Questions and Answers of Telecommunication Engineering

How does the symmetry of wireless links influence the routing algorithms proposed?
What could be quick 'solutions' and why don't they work?
Why are special protocols for the support of micro mobility on the network layer needed?
What are the benefits of location information for routing in ad-hoc networks, which problems arise?
Think of ad-hoc networks with fast moving nodes, e.g., cars in a city. What problems arise even for the routing algorithms adapted to ad-hoc networks? What is the situation on highways?
Name the requirements for a mobile IP and justify them. Does mobile IP fulfill them all?
List the entities of mobile IP and describe data transfer from a mobile node to a fixed node and vice versa. Why and where is encapsulation needed?
Show the steps required for a handover from one foreign agent to another foreign agent including layer 2 and layer 3.
Explain packet flow if two mobile nodes communicate and both are in foreign networks. What additional routes do packets take if reverse tunneling is required?
Explain how tunneling works in general and especially for mobile IP using IP-in-IP, minimal, and generic routing encapsulation, respectively. Discuss the advantages and disadvantages of these three
Name the inefficiencies of mobile IP regarding data forwarding from a correspondent node to a mobile node. What are optimizations and what additional problems do they cause?
Compare the different types of transmission errors that can occur in wireless and wired networks. What additional role does mobility play?
Why does the link speed not appear in the formulas presented to estimate TCP's throughput? What is wrong if the estimated bandwidth is higher than the link speed?
What is the reaction of standard TCP in case of packet loss? In what situation does this reaction make sense and why is it quite often problematic in the case of wireless networks and mobility?
Can the problems using TCP be solved by replacing TCP with UDP? Where could this be useful and why is it quite often dangerous for network stability?
How and why does I-TCP isolate problems on the wireless link? What are the main drawbacks of this solution?
Show the interaction of mobile IP with standard TCP. Draw the packet flow from a fixed host to a mobile host via a foreign agent. Then a handover takes place. What are the following actions of mobile
Now show the required steps during handover for a solution with a PEP. What are the state and function of foreign agents, home agents, correspondent host, mobile host, PEP and care-of-address before,
What are the influences of encryption on the proposed schemes? Consider for example IP security that can encrypt the payload, i.e., the TCP packet.
Why is strong consistency of file systems problematic in a wireless and mobile environment? What are the alternatives?
What are the primary goals of the WAP Forum efforts and how are they reflected in the initial WAP protocol architecture?
What migration paths does WAP 1.x offer for Internet and telephony applications and their protocols? Compare with WAP 2.0.
Is WDP a fixed protocol and why does WAP not define a SAP which WDP can use?
Why does WAP define its own security layer and does not rely on the security provided by the mobile phone network? What problems does the WAP security layer cause? Think of end-to-end security.
Name the advantages and disadvantages of user acknowledgements in WTP. What are typical applications for both cases?
Which WTP class reflects the typical web access best? How is unnecessary overhead avoided when using WSP on top of this class for web browsing?
What problems of HTTP can WSP solve? Why are these solutions especially needed in wireless mobile environments?
Why does WSP/B not put responses into the same order as the requests? Think, for example, of requests for different items on a web page.
What advantages does a connectionless session service offer compared to a simple datagram service?
What are the enhancements of WAE to the classic client/server model of the web? What are functions of this enhancement?
What is the fundamental difference of WML compared to HTML? Why can this difference be important for handheld devices? What is specified in addition to save bandwidth?
Why has a scripting language been added to WML? How can this language help saving bandwidth and reducing delay?
What are typical telephony events and how are they integrated into WAP? How can a user access features of mobile phones via the web browser?
What is the role of a WTA server? What are the different ways of integrating WTA servers into the WAP architecture?
What is the difference between WAP service indication and service loading? What applications could use these services? What is a push good for anyway?
Name key differences between WAP 1.x and i-mode. What were problems in the early WAP days and why was i-mode that successful in Japan?
Why is a common synchronization framework useful? What problems remain?
Compare the presented protocol stacks for WAP 2.0 and give application examples.
What advantages has the statelessness of HTTP? In what situations is state useful and how is it provided today? Where is long-term state stored, where is short-term?
Which properties of HTTP waste bandwidth? What is the additional problem using HTTP/1.0 together with TCP? How does HTTP/1.1 improve the situation?
How does caching improve access time and reduce bandwidth requirements? What are locations for a cache and their specific advantages?
What are problems of caches in real life? What type of content can be cached, which content causes problems? What are the additional problems with client mobility?
What discrepancies exist between the possibilities of HTML and the realities of wireless handheld devices? What are the proposed solutions? What is the role of plug-ins today and how do they
Name mechanisms to improve web access for handheld devices. What is their common problem and what led finally to the development of WAP?
What are typical enhancements to the basic client/server architecture of the web? Reconsider these enhancements for a mobile wireless user with web access over a mobile phone network. What are

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