ELSA Cable - Manual (Page 65)

Technical basics
ELSA MicroLink Cable
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All the router has to remember is that every address beginning with '192.168.100' is
located within the network of Example Inc.
Now imagine a router that is connected to the network of Example Inc. through an
interface. If it receives a packet with destination address '192.168.100.4' and netmask
'255.255.255.0', it will compare this with every network address it knows. In doing so it
carries out a logical AND with the netmask, and compares the results with the network
address: '192.168.100.4' AND '255.255.255.0' is '192.168.100.0'. This is the network
address of the Example Inc. network. The router recognizes that the recipient is located
within Example Inc. and passes the packet on to the appropriate interface for Example
Inc. Within Example Inc. the packet is then passed on to the appropriate subnet.
The same procedure is used for the transfer of IP packets within a network:
ቢ If a host in the subnet of the development department wants to send a data packet
to Mr. 'Smith', the sender attaches the destination address "Host 'Smith' –
Marketing – Example Inc.".
ባ The router in the development division receives the packet and extracts from the
address the information that it is directed at the marketing division of Example Inc.
Since it is itself part of Example Inc., but not of the marketing division, it passes the
packet on to the router in the superordinate network.
ቤ The router at the Example Inc. receives the packet and extracts from the address the
information that it is directed at Example Inc. Since it is itself part of Example Inc.,
it takes a closer look at the address to find the name of the division. It then passes
the packet on to the router in the marketing division, where the packet is passed on
to the recipient.
Expansion through local networks
Media access
control Up to now we have only considered the point-to-point connections. However, many
computer networks are based on multipoint cabling such as Ethernet. All computers
connected to the same network can then receive the signals of all other computers (so-
called broadcast transfer to a shared medium). If several computers are sending
simultaneously, the superimposed signals are destroyed. A variety of access methods
such as CSMA/CD or Token Ring are implemented in the MAC layer (Media Access
Control, MAC) for the avoidance and resolution of such collisions.
LAN and IP
network The connection of all computers communicating through a shared medium using a MAC
protocol is called a LAN. A LAN forms an independent network and is subordinate to the
IP network, i.e. IP networks can use the physical connections of the LAN to establish
connections between the hosts and the routers. LAN refers to a limitation of the area
covered by the network, not a restriction of the number of workstations connected to it.