CCNA-1: Chapter 1

Chapter 1 - Living in a Network-Centric WorldCCNA Exploration
Network Fundamentals
This chapter introduces the platform of data networks upon which social and business relationships increasingly depend. The material lays the groundwork for exploring the services, technologies, and issues encountered by network professionals as they design, build, and maintain the modern network.
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Describe the role of data networking in the human network
Identify the key components of any data network
Identify the opportunities and challenges posed by converged networks
Describe the characteristics of network architectures relating to fault tolerance, scalability, quality of service (QoS) and security
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Networks Supporting The Way We Live
Data networks that were once the transport of information for businesses are now also used to improve our quality of life
check bank balance and pay bills electronically
find the least-congested route to a destination
use instant messaging and chat for both personal and business use
post and share your photographs, home videos and experiences
shop and sell at online auctions
use Internet phone services
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Instant messaging (IM)
also supports voice, photo and video sharing, and file transfers
Blogs or weblogs
individuals publish their personal opinions and thoughts about any conceivable topic
allow unfiltered and unedited publication of ideas from anyone
Podcasting
Wikis
publicly created web content that groups of people can edit and view together
organizations and individuals build their own wikis to capture collected knowledge for use as collaboration tools
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Examples of Communication Tools
Instant messaging is everywhere and can include audio and video conversations. IM can send text messages to mobile phones.
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Traditional learning methods make use of textbooks and instructor-led classes
Courses delivered using networks or Internet resources are often called online learning experiences or e-learning
Online courses can contain voice, data and video
available to the students at any time from any place
Blended courses can combine instructor-led classes with online courseware to provide the best of both delivery methods
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Global Online Learning Experience
The instructor provides a syllabus and establishes a preliminary schedule for completing the course content
The way we learn is supported by courseware delivered over the data network
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Learning by Sharing and Exploring
Students can communicate with the instructor and fellow students using online tools
bulletin/discussion boards, chat rooms and instant messaging
Links provide access to learning resources outside the courseware
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Current and accurate training materials
collaboration among vendors, equipment manufacturers and training providers ensures that the courseware is up to date with the latest processes and procedures
Availability of training to a wide audience
online training is not dependent on travel schedules, instructor availability, or physical class size
Consistent quality of instruction
quality of instruction does not vary as it would if different instructors were delivering an in-person lesson
Cost reduction
facilities to support in-person training can be reduced or eliminated
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Networks Supporting The Way We Work
Business applications can be accessed remotely as if employees were on site
Workers in any location can reach each other and access multiple resources on the network
Remote Access
Networks Supporting The Way We Play
Explore places of interest interactively or preview actual destinations before a trip
Posting photographs about an event online for others to view
Participate in online games
Rules or agreements to govern the conversation are first established
these rules, called protocols, must be followed in order for the message to be successfully delivered and understood
A message with important information may need a confirmation that the message has been received and understood
As a message moves through the network, many factors can prevent the message from reaching the recipient or distort its intended meaning
internal or external factors
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External Factors
The quality of the pathway between the sender and the recipient
The number of times the message has to change form
The number of times the message has to be redirected or readdressed
The number of other messages being transmitted simultaneously on the communication network
The amount of time allocated for successful communication
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Internal Factors
The size of the message
it is more difficult to deliver a large bulky message, quickly and without damage, than it is to deliver a number of smaller, less complex messages
The complexity of the message
The importance of the message
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Four Elements of a Network
Rules or agreements to govern the messages are sent, directed, received and interpreted
The messages or units of information that travel from one device to another
A means of interconnecting these devices – a medium that can transport the messages from one device to another
Devices on the network that exchange messages with each other
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Rules
Rules govern every step of the process, from the way cables are designed to the way the digital signals are sent
These rules are called protocols, e.g. TCP/IP protocol stack
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Messages
Message is a generic term that encompasses text, voice or video information
The message must be converted to bits, binary coded digital signals, before they are transmitted on the medium
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Wired connections
Wireless connections
UTP cables
Common Data Network Symbols
The above figure shows some of the most common intermediate devices used to direct and manage messages across the network.
