Questions tagged [layer1]

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

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60
votes
9answers
21k 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 ...
49
votes
14answers
235k views

Does having a longer Ethernet cable slow your connection?

As the title suggests, Does a longer Ethernet cable slow your connection down?
35
votes
5answers
9k views

Why are Ethernet Standards written in the form of 10/100/1000? Why not just 1000?

I always have seen Ethernet Standards written in the form "low value/middle value/max value", and always wondered why. Won't a router just reproduce a lower speeds anything below its maximum if it's ...
21
votes
6answers
6k views

What is this thread-like material on this Cat6 U/UTP cable?

Does anyone know what this thread-like material to the right on the picture is? Does it have anything to do with grounding? It is a Cat6 U/UTP cable.
20
votes
5answers
98k views

Cable Colors and Purpose

I've been doing some work with some big businesses and so far I've learned yellow is internet and blue is phone. Is this a standard or is this just a personal chose? Do colors mean different tasks?
20
votes
7answers
63k views

Minimum Ethernet Cable Length?

I have heard from a few people that cables less than 1 meter are prone to transmission problems. Is there any minimum copper cabling length? Please explain if this is true or not and share any ...
20
votes
5answers
40k views

Where to cross RX/TX line in fibre optical cabling

I'm in the process of connecting together some sites via optical fibre. The trans-site multimode fibres are terminated with SC jacks on patch panels from where they are patched to the corresponding ...
16
votes
6answers
15k views

Reason for half-duplex mode in Ethernet?

Half-duplex connections were popular at the time of 10Mbps and 100Mbps Ethernet, and, according to standards, it is allowed also in case of 1Gbps Ethernet. Am I correct that half-duplex mode support ...
16
votes
5answers
100k views

What's the difference between an Ethernet cable and a UTP cable?

Is there such a thing as an Ethernet cable or technically no? Are they actually called UTP cables? From wikipedia UTP cables are found in many Ethernet networks and telephone systems.
16
votes
3answers
6k views

DWDM active and passive comparison

I am trying to understand the cross-over point for when I would deploy active DWDM over passive DWDM (as active seems to be more expensive based on my initial research); Passive DWDM takes in various ...
15
votes
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 ...
14
votes
2answers
2k views

What does the naming convention for Ethernet standards mean: 1000BASE-T, BASE-TX, BASE-SX, etc.? What is the meaning of the components of the name?

I understand the number in the naming convention. The number represents how many Megabits per second can the standard support. However, I do not understand the rest of the naming convention. What do "...
13
votes
1answer
4k views

How does a packet get corrupted in a network?

I recently read about CRC, a checksum to detect package corruption and drop corrupted packages. But how does a packet in an IP-based network get corrupted in the first place?
12
votes
3answers
24k views

Why do I need a crossover cable to connect devices of the same type?

I know that a crossover cable should be used to directly connect devices of the same type and patch cable is used to connect devices of different types. But I never understood why is it so exactly? ...
11
votes
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 ...
10
votes
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?
10
votes
3answers
29k views

What is the purpose of an Ethernet magnetic transformer, and how are they used?

I have been told that Ethernet magnetic transformers are used for base-t Ethernet when transmission is sent over a lengthy cable. What is the purpose of the transformer? (is it for signal filtering or ...
9
votes
6answers
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 ...
9
votes
3answers
6k views

Why one of the pairs on Ethernet is not adjacent?

I know that Ethernet over twisted pairs have two standards as the figure below: The pairs are twisted to avoid cross-talk. But why in both standards there is one pair that is not adjacent (pin 3 ...
9
votes
2answers
777 views

Multi-drop Cat5e/6 Cable?

I'm looking to install ethernet ports in a small business. There are 7-8 groups of cubicles each with 4 desks. Ideally I'd like to run a cable to each desk but if my math is correct I'm looking at ...
8
votes
4answers
22k views

The maximum length of CAT6 for intranet network?

Recently I purchased CAT6 cable with a length of 150 meter. I bought another CAT6 with a length of 148 meter. I joined both the cables using RJ45 cable coupler. I tested it using LAN TESTER, and ...
8
votes
4answers
29k views

Minimum ethernet frame is 64 bytes, Why the payload must be padded to at least 46 bytes

What is reason to pad payload to mininum 46bytes, to form a ethernet frame of 64 bytes. Following says min would be 41 bytes. https://stackoverflow.com/questions/14526139/what-is-the-minimum-packet-...
8
votes
1answer
2k views

Internet Cable Has Been cut in two and taped back together

Let me explain, we have a two analogue lines (something like 16 pair each, the standard cable that's put into buildings) that come into our building but they pass through the building next door. ...
8
votes
6answers
21k views

Can a single optical fiber support full-duplex communication?

