Network Architectures

data communication

the exchange of data between devices over a communication medium using different protocols and techniques // effectivness depends on: delivery, accuracy, timeliness;

communications components (5)

1. Sender

2. Receiver

3. Message

4. Medium

5. Protocol

Direction of data flow

The direction of signal flow between two linked devices.

Types of data flow direction

1. Simplex

2. (Half-) Duplex

3. Full-Duplex

Simplex data transfer

A communication channel that allows data transmission in only one direction. (e.g. brodcast radio)

Half-Duplex transfer

A communication mode where data transmission can occur in both directions, but not simultaneously; one device transmits while the other receives, and vice versa. (e.g. walkie-talkie)

Full-Duplex transfer

A communication mode that allows data transmission in both directions simultaneously. A full-duplex mechanism consists of two simplex mexhanisms, one carrying information in each direction (e.g. telephone conversation)

Network criteria

In order to be considered effective and efficient, a network must meet certain performance metrics such as performance, reliability, secutrity.

Computer network

An interconnected collection of autonomous computers.

Building blocks of the Internet

1. Hosts

2. Packet switches: forward packets (routers, switches)

3. Communication links (fiber, copper, radio, satellite) (transmission rate: bandwith)

4. Networks: collection of devices, routers, links

5. Internet (interconnected ISPs)

6. Protocols (control sending and receiving of messages (e.g. HTTP) )

7. Internet standards (RFC/IETF)

Applications and services of the Internet

1. Infrastructure that provides services to applications

2. Programming interface to distribute applications

Protocol

A set of rules that define how data is transmitted and communicated between devices in a network including formats, timing, and error handling. (e.g. TCP/IP)

Key elements of a protocol

1. Syntax- refers to the structure or format of data

2. Semantics- refers to the meaning of each section of bits

3. Timing- refers to when data is sent and how fast it is transmitted, ensuring synchronization between devices.

Standard

provides a model for development that makes it possible for a product to work regardless of the individual manufacturer. (e.g. IOD, IEEE)

Types of connections

1. Point-to-point

2. Multipoint

Point-to-point connection

a dedicated link between two devices

Multipoint connection

more than two devices share a link

Categories of networks

categories are determined by size, ownership, the distance the network covers, its physical architecture:

1. Local Area Network (LAN)

2. Metropolitan Area Network (MAN)

3. Wide Area Network (WAN)

LAN

a network, usually privately owned, that connects devices within a limited geographical area, such as a home or office, a building or campus

MAN

a network that spans a city or a large campus, providing connectivity within a metroploitan area. it’s larger than a LAN, but smaller than a WAN.

WAN

a network that covers large geographical areas, often connecting multiple devices and smaller networks. (e.g. The Internet)

Physical topology

refers to the physical layout of devices and connections in a network, including how cables and devices are arranged to form the actual network structure.

Mesh Topology

every device has a dedicated point-to-point link to every other device.

Advantages of a mesh topology

1. Guarantees full capacity

2. Highest level of robustness

3. Privacy

4. Fault identification/isolation

Disadvanatges of a mesh topology

1. Amount of cabling

2. Number of I/O ports

3. Expensive

Bus Topology

a multipoint connection- one long cable acts as a backbone to link all devices in the network, where each device connects at a different point along the cable

Advantages of a bus topology

1. Ease of installation

2. Less cabling

Disadvantages of a bus topology

1. Hard fault isolation

2. Fault in the bus is destructive

Ring Topology

Each device has a dedicated point-to-point connection with the devices on either side. A signal is passed along the ring in one direction until it reaches the destination.

Advantages of a ring topology

1. Easy installation

2. Fault isolation

Disadvantages of a ring topology

1. Unidirectional traffic

Star Topology

each device has a dedicated point-to-point link only to a central controller (hub or switch)

Advantages of a star topology

1. Less expensive

2. Robustness

3. Fault identification

Disadvantages of a star topology

1. Fault in switch is destructive

Internet structure

1. Netwrok edge

2. Access networks, physical media

3. Network core

Network edge

Consists of hosts: clients and servers that connect to the network core, providing services and applications to users.

Access networks

Physical connections between end-users and the core network, enabling data transmission through various mediums such as copper, fiber, or wireless communication links.

The network core

A mesh of interconnected routers.

Packet-switching

Hosts break appliication-layer messages into packets, network forwards them individually based on address information, optimizing data transfer efficiency, from one router to the next on path from source to destination.

Key network-core functions

1. Forwarding(“switching“): local action: move arriving packets from router’s input link to approptiate router output link.

2. Routing: global action: determine source-destination paths taken by packets

Access ISPs

Hosts connect to the internet vis acces Internet Service Providers (ISPs) that need to be interconnected so that any two hosts can send packets to each other.

