Questions tagged [layer1]

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

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2answers
39 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 ...
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1answer
558 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 ...
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1answer
253 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 ...
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4answers
103 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. ...
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1answer
63 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 ...
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1answer
42 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 ...
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1answer
51 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 ...
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3answers
69 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 ...
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1answer
72 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 ...
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1answer
46 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 ...
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0answers
22 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 =...
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1answer
19 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 ...
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1answer
109 views

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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2answers
108 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 ...
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1answer
33 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 ...
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2answers
122 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+ ...
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2answers
57 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?
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1answer
30 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 ...
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1answer
39 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 ...
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1answer
76 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 ...
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0answers
22 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 ...
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6answers
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 ...
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1answer
20 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 ...
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1answer
93 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 ...
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2answers
170 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 ...
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1answer
192 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 ...
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4answers
185 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 ...
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1answer
247 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 ...
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2answers
439 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, ...
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1answer
103 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 ...
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0answers
127 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 ...
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1answer
59 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 ...
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3answers
901 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 ...
2
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1answer
521 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 ...
2
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2answers
949 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 ...
6
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8answers
13k 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, ...
15
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5answers
7k views

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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1answer
298 views

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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2answers
354 views

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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1answer
417 views

Cat 6 life expectancy [closed]

how long will cat 6 cable survive outside if it is not an external grade cable. No sunlight touches the cable but only cold temperatures of around -10c, everyday every year. the cable has no holes, ...
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8answers
2k views

Using sound waves in layer 1

Is it possible, in theory, to use sound waves as the physical medium to transmit data over a network? In other words, could you implement layer 1 of the OSI networking model using sound waves or am ...
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1answer
81 views

Which layer and protocol takes care of power-down and power-up of ethernet port

Which layer and protocol takes care of power-down and power-up of ethernet port (based on cable connected or disconnected) in a Linux machine. I think it (power-up and power-down) will be taken care ...
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4answers
821 views

What is the difference between Ethernet types, considering bandwidth?

Different types of Ethernet (standard Ethernet, Fast Ethernet, Gigabit Ethernet) have different speed of data transfer (10 Mbit, 100 Mbit, 1 Gbit). Why is that? On the physical layer, the speed of ...
4
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2answers
189 views

Noticeable limitations or penalties from using inline fiber couplers

Is there any noticeable limitations or penalties from using inline fiber couplers, such as those in a patch panel to join multiple fiber runs together? Currently I have switches joined together ...
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1answer
600 views

How 1gbe works in full duplex? [duplicate]

1gb Ethernet works in full duplex and the maximum theoretical throughput is 2Gbps. Every pair gives 250 mbps in both directions. How it can work in full duplex on the one pair?
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1answer
53 views

Influence of a TAP

I want to use a passive TAP to sniff all the network (100 Mbps full duplex twisted pair). I have two interfaces for sniffing and only one pair for each direction. Will the TAP add any noise? Or if I ...
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2answers
2k views

Does bridging add delay?

If I use a bridge to perform traffic sniffing like man in the middle will the bridge add a delay? And what word should I use delay or latency?
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2answers
1k views

How does a router know the MTU of a network?

I've done several exercises where you're given the MTU of a net or subnet, but I wonder how routers know the MTU of the nets they're connected. I've learnt that in OSPF protocol this information is ...
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1answer
173 views

Is a fiber optic connection considered a "wired" connection?

https://en.wikipedia.org/wiki/IEEE_802.3 As Wikipedia says, 802.3 is for ..."wired Ethernet". How can I name copper and fiber networks in one word to describe 802.3 standard and to distinguish from ...
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2answers
28k views

RJ45 Cable only has 4 wires

The cable that connects to my rj45 only has 4 cables, blue, orange, blue stripe, orange stripe. When I connect them to their corresponding ports, there is no internet connection.(Blue = 4, Orange = 6, ...

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