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20

Only one device is allowed to transmit at any given time. At any other given time, another device is allowed to transmit. How can you have a conversation at a dinner table if only person can speak at any time?


19

When autonegotiation fails on one node, to choose (half/full-duplex) we must use the rule: If you have a 10/100 Mb/s interface -> use half-duplex If you have a 1000 Mb/s interface-> use full-duplex Why is that? Summary In brief, ethernet has been around since the 1980s... as a result Old ethernet NICs only supported half duplex operation ...


18

Some LAN protocols, on some media, are half duplex. That means that only one host on a LAN can send a frame at any given time. The classic example of this is the original ethernet, but the modern example is Wi-Fi. The original ethernet ran on coax, and it used CSMA/CD (Carrier Sense Multiple Access with Collision Detection) to detect collisions where two ...


15

By far the most common issue would be misconfiguration. Some people still hold on to old beliefs that auto negotation does not work reliably. If you have different vendors there can be issues but I don't see it very often. I would much rather rely on auto negotiation as my first solution and if that fails fall back to hard coding it. It is quite common to ...


14

Theory By convention, a collision domain is a contiguous wired and / or wireless half-duplex segment (typically using CSMA/CD), which is a subset of the subnet or vlan's broadcast domain. Collision domains are invariably a half-duplex segment, or a series of connected half-duplex segments. Ethernet hubs / Wifi Access Points (within the same RF-channel ...


12

When autonegotiation fails on one node, to choose (half/full-duplex) we must use the rule: ->If you have a 10/100 Mb/s interface -> use half-duplex In the event that a hub is connected, a default of full duplex would cause too many collisions. A default of half duplex ensures communications continue regardless of the connected device (Switch or hub) ->If ...


8

Can a single optical fiber support full-duplex communication? Yes. There are "BX" standards, e.g. 100BASE-BX, which use different wavelengths for send and receive. The transmit wavelength on one end needs to be the receive wavelength on the other end. For example, Cisco has these transceivers: 1000BASE-BX10-D and 1000BASE-BX10-U SFP for Single-Fiber ...


7

The usual suspects in the case of autonegotiations are: bad cables bad ports, SFPs or NICs port configs (are they both set to auto and do they both list the 1000BASE-T FD ability?) bugs, compatibility or legacy issues I would not recommend a fixed speed and duplex setting in this (or almost any) situation. The days of frequent autoneg issues and ...


6

Full-duplex basically means communication can happen both ways, negating the possibility of a collision. The below diagram should make it a little more clear. One pair is designated a transmit pair, and the other a receive pair. In most environments now, it isn't even necessary to match up transmit/receive pairs, as MDIX handles that for you. This doesn't ...


6

In reality, the legacy 10 Mbps ethernet interface probably can't negotiate, and it can probably only do half duplex (very few 10 Mbps interfaces can do full duplex). You should let the 1 Gbps interface auto-negotiate. It will try to negotiate, but if the 10 Mbps can't negotiate, it will detect (not negotiate) that the connection is 10 Mbps, and it will set ...


5

Actually, TCP and Ethernet are examples of different layers of the OSI model. TCP works in layer 4 (transport layer), which is used for making connections between nodes on a network. TCP is indeed bidirectional, and it's sometimes referred to as connection-oriented. Ethernet is a layer 2 (data link layer) protocol, which dictates how signals are to be ...


5

The very short answer: don't configure anything. Auto negotiation (or the lack thereof as Ron's detailed) works only when it's left alone. Manual settings can very easily cause problems either right away when done incorrectly or later on when hardware is upgraded. For 1000BASE-T, auto negotiation is required - most hardware won't allow you to manually ...


5

This is a buffering issue. I had the same problem with a new Level 3 circuit. Their NID apparently has no measurable buffers, so feeding it at a rate 10x the circuit rate (1000 vs. 100) leads to all manner of poor performance. (They had the customer side set to auto (1000) but manually set the network side to 100. After a week of arguing, they set both ...


5

The (naive) answer is, or rather used to be, simple: It tranlates to each sender having to wait a tiny fraction of a second. There is no way around this because that's how the network works at a physical level, but it is also not very much of a problem since we're talking about a few microseconds (micro, not milli). The somewhat less naive answer would be ...


