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CS402: Computer Communications and Networks Certification Exam Answers

Computer communications and networks refer to the systems and infrastructure that enable computers and other devices to communicate and share information with each other. This field encompasses a wide range of technologies, protocols, and techniques that facilitate data transmission and exchange across various types of networks.

Key components of computer communications and networks include:

  1. Networking Hardware: This includes devices such as routers, switches, modems, and network interface cards (NICs) that enable physical connectivity between computers and other networked devices.
  2. Networking Software: Software protocols and algorithms are essential for managing data transmission, routing, error correction, and other aspects of network communication. Examples include TCP/IP (Transmission Control Protocol/Internet Protocol), Ethernet, Wi-Fi, and DNS (Domain Name System).
  3. Types of Networks:
    • Local Area Network (LAN): A network that spans a relatively small geographic area, such as a single building or campus.
    • Wide Area Network (WAN): A network that covers a large geographic area, often connecting multiple LANs over long distances, typically using leased telecommunication lines.
    • Wireless Networks: Networks that utilize wireless communication technologies such as Wi-Fi, Bluetooth, and cellular networks.
    • Internet: The global network of interconnected networks, enabling worldwide communication and information exchange.
  4. Network Protocols: These are rules and conventions governing communication between devices on a network. Protocols define how data is formatted, transmitted, received, and acknowledged. Examples include HTTP (Hypertext Transfer Protocol), SMTP (Simple Mail Transfer Protocol), and FTP (File Transfer Protocol).
  5. Network Security: Techniques and mechanisms to protect networks and the data transmitted over them from unauthorized access, misuse, or modification. This includes encryption, firewalls, intrusion detection systems, and authentication mechanisms.
  6. Network Management: Tools and practices for monitoring, configuring, and optimizing network performance and reliability. This includes network monitoring software, traffic analysis tools, and configuration management systems.
  7. Emerging Technologies: Advancements such as cloud computing, Internet of Things (IoT), software-defined networking (SDN), and 5G networks are reshaping the landscape of computer communications and networks, offering new capabilities and challenges.

Overall, computer communications and networks are fundamental to modern computing and underpin the vast array of services and applications that rely on interconnected devices and systems for communication and collaboration.

