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Networks
Networks is a hierarchical model and has 3 layers:
Access, Distribution, Core
What pulses into pits in physical layer (transmission media) of network?
Voltage, radio frequency or light
Types of wired physical layer
Network can get Interferences
from external signals such as:
- Radio waves
- Electric engines
- Fluorescent tubes
Uses of unshielded twisted pair (UTP)
Ethernet networks, among many other uses (mainly indoor applications)
What advantages does unshielded twisted pair (UTP) have?
Twisted pairs cancel unwanted signals.
Describe physical aspect of unshielded twisted pair (UTP)
Four unshielded twisted pairs with different colours and plastic cover.
What type of performance does Cat (Category) 5e cable provide?
100MHz
suitable for10BASE-T, 100BASE-TX (Fast Ethernet), and 1000BASE-T (GigabitEthernet)
What is Cat (Category) 5e cable?
Cable standard
What is crosstalk?
a signal transmitted on one channel of a transmission system creates an undesired effect in another circuit or channel
Specifications of Cat 6 cable
Backward compatible
Specifications against crosstalk and noise
performance of up to 250 MHz
RJ-45 connectors when used as patch cable
Specifications of Cat 6a cable (augmented)
Unshielded and Foiled
defines the standard at frequencies up to 500 MHz
rates up to 10 Gbps
Specifications of Shielded Twisted Pair (STP)
Better transmission characteristics than UTP
Shielding is applied to all pairs individually and an additional overall shielding is also added.
Specifications of Cat 7 and 7A cables
It allows 10 Gigabit Ethernet
Up to 1000 MHz
Specifications of Cat 8 cables
It allows 40 Gigabit Ethernet
Up to 2000 MHz
Transmission problems - ATTENUATION
Attenuation is the gradual loss of signal intensity through a medium
Transmission problems - DELAY or LATENCY
It depends on the operating frequency
a measure of the time delay experienced by a system
The delay of a network specifies how long it takes for a bit of data to travel acrossthe network from one node or endpoint to another.
Transmission problems - THERMAL NOISE– ELECTRONS (Thermal agitation)
temperature-dependant
it adds White noise to signal and can distort it
Transmission problems - INTERMODULTION NOISE– NONLINEAR SYSTEMS (Pink noise)
Combined frequencies (f1+f2, f1-f2)
Pink noise can interfere with the transmitted signal and degrade its quality.
Transmission problems - PULSES
pulses problems are short time and
irregulars
Describe Optical Fiber
flexible, transparent fiber made by drawing glass (silica) or plastic to a diameter slightly thicker than that of a human hair
used most often as a means to transmit light between the two ends of the fiber and find wide usage in fiber-optic communications
they permit transmission over longer distances and at higher bandwidths (data rates)than electrical cables
Signals travel along them with less loss
Fibers are immune to electromagnetic interference
In optical fiber light is kept in
the core (by the phenomenon of total internal reflection)
Optical fibers typically include a core surrounded by
a transparent cladding material with a lower index of refraction. (so that light be kept inside of it)
To confine the optical signal in the core of optical fiber the refractive index of the core must be SMALLER/GREATER than that of the cladding.
Greater
Fibers that support a single mode are called single-mode fibers (SMF). While Fibers that support many propagation paths or transverse modes are called
multi-mode fibers
Multi-mode fibers generally have a WIDER/NARROWER core diameter and are used for LONG-DISTANCE/SHORT-DISTANCE communication links and for applications where high power must be transmitted.
Wider, Short distance
Single-mode fibers are used for most communication links longer than
1000 meters
Power over Ethernet (PoE) is a technology for implementing
wired Ethernet local area networks (LANs) that enables the electrical current necessary for operating each device to be carried by Ethernet data cables instead of standard electrical power cords and wiring.
PoE (Power over Ethernet) specifics
Powered via distributor
Power and data is transmitted
Standard IEEE 802.3af PoE
A collision domain is
a network segment connected by a shared medium or through repeaters where data packets may collide with one another while being sent. The collision domain applies particularly in wireless networks, but also affected early versions of Ethernet.
Carrier-sense multiple access with collision detection (CSMA/CD) is
a media access control method
In OSI model Host Layers include
Data and segments
In OSI model Media Layers include
Packets, frames, bits
OSI vs TCP/IP diagram
OSI vs TCP/IP diagram
A trunk port is
a port that is assigned to carry traffic for all the VLANs that areaccessible by a specific switch, a process known as trunking.
