Network Fundamentals
Suppose there is only one router between a source host and a destination host. Ignoring fragmentation, how many forwarding tables will be indexed to move an IP datagram from the source to the destination?
1
An ISP has been allocated the address block 200.23.87.0/27. The ISP wants to divide its address block into four equal-sized contiguous address blocks and give these address blocks to four organizations. Subnet masks for each of these organizations:
29
C onsider that an ISP may have been allocated the address block 200.23.16.0/26. The ISP wants to divide its address block into eight equal-sized contiguous address blocks and give one of these address blocks out to each of up to eight organizations that are supported by this ISP. What will be the subnet masks for each of these organizations?
29
Generally, how long does it take a packet of length L to propagate over a link of distance d, propagation speed s, and transmission rate R bps?
d/s
There are two broad approaches to congestion control that are taken in practice; Network-assisted congestion control, and end-to-end congestion control. Which of these congestion controls does the TC P use?
end-to-end congestion control
In a client-server interaction, if all of the requests and their corresponding responses are sent over the same TCP connection, then the application is said to use __________ connections.
persistent
In addition to knowing the address of the host to which a message is destined, the sending process must also identify the receiving process ( more specifically, the receiving socket) running in the host. This information is needed because in general a host could be running many network applications. A destination ______ number serves this purpose.
port
Fill in the two blanks: In the TC P implementation, consider the length of the timeout interval after a timer expiration. Whenever the timeout event occurs, TC P retransmits the not-yet-acknowledged segment with the smallest sequence number. For example, suppose TimeoutInterval associated with the oldest not yet acknowledged segment is 1.5 sec when the timer first expires. TC P will then retransmit this segment and set the new expiration time to ____ sec. If the timer expires again, TC P will again retransmit this segment, now setting the expiration time to ____ sec.
3 sec, 6 sec
Suppose Host A sends two TC P segments back to back to Host B over a TC P connection. The first segment has sequence number 40: the second has sequence number 70. a. How much data is in the first segment? b. Suppose that the first segment is lost but the second segment arrives at B. In the acknowledgment that Host B sends to Host A, what will be the acknowledgment number?
30 bytes ack number = 40
Suppose there is only one router between a source host and a destination host. Ignoring fragmentation, an IP datagram sent from the source host to the destination host will travel over how many interfaces?
4
C onsider sending a 280-byte datagram into a link with a MTU of 220 bytes. Two fragments are generated. Assume no options in IP header. How many byte of data is carried in the data field (payload) of the second fragment (second IP datagram)?
60
C onsider sending a 140-byte datagram into a link with a MTU of 100 bytes. Suppose the original datagram has the identification number 132. Two fragments are generated. Assume no options in IP header. For the second fragment, its size is ____, the value of its identification is ____, fragment offset is ____, and fragment flag is _____. Answer in this order; size, ID, offset, flag.
60, 132, 10, 0
C onsider sending a 220-byte datagram into a link with a MTU of 180 bytes. Suppose the original datagram has the identification number 322. Two fragments are generated. Assume no options in IP header. For the second fragment, its size is ____, the value of its identification is ____, fragment offset is ____, and fragment flag is _____. Answer in this order; size, ID, offset, flag.
60, 322, 20, 0
C onsider sending a 280-byte datagram into a link with a MTU of 220 bytes. Two fragments are generated. Assume no options in IP header. For the second fragment, its size is ____.
80
Generally, how long does it take to transmit a packet of length L over a link of distance d, propogations speed s, and transmission rate R bps?
L/R
After the handshaking phase, ________ connection is said to exist between the sockets of the two processes.
TCP
Which protocol provides flow control (sender/receiver speed matching)?
TCP
______ provides a congestion-control mechanism, so that a source throttles its transmission rate when the network is congested.
TCP
Layers four and five of the Internet protocol stack are implemented in the end systems but not in the routers in the network core. t f
True
OSPF routing is used for intra-AS routing in the Internet. t f
True
Routers within the same AS (autonomous system) all run the same routing algorithm. t f
True
SMTP can be used to transfer mail from the sender's user agen to the sender's mail server. t f
True
The NAT-enabled router does not look like a router to the outside world. Instead the NAT router behaves to the outside world as a single device with a single IP address. t f
True
The length of the queueing delay of a specific packet will depend on the number of earlier-arriving packets that are queued and waiting for transmission onto the link. (T/F)
True
The transport layer in the receiving host does not actually deliver data directly to a process, but instead to an intermediary socket. t f
True
Transport-layer protocols are implemented in the end systems, but not in network routers. t f
True
UDP provides for error detection. That is, it determines whether bits within the UDP segment have been altered. t f
True
When a host in a home network makes a HTTP request to a web server, the NAT router manipulates the leaving IP datagram. t f
True
When a web server receives an HTTP request from a host in a home network, the web server is unaware that the arriving IP datagram manipulated by the NAT router. t f
True
With FTP, the control connection remains open throughout the duration of the user session, but a new data connection is created for each file transferred within a session (that is, the data connections are non persistent). t f
True
_______ is the least expensive and most commonly used guided transmission medium. For over a hundred years, it has been used by telephone networks. In fact, more than 99 percent of the wired connections from the telephone handset to the local telephone switch use this type of wire.
