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 Field.
C = Type/Length Field.
D = Data Field.
E = FCS Field.
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Tags: switch, ip, study, router, 802.1q, interface
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Ethernet 802.3
By admin 28 July 2008 at 12:32 am and have Comments Off
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 contributes significantly to compatibility between diverse end devices.
802.2 describes LLC sublayer functions.
802.3 describes the Media Access Control (MAC) sublayer and L1 functions.
LLC – software (drivers) – independent physical equipment.
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Tags: study, wan, ip, cisco, interface, guides
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 each frame.
It also must retrieve signals from media, restore them to bit representations, and pass them to L2 as a complete frame.
The type of signal – depends on the type of media.
Copper = electrical pulses.
Fiber = patterns of light.
Wireless = patterns of radio transmissions.
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Tags: wan, 802.1q, guides, cisco, vlan, router
Data Link Layer
2 primary functions:
1. Prepares L3 packets for transmission.
2. Controls access to the physical media.
Accessing the media:
A L3 exchange may involve many L2 and media transitions.
At each hop, routers decapsulate and re-encapsulate frames to match the right media.
The L3 protocol is not aware of which media is used.
L2 includes many types of media and access methods (eg. how it is getting to the wire).
L2 protocols specify the frame type and how to get a frame on and off each medium (media access control method, MAC method).
Devices use adapters to connect to a network (eg. NIC)
The adapter manages the framing and media access control (generates the signal transition).
Routers have different physical interfaces that frame the data as suitable for each link.
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Tags: guides, vlan, router, wan, ip, switch
Planning & Cabling Networks
Media Required to Make a LAN Connection:
LANs use gateways to connect o other networks.
They use hubs or switches to connect end devices.
Each port on a router connects to a different network.
Routers break up broadcast domains and collision domains.
Routers can have both LAN and WAN interfaces.
Intranetwork Devices:
Hub
Receives signals, regenerates and sends them over all ports.
Creates a logical bus (i.e. multi-access media, everybody is on the same wire). [topologies].
Shared bandwidth approach – reduced performance (only one device can talk at a time).
A single collision domain.
Less expensive than switches.
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Tags: switch, ip, 802.1q, vtp, vlan, study