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Non-Converged Networks
In the past, every one of the services required a different technology to carry its particular communication signal
Each service has its own set of rules and standards
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Converged Networks
Convergence occurs when telephones, broadcasts (radio and TV), and computer communications all use the same rules, devices and media to transport messages
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Network Architecture
Refers to the conceptual plans on which a physical network is built
Must support a wide range of applications and services
Four basic characteristics of the network architecture
fault tolerance
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Fault Tolerance
A fault tolerant network limits the impact of hardware or software failure
recover quickly when a failure occurs
depend on redundant links, or paths, between the source and destination of a message
redundant connections allow for alternate paths
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Circuit Switched Connection-Oriented Networks
A physical, dedicated path or circuit is temporary setup between the source and destination
The circuit is maintained for the duration of the call
Early circuit-switched networks do not dynamically recover from drop circuits
The cost to create many alternate paths with enough capacity to support a large number of simultaneous circuits, and the technologies necessary to dynamically recreate dropped circuits in the event of a failure, led the Department of Defense (DoD) to consider other types of networks.
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Packet Switched Connectionless Networks
The entire message is broken into packets which are addressed and numbered
Any packets can be sent through the network using any available path
In the search for a network that could withstand the loss of a significant amount of its transmission and switching facilities, the early Internet designers reevaluated early research regarding packet switched networks.
The DoD researchers realized that a packet switched connectionless network had the features necessary to support a resilient, fault tolerant network architecture. The need for a single, reserved circuit from end-to-end does not exist in a packet switched network.
The problem of underutilized or idle circuits is eliminated -- all available resources can be used at any time to deliver packets to their final destination. By providing a method to dynamically use redundant paths, without intervention by the user, the Internet has become a fault tolerant, scalable method of communications.
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Scalability
A scalable network can expand quickly to support new users and applications without impacting the performance of the service being delivered to existing users
Depends on a hierarchical layered design for the physical infrastructure and logical architecture
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Internet Structure
Many individual networks that provide Internet connectivity cooperate to follow accepted standards and protocols
new products can integrate with and enhance the existing infrastructure
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QoS refers to the mechanism that manage congested network traffic
Congestion is caused when the demand on the network exceeds the available capacity
Some constraints on network resources cannot be avoided
technology limitations
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QoS Classification
Prioritize which types of data packets must be delivered at the expense of other types of packets that can be delayed or dropped
use queues to prioritize traffic
Classify applications in categories based on specific quality of service requirements
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increase priority for services like voice or video transmission
Delay-insensitive (or non-time sensitive) communication
decrease priority for web page retrieval or e-mail
High importance to organization
Undesirable communication
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Security
The Internet has become a widely accessible means of business and personal communications
the same environment that attracts legitimate business, however, also attracts scam artists and vandals
Compromising the integrity of company assets could lead to serious business and financial repercussions
Tools and procedures are being implemented to combat inherent security flaws in the network architecture
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physical securing of devices that provide network connectivity and preventing unauthorized access to the management software that resides on them
Content security
protecting the information contained within the packets being transmitted over the network and the information stored on network attached devices
tools to provide security for the content of individual messages must be implemented on top of the underlying protocols
There are two types of network security concerns that must be addressed to prevent serious consequences – network infrastructure security and content security.
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Consequences of Security Breach
Network outage causing a loss of communications and transactions occurring, with consequent loss of business
Misdirection and loss of personal or business funds
Theft of intellectual property such as project bids and strategic plans and used by a competitor
Exposure of confidential customer data, which may result in loss of market confidence in the business
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Security Measures
ensure confidentiality
maintain communication integrity
ensure availability
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Ensuring confidentiality
allowing only the intended and authorized users to read the data
a strong system for user authentication
encrypting the content
Maintaining communication integrity
data integrity is the assurance that the information has not been altered in transmission, from source to destination
source integrity is the assurance that the identity of the sender has been validated
using digital signatures and hashing algorithms
Ensuring availability
resources are available to authorized users
virus software and firewalls are used to combat virus and DoS attacks
building fully redundant network infrastructures
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a demand for more mobile connectivity to data networks
New and more capable devices
functions performed by cell phones, personal digital assistants, organizers and pagers are converging into single handheld devices with continuous connectivity to providers of services and content
Increased availability of services