43

They include this because not all ports are able to run at multiple speeds or certain speeds. Running at only one speed was probably most common when 100BASE-TX first came out and a number of switches had fixed 100BASE-TX ports as uplink ports with 10BASE-T ports for providing access. However, it is common for many GBIC/SFP based ports to only run at a ...


25

Good question. To answer it fully would involve a pretty deep look at Ethernet Wiring. But I'll try to explain it in simpler language. All three speeds (10, 100, 1000) run over the same physical wiring: Unshielded Twisted Pair (UTP). UTP is made up of 4 pairs of wires (8 total wires) -- each pair is twisted around each other. Each pair of wires work ...


23

My colleague believed it's because of the physical distance while I don't think it matters. My understanding is once you have done the initial handshake and the data flow has started, it doesn't matter where the server is located and the result should be almost the same. Am I missing something here? How does it really work? Both of you were right at some ...


20

You might care to read RFC 1547 "Requirements for an Internet Standard Point-to-Point Protocol" which explains how the PPP was chosen. The thing I'd suggest you are missing is that interoperability is one of the principal driving forces in the internet protocols, and efficiency is much less important. You do the highly talented engineers who designed PPP a ...


17

Modulation and symbols the number of occurrences of a repeating event per unit time. So what is repeating in the wire per unit time? The voltage patterns on the wire repeat. In extremely simple communication systems, you might cycle the line's DC voltage above or below a threshold, as shown in your ASCII-art... __|‾‾|__|‾‾|__|‾‾|__|‾‾. Suppose your ...


16

Ethernet packets 1.5k 1500 - 20 B (IPv4) - 20 B (TCP+checksum) = 1460 B DATA (and 40 B Overhead) Add 40 B + 14 B (Ethernet) + 4 B (FCS) + 12 B (Interframe gap) + 8 B (preamble) = 78 B Overhead 78 / 1460 * 100 = 5.34% overhead 1460 / ( 1460 + 78) * 100 = 94.93% Throughput/Goodput 1,000,000,000(1Gbit) * 94.93% = 949Mbit/s(0.949Gbit/s) you measured ...


15

Does it mean it's electric circuitry is capable of serializing/deserializing (SERDES) 400G bits per second of data onto a wire while maintaining a relativley clean signal (low SNR)? Yes, that's what 400GE is designed for. The physical coding sublayer (PCS) uses forward error correction (FEC) to achieve a block error rate of 10-13 or better. The acceptable ...


13

Mike offered an excellent answer but not exactly to what you were asking. Bandwidth, by definition, is a range of frequencies, measured in Hz. As you've said, the signal __|‾‾|__|‾‾|__|‾‾|__|‾‾ can be broken down (using Fourier) into a bunch of frequencies. Let's say that we've broken it down, and saw that our signal is (mostly) made up of frequencies 1Mhz,...


13

The bandwidth is the number of bits that can be sent on a link in one second. The throughput is the amount of data sent, and that will need to subtract the protocol overhead from the bandwidth, so no, the throughput cannot exceed the bandwidth. It may seem that way if you compress the data, but that is an illusion.


12

Looking over the frequency spectrum, I notice that light is at a relatively low Hz rate as compared to high frequency. What spectrum chart were you looking at, because this is not correct. Here's a spectrum chart from Wikipedia: Notice higher frequencies are to the left, and longer wavelengths are to the right. In fact these are related by the formula f = ...


11

In 802.11 wireless (which I assume is your case), typically broadcast/multicast frames (as well as many management frames) are transmitted at the lowest base/basic/required (term varies by vendor) data rate. This is separate from the supported data rates. Typically, for best range and maximum compatibility, this defaults to the 1Mbps data rate, although in ...


10

Adjusting the light frequency, theoretically will allow more data to transfer (i.e. UV -vs- IR) per unit time No this is not true. Please see this question's answer on the Electronics Stack Exchange site. The frequency of the light travelling down the fibre is not relational to the speed of data transmitted as you may think. I know that question I linked is ...


10

Just to address the SNMP portion of your question, I'm guessing that you are seeing the 4.3Gbps result from querying the SNMP object 'ifSpeed'. If so, you are simply getting back the maximum value that is possible from a 32-bit object (i.e. 2^32-1). This is the expected behaviour for a 10Gbps interface. You will need to query 'ifHighSpeed' for the interface ...


8

Traditional way to monitor usage by host is to use NetFlow. Most enterprise Cisco gear supports exporting NetFlow records. Configure your Cisco router to export flow data to a NetFlow Collector. There are many different NetFlow Collector software packages out there ranging in cost from "free" to "an arm and a leg". PRTG is one such NetFlow Collector and ...