4

This (autonegotiation) is explained in various sections of the IEEE 802.3 specifications. Auto-MDIX is mostly a function of gigabit interfaces being able to TX and RX on all four pairs. I don't recall this being part of 802.3, but the logic for it (looking for carrier signal, and/or link pulses) is simple enough that anything capable of gig will support it.


4

You seem to be confused about logical topology (bus, ring, star). Ethernet has a couple of different topologies, but token ring has only the logical ring topology. Full-duplex ethernet doesn't use CSMA/CD because it has separate send and receive paths between two devices. When you share send and receive paths, then you must use CSMA/CD in order to detect ...


3

A full duplex or Bidirection communication meaning that it can support both stations transmitting and receiving simultaneously. To accomplish this, a single optical fiber with WDM technology is required for optical tommunication. WDM stands for wavelength division multiplex. This multiplex method uses both 1310 nm and 1550 nm wavelengths.Two devices are ...


3

Think of a half-duplex connection as a single channel that you can turn around between packets. Then think of a full-duplex connection as two unidirectional channels that can be used simultaneously. Physically, all modern twisted-pair or fiber Ethernet connections have two channels, one for sending, one for receiving (most prominent in 10BASE-T, 100BASE-TX ...


3

No. There's a misunderstanding. A UTP cable consist of 8 wires, arranged in pair, so you have 4 pairs of wire in a single cable. Each pair is twisted, to reduce crosstalk and some kind of interferences, hence the name UTP: Unshielded Twisted Pair 10BasteT only use 2 of those 4 pairs. But nowadays you rarely see hubs or 10BaseT network.


3

Hubs do use two pairs for 10BASE-T or 100BASE-TX. One pair is for transmit, and one for receive; that is how the device interfaces are made, and the hub is really just a cable extension. What you need to understand is that in the hub, the transmit pair of one interface is connected to the receive pairs of all the other interfaces. Hubs cannot do full duplex ...


3

They can. A lot of security cameras work as half dulpex sending pictures to a server which is in full duplex. You will have packet loss but it will work


3

If you're asking about ethernet duplex, then the full- or half-duplex nature of a given link is negotiated when the link comes up, or alternatively set in configuration. (See autonegotiation at Wikipedia). All full-duplex ethernet links are capable of working in half-duplex, and will do so when connected to a half-duplex device. (Presuming correct ...


3

In 1000base-T there is circuitry called a hybrid which make the signal bidirectional. It's not really transmitting and receiving the wrong way round on the receive and transmit pairs, it's transmitting and receiving on all the pairs, which the other standards dedicate to transmit and receive. IEEE 802.3 defines them as "1.4.220 hybrid: A circuit (...


3

Why couldn't 10-BaseT (10Mb/s) or 100-BaseT (100Mb/s) do the same? What changed, specifically to allow this? The quality of the cabling improved drastically as well as the methods for transmitting data and the receivers used to “read” the signal from the cable. These days you could retroactively modoify the 10/100BASE-T standards to use the same ...


3

Time division duplex (TDD) concerns at least a 2 way communication. For example, a discussion is taking place between two people, say a and b, a talks whilst b listens, then b talks whilst a listens. A and b can't talk at the same time, hence timely divided and both share a time unit. Full duplex can be imagined as if both a and b talk and listen at the same ...


2

(this post is in the context of Ethernet, other procols may vary) What criteria is used to know the boundaries of a collision domain? A collision domain is an area of a network where collisions can happen and where only one packet may be successfully transmitted at a time. It passes through repeaters (hubs) but not through bridges (switches). All half ...


2

One of the symptoms of a duplex mismatch is late collisions. Having your NMS alert you on these collisions is a good way of finding them. At least some Cisco models/IOS versions can send SNMP traps for these collisions.


2

By manually setting the speed and duplex on one side with automatic detection on the other side, the side with automatic speed will detect (not negotiate) the correct speed. For the duplex, negotiation will fail. This results in the side with automatic duplex set to the default duplex for the speed. The default duplex for 1 Gb is FULL, and for 10 and 100 ...


2

To me the following analogy works: Think about you and your friend communicate each other by sending letters. You and your friend send/receive in full duplex manner but let's say the post office works in half duplex manner. You and your friend act like TCP(Full duplex) but the delivery of letters(post office) works in half duplex.


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