In the context of data communications, the following definitions are used
1 Data and Signal
2 Communication Channel
3 Network Address
4 Packet Switches: Router and Switch
5 LAN network
6 Network Node
7 Network Endpoint
1 Data and Signal
DATA and INFORMATION
Data consists of raw facts that need to be processed. When data is interpreted, processed, organized so as to make it meaningful, it becomes information.
Example: a list of dates is data, a list of holiday dates is information.
DATA and SIGNAL
Data has to be converted into a form suitable for transmission.
Signals are electrical or electromagnetic representations of data that are suitable for transmission.
Like data, signal may be either in analog or digital form.
All the combinations of the data and signal forms are possible: - analog data converted into analog signal form, for example telephone; - analog data converted to digital signal form, for example codec; - digital data converted to analog signal form, for example modem; - digital data converted to digital signal form, for example digital transmitter.
DATA TRANSMISSION AND SIGNAL TRANSMISSION
Data transmission involves the transfer of data in the form of signal, transmitted over a communication channel.
Signal transmission is the propagation and processing of signals. A sending node converts data into signal and transmits the signal through some medium, such as a cable or the airwaves, then the receiving node turns the signal back into the original data.
SIGNAL AS FUNCTION
Signals are functions of time; signals may be continuous or discrete in time: a continuous-time signal has values for all points in time in some (possibly infinite) interval, a discrete-time signal has values for only discrete points in time.
Signals can also be a function of space (images) or of space and time (video), and may be continuous or discrete in each dimension
ANALOG AND DIGITAL SIGNALS
Analog signals are continuous in both time and amplitude; example of analog waveforms are sounds, telephone systems, radio and television signals.
Digital signals are discrete both in time and amplitude, they represent data as a sequence of discrete values. A discrete-time signal is a sampled version of an analog signal: the value of the datum is only noted at fixed intervals (for example, every microsecond) rather than continuously.
DATA VS SIGNAL
| Data | Signal | |
|---|---|---|
| Function | information to transmit | the waveform used to transmit the data |
| Quantity of measurement and unit of measure | data rate or bit rate in bps/Kbps/Mbps/Gbps | signal rate or baud rate in baud/Kbaud/Mbaud |
| Trasmission speed parameter | Bitrate, is the measure of the volume of data transmitted over a transmission channel or via a data interface within a specified unit of time. A higher bitrate will result in higher-quality streaming | Bandwidth, is the maximum rate at which data can be transferred across a given path or medium. High bandwidth network can deliver more data than a low bandwidth network in the same amount of a time |
| Form | Analog (Continuous) or digital form (Binary or discrete) | Analog (Electric, EM, Optical) or digital form ( RZ (Return to Zero) or NRZ (Non Return to Zero) signals ) |
SIGNAL FUNDAMENTALS
Decibels (db) are units of measurement of signal strength. Decibel measurements are relative and logarithmic.
Signal Properties include: amplitude, frequency, spectrum, bandwidth and phase
SIGNAL NOISE AND ATTENUATION
Noise and attenuation affect the signal over a medium. Attenuation is the loss of the signal strength over distance. Noise is the additional unwanted energy that interferes with the signal.
SIGNAL SPECTRUM
In Physics, the term spectrum was introduced into optics to describe the full range of colors observed when white light was dispersed through a prism. The term applied to a chart of light intensity as a function of frequency or wavelength, also known as a spectral density plot. Later, the term was applied to the entire electromagnetic spectrum, to wavelengths that lie outside of the visible light spectrum.
Then, the term spectrum was also applied to other waves (for example sound waves) that could be measured as a function of frequency and to more abstract "signals".
Now, the term spectrum indicates a mapping of a range of wavelengths to a range of properties.
2 Communication Channel
In telecommunications and computer networking, a communication channel is about either a physical transmission medium or a logical connection over a multiplexed medium. Channels are used to transfer information from senders to receivers; channels convey signals carrying information. A channel has a certain capacity for transmitting information, measured by its bandwidth in Hz or its data rate in bits per second.
