1. Enumerate and describe three generations of networking systems ...

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26 Οκτ 2013 (πριν από 4 χρόνια και 7 μήνες)

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Enumerate and describe three generations of
networking systems proposed by Van Jacobsen

Generation 1: The phone system

circuit switching

Based on wires

very expensive to put them everywhere (make them ubiquitous
'wszechobecne'). Revenue ('dochód')

comes from calls, wires are sunk costs. Calls are treated

as a
side effect of connecting two points by wires

(system based on the paths)
. Phone number may be
treated as a program put in the system that builds a new path.
It started as a
very primitive

Throughout the history, when the operators where connecting the callers the phone number
stated coordinates of a point where the operator had to put one end of the wire. First automatic

switch (inwented around 1890) allowed to
select two
digit numbers

each pulse
caused the digit to increase (by switching horizontally), then when it got a long pulse the second
number could be chosen (this time by switching vertically after each pulse) [2D matrix] . Two
switches of this type lin
ed serially allowed to choose 4
digit numbers (10k possibilities).
Calling was
impossible when somebody was already using the section of a wire that was necessary for creating a
path for you or any element in the path fails (
reliability goes down exponenti
ally as the system
scales up

the only way of increasing the reliability was making individual elements of the system
extremely reliable

component reliable

[opposite of the internet philosophy, which focus on
creating numerous cheap component and doesn’t worry about
failure of one of them, making the
structurally reliable

A huge drawback of using telephony to send data is the
relatively long
of sett
ing up a
path (typically between 100ms and 1s

a small share of a phone call, but a really big part of sending
data). The problem was what to do to make quicker setups.

A large changed occurred in 60’s

electronics came up, enabling to dream abo

Generation 2: The

packet switching

It had a good start

all wires were already in their places. The main idea was to
focus more
on the endpoints rather than the paths

split the data into independent chunks

Another important thing was

(‘przechodniość’ ?)

a way of forcing node to sent the
packet that got to it
further if it’s not addressed for it. Those ideas were brought up to life in
, using already estab
lished phone
k [however, it could use also Ethernet, radio,
satellite etc.

it was designed agnostic about the delivery technology

possible due the change of
view: endpoints, not paths). The only thing seen externally were the addresses

all the knowledge
about top
ology became

to users

distributed routing spreading load and avoiding
hierarchy problems
. Joining a lot of independent networks bring out a need of regulate the
it was the beginning of TCP/IP.

reliability increases exponential
ly with system size

(more and more alternative paths available).
Transitivity allowed to remove the need of call setup

However, the TCP/IP have it own problems. First of all is treating a ‘connected’ state as a
binary attribute (you can talk to everythin
g or be isolated).
Next, the addresses need to be stable.
Finally, a huge

while broadcasting

if a lot of machines demand the same information,
the server needs to send it to each of them individually, creating numerous copies of it.

tion 3:


Both first and second generation focuses

on enabling conversations between two
. Nowadays, a huge part of internet traffic are just request for some named packets of data
, mails, files), which can be obtained not by conversation, but by

point to
multipoint or multipoint to multipoint

like in “Does anybody got the time ?”).

Dissemination through a conversation is possible, but

there’s a huge p
with a security (network is blind for data which is wrapped between TCP/IP headers)

and users have
to specifically state the goals and
their realization each time

they demand data.


of dissemination networking


enabling data r
equests by name

the means of obtaining it doesn’t bother the user; the protocol
uses them all (a bit of a analogue to using a lot of mediums to transmit internet packet data)

anything that hears the request and has a valid copy of the data can respond
to it

the responded data is signed and secured, and it’s validation could be checked

(security model
needed !)

trust are derived from the data, not the channel it arrives on

2. Describe advantages of packet switched networks over circuit switched

No need of call setup, which takes a significant part in overall time of c.s. networks

eliability increases

(in c.s.


exponentially with system size

Knowledge of topology is irrelevant

Easily spread load and avoidance of hierarchy

thanks to focusing on
endpoints rather the path between them

3. Describe the properties of dissemination oriented networks.

First of all,
let’s copy
the last point from the answer to the first question: data has a
name, not a location

trust a
re derived from the data, not the channel it arrives on
. Next,
anything that moves bits in time or space can
and will be used to communicate

there is not
distinction between data in a wire, in a memory or on a disc.

property of d.o.n. is the as
sumption, that

the network is doing more on user’s

the user is not giving a definite instruction but in a fact a he does simply state what he wants
and the network delivers it to him.

Also, the network do not depend on conversations, but on diss

the popular
content does not generate huge unnecessary traffic (like it does in TCP/IP).

Organizing local wireless or sensor nets are easier

the nods doesn’t need to have a name

The data can be remembered, so intermittent (‘przerywane’)
operations are possible, also
with use of opportunistic transport.

Trust and data integrity are foundation of dissemination network design, not an add
on like in