Week 4 Flashcards
What are layers of a network?
Each layer implements a service, relying on services implemented by a layer below
Why is layering good?
- modularization
- ease of maintenance
What are the 5 Internet Layer Stacks
- App
- Transport
- Network
- Link
- Physical
What does the Application Layer do?
supporting network apps through HTTP, IMAP, SMTP, DNS
Info: MESSAGE
What does the Transport Layer do?
Process to process data transfer (TCP and UDP)
Info: SEGMENT
What does the Network Layer do?
moving packets known as DATAGRAMS.
What does the Link layer do?
Data transfer between neighboring elements (within the same network) called FRAMES
What does the Physical Layer do?
bits “on the wire”
Order of layering?
App > Transport > Network > Link > Physical
What are the 2 Main Network Architechtures?
- Client-Server Architecture
- P2P Architecture
Explain the Client-Server structure
Server:
- always on host, permanent IP address
- ideally data centers
Client:
- initiates contact with the server.
- Clients do not interact with other clients
example: HTTP, IMAP, FTP
Explain the P2P Architechture
- minimal or no reliance on dedicated servers
- direct communication between hosts.
How do Client-Servers processes interact with each other?
Through SOCKETS. send/receive through sockets, like a door.
What are sockets?
where a process sends messages into and receives messages from.
“door” of 2 houses, connecting the inside, outside, + road (link)
What info do we need to identify a process?
- Host’s address
- Port number
4 types/dimensions of transfer service an app needs?
- Reliable data transfer
- Throughput
- Timing / delay
- Security
What are the 2 Main Transport services provided by the internet?
TCP and UDP
For text-apps, what transfer servies would it need?
-No data loss
- Time sensitive (FOR TEXTS)
For images/video apps, what transfer services would it need?
- Throughput
- Timing / delay sensitive
Explain the TCP service.
- Connection oriented
- Has congestion control
Pros of TCP
- No loss (provides reliability)
- Congestion controlC
Cons of TCP
- does NOT provide:
- guaranteed timing, security, throughput
Explain the UDP service model
- lightweight transport protocol with minimal services
- no handshaking required
Pros of UDP
- UDP has no constraints unlike TCP, you can send as much as you wantC
Cons of UDP
- unreliable data transfer
- Does not provide timing, throughput guarantee, congestion control
Which types of apps can use UDP?
- Internet telephone
- Interactive games
What are the 2 types of a network app?
- Open Network (rules dictated by RFC)
- Properiety Network
What are the parts of a destination address?
IP address and port number of BOTH client and server.
Parts of a Client Program with UDP: How do you create the client socket?
- initialize server name and port
- create client socket: USING SOCK_DGRAM
Parts of a Client Program with UDP: How do you send a message?
- encode message
- use .sendto() function
Parts of a Client Program with UDP: How do you receive message?
- use .recvfrom()
- close the socket
Parts of a Server Program with UDP: What socket do you need to make?
Server socket!
Using SOCK_DGRAM
Parts of a Server Program with UDP: How do you receive packets?
INSIDE THE INFINITE LOOP:
- use .recvfrom()
- decode the message!
- use .sendto()
Parts of a Client Program with TCP: How do you create the client socket?
- initialize servername and port
- Create client socket through SOCK_STREAM
Socket programming for TCP, how does client -> server handshake work exactly?
- client and server handshake before sending data
- client drops data into TCP connection
- server “hears” the data and creates a new socket dedicated for that client
Parts of a Client Program with TCP: How to sent request to server?
using socket.send()
Difference between TCP and UDP client?
Nothing, just the SOCK_STREAM vs SOCK_DGRAM
Parts of a Server Program with TCP: How does accepting requests from a client work?
In a LOOP FOREVER:
Server has to wait for incoming connection request: socket.accept()
then, a NEW SOCKET must be created for the server
Parts of a Server Program with TCP: How does sending messages to a client work?
send an encoded messages to the client and close the connection.
