CMSC 204 Final Exam

What is a VLAN?

A virtual local area network (VLAN) is a LAN configured by software, not by physical wiring. Advantages include a cost (less hardware) and time (easy to switch membership) reduction, creating virtual work groups, and security.

What are the three ways VLANS can be configured?

Manually - Use software to manually assign someone to a group, and change someone from one group to another

Semiautomatically - Typically initializing is done manually and migrations done automatically

Automatically - Devices automatically connect or disconnect from aa VLAN using criteria defined by the administrator

Switches communicate the VLAN using tables (table maintenance), frame tagging, and time-division-multiplexing

What algorithm can be used to eliminate looping problems in a set of switches?

Spanning tree algorithm - find the shortest path from the root to every other device and block all other paths to that device

How is membership in a VLAN determined (3 ways)?

Interface numbers - Switch interface numbers (i.e. stations connecting to ports 1, 5, and 8 are all in one VLAN and 2, 3, 4, 6, 7 are a different VLAN)

MAC addresses

Combination

What impacts the performance of a network?

Delay

Throughput - the number of bits passing through the point in a second

Packet Loss

Congestion Control - improves performance

What are the four types of delay?

Transmission - can’t send a packet instantaneously, putting the packet on the line

Propagation - time it takes for a bit to travel form point A to point B

Processing - receive from input port, remove header, error detection, deliver to output port

Queuing - waiting

How is an IPv4 address normally represented in dotted-decimal notation?

Dotted-decimal notation is base 265 and it takes 8 bits and turns it into one number (0-255) (4 numbers total)

How many classes is IPv4 addressing divided into in classful addressing?

5 class - A, B, C, D, E

D is for multicast and E is reserved for future use

What is DHCP?  What layer do we find DHCP?  What services does DHCP use?

Dynamic Host Control Protocol (DHCP) is a protocol the automatically provides a device using internet protocol with an IP address. DHCP is considered an application layer protocol, and uses services such as DSN and any communication protocols based on UDP or TCP.

What is NAT?  What is ICMP? What layer do these protocols operate in?

Network Address Translation (NAT) maps multiple private IP addresses in a network to one public IP address. Internet Control Message Protocol (ICMP) compensates for IPv4’s lack of error reporting and correcting mechanisms. They operate at the network layer.

Is IP connection-oriented or connectionless, reliable or unreliable?

IP is a unreliable connectionless protocol

What is an IPv6 address?  How many bits long?  How many octets?

IPv6 allows for more addresses because they are 128 bits or 16 bytes (octets) long.

How many bits is a MAC address?

48 bits long

What are the services of the network layer (7)?

Packetizing - Encapsulating and decapsulating the payload in a network layer packet

Routing - Routing and forwarding

Error control - Can be implemented at this layer, but is inefficient

Flow control - Regulates the amount of data a source 

Congestion control - Rate of traffic from the sender to the network

Quality of Service - Mostly implemented in the upper layer

Security

What are the differences between IPv4 and IPv6?

Different options (no record route, no timestamp, source route calls source rout extension header, fragmentations fields in the base header moved to fragmentation extension header new authentication extension header, new encrypted security payload extension header)

IPv6 has only ICMP, no other things

What methods are used while the world is switching from IPv4 to IPv6?

Dual Stack - Run IPv4 and IPv6 simultaneously

Tunneling - IPv6 packet is encapsulated in and IPv4 packet to get through a section of IPv4 internet

Header Translation - IPv6 header converted to IPv4 header

What is distance-vector routing?

Each node creates a least-cost tree with immediate neighbors, exchange incomplete trees with neighbors to make the trees more complete, a router constantly tells all of its neighbors what it knows about the whole internet (a table of the least-cost from one node to every other node)

What is path-vector routing?

Can avoid certain nodes, using a spanning tree created with the help of its neighbors

What is link-state routing?

The costs associated with an edge defines the state of the link, no direct link means infinity

What is RIP?

Routing Information Protocol (RIP) - intradomain based on distance-vector routing, advertises the cost of reaching different networks (not hosts within the network), uses the services of UDP (port 520),  runs at the application layer but creates forwarding tables for IP at the network layer

What is OSPF?

Open Shortest Path First (OSPF) - intradomain  based on link-state routing, cost calculated from the source router to the destination network but each link can be assigned a weight (based on throughput, round-trip time, reliability, and so on)

What is BGP?

