FL1 Kommunikationssystem
what is a service
basic ability to transfer information with some service attributes
what is application
use services to provide some functionality for users (humans or machines,ex email web browsing telephone
what is architecture
specification on how the network is built and operated
what are the Five Components of Data Communication
message, sender, reciever, transmission medium, protocol
what is message
data (block of bits) to be transferred
what is sender
device (computer, phone, …) that sends message
what is reciever
device that receives the message
what is tramsmission medium
physical medium, e.g., cable, fiber, radio channel
what is protocol
set of rules that governs communication
different Data Flow Types
simplex, half duplex and full duplex
what is simplex(Data Flow Types)
one-directional, Example: TV broadcast
what is half duplex (data flow types)
Bi-directional, but only one way at a
time, ex wifi
what is full duplex(data flow types)
Bi-directional, simultaneously
– Example: modern Ethernet
what kinds of connection types are there
point-to-point and multipoint
what is point-to-point (connectiontypes)
Transmission heard by a single device
what is multipoint (connection types)
Transmission heard by multiple devices
what are the network topologies
mesh and star
what is the difference between mesh and star
star has a connecting device, hub or switch
what are the network types in WAN
point-to-point and switched WAN
what is the switch types
circuit-switched network and packet-switched newwork
what are the three phases of Circuit-Switched Network
(switching types)
– Setup: reserve a path through the network
– Information transfer: interchange messages
– Te a r- d o w n : release network path
what defines curcuit switch networks (switching types)
-three phases
-switches do not store data
-low and stable latency but potentially low network utilization
what defines Packet-Switched Network
-Packets are buffered (stored) in routers and
forwarded when the output link is available
-Packets for a transmitter-receiver pair can go
over different network paths
-Packets need to contain addresses
-Good utilization of network links, but potentially
high and variable latency
give an example of packat-switched network and how it works
telepraph, based on
-messsages, reciever adress+sender adress+user message
-digital transmission,morse code
-message switching at recieving station, 1. recieve and store telegram, 2. determin next route, 3. forward to next station
-messeges are multiplex over transmission lines
-framing, i.e., a way to find start and stop of the message, is required to demultiplex
messages at the receiver
Example of Circuit Switching Network
old telephone.
1. connection setup. a. pick up -> telefon netwerk alerted
b. dial tone <- telefon network ready
c. dial number -> network selects rout, call recieving party
d. recieveing party picks up
2. information transfere bla bla
3. connection release, goodbye, hang up ->telefone network release connection
what is a protocal (computer networks)
A protocol is a set of rules that governs how two or more communicating parties should
interact,
give example fore some protocals (computer networks)
– Internet Protocol (IP)
– Transmission Control Protocol (TCP)
– HyperText Transfer Protocol (HTTP)
– Simple Mail Transfer Protocol (SMTP)
how is communication between computers
by exchanging packets(messages, segments, frames): header + data
also header contains adresses and other control information
packet switching
• Packets are sent by transmitting end node, without reserving a circuit, and are routed towards the receiving end node by packet switches (routers)
• Long messages can be fragmented into smaller packets that are individually transmitted for robustness and efficiency
• Short messages can be aggregated into a single larger packet for efficiency
• Congestion control is needed to avoid buffer overflow in the packet switches, i.e., congestion inside the network
• Flow control is needed to avoid overwhelming a receiver (end node), i.e., congestion at the edge of the network
• Medium access control needed for sharing a common broadcast medium. For example: shared cable (bus), radio spectrum
• Error control needed for reliable delivery of information
routing and forwarding
• Packet header contains sender and destination addresses
• Routing is the process of finding a path through the network from sender to destination
• Packet switches maintain forwarding tables (routing tables) that relate destination with next hop (i.e., output port of switch)
• Forwarding is the process of
– inspecting the destination address
– consulting the forwarding table to find the correct output port
– transmit the packet on the output port
• Hierarchical addresses are used to keep forwarding tables small
– analogous to regular mail addresses
country, city, zip code, street, street number, name
• For small networks, addresses can be flat (nonhierarchical)