14

A hub is really just a powered cable that repeats every signal it receives on one interface to all the other interfaces. If two devices transmit at the same time to the receive of the hub interfaces, the hub repeats both signals at the same time to the transmit of all the other hub interfaces, and both signals received will collide at the transmit of the ...


13

To understand this you need to understand the historical context. Originally Ethernet used a shared coaxial cable. Only one device could successfully transmit on this at a time. If two devices transmitted at the same time it was considered a collision. Then repeaters came along, to extend the distance and increase the number of nodes. A repeater would ...


9

Great question. In full duplex, there is a dedicated channel for traffic from "left to right" and a dedicated channel from traffic from "right to left": Therefore, in full duplex, collisions are impossible -- even if both NIC's transmit at the same time. In half-duplex, however, traffic in either direction is meant to only use the wire, one direction at a ...


6

With twisted pair and a repeater hub, the hub is not much more than a digital amplifier. For that it senses a carrier from an incoming signal on one port and switches all other ports to output mode. In this output mode, any additional incoming carrier is a collision. This triggers a jam signal to propagate the collision and make the sender stop transmitting. ...


5

However, I'm having trouble finding a definitive source for the recommended transmission speed for Cat 3, Cat, Cat 5e, Cat6, and Cat6a twisted pair cables. In fact, some of these sources seem to contradict each other. This is not at all surprising. The cable categories are determined by a number of standards bodies around the world. While they are often the ...


4

Switches and NICs don't actually detect the FCS and compare it with their own calculation. They receive a frame until the carrier stops or an idle symbol is detected, depending on the physical-layer variant. On reception, the FCS is calculated in real time across the whole frame, including the FCS field itself. Some clever math is used, so when the carrier ...


4

The end of a frame is signaled by loss of carrier or by a special symbol or sequence in the line coding scheme for a particular Ethernet physical layer, so the length of the frame does not always need to be encoded as a value in the Ethernet frame. However, as the minimum payload of an Ethernet frame is 46 bytes, a protocol which uses EtherType must include ...


4

A single MAC (ASIC/chip) can only handle a single PHY (Ethernet port). You could temporarily switch the PHY back and forth (e.g. between an 8P8C port and an SFP port), but you can't use them both simultaneously. A solution may be to use a small three-port switch (ASIC), with one port interfacing your project and two ports for outside communication. Note ...


4

http://ecomputernotes.com/computernetworkingnotes/communication-networks/fast-ethernet is the best in-a-nutshell explanation I managed to find. 100base-T4 is half duplex and uses four wire pairs, with one pair reserved for sending only (Rx-only at the other end), one pair used only for receiving (Tx-only at the other end) and two pairs swapping directions ...


4

First of all, capturing traffic on WLAN interfaces is tricky. I assume you're doing this with wireshark, so take a look here: http://www.wireshark.org/faq.html#q7.10 Next, 802.11 header is a little bit different than 802.3, take a look at standard: http://standards.ieee.org/getieee802/download/802.11-2007.pdf


3

Suppose machine A starts sending data to machine B. As the packet begins to be sent, machine C starts sending different data to machine B. There is only one signal path to machine B, so the transmissions from A and C collide and B cannot possibly receive both of them. The fact that a different circuit is used for transmissions from machine B, to machine A, ...


3

How can this happen? Ensure that you have proper 4-pair cabling. Some premises use non-standard 2-pair or split cabling which can't work with 1000BASE-T. The margins for damaged cables, improper termination and such are considerably thinner for 1000BASE-T, so any used-to-be-good cable can fail you with GbE. If you want/need to make sure, recertify your ...


2

dot3StatsInternalMacReceiveErrors refers to framing errors only - as stated, misalignment, FCS errors, giants, runts. A VLAN mismatch is not an error on the MAC level in that respect. Nitpicking, VLAN tags belong to 802.1 while the general framing belongs to 802.3.


2

I've had the pleasure to participate in upgrading from CAT5 to CAT5e on several offices throughout the years. The amount of employees varied from down to the twenties up to several thousands. We ran different scenarios from a complete upgrade, where all cabling was changed, to only upgrading what was necessary. Since the last option was the most economical, ...


2

The cable category speeds are not calculated the way you seem to think. Remember that the whole world isn't ethernet, and UTP cables are used for many different things. The physical cable bandwidth is measured in Hertz (cycles per second), but the bandwidth of a protocol that runs on a cable is measured in bits per second. These values may be equal or ...


2

CSMA/CA is used with Wifi and it's useful. Since "air" is generally a shared medium, no two stations must transmit simultaneously. Collisions are possible and need to be avoided/handled with. "How does it work?" is much too broad to answer here. With full-duplex links, no collision handling is required at all since there can be no collisions.


1

Two waves can propagate down the same pair in opposite directions without interfering with each other. With the right circuitry (known as a "hybrid")you can launch a wave and receive a wave at the same time. In principle with perfect components you can design a circuit that will keep the launched waveform and received waveform completely seperate. In ...


1

These transceivers speak standard 10BASE-T on the network end (I'm using the very same model with an A2060 NIC) - they're compatible with any common 10/100/1000 twisted-pair port. You might want to make sure though that the legacy NIC supports proper auto negotiation - not all legacy equipment does. Depending on the exact hardware, leaving the switch port ...


1

Usually the port comes up - due to lack of autonegotiation, the auto side will choose half duplex, resulting in a duplex mismatch. Fast Ethernet uses "fast link pulses", an expanded scheme. Autoneg disabled on both sides leaves only the carrier (pause symbols) to detect the link. FDX/HDX will be as set up, potentially mismatching.


1

My question is: Is there any RFC/protocol which would allow traffic to ignore flow-control. (Probably not) Ethernet is not controlled by the IETF RFCs, it is from the IEEE 802.3 committee. Many devices do ignore ethernet flow control; it is poorly supported, and it is not required. Even among network devices which do support it, you must often enable it. ...


1

I will start by saying that you should not be disabling auto-negotiation with Gigabit connections. This is what the standard has to say (from 802.3-2012 Section Three, which you can reference here): 37.1.4.4 User Configuration with Auto-Negotiation Rather than disabling Auto-Negotiation, the following behavior is suggested in order to improve ...


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