CS402: Computer Communications and Networks Exam Quiz Answers

  • Tim Berners-Lee invented the World Wide Web
  • Reports by Paul Baran Outlining packet networks were released
  • GOPHER was released by researchers at the University of Minnesota
  • Marc Andreessen and Eric Bina developed and introduced the Mosaic web browser
  • A network, because networks are the only way to interconnect different types of hardware
  • A network, because users in the organization need to be exposed to all the actual machines, including the printers
  • A distributed system, because all printers must operate on top of the middleware that is present in distributed systems
  • A distributed system, because that is the best way to prevent end-users from having to deal with the complexities of networks
  • It uses the port number to deliver traffic
  • It changes the value of a bit being transmitted due to electromagnetic interference
  • It specifies the shared protocols and interface methods used by hosts in a communications network
  • It provides the mechanism for opening, closing, and managing a session between end-user application processes
  • A document published by the IEEE to define protocols such as 802.3/Ethernet
  • A document published by vendors to describe the network capabilities of their devices
  • A document published by Cisco that is used to develop network protocols using their devices
  • A document published by the IETF that defines new networking standards and shares technical information
  • A DNS message requesting the common name for 172.217.10.238
  • A DHCP message with an L3 destination address of 172.217.10.238
  • An ARP message requesting the physical address of 172.217.10.238
  • An ICMP message with an L2 destination address of 16-1b-eb-76-42-9b
  • OSPF sends update packets every 30 seconds, while RIP only sends update packets when a topology change is detected
  • OSPF is slower to converge since it has a hop count limit of 100, while RIP is much faster since its hop count limit is only 50
  • RIP solves the count-to-infinity problem using a simple Split Horizon algorithm, while OSPF uses Split Horizon with Poison Reverse
  • An OSPF router floods updates through all the network, while a RIP router only exchanges updates with connected routers
  • Type 5, Redirect Message
  • Type 9, Router Advertisement
  • Type 10, Router Solicitation
  • Type 15, Information Request
  • 40 bits
  • 160 bits
  • 320 bits
  • 640 bits
  • 00000100 01000001 11110000 00111100 11110000
  • 00111100 01000001 11110000 00111100 11110000 00111100
  • 11110000 01000001 11110000 00111100 11110000 11110000
  • 00111100 01000001 11110000 11110000 11110000 00111100 11110000 00111100
  • CSMA waits to receive a token before sending data, while CSMA/CD sends data as soon as no collision has been detected.
  • CSMA sends data as soon as the media is free, while CSMA/CD will send a token to the destination host in order to preserve the media
  • With CSMA, a station will always finish transmitting all of its data, while CSMA/CD stops as soon as collision is detected and retransmits at a random time
  • CSMA will start a random timer before retransmission after a collision, while CSMA/CD will retract and start monitoring the media until it becomes available again
Computer Communications and Networks Saylor Academy 1
AddressPort
aa-ab-ac-11-12-13
cc-cd-ce-11-12-13          
1
3
  • The frame floods ports 2 and 3 in the switch and ports 4 and 5 of the repeater
  • The switch sends ARP for MAC bb-bc-bd-11-12-13 before forwarding the frame.
  • The switch drops frame, as there is no entry in the FDB for MAC bb-bc-bd-11-12-12
  • The switch saves the frame in a buffer until an entry for that address appears in the FDB
Computer Communications and Networks Saylor Academy 2
  • Bridge 1
  • Bridge 2
  • Bridge 3
  • Bridge 4
  • For an environment that is entirely indoors
  • When cost is a factor, since DSSS is cheaper
  • When short synchronization times are needed
  • For an environment with high narrow band noise
  • TCP to initiate a call and RTCP to control the transfer of audio and video
  • ICMP to ensure that the communication path is present and TCP as the transport for the IP traffic
  • RIP to find the path from IP source to destination [and x to do y]
  • SIP to initiate a call and RTP to provide end-to-end network transport of audio and video
  • Use a Diffie-Hellman key exchange scheme for the private key
  • Use a long period for allowing key changes, to be sure that both parties have ample time
  • Switch to asymmetric encryption and use a public key to encrypt and a private key to decrypt
  • Increase the length of the encryption and decryption keys in the DES standard from 64-bit to 128-bit
  • A PPTP-based system
  • An L2TP-based system
  • An SSTP-based system
  • An OpenVPN-based system
  • RADIUS runs on top of TCP, while TACACS+ runs on top of UDP
  • RADIUS does not support protocols like ARA, NetBios, and NASI, while TACACS+ supports all of them
  • RADIUS addresses the authentication and authorization issues but lacks accounting, while TACACS+ addresses all of them
  • RADIUS encrypts only the password in the access request, while TACACS+ encrypts the whole body of the packet except for the header
  • When you need to support load balancing
  • When your network uses only Cisco routers
  • When your network uses multiple router vendors, like Cisco and Juniper
  • When you need to save address space and receive only one IP address for your virtual router
  • Coaxial
  • Plenum
  • Optical fiber
  • Twisted pair
  • Session
  • Transport
  • Data link
  • Physical
  • SIP
  • SMTP
  • TCP
  • UDP
  • SMTP is a UDP-based protocol, while IMAP is a TCP-based protocol
  • SMTP provides support for images in messages, while IMAP is a text-based protocol
  • SMTP is a network management protocol, while IMAP is used to send and retrieve email messages
  • SMTP could be used to send and retrieve emails, while IMAP is only used to retrieve email messages
  • HTTP normally runs on top of UDP, while HTML runs on TCP
  • HTTP is the same as HTML, but works on IPv6 instead of IPv4
  • HTTP posts and retrieves web pages, while HTML is a language used to define elements of web pages
  • HTTP is a scripting language used to display web pages in a browser, while HTML is the protocol used to secure an HTTP connection
  • When you need to be able to authenticate users
  • When you need to use bootstrap protocols such as BOOTP
  • When you need to use initialization protocols such as DHCP
  • When you need to use a protocol such as ICMP to troubleshoot a network connection
  • In a school network where sensitive information needs to be protected
  • In a content delivery organization that is expected to grow rapidly in the coming months
  • In an engineering firm where, multiple users will share a central computer running company-specific software
  • In a bank environment with a great amount of users that will be accessing the network via their personal devices
  • By sending data through an encrypted TLS tunnel
  • Authenticating end users and encrypting the data sent between them
  • Using public/private asymmetric key pairs to encrypt the whole connection
  • Using a single “Well-Known Key” that is paired with all data sent through the network
  • Socket type and address format
  • Socket address and socket family
  • Socket message and socket header
  • Socket stream and datagram socket
  • UDP is more reliable
  • UDP supports flow control
  • UDP has a higher overhead
  • UDP data transmission is more efficient
  • Checksum
  • Source Port
  • Destination Port
  • Sequence number
  • IP Address and port number
  • Sequence number and option type
  • MAC address and time-to-live number
  • Protocol number and packet ID number
  • Reliable and message-oriented
  • Reliable and character-oriented
  • Unreliable and message-oriented
  • Unreliable and character-oriented
  • It uses an asymmetric release protocol
  • It allows both sides to release independently
  • It is the only way to avoid deadlock situations
  • It avoids the delays typical to other forms of release
  • Seq = 2048, ACK = 2048, W = 2048, and 2048 B of data
  • Seq = 2048, ACK = 4097, W = 2048, and 2048 B of data
  • Seq = 4096, ACK = 2048, W = 4096, and 4096 B of data
  • Seq = 4096, ACK = 4096, W = 4096, and 4096 B of data
  • Limited the mix of data streams
  • Introduced a fixed-size header with optional extension headers
  • Increased the TTL field to allow packets longer travel distances
  • Eliminated the support for QoS at an IP level, instead relying on TCP
AddressMaskOutput Port

