Questions tagged [layer1]

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

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23 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 ...
5
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3answers
7k views

How is it possible to run VoIP on CAT3. Do you not need CAT5 for the voice data?

So I never knew this till today but I thought you needed CAT5 for VoIP but this business is running VoIP on CAT3. Don't you need the extra wires for the voice, data and power?
3
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3answers
430 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
40 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 ...
2
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2answers
2k 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, ...
13
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5answers
3k 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 ...
9
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5answers
3k views

Do network adapters read incoming bits in a single stream?

When a Gigabit network adapter is receiving data, how is it receiving the bits? Is it seeing it all in one stream of 0's and 1's? Or is there somehow multiple streams of 0's and 1's coming in at the ...
3
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3answers
2k views

Cabling standard for Layer-3 switch

I want to know the appropriate cable type between: Layer-2 and Layer-3 switch Layer-3 switch and router Is it cross-over or straight through?
2
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1answer
78 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
62 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 ...
2
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3answers
2k views

What is the maximum distance for blowing optical cable through pipes?

What is the maximum distance for blowing optical fiber cable with compressed air through pipes? The method known also as Cable jetting. Taking into consideration no lubricant is used. I am asking ...
6
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8answers
3k 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, ...
4
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1answer
793 views

NEXT Crosstalk calculation

The NEXT value for a given cable type is generally expressed in decibels per feet or decibels per 1000 feet. NEXT value varies with the frequency of transmission. The higher the NEXT value, the ...
4
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3answers
166 views

The recommended settings for giga ethernet connected to Ethernet port

What is the recommended duplex and speed configuration for giga ethernet port connected to legacy ethernet (10 mbps) port and there is no available duplex command available on the ethernet side? If ...
0
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1answer
82 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 ...
56
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9answers
19k views

Is 30 Mbit/s fibre faster than 30 Mbit/s copper? [duplicate]

A network engineer professional is overseeing our town's installation of fibre and was explaining how much faster it was. I pointed out that it wasn't a silver bullet as you had to pay the provider ...
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2answers
46 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 ...
0
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1answer
49 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, ...
2
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1answer
131 views

T-568A/B on the same cable

I'm helping my friend punch down all of the Cat5-e cable in his office. Some of it went to existing patch panel and some went directly into a switch. There are two patch panels, each was about half ...
10
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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 ...
1
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1answer
57 views

Velocity(factor) of different cable types - Collision domain

I need to calculate the max length of a collision domain. There is this formula. In short: maxLength = (c * velocityFactor * 512 Bit)/(vBit) c = speed of light velocity factor = ? vBit = bit ...
2
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4answers
349 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 ...
1
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1answer
49 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 ...
4
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2answers
167 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 ...
0
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1answer
56 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
47 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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6answers
2k views

SFP+ transceiver's ability to do 1GbE

I understand that most ports that support SFP+ transceivers can step down to allow an SFP to be plugged into it, but my question is around the transceivers/optics themselves. Can an SFP+ transceiver ...
0
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1answer
130 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 ...
7
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4answers
4k views

Why preamble is not considered a part of the Ethernet Header?

If I search where does my data start in an Ethernet frame, I get a common answer which says TCP header( 20 bytes) + IP header ( 20 bytes) + Ethernet header( SA + DA + Type) i.e 14 bytes. So, in short ...
5
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2answers
943 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 ...
2
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1answer
62 views

How many 3 dB couplers are needed to construct a 16 way fiber optic splitter?

Wikipedia says we need 31 couplers. Can't we do it with 8 couplers?
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1answer
64 views

HP Access Switch 1920-48G POE switch

I would like to know whether we can use an HP 1920-48G POE access switch with an HP 5406zl as Core switch. The access switch will be connected through 1 Gbps SFP to the core switch.
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2answers
448 views

What certifications are there for Fiber Optic termination and splicing?

As a knowledgeable person in computer networks I have always had an itch for learning how to create custom-length fiber optic cables. So, as a personal goal, I want to get trained and certified in ...
1
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2answers
114 views

What classifies as crossover cable?

