Routing & Packet Forwarding

Routing Protocols & Concepts

Router as a Computer:

Computers that specialize in sending packets over the data network.
Responsible for interconnecting networks.
Routers are the network center.
Generally have a min of 2 connections:
WAN connection (Connection to ISP).
LAN connection.
In addition to packet forwarding, routers provide other services as well.
A router connects multiple networks.
This means that it has multiple interfaces that each belong to a different IP network.
Each network… Continue reading

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LAN Design:

The Hierarchical Network Model:

CCNA focuses on networks for SMBs (small, medium businesses).
A hierarchical design model is recommended.
Easier to manage and expand.
Problems are solved more quickly.

Hierarchical design divides the network into 3 layers.
Core, (CL).
Distribrution, (DL).
Access, (AL).

Each layer provides specific functions.
This “modularity” facilitates scalability and performance.

Access Layer, (AL): lowest

Interfaces with the end device (user).
Includes routers, switches, bridges, hubs and wireless APs.
Provides a means… Continue reading

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Interframe Spacing:

Minimum spacing between 2 frames following each other on the line.
Time for media to stabilize and devices to process frame.
From the last bit of FCS to the first bit of the Preamble.
96 bit times (9.6 microsec)– time shortens as speed increases.
As we speed up, gap gets shorter as the bits get shorter.
Allows time for slow hosts to process frames.

A = Start Frame Field.
B = Address

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Standards and Implementation:

The first LAN ever was Ethernet.
Robert Metcalfe and coworkers at Xerox in mid 70s.
The first Ethernet standard published 1980 by DigitalEquipCorp, Intel, Xerox (DIX).
Metcalfe wanted it to be a shared open standard.
1985 IEEE published standards for LANs.
For compatibility with OSI, small mods made to Ethernet standards with 802.3.

Ethernet –L1 and L2:

Ethernet implemented in MAC sublayer and L1 only.

LLC:

The use of these sublayers… Continue reading

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Physical Layer Protocols and Services:

L1 controls how data is placed on the media.
It has to encode bits into signals and Tx/Rx these signals across the physical media.
The delivery of frames across media requires.

Physical media and connectors.
A representation of bits – code.
Encoding of data and control information.
Tx and Rx circuitry on devices.

The purpose of L1 is to create the electrical, optical, or radio signal that reqresents the bits in… Continue reading

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