192.24.0.0255.255.248.01
192.24.16.0      255.255.240.0         2
192.24.8.0255.255.252.03
 Default  4
  • It will be sent to output port 1
  • It will be sent to output port 2
  • It will be sent to output port 3
  • It will be sent to default port 4
  • 194.24.0.0/16
  • 194.24.0.0/21
  • 192.24.0.0/24
  • 218.238.0.1
  • ARPANET
  • GOPHER
  • LAN
  • OSPF
  • Data link layer
  • Network layer
  • Transport layer
  • Physical layer
  • To troubleshoot the reason why a router suddenly stops forwarding data
  • When your team is designing the network that a community college will use
  • To understand how an OSPF router recalculates routes quickly with topology changes
  • When you need to choose between two different types of routers for your existing home network
  • The TTL field became too high
  • There was an RPF check failure
  • An IGMP Graft message was sent
  • The PIM protocol changed from Dense to Sparse
  • The host first sends an ICMP Router discovery message
  • The gateway responsible for the network is configured as a proxy ARP
  • The host issues an ARP request sent to the broadcast Ethernet address
  • The sending and destination hosts have both been configured with a mask of 255.255.0.0
  • 1 to 19 bits
  • 20 or more bits
  • 80 or more bits
  • 160 or more bits
  • Best effort
  • Constant bit rate
  • Real-time variable bit rate
  • Non-real-time variable bit rate
  • 4
  • 9
  • 11
  • 64
  • It is harder to maintain
  • It typically has slower performance
  • It is dependent on devices and their locations
  • It can be hard to implement elastically and at scale
  • It is more resilient than other methods in the event of a router failure
  • Packets arrive out of order and must be rearranged at the destination
  • Each packet has a header with full address of destination and source hosts
  • The route from source to destination is determined when a connection is established
  • Presentation
  • Network
  • Transport
  • Session
  • The call is encrypted with a the key g726-32
  • It is for a video call that will take place using port 8000
  • It is for an audio call that will take place using port 49756
  • The connection uses UDP as its main transport mechanism
  • TLS runs on top of UDP, while SSH runs on TCP
  • TLS uses a peer-to-peer model, while SSH uses a client-server architecture
  • SSH provides for secure data transmission, while TLS provides additional encryption on top of SSH
  • SSH provides for secure data transmission, while TLS ensures the integrity and privacy of the message
  • It is connectionless
  • It supports user authentication
  • It has an unlimited message size
  • It is more reliable than other protocols
  • Check the digital signature
  • Translate the network address
  • Store the state information about the packet
  • Forward the data packets between networks
  • 171.157.34.112
  • 171.157.34.113
  • 171.157.34.126
  • 171.157.34.127
  • A LAN
  • A WAN
  • A MAN
  • A home networks
  • RIP is a TCP-based protocol, while BGP runs directly over IP
  • RIP is an exterior routing protocol, while BGP is an interior routing protocol
  • RIP is based on distance vector routing, while BGP is based on link state routing
  • RIP uses a metric based on hop count, while BGP uses a metric based on path information
  • When you want your multicast group to run faster
  • When you want to implement a “tagging” protocol operating over UDP
  • When you want to implement a “reservation” protocol operating over IP
  • When you need a protocol similar to a unicast routing protocol but you are using multicast applications
  • 15.36 Mbps
  • 230.4 Mbps
  • 115.2 Mbps
  • 921.6 Mbps
  • The system is using IPsec ESP mode
  • The system is using IPsec Tunnel Mode
  • The system is using IPsec Transport Mode
  • The system is experiencing data corruption
Remote Registry

