C4. The current ethernet specs Flashcards
What’s Ethernet, friend? Why is it sO popular? oO
Ethernet is a contention media-access method that allows all hosts on a network to share the same bandwidth of a link
Popular bc it’s (1) scalable (2) easy to integrate new technologies into (3) simple to implement
What’s a collision domain?
A network scenario where one device sends out a packet on a network segment and forces every other device on the same network segment to pay attention to it
What’s a collision event?
It’s when each device’s digital signals interfere with one another on the same physical network segment, because both of them were transmitting at the same time
Broadcast domain
A set of all devices on a network segment that hear all the broadcasts sent on that segment; the boundary delimited by broadcast domain is typically physical - in terms of the physical devices s.a. switches and repeaters
CSMA/CD
Carrier Sense Multiple Access with Collision Domain is a media access control method that helps devices share the bandwidth evenly, without having two devices transmit at the same time on a network medium
How does a CSMA/CD work?
When a hosts wants to transmit a message, it checks for the presence of a digital signal on the wire. If all is clear, the host transmits data and keeps monitoring to ensure that no other host begins transmitting.
- Has another signal been detected? If so the host sends out an extended jam signal that causes all hosts on the segment to stop sending data
- The host waits for a while before transmitting the signal again
What happens when a collision occurs on the Ethernet LAN?
1) a jam informs all devices that a collision
2) the collision involves a random backoff algorithm
3) each device on the Ethernet segment stops transmitting for a while until the timers expire
4) all hosts have equal priority to transmit after the timers expired
What are the three things we’ll observe in the network when a collision happens?
We’ll have 1) delays 2) low throughput 3) congestion
What does broadband mean?
Hi it means we are using analog voice and digital data carried on the same network cable or physical medium
- we’ve got multiple frequencies of different signals
What does baseband mean?
It means that all the bandwidth of the physical media is used by only one signal
- if multiple signals are sent from different hosts at once, we get collisions
- LANs only do digital signals
- Wireless networks do analog signals only
What’s a bit rate?
It’s a measure of the number of bits transmitted per second
What’s a band rate?
BR is a speed of transmission (that we often consider in, say, telegraph stuff)
What is the benefit of having multiple wavelengths going around?
If that’s the case, if two wave patterns are different, then we can tell different kinds of electromagnetic energy apart; this is good - we end up sending traffic on different wavelengths at the same time
What’s the difference between half- and full-duplex Ethernet, friend?
Full duplex can run with just about any device except a hub! Half duplex is way more specific, and I dearly hope that you’ll dig out the respective flashcards and remember all that
Full duplex uses two pairs of wires and a point-to-point connection
Half duplex uses one pair of wires with a digital signal - and it either transmits or receives signals. One thing at a time!
What is the auto-detection mechanism in all this network stuff?
It’s a kind of mechanism that decides on the data exchange capability such as speed, then checks to see if it can run full duplex, and if it can’t, it runs in half-duplex mode instead
Are there any collisions in full-duplex mode?
Nope
What does each host on the full-duplex mode need?
A dedicated switch port, sir
