Technical data

124 Theoretical and general applications www.westermo.com
Router
The word route means to select or find the right path. A router is a device, or in some
cases software in a computer, that determines where a packet should be sent on its
way to the end destination (the router is the end destination from a LAN’s perspec-
tive). Subsequently, the router is a network device that links together two or more
logically separate net-
works. It does not con-
nect networks blindly,
but acts more as a
packet switch for the
interconnection of local
networks over short or
long distances. In addi-
tion to equipment being installed in separate networks, the network can also utilise dif-
ferent topologies and standards.
As all devices have a unique address, sending equipment can always address a special
recipient in the same or in a different network. When a recipient in another network is
addressed, the data is directed in an appropriate manner through a logical connection
between the networks.
This information is
gathered in a routing
table, which defines the
routing and alternative
connection options.
In the example
opposite we adopt a
simplified addressing technique. The network addresses are 1, 2, 3 or 4. Devices on
the same network have the address 1.1, 1.2, etc.
Assume the computer with the address 1.1 wants to communicate with the com-
puter at 4.2. Router A receives a packet addressed to 4.2, detects that the address
belongs to another network, which results in the packet being routed forward, in this
case to 2.1 and on to 2.2. The same procedure occurs between routers B and C.
Finally the packet reaches router C and is transferred to network 4 to the computer
with the address 4.2.
Besides routing traffic, there is usually the possibility to control and filter traffic. A
routing table lists where different equipment and networks are located, a table can be
Network
Router A Router B Router C
Network
Network
Router A
Address 1.1
Address 4.2
1.2 2.1 2.2 3.1 3.2 4.1
Router B Router C
Network
B A C K