Examples of communications channels:
- In telecommunications, a connection between initiating and terminating communication endpoints of a circuit.
- In telecommunications and computer networking, a single path provided by a transmission medium, such as a dedicated multipair cable or shared/mupliplexed medium.
- A specific radio frequency, pair or band of frequencies, usually named with a letter, number or codeword, for example: Marine VHF radio, Television channels (in analog television signals, each channel is 6 MHz wide, requiring a bandwidth of 6 MHz), Wi-Fi using 13 channels in the ISM radio bands from 2.4 GHz to 6 GHz frequency bands, in 5 MHz steps and a bandwidth of 22 MHz.
3 Network Address
IP ADDRESS
Every device that connects to the Internet is assigned a IP address by the network, using the DHCP protocol. Devices that connect to the Internet are typically assigned IP addresses dynamically using DHCP (although addresses can also be configured statically). The IPv4 address uses a 32-bit number; the IPv6 address uses a 128 bits number.
PUBLIC IP AND DYNAMIC IP ADDRESS
IP addresses can be public (on the Internet) or private (in a LAN). A public IP address is used to access the Internet. In a home or small office access network, the router is assigned a public IP address by the ISP. The public IP address is unique on the Internet. A private IP address is used in a local network not on the Internet. A device connected to an access router is assigned a private IP address by the router. Private IP addresses must be unique within the same local network.
Most user devices are assigned an IP addresses that changes: an IP address that changes is called a dynamic IP address. Dynamic IP addresses change every time a device establishes a new connection with a network or the DHCP lease time expires. On the other side, servers are assigned IP address that does not change: an IP that does not change is called permanent IP address
WHAT IS THE FUNCTION OF THE IP ADDRESS?
An IP address serves two functions: it identifies the host and it provides the location of the host in the network.
The IP address acts as an email address, making it possible for the Internet traffic directed to that address to arrive at the device. IP addresses are used at layer 3, this is why all hosts on Internet use a public IP address for exchanging packets, independently of the network the hosts are connected to.
The header of all IP packets contain the IP address of the source host and the IP address of the destination host, just like an email message has a source address and a destination address.
MAC ADDRESS
Every network controller (NIC) is assigned a media access control (MAC) address by the hardware manufacturer.
The MAC address is a unique identifier that does not change: it is like a serial number
The MAC address acts as a network address for communication within a network segment in many common networking technologies, such as Ethernet, Wi-Fi and Bluetooth.
IP AND MAC NETWORK ADDRESSES
MAC addresses are used at layer 2, not layer 3, so they are not included in the header of IP packets.
Source and destination IP addresses do not change as the packet is transmitted across Internet, instead the MAC addresses change for each new local network the packets traverse and each pair of routers the packets are sent between
4 Packet Switches: Router and Switch
ROUTER
A router is a Layer 3 device that connects two or more packet-switched networks.
The primary function of a router is to determine the best path for packets and forward them between networks.
In home and business local networks, edge routers also enable multiple devices on the local network to share a single public IP address, typically through Network Address Translation (NAT).
There are two types of routers: - the edge router: they connect subscribers to their provider’s network so they can access the Internet; they connect an organization's internal LAN network to external WAN networks. - core routers: they forward packets across the Internet backbones to interconnect communication networks.
What is the difference between a router and a modem? Even if manufacturers combine a router and a modem within a single device known as edge routers or gateways, they are not the same: a router joins networks together, whereas a modem connects a device to the Internet. By using a router and a modem together, you can create a network with multiple devices and allow all them to connect to the Internet simultaneously.
NETWORK SWITCH
A switch is a multiport network device that allows devices to be connected within a network, often a LAN network.
A switch allows devices to communicate by forwarding Ethernet frames at the data link layer using the MAC address
A switch enables devices to share resources such as printers, servers and broadband access
Switches come in different forms: they can be a dedicated appliance or a component of other device, such as a network router and a wireless access point.
