Behrouz A. Forouzan” Data communications and Networking

NET 221D:COMPUTER NETWORKS FUNDAMENTALS

Lecture : Application Layer

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Introduction

Protocol Layer PDUHTTP, FTP Application layer

messageTCP, UDP Transport layer segmentICMP, IP Network layer datagramPPP, Ethernet, Data link layer frameIEEE 802.11

Behrouz A. Forouzan” Data communications and Networking

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Application Layer

Processes communicating across networks

Behrouz A. Forouzan” Data communications and Networking

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HTTP: Hyper Transfer Protocol What is HTTP?

Hypertext Transfer Protocol – the Web’s application layer protocol

HTTP 1.0, HTTP 1.1 Pipelined – requests sent as soon as it is

encountered Persistent – multiple objects can be sent

over a single TCP connection between the server and the client

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DNS :Domain Name Server

Internet hosts: IP address (32 bit) - used for addressing

datagrams “name”, e.g., ww.yahoo.com - used by

humans

DNS: provides translation between host name and IP address distributed database implemented in

hierarchy of many name servers Distributed for scalability & reliability

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DNS :Domain Name Server

Hostname to IP address translation Host aliasing

Canonical and alias names Mail server aliasing Load distribution

Replicated Web servers: set of IP addresses for one canonical name

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DNS

Host at cis.poly.edu wants IP address for gaia.cs.umass.edu

Infrastructure: Client resolver Local DNS server Authoritative DNS Server Root DNS Server Top-Level Domain DNS Server

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Electronic Mail

Three major components: user agents

e.g., Eudora, Outlook, Netscape Messenger mail servers

Incoming, outgoing messages Push protocol –SMTP

Pull protocol – HTTP, IMAP, POP3