In Part 1of this topic I described how a T1 carrier is used to transmit data. Data transmission by nature is "bursty" meaning large amounts of information are typically transmitted and then followed by relatively quiet transmission periods. This can cause transmission problems for T-carrier systems since they rely on timing synchronization. Let's take a look how this potential problem is avoided.
Wednesday, May 2, 2012
Data Transmission on T1 Carriers - Part 2
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Labels: Analog, communications, Data, Digital, ebook, Education, Engineering, Information, technician, Technology, Telecommunications, Voice
Monday, April 16, 2012
Data Transmission on T-1 Carriers Part 1
Back in December I wrote a post here titled T1 Lines - What They Are. In the post I discuss the Digital Signal (DS) Level System and how combining the equivalent of 24 DS-0 voice channels along with overhead consisting of timing and synchronization bits brings the DS-1 bit rate to 1.644 Mbps - that's a T1. In this post, let's have a look in more detail to get a better idea of how the entire system works.
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Gordon F Snyder Jr
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Labels: Analog, communications, Data, Digital, ebook, Education, Engineering, Information, technician, Technology, Telecommunications, Voice
Wednesday, March 21, 2012
SONET Packet-Oriented Data Framing
Timing is critical here (that's why it's called synchronous) for communications across the entire network.
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Gordon F Snyder Jr
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10:53 AM
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Labels: communications, Data, ebook, Education, Engineering, Ethernet, fiber, Information, optics, technician, Technology, Telecommunications
Tuesday, March 13, 2012
Synchronous Optical Network - SONET
In the United States T-1 carriers have been replaced in many locations with Synchronous Optical Network (SONET) systems. Internationally, the SONET equivalent is called Synchronous Digital Hierarchy (SDH). Both SONET and SDH systems consist of rings of fiber capable of carrying very high bit rates over long distances. Copper has been replaced by fiber to inter-connect most Central Offices (CO’s) in the United States at bit rates ranging from the SONET base rate of 51.84 Mbps up to 39,813,120 Gbps.
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Labels: Analog, communications, ebook, Education, Engineering, Information, technician, Technology, Telecommunications, Voice
Tuesday, February 21, 2012
No T1 Lines in Europe - The E-Carrier Hierarchy
Today I'll continue with a post on what I've been calling the legacy Public Switched Telephone Network (PSTN). In my last legacy post we covered T-4 and T-5 lines, today let's take a look at the European or “E” carrier system.
The European or “E” digital transmission format is slightly different than the North American T-carrier system format. With the E-Carrier system we are still taking individual voice call analog signals and converting to a digital signal by sampling the analog signal 8000 times per second and, after matching the instantaneous voltage sample level to one of 256 discrete levels, generating an 8 bit code for each sample. We are still dealing with the fundamental DS-0 building block of 64Kbps of digital bandwidth per single analog voice channel we used for the T-Carrier system. The differences between E-Carrier and T-Carrier deals with the number of channels and how these channels are used. Let’s start by looking at a European E-1 system and how it compares to a North American T-1 system.
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Gordon F Snyder Jr
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2:24 PM
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Labels: Analog, communications, ebook, Education, Engineering, Information, technician, Technology, Telecommunications, Voice
Monday, February 13, 2012
DS-4 and DS-5 Lines
It's been a while since I've posted on what I've been calling the Legacy Public Switched Telephone Network (PSTN). My last related post was way back on December 15, 2011 titled What's a T3 Line? Today, Let's take a look at higher bit rate signals in the DS system.
DS-4 Signal
Back on December 15th, we said each DS-3 signal carries a bit rate of 44.736 Mbps. Six 44.736 Mbps digital DS-3 signals are multiplexed into one DS-4 signal. If we have six DS-3 signals per DS-4 signal and each DS-3 signal is 44.736 Mbps we can calculate:
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Gordon F Snyder Jr
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Labels: Analog, communications, ebook, Education, Engineering, Information, technician, Technology, Telecommunications, Voice
Thursday, December 15, 2011
What's a T3 Line?
In my last post I described what a T1, also called a DS-1, line was. Most of us have also heard the "T3 Line" term used. Let's take a look at what a T3 or DS-3 line is.
DS-2 Signal
Before we can describe a DS-3 line, let's first take a look at a DS-2. In that last post we figured out how each DS-1 signal (T1 line or circuit) carries a bit rate of 1.544 Mbps. Four 1.544 Mbps digital DS-1 signals are multiplexed into one DS-2 signal. If we have 4 DS-1 signals per DS-2 signal and each DS-1 signal is 1.544 Mbps we can calculate:
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Gordon F Snyder Jr
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Labels: Analog, communications, ebook, Education, Engineering, Information, technician, Technology, Telecommunications, Voice
Tuesday, December 6, 2011
T1 Lines - What They Are
Most of us have heard about "T1" lines. We know they are some kind of (expensive) communications line you can get from one of the telephone companies. It turns out T1's are part of the Digital Signal (DS) Level System.
