Guests Host Telephone Telephone line Pizza cook Order clerk Telephone Guests Host Delivery van Road Pizza cook Order clerk Delivery van Figure 2.15 Architecture for Problem 2.1 1. 2. 3. Homework 1 Using the layer models in Figure 2.15, describe the ordering and delivery of a pizza, indicating the interactions at each level. a. The French and Chinese prime ministers need to come to an agreement by tele- phone, but neither speaks the other's language. Further, neither has on hand a translator that can translate to the language of the other. However, both prime ministers have English translators on their staffs. Draw a diagram similar to Figure 2.15 to depict the situation, and describe the interaction at each level. b. Now suppose that the Chinese prime minister's translator can translate only into Japanese and that the French prime minister has a German translator available. A translator between German and Japanese is available in Germany. Draw a new diagram that reflects this arrangement and describe the hypothetical phone conversation. In Figure 2.5, exactly one protocol data unit (PDU) in layer N is encapsulated in a PDU at layer (N-1). It is also possible to break one N-level PDU into multiple (N-1)-level PDUs (segmentation) or to group multiple N-level PDUs into one (N-1)-level PDU (blocking). a. In the case of segmentation, is it necessary that each (N-1)-level segment con- tain a copy of the N-level header? b. In the case of blocking, is it necessary that each N-level PDU retain its own header, or can the data be consolidated into a single N-level PDU with a single N-level header? 4. A TCP segment consisting of 1500 bits of data and 160 bits of header is sent to the IP layer, which appends another 160 bits of header. This is then transmitted through two networks, each of which uses a 24-bit packet header. The destination network has a maximum packet size of 800 bits. How many bits, including headers, are delivered to the network layer protocol at the destination? 5. Why is UDP needed? Why can't a user program directly access IP? 6. IP, TCP, and UDP all discard a packet that arrives with a checksum error and do not attempt to notify the source. Why? IP header TCP header User data Application byte stream TCP segment IP datagram Network header Figure 2.5 Protocol Data Units (PDUs) in the TCP/IP Architecture Network-level packet