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Ethernet II Frame:

7 bytes 1 byte 6 bytes 6 bytes 2 bytes 64-1500 bytes 4 bytes

Preamble

Start of Frame Delimiter

Destination Address

Source Address

Type

Data

FCS
Frame Check Sequence

 

802.3 Frame:

7 bytes 1 byte 6 bytes 6 bytes 2 bytes 46-1500 bytes 4 bytes

Preamble

Start of Frame Delimiter

Destination Address

Source Address

Length

802.3 Header and Data

FCS
Frame Check Sequence

 

Preamble – Synchronization. They give components in the network time to detect the presence of a signal and read the signal before the frame data arrives.

Start of Frame (SOF) – Start of Frame sequence

Destination and Source Addresses – Physical or MAC addresses. The source address is always a unicast address, the destination address can be unicast, multicast, broadcast.

Length – Indicates the number of bytes of data that follow this field.

Type – Specifies the upper layer protocol to receive the data.

Data – User or application data. Ethernet II expects a minimum of 46 bytes of data.

If the 802.3 frame does not have a minimum of 64 bytes, padded bytes are added to make 64.

Frame Sequence Check (FCS) – CRC value is used to check for damaged frames. This value is recalculated at the destination network adapter. If the value is different from what is transmitted, the receiving network adapter assumes that an error has occurred during transmission and discards the frame.

Ethernet Cabling:

Type 10Base5 10BaseT 100BaseFl 100BaseTX 100BaseFX 1000BaseT
Media Thick Coax

RG-8,

RG-11

UTP Cat 3, 4, 5+

4 Pair cable,

Uses 2 pair

62.2/125 micron multi-mode fiber UTP Cat 5+

4 Pair cable,

Uses 2 pair

62.2/125 micron multi-mode or single mode fiber UTP Cat 5+

4 Pair cable,

Uses 4 pair

Max Segment
Length
500 Meters 100 Meters 2000 Meters 100 Meters 400/2000 Meters (full/half duplex)

10,000 Meters (single mode)

100 Meters
Physical
Topology
Bus Star, Extended Star Star Star Star Star
Logical
Topology
Bus Bus Bus Bus Bus Bus
Transfer
Rate
10Mbps 10Mbps 100Mbps 100Mbps 100Mbps 1000Mbps
             

 

EIA/TIA Horizontal Cabling:
(Using CAT5 cabling in an Ethernet network)

3 Meters – 90 Meters – 6 Meters

3 Meters:

Work area patch cable.  From computer to wall

90 Meters:

What is considered the Horizontal Cabling. From wall outlet to the patch panel in the MDF or IDF (Server Room).

6 Meters:

The patch cable that cross connects a patch panel



Collision Domains
- A collision domain is defined as a network segment that shares bandwidth with all other devices on the same network segment. When two hosts on the same network segment transmit at the same time, the resulting digital signals will fragment or collide, hence the term collision domain. It's important to know that a collision domain is found only in an Ethernet half-duplex network

Broadcast Domain - A broadcast domain is defined as all devices on a network segment that hear broadcasts sent on that segment.

All devices plugged into a hub are in the same collision domain and the same broadcast domain.

All devices plugged into a switch are in separate collision domains but the same broadcast domain. Although, you can buy special hardware to break up broadcast domains in a switch, or use a switch capable of creating VLANs. VLANs breakup broadcast domains.

Hubs and Repeaters extend collision and broadcast domains.

Switches, Bridges and Routers break up collision domains.

Routers (and Switches using VLANs) break up broadcast domains.


Device OSI Layer Filtering Breaks up Collision Domains Extends
Collision Domains
Breakups
Broadcast Domains
Extends
Broadcast Domains
Hubs

1

No

 

X

 

X

Repeaters

1

No

 

X

 

X

Bridges

2

Yes

X

   

X

Switches

2

Yes

X

   

X

Switches using VLANs

2

Yes

X

 

X

 
Routers

3

Yes

X

 

X

 


Repeater Rules in 10baseT Networks (802.3 / UTP Cabling)
(5, 4, 3 Rule)

  • Between any two points on the network, the maximum number of Ethernet cable segments, each with a 100-meter diameter, is 5 (five).
  • Between any two points on the network, the maximum number of repeaters is 4 (four).
  • Between any two points on the network, only 3 (three) of the five cable segments can have network devices on them (other than repeaters), with the other segments serving only as inter-repeater links.

When counting the number of repeaters, count only the repeaters between any two points along the path on the network.

 

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