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35 votes
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How can the latency value be so low from Singapore to USA (~2ms)?

As others have pointed out, Google DNS uses IP anycast, which allows multiple servers in multiple locations to effectively share an IP address. Google (like many others) has many servers around the ...
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30 votes
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What's the difference between `Latency` and `Round Trip Time`?

Network latency is how long it takes for something sent from a source host to reach a destination host. There are many components to latency, and the latency can actually be different A to B and B to ...
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19 votes

Network latencies between opposite ends of the Earth

Google in particular uses distributed datacenters around the globe. They announce the same IP network at various places and due to the way routing protocols work, you reach the nearest one. This is ...
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16 votes

Serialization and serialization times in 40G/10G and 100G/25G Ethernet

You're overthinking. The number of lanes used doesn't really matter. Whether you transport 50 Gbit/s over 1, 2, or 5 lanes, the serialization delay is 20 ps/bit. So, you'd get 5 bits every 100 ps, ...
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14 votes
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Serialization and serialization times in 40G/10G and 100G/25G Ethernet

The part that does the division to multiple lanes is called Physical Coding Sublayer in IEEE 802.3ba standard. This presentation by Gary Nicholl gives a good overview of it. The short explanation is ...
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13 votes
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If TCP packets are pre acknowledged, what happens if packets are dropped?

Pre-ACKing is only possible because the near accelerator keeps the segment data in queue. Therefore, it can ACK in stead of the far destination, prompting the sender to advance the send window and ...
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12 votes
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Does bridging add delay?

Hi and welcome to Network Engineering. As for "delay" vs "latency": The terms are not always used consistently. Some hints may be found here. I think generally, the term latency is used when ...
11 votes

What's the difference between `Latency` and `Round Trip Time`?

"Latency" can mean different things. Generally, it's a delay of some sort - application latency is the reaction time of an application (from input to output), network latency the delay for getting a ...
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10 votes

Network latencies between opposite ends of the Earth

A cable half-way around the globe has a minimum latency of 100 ms, 200 ms round-trip (20,000 km distance / 200,000 km/s signal speed) - that's the physical, lower limit.[*1] In reality, links aren't ...
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9 votes

How can the latency value be so low from Singapore to USA (~2ms)?

IP geolocation databases essentially represent a geolocation company's guess as to where an IP is located. Often they are based on the addresses in whois registrations, sometimes supplemented with the ...
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8 votes
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does the DSL distance really add more latency

Twisted pair cable used for the local loop has a velocity factor of about .58 - each km of cable takes ca. 6 µs to travel, adding ca. 12 µs to latency. The rest of the Internet probably uses fiber ...
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8 votes

Does bridging add delay?

Yes, a bridge / switch adds some delay to a frame - in the order of 1 to 20 µs. For switches you usually speak of latency - the delay between receiving a frame and forwarding it out another port. A ...
  • 75.5k
6 votes

What's the difference between `Latency` and `Round Trip Time`?

Round-trip time (RTT) is the time it takes for a packet to go from the sending endpoint to the receiving endpoint and back. There are many factors that affect RTT, including propagation delay, ...
5 votes

What causes packet loss when using full bandwidth from ISP?

There are a number of possibilities here, not limited to, but including: The CPE's CPU is maxing out. (CPE=Customer Premesis Device) Check the specifications for the router you are using to make ...
5 votes

Why can insufficient bandwidth reduce latency?

First, the linked article contains several poor approximation and is not IMHO a good source. Back to the question, insufficient bandwidth leads to link congestion, that means that the equipment ...
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4 votes

Measuring per-link latency/jitter/packet-loss

Etherate enables you to measure throughput, latency and packet (frame) loss down at layer 2 directly over Ethernet (which sounds like what you are looking for). It doesn’t measure jitter at present ...
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4 votes
Accepted

Meaning of 2 Mbps

Well, every link transmits only either 0 or 1 at any specific moment. So if your router connected to 2Mbit/s link receives first 250 bytes packet, and assuming that it doesn't have anything at the ...
4 votes
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Loosely speaking, at any given moment, how much of the internet is buffered?

I'm not sure what you mean by buffer. There no buffering like when you want to watch a video. Besides the inherent latency of the bits traveling the various media in a path, there are delays due to ...
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4 votes
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Difference in latency between public and internal IP addresses

Technically yes there will be a small difference and notability will depend on your devices/configuration. This is because of the different paths the packets have to take, but like i said, depends on ...
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4 votes

Switch Buffer Sizing

First, there is a relationship between buffer size and latency only if there is congestion in the path (too many incoming packets on the input interface, or too many packets for the switching engine (...
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4 votes

What's the difference between `Latency` and `Round Trip Time`?

To add a little bit of background to the other answers, one has to remember that network latency can vary significantly, and can impact a user's experience. One of the most obvious sources of network ...
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4 votes
Accepted

What is the relationship between throughput and latency

i.e. 1000 packets * 400ms latency (i.e. 400ms RTT - I understand latency to usually refer to RTT) = at least 400 seconds to deliver the HTTP payload. Well that would only be true if every single ...
4 votes
Accepted

How to calculate the latency in vehicular network?

Is this the right way to calculate the latency? No, and I don't know how one would support such an estimate. Use of cellular data involves one set of calculations and direct-to-roadside involves ...
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4 votes
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Best way to Fast Reconnect TCP with dynamic IP

That won't work with classic TCP alone. On an end system, (a bit oversimplified) TCP exposes a "socket interface" towards the upper layer, the application. Such a "socket" is defined by the tuple of ...
4 votes
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Copper or Glass for Low Latency?

You already provide most answers. Propagation time: apart from (good) coax, copper and fiber are nearly equal. Decent twisted pair is slightly faster than fiber, high quality TP even more so - but ...
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4 votes
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Transmission and propagation delays

"Transmission delay" is ambiguous and shouldn't be used when you need precision. Each bit has a propagation delay of tp = distance / velocity. Since the bits are serialized - one sent after ...
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3 votes

Random latency on a wireless LAN

You need to discover what is on the airwaves. It sounds like you are experiencing wireless interference. You can hire a company to come in and do a wireless site survey. This will give you ...
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3 votes
Accepted

On a Layer 3 switch, what part does the CPU play in forwarding packets?

This article has a decent breakdown of what a Catalyst 3750 will use its CPU for. Notice the CPU doesn't normally process any "user" frames, it mainly deals with management tasks, like STP and routing ...
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3 votes

Latency in P2P Circuit

This is to be expected if your routers are filling the buffers. If you are using ping to test this, understand that ping has the lowest priority. Depending on your traffic mix, you may want to use ...
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3 votes
Accepted

What's the difference among bandwidth, ping, ping rate and latency?

Ping is a utility to test network connectivity. It uses ICMP echo request/reply to do this. The originating host sends an ICMP echo request, and the receiving host sends an ICMP echo reply. There are ...
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