Global Transit ISP

A large-scale internet provider that operates internationally, connecting entire countries and regions to the internet. ISPs are connected to a global transit ISP in otder to be able to access each other.

IXP

Internet Exchange Port - a physical location where multiple ISPs and networks connect to exchange traffc directly.

Regional ISP

Operates within a specific country or region, providing internet access to businesses and individuals.

“Center“ of the Internet

A small network of well-connected large networks: “tier-1“ commercial ISPs, content providers networks (e.g. Facebook, Google)

Content provider networks

Private network that connects its data centers to the Internet , often bypassing(not relying on) tier-1, regional ISPs.

Packet “sniffing“/ packet interception

the process of capturing and analyizing data packets as they travel across a network

IP spoofing

the process of forging the source IP address in network packets to disguise ones identity/impersonate another device

Denial of Services (DoS)

attackers make resources unavailable to legitimate by overwhelming resources with bogus traffic

Lines of defense:

1. Authentication

2. Confidentiality - via encryption

3. Integrity checks

4. Access restrictions - password-protected VPNs

5. Firewalls - detecting/reacting to DoS attacks

Cerf and Kahn’s Internetworking Principles(1974)

Defines today’s Internet architecture:

1. Minimalism, autonomy - no internal changes required to interconnect networks

2. Best-effort service model

3. Stateless routing

4. Decentralized control

The Network Access Module

deals with how devices physically connect to a network and transmit data

only provides raw data transmission services

Transport Module

responsible for ensuring reliable communication between devices across a network.

works above the Networks Access Module to manage data transmission efficiently

Layering

A structuring technique to organize networking software design and implementation. The layering model solves the problem of complexity in networking.

A layer provides a service to the one above and uses the service provided by the layer below, A layer talks to other layers using a protocol.

Advantages of layering

1. Code Reuse

2. Extensibility

3. Divide each task into pieces and then solve eaxh piece independently

4. Easier maintenance

The Internet Model (TCP/IP Protocol Suite)

Has 5 layers, each layer calls upon the service of the layer below and provides services to the layer above:

5.Application

4.Transport

3.Network

2.Data link

1.Physical

Physical Layer

Coordinates the functions required to transmit a bit stream over a physical medium. It is concerned with physical characteristics of interfaces and media, representation of bits, data rate, line configuration, physical topology, transmission mode(simplex, etc.), synchronization of bits. (bits on the wire)

Data Link Layer

Provides node-to-node data transfer and handles error correction from the Physical Layer. It is responsible for framing, addressing, and flow, error and access control. (main device: switch)(Ethernet)

Network Layer

Manages data forwarding, routing, and addressing between devices across multiple networks. It ensures that data packets are sent from the source to the destination via the best path. (main device: router(IP, routing protocols))

Transport Layer

Responsible for the delivery of an entire message from one application program on one computer to an application program on another. Its responsibilities are service-point addressing, segmentation and reassembly, connection, flow and error control. (e.g. TCP, UDP)

Application Layer

Enables the user to access the network - it provides user interfaces and support for services like electronic mail, remote file access and transfer, www, etc. (e.g. HTTP)

Header and layers

are used in networking to encapsulate data as it is passed through different layers of the Internet model. Each layer adds its own header information, which is essential for the proper interpretation of the data at the destination. Each layer on. the sending computer prepends extra information onto the packet(header), the corresponding protocol layer on the receiving computer removes and uses the extra infromation.

Encapsulation

The process of wrapping data in layers of protocol information as it moves through the Internet model, allowing for proper delivery and interpretation across different network communication layers. (A physical layer header is optional)

message (application) → segment (transport) → datagram (network) → frame (link)

Switch

A network device that connects devices on a local area network (LAN) by using packet switching to forward data to its destination. Switches operate at the data link layer (Layer 2) amd implements only layers 1 and 2.

Router

A networking device that forwards data packets between computer networks (routing), operating at Layer 3 (Network layer) of the Internet model. It determines the best path for data transmission across multiple networks. It implements layers 1, 2 and 3

The OSI Reference Model

A conceptual framework used to understand and implement network protocols in a seven-layer structure. Created by the International Organization for Standardization (ISO).

7.Application

6.Presentation

5.Session

4.Transport

3.Network

2.Data Link

1.Physical

Presentation

The sixth layer of the OSI model, responsible for data translation, encryption, and compression, ensuring that data is presented in a readable format // allows application to interpret meaning of data.

Session

The fifth layer of the OSI model, responsible for managing sessions between applications, coordinating communication (synchronization), and ensuring data exchange is properly organized and established.

Critique of OSI Model

+Very influential model with clear concepts

- Models, protocols and adoption all bogged down by politics and complexity (TOO COMPLEX)

Critique of Internet Model

+Very successful protocols that worked well and thrived.

