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Questions tagged [layer1]

For questions about the OSI layer-1 (physical layer).

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Baffled: No continuity but excellent speed on six new Cat6 runs

For my first post on Stack Exchange I have a situation that seems to be impossible: fast internet on cables that show no continuity. I just installed 16 Cat6 ethernet runs in an office. All of them ...
WolfeWires's user avatar
4 votes
4 answers
1k views

TCP/IP and data cut

I would like to clarify my understand about TCP/IP model and packet cutting. I think it's done by layer 3 (Transport, eg. TCP) but I'm note sure about layer 2 (Network, eg. IP) or even layer 1 (...
PanCho's user avatar
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0 votes
1 answer
131 views

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 ...
SUNITA GUPTA's user avatar
0 votes
1 answer
84 views

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 ...
dpnv's user avatar
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1 vote
1 answer
67 views

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 ...
Ramzi Baaguigui's user avatar
2 votes
1 answer
305 views

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 ...
Marcus's user avatar
  • 183
3 votes
1 answer
586 views

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 ...
Erik Parkinson's user avatar
2 votes
1 answer
1k views

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 ...
Kode1000's user avatar
1 vote
3 answers
260 views

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 ...
S. M.'s user avatar
  • 398
0 votes
1 answer
293 views

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 ...
S. M.'s user avatar
  • 398
1 vote
2 answers
365 views

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 ...
Albin's user avatar
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1 answer
35 views

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. ...
user4779's user avatar
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0 votes
2 answers
66 views

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 ...
Thomas LEFORT's user avatar
19 votes
3 answers
8k views

Why does an Ethernet cable have four pairs?

I'm curious about why 10Base-T and then 100Base-T Ethernet networks used cables which had four pairs if they only needed two? Were there some cables that only had two pairs? If we wanted to increase ...
UnderAnOpenSky's user avatar
2 votes
1 answer
566 views

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 ...
HKIT's user avatar
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1 answer
2k views

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 ...
PowerCat's user avatar
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1 answer
918 views

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. ...
David Roonie's user avatar
1 vote
4 answers
422 views

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. ...
AJ HUNTER's user avatar
0 votes
1 answer
236 views

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 ...
johnny is here's user avatar
1 vote
1 answer
466 views

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 ...
mark's user avatar
  • 113
0 votes
1 answer
598 views

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 ...
The Pointer's user avatar
2 votes
5 answers
318 views

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 ...
Kamal S.'s user avatar
1 vote
1 answer
713 views

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 ...
Lkaf Temravet's user avatar
2 votes
1 answer
188 views

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 ...
The Pointer's user avatar
0 votes
0 answers
24 views

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 =...
The Pointer's user avatar
1 vote
1 answer
67 views

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 ...
user74012's user avatar
2 votes
1 answer
2k views

What is the difference between LR1 and LR4 optics?

Does anyone know what's the difference between LR1 and LR4 optics?
Rakesh Nittur's user avatar
0 votes
2 answers
510 views

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 ...
huseyin39's user avatar
  • 107
1 vote
1 answer
134 views

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 ...
Vencat's user avatar
  • 115
2 votes
2 answers
133 views

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+ ...
g491's user avatar
  • 123
1 vote
2 answers
67 views

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?
Rakesh Nittur's user avatar
0 votes
1 answer
65 views

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 ...
Noob_Guy's user avatar
  • 491
0 votes
1 answer
96 views

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 ...
Noob_Guy's user avatar
  • 491
1 vote
1 answer
172 views

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 ...
Albin's user avatar
  • 173
1 vote
0 answers
37 views

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 ...
Mys_721tx's user avatar
  • 111
2 votes
6 answers
2k views

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 ...
ShayakSarkar's user avatar
0 votes
1 answer
21 views

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 ...
eric tyrrell's user avatar
2 votes
1 answer
144 views

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 ...
Noob_Guy's user avatar
  • 491
0 votes
3 answers
640 views

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 ...
Noob_Guy's user avatar
  • 491
1 vote
1 answer
360 views

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 ...
The Pointer's user avatar
2 votes
4 answers
1k views

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 ...
HungryFodder's user avatar
1 vote
1 answer
640 views

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 ...
Jono's user avatar
  • 111
0 votes
2 answers
1k views

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, ...
Dale Mahalko's user avatar
0 votes
1 answer
306 views

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 ...
fiedel's user avatar
  • 17
0 votes
0 answers
575 views

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 ...
Mike's user avatar
  • 1
2 votes
1 answer
89 views

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 ...
G. Hall's user avatar
  • 21
4 votes
3 answers
1k views

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 ...
PowerTowerDad's user avatar
2 votes
1 answer
890 views

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 ...
user avatar
2 votes
2 answers
1k views

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 ...
victorhooi's user avatar
6 votes
8 answers
24k views

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, ...
haxonek's user avatar
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