How It All Works: A Simple Overview of LAN Operation Briefly, if a device (say a PC)
wants to communicate with another device (let??™s say a printer) on a LAN requesting a
service (printing, in this case), then the sending device??™s print application request will be
essentially converted into an appropriate Ethernet frame. The Ethernet frame will have
the PC??™s MAC address as the source address (SA) and the printer??™s MAC address as the
destination address (DA). Other parameters in the frame will be filled in appropriately.
The frame is then transmitted using the CSMA/CD protocol (described in section
on CSMA/CD) if the device MAC is operating in a half-duplex mode (i.e., it can either
send or receive but not send and receive simultaneously). This protocol was developed
Figure 1.3 A typical enterprise Local Area Network (LAN)
IP Phone
IP Phone
IP Phone
Ethernet Switch (DCE )
Service Provider
Router
Servers
(E-mail, File,
Storage
backup,
Web...)
PC
PC
PC
PC (DTE )
PC
IP PBX
Service
Provider
Network
CAT5
Service
Demarcation
CAT5
Access Link (TDM, Ethernet, FR, ATM)
CAT5
CAT5
CAT5
CAT5
CAT5
CAT5
CAT5
Ethernet: From LAN to the WAN 9
to more efficiently send and receive messages between multiple sets of devices (without
having a large number of collisions).
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