Final questions I could think of. What is the purpose of the bind system call? Give a short piece of code to implement a 5 second timeout. Given, char name [5] = "TEST"; short count = 85; and assuming that a TCP connection has been established with socket s, give a short piece of code to send a buffer containing the string test, followed by the value of count in network byte order. A satellite is used to transpond communications from one earth station to another. It takes 0.25 sec to travel from the earth to the satellite and processing latency is negligible. If the signal bandwidth is 1 Mbps, what is the appropriate window size for a sliding window protocol? In the previous question, two packet sizes have been proposed -- 400 bits and 4000 bits. Discuss the advantages and disadvantages of the two alternatives. If there are 100 possible users of the signal, what are three ways that you could allow them to share the bandwidth? You could use either analog or digital signalling on this link. What are the advantages and disadvantages of each. If you choose digital, what are the encoding methods you might use? For analog what methods could you use? You are sending a byte of data that represents your bet to the Blackjack server. If you looked at the actual message on the network cable, what would you see in the packet? What OSI layer is responsible for insuring that your message is received correctly by the server? Why would you use 4B/5B encoding? Shannon's Theorem is "R = H log2 (1 + N)". Define R, H and N. Why does the Ethernet specify a maximum length of cable? What bad thing happens to the Ethernet protocol if you increase the data rate to 100 Mbps? What is the solution? How much time is saved by using early release in an FDDI ring with a length of 1000 m? You may give the answer mathematically or descriptively. Under what usage conditions would a token ring be superior to CSMA/CD? Given a slot time, S, in a CSMA/CD network, how much time is saved by using CD? Given a slot time, S, if a host tries to send a message over an Ethernet three times and collides, what is the best and worst case time on the fourth attempt? What type of framing does IP use? Ethernet? Under what conditions would you use a simplex stop--and--wait protocol? Give an example of such a protocol that is commonly used. What are the advantages and disadvantages of using NAK's in a sliding window protocol? Given the following diagram Show the virtual circuit forwarding tables at R3 after the following connections are opened: H5 to H4, H3 to H4 and H4 to H1. Assume that each host actually represents a subnetwork. Show the routing tables for R3 if link state routing is used. What is the purpose of the ATM Adaption Layers? When would you use a bridge instead of a router? What is meant by the term "learning bridge"? If a bridge using the spanning tree algorithm fails, how does that portion of the subnet get connected to the rest of the subnet? Explain why Internet multicast is a major problem for bridges and routers? Why does IP have a Header Length field in its header? The IP header has an Identifier field. Why does it not have to be set to a random integer as the TCP sequence number field is? An IP packet with a length of 2000 bytes reaches a router with an outgoing MTU of 1000 bytes. Later, the first fragment passes through a subnet with an MTU of 500 bytes. Ignoring the header length in the fragmentation, show the fragments that arrive at the destination? What happens if a fragment of an IP packet is not delivered? IP uses a store-and-forward routing method. What does an IP router do with a packet whose IP address is not in its routing table? Currently, we have the following situation with respect to our subnet. A host looks at the IP address of a destination and sees that it is the same as its own and then uses ARP to get the hardware address. Explain how the router make the two segments look like they are on the same network. Give two reasons that ICMP cannot make IP a reliable protocol. Why would you use subnetting? Supernetting? Which routing method, distance-vector or link-state, is able to handle the loss of a router? Why? Why are interdomain routing protocols often different than intradomain routing protocols? BGP uses reachability rather than distance as a metric. Why? How does IPv6 negate the need for ARP? What is the biggest advantage of IPv6 addressing? Biggest disadvantage? Explain how IP can tunnel through IPv6. Why are the fragmentation fields no longer present in IPv6? What happens if you execute a gethostbyname call in a program? What is the maximum number of DNS requests that might be generated by a non-recursive request from a host? Explain why? Why do routers often have more than one IP address? Why does ARP have a timeout procedure for its cache? What would you do to allow IP to run over a connection-oriented network like X.25? What is the purpose of the port entries in the UDP and TCP headers? What is the difference between flow control and congestion control? What would be the purpose of putting a 32-bit time stamp in the TCP header? Why is the TCP timeout not fixed for a given connection? Describe the three way handshake that TCP uses. What is the purpose? What is meant by out-of-band data? How does TCP handle this problem? When TCP sends a frame, the ACK value is giving the receiver what specific information? What is the difference between the Advertised Window and the Effective Window for a TCP connection? If a TCP receiver advertises a zero byte window, how does the sender know when it can send again? What is the problem with the AdvertisedWindow field in the TCP header? If the length of a run is limited to 15 occurrences, what is the best case compression that RLE encoding can produce? The worst case? Give an example of a JPEG quantization table that will cause the low frequency elements of the image to be reduced while the high frequency remain. Show how the JPEG quantization process results in data compressesion. Why do networks have more security problems than centralized systems? What are the types of security problems that encryption can help resolve? Explain authentication.