser interprets the three parts of the URL: 1. http (the protocol or scheme) 2. www.cisco.com (the server name) 3. index.html (the specific file name requested) Browser checks with a name server to convert

www.cisco.com into a numeric address (IP) Using the HTTP protocol requirements sends a GET request to the server and asks for the file index.html Server sends the HTML code for this web page Browser deciphers the HTML code and formats the page Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 19 Common Application Layer Protocols HTTP and HTTPS Developed to publish and retrieve HTML

pages Used for data transfer Specifies a request/response protocol Three common message types are GET, POST, and PUT GET is a client request for data POST and PUT are used to send messages that upload data to the web server Presentation_ID 2008 Cisco Systems, Inc. All rights reserved.

Cisco Confidential 20 Common Application Layer Protocols SMTP, POP, and IMAP Typically use an application called a Mail User Agent (email client) Allows messages to be sent Places received messages into the client's mailbox SMTP - Send email from either a client or a server POP - Receive email messages from an email server

IMAP - Internet Message Access Protocol Email client provides the functionality of both protocols within one application Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 21 Common Application Layer Protocols SMTP, POP, and IMAP Presentation_ID

2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 22 Common Application Layer Protocols SMTP, POP, and IMAP (Continued) Simple Mail Transfer Protocol (SMTP) transfers mail Message must be formatted properly SMTP processes must be running on both the client and server Message header must

have a properly formatted recipient email address and a sender Uses port 25 Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 23 Common Application Layer Protocols SMTP, POP, and IMAP (Continued) Post Office Protocol (POP) Enables a workstation to

retrieve mail from a mail server Mail is downloaded from the server to the client and then deleted on the server Uses port 110 POP does not store messages POP3 is desirable for an ISP, because it alleviates their responsibility for managing large amounts of storage for their email servers Presentation_ID 2008 Cisco Systems, Inc. All rights reserved.

Cisco Confidential 24 Common Application Layer Protocols SMTP, POP, and IMAP (Continued) Simple Mail Transfer Protocol (SMTP) Transfers mail reliably and efficiently Post Office Protocol (POP) Enables a workstation to retrieve mail from a mail server With POP, mail is downloaded from the server to the client and then deleted on the server Internet Message Access Protocol (IMAP) Another protocol that to retrieves email messages Unlike POP, when the user connects to an IMAP-capable server, copies of the messages are downloaded to the client application Original messages are kept on the server until manually

deleted Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 25 Providing IP Addressing Services Domain Name Service A human legible name is resolved to its numeric network device address by the DNS protocol

Presentation_ID www.cisco.com ? 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 26 Providing IP Addressing Services Domain Name Service A human legible name is resolved to its numeric network device address by the DNS protocol

Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 27 Providing IP Addressing Services DNS Message Format DNS server stores different types of resource records used to resolve names Contain the name, address, and type of record Record types are: A - an end device address NS - an authoritative name server CNAME - the canonical name for an alias; used when

multiple services have the single network address but each service has its own entry in DNS MX - mail exchange record; maps a domain name to a list of mail exchange servers Unable to resolve the name using its stored records, contacts other servers Server temporarily stores the numbered address that matches the name in cache memory Windows ipconfig /displaydns displays all cached DNS Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 28 Providing IP Addressing Services

DNS Message Format Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 29 Providing IP Addressing Services DNS Hierarchy Examples toplevel domains: .au - Australia .co - Colombia .com - business or industry .jp - Japan

.org - non-profit organization Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 30 Providing IP Addressing Services nslookup Operating system utility called nslookup allows the user to manually query the name servers to resolve a given host name Utility can be used to troubleshoot name resolution issues and to verify the current status of the name servers

Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 31 Providing IP Addressing Services Dynamic Host Configuration Protocol DHCP allows a host to obtain an IP address dynamically DHCP server is contacted and address requested - chooses address from a

configured range of addresses called a pool and leases it to the host for a set period DHCP used for general purpose hosts such as end user devices, and static addressing is used for network devices such as gateways, switches, servers and printers Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 32

Providing IP Addressing Services DHCP Operation Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 33 Providing File Sharing Services File Transfer Protocol FTP allow data transfers between a client and a server

FTP client is an application that runs on a computer that is used to push and pull data from a server running an FTP daemon To successfully transfer data, FTP requires two connections between the client and the server, one for commands and replies, the other for the actual file transfer Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

34 Providing File Sharing Services Server Message Block Clients establish a long term connection to servers After the connection is established, the user can access the resources on the server as if the resource is local to the client host

Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 35 Providing File Sharing Services Server Message Block Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 36

Move It! The Internet of Things Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 37 Move It! Message Travels Through a Network Presentation_ID

2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 38 Move It! Message Travels Through a Network Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 39 Move It!

Message Travels Through a Network Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 40 Move It! Getting the Data to the End Device Presentation_ID 2008 Cisco Systems, Inc. All rights reserved.

Cisco Confidential 41 Move It! Getting the Data through the Internetwork Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 42 Move It! Getting the Data to the Right Application

Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 43 Application Layer Summary Applications are computer programs with which the user interacts and which initiate the data transfer process at the users request. Services are background programs that provide the connection between the application layer and the lower layers of the networking model.

Protocols provide a structure of agreed-upon rules and processes that ensure services running on one particular device can send and receive data from a range of different network devices. Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 44 Application Layer Summary HTTP supports the delivery of web pages to end devices SMTP, POP, and IMAP support sending and receiving email

SMB and FTP enable users to share files P2P applications make it easier for consumers to seamlessly share media DNS resolves the human legible names used to refer to network resources into numeric addresses usable by the network All of these elements work together, at the application layer. The application layer enables users to work and play over the Internet. Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 45 Presentation_ID

2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 46

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