Questions tagged [layer1]
For questions about the OSI layer-1 (physical layer).
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What are different encoding schemes used in gigabit ethernet?
I was reading about digital transmission, there are many steps namely:
Analog to Digital conversion
Source coding
Channel coding
Line coding
Pulse shaping
Modulation
Multiple access techniques
...
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Camera instead of ethernet cables
My electricians messed up and installed some sort of camera (or very old cat3?) cables, instead of the requested ethernet cables (see picture). Now I have two of those, running for about 15 meters ...
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How does a network hub work? [closed]
When reading about hubs, I always found some information in the following sense:
"The hub is a dumb device, it has no information about the devices that are connected to, his mission is all about ...
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What is Ethernet MDI in the case of SFP interfaces
I am reading on Ethernet and I understand that for copper ports, the MDI is the physical connections from the PHY to the medium's connector, including the physical port itself, where the cable is ...
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Length of Ethernet Preamble on 10Gb network
I know (see https://en.wikipedia.org/wiki/Ethernet_frame) that an Ethernet frame includes a 7 byte preamble of 0x55s and a one byte start frame delimiter (SFD) 0xD5, for a total of 8 bytes before the ...
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MTU mismatch scenario, two hosts handle in a different way ingoing packets bigger than local interface MTU. How does MTU really work?
I’ve been struggling with the MTU topic for a while and I still can’t get how it really works. The majority of books that I read and the courses that I attended all seem to treat this subject in a ...
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Do telephone calls work at Layer2?
We know that Wi-Fi works in both layer1 and layer2 and travel through air in layer1.
My question is when we create mobile phone call during connection establishment phase sender Mac address and ...
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What is difference between broadband and baseband signal with respect to full duplex?
We know that broadband signal is full-duplex, for example television cable line where all TV channel is used portion of bandwidth not full bandwidth. And modern baseband is also full duplex but all ...
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Certified 0,15m CAT6a cable - what to expect?
We are thinking of patching our new network rack using 0,15m cables due to costs and cable management requirements. There will be around 400-500 connections using this cable length and we will be ...
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Does the length of a frame influence the likelihood of a collision?
Considering two separate analog signals on the same frequency transmitting digital data that represents a frame, from my understanding if any portion of the two signals overlap, this is a collision.
...
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Robust Ethernet connection next to high power machines
We are creating a robot for facade treatment (cleaning, painting, drilling). I have few beginner level questions.
An industrial robot with it's controller and our computer is placed at the top of a ...
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How two computer sync to read data?
Recently I try to understand how data is transferred. So as far as i know, digital data can be transferred in the form of voltage from one computer to another through a wire.
But I don't understand ...
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C2960 %LINEPROTO-5 UPDOWN and %LINK-3-UPDOWN when speed is not set on 100
I have 4 ports.
3 are like this, Gi 0/1-3
switchport access vlan xxx
switchport mode access
power inline never
speed 100
spanning-tree portfast edge
One Trunk, Gi 0/8
switchport mode trunk
power ...
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How does data flow in a twisted-pair cable?
If I use an Ethernet cable (twisted pair cable) in what form is the data flowing - digital or analog signal?
And in pair 1, that is wire number 1 and 2, there is Transmit+ and Transmit- respectively. ...
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If router is a layer 3 device how can it have an application interface (GUI)?
It is said that layer 3 devices such as routers do not have an application layer. But whenever I want to configure my home router I punch in the IP address and open up its graphical user interface. ...
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can two devices communicate without physical layer?
can 2 device communicate with each other without data going to physical layer?
for example we just use protocol of data link layer that use MAC address , but transferring this frame data between 2 ...
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Are there any advantages of using a crossover cable to directly connect modern devices?
Modern devices no longer need a crossover cable to directly connect via an ethernet cable.
But are there any advantages of using a crossover cable anyway?
For example, does a crossover cable decrease ...