Simple switches and advanced switches
a simple switch offers connectivity to devices on a LAN, whereas advanced switch connect devices from multiple LANs
a simple switch forwards data at layer 2 and is also called layer 2 switch; an advanced switch can also forward data at the network layer (incorporating routing functionlity); these switches are known as layer 3 switches or multilayer switches.
advanced switches add also routers' and firewalls' functionalities, nevertheless they continue to be called switches.
There also switches for other types of networks, such as: Fibre Channel, Asynchronous Transfer Mode and InfiniBand, but the most common network switches are the layer 2 switches for Ethernet networks.
Unmanaged switch and managed switch
an unmanaged switch simply adds more Ethernet ports and allows more devices to connect to the LAN
a managed switch carry out the same task for larger networks and give network administrator more control on the network traffic; also it allows to create virtual networks
COMPARING SWITCHES AND ROUTERS
a switch forwards packets to a single device, whereas a router forwards packets from a network to another network
a switch allows different devices on a network to communicate, a router allows different networks to communicate.
routers are used for connecting to Internet, switches are used for interconnecting devices
home and small offices need a router, they do not need a network switch, but large offices and data centers with hundreds of computers need a switch
5 LAN network
LAN DEFINITION
A local area network (LAN) is a computer network that interconnects devices within a small geographic area, such as house, school, university campus and office building. Examples of simple LAN networks are: a WiFi network and a small business network
LAN COMPONENTS
A LAN consists of cables, access points, switches, router and other components. Small LANs connect to the Internet using a single router (and a way to connect to the router, such as Ethernet cable or WiFi access point), larger LANs use additional network switches.
ADVANTAGES OF USING LANS
A LAN connects multiple devices and allow them to exchange information.
Users on a LAN can access internal servers, local websites and other LANs belonging to the same wide area network.
Connected devices can share expensive resources, such as printers, applications, data store and other services.
Connected devices are protected by network security tools.
Multiple devices share a single internet connection.
HOW LAN WORKS - LAN TECHNOLOGY
LANs use Wi-Fi or Ethernet technologies or both to connect devices within the network.
Ethernet LANs are also kwown as wired LANs, whereas Wi-Fi LANs are also known as wireless LANs (WLANs)
Wired LANS
- a wired LAN connect devices using switches and Ethernet cabling
- small wired LANs consists of only a single unmanaged LAN switch
- larger LANs use extra hardware and software as well as virtual LANs (VLANs) (If an organization has too many devices connected to the LAN, the broadcast traffic can create congestion. VLANs can reduce the broadcast traffic, by breaking up the broadcast domain in smaller broadcast domains. So, network administrators logically group network nodes, by breaking up the network in multiple virtual LAN).
Wireless LANS
- they are based on the IEEE 802.11 standard
- they use high frequency radio waves (in the 2.4 GHz and 5 GHz spectrum) to connect devices
- they are preferable to wired LAN connection because it is not required to deploy cabling within buildings
LAN ARCHITECTURE
There are two types of LAN architechture: client/server and peer-to-peer LANs
-
CLIENT/SERVER
the client/server LAN consists of several client devices connected to a central server
the server controls file storage, applications and network traffic
the client accesses the Internet or applications
the server keeps a suite of applications and users of the applications access datatabase, email, document sharing and printing and other services
many medium-sized businesses and enterprises employ server-based LANs -
PEER-TO-PEER
peer-to-peer LANs are smaller than client-server LANs, because they can't hold heavy workloads like the client-server LAN
with peer-to-peer LAN, each device shares its resources to a switch or router to make the network function
most home networks have peer-to-peer architecture
LANs CONNECT TO OTHER LANs: LAN, MAN and WAN
LANs connect to other LANs using private leased lines or through Internet using virtual private networks (VPN). If the connection between the LANs covers long distance, these network of LANs may be classified as a metropolitan area network (MAN) or a wide area network (WAN). LAN, WAN and MAN differs in terms of size and technology.
A Local Area Network connects devices that are relatively close. A LAN is deployed inside a building. Ethernet is the most used technology for LANs.
