清華大學 計算機網路 第1週小考

(+10)	(10%)Which of the following are “internet applications” ? (多選)
		(a)Wechat
		(b)Routers
		(c)Facebook
		(d)On-line games
		(e)Internet protocol (IP protocol)

(+10)	(10%)Which of the following statements are correct for “links” of a network? (多選)
		(a) A “point-to-point” link is a link to connect two devices or hosts.
		(b) A “point-to-point” link is a link to connect more than two devices or hosts.
		(c) A “multiple access” link is a link to connect multiple devices or hosts.
		(d) The IEEE 802.11 wireless LAN (WiFi) is a multiple access link.
		(e) A “multiple access” link is a link to connect only two devices or hosts.

(+10)	(10%)Which of the following statements are correct for “store-and-forward” concept ? (多選)
		(a) It’s a way for a network device to handle an incoming packet by storing the packet first and then forwarding the packet according to some switching/routing policy.
		(b) A router usually stores an incoming packet in the memory first and then lookups the IP routing table to determine which port to forward the packet.
		(c) A layer 2 switch usually stores an incoming frame in the memory first and then lookups the IP routing table to determine which port to forward the frame.
		(d) A layer 2 switch usually stores an incoming frame in the memory first and then lookups the MAC address table to determine which port to forward the frame.
		(e) The store-and-forward technology is usually used in a packet switched network.

(+10)	(10%)Which of the following statements is correct for delivering packets (datagrams) over the Internet ? (單選)
		(a) All packets destined to the same destination will be forwarded along the same routing path.
		(b) The routing path of a packet is determined first before the packet is sending into the Internet.
		(c) The Internet is reliable so that all packets will be received by the destination correctly.
		(d) A packet may be partitioned into several fragments by routers.
		(e) All fragments of a packet will be forwarded along the same path to the destination.

(+10)	(10%)Which of the following statement is correct for “statistical multiplexing” ? (單選)
		(a) The bandwidth used by different flows is the same.
		(b) Data are transmitted only based on the arrival time of each flow.
		(c) Data are transmitted based on demand of each flow.
		(d) The statistical multiplexing is fair due to the bandwidth used by different flows are the same.
		(e) Compared to TDM (Time-Division-Multiplexing) and FDM (Frequency-Division-Multiplexing), the statistical multiplexing provides the same link utilization

(+6)	(10%)Which of the following statements are correct to describe the “packet encapsulation” ? (多選)
		(a) For sending node, the data from application level will be encapsulated larger and larger until to the physical level.
		(b) For receiving node, the data from physical level will be decapsulated smaller and smaller until to the application level.
		(c) The TCP segment is encapsulated into the IP datagram. That’s the IP protocol treats the TCP segment as data.
		(d) The IP datagram is encapsulated into the underlying MAC frame. That’s the MAC protocol treats the IP datagram as a data.
		(e) For a router, it first uses decapsulation scheme to get an IP datagram from the receiving port, and then uses encapsulation scheme to transmit the IP datagram.

(+10)	(10%)Which of the following links belong to the “physical layer” ? (多選)
		(a) Coaxial cable
		(b) Twisted pair cable
		(c) Optical Fiber
		(d) Air space
		(e) Power line

(+10)	(10%)We say that a device is a “layer 2” device if it implements only data link layer protocol and physical layer protocol. Which of the following devices are usually layer 2 devices ? (多選)
		(a) Routers
		(b) Bridges
		(c) Firewalls
		(d) Switches
		(e) Load Balancers

(+10)	(10%)The “transmission time” of a network interface (card) to transmit a packet is defined as “packet size/bandwidth”. For a 1Mbps Ethernet interface, what is the transmission time to transmit a packet of size 500 bytes ? (note that 1 byte = 8 bits) (單選)
		(a) 800 us
		(b) 4 ms
		(c) 8 ms
		(d) 40 ms
		(e) 80 ms

(+10)	(10%) The channel between a pair of processes can be viewed as a pipe. Delay x Bandwidth means how many data can be stored in the pipe. For a pipe with a delay of 40 ms and bandwidth of 1000 Mbps, how many data can be stored in the pipe ? (Mbps = Mega bits per second, and MB = Mega Byte) (單選)
		(a) 1 MB
		(b) 5 MB
		(c) 10 MB
		(d) 40 MB
		(e) 100 MB