1300 Mbit S In Mb S

MHz vs Mbits and Encoding

• MHz: A unit of frequency, describes electric signals. Pertains to the Physical Medium
• Mbits: A data rate, describes throughput achieved by the arrangement (electronics, software and medium)

Fourth dimension for a story

Once upon a time, I was very happy if I could get my modem to work reliably at 4800 bps, equally a matter of fact, I was ecstatic if got connected at 9600 or nine.6 kbps. Now I am using a 56 kbps modem that seems to practise only fine (although you never get connected at exactly 56k). The phone line to my house hasnt changed; it still the aforementioned copper wire. The bespeak encoding (standard V.90) combined with error correcting codes and pinch has made this faster data transfer possible and fifty-fifty more than reliable. A similar scenario is unfolding for Gigabit Ethernet over Cat 5.

Digital Signal Encoding

"Man" in the second line designates "Manchester" encoding which is used for standard Ethernet. The lesser line depicts "Differential Manchester" encoding which is very similar (but dissimilar, as you lot can encounter) and is used by Token Band. In both Manchester systems, the signal goes through a transition from high to low or the reverse direction in the center of each bit time slot. This transition guarantees good synchronization between sender and receiver. Therefore, people sometimes state that 10BASE-T runs over "barb wire". Indeed it uses a very robust signal encoding technique. Just as well note that the Manchester point encoding goes through roughly twice equally many level changes per time as the NRZ bespeak above. Therefore, Manchester encoding is very inefficient as far equally bandwidth requirements. To transmit ten Mbps you need at least a 10MHz bandwidth for the signal on the cable. (That is a very bare minimum. Fortunately, True cat three behaves pretty well up to 16 MHz.)

Plain, to get higher data rates over twisted pair cabling, we had to notice other point encoding systems that could still provide for reliable synchronization. I such organization is the 4 fleck- 5 fleck encoding. Every four $.25 of data are translated into a sequence of 5 $.25 for transmission. V bits provide 32 dissimilar combinations. Out of these 32 combinations only xvi (half) have to be selected for data encoding. We can select those 5-bit sequences that provide the maximum number of "transitions" for good synchronization. For example 00000 and 11111 volition be excluded, for certain.

Some additional advantages are listed: we tin can apply the remaining 16 codes for delimiters or idle patterns, and if an "illegal" design appears, we have detected that the cable transmitted something in fault. The data stream has grown 25% though. To transmit 100 million bits of information, we need to transmit 125 million signal on the cable and signal level is valid for viii nsec. To contain the bandwidth requirement for this signaling rate. The signaling uses a "pseudo-ternary" encoding. This is non a tri-level logic betoken simply instead, we will chose 0 volt for a bespeak that represents a logical 0. The logical ane indicate volition "toggle" between +1V and -1V. Meet below. It will appear intuitive that fewer indicate transitions are required per unit of fourth dimension. In that location is also a mathematical proof for the signal bandwidth requirements.

100BASE-TX Indicate Encoding

We will explain a four-level bespeak encoding. Gigabit Ethernet really uses PAM-5, a 5 level encoding scheme. The "fifth" level is used for boosted synchronization equally well as error detection/error correction. Annotation that the signal timing is viii nsec which is exactly the same value every bit nosotros encountered in Fast Ethernets 4B-5B encoding.

The signals on the cable can take five different levels while the full voltage swing from min to max is nonetheless the aforementioned 2V swing (from -1V to +1V). The signal levels are no longer separated past 2V, just by 0.5 V. The direct result of this separation is that if a noise spike of 0.25V hits the cable, the receiver will nigh likely not be able to make up one's mind which betoken level had been transmitted. This state of affairs is somewhat alleviated by the error detection/mistake correction encoding level.

Iv-level Point Encoding

This is an example of what a iv-level encoding scheme might look like. Recollect this illustrates the blazon of signal encoding used in 1000BASE-T. The existent encoding organisation is called PAM-5, which is a five-level system.

