1.3 Flashcards
define packet switching
a mode of data transmission in which a message is broken into a number of parts which are sent independently, over whatever route is optimum for each packet, and reassembled at the destination.
What is store and forward transmission?
Store-and-forward transmission means that the packet switch must receive the entire packet before it can begin to transmit the first bit of the packet onto the outbound link
What is the end to end delay for store and forward transmission?
2L/R(assuming zero propagation delay)
What is packet switching queuing and loss?
If the arrival rate(in bits) of packets exceeds the rate of transmission of the link for a period of time packets will enter a queue and wait to be transmitted on the link or packets will be dropped if the memory buffer fills up
What are 2 key network functions?
Routing: determines the destination route taken by packets
forwarding: move packets from router’s input to appropriate router output.
What is circuit switching?
Essentially each link has a dedicated line so there is guaranteed performance for a limited number of users
circuit segment idle if not used by call(no sharing)
i.e telephone networks
FDM vs TDM
TDM: time division multiplexing
-time is divided into frames of fixed duration, and each frame is divided into a fixed number of time slots. When the network establishes a connection across a link, the network dedicates one time slot in every frame to this connection. each time slot is dedicated to one user and one slot is dedicated to transmitting data
FDM: frequency divison multiplexing
-the frequency spectrum of a link is divided up among the connections established across the link. Specifically, the link dedicates a frequency band to each connection for the duration of the connection.
Pros and cons of packet switching?
Great for bursty data
- resource sharing
- simpler with no call setup
Cons:
excessive congestion is possible
- packet delay, loss needed for reliable data transfer + congestion control
How is the internet structured?
Network of Networks
access nets/ISP are what end users connect to (can be uni or company)
Tier 1 ISP’s connected to each other via Internet exchange point(IXP)
content providers like google can be connected to Tier one ISP’s and access ISP
regional networks connect access ISP to Tier 1 provider
