Chapter 1 Flashcards
Host or end systems
A network of billions of computing devices
Internet Protocol address
unique, numeric value assigned to each host
packets
clusters of data. labeled with IP address of sender and receiver
Direct traffic using addresses on the packets
routers and switches
Internet
worldwide network of interconnected computers
Web
worldwide network of interconnected hypertext pages, connects to web server apps, one of many apps built on top of the internet
protocols
define how devices should interoperate
network protocol
defines proper communication patterns between devices; types of messages that can be sent; structure of the messages; possible responses and actions to take
Network edge
hosts: clients and servers; have only one link to the internet
network core
routers connecting various Internet parts; like hosts with multiple links and living only to relay others’ packets
physical media
wired and wireless communications links
circuit switching
electrical connection is established end-to-end for each call; originally done by moving cabled plugged into switchboards; later pulse and tone dialing automated switching
Public Switched Telephone Network (PSTN)
still uses analog signals on twisted pair cables
coaxial cables
much better signal carrier, less sensitive to noise, and carry more data; designed to carry video
Digital Subscriber Line
phone calls do not interfere with data exchange; splitter after the DSLAM and before the modem
Frequency Division Multiplexing
way to share a single communication medium; different channels are simultaneously transmitted on different frequency bands; no taking turns; coaxial cable
Radio
wireless/unguided medium; signal flows through open space; objects can block or reflect signal; no need to wire up every device; lots of noise, interference, and competition for the spectrum
circuit switching in the PSTN
need a dedicated electrical path that remains that way until the parties hang up; guaranteed performance; may have to wait for a free line; wasting during silence
Packet switching
way in which computer networks send data by sending packets
Packet
destination address; sender address; limited space for message; large messages must be split into multiple pockets; may arrive in any order; may take different paths to destination; delivery is “best effort” and not guaranteed
throughput
rate of data transfer (bandwidth); measured in bps; data arrives in discrete packets so throughput is calculated as an average over some time window
latency
delay of an action; network latency is the time it takes for a bit of data to arrive at the destination
communication link
bi-directional, point-to-point connection, allow 0’s or 1’s to be transmitted or idle, propagation delay, operates at a certain, constant bitrate
propagation delay
the time it takes for bits to flow from sender to receiver
store and forward
data takes several hops to reach destination; each intermediate router has a queue of packets waiting to be sent along to the next hop; FIFO order
Packet switching
1) no fixed resource allocation
2) no theoretical limit to the number of users
3) In practice, it allows more users to use network
Routers 2 responsibilities
1) distributed routing algorithms
2) packet forwarding
Distributed routing algorithms
determine which address ranges are most quickly reachable on each of its outbound links
Packet forwarding
direct packets according to the decisions made by the distributed routing algorithms
Fours sources of packet delay
1) dproc: nodal processing delay - check bit errors
2) dqueue: queueing delay - time waiting at output link for transmission
3) dtransL transmission delay - packet size/ link bandwidth
4) dprop: propagation delay - length of the link / speed of light
Structure of the Internet
Tiers
TCP/IP stack
app; transport; network; link; PHY
Application
supporting network applications
transport
process-to-process data transfer
network
routing of diagrams from source to destination hosts
Link
data transfer between neighboring network elements
PHY
bits “on the wire”
Network layers in WWW
HTTP, TLS, TCP, IP, Ethernet Wifi
HTTP
get web pages, images, etc. and post data to servers
TLS
encrypt traffic
TCP
byte streams (ordering, delivery confirmation, pacing); gives a file-like interface to network connections (read and write bytes); handles limited packet size, dropped and reordered packets
IP
Forward packets across multiple hops; makes best-effort attempt to route packets to their destination IP
Ethernet/wifi
share a communication link with multiple local devices
sockets
analogous to a door; sending process shoves message door; sending process relies on transport infrastructure on other side of door which brings message to socket at receiving process; IP address is device’s unique identifier
TCP Streams
provides applications with a file-like abstraction for a network connection (read and write); packets are a reassembled and ordered automatically by the OS/library; must establish a connection first (3 way handshake)
TCP provides
- port numbers os a computer can have multiple network connections
- message fragmentation and reassembly
- delivery confirmation and retransmission
- flow control: sender won’t overwhelm receiver
- congestion control: throttle sender when network is overloaded
UDP
- simpler than TCP
- No reliable connection
- ## Protocols deal with more error conditions