Border Gateway Protocol (BGD) - only interdomain routing protocol used in the Internet today, based on path-vector routing

What is he difference between unicast, multicast and broadcast traffic?

Unicast - One-to-one, each router in the path of the datagram tries to forward the packet to one and only one of its interfaces

Multicast - One-to-many, (sent to multiple interfaces if there are group members in those inerfaces)

Broadcast - One-to-all, sent to every inbterface

What is the primary role of the transport layer?

Provide process-to-process communication between two application layers

What is the client-server model?

A process on the local host (client) needs services from a process usually on the remote host (server)

What is multiplexing/demultiplexing?

Multiplexing - many to one

Demultiplexing - one to many

What is encapsulation/decapsulation?

Encapsulation - occurs at sender cite

Decapsulation - occurs at receiver site

What is pulling/pushing?

Pulling - when the producer delivers an item after the consumer has requested it

Pushing - delivering an item when ever it is produced with out a prior request from the consumer

What is UDP?

User Datagram Protocol (UDP) is an unreliable connectionless transport-layer protocol used for its simplicity and efficiency in applications where error control can be provided by the application-layer process

What is TCP?

Transmission Control Protocol (TCP) is a reliable connection-oriented protocol that can be used in any application where reliability is important

Is TCP simplex, half-duplex or full-duplex?

Full-duplex

What is congestion on a network?  How is it kept in check? 

Congestion occurs when the sender says more packets than the receiver can handle. This is kept in check using different congestion control methods, including sending and receiving windows. Timeout timers and three duplicate ACKs alert to congestion.

What are errors on a network, how are the managed?

Errors occur when packets arrive out of order, or they are duplicated or lost in transmission. Checksum and acknowledgements are used. Lost segments are retransmitted, out-of-order segments are stored in a queue

What is a connectionless service?

There is no relation between chunks of data

What is connection-oriented service?

The client and the server first need to establish a logical connection between themselves. The data exchange can only happen after the connection establishment.

What is the client-server paradigm?

Traditional paradigm, server process runs continuously, waiting for the client process to make a connection and ask for service

HTTP uses what type of services?

HTTP is a client-server protocol, and the client typically uses TCP.

What is a persistent connection?

There server maintains the connection even after the data is sent.

What are the key components of an e-mail?

There is first an envelope, then the message that consists of a header and the body

What are the key components of an e-mail address?

Mailbox address of the recipient and the domain name of the mail server

What is MIME?

Multipurpose Mail Extension (MIME) - allows email to send non-ASCII data

SMTP is push, pull, push and pull?

Push

What is TELNET?

TELNET allows a user on one computer to long in remotely to another computer.

What server has authority over a name space?

DNS servers

What type of abbreviations are used for country domains?

Typically two or three letters (us, fr, uk, ect.)

What are the primary forms of peer-to-peer networks?

Centralized networks - directory uses the client-server paradigm, storing and downloading of the files are done using the peer-to-peer paradigm (Napster)

Decentralized network - doesn’t depend on a centralized directory system (BitTorrent)

What is HTTP?

HyperText Transfer Protocol (HTTP), defines how the client-server programs can be written to retrieve web pages from the Web

What is HTTPS?

HTTP run over the Secure Socket Layer (SSL), provides confidentiality, client and server authentication, and data integrity

What is FTP?

File Transfer Protocol (FTP), standard protocol provided by TCP/IP for copying a file from one host to another

What is DNS?

Domain Name System (DNS), directory system that can map a name to an address

What is the difference between lossless and lossy compression?

Lossless - integrity of the data is preserved because the compression and decompression algorithms are exact inverses of each other, no part of the data is lost in the process (text)

Lossy - Sacrifice some accuracy to increase the compression rate, some data is lost in the process (images, video, audio)

What is the difference between streaming live and streaming stored video?

Stored video - files are compressed and stored on a server, the client downloads the files through the internet

Streaming - User listens to a broadcast audio and video through the internet.

What application layer protocol manages a multimedia session?

Session Initiation Protocol (SIP)

What is H.323?

H.323 - allows public telephone networks to talk with computers on the Internet

What is SIP, H.323, RTP, SRTP?

Application layer protocols for real-time interactive multimedia

Network management is composed of what?

Configuration management - know, at any time, the status of each entity and its relationship to other entities (reconfiguration and documentation)

Fault management - ensure proper operation of each component individually and in relation to each other (reactive and proactive fault management)

Performance management - monitor and control the network to ensure it is running as efficiently as possible (capacity, traffic, throughput, response times)

Security management - controlling access to the network based on predefined policy

Accounting management - controlling of users’ access to network resources through charges

What is the difference between the server and client in SNMP?