Disabled
RPC Endpoint Mapper        Running       Automatic
Routing and Remote AccessDisabled
Secondary LogonManual
Sensor ServiceManual
ServerAutomatic
Shared PC Account ManagerDisabled
  • Remote Registry is disabled
  • Secondary Logon is not running
  • Routing and Remote Access is disabled
  • Shared PC Account Manager is disabled
  • Application
  • Internet
  • Network interface
  • Transport
  • ICMP
  • IP
  • TCP
  • UDP
  • IPv6 is disabled
  • The server option is disabled
  • The IP address is not available in the scope of the DHCP
  • The IP address for the DNS Server is not available in the scope option
  • Connection-oriented; port 70, retrieves Hypertext messages from a server
  • Connectionless; port 80; retrieves resources like HTML documents from a server
  • Menu-driven; port 7070; distributes, searches, and retrieves documents over IP networks
  • Peer-to-peer; port 636; establishes secure connections between two machines on a network
  • Telnet
  • Trivial FTP (TFTP)
  • Simple FTP (SFTP)
  • FTP over SSL (FTPS)
  • It sends a SIP INFO packet
  • It sends a SIP DIAL message
  • It sends an RTCP SDES packet
  • It sends an IGMP REPORT message
  • The packet formats
  • The packet encoding
  • The number of packets
  • The username associated with packets
  • When you need to allow two processes within a single machine to communicate
  • When you need to allow two processes in two machines on the same network to communicate
  • When you need to establish a client/server connection between two computers on the same network
  • When you need to create a connection between two processes in different computers or within the same computer
  • Multistream
  • Single-homing
  • Congestion control
  • Head-of-line blocking
  • After 4 ACKs are received for the same segment, the sending host reverts to the Slow Start algorithm and starts with a window size of 1
  • The sending host will wait for RTO timers to expire and resend lost packets as many times as needed to assure that TCP remains reliable
  • After 4 ACKs are received for the same segment, the Fast Retransmit rule is applied and the lost packet is sent without waiting for RTO timers to expire
  • After 10 ACKs for the same segment are received, the system automatically switches to the ATM transmission protocol, which is much faster than TCP
  • A distributed system does not allow machines to share resources to accomplish a given task, while a network does
  • A distributed system requires the use of exterior routing protocols to move data between computers, while a network only uses interior routing protocols
  • A distributed system is a collection of autonomous computers operating as one, while a network involves users who each work on individual machines
  • In a distributed system all messages have to go through a central node, while a network allows machines to send messages to one another independently
  • LAN
  • MAN
  • WAN
  • PAN
  • It floods the network with a link state advertisement at regular intervals
  • It exchanges a link state advertisement table with its neighbors at regular intervals
  • It uses Dijkstra’s algorithm to find the shortest path between two nodes in the network
  • It uses a Poison Reverse algorithm to find the best path between two nodes in the network
  • Verify that all routers in the environment are MPLS enabled
  • Ignore it, because all links can be used in an MPLS-enabled environment
  • Make sure that traffic engineering is correctly guaranteeing the required bandwidth
  • Restart the label distribution process which failed to select the best route at startup
  • It provides for automatic means of address assignment within a network
  • It provides for a convenient way of translating from an IPv4 address to an IPv6 address
  • Most hosts are attached to a LAN interface that by definition only understands Ethernet addresses
  • Address resolution is required to translate unintelligible IP addresses into familiar, user-friendly names
  • Ethernet V2 has a maximum frame size of 64KB, while the max frame size of 802.3 is 1500B
  • Ethernet V2 uses a CSMA access mechanism, while 802.3 uses a CSMA/CD access mechanism
  • Ethernet V2 frame format has a “Type” field, while 802.3 uses a frame format with a MAC subheader
  • Ethernet V2 contains the CRC field toward the start of the frame, while 802.3 contains the CRC toward the end of the frame
Computer Communications and Networks Saylor Academy 1
  • It is received by PC C
  • It is received PCs B, C, and D
  • It is received by PCs C and D
  • It is dropped by the switch, since PC C is not directly connected
Computer Communications and Networks Saylor Academy 3
  • It will be dropped by SW1
  • It will reach both SW2 and SW3, but both will drop it
  • It will reach both SW2 and SW3, but go out of port 8 on SW3
