serial v ethernet...

some basic differences...

serial communications (both async and sync) use nrz encoding...  conversely, ethernet communications use manchester encoding...

r4#sh int s0/0                                                               

Serial0/0 is up, line protocol is up                                         

  Hardware is PowerQUICC Serial                                              

  Internet address is 10.1.1.10/30                                           

  MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,

r4#sh int f0/0                                                               

FastEthernet0/0 is up, line protocol is up                                   

  Hardware is AmdFE, address is 0011.5c2d.b8c0 (bia 0011.5c2d.b8c0)          

  Description: ---->fa0/5 dsw1                                               

  Internet address is 172.16.0.4/24                                          

  MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,             

another difference is serial ports do not have mac addresses. whereas ethernet interfaces do... speed is also different...

they also use different hardware...

however, and this is important, they both use serial bit transmission at the physical layer...