Коммуникации и сети - Контрольные вопросы и ответы - CS 2204 Срок 1

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Коммуникации и сети – Контрольные вопросы и ответы

The terms “throughput” and “data rate” are considered to mean the same thing

FALSE

________________

ATM packets are often called cells which are of the following size:

Fixed-size 53 bytes

________________

In the Internet, most packet losses are due to:

Congestion

________________

True or False: The Wi-Fi 5 GHz band (vs. 2.4 GHz) has increased ability to penetrate walls, often resulting in a higher effective range.

FALSE

________________

True or False: In unswitched Ethernets, every packet is received by every host and it is up to the network card in each host to determine if the arriving packet is addressed to that host.

TRUE

________________

True or False: Token Ring LAN is a simple multiple-access mechanism that is not only collision-free, but which supports fairness in the sense that if N stations wish to send then each will receive 1/N of the opportunities.

TRUE

________________

True or False: In the context of data networking, a protocol is a formal set of rules and conventions that governs how computers exchange information over a network medium. A protocol implements the functions of one or more of the OSI layers.

TRUE

________________

What is the fundamental alternative to datagram stateless forwarding?

Virtual circuits

________________

A virtual private network, or VPN, supports creation of virtual links that join far-flung nodes via:

The Internet

________________

In datagram switching, packets are addressed by destination. In virtual-circuit switching, packets are “addressed” by a connection ID. So, datagram switching and virtual-circuit switching are examples of:

Connectionless, connection-oriented services respectively

________________

True or False: ATM Adaptation Layer AAL 5 uses a CRC-32 checksum and is able to detect lost ATM cells.

TRUE

________________

How is an Ethernet card (or network interface) assigned a unique MAC address?

By the Ethernet card manufacturer

The term “frames” normally refers to data packets at which layer?

Data Link (e.g. Ethernet)

________________

Which of the following is not a key element of a protocol

Entities

________________

True or False: A store-and-forward switch or router begins forwarding a packet before it has fully arrived.

FALSE

________________

True or False: At the LAN layer, traffic-engineering mechanisms are historically/generally limited.

TRUE

________________

True or False: The Internet protocols use big-endian byte order (also referred to as network byte order).

TRUE

________________

True or False: Wi-Fi MAC (physical) addresses have the same 48-bit size as Ethernets and the same internal structure.

TRUE

________________

The documents that contain all the formal Internet protocol standards are referred to as:

Request For Comments (RFCs)

________________

Wi-Fi designers can improve throughput through a variety of techniques, including:

All of the above [FIX_ME]

________________

If an Ethernet switch does not have an entry for a particular destination, it will:

Fall back to flooding

________________

True or False: Ethernet LAN-layer addresses are most often called MAC addresses.

TRUE

Manchester encoding is principally designed to

Ensure that a transition occurs in the centre of each bit period

________________

Ethernet switches have incorporated a switch-to-switch protocol to construct a subset of the switch-connections graph that has no loops and yet allows reachability of every host. This protocol is called:

Spanning Tree

________________

True or False: The popular USB (Universal Serial Bus) standard for connecting computer peripherals uses Manchester encoding.

FALSE

________________

True or False: Gigabit Ethernet slot time is largely irrelevant, as full-duplex (bidirectional) operation is almost always supported.

TRUE

________________

The physical layer is concerned with the transmission of _______ over the physical medium.

Bits

________________

Gigabit Ethernet 1000Base-T uses the following encoding:

PAM-5

________________

True or False: Ethernet switches have an additional privacy advantage in that traffic does not flow where it does not need to flow.

TRUE

________________

Category 5 UTP cable is often used in which networks?

100 Mbps Ethernet

________________

True or False: A VLAN looks like a single LAN and all VLAN members will see broadcast packets sent by other members.

TRUE

________________

Fast (100 Mbps) Ethernet uses the following encoding:

4B/5B

Different VLANs can usually be connected together via:

An IP router

________________

True or False: The IEEE 802.1Q 32-bit VLAN tag is required to be added to frames with source and destination ports on the same switch.

FALSE

________________

True or False: According to Nyquist, a perfect (noiseless) channel has infinite transmission capacity.

FALSE

________________

A common recommendation is to have no more than _____ hosts per LAN or VLAN

1000

________________

True or False: All Ethernet devices also agree on a broadcast address of all 1’s: a packet sent to the broadcast address will be delivered to all attached hosts.

TRUE

________________

True or False: Fast Ethernet introduced the concept of full-duplex Ethernet which is entirely collision-free.

