ComputerArchitecture

Final Exam prep for computer architecture, networks and OS

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.)