cs final study
Suppose a packet is L = 1500 bytes long (one byte = 8 bits), and link transmits at R = 10 Mbps (i.e., a link can transmit bits 10,000,000 bits per second). What is the transmission delay for this packet?
0.0012 secs - (1500 * 8) / 10,000,000 = 0.0012
Consider the scenario shown below, with a single source client sending data to a server over three links of capacities R1=100 Mbps, R2=50 Mbps, and R3=25 Mbps. What is the utilization of the link of capacity R1?
0.25 (lowest / r1)
Consider the scenario below, with four servers connected to four clients. The four pairs fairly share a common middle hop with a transmission capacity of R = 500 Mbps. Each of the four links from the servers to the shared link has a transmission capacity of RS = 50 Mbps. Each of the four links from the shared middle link to a client has a transmission capacity of RC = 150 Mbps. What is the utilization of each of the Rc links, assuming that all servers are trying to transmit at their maximum rates at the same time?
0.33 Effective throughput = 50 Mbps Utilization = used/available = 50/150 = 0.33
Compute the Internet checksum value for these two 16-bit words: 01000001 11000100 and 00100000 00101011
10011110 00010000
HTTP port
80
What is the value of ACK in the following scenario?
90
Please order the TCP/IP Internet protocol stack from top to bottom
Application Transport Network Link Physical
Which of the following is an example of an application that is NOT loss tolerant?
What is the role of the authoritative DNS name server?
It provides the definitive answer to the query with respect to a name in the authoritative name server's domain.
Which of the following is an example of a loss-tolerant application?
Video streaming
TCP properties
reliable, in-order delivery
Briefly explain how CDNs (Content Distribution Network) work.
store/serve multiple copies of videos at multiple geographically distributed sites
Time spent transmitting ("pushing") bits into the link.
transmission delay
We need a bigger range of sequence numbers for pipelined reliable data transfer.
true
WiFi is an example of unguided physical media.
true
The TCP sender sends an initial window of 5 segments. Suppose the initial value of the sender->receiver sequence number is 300, and the first 5 segments each contain 150 bytes. The delay between the sender and receiver is 8 time units, and so the first segment arrives at the receiver at t=8. The receiver's ACKs are (starting from t=9):
x, 300, x, x, 300
Refer to the network topology above. According to NAT terminology, (a) the IP address 165.129.15.38 is considered an (b) the IP address 160.27.9.5 is considered an
(a) outside global address (b) inside global address
Which of the characteristics below are associated with the technique of packet switching? Select all correct answers.
- Resources are used on demand, not reserved in advance. - Congestion loss and variable end-to-end delays are possible with this technique.
Which two values are used to identify a UDP socket?
- destination port number - destination IP address
Explain how Frequency Division Multiplexing (FDM) works in circuit switching.
- optical, electromagnetic frequencies divided into (narrow) frequency bands - each call allocated its own band, can transmit at max rate of that narrow band
What advantages do web caching offer?
- reduce response time for client request - reduce traffic on an institution's access link
Suppose a packet is L = 1200 bytes long (one byte = 8 bits), and the link transmits at R = 100 Mbps (i.e., a link can transmit 100,000,000 bits per second). What is the transmission delay for this packet?
0.000096 secs - (1200 * 8) / 100,000,000 = 0.000096
Consider the scenario shown below, with a single source client sending data to a server over three links of capacities R1=300 Mbps, R2=50 Mbps, and R3=25 Mbps. What is the utilization of the link of capacity R2?
0.50 - Utilization = (Used/Available) = (25/50) = 0.5
Two clients are sending data to a server. The links attached to the clients each have a capacity of R1= R2 = 10 Mbps. The link from the router to the server has a capacity of R3 = 100 Mbps, which is shared evenly between the two sources when they are each sending at their maximum rate. What is the utilization of the R1 link, assuming that both clients are trying to send at their maximum rates?
1.0
Two clients are sending data to a server. The links attached to the clients have the following capacities: R1= 30 Mbps and R2 = 10 Mbps. The link from the router to the server has a capacity of R3 = 500 Mbps, which is shared evenly between the two sources when they are each sending at their maximum rate. What is the utilization of the R1 link, assuming that both clients are trying to send at their maximum rates?
1.0 Both sources can transmit at their full capacity as R3 does not create a bottleneck. Therefore, the utilization of R1 will be 1.0 (full utilization).