Can a single-mode single optical fiber support full-duplex communication, or does it have to be two fibers, one for each direction?
8
votes
7answers
4k views

Signaling vs encoding

Here are Cisco's definitions. Signaling The physical layer must generate the electrical, optical, or wireless signals that represent the "1" and "0" on the media. The method of representing ...
8
votes
3answers
3k views

Running Cat 7 STP cables in the same cable trays as 3-phase power cables

I am doing some work in a factory that is quite new, and have been asked to terminate some network cables - simple enough. However on looking up at the cable trays, which are suspended from the ...
8
votes
4answers
293 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?
8
votes
3answers
7k views

1000Base-T Ethernet limited to 100 m, why?

In 1000Base-T Ethernet connection, why is there a 100 m link length limit? CSMA/CD links normally are limited to a few hundred meters because of the limitations that CSMA/CD implies (collision domain ...
7
votes
7answers
3k views

How LAN works in video games if only one station is permitted to transmit?

I've read the in a LAN the data is transmitted in packets so as to allow only one station to transmit at a given time, so how could this be applied in video games LAN parties if only one device is ...
7
votes
4answers
7k 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 ...
7
votes
4answers
19k views

what is the difference between a CSU/DSU and a modem?

I'm so confused, both do the same function, converting the analog to digital, but what's the difference?
7
votes
2answers
601 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 ...
6
votes
8answers
12k 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, ...
6
votes
3answers
2k views

Ethernet Cable Orientation

I'm in an A+ course and was just working on wiring Ethernet cables. I was wondering, will an Ethernet cable function if the wires are reversed? Say instead of wiring 568B like striped orange, orange, ...
6
votes
6answers
5k 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 ...
6
votes
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 ...
6
votes
2answers
2k views

What is "Twisted pair with loading" cable?

What is "Twisted pair with loading" cable ? please explain and if possible please share a picture. Thanks, Note: Below image is taken from: Data And Computer Communications - 8e - WilliamStallings
6
votes
1answer
461 views

Why is there a separate set of 10 Gigabit fiber-optic transmission standards for WANs/SONET?

So, I'm reviewing the different IEEE transmission standards for an exam, and I've noticed that for the 10GBASE-X standards, there's two different sets of fiber-optic standards, 10GBASE-xW and 10GBASE-...
6
votes
2answers
4k views

Full Duplex and Collision Domain

I have a very basic query on Collision Domain and Full Duplex Mode. There are two types of logical topology: Ethernet and Token Ring . Whenever we read about Ethernet the first thing that we are ...
6
votes
1answer
5k views

What is the correct way to determine SFP+ Direct Attach cable compatibility between switches and NICs?

I'm contemplating a 10 Gigabit link between an Intel x520 NIC and a Cisco SG500X switch. These two would be within 5m of one another, so using one of the Cisco SFP+ passive Direct Attach cables like ...
6
votes
1answer
2k views

How does priority work in token ring?

Token rings have an optional priority feature, for which the 8 access control bits in the token ring non-token frame are used. Suppose we are working with the delayed token reinsertion scheme. How ...
6
votes
2answers
541 views

How to properly name TIA-606-B Cabling Subsystem 1 far end identifier for work area equipment outlets?

We are moving to TIA-606-B for labeling. I have read most of the TIA-606-B standard. Some parts I have only skimmed, while others I have studied in depth. I do not understand the rationale behind the ...
5
votes
3answers
4k views

How to debug L1 Auto negotiation issues?

One of our Linux hosts has started switching its gears recently. While checking the interface speed, I could see that the interface has switched down to 10Mbps. The NIC and Switch are capable of 1G ...
5
votes
3answers
2k views

Importance of encoding data to signal

We all know that there are various encoding schemes to encode data like Manchester Encoding, before sending it. But why is there a need to encode the data to a signal? Why can't we just transmit the ...
5
votes
5answers
3k views

Why can't two hosts (in two different logical networks) connected to each other through cross-over cable communicate?

Let us say, i have two computers (hosts) A and B. Where A has been assigned an IP address of 192.168.1.10/24 and host B has been assigned an IP address of 192.168.2.11/24. And both of them has been ...
5
votes
3answers
1k views

Cables on a closed rack

I've just spent the last few days building my first server rack. It will be a significant upgrade to our current mess. I was asked to buy and install one and so I did. I was not completely aware of ...
5
votes
4answers
38k views

CAT7 Ethernet cable: order of wires in the clamp

On a CAT 7 Ethernet cable each twisted pair is individually shielded, and all pairs together are inside a shielded jacket: Colors of the wires may change, for instance I recently got my hands on a ...
5
votes
3answers
253 views

Are all same type fiber optic transceiver compatible?

Can I order a 1000BASE-LX transceiver from any source and it will be compatible with all others 1000BASE-LX ? Would a link with a Juniper 1000BASE-LX and a TrendNet 1000BASE-LX transceiver work?
5
votes
1answer
12k views

How to repair a break in a long Cat-5e cable run

I have a long run of Cat5e which is broken at about 20' from one end. Replacing the entire cable isn't an option, as it's fairly long and is going through walls and such. Searching this on google ...
5
votes
3answers
6k views

Can normal CAT6 be buried? [closed]

I have the leftover from a long spool of CAT6. I'd like to run a line to my garage, which is separate from the house. Can "typical" CAT6 be directly buried, or should I buy one of the "waterproof" ...

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