A Metropolitan Area Network is used by an organization that is located in multiple buildings within a city or municipality. The different buildings are connected using fiber optic cables, metropolitan-area Ethernet or wireless technologies.
A Wide Area Network connects company locations that are spread throughout a state or a country.
Business organizations buy WAN connectivity from a telecommunication service provider, including metropolitan-area Ethernet (metro Ethernet), Virtual Private LAN Service (VPLS), Ethernet over Synchronous Optical Networking (SONET) and satellite broadband.
6 Network Node
A network node is a point of connection within a data communication network. Network nodes can take many forms, including computers, servers, routers, switches, and other devices that are capable of sending, receiving and forwarding data packets within the network.
7 Network Endpoint
A network endpoint represents the point of entry or exit for data on a network and allows communication and data exchange within a network environment.
Endpoints enable communication between different entities in a network. Client applications interact with a server or a service using endpoints.
Types of Endpoints
The types of endpoints vary depending on the context in which they are used
ENDPOINT IN THE WEB
In the client-server architecture of the World Wide Web, an endpoint is an URI used to access a resource or service on a network. If a client, for example a web browser, want to access a resource or service, it will send a HTTP request to a known endpoint and it will get a HTTP response. Endpoints are represented by URIs.
A web API is contract that defines a set of rules to interact with a web service; an endpoint is a specific URI exposed by a web API, each API endpoint represents a specific functionality provided by the web API.
NETWORK ENDPOINTS
In computer networking, an endpoint is a node that indicates the start of the end of a communication path; they can be physical devices, such as a computer or virtual entities, such as a container. Network endpoints are assigned an network address such as a IP address, used to route the data packets.
SECURITY ENDPOINTS
In cybersecurity, an endpoint is about a networked device that is vulnerable to security threats.
8 URI, URL, URN
URI
A Uniform Resource Identifier (URI) is a sequence of characters that identifies an abstract or physical resource.
URI Syntax Components
The URI generic syntax consists of five components organized hierarchically:
URI = scheme ":" ["//" authority] path ["?" query] ["#" fragment]
A component is undefined if it has an associated delimiter and the delimiter does not appear in the URI; the scheme and path components are always defined.
The authority component consists of subcomponents:
authority = [userinfo "@"] host [":" port]
The scheme and path components are required, though the path may be empty.
When authority is present, the path must either be empty or begin with a slash ("/") character.
When authority is not present, the path cannot begin with two slash characters ("//").
The following are two example URIs and their component parts:
http://example.com:8080/app2/page3?name=ferret#nose
\__/ \______________/\_________/ \_________/ \__/
| | | | |
scheme authority path query fragment
| _____________________|__
/ \ / \
urn:example:animal:ferret:nose
Examples
The following example URIs demonstrate several URI schemes:
ftp://ftp.is.co.za/rfc/rfc1808.txt
http://www.ietf.org/rfc/rfc2396.txt
telnet://192.0.2.16:80/
ldap://[2001:db8::7]/c=GB?objectClass?one
mailto:john.doe@google.com
tel:+1-816-555-1212
urn:isbn:0451450523
URLs and URNs
A URI can be further classified as a locator, a name or both.
The term "Uniform Resource Locator" (URL) is about the subset of URIs that, in addition to identifying a resource, provide a means of locating the resource or retrieving a resource's representation on a network (on the Internet or on a computer filesystem or an Intranet).
The term "Uniform Resource Name" (URN) is about URIs that provide globally unique persistent identifiers assigned within defined namespaces, without a means of retrieving the resource information. URNs identify a resource in persistent way, even after the resource ceases to exist or becomes unavailable.
Comparing and Contrasting URI and URL
A URI (Uniform Resource Identifier) is a string that identifies a resource. A URL (Uniform Resource Locator) is a type of URI that also specifies the protocol and location used to access the resource. In other words, every URL is a URI, but not every URI is a URL.
Application Examples
- HTTP requests needs a pair of resource's URI and HTTP verb
- HTML LINKs (IMG src attribute and Anchor href attribute) uses an URI
- XML namespace declarations uses an URN
- Web Endpoints uses URIs
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