Three servers are connected to three clients as shown in the diagram below. The three server-client pairs share a common middle link with a transmission capacity of R = 1 Gbps. Each of the three links from the servers to the shared link have a transmission capacity of Rs = 200 Mbps. Each of the three links from the shared middle link to a client has a transmission capacity of Rc = 100 Mbps. What is the maximum achievable end-end throughput for each of three client-to-server pairs, assuming that the middle link is fairly shared (divides its transmission rate equally)?
100 Mbps
How many hosts are available if you have a network with a subnet mask of 255.255.252.0?
1022 Available hosts = (2^10) - 2 = 1024 - 2 = 1022
IPv6 length
128 bits
Consider the network shown in the figure below, with three links, each with a transmission rate of 2 Kbps, and a propagation delay of 1 msec per link. Assume that there is no queuing or processing delay. If the length of a packet is 10 bits, what is the end-to-end delay of a single packet from when it first begins transmission from PC A, until is it received in full by the Server?
18 msec
Determine which two of the following devices are on the same network as host M. Host M: 192.168.8.46/23
192.168.9.4/23 and 192.168.8.152/23
Three servers are connected to three clients as shown in the diagram below. The three server-client pairs share a common middle link with a transmission capacity of R = 600 Mbps. Each of the three links from the servers to the shared link have a transmission capacity of Rs = 300 Mbps. Each of the three links from the shared middle link to a client has a transmission capacity of Rc = 250 Mbps. What is the maximum achievable end-end throughput for each of three client-to-server pairs, assuming that the middle link is fairly shared (divides its transmission rate equally) and all servers are transmitting simultaneously?
200 Mbps Maximum end-to-end throughput depends on the bottleneck link (link with the smallest capacity). Here, the bottleneck is R. With fair sharing of the common middle link, per-connection end-to-end throughput = min(Rc, Rs, R/3) = 200 Mbps
SMTP port
25
The TCP sender sends an initial window of 5 segments. Suppose the initial value of the sender->receiver sequence number is 300, and the first 5 segments each contain 150 bytes. The delay between the sender and receiver is 8 time units, and so the first segment arrives at the receiver at t=8. The sender's sequence numbers associated with each of the five segments (starting from t=1) are:
300, 450, 600, 750, 900
IPv4 length
32 bits
DNS port
53
Suppose a Web server has five ongoing connections that use TCP receiver port 80. How many TCP sockets are currently open at this server?
6 (One welcoming socket and five client sockets.)
Consider the circuit-switched network shown in the figure below, with four circuit switches A, B, C, and D. Suppose there are 10 circuits between A and B, 15 circuits between B and C, 25 circuits between C and D, and 10 circuits between D and A. What is the maximum number of connections that can be ongoing in the network at any one time?
60 sum of all circuits
What is the valid IP host range for the network where 64.9.7.18/27 belongs to?
64.9.7.1 - 64.9.7.30
Suppose a webpage consists of one index.html file that references five image (JPG) files located on the same server. If persistent HTTP is used to access that webpage, what will be the total response time?
7 RTT + file transmission time Persistent HTTP requires 1 RTT for TCP connection, and then 1 RTT per object.
Consider the circuit-switched network shown in the figure below, with four circuit switches A, B, C, and D. Suppose there are 20 circuits between A and B, 15 circuits between B and C, 25 circuits between C and D, and 10 circuits between D and A. What is the maximum number of connections that can be ongoing in the network at any one time?
70
Suppose a webpage consists of one index.html file and three image (JPG) files. If non-persistent HTTP is used to access that webpage, what will be the total response time?
8 RTT + file transmission time (non-persistent HTTP requires 2 RTTs per object)
Consider the network shown in the figure below, with three links, each with a transmission rate of 5 Kbps, and a propagation delay of 1 msec per link. Assume that there is no queuing or processing delay. If the length of a packet is 10 bits, what is the end-to-end delay of a single packet from when it first begins transmission from PC A, until is it received in full by the Server?
9 msec Transmission delay per link = (10 bit / 5Kbps) = (10/5000) sec = 0.002 sec = 2 msec Propagation delay per link = 1 msec So, total end-to-end delay = 3 * (2+1) = 3 * 3 = 9 msec
Order the Transport layer actions at the receiver
Begin - receives segment from network layer - checks header and extracts the application layer message - demultiplexes message up to the application via socket
Optical fiber is an example of unguided physical media.
False
Briefly explain how the traceroute program works. What information can we find by using traceroute?
Function: - sends three "probe" packets to each router on the path toward the destination - routers will return packets to the sender - the sender measures the time interval between transmission and reply Information: Delay measurement from source to each hop (router) along end-end Internet path toward the destination
Consider the following scenario where Alice is sending an email to Bob. Which protocol is used in step 6 to transfer Alice's message from Bob's mail server to Bob's user agent?