TRUE

________________

Baseband transmission may be defined as the transmission of a signal over a link:

Without any change in frequency

________________

In 4B/5B encoding, some symbols are used for signaling rather than data. The following provide an example of these:

All of the above [Start, End, Reset]

________________

Wi-Fi WPA2 uses the presumptively stronger encryption system called:

Advanced Encryption Standard (AES)

________________

AMI (Alternate Mark Inversion) still has synchronization problems with long runs of 0-bits. The solution used on North American T1 lines (1.544 Mbps) is known as

B8ZS

True or False: The Internet Checksum is usually better than CRC at detecting transposition errors.

FALSE

________________

True or False: Bandwidth delay is more significant than propagation delay within a small LAN.

TRUE

________________

What are the frequency bands used by Wi-Fi 802.11n?

2.4 GHz and 5 GHz

________________

True or False: Short Message Service (SMS) first became available on 3G mobile phones.

FALSE

________________

For the Internet Checksum, the value 0000 in the checksum represents:

No checksum calculated

________________

The telephone system is tightly intertwined with (wide area) computer networks. The limiting factor for networking purposes turns out to be:

“the last mile” over which telephone customers connect

________________

True or False: If Wi-Fi error rates or collision rates are high, a sender can send a large packet as multiple fragments, each receiving its own link-layer ACK.

TRUE

________________

The use of _________ lets the base station receive CDMA messages from unsynchronized mobile phones.

pseudorandom sequences

________________

True or False: The network layer interacts with the Wi-Fi LAN exactly as it does with Ethernet; no changes are required.

TRUE

________________

What is the bandwidth delay to get 1500 bytes onto the wire for Gigabit Ethernet?

12 microseconds

Bluetooth is a low-power network; for many applications the working range is about:

10 m

________________

True or False: Ethernet-like collision detection is no longer feasible over radio communications:

TRUE

________________

True or False: The preferred Wi-Fi encryption standard is Wired-Equivalent Privacy, or WEP.

FALSE

________________

All else being equal, the data rate achievable with a radio signal is proportional to:

the width of the frequency band

________________

Wi-Fi Link-Layer ACKs contain the following information:

None [FIX_ME?]

________________

True or False: For long (multi-kilometer) electrical serial lines, in addition to the clock-related serial-line requirements, we also want the average voltage to be zero.

TRUE

________________

What enables an Internet site to appear to the outside world as a single IP network, but further IP-layer routing to be supported inside the site?

subnets

________________

If an IPv4 address has all 1-bits for the host bits, it is of type:

broadcast

________________

Generally speaking, IPv6 addresses consist of a 64-bit network prefix (perhaps including subnet bits) followed by a 64-bit part called:

interface identifier

________________

True or False: An IPv6 address has 2 times the number of bits compared to IPv4.

FALSE

________________

Which of the following is not supported by IPv6?

LAN broadcast

________________

The IPv6 address ::1 (i.e. 127 0-bits followed by a 1-bit) is called the:

loopback address

________________

The number of bits in the network part of IPv4 class A, B, C addresses are:

8, 16, 24 respectively

________________

A possible Internet compatibility issue is that a packet is too large for a given network. IPv4 handles this by supporting:

fragmentation

________________

True or False: IP is a best effort system; there are no IP-layer acknowledgments or retransmissions.

TRUE

________________

True or False: One thing DNS makes possible is changing a website’s IP address while leaving the fully qualified domain name (FQDN) alone.

TRUE

________________

The IPv6 fixed header is twice the size of the IPv4 header, so it amounts to:

40 bytes

________________

IPv4 class D addresses are used for:

multicast traffic

________________

True or False: ARP (Address Resolution Protocol) takes advantage of the existence of LAN-level multicast frames.

FALSE

________________

Which one of the following IPv4 addresses can be used as a valid host IP address?

10.0.0.80/24

________________

True or False: The subnet mask for an IPv4 147.126.16.0/20 subnet would be 255.255.224.0.

FALSE

________________

True or False: IPv6 routers periodically send Router Advertisement (RA) packets to the IPv6 broadcast address.

FALSE

________________

True or False: The IPv4 Time-to-Live (TTL) header field is incremented by 1 at each router; if it reaches 10, the packet is discarded.

FALSE

________________

ARP-cache entries eventually expire and the timeout interval is on the order of:

from half a minute to a few minutes

________________

True or False: With IPv6, routers can use CIDR (Classless Internet Domain Routing) but must base forwarding decisions on prefixes longer than /64.