Twisted Pair Copper Wire
Suppose you wanted to do a transaction from a remote client to a server as fast as possible. Would you use UDP or TCP?
UDP
The _______ protocol provides a connectionless service to its applications. This is a no-frills service that provides no reliability, no flow control, and no congestion control.
UDP
Suppose there are one router and two links between a source and a destination. The first link has transmission rate 100 Mbps and the second link has transmission rate of 10 Mbps. Assuming that the only traffic in the network comes from the source, what is the throughput for a large file transfer?
10 Mbps
C onsider sending a 140-byte datagram into a link with a MTU of 100 bytes. Suppose the original datagram has the identification number 132. Two fragments are generated. Assume no options in IP header. For the first fragment, its size is ____, the value of its identification is ____, fragment offset is ____, and fragment flag is _____. Answer in this order; size, ID, offset, flag.
100, 132, 0, 1
Suppose your browser wants to download a html page with 10 embedded images (with file names img01.jpg, img02.jpg, ... img10.jpg). The page and the 10 images are stored on the same server. Assume non-persistent HTTP but assume that the browser can open as many parallel TC P connections to the server as it wants. How many HTTP GET requests will be sent to server?
11
Suppose your browser wants to download a html page with 10 embedded images (with file names img01.jpg, img02.jpg, ... img10.jpg). The page and the 10 images are stored on the same server. Assume persistent HTTP (HTTP1.1) and no pipelining (no parallel TC P connections). How many HTTP GET requests will be sent to server?
11
C onsider sending a 220-byte datagram into a link with a MTU of 180 bytes. Suppose the original datagram has the identification number 322. Two fragments are generated. Assume no options in IP header. For the first fragment, its size is ____, the value of its identification is ____, fragment offset is ____, and fragment flag is _____. Answer in this order; size, ID, offset, flag.
180, 322, 0, 1
Most IP datagrams do not contain options, so the typical IP datagram has a ____ byte IPv4 header.
20
C onsider sending a 280-byte datagram into a link with a MTU of 220 bytes. Two fragments are generated. Assume no options in IP header. How many byte of data is carried in the data field (payload) of the first fragment (first IP datagram)?
200
C onsider sending a 280-byte datagram into a link with a MTU of 220 bytes. Two fragments are generated. Assume no options in IP header. For the first fragment, its size is ____.
220
FTP is located at which layer of the Internet protocol stack?
Application layer
HTTP is located at which layer of the Internet protocol stack?
Application layer
Suppose a router receives an IP datagram from one link. It checks its forwarding table to determine the outgoing link, and this outgoing link has a maximum transmission unit (MTU) that is smaller than the length of the IP datagram. The data in the IP datagram is fragmented into smaller IP datagrams. Where does the reassembling these datagrams take place?
At destination host only
Post Office Protocol - Version 3 (POP3), Internet Mail Access Protocol (IMAP). Where are these protocols used?
Between recipients mail server and recipients user agent.
________ consists of two copper conductors, but the two conductors are concentric rather than parallel. With this construction and special insulation and shielding, this cable can achieve high data transmission rates.
Coaxial Cable
For a newly arriving host, the DHCP protocol is a four-step process. The four steps are (in order):
DHCP discover DHCP offer DHCP request DHCP ACK
"multicasting" -- the transfer of data from one sender to many receivers in a single send operation- is possible with TCP. t f
False
Before sending a packet into a datagram network, the source must determine all of the links that packet will traverse between source and destination. (T/F)
False
In a decentralized routing algorithm, all of the nodes have complete information about the costs of all network links. t f
False
Link-layer switches forwards the packets by using packets' IP addresses. t f
False
Maximum Segment Size (MSS) is the maximum size of the TCP segment including headers. t f
False
OSPF (Open Shortest Path First) is a distance-vector protocol. t f
False
Queueing delay depends on packet length. (T/F)
False
Queueing delay is fixed for a router(T/F)
False
Suppose that a Web server runs in Host C on port 80. Suppose this Web server uses persistent connections, and is currently receiving requests from two different Hosts, A and B. All of the requests are being sent through the same socket at Host C . t f
False
The DNS protocol runs over TCP. t f
False
The application developer has control of everything on the application-layer side of the socket but has no control on the transport-layer side of the socket. t f
False
The link-state routing algorithm is also known as Dijkstra's algorithm. Dijkstra's algorithm computes the least-cost path from every node to every other node in the network. t f
False
Twisted-pair copper wire is no longer present in computer networks. (T/F)
False
Two arriving TC P segments with different source IP addresses or source port numbers, but the same destination IP address and destination port number will be directed to the same sockets. t f
False
When the underlying network protocol is unreliable, a transport protocol cannot offer reliable data transfer service to an application. t f
False
With OSPF, a router does not broadcast routing information to all other routers in the autonomous system, but sends to its neighboring routers only. t f
False
With best-effort service of IP, packets are guaranteed to be received in the order in which they were sent. t f
False
With best-effort service of IP, timing between packets is guaranteed to be preserved. t f
False
With non-persistent connections between browser and origin server, it is possible for a single TCP segment to carry two distinct HTTP request messages. t f
False
________ refers to the router-local action of transferring a packet from an input link interface to the appropriate output link interface. ________ refers to the network-wide process that determines the end-toend paths that packets take from source to destination.
