1. Multiple Choice (30 points, 1.5 points for each question)
(1). Which of the following protocols is NOT an application protocol ? _________
A. FTP
B.HTTP
C.ARP
D.DHCP
(2). Among the following applications, which one is not suitable for P2P architecture ?
___
A. file sharing
B. electronic banking
C. video streaming
D. instant message
(3). The transfer of an Web document from one host to another is:
A. loss-intolerant and time insensitive
B. loss-tolerant and time sensitive
C. loss-intolerant and time sensitive
D. none of the above
(4). Suppose a browser sends an HTTP request message with the If-modified-since:
header. Suppose the object in a server has not changed since the last time a client retrieved the object. Then the server will send a response message with the status code:
A 404 Not Found
B 304 Not Modified
C 200 OK
D None of the above
(5). In modern packet-switched networks, the source host splits long, application-layer
packets (for example, an image or a music file) into smaller packets and sends the packets into the network. This technic is called _________
A. route aggregation
B. IP fragmentation
C. IP reassemblysegment datagram
D. message segmentation
(6). If a segment carries data along with an acknowledgment, this is called _______.
A. backpacking
B. piggybacking
C. out-of-band
D. piggy packing
(7). UDP offers which of the following benefits relative to TCP?
A. UDP consumes fewer computer resources by not maintaining connection state
B. UDP supports a self-regulating “throttle” feature that prevents network saturation
C. UDP guarantee s that Individual packets of a transmission will arrive “in order”
D. None of the above
(8). In TCP, the timeout interval is a function of ______:
A. estimated RTT at the sender
B. MSS and the overhead of a
segment
C. the size of buffer at the receiver
D. the size of sending window
(9). How many bits are there in IP v6 ? _________
A. 32
B. 64
C. 128
D. 256
(10). In CIDR notation, which of the following networks contains host 192.168.14.2?
A. 192.168.10.0/22
B. 192.168.11.0/21
C. 192.168.12.0/23
D. 192.168.13.0/24
(11). Which of the following protocol belongs to intra-AS routing protocol? _________
A. RIP
B. BGP
C. DV (Distance Vector)
D. LS (Link State)
(12). IP is a _________ protocol.
A. connection-oriented unreliable
B. connection-oriented reliable
C. connectionless unreliable
D. connectionless reliable
(13). In ________ , each station sends a frame whenever it has a frame to send.
A. ALOHA
B. sloted ALOHA
C. CSMA
D. CSMA/CD
(14). __________ layer handles the physical addre ssing of communicating devices
A. Physical
B. Logical
C. Data link
D. Network
(15). Which best describes the Ethernet protocol?
A. T alk only if you hear no one else talking, but stop as soon as you hear anybody
else.
B. Pass a ticket around and only talk if you are holding the ticket.
C. Raise your hand and wait till a moderator gives you permission to talk.
D. Every person is scheduled a time to talk.
(16). In an Ethernet frame, the preamble is responsible for ______
A. collision detection
B. error detection
C. synchronization of the receiver’s clock to the sender’s clock.
D. multiplexing/ demultiplexing
(17). Which of the following packet delay is the time waiting at the output link for
transmission and depends on the congestion level of router? _________
A. transmission delay
B. propagation delay
D.processing delay
(18). The following technologies may be used for residental access, except _________
A. HFC
B. DSL
C.dial-up modem
D. FDDI
(19). The performance of a network can be measured in terms of ________.
A. delay
B. throughput
C. packet loss
D. all of the choices are correct
(20). What is the name of the algorithm used in CSMA/CD networks in order to avoid
repeated collisions?
A. collision avoidance
B. crash prevent
C. exponential back-off
D. exponential collisions
2. True or False ( 20 points, 2 point for each statement )。
(1). When a user request a Web page that consists of some text and two images. For
this page, the client will send one request message and receive three response messages.
(2). Local DNS name servers cache resource records, but discard them after a period of
time that is on the order of a few days.
(3). A source’s retransmi ssion timeout value is always set equal to the measured RTT.
(4). In TCP, the acknowledgement number that a host puts in a segment is the
sequence number of the next byte the host is expecting from the sender.
(5). Suppose that host A wants to send data over TCP to host B, and host B wants to
send data to host A over TCP. Two separate TCP connections - one for each direction - are needed.
(6). The stop-and-wait protocol is highly inefficient when there is a large distance
between source and destination and the transmission rate is high.
(7). As a link state algorithm, RIP plays an important role in LAN.
(8). A gateway router can obtain subnet reachability information from another gateway
router in neighboring As by iBGP.
(9). Suppose a router has n input ports each with identical line speeds, n output ports
each with identical line speeds, and the line speed of an output port is at least n
times as that of an input port. Further suppose that the switching fabric speed is at
least n times as fast as an input line speed. Then queuing can occur in an output
port
(10). Switches decrement the TTL field in the IP header
3. please answer the following questions briefly (30 points, 10 points for each question)
(1)The fig 1 shows a portion of the internet with four autonomous systems, one of which is shown with four routers,
each with its own /16 subnet. Note that each of the other ASs has a /8 subnet.
A.Assume that AS1 uses a LS algorithm as its intra-AS routing algorithm and each node initially knows the
costs to each of its neighbors. Show how node C compute the shortest path to all the other nodes (5 points)
Fig 1
B.Assume that BGP as the inter-AS routing algorithm among these ASes and there are no policy constraints
that must be satisfied. Please complete the forwarding table of node C.(3 points)
C.Suppose the link joining router B with AS3 fails, which entries would change, and how would they change? (2
points)
(2) A host using TCP/IP receives the following 10 fragments in the following order. For ease of reference, the
fragments are labeled from A-J. Assume an IP header is 20 bytes and a TCP header is 20 bytes.
A.In what order are the fragments delivered from the network layer to the transport layer, starting with the first? (3
points)
B.How many total bytes are sent in these 10 fragments (ignore link layer headers)? (3 points)
C.How much application layer data (application layer header + message) is sent in these 10 fragments? (4
points)
(3)Consider a TCP connection using the slow-start congestion control scheme with an initial THRESHOLD value of
64 kB and a Maximum Segment Size (MSS) of 4 kB. The receiver’s advertised window is initially 24 kB. The first
transmission attempt is numbered 0, and all transmission attempts are successful except for Timeouts on attempt number 4. In the A CKs for transmission attempt number 9 and subsequently, the receiver’s advertised window is reset to 20 kB. Find the size in kB of the sender’s sending window for its first 11 transmission attempts (numbers 0 – 10)
5. Analysis (20 points,)
(1) As in fig 2. There is new host moves into a network. Thus the new host has to get its IP address
from the DHCP server running on the router. Please list the sequence of packets sent or received by the new host until it gets a IP address 192.168.1.4. Please indicate the source and destination MAC address, the source and destination IP address, and the source and destination port number of each packet.(8 points)
new host is set as 192.168.1.2 and 192.168.1.3, respectively. Now, the user of the new host wants to access an url on the web server www.scu.edu. Luckily the dns cache of local dns server has cached the RR of www.scu.edu. On the other hand, ARP table of all the nodes in fig 3 are empty. Please list the sequence of all the packets sent/received by the new host as well as any other packets sent/received by as other nodes. Please idicate the source and destination
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