1. Net 221D:Computer Networks Fundamentals
Behrouz A. Forouzan” Data communications and Networking
Lecture : Application Layer

2. Introduction Protocol Layer PDU HTTP, FTP Application layer message
TCP, UDP Transport layer segment
ICMP, IP Network layer datagram
PPP, Ethernet, Data link layer frame
IEEE
Behrouz A. Forouzan” Data communications and Networking

3. Application Layer Processes communicating across networks
Behrouz A. Forouzan” Data communications and Networking

4. 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
Behrouz A. Forouzan” Data communications and Networking

5. 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
Behrouz A. Forouzan” Data communications and Networking

6. 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
Behrouz A. Forouzan” Data communications and Networking

7. 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
Behrouz A. Forouzan” Data communications and Networking

8. Electronic Mail Three major components: user agents mail servers
e.g., Eudora, Outlook, Netscape Messenger
mail servers
Incoming, outgoing messages
Push protocol –SMTP
Pull protocol – HTTP, IMAP, POP3
Behrouz A. Forouzan” Data communications and Networking