FALSE

________________

If the IPv4 “Don’t Fragment” (DF header flag) is set to 1 by the sender, then a router must not fragment the packet and must _____ instead.

drop it

________________

True or False: If a given IPv4 destination address matches the first k bits of one of the host’s addresses (w.x.y.z/k), the destination is on the local LAN.

FALSE

________________

Which of the following IPv4 addresses is NOT a private address? A) 10.0.0.1 B) 24.4.202.93 C) 172.16.1.1 D) 192.168.11.12

________________

True or False: IPv6’s extension headers must be processed in order.

TRUE

________________

Two things are gained from station “A ” doing gratuitous ARP on starting up: first, all stations that had A in their cache are now updated with A’s most current LAN address, and second:

duplicate IP address may be detected

________________

In the IPv6 fixed header, the IPv4 header Time To Live (TTL) field has become the:

Hop Limit

________________

An essential feature of IPv4 (and IPv6) addresses is that they can be divided into 2 parts:

network part and host part

________________

The checksum field in the IPv4 packet header is the “Internet checksum” applied to:

the header only

________________

True or False: IPv4 addresses are half the size of IPv6 addresses.

FALSE

________________

True or False: IPv6’s link-local addresses are intended to be used only within a LAN and never routed.

TRUE

________________

CIDR has essentially eliminated the IPv4 Class A/B/C mechanism from the:

the Internet backbone

________________

A link-state routing algorithm computes routes from the network map using:

the Shortest Path First algorithm

________________

In order to fix the slow-convergence problem, most flavors of the RIP protocol use a value of “infinity” set to:

________________

True or Fasle: BGP speakers exchange with neighbors only the routes they (and thus their AS) use themselves.

TRUE

________________

True or Fasle: Subnetting allows aggregation of IP address blocks in a way that is visible to the Internet backbone.

FALSE

The CIDR longest-match rule for choosing the routing table entry to be used means:

using the most specific matching prefix

________________

True or Fasle: The terms autonomous system (AS) and routing domain are used to refer to a set of routers under common administration, using a common link-cost assignment.

TRUE

________________

The link-state flooding algorithm avoids the usual problems of broadcast in the presence of loops by:

discarding old or duplicate Link State Advertisements or None of the above

________________

An example of distance-vector routing-update algorithms that eliminate routing loops is:

A and B Only (a. Destination-Sequenced Distance Vector, b. Enhanced Interior Gateway Routing Protocol)

________________

True or False: The Split Horizon fix to the slow-convergence problem prevents all linear routing loops.

TRUE

________________

What kind of routing-update algorithm is a preferred choice for networks such as those of ISPs?

Link State Routing

________________

The job of handling exterior routing (that is handling exchange of routing information between Autonomous Systems) is done by the following protocol:

Border Gateway Protocol

________________

True or Fasle: Routers have the option of fallback-to-flooding for unknown destinations (i.e. those which are not in their routing table).

FALSE

________________

BGP implements policy through filtering rules which allow rejection of certain routes at three different stages. Which of the following is NOT one of those stages?

Route path optimization

________________

Distance-vector is the simplest routing-update algorithm and it is used by:

Routing Information Protocol

________________

True or Fasle: In link-state routing, each node keeps a maximum amount of network information about of all nodes and all links.

TRUE

________________

True or Fasle: In link-state routing implementations, link-state records must be periodically renewed.

TRUE

________________

True or Fasle: Internet Service Providers (ISPs) always connect to one another directly via high-speed links.

FALSE

________________

True or Fasle: In distance-vector routing, each node has a complete view of the network topology.

FALSE

________________

The Border Gateway Protocol’s primary goal is to provide support for choosing routes based on:

administrative input

________________

True or False: The reverse address resolution protocol (RARP) allows a host to discover its Internet address when it knows only its physical address.

TRUE

________________

Which of the following is a characteristic of single-mode fiber-optic cable?

generally uses semiconductor lasers as the light source

________________

What is the purpose of the preamble in an Ethernet frame?

It is used for timing synchronization with alternating patterns of ones and zeros

________________

A network cable lies in the ____________ layer.

Physical

________________

True or False: The degeneration of a signal over distance on a network cable is called attenuation.

TRUE

________________

In bridged LANs, the _______ algorithm creates a topology in which each LAN can be reached from any other LAN through one path only.

spanning tree

________________

What is a possible effect of improperly applying a connector to a network cable?

Data transmitted through that cable may experience signal loss.