The definitions I've read say that crossover cable is cabling which the receive and transmit pairs are swapped around. My question is based on the fact that beyond this, I've seen some diagrams which ...
3
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2answers
1k views

Why use T1, T3, OC3 in 2015? Why not just pull fiber?

I am currently looking to upgrade internet connections in our major offices. Given that our reliance on cloud services has grown, some users are complaining of sluggishly behavior. After testing, as ...
1
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2answers
202 views

Why Ethernet was chosen to be the primary protocol + why carrier ethernet was created?

I'm currently trying to investigate the extra benefit that Ethernet has to offer for the internet today. As far as i investigated & know, Ethernet gives us a new hardware, cables and functionality ...
2
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2answers
421 views

Reasons not to combine daisy chaining with path redundancy

Is there any specific (maybe obvious) reason why path redundancy and daisy chaining is not combined? Cisco does show some network topologies HERE, but the combination of path redundancy and daisy ...
5
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1answer
142 views

Is there an IEEE recognized method for splicing Category 5e or 6 cabling?

Is there an IEEE recognized method for splicing Category 5e or 6 cabling, and maintaining the expected data rates? Such as the junction box shown in the link below. https://www.lowvoltagecables.com/...
2
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3answers
1k views

using fiberoptic for long-distance ethernet connection [closed]

I am trying to help provide decent (better than ATT's awful 3Mbps-on-a-good-day DSL) internet service to a cluster of homes in our rural neighborhood. The first house (near the main road) has good ...
2
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4answers
96 views

What is a standard term that includes patch panels but is broader?

I work in network infrastructure documentation at a public university. In discussions with coworkers, I frequently need to refer to devices that connect cables end-to-end. These devices are usually ...
-2
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1answer
41 views

Category-6 cable for CCTV [closed]

T568A or T568B? Which one (1, 2, or 3)? Straight-through Cross-Over Roll-Over
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2answers
359 views

New crimped UTP cable connects and disconnects

I was just making new short UTP cables, and I was happy that when I checked the cable through an Ethernet Cable Tester, all 8 wires were straight to each other and was perfect. When I plugged the UTP ...
5
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2answers
202 views

I need the functionality of a pair of patch panels but I don't want to run one cable per port

My needs will be met by two patch panels with dedicated copper running between them for each port. But I'm looking at a few hundred ports and I'd rather not have to run a few hundred cables. ...
1
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2answers
97 views

Need an estimate of the max power density

Here is an image of a 1x64 fiber optic splitter/combiner: I am assuming these are plastic/polymer fibers. A very similar box (http://www.ebay.co.uk/itm/SC-UPC-1x32-Fiber-Optic-Splitter-PLC-Splitter-...
2
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1answer
623 views

Intermittent periods of high packet loss, one hop beyond router

I've been trying to diagnose internet connection issues at a remote small business for which I am the system administrator. If this is not the proper Stack Exchange to post to, I'd really appreciate ...
1
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2answers
118 views

Would using a cat6 rj45 coupler strip VLAN out when connecting 2 VLAN aware devices ?

Ive got a project where i have to use some existing wiring and some new wiring as we can not run new wiring in one part of the building. At the moment my network diagram looks like this Becuase i ...
2
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3answers
1k views

Reason for excessive amount of collisions in hub networks?

I ran a test-setup which caused excessive amount of collisions on Cisco FastHub 400 port. This caused switch to isolate this port. For example in case of port 6, this has happened 766 times: Hub#sh ...
2
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2answers
83 views

Strengthening Wi-Fi signal

The company has a Wi-Fi network, and the company area is quite large. There is a dead zone in which the Internet is not available by client devices (about 30% of the total area). There were attempts ...
7
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4answers
204 views

Is ethernet a term describing just the protocol or the interfaces also?

Is ethernet describing the protocol and therefore cat5 cables became labelled ethernet cables because they are used for this protocol?