S-38.188 exam, September 29, 2003

Answers and grading policy (Lx:Sy = lecture nr. x, slide nr. y)

• Correct acronym (0.5p), short explanation (0.5p)

• Addresses (2p): nof bits, uniqueness, hierarchical/not hierarchical
• Forwarding/routing (3p): extended LANs use simple bridges or learning bridges, no optimality criteria used; in intra domain shortest path routing is used, RIP or OSPF algorithms (+short explanation of their basic operation)
• topology (1p): in extended LANs topology must be tree-like unless spanning tree algorithm is used which allows loops in the topology; intra-domain routing allows arbitrary topologies

• a) problem: inefficient address allocation, solution: CIDR defines a variable length network mask, address notation x.x.x.x/y, y = prefix length (2p); packet forwarding: AND(dest addr, CIDR network address), "longest match" rule, NOTE! each packet carries just a normal IP address in the packet header, CIDR addresses are only known by routers (distributed through BGP-4) (1p)
• b) DHCP role and operation (2p), IPv6 and "stateless autoconfiguration" (1p)

• a) flow control = sender does not over load receiver's buffer; cong control = sender does not over load network
• b) explanation of slow start (1p) (note! cwnd increased by 1 for each ACK! => doubled/RTT!); explanation of AIMD (1p) (note! cwnd increased by 1/cwnd for each ACK => 1/RTT!)
• c) Typically, TCP retransmissions are useless for real time operation and therefore use of UDP is often more appropriate.
• d) basic idea (1p): try to control congestion when it is building up (not react when it has already happened); RED operation (1p); NOTE! RED packet dropping is a function of AVERAGE queue length

• a) MIME L11:S13 (1p), POP/IMAP, SMTP, push-technique (from server to server)) (2p)
• b) terminology (1p), explanation of MD5 (1p), explanation of RSA (1p)
• NOTE! The last part of question b), i.e., about explaining the use of RSA and MD5 for authentication and integrity, was not evaluated (any errors there were not taken into account). The question was complicated enough for a 3p question without it.

Valitustilaisuus

If you have questions or want to inspect your paper, the official "valitustilaisuus" is on Wednesday, October 29, at 10-11 o'clock. The place is D302 (meeting room of Networking Laboratory)).

Results

Note! The final grade for the course is determined by giving the weights 25% to the assignment and 75% to the exam grade, i.e., final_grade = (assignment_grade + 3*exam_grade)/4.