Ethernet LANs

Ethernet LANs

Thursday, June 10, 2021

8:00 AM

1.0 Network Fundamentals

1.1 Explain the role and function of network components

1.1.b L2 and L3 Switches

1.2 Describe characteristics of network topology architectures

1.2.e Small office/home office (SOHO)

1.3 Compare physical interface and cabling types

1.3.a Single-mode fiber, multimode fiber, copper

1.3.b Connections (Ethernet shared media and point-to-point)

802.3 (Ethernet Standards

10BASE-T

10 Mbps
Ethernet
802.3
Copper/ 100 m

100BASE-T

100 Mbps
Fast Ethernet
802.3u
Copper/ 100m

1000BASE-LX

1000 Mbps
Gigabit Ethernet
802.3z
Fiber, 5000 m

1000BASE-T

1000 Mbps
Gigabit Ethernet
802.3ab
Copper, 100m

10GBASE-T

10 Gbps
10 Gig Ethernet
802.3an
Copper 100m

Three most common

10BASE-T, 100BASE-T, and 1000BASE-T

Twisting of the wires helps reduce EMI.

Crosstalk

-EMI between wire pairs

Gigabit Ethernet interface Converter (GBIC)

The original form factor for a removeable transceiver for Gigabit interfaces; larger than SFPs

Small Form Pluggable (SFP)

The replacement for GBICs, used on gigabit interfaces, with a smaller size, taking less space on the side of the networking card or switch.

Small Form Pluggable Plus (SFP+)

Same size as the SFP, but used on 10-Gbps interfaces

UTP Cabling Pinouts for 10BASE-T and 100BASE-T

10BASE-T and 100BASE-T

2 wire pairs,
one pair for each direction

Crossover

PC/ Router/ AP

transmits on pins 1/2
RECEIVES ON PINS 3/6

Switch/ Hub

Transmits on pins 3/6
receives on pins 1/2

Ethernet NIC transmitters send on pins 1 and 2

NIC receivers receive on pins 3 and 6

Straight through cable

Pins 1/2 > 1/2
Pins 3/6 > 3/6

autoix (cisco)

Notices when a wrong cable is used
automatically changes it’s logic to make the link work.

1000BASE-T

4 wire pairs
Both ends transmit and receive simultaneously on each wire pair.
pairs 1/2, 3/6, 4/5, 7/8
Crossover cable crosses the pairs at pins 1/2 and 3/6, it also crosses pairs 4/5 with 7/8

Fiber Cabling Transmission Concepts

Physical cable

Core >
Cladding >
Buffer >
Strengthener >
Outer Jacket

Optical Transmitter

Shines light into the core

Multimode fiber

multiple angles (modes) of light waves
Less expensive
10 gigabit over ethernet allows for distance up to 400m

Single mode fiber

Smaller diameter (around 1/5 of multimode) core
laser-based transmitter
single angle

More expensive SFP/ SFP+ hardware

Distances up to tens of kilometers

Transmit port on one end of the fiber connects to the receive port on the other end (Tx and Rx)

10Gbps Fiber Standards

10GBASE-S/ MM/ 400m
10GBASE-LX4/ MM/ 300m
10GBASE-LR/ SM/ 10km
10GBASE-E/ SM/ 30km

UTP, MM, and SM comparisons

UTP

low cable cost
low switch port cost
100m Max Distance
Some susceptibility to interference
Some risk of copying from cable emissions

Multimode

Medium cable cost
Medium switch port cost
500m Max Distance
No susceptibility to interference
No risk of copying from cable emissions

Single-Mode

Medium cable cost
High switch port cost
40Km Max Distance
No susceptibility to interference
No risk of copying from cable emissions

Sending Data In Ethernet Networks

Ethernet Header (preamble/sfd/Destination/Source/Type/Dataandpad/FCS)

Header

Preamble
7 bites
Synchronization
Start Frame Delimiter (SFD)
1 Byte
Signifies next byte begins the Destination MAC Address Field
Destination MAC Address
6 Bytes
Source MAC Address
6 Bytes
Type
2 bytes
Type of protocol listed in the frame (IPv4 or IPv6)
Data and Pad
46-1500Bytes
padding can be added to meet the minimum length requirement

Trailer

Frame Check Sequence (FCS)
Used to determine if the frame experienced transmission errors

Maximum Transmission Unit (MTU)

Maximum layer 3 packet that can be sent

Ethernet Addressing

6 bytes long (48 bits)
12 digit hexadecimal
Cisco switch may list a mac address with periods: 0000.0C12.3456
Unicast address
an address for a single NIC or port

OUI (Organizationally unique indentifier)

Universally unique manufacturer code
24 Bits
6 Hex Digits

Vendor Assigned

24 Bits
6 Hex Digits

Group addresses

Broadcast Address

Delivered to all devices on the Ethernet LAN.
FFFF.FFFF.FFFF

Multicast Address

Copied and forwarded to a subset of devices on the LAN

Identifying Network Layer Protocols with the Ethernet Type Field

The type field identifies which type of layer 3 packet exists within the ethernet frame (IPv6 or IPv4)

Ethertype is the term used for the type field in an ethernet frame

Error Detection with FCS

Error detection does not mean error recovery
Ethernet decide whether the frame should be discarded and does not attempt to recover the lost frame.

Sending Ethernet frames with switches and hubs

Switches allow the use of Full Duplex Logic
Hubs use half-duplex logic

Sending in Modern Ethernet LANs Using Full Duplex

Half duplex

must wait to send if it is currently receiving a frame
cannot send and receive at the same time

Full Duplex

Does not have to wait before sending,
send and receive at the same time.

Hubs

Uses physical link standards instead of data link standards and are considered layer 1 devices

Carrier Sense multiple access with Collision Detection (CSMA/CD)

Listen until line is not busy
Send frame
Listen for a collision while sending if a collision occurs:
Send jamming signal telling all nodes a collision has occurred
each node waits a random time then tries to send again
Back to step one

All links between PCs and switches use full duplex
A link connected to a hub should be half duplex
Ethernet Shared media
refers to hubs that use CSMA/CD and share bandwidth
Ethernet point-to-point
network built with switches where links work independently of others
A frame can be sent on every Point-to-point link in an ethernet at the same time.