Nyquist theorem for a noise-free channel

To throw some theory into the flick. Yous may take heard of the Nyquist frequency. Here is the explanation in short. Shannons law applies to predict how much bandwidth needs to be available above the Nyquist minimum based on the expected point-to-noise ratios.

Limitation adamant past signal bandwidth R=2Wlog₂M

Where R is the rate of data transmission, W is the maximum frequency and One thousand is the number of levels of encoding

Case 1: 10BASE-T

This is a two level encoding so M=2,
Therefore the bandwidth (Westward) = R / log_ii2 * 2 which gives 10MHz (Remember that throughput of 10BASE-T is 20Mbits)

Instance 2: 1000BASE-T

This is a four level encoding so M=4 (5th Level is for synchronization only)
Therefore the bandwidth (W) = R / log₂iv * 2 which gives 62.5MHz (R = 250Mbits/south)
This is theory, and in real life the protocol for 1000BaseT needs a petty more than typically 80MHz, so the IEEE specifies cable testing on all pairs upwardly to 100MHz.

Transmission performance for True cat 6 components and installations needs to be verified to 250 MHz. Using the ACR model of bandwidth, the installation is predicted to have a positive margin similar in the size to the margin of a Cat 5 installation at 100 MHz. At 250 MHz the installation volition have a negative ACR margin. The IEEE has been the instigator to encourage testing to 250 MHz with an heart on the possibility that the connected evolution of DSP technology will allow manual beyond the ACR bandwidth. Recall that this technology had initially been developed for 100BASE-T2, which never was implemented. The 1000BASE-T standard relies heavily on these DSP techniques to guarantee reliable transmission over Cat five. MHz Mbits MHz Mbits MHz Mbits MHz Mbits MHz Mbits MHz Mbits MHz Mbits

The development of I-Gbps Ethernet started out within the IEEE 802.3 committee as the IEEE 802.3z project. Withal, it became clear that the development of the 1000BASE-T (100 chiliad on category v) would require more work and was going to be delayed relative to the fiber and short-haul (25 m) copper solution. Since Gigabit Ethernet would first notice application in the courage where fiber is the predominant medium information technology made skilful sense to divide the ii efforts and expedite the fiber solution.

Therefore a dissever projection IEEE 802.3ab was created to specifically address 1000BASE-T evolution.

• 1000BASE-Threescore (long wavelength: >1300 nm)
  MM Cobweb upwards to 550 grand
  SM Cobweb upward to ii,500 m
• 1000BASE-SX (short wavelength: 850 nm)
  MM Fiber 62.5 thousand up to 220 m
  MM Cobweb fifty k upward to 300 m
• 1000BASE-CS
  Brusk haul copper (25 m)

The short haul copper solution uses (IBM) triax cable, and is intended but for backbone applications in an equipment room --interconnecting of hubs or other networking electronics in an equipment room. It is definitively not considered part of a generic cabling solution. It is expected that these short haul copper cables will be manufactory produced in stock-still lengths.

This portion of I-Gbps Ethernet was approved June 1998. The fiber standards development encountered some remaining issues with modal bandwidth resulting in excessive jitter on multimode fiber. This resulted in the definition of the maximum altitude on MM fiber as shown above. The modal dispersion and resulting jitter is a office of the diameter of the cadre and the wavelength (and spectrum) of the low-cal source.

IEEE 802.3ab is now fully devoted to 1-Gbps Ethernet on category 5 twisted pair cabling. All iv wire pairs in the standard four-pair cable are used, and manual is full duplex on all 4 wire pairs. NEXT cancellation techniques are also implemented. This technique was first adult (merely never implemented) for the proposed 100BASE-T2. The latter was divers as a two wire-pair solution on category three for Fast Ethernet (100 Mbps information rate). A five level encoding system was adopted; it is called PAM-5, more than about this subsequently. The initial goal of the IEEE 802.3 commission was to obtain a completed standard past late 1998; delays over Return Loss caused a filibuster. It was nevertheless resolved an agreed in August 1999.

