Suppose two packets arrive to two different input ports of a router at exactly the same time. Also suppose there are no other packets anywhere in the router. Suppose the two packets are to be forwarded to two different output ports. Is it possible to forward the two packets through the switch fabric at the same time when the fabric uses a shared bus? Suppose the two packets are to be forwarded to two different output ports. Is it possible to forward the two packets through the switch fabric at the same time when the fabric uses switching via memory? Suppose the two packets are to be forwarded to two different output ports. Is it possible to forward the two packets through the switch fabric at the same time when the fabric uses a crossbar? Suppose the two packets are to be forwarded to the same output port. Is it possible to forward the two packets through the switch fabric at the same time when the fabric uses a crossbar?

Consider a local area network (LAN) with multiple stations connected to the same bus using the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) protocol for medium access control. Assume that each station has a packet to transmit and follows the CSMA/CD protocol to access the medium. The first station to sense the medium finds it idle and starts transmitting its packet. The second station also senses the medium as idle and starts transmitting its packet, but halfway through the transmission, it detects a collision with the first station’s packet. After detecting the collision, the second station follows the backoff and retransmission procedure specified by the CSMA/CD protocol. Assume that the backoff algorithm uses binary exponential backoff with a maximum number of retries of 10 and that the slot time is 512 bit times. (a) What is the minimum number of slots the second station must wait before attempting to retransmit its packet after detecting the collision? Show…

Skype is a well‑known VoIP system used not only for peer‑to‑peer conversations but also for audio and video conferencing involving three or more callers. Assume a video conference with a central server on Skype has N callers, and each caller generates a constant data stream at rate r bps. How many bits per second does the call initiator need to send?  How many bits does each of other N‑1 callers need to send?

The message to be sent from source to destination is 4000B.  The link MTU's from source to destination are 1500, 1000, and 750. If we  DO NOT use Path MTU, what are the respective fragment sizes to be reassembled? If we DO use Path MTU, what are the respective fragment sizes to be reassembled? Remember, assume that the L3 and L4 headers have length=0.

In modern packet-switched networks, including the Internet, the source host segments long, application-layer messages (for example, an image or a music file) into smaller packets and sends the packets into the network. The receiver then reassembles the packets back into the original message. We refer to this process as message segmentation. Figure 1.27 illustrates the end-to-end transport of a message with and without message segmentation. Consider a message that is 8. 106 bits long that is to be sent from source to destination in Figure 1.27. Suppose each link in the figure is 2 Mbps. Ignore propagation, queuing, and processing delays. a. Consider sending the message from source to destination without message segmentation. How long does it take to move the message from the source host to the first packet switch? Keeping in mind that each switch uses store-and-forward packet switching, what is the total time to move the message from source host to destination host? b. Now suppose that…

Consider an application which transmits data at a bursty rate (e.g., the sender generates  data for short burst of time and the sender is idle almost all the time)Would a packet-switched network or a circuit-switched network be more appropriate for this application?Why?

Suppose Alice and Bob are going to communicate using AES in CBC mode. Unfortunately Alice's message length (in bytes) is not a multiple of 16. Suppose the last block of her message is just a single zero byte. How can she pad out the last block so that she can use CBC mode? Since this needs to be a reversible operation, how does Bob recognize the padding and remove it?

Give a simple heuristic for finding two paths through a network from a given source to a given destination that can survive the loss of any communication line (assuming two such paths exist). The routers are considered reliable enough, so it is not necessary to worry about the possibility of router crashes.

4. In this problem, you will derive the efficiency of a CSMA/CD-like multiple access protocol. In this protocol, time is slotted and all adapters are synchronized to the slots. Unlike slotted ALOHA, however, the length of a slot (in seconds) is much less than a frame time (the time to transmit a frame). Let S be the length of a slot. Suppose all frames are of