Appendix E: Ethernet; Ethernet - Siemens SIREC D200 Manual

Appendix E: Ethernet

Ethernet

Ethernet is a local area network (LAN) technology that transmits information between com-
puters and other devices, at speeds of 10 or 100 million bits per second (Mbps). Each Ether-
net equipped device operates independently of all other devices on the network.
All devices attached to an Ethernet network are connected to a shared signalling system.
Ethernet signals are transmitted serially, one bit at a time, over the shared signal channel
attached to each device.
It is up to the high-level protocol that is sending data over the network to make sure that the
data is correctly received at the destination device.
Devices attached to an Ethernet network can send application data to one another using
high-level protocol software, such as TCP/IP protocol suite.
High-level protocols have their own system addresses, such as the 32-bit addresses used
in the current version of IP. The high-level IP-based networking software in a device is aware
of its own 32-bit IP address and can read the 48-bit Ethernet address of its own network in-
terface, but it doesn't know the Ethernet addresses of the other devices on the network.
To discover the Ethernet addresses of other IP-based devices on the network another high-
level protocol is used. For TCP/IP, this is done using a protocol called Address Resolution
Protocol (ARP).
Example:
Device X has an IP address of 195.23.37.1 and sends data over the Ethernet channel to
another IP-based device, Device Y with IP address 195.23.37.2. Device X sends the pack-
ets of information containing an ARP request. The ARP request is asking the device with the
IP address of 195.23.37.2 to identify the address of the Ethernet Interface.
Only Device Y with the IP address of 195.23.37.2 will respond, sending a packet with the
Ethernet address of device Y back to device X. Now device X and Y have each others Ether-
net addresses to which data can be sent.
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