Application Layer 1 Flashcards
What are some networking apps?
- Social networking
- Web
- Text messages
- Streaming videos
When creating a network app, programs are written to…
- Run on (different) end systems
- Communicate over network
- e.g. web server software communicates with browser software
When creating a network app, we don’t need to write software for…
- Network-core devices
- Do not run user applications
- Applications on end systems, allow for raid app development
In the client-server paradigm, what does the server contain?
- Always-on host
- Permanent IP address
- Often in data centres, for scaling
In the client-server paradigm, what does the client contain?
- Contact, communicate with server
- Intermittently connected
- Dynamic IP address
- Don’t directly communicate with eachother
What does peer-peer architecture contain?
- No always-on server
- Arbitrary end systems directly communicate
- Peers request service from other peers
- Peers are intermittently connected
What is process communication?
- Within the same host, two processes communicate using inter-process communication
What are sockets?
- Process sends/receives messages to/from its socket
- Socket = door
- 2 sockets on each side (client and server)
To receive messages, processes must have an?
- Identifier
What are identifiers?
- Include both IP addresses & port numbers associated with process on host
What port number is used for HTTP?
- 80 or 8080
Host devices have a unique …-bit IP address
- 32-bit
An application-layer protocol defines:
- Types of messages exchanged
- Message syntax
- Message semantics
- Rules
- Open protocols
- Proprietary protocols
What transport services does an app need?
- Data integrity
- Timing
- Throughput
- Security
What does the TCP service provide?
- Reliable transport
- Flow control
- Congestion control
- Connection-oriented
What doesn’t TCP service provide?
- Timing
- Minimum throughput guarantee
- Security
What does the UDP service provide?
- Unreliable data transfer
What doesn’t the UDP service provide?
- Reliability
- Flow control
- Congestion control
What are the 3 major components of an email system?
- User agents
- Mail servers
- Simple mail transfer protocol (SMTP)
What does a user agent do in an email system?
- “mail reader”
- Composing, editing, reading mail messages
- Gmail, Outlook
- Outgoing, incoming messages stored on server
What do mail servers contain?
- Mailbox contains incoming messages for user
- Message queue of outgoing mail messages
Describe the SMPT RFC (5321)?
- Uses TCP to reliably transfer email messages from client to server (port 25)
What are the 3 phases of transfer in the SMTP RFC (5321)?
- SMTP handshaking (greeting)
- SMTP transfer of messages
- SMTP closure
How do clients retrieve emails?
- Mail access protocol
- Post office protocol (POP)
- Internet mail access protocol (IMAP)
Describe the POP3 protocol?
- Can download and delete
- Download and keep copies of messages on different clients