The servers, called managers, collect and process information about devices on the network. The clients, called agents, are any type of device or device component connected to the network.

What is the goal of cybersecurity?

Confidentiality - hidden from unauthorized access

Integrity - protected from unauthorized change

Availability - available to an authorized entity when it is needed

What types of attacks threaten confidentiality, integrity & availability?

Confidentiality - snooping and traffic analysis

Integrity - modification, masquerading, replaying, repudiation

Availability - denial of service

What is the difference between Steganography & Cryptography?

Cryptography - “secret writing”, concealing the contents of a message by enciphering

Steganography - “covered writing”, concealing the message itself with something else

What are the four characteristics data communications depends on?

Delivery - Delivered to the correct destination, only received by the intended user

Accuracy - Accurate, unaltered data

Timeliness - Deliver data in a timely manner

Jitter - Deliver data packets at the same speed

What are the five components of a data communications system?

Message - Information/data

Sender - Device that sends the message

Receiver - Device that receives the message

Transmission medium - Physical path the message takes to get from the sender to the receiver (twisted-pair, fiber-optic, radio waves, ect.)

Protocol - Set of rules that govern data communications

What is simplex, half-duplex, full-duplex?

Simplex - communication flows in one direction (one device is always the sender, the other is always the receiver

Half-duplex - communication flows in both directions but not at the same time

Full-duplex - communication flows in both directions and can happen at the same time

What are three network criteria?

Performance - Many ways to measure, such as transit and response times. Depends on things like number of user, type of transmission medium, ect.

Reliability - Measured by the frequency of failure, the time it takes to recover from failure, robustness

Security - Protecting data from unauthorized access and damage and development, implementing policies and procedures for recovery from breaches and data losses.

What are the two possible types of connection in a network?

Point-to-point - Dedicated link between two devices

Multipoint - More than two devices share a single link

What is physical topology and what are the four basic topologies?

Physical topology refers to the way a network is laid out physically.

Mesh - Every device has a dedicated point-to-point connection with every other device

Star - Each device has a dedicated point-to-point link only to a central controller, usually a hub

Bus - One long cable that acts as a backbone, devices connect to this cable via drop lines and taps, multipoint

Ring - Each device has a dedicated point-to-point connection with only the two devices on either side, the signal is passed from device to device around the ring in one direction until it gets to its destination

What are three causes of signal impairment?

Attenuation - Loss of energy, fixed by amplification

Distortion - Signal changes form or shape

Noise

What things measure network performance?

Bandwidth

Throughput - How fast data can actually be sent through a network

Latency (Delay)

Jitter - Different data packets having different delays

What three techniques are used in digital-to-digital conversion?

Line Coding - Process of converting digital data to digital signals

Block Coding - Adds redundancy to ensure synchronization and provide inherent error detecting

Scrambling

What two techniques are used in analog-to-digital conversion?

Pulse-Code Modulation (PCM) - A PCM encoder samples the signal every T seconds, quantizes the signal, and decodes the values as streams of bits.

Delta Modulation (DM) - Similar to PCM, but instead of finding the value of the amplitude, it finds the change from the previous sample

What are the three types of digital-to-analog conversion?

Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK), Phase Shift Keying (PSK)

What are the three types of analog-to-analog conversion?

Amplitude Modulation (AM), Frequency Modulation (FM), Phase Modulation (PM)

What are three examples of guided transmission media?

Twisted-Pair Cable - Two conductors, each with its one plastic insulation, twisted together, can be shielded or unshielded, used in telephone lines for voice and data channels

Coaxial Cable - Carries signals with higher frequency ranges that twisted-pair cables, central core enclosed in an insulating sheath, used for cable TV

Fiber-Optic Cable - Made of glass or plastic and transmits signs in the form of light, backbone of networks

What are three examples of unguided transmission media?

Radio Waves - 3kHz to 1GHz, omnidirectional

Microwaves - 1 GHz to 300 GHz, unidirectional

Infrared - 300 GHz to 400 THz, short-range communication

What are the two sublayers in the data-link layer?

Data-link control (DLC), Media access control (MAC) (only in a broadcast link)

What are some examples of random access protocols in the MAC sublayer?

