Skip to main content
The 2024 Developer Survey results are live! See the results
35 votes
Accepted

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 ...
Ron Trunk's user avatar
  • 67.8k
32 votes
Accepted

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 ...
Ron Maupin's user avatar
  • 100k
20 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 ...
JFL's user avatar
  • 19.8k
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, ...
Zac67's user avatar
  • 85.8k
14 votes
Accepted

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 ...
jpa's user avatar
  • 366
13 votes
Accepted

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 ...
Zac67's user avatar
  • 85.8k
12 votes
Accepted

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 ...
Marc 'netztier' Luethi's user avatar
12 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 ...
Zac67's user avatar
  • 85.8k
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 ...
Zac67's user avatar
  • 85.8k
9 votes
Accepted

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 ...
Zac67's user avatar
  • 85.8k
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 ...
Peter Green's user avatar
  • 13.5k
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 ...
Zac67's user avatar
  • 85.8k
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, ...
allieatcsio's user avatar
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 ...
JFL's user avatar
  • 19.8k
5 votes

Network latencies between opposite ends of the Earth

Major domains have servers around the world, and DNS set up so that you get an IP address that's close to you. You can avoid this by pinging a specific host. For example, the Debian (GNU/Linux) ...
Peter Cordes's user avatar
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 (...
mere3ortal's user avatar
  • 2,416
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 ...
jcaron's user avatar
  • 783
4 votes
Accepted

What are the differences between TCP iRTT and ICMP Ping?

What are the differences between TCP iRTT and ICMP Ping? The real difference is the protocols used. Ping is an application that uses ICMP, an integral part of IP. One problem with ICMP is that ICMP ...
Ron Maupin's user avatar
  • 100k
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 ...
Marc 'netztier' Luethi's user avatar
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 ...
Rob's user avatar
  • 261
4 votes
Accepted

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 ...
Marc 'netztier' Luethi's user avatar
4 votes
Accepted

Copper or Glass for Low Latency?

You already provide most answers. Propagation delay: 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 ...
Zac67's user avatar
  • 85.8k
4 votes
Accepted

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 ...
Zac67's user avatar
  • 85.8k
3 votes

Dynamically generate OSPF/BGP routes based on Internet latency

Cisco routers have a feature called Performance-based routing (PfR) that does exactly what you're looking for.
Ron Trunk's user avatar
  • 67.8k
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 ...
Todd Wilcox's user avatar
  • 1,135
3 votes

How can I determinte the reason of server-to-server latency in my network?

First off I'd want to identify exactly how the latency in question is being identified. Is it a particular application running slowly or a wide variety of traffic that can be specifically observed ...
rnxrx's user avatar
  • 6,124
3 votes
Accepted

How to find out TCP/UDP latency of your network?

If you're asking if you can measure latency using TCP or UDP packets, the answer is a qualified yes. There is software you can install on servers that will generate TCP/UDP flows, and you can measure ...
Ron Trunk's user avatar
  • 67.8k
3 votes

How to find out TCP/UDP latency of your network?

in practice your concerns are not generally a significant factor. but here's a way to confirm: sudo nmap --packet-trace -p 80 hostname SENT (0.4506s) [..] RCVD (0.4990s) [..] that shows you 49ms of ...
Patrick McManus's user avatar
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 ...
Ron Maupin's user avatar
  • 100k
3 votes

Why can insufficient bandwidth reduce latency?

The author of your reference article does not appear to fully understand or clearly illustrate the relationship of Bandwidth/Latency. Latency doesn't affect bandwidth, but insufficient bandwidth ...
TDurden's user avatar
  • 1,241

Only top scored, non community-wiki answers of a minimum length are eligible