Week 9 - Application Layer Flashcards
What is the highest layer on the TCP/IP stack?
It is the application layer
What’s the protocols of this layer?
It define communication for network applications. Such as WWW, email, P2P file sharing etc.
(Refer back to PowerPoint for me examples)
Who uses network applications? Give an example
Network applications run on network edge devices (hosts/end-systems)
- Hosts include both clients of applications and the servers for those applications.
An example can be a web server communicates with browser client software
What does network Core not use?
It is devices (routers) where it does not run user applications.
What are the network application processes?
The process is part of a program or application running within a host machine.
What happens in the network application processes when there is a different or same host?
Within a same host, processses communicate using inter-processes communication protocols defined by the operating system.
Within different hosts,processes communicate by exchanging messages on the network (i.e using network protocols)
What are the two types of processes in terms of network communication?
- Client processes - initiates communication
- Server process - waits to be communicated with
What are the two common structures of network applications in network application architectures?
- Client-server
- Peer-to-Peer (P2P)
Define what the two structure does in the network applications
- Client-server - it is basically defining who runs the client processes and who runs the server processes
- P2P - it is where both client processes and server processes
What is it like in the P2P architecture?
- They have both client and server processes
- There’s no always-on server, so this means that they have arbitrary end systems directly communicate with each other
Define ‘Sockets’
It is the process-to-network interface between the application layer and the transport layer. So this means that it sends/receives messages to/from its socket, which communicates with the transport protocol.
- Each socket must be uniquely identifiable from the outside world
What is the socket addresses?
What services an application needs from a transport protocol?
- Data intergrity
- Timing
- Throughput
- Security
What does the data integrity do?
- Some apps (e.g file transfer/transactions) require 100% reliable data transfer
- Some other (e.g audio) can tolerate some loss
What does the timing do?
- Some apps (e.g. games) require low delay to be effective
- For others (e.g. webpages), this doesn’t overly matter
What does the ‘Throughput’ do in the services?
- Some apps (e.g. videos) require a minimum amount of throughput
- Other apps (e.g. email) make use of whatever they get
What does ‘Security’ do in the services?
- Encryption, etc., which we will learn about in the Network Security lecture
What are the 2 key transport protocols that provide such services to network applications and define it
- TCP - It is connection - oriented, reliable data transfer
- Flow and congestion control
- UDP - Connectionless, unreliable data transfer
- No flow or congestion controls
What does the HTML objects do?
The HTML object are sent and received using the HyperText Transfer Protocol (HTTP)
What’s the different between Non- persistent HTTP and Persistent HTTP?
If they are non - persistent, they closed after each server response.
If they are persistent, the server leaves the connection open after response.
What happens between clients and servers when there is non-persistent HTTP?
- Host has to go through TCP initiate, request,respond and close once per HTML object.
- Browsers open parallel TCP connections to fetch objects
- OS overhead for each individual TCP connection
What happens in the connections when there is persistent HTTP?
- It is when the HTTP messages between the same client-server duo are sent over the open connection.
- Client sends requests as soon as it encounters a referenced object.
What is the timing between Non-persistent HTTP and Persistent HTTP?
- Non-persistent HTTP response time = 2RTT + FTT
- 1 RTT to initiate TCP connection
- 1 RTT for HTTP request and first bytes of HTTP response to return
- File transmission time (FTT)
- Persistent HTTP response time can be little as 1RTT for all referenced objects
What are the two type of HTTP messages?
- Requests for HTML objects
- Responses with HTML objects