-Derived from working protocols rather than a formal layered design: Lacks strict layering and can be less structured than the OSI model, less ideal for conceptual understanding.

Data transmission

The process of sending and receiving data across a network. To be transmitted data needs to be transformed into electromagnetic signals. It requires encoding bits as energy, transmitting energy through medium, decoding energy back into bits. (energy can be electric current, radio, infrared, light)

Analog Signals

A continuous wave form that changes smoothly over time and includes an infinte number of values along its path. (e.g. the output of a microphone)

Digital Signals

has a fixed set of valid levels (defined values), and each change consists of an instantaneous move from one valid level to another. (e.g. the output of a computer keyboard)

Carrier

A continuous, oscillating signal, used for long distnace communications. A waveform for carrier can be described by:

• Amplitude

• Frequency

• Phase

Amplitude of a signal

The difference between the maximum and minimum signal heights; the value of the signal at any point on the wave. Equal to the vertical distance from the given point on the wave to the horizontal axis.

Period

the amount of time, in seconds, a signal needs to complete one cycle

Frequency of a signal

The number of periods in one second, measured in hertz (Hz), which indicates how often the waveform repeats.

Phase of a signal

The relative starting point of a wave cycle, measured in degrees. It indicates the position of the wave at a specific moment in time, relative to a reference point.

Bandwidth

• In digital systems, bandwidth is expressed as data speed in bits per second.

• In analog systems, bandwidth is expressed in terms of the difference between the highest-frequency signal and the lowest-frequency signal.

Bit rate

The number of bits transmitted during one second.

Bit rate = baud rate * number of bits represented by each signal

Bit rate is always greater than or equal to the baude rate.

Baud rate

the number of signals per second (changes in signal) that our communication system can transmit

Channel capacity

The rate at which data can be transmitted over a given communication path or channel, under given conditions, is referred as the channel capacity.

Data encoding

A method used to convert data into a specific format for efficient transmission or storage. It uses the creation of a composite signal (modulation) at the sending end.

Amplitude Modulation

The strength of the carrier signal is varied to represent 1 or 0. Frequency and phase remain constant.

Frequency Modulation

The frequency of the carrier signal is varied to represent binary 1 or 0. Amplitude and phase remain the same.

Phase Modulation

The phase of the carrier signal is shifted to represent binary 1 or 0. Amplitude and frequency remain constant.

Synchronisation

The process of coordinating and aligning the operations of various signals to ensure they work together effectively - in receiver and sender.

Digital data transmission

The transmission of binary data across a link can be accomplished either in parallel or serial modes.

Parallel Transmission

The simultaneous transmission of multiple bits of data across several channels or wires, allowing for faster data transfer rates compared to serial transmission. Use N wires to send N bits at one time. More expensive.

Serial Transmission

The method of sending data one bit at a time over a single channel or wire, resulting in slower data transfer rates compared to parallel transmission, but often at a lower cost.

Modems

The name Modem stands for Modulator/Demodulator

→ A modulatore converts a digital signal into an analog signal

→ A demodulator converts an analog signal to a digital signal

Multiplexing

Multiplexing is the set of techniques that allows the simultaneous transmission of multiple signals across a single data link.

→ Multiplexer: combones signals into a single stream

→ Demultiplexer: separates the stream back into each component transmissions

→ A path/link can have many channels

Categories of Multiplexing

1. Frequency-division multiplexing (FDM)

2. Time-division multiplexing (TDM)

   1. Synchronous

   2. Statistical

3. Wave-division multiplexing (WDM)

Frequency-division multiplexing

FDM is a technique that allows multiple signals to be transmitted simultaneously over a single communication channel by allocating different frequency bands to each signal.

Wave-division multiplexing

WDM uses the same concept as FDM but involves light signals transmitted through fiber optic channels.

Time-division multiplexing

• Synchronous TDM - arranges for sources to proceed at a round-robin scheme, providing absolute guarantee of fairness.

• Statistical TDM - works the same but the multiplexer skips the source if there is no data to send.

Classes of transmission media

• Guided

• Unguided

Guided transmission media

Includes physical media like cables (fiber optic, coaxial) that guide signals from one device to another.

ex: - UTP, STP, Coaxial Cable, Optical Fiber

Unguided transmission media

Refers to wireless transmission methods that do not use physical conduits, relying on air or vacuum for sending signals. Examples include radio waves, microwaves, satellites and infrared signals.

Unshielded Twisted Pair Cable

A type of guided transmission media commonly used for network connections, consisting of pairs of wires twisted together to reduce electromagnetic interference between the wires. It is the most common medium, transmits both data and voice, is used in telephone system.