Remember each channel is sampled 8000 times per second so a single frame represents one eight-thousandth of 24 individual channels or telephone calls. We can also say that, in one second a DS-1 signal transmits 8000 193 bit frames. We can use these numbers to calculate the true DS-1 bit rate which includes both data and overhead (framing) bits:
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Gordon F Snyder Jr
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Labels: Analog, communications, ebook, Education, Engineering, Information, technician, Technology, Telecommunications, Voice
Thursday, November 24, 2011
Wavelength Division Multiplexing (WDM)
In my last legacy Public Switched Telephone Network (PSTN) post I covered Statistical Time Division Multiplexing (STDM). In this post let's take a look at Wavelength Division Multiplexing (WDM and DWDM) methods.
As bandwidth requirements continue to grow for both the legacy Public Switched Telephone Network and the emerged Internet/IP network most of the high bandwidth backbone transmission is being done with fiber optics and a method called Wavelength Division Multiplexing or WDM. WDM functions very similarly to Frequency Division Multiplexing (FDM). With FDM different frequencies represent different communications channels with transmission done on copper or microwaves. WDM uses wavelength instead of frequency to differentiate the different communications channels.
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Gordon F Snyder Jr
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Labels: Analog, communications, ebook, Education, fiber, legacy, light, optics, PSTN, technician, Technology, Telecommunications, Voice, wavelength
Wednesday, November 16, 2011
Digital Multiplexing - Statistical Time Division Multiplexing
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Gordon F Snyder Jr
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10:10 AM
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Labels: Analog, communications, dialtone, ebook, Education, legacy, PSTN, technician, Technology, Telecommunications, Voice
Friday, November 11, 2011
Digital Multiplexing - Time Division Multiplexing
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Gordon F Snyder Jr
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7:01 PM
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Labels: Analog, communications, dialtone, ebook, Education, legacy, PSTN, technician, Technology, Telecommunications, Voice
Tuesday, October 25, 2011
Analog or Frequency Multiplexing
In this post I continue discussing some of the different legacy technologies used by the Public Switched Telephone Network (PSTN). Today let's take a dive into analog or frequency multiplexing.
This 240KHz is placed in the frequency range of 312 – 552 KHz.
This 2.40MHz is placed in the frequency range of 564 – 2.964 MHz.
This 14.4 MHz is placed in the frequency range of 3.084 – 17.484 MHz.
Frequency multiplexing is now considered obsolete technology on the telecommunications network. Analog signals are more sensitive to noise and other signals which can cause problems along the transmission path. Those long coaxial cables make pretty good antennas. They have been replaced with digital multiplexers. In my next legacy PSTN post I'll cover how digital multiplexing works.
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Gordon F Snyder Jr
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9:18 AM
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Labels: Analog, communications, dialtone, ebook, Education, legacy, PSTN, technician, Technology, Telecommunications, Voice
Sunday, October 23, 2011
Multiplexing - A Brief Introduction
In this post I continue discussing some of the different legacy technologies used by the Public Switched Telephone Network (PSTN). Today let's take a quick look at what multiplexing is.
Before the invention of the telephone both Alexander Graham Bell and Thomas Edison were experimenting with ways to transmit more than one telegraph signal at a time over a single wire. They both realized this was a critical piece if any communications network was to grow in the number of users.
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Gordon F Snyder Jr
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10:11 AM
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Labels: Analog, communications, dialtone, ebook, Education, legacy, PSTN, technician, Technology, Telecommunications, Voice
Thursday, October 20, 2011
The SLC-96
In this post I continue discussing some of the different legacy technologies used by the Public Switched Telephone Network (PSTN). Today let's take a look at how the PSTN designed and tuned for voice communications started to change in the late 1970's with something called an SLC-96 (pronounced "Slick 96").
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Gordon F Snyder Jr
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2:42 PM
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Labels: Analog, communications, dialtone, ebook, Education, technician, Technology, Telecommunications, Voice
Friday, October 7, 2011
A Few Additional Telephone System Features
In this post I continue to describe the legacy Public Switched Telephone Network (PSTN), looking at a few other common telephone system features we are all used to having and relying on. These are additional handset signals and PIC. I would also want to include Caller ID here but I've already covered how it works in a previous post.
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Gordon F Snyder Jr
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9:37 AM
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Labels: Analog, communications, dialtone, ebook, Education, technician, Technology, Telecommunications, Voice
Friday, September 30, 2011
Telephone Set Function 4. To convert voice frequencies to electrical signals that can be transmitted
In my last few legacy Public Switched Telephone Network (PSTN) posts, I covered pulse or rotary dial service, dual tone multi frequency (DTMF) dialing service and what makes a telephone ring. In this post let's look at microphones and speakers.
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Gordon F Snyder Jr
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9:51 AM
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Labels: Analog, communications, dialtone, ebook, Education, technician, Technology, Telecommunications, Voice