SECTION 6 : ETHERNET FUNDAMENTALS Flashcards
What were the first Ethernet networks ?
10BASE2 ThinNet 200m
10BASE5 ThickNet 500m
At the beginning ethernet was one standard among others competitors. It ended up winning.
What was the new type of network ?
10BASE-T allows up to 10 Mbps of speed but only covers a distance of up to 100 meters. CAT3
What is a deterministic network ?
Very organized and orderly and requires an electronic token to transmit. Each device waits its turns. Token ring or bus network. Zero collisions because they wait their turn.
What is a contention based network ?
Very chaotic and can transmit whenever possible. You speak when you hear a gap. Contention based access is chaotic and can cause collisions. Ethernet used contention-based network access.
What is the main drawback of deterministic ?
You don’t use all the bandwidth because you have to leave some for the other devices. The efficiency of the network is not maximized.
What is CSMA/CD ,
Carrier Sense Multiple Access With Collision Detection.
It prevents collisions by using carrier-sensing to defer transmissions until no other stations are transmitting.
CS = ethernet needs to listen to the network and determine the sender of the data. When there is a gap the MA intervenes.
If the CD detects a collision allows to determine who waits or not. If a collision is detected Both Ethernet will stop transmitting and then retransmits. They take a random number and count to it (for instance 150 ms backoff and the other 30ms)
What is Collision Domain ?
Each are of the network that shares a single segment. The more devices communicating on a single network segment the more collision there is. That’s why devices operate in half-duplex mode when connected to a hub (layer 1devices) because they have to listen before communicating. You need to keep collision domains small inside your networks. The entire bandwidth is minimized. You have to segment your network.
What are the purpose of Ethernet switches when it comes to collision domain ?
It increases scalability of network by creating multiple collision domains. Each port is a collision domain. Besides switch ports can operate on full duplex. One computer connected to one switch avoids every trouble so full duplex.
What is the bandwidth ?
Measures how many bits the network can transmit per second. Types of cables determine the bdwdth of cable.
What are the standards when it comes to Ethernet and fibers ?
Number BASE - T —> ethernet
Nimber BASE - FX / SX / LX / SR / LR
Needs to memorize when it comes to distances
- Copper cables have a maximum distance of 100 meters
- Using CAT 6 at 100 meters will limit the speed from 10Gbps to 1Gbps
- Using CAT 6 at under 55 meters can reach 10 Gbps of speed
- MMF deal with shorter distances between 200-500 meter range
- SMF for long distances (kilometers)
If you need short distances with fiber use MMF or else copper.
What are the primary devices on network ?
Router
switches
hubs
bridges
What are hubs ?
Also known as a multiport repeater it is a L1 device that connects multiple network devices and workstations.
What are the three different types of hubs ?
Passive : repeats signal with no amplification.
Active : repeats signal with amplification. Take the signal and boosts it. Try to reach the 100 meter limit of the TPC. Good to overcome the distance limit.
Smart : active hub with enhanced feature like SNMP
What about collision domains when it comes to hub?
Multiple network segments connected together by hubs. Hubs increase the probability of collision domains because it broadcasts the signal.
How does a bridge reduce collision domain ?
You can split a network in two with a hub and reduce the collision domain.
It retransmits data based on MAC adresses.
What is a switch ?
L2 device just like a bridge.
Also known as a multiport bridge, it is a L2 device that connects multiple network segments together.
It has a bridge on every port that allows to minimize collision domain to each port. But everything on the switch is part to the same broadcasting domain.
Switches make forwarding decisions just like a bridge, based on MAC adresses.
What is the cinematic of connection ?
When there are two switches, devices will send an ARP request to the switch.
The switch will forward to every devices connected on each of its port.
If it doesn’t find eat it will redirect to another switch.
Every one got the question who is the device. But when they know it the keep in memory.
Besides, switches support full duplex so every PC can produce ARP requests.
What is a router ?
L3 device that connects multiple networks and makes forwarding decisions based on logical network information.
Router allows to reduce the traffic and the noise because they split the broadcast domain.
What is a L3 switch ?
Makes L3 routing decisions and then interconnects entire networks not just segments. Hubs and bridges are combined to make a switch.
L2 switch and a router are combined to make a L3 switch.
They can do routing decisions and can connect network segments. Each port acts as its own broadcast and collision domain. With a small office a L3 switch can be convenient.
What is the specificity of a home router ?
Usually it combines different functions such as Ethernet CAT 4 cable, WAP, router and so on.
It’s like a big media converter that converts data from CAT4 for instance to WAP.
What are the other switch features ?
VLANs,
Trunking
Spanning tree protocol
Link aggregation
Power over Ethernet
Port monitoring
User authentification
What is link aggregation ?
IEEE 802.3ad standard
Combines multiple physical connections into a single logical connection to minimize or prevent congestion.
When does congestion occur ? I
When ports all operate at the same speed. Switches are full duplex so every port can operate at 100Mb/s. But the switch need to send out the total amount. We solve that with link aggregation. It’s rare that every PC uses full bandwidth to the switch.