The IEEE 802.3ab working group requested assistance from the TIA TR41.8.1 UTP task group to fill in requirements needed for Ane-Gbps performance over category five cabling. (Notation that in December 1998 the name of this TIA group inverse to TR.42.)

This task grouping has adopted a "fast" rails projection to do and then, and the goal was to match the timeline for 1000BASE-T. Both projects take "slid" together. It is emphasized in every possible way that it is expected that the existing -- and currently installed -- category 5 cabling should normally meet the additional requirements, which were previously left unspecified. Equally a upshot, the TIA will yet phone call the newly compliant cable "category 5", and not annihilation like "category 5e" or "category half dozen". The True cat five specifications have been amended with a recommended performance level for the new test parameters (FEXT-related measurements and Return Loss). The recommendations are specified in a Telecommunications Systems Bulletin (TSB95). TSBs dont accept the weight of a "standard"; they are recommendations. (TSB67 was an exception; it has the normative weight of a standard.)

We are maxim that the ultimate measure of success in data transmission is the fact that frames are successfully transmitted. There are no bit errors (no FCS errors) and no re-transmissions. The physical layer plays a critical role in achieving error free transmission on the data link layer. The bandwidth characteristics of the physical layer must friction match the requirement of the physical bespeak encoding used by the network.

(1) We need to explicate the basic footing rules for all of the "frequency" plots we will be using during the discussions of the standards and specially to depict the performance of parameters that vary with the frequency such as Next and attenuation. In the frequency domain, we plot frequency along the horizontal axis and nosotros bear witness "something" about a signal with that frequency in the vertical centrality. The simple example beneath represents at the left side how a pure sinusoidal frequency signal varies in fourth dimension. If we assume that the period is one microsecond, the signal volition repeat ane million times per 2d or is called one megahertz (MHz). In the time domain plot on the right, we represent the amplitude of that signal.

The beginnings of the Fourier assay

(two) We accept a second goal. To lay the groundwork to explain that digital signaling contains a multitude of frequencies and that the transmission medium needs to practice an "adequate job" -- defined by a standard -- for all the frequencies of interest.

Lastly, this set up of drawings may be used to introduce the digital test technique. The DSP Series testers from Fluke ship pulses that contain many frequencies.

Add two sinusoidal signals to get the fourth dimension domain signal depicted in the left-hand side plot. We have added to the i MHz signal of the previous slide a signal of iii MHz with amplitude equal to 1/3 of the ane MHz indicate. The frequency domain picture in a higher place shows the two frequencies each with its amplitude value.

We now have added 4 signals together. The signals with higher frequencies, called harmonics, have successively smaller amplitudes: i/3, 1/five, 1/7, etc.. Y'all tin can see that the fourth dimension domain picture is approaching digital signaling, i.e. ii distinct voltage levels.

Finally, we are set up to flip the whole affair into the other direction. In theory, we are transmitting the digital signal shown in the time domain picture, a perfect foursquare wave. The frequency domain shows that such a digital indicate contains a number of frequencies. As a matter of fact, every frequency between 0 and some upper value is represented. For a ii-level digital signal, the upper value is the frequency equal to the data rate.

Case: using the NRZ encoding for ATM 155, this null point is at 155 MHz. Shouldnt nosotros test to 155 MHz? The bespeak created past the transmitter does non exhibit the perfect rise and fall times that you see in the theoretical model. Changes from one voltage level to another require a finite amount of time (measured as the rise and fall times). The frequency spectrum of the "real" ATM NRZ signal is such that the "tail" in the frequency domain picture drops dramatically. Information technology has been debated by several people as to how much energy is really present to a higher place 100 MHz. The 2nd outcome to remember is that the receiver may not need or wait any frequencies above 100MHz to properly decode the digital bespeak that is transmitted.

Megahertz (MHz) is not equal to Megabits per second (Mbps)

Source: https://www.flukenetworks.com/knowledge-base/applicationstandards-articles-copper/mhz-vs-mbits-and-encoding

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