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What does even/odd mean in HDB3 scrambling, and how does one ascertain these values?
I am currently studying encoding techniques. The scrambling technique HDB3 is introduced as follows:
High-Density Bipolar-3 Zeros
Based on bipolar-AMI
String of four zeros is replaced with sequences ...
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5
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Is it possible to have a local area network with only layer 1 and not layer 2 of the OSI model?
I know the OSI model has seven layers. Can you consider a LAN to exist without layer 2 and just layer 1? The answers that I saw on Quora were not clear. Some of the answers on Quora came close to ...
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100BaseTX Ethernet Idle code ("/I/") 4B/5B origin
While searching how the PHY LINK status is determined, I stumbled across this answer :
In 100BaseTX Ethernet, link pulses aren't used, but instead, link
status is detected and maintained via the ...
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Manchester encoding: 'signal' and 'bit sent'
I just learned the following about the so-called 'Manchester encoding':
There is a transition at the middle of each bit period.
The midbit transition serves as a clock mechanism and also as data: low ...
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T_Latency = T_Propagation + T_Transmit + T_Queue? [duplicate]
I am currently learning about the so-called 'physical layer' of a computer network. The following claim is made:
The latency of a message is the total time for the whole message to arrive:
T_Latency =...
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What causes a media converter to turn on the Link LED for 100BASE-FX
I'm working on a custom board with Texas Instruments DP83822 PHY and 100BASE-FX SFP transceiver. This is connected to a media converter via mmF fiber. The link led on the media converter never comes ...
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What is the difference between LR1 and LR4 optics?
Does anyone know what's the difference between LR1 and LR4 optics?
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Link failure detection between 2 routers
When 2 routers are linked directly together with eBGP between them, how is a link failure detected ? With the BGP timers ? Or faster with some sort of L1 tool?
For instance, assume we have the ...
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Relation between Precision Time Protocol and self-clocking signals
I'm quite confused between time synchronization and clock synchronization.
Self-clocking signal is used to tell the receiver at which rate sender sending the bits so that it can read the bits at the ...
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LC dual pair converter to 10GBASE-T
If using dual pair LC fiber to run 10GbE over a long distance, what's the best way to connect it to a server on one end which has a 10GBASE-T port?
On the other end there's a switch with 10G SFP+ ...
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Is there a way to know the length of the cable used between the connected SFPs on a switching/routing device?
I have connected two Juniper routers with a QSFP28 optics and I need to find out the length of the optical cable I have used. Is there a command to check that in the router?
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Why does SONET need atomic clock but T-carrier does not?
SONET and T-carrier are both synchronous TDM.
But T-carrier does not use atomic clock. Why does SONET?
Is it because SONET does not use buffer? But how does it prevent bit loss if there is no ...
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Is SONET a physical layer or a data link layer?
According to some sources, SONET is physical layer.
But some sources say that SONET can carry IP directly. Also, SONET defines its own frame -- it has a header and a payload. That must make SONET a ...
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Calculating stranded and solid cable length (for 22AWG)
Reading up on how to calculate cable lengths as a follow-up to my previous question, I understand that you have to use (102-H)/(1+D) to calculated the stranded length (C) and H+C to calculate the ...
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How strong a ground loop would necessitate the use of isolation transformer in Ethernet? [closed]
One reason against the use of shielded twisted pairs in residential environment is the possibility to create a group loop between equipments, as discussed in Shielded Twisted Pair (STP) termination ...
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Why can't we create a hierarchy of hubs?
I was reading the Comptia Network+ All in One book and I came to know that we cannot create a hierarchy of hubs. My question is why so? Are MDIX ports simplex? Why is it not possible for the hubs to ...
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characteristics of different bit sequences over network
Do different sequences of bits exhibit different characteristics when sent over a network.
For example, does one sequence of bits have a higher error rate than another sequence? If there are ...
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Is MIMO equivalent to link aggregation?