ALOHA - Stations send data and wait for an acknowledgment from the receiver, if it doesn’t receive an acknowledgment it assumes there was a collision and resends it

CMSA - Every station has to listen to the medium before sending, reducing the possibility of collision

CMSA/CD - A station monitors the medium after it sends a Fram to see if the transmission was successful, resends if collision is detected

CMSA/CA - Used for wireless networks

What are some examples of controlled access protocols in the MAC sublayer?

Reservation - Stations reserve a slot of time to send their data

Polling - A primary device controls the link and decides which device is allowed to use the channel at a given time

Token Passing - If you have the token and need to send data, you send it, if you don’t need to send data, you pass the token on

What are the four types of Ethernet and what are their data rates?

Standard - 10 Mbps

Fast - 100 Mbps

Gigabit - 1 Gbps

10 Gigabit - 10 Gbps

What is the IEEE standard for WiFi?

IEEE 802.11

What is Bluetooth?

A ad hoc wireless LAN designed to connect devices of different functions when they are at a short distance from each other

Piconet - up to eight stations, 1 and 1 only primary

Scatternet - multiple piconets, the secondary station in one piconet can be a primary in another

10 meter range, 1 Mbps

What is auto-negotiation?

Allows two incompatible devices to negotiate the mode or data rate of transmission and connect to one another

 What are the three major components of a telephone network?

Local Loops - A twisted-pair cable that connect the subscriber telephone to the nearest end office or local central office

Trunks - Transmission media that handle the communication between offices

Switching Offices - Connects several local loops or trunks and allows a connection between different subscribers

What are Intra and Inter-LATA services?

Intra - Services offered by the common carriers (telephone companies) inside the LATA, carrier is called a local exchange carrier (LEC) (ILEC - incumbent local exchange carrier, CLEC - competitive local exchange carriers)

Inter - Services between LATAs that are handle by interexchange carriers (IXCs, also called long-distance companies), provide communication services between two customers in different LATAs

What is a point of presence (POP)?

Allows people in a LATA to connect to an IXC, companies must have a POP in a LATA if they want to provide service there, the LEC provides connection to the POPs

How does a traditional cable network work?

A receiving antenna at the head end receives video signals from broadcasting stations and feeds the signals into coaxial cables, amplifiers are used throughout the line, a splitter splits the cable that go into different areas, and houses connect to these split lines via drop cables and taps, one-way communication

How does a hybrid fiber-coaxial (HFC) network work?

A regional cable head (RCH) feeds distribution hubs, the signals are sent through fiber-optic cable, the fiber-optic cable is split and changes to coax at a fiber node, and the house connect to the coax, there is less need for amplifiers, the network is bidirectional

What is cellular telephony used for?

Provides communication between to moving units (mobile stations (MSs)) or between on MS and one stationary unit (land unit)

How does transmitting work in cellular telephony?

Caller enters a phone number, the MS seeks a setup channel with a strong signal, sends the phone number to the closest BS, BS relays the phone number to the MSC, MSC sends it to the telephone central office

How does receiving work in cellular telephony?

Telephone central office sends number to the MSC, MSC searches for location of MS by sending query signals to each cell, once the MS is found the MCS transmit a ringing signal, when the MS answers, the MSC assigns a voice channel to the call and communication can begin

What is handoff?

Mobile stations move from one cell to another, the MSC changes the channel carrying the call, hard handoff - communication must be broken creating a rough transition, soft handoff - MS and communicate with two BS at the same time

What is roaming?

A user can have access to communication or can be reached where there is coverage, service providers have an agreement to provide extended coverage

What are the generations?

1st - analog signals

2nd - digitized

3rd - 14 Mbps

4th - 100Mbps, Long Term Evolution (LTE)

5th - Currently 10Gbps, designed for 20 Gbps

What are the three ways a satellite can orbit the earth?

Equatorial, inclined, or polar

What are the three categories of satellites, and what is the reason for them?

Geostationary Earth orbit (GEO) - 35,786 km, always above the same point on earth following the rotation of the earth

Medium-Earth-orbit (MEO) - 5,000 to 15,000 km, 6 to 8 hours to circle the earth, GPS

Low-Earth-orbit (LEO) - below 2,000 km, polar orbits, circle the earthen 90 to 120 minutes, cellular type of access similar the the cellular telephone system, a system is made up of a constellation of satellites working together, Starlink (a lot more satellites than competitors

There are two Van Allen belts where satellites will be destroyed if they stay there