GATE CS - COMPUTER NETWORKS:Application Layer Protocols
Mastering application layer protocols concepts and implementation.
Application Layer Protocols
Application Layer provides network services to applications.
HTTP (Hypertext Transfer Protocol)
HTTP is protocol for web communication.
HTTP Methods
GET: Retrieve resource
POST: Submit data
PUT: Update resource
DELETE: Delete resource
HEAD: Get headers only
HTTP Versions
HTTP/1.0:
- One request per connection
- Non-persistent
HTTP/1.1:
- Multiple requests per connection
- Persistent connections
- Pipelining
HTTP/2:
- Multiplexing
- Header compression
- Server push
HTTP/3:
- Uses QUIC (UDP-based)
- Faster connection
HTTP Status Codes
2xx Success:
- 200 OK
- 201 Created
- 204 No Content
3xx Redirection:
- 301 Moved Permanently
- 302 Found
- 304 Not Modified
4xx Client Error:
- 400 Bad Request
- 401 Unauthorized
- 403 Forbidden
- 404 Not Found
5xx Server Error:
- 500 Internal Server Error
- 502 Bad Gateway
- 503 Service Unavailable
DNS (Domain Name System)
DNS translates domain names to IP addresses.
DNS Hierarchy
Root Domain: .
Top-Level Domains: .com, .org, .edu
Second-Level Domains: example.com
Subdomains: www.example.com
DNS Records
A Record: IPv4 address
AAAA Record: IPv6 address
CNAME Record: Canonical name
MX Record: Mail exchange
NS Record: Name server
DNS Query Types
Recursive Query: Server resolves completely
Iterative Query: Server returns referral
FTP (File Transfer Protocol)
FTP transfers files.
FTP Modes
Active Mode:
- Client connects to server port 21
- Server connects to client for data
Passive Mode:
- Client connects to server port 21
- Client connects to server for data
FTP Commands
Commands:
- USER: Username
- PASS: Password
- LIST: List files
- RETR: Retrieve file
- STOR: Store file
- QUIT: Quit
SMTP (Simple Mail Transfer Protocol)
SMTP sends email.
Port: 25
Process:
- Client connects to server
- HELO/EHLO
- MAIL FROM
- RCPT TO
- DATA
- Message
- QUIT
POP3 and IMAP
POP3 (Post Office Protocol):
- Download emails
- Port 110
- Emails stored locally
IMAP (Internet Message Access Protocol):
- Access emails on server
- Port 143
- Emails stay on server
GATE CS Important Points
- HTTP: Methods, versions, status codes
- DNS: Hierarchy, record types, query types
- FTP: Modes, commands
- SMTP: Email sending process
- Port Numbers: Know common ports
Practice Tips
- HTTP: Understand methods and status codes
- DNS: Know hierarchy and record types
- FTP: Understand active vs passive mode
- Email Protocols: SMTP, POP3, IMAP
- Previous Year Questions: Solve GATE application layer questions