Mobile Computing:-Introduction Part-II

Wireless Networks:-
-Two types
1)Voice network
Cellular systems (GSM, CDMA etc.)
2)Data network
WiFi, HiperLAN
-Networks are moving towards an integrated network
GPRS
Voice over WiFi

---Physical Layer (PHY)
-Binary (digital) data transmitted over airwave
-Requires antenna
-characterized by transmission range, power, modulation scheme, frequency range

--MAC Layer
-How wireless stations share the air medium and avoid contention to transmit data successfully
-“listen before you speak” or “speak at predetermined interval”
-Unique problems
Hidden node
Exposed node


--Network Layer
Responsible for facilitating multihop communication
Need to run some routing protocol
Traditional routing protocols may not work efficiently
Mobility at IP layer


--Transport Layer
Reliable Transport such as TCP may not work well in wireless medium
TCP inherently assumes that packet loss is due to congestion
Needs modification for wireless network