- Communication between computers:
- The sender transmits electrical signals that form "words" in some "language"....
- The receiver receives the electrical signals and interprete the "words"....
- Communication
infra-structure for
electrical communication:
- Transmission scheme:
- We need a mechanism
to convert
the message into
electrical signals
(So that we can transmit the electrical signals
- We also need a
mechanism to
convert the
electrical signal
back into
something
humans can
interpret
Example: a simple touch circuit transmitter
- We need a mechanism
to convert
the message into
electrical signals
- Communication link:
- We need a medium to carry the electrical signal to the destination
Example: copper wires
- Routing scheme:
- Because the commincation network is like a maze, we need a system to find a route through the communication network
Graphically:
(Two devices have been developed that can perform routing: routers (high level) and switches (low level))
- Transmission scheme:
- Host:
- Host =
a sender or
receiver
I.e.: host = a source or a destination of information
- Host =
a sender or
receiver
- Router/switch:
- Router/switch =
a device that
relay electrical signal
(towards the
destination host)
(A riuter/switch is not a source/destination of information
- Router/switch =
a device that
relay electrical signal
(towards the
destination host)
- In order to communicate over
large distances, we build
a communication relay
infra-structure:
- The communication relay
infra-structure
(= communication network)
relays
messages from
one (source) host to
another (destination) host:
Explanation:
- There are 2 kinds of nodes in
a communication network:
- Hosts:
the sending/receiving devices (nodes)
- Routers/switches: devices that relay the messages towards destination nodes
- Hosts:
the sending/receiving devices (nodes)
- Router/switches ---
Internal/intermediate devices
- Routers/switches
relay
electrical signals
- The routers/switches
do
not need to
decode
the messages
Result:
- Routers/switches do
not need to be
very "intelligent"
(I.e., routers/switches do not have a lot of different kinds of software)
- Routers/switches do
not need to be
very "intelligent"
- Routers/switches
relay
electrical signals
- Hosts ---
end/user devices
- Hosts are
sources and
destinations
of messages.
- A destination node is the
final node in the
transmission path
- The message received is
used
by a destination node
Consequently:
- A destination
must
decode
a messages
(I.e., a destination node has a high degree of intelligence (= or more software)
- A destination
must
decode
a messages
- Hosts are
sources and
destinations
of messages.
- The communication relay
infra-structure
(= communication network)
relays
messages from
one (source) host to
another (destination) host:
- Routers/switches:
- Routers/switches
are specialized devices:
- Routers/switches can only perform the routing operation (= a specilization)
- Routers/switches are
simple devices
(= less complex)
- Because they only perform one task !!!
Example routers/switches:
- The Ethernet switch you
buy for $50 or so
(More powerful switches can cost a lot of money...)
- Routers/switches
are specialized devices:
- Hosts:
- Host nodes are
more complex
(= more expensive) because:
- Hosts perform compututaion for the user !!!
Example of host nodes:
- Your laptop (end user equipment !!!)
- Your cell phone
- MathCS department's servers
- And so on....
Comment:
- Since hosts are general purpose computers, a host can also be programmed to perform routing function !!!
- Host nodes are
more complex
(= more expensive) because: