Computer Networks Exam 1

Topics are derived from the study sheet provided in class that go over chapters 1-2

host / end system

This is a device that connects to the internet.

router & link layer switches

These are the two types of packet switches that exist in today’s internet.

packet switch

This is what takes a packet arriving on one of its incoming communication links and forwards the packet on one of its outgoing communication links.

communication link & packet switches

End systems and hosts use a network of these to connect together.

packets

This is a package of information that are sent through the network to the destination host.

Internet Service Providers (ISPs)

Hosts use these to access the internet. They provide a variety of types of network access to the end systems, including residentials broadband access (cable model or DSL), high-speed local area network access, and mobile wireless access. They also provide internet to content providers, connecting servers directly to the internet.

lower tier

This type of ISP are regional providers.

upper-tier

This type of ISP is the backbone that form the internet’s core. They operate global or national networks and connect to one another.

protocol

This controls the sending and receiving of information within the Internet. This defines the format, order of messages sent and received, and actions taken on message transmission, receipt.

Transmission Control Protocol (TCP) & Internet Protocol (IP)

These are the two most important protocols in the internet. (Include their full names and acronyms).

Internet Standards

These are developed by the Internet Engineering Task Force that sets the base for what each and every protocol does so people can create systems and products that interoperate.

Distributed applications

This type of application involve multiple end systems that exchange data with each other.

Socket interface

This is what specifies how a program running on one end system asks the internet infrastructure to deliver data to a specific destination program running on another end system. It is a set of rules that the sending program must follow so the internet can deliver the data to the destination program.

client and server

Hosts can be divided into these two categories.

data centers

Where are servers usually located?

Digital subscriber line (DSL), cable, fiber to the home (FTTH)

What are the 3 most prevalent types of broadband residential access?

DSL

This is a broadband internet technology that sends data over the same copper telephone line used for traditional landline phone service. It uses high frequency signals for internet data.

1 Gbps

The most recent DSL standard can provide for up to this much downstream rate over short distances.

500 mbps

The most recent DSL standard can provide for up to this much upstream rate over short distances.

cable internet access

This is a broadband service that delivers internet data over the coaxial cable network originally built for cable television. It is shared among nearby homes in the same area.

Cable modem

What is required in order for the home to connect the network to the user’s device?

short broadcast medium

Cable internet access is a _________ meaning every packet sent by the head end travels downstream on every link to every home. This means the more people online the slower the rates.

Fiber to the Home (FTTH)

This broadband service delivers internet by using an optical fiber path from the CO directly to the home.

optical distribution network

This is the fiber-optic part of a network that carries data between the service provider’s equipment and customers’ locations.

Active optical networks (AONs) & Passive optical networks (PONs)

What are the two competing optical-distribution network architectures that perform the splitting in FTTH.

ethernet

What is the most prevalent LAN access technology in corporate, university, and home networks?

twisted-pair copper wire

What do ethernet uses use to connect to an ethernet switch?

Ethernet switch

This is a network of such interconnected switches that is connected into the larger internet.

Wi-Fi

This network allows people to “roam,” not limiting them to a specific spot in the building or house.

physical medium

This can take many shapes and forms and does not have to be the same type for each transmitter-receiver pair along the path. This is what bits are propagated on using electromagnetic waves or optical pulses.

twisted pair, coax, fiber, radio

These are the 4 types of physical medium that were discussed in class.

guided and unguided

Physical media fall into these two types of categories.

Guided media

This type of media creates a set path or solid medium for the waves to travel on.

Unguided media

This type of media does not provide a solid medium for the waves to travel.

Twisted Pair

This type of physical media is the least expensive and most commonly used in guided transmission medium. It consists of two copper wires arranged in a regular spiral pattern.

Unshielded twisted pair (UTP)

This is commonly used for computer networks within a building that is for LANs. (Hint: related to the physical media section)

Coaxial cable

This consists of two copper conductors, but the conductors are concentric instead of parallel. IT is common in cable television systems and can be used as a guided shared medium.

Fiber optics

This is a thin, flexible medium that conducts pulses of light. It can support tremendous bit rates and are immune to electromagnetic interference. They are high cost, but they are prevalent in creating the backbone of the internet.Ts

Radio

This carries signals in the electromagnetic spectrum and require no physical wire to be installed.

Geostationary & low-earth orbiting

These two types of satellites are used in communications.

Geostationary

This type of satellite permanently remains above the same spot on earth.

Low-earth orbiting

This type of satellite is placed closer to Earth and do not remain in place above one spot.

store-and-forward transmission

In packet switching, this type of transmission means the packet switch must receive the entire packet before it can begin to transmit the first bit of the packet onto the outbound link.

Transmission delay = L/R

This is the delay required to push an L-bit packet onto a link with transmission rate R. What is the formula?

output buffer (queue)

In packet switching, this is what stores packets that the router is about to send into a link.

Queuing delay

This delay is variable depending on the level of congestion in the network.

Packet loss

If the queuing delay is too great, it risks ________ which means the arriving packet or one of the already-queued packets will be dropped.

Forwarding table

In packet switching, each router maps destination addresses to the router’s outbound links using this.

circuit switching

In these types of networks, the resources needed along a path are reserved for the duration of the communication session between the end systems. An example would be traditional telephone networks and it provides guaranteed constant rate.

Circuit

This is the connection for which switches on the path between the sender and receiver maintain connection state for that connection.

end-to-end connection

In circuit switching, the network can establish this kind of connection between two hosts when they want to communicate. It creates one circuit on each of two links.