8

At layer 2, all load balancing is, at best, done by an XOR or hash of the source and destination MAC, and if you're lucky, it may even read into layer 3 and hash that data too. At layer 3, however, where we're basically talking about multiple gateways (so, effectively, two physical links with a unique next-hop across each) you can max out the bandwidth ...


8

IOS includes ttcp, albeit it might not be supported officially by Cisco it can come in handy in situations like this. JUNOS does not support ttcp as far as I know, but it's probably not too much hassle adding one central Linux machine connected to the PE that you can do measurements with. On IOS, you simply run 'ttcp', like so; LAB-C7600-1#ttcp transmit ...


8

Neither of the routers you are referencing will ever be able to run at line rate. While the 2621XM is a better "class" of device, it is much older, so the performance is actually similar. While dated, this document contains details for both routers you mention. The "overrun" and "ignored" errors in your interface output indicate you are trying to pass ...


8

Some of these terms are used differently by different people, but below is what is generally accepted. Bandwidth is the number of bits per second that a link can send or receive, including all flows. For example, the bandwidth of a 100 Mbps connections is 100 Mbps, but that doesn't mean it is always sending or receiving 100 Mbps, but that is the maximum ...


8

Daily I see peoples even specialists in communication do mistakes about the three mentioned terms: Bandwidth: The unit of it is Hz, so it is mathematically is: High_Used_Frequency - Low_Used_Frequency. So, when we measure bandwidth in bps, i.e we do mistake. Beside, some guys working in Network field, totally they treat with the bandwidth as Data rate. So, ...


8

The -l option is for the buffer and doesn't influence the amount of data transferred. You have to specify the desired amount of data with the client-only option -n in KByte or MByte. So for 10GB, use -n 10240M Example: With the defaut buffer size of 8KB: iperf -c 10.1.1.1 -n 10240M ------------------------------------------------------------ Client ...


8

IP subnetting / address ranges and bandwidth have absolutely no correlation whatsoever. IP networks are based on packets. Packet networks don't allocate bandwidth for devices that are just connected. Packet networks (so to speak) allocate bandwidth ad hoc when there's a packet to be transported. You can connect 16 million nodes (10.0.0.0/8) all with each ...


8

I would imagine that with TCP A will resend the packages until it's gotten an acknowledgement for them all which would degrade A's performance because of having to resend packages all day long (need confirmation on that thought as well) but with UDP or other such protocols the question remains. TCP has "the sliding window mechanism that controls the ...


7

Multicast rate has to be the lowest common denominator so that all devices can receive it successfully. Multicast frames cannot be acknowledged[1], so if a peer fails to receive it, the sender will not know, and will not retransmit the frame. Having loss rates of more than 1% per receiver is common. Much higher loss rates can be expected if there is heavy ...


7

Assuming you're untagged, your current stack on the wire is: 7B preamble 1B SFD 6B DMAC 6B SMAC 2B type 20B IPv4 20B TCP nB application data 4B CRC 12B IFG First thing is very important, you are looking at L2 overhead, you must consider L1 overhead also. For ethernet preamble, sfd and ifg are L1, they are not really bytes but ethernet defines them strictly ...


7

Generally speaking you can install MRTG or any network graphing and historical data software which can pull interface statistics via SNMP. A nice and easy free software for this is CactiEZ. It can be easily run out of the box on an old server or mounted and installed easily on a VM. However, since you're using a Cisco router, you can enable NetFlow on your ...


7

I am unable to throttle the network by submitting my UDP packets among such links because I worry about packet drops and message losses. At first blush, this sounds more like a design problem with the application, not the network: Networks are not reliable. UDP was never intended to transport messages reliably without adding application layer loss ...


7

It really boils down to needing to support legacy devices and cabling. Cisco has a pretty good document, Ethernet Technologies, which explains a lot in depth. Ethernet has been around for a very long time. It was commercialized in 1981 at 10 Mbps. At first, it was pretty expensive. I remember ethernet cards costing $750 at a time when that was a lot of ...


7

What really happens is that any one flow only uses one of the links. Different flows are assigned to different links based on a hashing algorithm, so, in aggregate, you get the full bandwidth of the combined links, but any one flow will only get the bandwidth of a single link. You don't want to spread a single flow across multiple links because that will ...


7

You are conflating many things here, so let's try to detangle the issues in your question. Data rate is data rate, regardless of the physical medium. A 1Gb connection has the same data rate whether it is fiber or copper. As @toddwilcox mentions, the advantages of fiber over copper are longer spans and electromagnetic isolation. Data rates are independent ...


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