CHAPTER 3

NETWORKS
Networks provide the ability to connect people and equipment no matter where they are in the world.

VOICE NETWORK COMPUTER NETWORK VIDEO NETWORK

The Internet is considered a "network of networks" because it is literally made up of thousands of networks that are connected to each other.

Here are other uses of a network and the Internet:
Sharing music and video files
Research and on-line learning
Chatting with friends
Planning vacations
Purchasing gifts and supplies

CATEGORIES:

PERIPHERALS
it doesnt communicate directly on the network. instead,it relies on its connected host to perform all network operations.
cameras, sacnners, and local attached prinetrs.

HOSTS
send and receive user traffic.it has an IP network address.
personal computers and network attached printers.

NETWORK DEVICES
connect other devices, mainly hosts. these devices move and control network traffic.
hubs,swithces and routers.

NETWORK MEDIA
provides connections between hosts and network devices. it can be wired, such as copper and fiber optic or use wireless technologies.

COMPUTER ROLE IN NETWORK

ALL CONNECTED TO THE SWITCH

file access client/ file server
store the file, the client accesses with client sofware such as windows explorer.

web server/ browser client
runs server software and cleints use their browser software, such as Windows internet to access web pages.

email server/ email client
runs server software and clients use their mail client software, such as microsoft outlook to access.

PEER-TO-PEER NETWORKS
many computers function as the servers and clients on the network. This type of network is called a peer-to-peer network.

ADVANTAGES:
easy to set up
less complexity
lower cost
can be used for simpel tasks, such as transferring files and sharing printers.

DISADVANTAGES:
no centralized administration
not as secure
not scalable
all devices may act both clients and servers which can slow their performance.

NETWORK TOPOLOGIES
When networks are installed
PSYSICAL TOPOLOGY MAP
created to record where each host is located and how it is connected to the network.
shows where the wiring is installed and the locations of the networking devices that connect the hosts.

LOGYCAL TOPOLOGY MAP
groups hosts by how they use the network
Host names, addresses, group information and applications can be recorded on it.

SURCE, CHANNEL and DESTINATION

MESSAGE SIGNAL SIGNAL MESSAGE
MESSAGE----TRANSMITTER-----TRANSMISSION MEDIUM-----RECEIVER----MESSAGE DESTINATION

RULES OF COMMUNICATION
Message format
Message size
Timing
Encapsulation
Encoding
Standard message pattern

MESSAGE ENCODING
emite una idea------la cuenta a otro------el otro por fin se imagina la idea contada
SOURCE ENCODED--------------------DESTINATION DECODED

MESSAGE FORMATTINGH

DESTINATION: physcial hardware address
SOURCE: physcial hardware address
START FLAG: start of message indicator
RECIPIENT: destination identifier
SENDER: source indentifier
ENCAPSULATED: data bits
END OF FRAME: end of message indicator

MESSAGE SIZE
Too short or long messages cant be delivered,they need to be divided in small pieces.

MESSAGE TIMING

Access Method
Hosts on a network need an access method to know when to begin sending messages and how to respond when errors occur.

Flow control
Source and destination hosts use flow control to negotiate correct timing for successful communication.

Response Timeout
Hosts on the network also have rules that specify how long to wait for responses and what action to take if a response timeout occurs.

MESSAGE PATTERNS

UNICAST: A one-to-one message pattern
MULTICAST: When a host needs to send messages using a one-to-many pattern,
BROADCAST: If all hosts on the network need to receive the message at the same time

Protocols
In a wired environment, a local network is defined as an area where all hosts must "speak the same language" or in computer terms "share a common protocol".

SATANDARIZATION OF PROTOCOLS

Standards are beneficial to networking in many ways:
Facilitate design
Simplify product development
Promote competition
Provide consistent interconnections
Facilitate training
Provide more vendor choices for customers

Ethernet, has become more common than the others. It has become a de facto standard.

PHYSICAL ADDRESSING

Every Ethernet network interface has a physical address assigned to it when it is manufactured. This address is known as the Media Access Control (MAC) Address. The MAC address identifies each source and destination host on the network.

ETHERNET COMUNICATION

The format for Ethernet frames specifies the location of the destination and source MAC addresses, and additional information including:
Preamble for sequencing and timing
Start of frame delimiter
Length and type of frame
Frame check sequence to detect transmission errors

HIERACHICAL DESIGN OF ETHERNET
In networking, hierarchical design is used to group devices into multiple networks that are organized in a layered approach.

It has three basic layers:
Access Layer - to provide connections to hosts in a local Ethernet network.
Distribution Layer - to interconnect the smaller local networks.
Core Layer - a high-speed connection between distribution layer devices.

LOGYCAL ADDRESSING

The IP address is known as a logical address because it is assigned logically based on where the host is located.

The IP address, or network address, is assigned to each host by a network administrator based on the local network.

SWITHCES

An Ethernet switch is a device that is used at the Access Layer. Like a hub, a switch connects multiple hosts to the network. A switch can forward a message to a specific host. When a host sends a message to another host on the switch, the switch accepts and decodes the frames to read the physical (MAC) address portion of the message.