Frequency Division Multiplexing (FDM) or Time division multiplexing (TDM)

What are the two ways a circuit link can be implemented?

FDM

In circuit switching, this technique lets multiple signals share one communication link at the same time by giving each signal its own frequency band.

Bandwidth

This is the maximum amount of data a network link can carry in a given amount of time.

Time division multiplexing (TDM)

In circuit switching, this is when time is divided into frames of fixed duration and each frame is divided into a fixed number of time slots. The network will dedicate one time slot in every frame to this connection to allow transmission of data.

reserves a dedicated path that can lead to silent periods, shares network links with other traffic that can lead to congestion.

What are the main differences (and downsides) to both packet and circuit switching?

points of presence (PoP)

This is a group of one or more routers (at the same location) in the provider’s network where customer ISPs can connect into the provider ISP.

peer

This is when a pair of ISPs (at the same hierarchy) can directly connect their networks together so that all the traffic between them passes over the direct connection instead of through upstream intermediaries.

Reserved resources

This is the network capacity set aside exclusively for one connection such as a fixed amount of bandwidth in circuit switching. Other users cannot u se it, even when the connection is idle.

statistical multiplexing

This is a method where many users share the same network capacity dynamically. Resources are used by whichever users are actively sending data, based on the expectation that not everyone transmits at once. Used by packet switching.

pass through

This is when data travels through a reserved circuit continuously; intermediate switches do not need to receive the full message before it continues.

Forwarding

This is the action a router takes to move an arriving packet from an input link to the correct output link using the table.

Routing

This process determines the paths packets should take through the network and building the router’s forwarding table. The overall path.

Bursty traffic

This is when traffic arrives in uneven chunks instead of a steady rate.

Processing delay

This is the time required to examine the packet’s header and determine where to direct the packet.

Queuing delay

This is the time a packet needs to wait before being transmitted onto the link.

Transmission delay

This is the amount of time required to push all of the packet’s bits into the iink

packet size (L) / link’s rate (R)

This is the formula for transmission delay.

Propagation delay

This is the time required to propagate from the beginning of the link to the router.

Distance (d) / Link speed (s)

This is the formula for propagation delay.

La/R (a = units of packets per second)

This is the traffic intensity formula.

La/R > 1

This ratio means that the average rate that bits arrive at the queue exceeds the rate that bits can be transmitted onto the queue which results in a queuing delay of infinity.

processing, transmission, propagation

What are the 3 variables that impact the end-to-end delay for packets to get from source to destination?

Traceroute

This program can run in any Internet host. When the user specifies a destination hostname, the program int he source host sends multiple, special packets toward that destination.

name and address of router

In traceroute, when the router receives one of the special packets, it sends back a message that includes these 2 things.

media packetization delay

This delay is present in video conferencing applications such as Zoom where the sending side must first fill a packet with encoded digitized video and speech before passing the packet to the internet.

P(x=k) = (n k) p^k (1-p)^n-k

What is the binomial distribution? (write out the formula)

throughput

This is the actual rate at which data is successfully delivered across a network usually measured in bits/s.

Instantaneous throughput

This type of throughput is the rate at which data is being delivered at one specific moment in time.

Average throughput

This is the total amount of data delivered over a period of time divided by the length of that time period.

Bottleneck link

In packet switching, this is the link along a packet’s path with the lowest transmission rate. It limits the maximum end-to-end throughput because all data must pass through it.

bandwidth delay product

This is the amount of data that can be “in flight” on a network at one time.

bandwidth * propagation delay

How do you calculate the bandwidth delay product (BDP)?

Application, transport, network, datalink, physical

From top to bottom, what are the 5 layers of the TCP/IP model?

Application, presentation, session, transport, network, datalink, physical

What are the 7 layers of the OSI model?

Application layer

This layer of the TCP/IP model is where protocols reside.

message, segment, datagram, frame

What are the packets of information called when they’re in the application layer? What about transport, network, link and physical?

Transport layer

This layer of the TCP/IP model provides communication between applications on different hosts. It uses port numbers and provides reliable delivery if using the proper protocol.

TCP

In the transport layer, which protocol breaks long messages into shorter segments and provides a congestion-control mechanism?

UDP

In the transport layer, which protocol provides a connectionless service to its applications? It has no additional features meaning it doesn’t provide reliability, flow or congestion control.

Network layer

This layer of the TCP/IP model moves packets between different networks from the source host to the destination host. It uses IP addresses and routing.

Datalink layer (link)

This layer of the TCP/IP model transfers data across one local link, such as from a computer to a Wi-Fi router or from one router to the next. It uses frames and local hardware addresses.

Physical layer

This layer of the TCP/IP model transmits the actual bits as electrical signals, light pulses, or radio raves through a medium.

reliable over one link, reliable from source to destination.

What’s the main difference between link-layer reliability and TCP reliability?

Encapsulation

This is the process of adding headers and sometimes a trailer as data moves down the protocol stack.

header and payload

What are the 2 fields that a packet will have as it moves down the protocol stack?

botnet

This is when a compromised host is enrolled in a network of thousands of similarly compromised devices.

self-replication

This is when an infected host seeks entry into other hosts over the Internet and the cycle continues.

Denial of Service (DoS) attack

This is when a network, host, or other piece of infrastructure is unusable by legitimate users.

Vulnerability, bandwidth, connection flooding

What are the 3 categories that DoS attacks can fall into?