Is MIMO the wireless version of link aggregation in wired networks?
I'm not asking if MIMO is a similar link aggregation protocol like LACP or PAgP, what I'm asking is if it is the same concept as ...
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How could the line rate of T1 be 1.544 Mbps?
T1 signal is the output of a 24-to-1 digital multiplexer whose inputs are 64 kbps each (plus one framing bit).
But a multiplexer is simply an electronic device that selects between several inputs and ...
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Questions regarding incoming packets at optical splitter from optical line terminator (OLT)
I am currently studying the textbook Computer Networking -- A Top-Down Approach (7th Edition) by Kurose and Ross. In a chapter on Home Access: DSL, Cable, FTTH, Dial-Up, and Satellite, the authors say ...
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does fiber optic transmit data as fast as light?
I dont know where to ask this question. So i think its best suited for networking community.
As fiber optic transmit data using light. So we are getting/sending data at the speed of light ??
I did ...
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SFP to RJ45 for 10Gbit network
I am in the process of upgrading some of our network into 10Gb and grabbed the following:
A network switch by netgear, mode:GS110EMX
A bunch of assorted cat8 cables(for future proofing)
Two 10gtek ...
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SFP/SFP+: Extender? F/F panel passthrough?
My primary question is this:
Is it possible to have a simple passive SFP/SFP+ bulkhead passthrough connector, with two female SFP/SFP+ sockets facing opposite directions and wired directly together, ...
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Inital value for the scrambler in 10GBASE-R
The standard says "There is no requirement on the initial value for the scrambler. The scrambler is run continuously on all payload bits".
I'm curious how the scrambled data can be recovered. To my ...
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What are the differences between the Optical Carrier (OC) and Synchronous Transport Mode (STM) protocols, in regards to SONET/SDH?
I understand that OC-3c and STM-1 are technically consistent, and STM-1 can transport different quantities of CEPT-N signals, but why not just use OC-3c and forget STM altogether?
Edit:
Originally ...
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Reliable transfer but unreliable auto-negotiation?
I have two servers, the first with a built-in and add-on 10gbit port, and the second with built-in gbit and add-on 10gbit (Syba AQC107), communicating through a feed-through rated for gigabit ...
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Collision domain question
I'm studying for my CCENT exam, and not quite sure why the book (official Cisco) says that there are 5 collision domains in this example. Isn't it supposed to be 4? The hub on the left, the hub in the ...
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Using an Ethernet cable and USB Ethernet adapter at the same time?
What would happen on using an Ethernet cable connected to one network and
then plugging in another Ethernet cable but using an USB Ethernet adapter from a
different network.
Would it connect to both ...
user56915
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How to extend CAT6 ethernet 2m from ceiling down to server rack?
Previously, we had a 6RU comms cabinet near the ceiling.
We've now replaced this with a full-depth server rack sitting on the ground.
The plan was to remove the old patch panel, and punch it down ...
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What do the positive and negative (+/-) transmit and receive pins mean on Ethernet cables?
So I'm trying to understand the pin layout of an Ethernet port, specifically for 8P8C which to my understanding is the most common. Of the eight pins, only four are apparently used for communication, ...
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How exactly does an Ethernet collision happen in the cable, since nodes use different circuits for Tx and Rx?
I am trying to understand how a collision occurs in Ethernet, especially when a duplex mismatch exists or when on a legacy Ethernet network two nodes transmit simultaneously.
Everyone explains the ...
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Does the PHY signal interframe gap to the MAC?
I'm trying to decode an Ethernet II frame with type instead of length indication. Theoretically this should be done by receiving and storing the data between start of frame and interframe gap. However ...
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Cat6A Junction Boxes in the US
I'm looking around the internet and can't seem to find a Cat6A junction box available in the US. Is there a reason they aren't sold in the US?
Basically, I have a Cat6A cable that is run to the wrong ...
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