Notes, summaries, assignments, exams, and problems for Computers

OPENFLOW:

defines OpenFlow as the first standard communications interface defined between the control and forwarding layers of an SDN architecture. OpenFlow allows direct access to and manipulation of the forwarding plane of network devices such as switches and routers, both physical and virtual 

OPENFLOW CONFIG CONCEPTS

OF Capable Switch: Physical OF switch.  Can contain one or more OF logicalswitches.

OpenFlow Configuration Point: configurationservice

OF Controller: Controls logical switch via OFprotocol

Operational Context: OF logicalswitch

OF Queue: Queues of packets waiting forforwarding

OF Port: forwarding interface. May be physical orlogical.

OF Resource: ports, queues, certificates, flow tables and other  resources of OF capableswitches 

Discuss the advantages of address aggregation (summarization) with respect to routing table size, routing update exchange, and routing optimization?

Route aggregation and subnetting shrink the size of routing tables used by routers. Without CIDR, a router must maintain many individual entries for routes within the same network. CIDR guarantees more efficient routing and reduces the number of CPU cycles when updating a routing table. It also reduces router memory requirements.

What are the key characteristics or requirements that should be fulfilled by any routing protocol?

A routing protocol should guarantee loop-free paths, calculate multi-hop optimal paths, use simple or composite network metrics, be scalable, converge rapidly, use network resources... Continue reading "Advantages of Address Aggregation and Key Characteristics of Routing Protocols" »

Managing operating systems on workstations boils down to three basic tasks: loading the system
software and applications initially, updating the system software and applications, and
configuring network parameters.
We call these tasks the Big Three.

The Five States

The diagram depicts five states: new, clean, configured,
unknown, and off.

• New refers to a completely new machine.
• Clean refers to a machine on which the OS has been installed
  but no localizations performed.
• Configured means a correctly configured and operational
  environment.
• Unknown is a computer that has been misconfigured or has
  become out of date.
• Off refers to a machine that has been retired and powered off.

Transitioning Between States

There are many ways to get from one lifestyle... Continue reading "Managing Operating Systems on Workstations: The Big Three" »

Computer System Essentials

Core Operating System Components

Kernel: The OS's Foundation

The operating system's core, a platform that allows other software to execute.

Shell: User Interaction Interface

The operating system's interface for users to interact with all computer elements.

Thread: A Running Program or Task

Any program or task that is currently running.

File System: Data Storage & Retrieval Protocol

A protocol that defines how files are stored and retrieved on disk drives, or by threads and programs.

Disk Formatting: Setting a File System

The process of setting a disk's file system.

Major Operating Systems and Their Focus

• Microsoft Windows: Focuses its operating system on security.
• Linux: Emphasizes customizability.
• Chrome OS: Centered on web

Set Cover to Efficient Recruiting

Input: Set U of elements, collection S₁, ..., S_m of subsets of U, integer k ≥ 0

Construct an instance of the Efficient Recruitment Problem:

• Sports are represented by U.
• Applicants are represented by {1, ..., m}.
• For every s ∈ U and 1 ≤ i ≤ m, M[s, i] = 'qualified' if s ∈ S_i and 'not qualified' otherwise.

Steps:

1. Call the oracle for Efficient Recruiting with input M and k.
2. Return the result (yes or no) of the previous call.

Vertex Cover and Hitting Set

Graph: G = (V, E)

• U = V(G)
• S_i = {u, v}, where (u, v) is an edge of G.

Vertex Cover ⇒ Hitting Set:

If C is a vertex cover for G of size k, then by definition, for every edge (u, v) in G, either u ∈ C or v ∈ C. Therefore, C is a solution for Hitting Set because... Continue reading "Efficient Recruiting and Algorithm Design: Set Cover, Hamiltonian Path, and Longest Increasing Subsequence" »

Dynamic Host Configuration Protocol (DHCP) Servers

What is a DHCP Server?

A DHCP Server is a network server that automatically provides and assigns IP addresses, default gateways, and other network parameters to client devices. It relies on the standard protocol known as Dynamic Host Configuration Protocol (DHCP) to respond to broadcast queries by clients.

Benefits of DHCP

A DHCP server automatically sends the required network parameters for clients to properly communicate on the network. Without it, the network administrator has to manually set up every client that joins the network, which can be cumbersome, especially in large networks. DHCP servers usually assign each client with a unique dynamic IP address, which changes when the client’s... Continue reading "Network Fundamentals: DHCP, Subnetting, and Transport Protocols" »

This section details the implementation of the Jacobi method in Fortran for solving a system of linear equations. The subroutine solucion_Jacobi takes a matrix A, a vector b, and an initial guess X as input, and returns the solution vector X.

Subroutine: solucion_Jacobi(A, b, X)

The subroutine begins with the following declarations and initializations:

• use normas
• integer, parameter :: Kx = 100
• real(8), parameter :: tolerancia = 1E-6
• real(8), allocatable :: X0(:), ERROR(:)
• real(8), intent(in) :: A(:,:), b(:)
• real(8), allocatable, intent(out) :: X(:)
• integer :: i, j, k, n
• real(8) :: sum, zero, ek

Where:

• Kx is the maximum number of iterations.
• tolerancia is the error tolerance.
• X0 is the previous iteration's solution vector.
• ERROR is the error vector.
• A is the

Binary Conversion

Single-Precision Floating-Point

Format: 1 sign bit, 8 exponent bits, 23 fraction bits

Bias: +127 (decimal to binary), -127 (binary to decimal)

Double-Precision Floating-Point

Format: 1 sign bit, 11 exponent bits, 52 fraction bits

Bias: +1023 (decimal to binary), -1023 (binary to decimal)

Example: -17.6875 (Single-Precision)

1. Sign Bit: + = 0, - = 1 (In this case, 1)
2. Integer Part to Binary: Repeatedly divide the integer part by 2 and record the remainders.
3. Fractional Part to Binary: Repeatedly multiply the fractional part by 2 and record the integer parts.
4. Combine and Normalize: Combine the binary integer and fractional parts. Normalize to the form 1.xxx * 2^exponent.
5. Calculate Exponent: Add the bias to the exponent.

Intra-AS Routing

RIP – Based on Distance-Vector (D-V), fewer messages, converges slower, smaller size.

OSPF – Based on Link-State (L-S), converges faster, more messages, larger networks.

Distance-Vector is distributed, and each router only knows the costs to its neighbors and their distance vectors.

Link state is global and requires that each router knows the network topology and link costs to all nodes.

OSPF: Used internally inside a network, an intra-network/domain protocol used in an AS.

BGP: An internetwork protocol used between two different ASs, used at the edge of your network to connect your network to the internet.

RIP: An intra-network protocol used in an AS, used for small networks (maximum number of hops is 16).

EBGP: Runs between two... Continue reading "Routing Protocols: RIP, OSPF, BGP, CSMA/CD, CSMA/CA" »

• Accuracy

  Tells us how correct a GPS measurement is.

• Array

  A group of disk drives that are connected and used as a single unit.

• Assembler

  A program that translates low-level programming language into machine code.

• Attachment

  A file sent as part of an email.

• Avatar

  An image in a computer game that represents a person.

• Barcode

  An arrangement of lines and spaces that represent data.

• Bit

  The smallest unit of computer data.

• Bitrate

  A measurement of the amount of data that is processed.

• Broadband

  A system that allows computers to transfer large amounts of information.

• Calibration

  The act of adjusting printers and scanners to display colors correctly.

• Capacity

  The amount of space an MP3 player has to store files.

• Catalog

  An inventory of books in a library.

• Cell phone

  A wireless