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Switched Networks Vs. Dedicated Links
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joreilly925
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joreilly925,
User Rank: Ninja
6/18/2014 | 11:49:24 AM
Re: Markov chains post?
@huittinen massive, Thank you for your comments. Perhaps a little clarification might help you:

1) You are right about the point-to-point nature of Ethernet. Vampire traps went out of fashion a long time ago! Each link is quite efficient.

However, switched Ethernet is NOT an end-point to end-point connection, When two sources both address the same target it's a bit like airplanes trying to land on the same runway. One gets to go round again. This occures in the switch. It reduces efficiency considerably in most cases.

Converged Ethernet buffers some number of messages, so the sending port doesn't need to go around. It also has a Pause operation to prevent the buffers over-filling.

2) See 1)

3) You are incorrect in stating that RDMA writes to NIC memory. It writes to application space, bypassing buffering in and copying from kernel space. It also bypasses the complexity of protocol stacks.

4) Not all blade systems are equal! ATCA blades use a point-to-point fabric rather than switches for example.

5) 56 GbE is not standard, but Mellanox has a product, based on their IB technology.

6) Performance is usually defined as doing the job as fast as possible. If QUIC has all the benefits you list, it probably speeds up Ethernet!
huittinen massive
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huittinen massive,
User Rank: Apprentice
6/18/2014 | 10:05:11 AM
Markov chains post?
This post is so incoherent it might be generated by Markov chains.

 

It's like author has some information from 80s and then picked some recent technology buzzwords then creatively combined them to post generating information which seemed to fit the context. Atrociously bad article.

 

1)

Ethernet almost invariably is 97.5% efficient, no modern network experiences collisions as all links are full-duplex, point-to-point links to a switch interface.

Efficiency problems are from 80s and 90s using hubs. 

 

2)

Author tries to talk about 'microbursts' in 'converged' ethernet, but does not understand the issue. This is fundamental problem with any technology if offered ingress capacity exceeds egress capacity, someone has to buffer, and if issue persits, buffers run out. 

 

3)

RDMA isn't a thing, this is normal DMA when data is written directly to NIC memory instead of system memory. It is internal ain computer, nothing to do with network.

 

4)

Blade systems solve nothing, blades are interconnected by ethrenet switches, like everything else.

 

5)

There is no 56G Ethernet, 100GE has been shipping for year and is in production in most large networks and it has become cheaper than 10x10GE. 400GE is next-up standard actively being worked on.

 

6)

QUIC has nothing to do with this, QUIC is L4 protocol whose main benefits are when compared to TCP ability to multiplex many stream insde single QUIC session without internal sessions creating HOLB to each other when one stream blocks (i.e. problem google has when SPDY multiplex many sessions in single TCP). 

Other benefits QUIC delivers is ability to roam between IP addresses, as session is not bound to particular IP as it's cryptogrpahically authenticated we can receive next packet from any IP

It offers FEC by having ability to send redundant parity packets, so if packet loss is 1% it can send 101 packets for every 100 packet and receiver can reconstruct any dropped packet, no resending needed, offering much better potential capacity than TCP in lossy conditions.

It has 0 RTT penalty for estabilshing session (First packet is payload packet), apart from first session ever where crypto keys need to be exchanged. 

It has no packet amplification potential.

It's great protocol and we need to have in our toolbox new L4 protocl taking lessions from QUIC and MinimaLT, but nothing to do with SDN or Ethernet performance or anything in the article.

 

 

 
joreilly925
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joreilly925,
User Rank: Ninja
6/17/2014 | 11:18:07 AM
Re: how about infiniband
When you say the cost is cheaper, you forget you need a specially-trained admin or two!

IB has its points, but even Mellanox is hedging to IB over ethernet (RoCE)
soldack
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soldack,
User Rank: Strategist
6/16/2014 | 9:50:26 PM
how about infiniband
Infiniband supports reliable remote DMA with hardware segmentation/reassembly, hardware retries.  It also has send/receive style semantives and even an unreliable datagram mode.  There are lots of protocols for network and storage and HPC and even sockets and multiple OSs support.  The cost per bps is much lower than 10 or 40 gigabit ethernet, especially when you factor in large switches.
OrhanErgun
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OrhanErgun,
User Rank: Moderator
6/16/2014 | 3:37:08 PM
Re: Perhaps a job for statisticians?
You stated ' Creating lossless "Converged" Ethernet is both expensive and difficult to do today. There are also limits to scale involved. Even loss-less operation involves delays, as buffers get filled up quickly. These delays can be substantial in a loaded system since the process is akin to turning off a tap then sending instructions to turn it on again.'

 

expensive and difficult part , as I also stated, configuration and management complexity might be , I also mentioned from the buffer related issue , but again these all our design tools , so If you want to use you should know the drawbacks, there are pros and if your business and technical requirements match so no problem to use it.

So nothing is the best , if one of them would be the best , we would not need the others..
joreilly925
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joreilly925,
User Rank: Ninja
6/16/2014 | 3:27:15 PM
Re: Perhaps a job for statisticians?
Creating lossless "Converged" Ethernet is both expensive and difficult to do today. There are also limits to scale involved. Even loss-less operation involves delays, as buffers get filled up quickly. These delays can be substantial in a loaded system since the process is akin to turning off a tap then sending instructions to turn it on again.
joreilly925
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joreilly925,
User Rank: Ninja
6/16/2014 | 3:23:08 PM
Re: Good observations about links
I assume you are thinking of speech to text conversion. It's possible to process any spoken words into text automatically, but the quality of translation for general speech from an occasional speaker is still not good.

However, for deaf people, there is a wealth of real-time speech to text software. Just Google "speech to text deaf"
OrhanErgun
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OrhanErgun,
User Rank: Moderator
6/15/2014 | 10:48:55 AM
Re: Perhaps a job for statisticians?
Thats why fiber channel introduced to carry SCSI commands. The lessons are learned from the ethernet.

 

Actually ethernet has pause frame but once the congestion occur, all the traffic are stopped regardless of their importance.

If you want to make this operation efficient, you can separate traffic into classes and you treat them based on their importance. Thus data center bridging has been invented. PFC is the priority flow control can give us the ability to put traffic into classes and control the flows based on their pirority.


Also efficient quening is possible with ETS Enhanced Transmission selection which can be thought as a sub category of DCB.

All these protocols help the ethernet become lossless, so for the storage traffic you can carry SCSI over FC over Ethernet or IP networks.

 

Dealing with the configuration can increase configuration complexity and also buffer management might be a concern but these are all our design tools.

 
AbeG
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AbeG,
User Rank: Ninja
6/14/2014 | 10:05:21 PM
Perhaps a job for statisticians?
I agree with Jim here, Ethernet is not the most efficient system, especially as traffic collisions increase.  It seems as though a more scientific approach may be necessary.  Such fancy terms as regression analysys normally relegated to statisticians, may be needed in the search for a solution here.
rubyliu
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rubyliu,
User Rank: Apprentice
6/13/2014 | 3:53:44 AM
Re: Good observations about links
So, when talking on a FIOS home phone, is the conversation real time or is it data?  Not sure how to phrase this - but can a circuit-switch conversation be captured and stored as data as opposed to recording it? I am think of that software that stores phone calls and then lets you search them for key words, does it act the same for circuit-switched and packet-switched? This answer by fiberstore
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