1a. Handover means moving from area of one base station to area of 
another. Roaming means using your phone in the network of foreign 
operator. Both are related to mobility but have otherwise little in 
common.

1b. BTS (Base Transceiver Station) and BSC (Base Station Controller). 
There are meny BTSs at the area of one BSC. When handover is between the 
BTSs can BSC handle it. If handover is between BSCs, MSC (Mobile Switching 
Center) is needed.

1c. Mobile phone is always registered in nearby Visitor Location Register 
(VLR). Information on SIM card can be used to find phone's (card's) Home 
Location Register (HLR). VLR and HLR doesn't need to be in the same 
network. Phone can be found by contacting HLR and by asking, under which 
VLR was the phone's last know position.

BTS etc. are of course needed, so that phone can connect to the network.


2a. GPRS uses several timeslots at the same time.

2b. EDGE uses more efficient coding (more data in timeslot).

2c. Frequence, Time and Code Division Multiply Access. They are different 
ways to multiplex signals. GSM uses FDMA and TDMA. FDAM means dividing 
available frequence bandwidth to several narrower channels. For example, 
in GSM the bandwidth is divided to 200 kHz channels. Each channel is then 
divided in time slices (TDMA).

CDMA is quite different from FDMA and TDMA and it is not used in GSM. 
In newer technologies CDMA is often in use. In CDMA the whole bandwidth is 
always in use. Signals are separated with codes. Codes are (pseude) random 
binary sekvensis that are used to modulate the signal. Receiver knows the 
code and can use it to extract the information. Other signals (modulated 
with different codes) seem like noise to the receiver.


3b. In TCP/IP networks the idea is to offer simple host-to-host
connections that can be used by intelligent clients and servers to
comminicate with each other. Network itself doesn't offer anything more
but best-effort packet service. If someone wants to offer new services,
every client who wants to use them must be updated (new software and
such).

In intelligent network, on the other hand, clients can be simple and
stupid since the network itself is intelligent. Services are in the
network and client is only a terminal, user interface for the service. 
Only network operator can offer new services. Client side updates are not 
(generally) needed to use new services.

4a. Ethernet uses CDMA-CD (Carrier Detection Multiply Access - Collision 
Detection), WLAN CDMA-CA (Collision Avoidance). In Ethernet, host first 
listens to the medium (cable) to find out if it is free. If it is, host 
can start sending. If someone happens to start sending at the same time, 
there is collision. Both parties back off and try again little later. 
There isn't any kind of reservation system.

In CDMA-CA host who wants to send something announces his intent with RTS 
(Request-to-Send) frame. Receiver replys with CTS (Clear-to-Send) letting 
other host know who has permission to send. This minimizes the risk of 
collision and also shortens the wasted time in case of RTS collision. This 
also solves so called hidden-station problem.

Differencies between CDMA-CA and -CD are because they have different 
medium. Cable is easy to control and everybody know, if there is a 
collision. Radio networks on the other hand suffer from multitude of 
disturbances and noise. Because of hidden station problem it is sometimes 
impossible to notice all the collisions.

4b. Hidden station problem means that two stations cannot see each other 
even though they are, in princible, in the same network. For example 
stations A and C are too far apart to notice when one or the other is 
sending something. Between them is B who is able to see both A and C. If A 
starts to send to B when C is already sending, transmissions are garbled 
at B. So A and C are hidden from each other although B can see them both.