________________

True or False: In a baseband transmission, the entire bandwidth of the cable is consumed by a single signal. In broadband transmission, signals are sent on multiple frequencies, allowing multiple signals to be sent simultaneously.

TRUE

________________

True or False: Switches are used to connect distant LANs whereas a Router is most often used to connect individual computers.

FALSE

________________

What characteristic of UTP cable helps reduce the effects of interference?

the twisting of the wires in the cable

________________

True or False: In Stop-and-Wait, deadlock can be avoided by the sender side doing retransmit-on-timeout while the receiver does not do retransmissions.

FALSE

________________

True or False: In the context of Sun RPC’s at-least-once semantics, duplicate request execution is a possibility.

TRUE

________________

True or False: UDP (like TCP) avoids IP fragmentation by relying on the Path MTU Discovery mechanism.

FALSE

________________

TFTP prevents internal old duplicates simply by not allowing its 16-bit block numbers to wrap around; this is effective, but limits the maximum file size to:

about 32 MB

________________

True or False: If an 8 KB block of data is sent as a single UDP send operation over Ethernet (without jumbo frames), IP fragmentation is just avoided.

FALSE

________________

True or False: Suppose a Sun RPC read() request ends up executing twice. In between successive read() operations, the block of data is updated by another process. So different data is returned. This is failure of idempotence.

FALSE

________________

True or False: The Real-time Transport Protocol (RTP) is built on top of UDP because of its packet loss intolerance.

FALSE

________________

True or False: UDP packets with spoofed source address are difficult to deliver to the application.

FALSE

________________

True or False: Sliding Windows can work even if the receiver assumes that the window size is much less than the sender’s window size value.

TRUE

________________

The UDP 16-bit Internet checksum on the data can be disabled by setting the checksum field to:

all 0 bits

In Sliding Windows, once a full timeout has occurred, there are usually no packets remaining in flight and this is referred to as:

pipeline drain

________________

Which application made the greatest use of early Remote Procedure Call?

Network File System

If the TFTP client changes its port number on a subsequent connection, but the server does not, what prevents an old duplicate data packet sent by the server from being accepted by the new client?

the old dup packet has the wrong client UDP port number

________________

In Sliding Windows, if a sender chooses window size larger than the bandwidth x RTT product, then the RTT simply grows until the bandwidth x RTT matches the chosen window size. RTT increase is due to:

queueing delays

________________

True or False: UDP ports are considered a shared namespace with TCP ports. Therefore, 2 processes cannot share the same port number even if one process is using UDP and the other is using TCP.

FALSE

________________

True or False: To avoid stop-and-wait becoming a performance bottleneck, TFTP has an option to allow small window size sliding windows operation.

FALSE

________________

True or False: The most common binary data encoding on the Internet – at least below the application layer – is big-endian encoding.

TRUE

________________

Which of the following message types is NOT a valid TFTP message type?

Connection request

________________

In Sliding Windows, the sender is allowed to send up to this many packets (starting with the next packet after the last acknowledged packet):

window size

________________

What is the functionality that UDP ports provide?

Allow communication with a specific process within the host

________________

What is the primary reason for the development of IPv6?

expanded addressing capabilities

________________

What is the primary reason for the eventual retirement of IPv4?

limited addressing capabilities

________________

What OSI layer identifies the communicating applications?

Layer 4

________________

The Routing Information Protocol (RIP) is an intra-domain routing protocol based on _________ routing

distance vector

________________

Which statement describes the purpose of a default route?

to transfer data to a host outside the local network when no other route to the destination exists.

________________

Which information is found in the UDP header?

Source and Destination Port

________________

What is the size of IPv6 addresses?

128 bits

________________

What version of IP is the most common in the world?

IPv4

________________

True or False: In link-state routing implementations, link-state records must be periodically renewed.

TRUE

________________

Which is an important characteristic of UDP?

minimal delays in data delivery

________________

The size of the UDP port field is:

16 bits

________________

A TCP socket application can use setsockopt() with the TCP_NODELAY flag to:

disable the TCP Nagle algorithm for the connection in question

________________

What is the functionality that TCP ports provide?

Allow communication with a specific process within the host

________________

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arkadmin

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Коммуникации и сети – Контрольные вопросы и ответы – CS 2204 Срок 1

Коммуникации и сети – Контрольные вопросы и ответы

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Коммуникации и сети – Контрольные вопросы и ответы – CS 2204 Срок 1

Коммуникации и сети – Контрольные вопросы и ответы – CS 2204 Срок 1

Коммуникации и сети – Контрольные вопросы и ответы

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Около arkadmin

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