  • It will reach both SW2 and SW3, but go out of ports 4 and 5 on SW2
  • Token ring is an actual ring with a circulating token, while token bus is a virtual ring where the token circulates on a bus
  • Token ring uses a transmission timer to transmit once it gets the token, while token bus transmits as soon as the token is available
  • Hosts with data in a token ring must wait for the token to arrive before transmission, while hosts with data in a token bus can transmit at any time
  • A host in a token ring does not monitor the media since access is based only on having the token available, while a host in token bus monitors the media before sending data
  • By exchanging the roles of the Authentication field (AH) and the Encapsulating Security Header (ESP) field in the IPsec header
  • By using a tunnel-mode algorithm where the sender encrypts a signature and sends it through a tunnel previously made with the receiver
  • By the sender encrypting a signature using a private key and the receiver using a public key to decrypt the signature to verify authenticity of the sender
  • By the sender encrypting a signature using a private key and the receiver using the same private key to decrypt the signature to verify authenticity of sender
  • Another program is using port 3389
  • IKE services are disabled on the remote system
  • Shared PC Account Manager is disabled in the remote system
  • There is a mismatch in the Security Associations for the connection
  • AWS uses SQL databases like MYSQL, while Azure uses a relational database like RDS
  • AWS is based on Elastic Compute Cloud (EC2), while Azure is based on virtual machines
  • AWS uses the more efficient block storage, while Azure uses object storage through a web interface
  • AWS uses a network platform based on virtual networks, while Azure is based on a virtual private cloud
  • Each packet’s path is chosen randomly between a limited set of paths
  • Each packet has a header with full address of destination and source hosts
  • A path must be established from source to destination before data starts flowing
  • Even though a path is not established ahead of time, each packet must follow the exact same path
  • They cannot be lost
  • They can be modified
  • They can be duplicated
  • They can suffer transmission errors
  • Class A
  • Class B
  • Class C
  • Class D
  • Window size
  • Urgent pointer
  • TCP checksum
  • Destination port
  • Buffer control
  • Sliding window
  • Traffic avoidance
  • Congestion control
  • 10 ms
  • 20 ms
  • 30 ms
  • 40 ms
  • It floods the network with a distance vector table at regular intervals
  • It exchanges a distance vector table with its neighbors at regular intervals
  • It uses Dijkstra’s algorithm to find the shortest path between two nodes in the network
  • It uses a count-to-infinity algorithm to find the best path between two nodes in the network
  • The router is running IGMP version 1, which is outdated
  • There is a failing DVMRP router that times out in exactly 3 minutes
  • The router is sending the leave request to the wrong multicast address, 224.0.0.2
  • The Protocol Independent Multicast (PIM) enabled router times out in exactly 3 minutes
  • The packets are looping endlessly
  • The datagram is too big and the DF bit is set
  • An illegal value has been detected in a header field
  • The router has noticed that a packet seems to be routed incorrectly
  • 011110111101011110110
  • 011110111110011111010
  • 001111001111100111111100
  • 0111110011111010111110100
  • Determine who accesses the media in a multi-host environment
  • Route L2 traffic from source to destination based on the state of the media
  • Monitor transmission media to determine when it is congestion and alert users
  • Retransmit a damaged packet based on a random timer that is started when a collision occurs
  • TCP is a connection-oriented service, which means that connections are very reliable
  • TCP is a connectionless service, which means that segments are always accounted for
  • In a connection-oriented service like UDP, lost segments are accounted for, but not retransmitted
  • In a connectionless service like UDP, all segments are always acknowledged and lost ones retransmitted
  • User authorization
  • Transmission of long messages
  • Transfer of data frames from one node to another
  • Mechanical and electrical properties of transmission media
  • IMAP is used to retrieve emails from a server, while POP is used to send emails
  • POP is used to retrieve emails from the server, while IMAP is used to send emails
  • IMAP messages are stored in a mail server, while in POP messages are downloaded to the local machine
  • POP messages are accessible from any machine anywhere, while IMAP can only retrieve emails from the local machine
  • Client
  • Server
  • TCP
  • UDP

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