lecture 2 Flashcards
3 kinds of data flow
- simplex
- half duplex
- full duplex
describe a simplex data flow
- one way flow
- A sends to B
describe a half duplex data flow
- two way flow
- one at a time
- A sends to B
- B sends to A
e. g fibre optics
describe a full duplex data flow
- A and B can send to each other simultaneously
what is a subnet
everything between the hosts
e.g the routers,
what is a host or end-system
- a computer that a user logs into to do work
- attached to network, not part of network (usually)
3 ways to classify networks
- transmission technology
- size
- topology
3 kinds of transmission technology
- broadcast
- multicast
- unicast (p2p)
describe broadcast transmission
- one to all
- in bus topology everybody receives it but ignore it and only destined receiver will respond
- a 0 bit is broadcast
describe multicast transmission
- communication with specified groups
- a 1 bit is multicast
- uses a GID (group ID)
describe unicast transmission
(p2p, end to end, host to host)
(3)
- links between nodes
- from source to destination: visit one or more nodes
- uses protocols to optimize routing (find best path)
large networks tend to use what kind of transmission technology and why?
- UNICAST (P2P)
e.g internet, sending an email
why? - decrease collisions and traffic
- increase efficiency
where do routing algorithms play an important role (broadcasting, multicasting, P2P)?
UNICAST (P2P)
4 types of network structures
- LAN (10m to 1Km)
- MAN (10km, city)
- WAN (100km - countries, continents, planets)
- Wireless
why do we need to classify network structures, what changes?
- protocols used
LANs (6)
- used in small geographic regions
- high data rates (min: 10-100Mbps ++)
- low cost
- typically use BROADCAST transmission technology
- can be used a testing environment for other protocols
- IEEE 802.3
in LAN bus topology, what protocol do we use to transmit
CSMA
- to make sure corresponding node is not broadcasting, otherwise collision happens
ad hoc network (4)
- no router
- connecting devices directly
- similar to hotspot/bluetooth
- IoT uses this tech
MANs (4)
- used in medium size geographic regions
- does not use switching elements, single wires instead
- e.g. is cable TV
- IEEE 802.6 (DQDB)
- slower than a LAN (bigger)
what is dual queue dual bus?
- used in MANs
- uses two unidirectional broadcast buses with different directions
WANS (4)
- used in large geographic regions
- low data rates (hella big)
- high cost
- uses transmission lines and switches, routers and hubs
- e.g. Internet
examples of wireless networks
- bluetooth
- flying LAN in airplanes
6 types of topologies
- bus
- ring
- tree
- star
- mesh
- hybrid
if we have bidirectional bus flow
- use baseband cable and repeater
bus pros (2) and cons (3)
pros
- Requires less cable length this less cost
- Easy to set up for small networks
cons
- Adding nodes/devices can slow the network (high traffic)
- Troubleshooting is not easy because all devices are connected to a central cable
- If central cable (bus) fails, then the network fails
how can we fix a unidirectional ring
- add an extra ring to make it bidirectional
best case and worst case in uni ring
best= A to B 1 links/hop worst= A to last one n - 1 links/hops n = number of nodes
best, average, worst case in bi ring
best: 1
average= n+2/4
worst= n/2
what network structure uses tree topology
MANs
star pros and cons
Pros:
- Easy to troubleshoot
- Devices can be easily added/removed without affecting overall connectivity and performance
Cons:
- If the central hub fails, then the whole network is disrupted (it is centralized)
- Devices can only be added depending on the number of outlets present in the hub
bi star pros (3) and cons (2)
Pros:
- Can provide an alternative path in the case of failure of 1 node
- Minimal packet collisions
- High speed of data transfer
Cons:
- Addition/removal of nodes is difficult
- Failure of two adjacent nodes can disrupt the network
uni star pros (1) and cons (2)
Pros:
- Less packet collisions
Cons:
- If one node fails, the whole network is disrupted since data packets can only be moved in one direction
- Adding/removing nodes without interfering with the network is difficult
what topologies use broadcast
- bus
- ring
mesh pros and cons
Pros
- Many alternative paths
Cons:
- Hella costly to make and add (NOT SCALABLE)
types of connections
- P2P: station to station
- Multipoint: mainframe to many stations
switched WAN vs p2p WAN
- switched: going through multiple WAN networks before reaching destination
- p2p
best, average, worst case in star
best= 2 average= n+2/4 worst= 2
best, average, worst case in mesh
best= 1 average= 1 worst= 1