4 Basic processes in the network layer:
Addressing
Encapsulation
Routing
Decapsulation
Networks can be grouped by:
Geographic location
Purpose
Ownership
Why do we need to separate hosts in networks?
avoid degradation in performance
Security
Addressing management
VLAN is a
subnet, broadcast domain
(virtual local area network)
VLANs are able to logically segment switched networks, based on
Physical location
organizations
Switches are level 2 devices which are able to understand (IP or MAC ) addresses
MAC
VLANs provide segmentation based on
broadcast domains
hosts in different subnets will be able to communicate with each other through
a Router
VLANs are assigned in the switch and are associated to the
hosts’ IP addresses
Ports assigned to the same VLAN share the same broadcast domain. TRUE/FALSE
TRUE
Members of static VLANs are known as
port based
Routable protocols VS Routing protocols
Routable protocols:- IP, IPX/SPX
Routing protocols:- RIP, EIGRP, OSPF
Routable Protocols VS Routing protocols definitions
Routable protocols:
A communications protocol that contains a network address as well as a device address. It allows packets to be forwarded from network to another.
Routing protocols:
They specify how routers communicate with each other, distributinginformation that enables them to select routes between any two nodes ona computer network. Routing algorithms determine the specific choice ofroute.
By default, L3 switches don’t operate in layer 3. That’s why, first of all, to activate it X is required
IP routing
To save the configuration backups we use
TFTP (Trivial File Transfer Protocol)
DNS is a
Domain Name System
Zone Authority is the part of a (X) on which a server is responsible
Name Space
What Name Server does?
replies to all the client questions
keeps the names assignment for all IP addresses of the area.
What has static vs dynamic IP addresses?
Static IP addresses
Servers, Switches, routers
Dynamic IP addresses
Clients (end devices)
What does DHCP (Dynamic Host Configuration Protocol) automate?
DHCP enables the network devices to obtain IP address automatically andsome additional information from a DHCP server. This software serviceautomates the IP addresses, subnet masks and gateways allocation
Wireless security types
Wired Equivalent Privacy (WEP)
Wi-Fi Protected Access (WPA) best one now si WPA3 = improved WEP
pre-shared key (PSK)
TKIP - no longer considered secure
AES-CCMP = encryption
protocol (better than WEP)
Extensible Authentication Protocol (EAP) = authentication
framework
Remote Authentication Dial-In User Service (RADIUS) = networking protocol
Operating system is USER/KERNEL mode?
KERNEL
Driver is a
group of files that enable one or more hardware devices to communicate with the computer's operating system.
What resources does the operating system manage?
Processors● Memories● Timers● Disks● Mice● Network Interfaces
What is a system bus?
A bus is a subsystem that is used to connect computer components and transfer data between them.
System bus is made of 3 components
Control Bus, address bus, data bus
Types of operating systems:
Mainframes● Servers● Multiprocessors● Personal Computers● Handheld (Mobile)● Embedded● Sensor Node● Real Time● Smart Cards
What is a kernel?
It is the main layer between the OS and underlying computer hardware, and it helps with tasks such as process and memory management, file systems, device control and networking
What is the purpose of a Kernel?
1. It provides the interfaces needed for users and applications to interact with the computer.
2. It launches and manages applications.
3. It manages the underlying system hardware devices
What is scheduling?
The process scheduling is the activity of the process manager that handles the removal of the running process from the CPU and the selection of another process on the basis of a particular strategy.
Goals of a scheduler:
maximizing throughput
minimizing wait time
What is race conditions?
When two or more processes are reading or writing some shared data and the final result depends on who runs precisely when, are called race conditions.
What are critical regions?
It is the resource that is being shared between the processes.
How to solve problem with critical regions?
No two processes may be simultaneously inside their critical regions.
No assumptions may be made about speeds or the number of CPUs.
No process running outside its critical region may block any process.
No process should have to wait forever to enter its critical region.
What is memory management?
The task of subdividing the memory among different processes is called memory management.
Memory management algorithms:
First fit (In the first fit, the first available free hole fulfills the requirement of the process allocated.)
Best fit (In the best fit, allocate the smallest hole that is big enough to process requirements. For this, we search the entire list, unless the list is ordered by size.)
Worst fit (Allocate the largest available hole to process. This method produces the largest
leftover hole.)
Note 
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