Chapter 1

Packet Switching = Divides data into packets and sends them individually to their destination Store and Forward = Entire packet must arrive at router before being transmitted to the next link End to End Delay = $2L/R$ (assuming 0 propagation delay) Queuing and Loss = If arrival in bits to link exceeds transmission rate of link for a period of time packet will be queue and wait to be transmitted packet can be lost if memory buffer fills up

$n$ = Total number of users $k$ = Number of active users $p$ = Probability of a user being active

$p(k)= (n choose k) (p)^k(1-p)^(n-k)$ = Computes the probability that exactly $k$ users are transmitting simultaneously at any given time in packet switching $1- (probability that less than 1$ using simultaneously = Finds the probability that there are one or more users transmitting simultaneously in packet switching

Optimizes network efficiency and resilience because each packet might take a different path to reach the destination where they are reassembled = Routing protocol Efficient for bursty data and doesn’t waste bandwidth = Packet switching protocol Protocols needed for reliable data transfer, congestion control = Congestion control protocol

When loading a webpage, each image, text block or video can be sent as separate packets = Packetization If arrival in bits to link exceeds transmission rate of link for a period of time, packet will be queue and wait to be transmitted = Queuing and loss

$1- (probability that less than 1$ using simultaneously = Finds the probability that there are one or more users transmitting simultaneously $2L/R$ (assuming 0 propagation delay) = Calculates the end-to-end delay

Packet delay and loss due to excessive congestion = Disadvantage of packet switching Efficient for bursty data and doesn’t waste bandwidth = Advantage of packet switching Divides data into packets and sends them individually to their destination = Basic concept of packet switching

Hosts = End-user devices that send and receive data Switches/Routers = Devices that direct data packets within a local network or between different networks Network Edge = Consists of hosts (clients and servers) where data originates and can flow both ways Network Core = Contains routers and networks that form the Internet backbone

LAN = A network within a limited area, e.g., a building, offering faster speed and lower latencies WAN = Spans broader areas like cities or countries, covering vast distances Wi-Fi = A wireless networking standard that allows devices to connect to a LAN wirelessly Cellular communication = Enables mobile devices to communicate over long distances, transitioning between cell towers

Protocol = A standard that defines the format, order of messages sent and received among network entities, and actions taken on message transmissions Standards = Agreed upon rules or specifications for consistency across devices and systems RFCs = The primary method for proposing and commenting on Internet standards, including the protocols and systems forming the Internet Circuit Switching = Establishes a dedicated communication path between nodes, guaranteeing bandwidth but may be wasteful if the full capacity isn’t used

Accessing the internet on your phone = Involves the network edge Your home Wi-Fi = Typically a LAN An enterprise with offices globally = Uses a WAN to interconnect them Data traveling from a server in Europe to your PC in the US = Goes through the network core

Circuit Switching = Real life scenario: Traditional phone system used circuit switching Protocol = Real Life Scenario: When you send an email, your email system uses the SMTP protocol to ensure the recipient's email system understands and correctly receives your message Standards = Real Life Scenario: Website uses the HTTP or HTTPS standard to ensure they can be accessed by any web browser Network Edge = Real Life Scenario: accessing the internet on your phone involves the network edge

LAN = High speeds, more control over configuration WAN = Wide coverage Wi-Fi = Allows devices to connect to a LAN wirelessly Cellular communication = Each generation (1g to 5g) improving speed and reliability

Hosts = End-user devices like computers and smartphones that send and receive data Switches/Routers = Devices that direct data packets, either within a local network or between different networks Network Edge = Consists of a host (clients and servers) where data originates and can flow both ways Network Core = Contains routers and networks that form the Internet backbone

Physical and Data Link = Network Interface Network = Internet Session, Presentation, and Application = Application

Open = Publicly available, like TCP/IP Proprietary = Owned and controlled by an organization, usage might require a license Ad-hoc = Develop out of necessity, arise informally and get adopted because they become popular or fill a need De jure = Officially recognized and sanctioned by a formal body

Physical = Deals with the physical medium of transmission Data Link = Provides reliable data delivery across a physical link Network = Routes data from one node to another

Network access = Handles the physical and data link layers Internet = Routes data across networks Transport = Provides reliable data delivery

Physical = Network access Data Link = Network access Network = Internet Transport = Transport Session, Presentation, and Application = Application

Session = Establishes, manages, and terminates sessions between applications Presentation = Formats data for presentation to the application layer Application = Provides access to the network for applications

Network access = Handles the physical and data link layers Internet = Routes data across networks Transport = Provides reliable data delivery Application = Provides access to the network for applications

Physical = Deals with the physical medium of transmission Network = Routes data from one node to another Application = Provides access to the network for applications

Network access = Handles the physical and data link layers Internet = Routes data across networks Transport = Provides reliable data delivery Application = Provides access to the network for applications

Guided media = Directs data along a specific path, ensuring higher reliability and speeds. Communication takes place using physical wires or fibers. Unguided media = Is wireless and offers flexibility but can be more susceptible to interference. Signal propagates freely in the air and can penetrate through walls. Fiber optic cables = Consists of glass fiber carrying light pulses, each pulse represents a bit. It has high speed operation and low error rate because repeaters are spaced farther apart and is immune to electromagnetic noise. Coaxial cables = Consists of copper and carries data using electricity. It can be affected by environmental effects on wireless signals.