IMAP
Briefly explain how spatial (within image) coding works in video compression.
If an image has a portion where there are a lot of pixels (N) with the same color, we could send only two values: color value (e.g., purple) and the number of repeated values (N). This is way better than sending N values of the same color (all purple).
How does packet loss happen in a network?
If arrival rate (in bps) to link exceeds transmission rate (bps) of the link for a period of time, packets can be dropped (lost) because memory (buffer) in router fills up.
Consider again the SDN OpenFlow network shown above. Suppose that the desired forwarding behavior for datagrams arriving at s1 is as follows: any arriving datagrams on input port 4 and destined to hosts h5 or h6 should be forwarded over output port 1; Write a single match+action flow table row entry to implement that rule in s1. The * is a wildcard match, which matches everything.
Match Port = 4 IP Src = * IP Dst = 10.3.0.* Action: Forward(1)
We know IPv4 address space is insufficient for the growing number of Internet-connected devices, and ICANN ran out of available IPv4 addresses in 2011. Explain how this shortage of IPs has been solved. In other words, (i) which technologies and (ii) how have they allowed us to support the enormous number of hosts?
NAT is the main technology. As we have discussed in class, adoption of IPv6 in routing has been minimal and IPv4 is still the primary way networking works as of now. NAT: one or more local IP address is translated into one or more Global IP addresses and vice versa
What do you understand by public vs. private IP addresses? Explain the use cases or applications for both types.
Private IP addresses: non-routable over the Internet. Used to create LANs and Intranets (inside networks). There are 3 ranges that we can pick from. These addresses are free to use. Public IP addresses: Routable over the Internet and costs money to get such an address.
Consider the following scenario where Alice is sending an email to Bob. Which protocol is used in step 4 to transfer Alice's message from her mail server to Bob's mail server?
SMTP
What is the purpose of using TLS (Transport Layer Security)?
TLS provides encrypted TCP connections, and thus protects sensitive information sent into TCP socket as cleartext.
Explain how DASH (Dynamic, Adaptive Streaming over HTTP) works.
The server divides the video file into multiple chunks of different qualities. The client uses a manifest file to request chunks based on the link quality. Clients can switch to a different quality level depending on the available bandwidth.
Which of the following is responsible for a domain (e.g., *.com, *.edu), and knows how to contact authoritative name servers?
Top Level Domain (TLD) servers
Briefly explain how BitTorrent uses the "tit-for-tat" approach when sending chunks to peers.
a user sends chunks to those four peers currently sending chunks to him/her at highest rate. Reevaluate every 10 secs. Random peer selected every 30 secs
Routing
determine the entire trip from source to destination
Determine if the following devices are on the same subnet or different subnets. Device A: 172.16.29.30/20 Device B: 172.16.32.25/20
different 172.16.29.30 = 10101100.00010000.0001 1101.00011110 172.16.32.25 = 10101100.00010000.0010 0000.00011001 (keep dividing number by 2, if its even its 0, if not its 1) (also, if it was 43/2, ROUND DOWN to 21)
TCP segments from four different processes, all destined to the same IP address (136.15.10.2) and same destination port (80) are demultiplexed to
different sockets
Which is NOT true about client-server architecture?
end systems directly communicate
Which of the following physical layer technologies has the highest transmission rate and lowest bit error rate in practice?
fiber optic cable
Suppose a router has five interfaces, numbered 0 through 4, and packets are to be forwarded to the interfaces as follows: Determine the appropriate interface for a datagram with the following destination address: 11100001 01000000 11000011 00111100
interface 2
Forwarding
move packets from a router's input link to appropriate output link
Time needed to check bit errors, determine output link.
processing delay
Time needed for bits to physically travel through the transmission medium from one end of a link to the other.
propagation delay
Time waiting at output link (packet buffer) for transmission
queueing delay
When requesting missing chunks from peers, which policy is followed by the BitTorrent protocol?
rarest first
What does the HTTP response status code 200 mean?
request succeeded, requested object later in this message
Traditional routing plane
routers interact with each other and use routing algorithms to build forwarding table
Software-Defined Networking (SDN) routing plane
routers receive their forwarding table from a central, remote controller
Why is client-side buffering is used in video streaming?
to compensate for network-added delay
When multiple UDP clients send UDP segments to the same destination port number at a receiving host, those segments (from different senders) will always be directed to the same socket at the receiving host.
true
UDP properties
unreliable, unordered delivery
Where are cookies stored?
user device
