Due: November
15
(Due in class
at the start of the day)
Instructor: T. Kunz
1) GPRS (10 marks)
In a circuit switched connection in GSM, the ciphering is
done between MS and BTS, but in GPRS the ciphering is done between MS and SGSN.
a)
What do you think are possible reasons for this?
b)
How does ciphering differ in GPRS from the ciphering in
circuit switched case?
c)
What happens if the ciphering is switched off (not
used) in GPRS?
2) MAC Protocols (20 marks)
a) The
course notes contain two diagrams, explaining how multiple stations A to E
compete for access to a shared channel in WaveLan (page 173) and under DCF for
IEEE 802.11 (page 186). Draw similar diagrams for the same scenario under CDPD,
PCF mode in IEEE 802.11, and Bluetooth. Use the following scenario:
·
Five stations A, B, C, D, E plus one base
station/access point/master where necessary
·
All destinations are outside the cell/network/piconet
·
A is transmitting to W (starting or in progress)
·
A desires to transmit to X
·
B desires to transmit to Y
·
E desires to transmit Z
b) Could
the Bluetooth MAC protocol have been chosen as basis for the DCF mode of the
IEEE 802.11 standard? Explain your answer!
3) Mobile IP (20 marks)
a) CDPD
allows an end-user to run TCP/IP applications in a cellular network, roaming
between cells and/or service providers. Summarize the main similarities and
differences in the mobility management for MobileIP and CDPD. Will the end-user
see/experience any difference?
b) MobileIP
suffers from the problem of triangular routing. To overcome this disadvantage,
a route optimization draft exists that allows correspondent hosts to basically
keep a cache of “care-of” addresses for mobile hosts they are communicating
with. Outline a route optimization proposal that does not cache addresses at the
correspondent hosts. What are its advantages/disadvantages compared to the
proposed route optimization protocol? (Hint: avoiding caching “care-of”
addresses at the correspondent hosts does not mean that such addresses should
not/can not be cached at all…)
c) MobileIP,
as proposed, requires updates at the home agent every time the
point-of-attachment to the wired network changes. Outline a proposal to reduce
the number of these update messages. (Hint: think about organizing the
foreign/home agents in a hierarchical manner).
For parts b) and c), describe both the suggested
architecture and its operation. That is, describe:
·
what functional entities do you add to the
network
·
where in the network do you add them
·
what information do these entities contain/maintain
·
how is this information updated as mobile hosts
move
·
how are these entities used in delivering data
packets to mobile hosts.