Propagation delay = $D(length of physical length)/ S (propagation speed)$ Transmission delay = $L( packet length, bits)/ R(transmission rate, bits/sec)$ Queuing delay = Time waiting at output link for transmission, depends on congestion level of router Nodal processing delay = Time taken by a router to check bits errors and determine output link, typically less than a millisecond

End-to-end communication delay = Total time for a packet to travel from the source to the destination, including all the delays experienced Routing = Determines the source-destination route taken by packets using routing algorithms Forwarding or switching = Refers to the actual process of sending a packet from an input to an appropriate output link/ what port the packet should be sent from Throughput = The rate at which data is transferred through a network, often determined by the slowest link

Protocol layers = Divide communication into layers allowing for modularity and specialization Application layer = You write the letter in this layer Transport layer = You put the letter in an envelope in this layer Network layer = You add an address to the letter in this layer Link layer = You hand the letter over to the post in this layer

Packet switching = Used in 'Store-and-forward' communication. In this, devices like routers receive the entire packet and then forward it, ensuring data integrity but potentially adding delay Store and Forward (packet switching) = Takes $l/r$ seconds to transmit a packet at bandwidth. The entire packet must arrive at the router before being transmitted to the next link Traffic Intensity = $(L*a)/R$, where $a$ is the average packet arrival rate. If larger than 1, there is more arrival that can be serviced Protocol stack = A concept where different layers of communication are stacked on top of each other

Guided media (Wire) = Advantages: Typically faster and less prone to interference. Disadvantages: Signal requires physical path, Higher installation cost and maintenance, Limited by length of conductor Unguided media (Wireless) = Advantages: Flexibility. Disadvantages: Can be more susceptible to interference Fiber optic cables = Advantages: High speed operation, Low error rate because repeaters are spaced farther apart, and is immune to electromagnetic noise Coaxial cables = Advantages: Consists of copper and carries data using electricity

Bit Error Failure = Failure in the transmission of a bit Node Failure = Failure of a network node, such as a router or switch Link Failure = Failure of a link in the network Packet Loss = Loss of a packet during transmission

The purpose of circuit switching is to establish a dedicated communication path between nodes.

Circuit switching guarantees bandwidth, ensuring a constant quality of service.

Circuit switching can be inefficient if the full capacity isn't used, as the dedicated channel cannot be used by other conversations.

Hosts are end-user devices like computers and smartphones that send and receive data.

Switches/routers are intermediary devices that direct data packets within a local network or between different networks.

A protocol is a standard that defines the format, order of messages, and actions taken on message transmissions, ensuring effective communication.

RFCs historically serve as the primary method for proposing and commenting on Internet standards, documenting the agreed-upon rules and specifications for internet technologies.

$p(k)= \inom{n},{k} p^k(1-p)^{n-k}$ (where $n$ is the total number of users, $k$ is the number of active users, and $p$ is the probability of a user being active)

$1- \ ext{probability that less than 1 user is transmitting simultaneously}$

$\ ext{end-to-end delay} = \ rac{2L},{R}$ (assuming zero propagation delay, where $L$ is the size of the packet and $R$ is the transmission rate)

The packets will be queued and wait to be transmitted. If the memory buffer fills up, packets can be lost.

Packet switching allows more users to use the network and is efficient for bursty data. It also optimizes network efficiency and resilience because each packet can take a different path to reach the destination.

Packet switching is prone to packet delay and loss due to excessive congestion. Reliable data transfer and congestion control protocols are needed to mitigate these issues.

Internet browsing, where each image, text block, or video on a webpage can be sent as separate packets.

Guided media, such as cables, direct data along a specific path, ensuring higher reliability and speeds. Communication takes place using physical wires or fibers. Unguided media, like radio waves, is wireless and offers flexibility but can be more susceptible to interference. Signal propagates freely in the air and can penetrate through walls.

Advantages: High speed operation, low error rate, immune to electromagnetic noise. Disadvantages: Limited by length of conductor.

Advantages: Consists of copper, carries data using electricity. Disadvantages: Environmental effects can have an impact on wireless signals.

In 'store-and-forward' communication, devices like routers receive the entire packet and then forward it, ensuring data integrity but potentially adding delay.

End-to-end delay = 2L/R, where L is the length of the packet and R is the transmission rate.

Factors like bandwidth and network congestion can influence the throughput of a network.

Protocol layers divide communication into layers, allowing for modularity and specialization.

A protocol stack is the combination of all the layers in a system, with each layer using the services of the layer beneath it.

Protocol layers in a networking model often interface with the layers immediately above and below them. Each layer interacts with the one above it and below it.

In the OSI model, the transport layer takes from the session layer above it, adds its own header, and passes the resulting packet to the network layer below.

True. Between modules/layers on the same machine, protocol layers can communicate with each other.

True. Between same modules/layers on peer machines, protocol layers can communicate with each other.

A protocol stack is the set of layers and protocols used by a network.

Examples of protocols used in the application layer include FTP, HTTP, and SMTP.

The layers in the OSI model are Physical, Data Link, Network, Transport, Session, Presentation, and Application.

The layers in the TCP/IP model are Network access, Internet, Transport, and Application.