5. RETI DI CALCOLATORI
Una Rete di Calcolatori è un insieme di
elaboratori autonomi ed interconnessi.
Autonomi: tutti hanno “pari dignità”,
nessuno può controllare gli altri
Interconnessi: tutti sono in grado di
scambiarsi informazioni
6. RETI DI CALCOLATORI
NON SONO reti di calcolatori:
Un sistema distribuito, che è una Rete di calcolatori + Software di
gestione (middleware) che presenta la rete agli utenti come un unico
sistema, assicurando coesione e trasparenza
Internet, che è invece una rete di reti potenzialmente diverse fra loro
Il Web, che è invece un sistema distribuito che poggia su Internet
9. CONNESSIONE
Connessione hardware
Mette in collegamento tra loro due o più apparecchiature
elettroniche attraverso un'interfaccia. Il mezzo più usato per
stabilire la connessione è tipicamente il cavo elettrico fornito di
connettori alle estremità. Esistono diversi tipi di cavo ciascuno
progettato per un determinato standard di trasmissione dati. Oltre
al cavo elettrico è possibile effettuare una connessione anche
tramite fibre ottiche oppure onde radio. I collegamenti di
connessione possono essere seriali o paralleli.
10. CONNESSIONE DI
RETE
Connessioni di rete
Le connessioni di rete sono connessioni logiche e/o fisiche tra
terminali di una rete ovvero collegamenti verso l'esterno e non
verso gli elementi hardware interni del medesimo computer o
apparato elettronico per l'espletamento di un certo servizio quale
ad esempio una comunicazione vocale tra utenti o una
comunicazione dati.
11. PROTOCOLLI
PROTOCOLLI DI RETE
Un protocollo è un insieme di regole per la
gestione della comunicazione tra due
soggetti della rete.
Un protocollo stabilisce il comportamento
d’ingaggio, di comunicazione, di chiusura
12. PROPRIETÀ DEI
PROTOCOLLI
Data formats for data exchange. Digital
message bitstrings are exchanged. The
bitstrings are divided in fields and each field
carries information relevant to the protocol.
Conceptually the bitstring is divided into two
parts called the header area and the data
area.
13. PROPRIETÀ DEI
PROTOCOLLI
Address formats for data exchange.
Addresses are used to identify both the sender
and the intended receiver(s).
Address mapping. Sometimes protocols need
to map addresses of one scheme on
addresses of another scheme. For instance to
translate a logical IP address specified by the
application to an Ethernet hardware address.
This is referred to as address mapping.
14. PROPRIETÀ DEI
PROTOCOLLI
Routing. When systems are not directly
connected, intermediary systems along the
route to the intended receiver(s) need to
forward messages on behalf of the sender.
Detection of transmission errors is necessary
on networks which cannot guarantee error-
free operation.
15. PROPRIETÀ DEI
PROTOCOLLI
Acknowledgements of correct reception of
packets is required for connection-oriented
communication.
Loss of information - timeouts and retries.
Direction of information flow needs to be
addressed if transmissions can only occur in
one direction at a time as on half-duplex links.
16. PROPRIETÀ DEI
PROTOCOLLI
Sequence control. We have seen that long
bitstrings are divided in pieces, and then sent
on the network individually. The pieces may
get lost or delayed or take different routes to
their destination on some types of networks.
As a result pieces may arrive out of sequence.
Flow control is needed when the sender
transmits faster than the receiver or
intermediate network equipment can process
the transmissions.
19. LINK LAYER
The link layer is the networking scope of the
local network connection to which a host is
attached. This regime is called the link in
TCP/IP literature. It is the lowest component
layer of the Internet protocols, as TCP/IP is
designed to be hardware independent. As a
result TCP/IP may be implemented on top of
virtually any hardware networking technology.
20. INTERNET LAYER
The internet layer has the responsibility of
sending packets across potentially multiple
networks. Internetworking requires sending
data from the source network to the
destination network. This process is called
routing.
21. INTERNET LAYER
In the Internet protocol suite, the Internet Protocol
performs two basic functions:
Host addressing and identification: This is
accomplished with a hierarchical IP addressing
system.
Packet routing: This is the basic task of sending
packets of data (datagrams) from source to
destination by forwarding them to the next
network router closer to the final destination.
22. INTERNET LAYER
The transport layer establishes a basic data channel
that an application uses in its task-specific data
exchange. The layer establishes process-to-process
connectivity, meaning it provides end-to-end services
that are independent of the structure of user data and
the logistics of exchanging information for any
particular specific purpose. Its responsibility includes
end-to-end message transfer independent of the
underlying network, along with error control,
segmentation, flow control, congestion control, and
application addressing (port numbers).
23. APPLICATION LAYER
The application layer contains the higher-level protocols
used by most applications for providing user services over a
network and for some basic network support services.
Examples of application layer protocols include the File
Transfer Protocol (FTP), the Simple Mail Transfer Protocol
(SMTP), and Dynamic Host Configuration Protocol (DHCP).
Data coded according to application layer protocols are
then encapsulated into one or (occasionally) more transport
layer protocols (such as TCP or UDP), which in turn use
lower layer protocols to effect actual data transfer.