Forwarding, Routing
_____ is used by hosts and routers to communicate network-layer information to each other.
ICMP
TC P provides flow control by having the sender maintain a variable called the receive window. Suppose that Host A is sending a large file to Host B over a TC P connection. Host B allocates a receive buffer to this connection; denote its size by RcvBuffer. From time to time, the application process in Host B reads from the buffer. Define the following variables: LastByteRead: the number of the last byte in the data stream read from the buffer by the application process in B. LastByteRcvd: the number of the last byte in the data stream that has arrived from the network and has been placed in the receive buffer at B. The receive window, denoted rwnd is set to the amount of spare room in the buffer. Host A in turn keeps track of two variables, LastByteSent and LastByteAcked. By keeping the _________________ less than the value of rwnd, Host A is assured that it is not overflowing the receive buffer at Host B.
LastByteSent - LastByteAcked or? amount of unacknowledged data
Ethernet is located at which layer of the Internet protocol stack?
Link Layer
WiFi is located at which layer of the Internet protocol stack?
Link layer
Indicate whether TCP or UDP (or both or neither) provide the following service to applications: A guarantee that data will be delivered within a specified amount of time
Neither
Indicate whether TCP or UDP (or both or neither) provide the following service to applications: Minimum data transmission rate between processes.
Neither
The time required to examine the packet's header and determine where to direct the packet is part of the ________.
Processing delay
TC P provides flow control by having the sender maintain a variable called the receive window. Suppose that Host A is sending a large file to Host B over a TC P connection. Host B allocates a receive buffer to this connection; denote its size by RcvBuffer. From time to time, the application process in Host B reads from the buffer. Define the following variables: LastByteRead: the number of the last byte in the data stream read from the buffer by the application process in B. LastByteRcvd: the number of the last byte in the data stream that has arrived from the network and has been placed in the receive buffer at B. The receive window, denoted rwnd is set to the amount of spare room in the buffer. How is the rwnd calculated? Write the formula by using the terms defined above.
RcvBuffer - [LastByteRcvd - LastByteRead]
Indicate whether TCP or UDP (or both or neither) provide the following service to applications. Reliable data transfer between processes.
TCP only
Indicate whether TCP or UDP (or both or neither) provide the following service to applications: Congestion-controlled data transfer between processes.
TCP only
Indicate whether TCP or UDP (or both or neither) provide the following service to applications: Guaranteed in-order delivery of data to the receiver.
TCP only
______ is the amount of time required to push all of the packet's bits into the link.
Transmission delay
TCP and UDP are located at which layer of the Internet protocol stack?
Transport Layer
A circuit-switched network can guarantee a certain amount of end-to-end bandwidth for the duration of a call. Most packet-switched networks today (including the Internet) cannot make any end-to-end guarantees for bandwidth. (T/F)
True
C onsider a NAT-enabled router in a home network. The router gets its address from the ISP's DHC P server, and the router runs a DHC P server to provide addresses to computers within the NAT-DHC P-routercontrolled home network's address space. t f
True
HTTP is mainly a pull protocol, and SMTP is primarily a push protocol. t f
True
If two UDP segments have different source IP addresses and source port numbers, but have the same destination IP address and destination port number, then the two segments will be directed to the same destination process via the same destination socket. t f
True
In a link-state algorithm, the network topology and all link costs are known, that is, available as input to the LS algorithm. t f
True
It is possible for a mail client to send e-mail messages over HTTP rather than SMTP. t f
True
It is possible for an AS (autonomous system) to have multiple subnets. t f
True
Message, segment, datagram, frame
application layer, transport layer, network layer, link layer
The job of delivering the data in a transport-layer segment to the correct socket is called _______.
demultiplexing
A UDP socket is fully identified by a two-tuple consisting of a _____ and a ______.
destination IP address destination port number
Traceroute is implemented with IC MP messages. To determine the names and addresses of the routers between source and destination, Traceroute in the source sends a series of ordinary IP datagrams to the destination. The source Traceroute stops sending UDP segments when it receives ____________ IC MP message from the destination host.
destination port unreachable
RIP routing is used for ______ routing in the Internet.
intra-AS
The transfer of an html file from one host to another is...
loss-intolerant and time insensitive
The job of gathering data chunks at the source host from different sockets, encapsulating each data chunk with header information to create segments, and passing the segments to the network layer is called _______.
multiplexing
Process sends/receives messages to/from its ______. It is analogous to door; sending process shoves message out door. Sending process relies on transport infrastructure on other side of door to deliver message to _____ at receiving process. (Note: These blanks are the same word). Type this word in all lowercase letters. ________
socket
A TCP socket is identified by which of the followings?
source IP address source port number destination IP address destination port number
SMTP is used to...
transfer messages from one mail server to another.