Re: SLA for voice and video over IP/MPLS
On Sun, Feb 27, 2011 at 4:20 PM, Anton Kapela tkap...@gmail.com wrote: One won't find many, but a common rule of thumb is most apps will be 'fine' with networks that provide 10E-6 BER or lower loss rates. Anton, Who uses BER to measure packet switched networks? Is it even possible to measure a bit error rate on a multihop network where a corrupted packet will either be discarded in its entirety or transparently resent? Regards, Bill Herrin -- William D. Herrin her...@dirtside.com b...@herrin.us 3005 Crane Dr. .. Web: http://bill.herrin.us/ Falls Church, VA 22042-3004
Re: SLA for voice and video over IP/MPLS
On Mon, Feb 28, 2011 at 5:23 PM, William Herrin b...@herrin.us wrote: Who uses BER to measure packet switched networks? I do, some 'packet' test gear can, bitstream oriented software often will, etc. Is it even possible to measure a bit error rate on a multihop network where a corrupted packet will either be discarded in its entirety or transparently resent? Absolutely -- folks can use BER in the context of packet networks, given that many bit-oriented applications are often packetized. Once processed by a bit, byte, or other message-level interleaving mechanism and encoded (or expanded with CRC and FEC-du-jour), BER is arguably more applicable. These types of packetized bitstreams, when subjected to a variable and sundry packet loss processes, may only present a few bits of residual error for to application. I would argue that in this way, BER and PER are flexible terms given (the OP's A/V) context. For example, if we have 1 bit lost in 100, that'd be ~1 packet lost every 82 packets we receive, for a IP packet of 1500 bytes. More importantly, this assumes we're able to *detect* a single bit error (eg. CRC isn't absolute, it's probabilistic). Such error-expansion due to packetization has the effect of making 10E-6 appear as if we lost the nearest 11,999 bits as well. However, not all networks check L2 CRC's, and some are designed to explicitly ignore them--an advantage given application-level encoding data encoding schemes. It follows that if 1 in ~82 packets becomes corrupted, regardless of a CRC system detecting and dropping it, then we have a link no *better* than 10E-6. If the CRC system detected an error, then it's possible that 1 bit was corrupted. This implies that we can't know precisely how much *worse* than 10E-6 the link is, since we're aggregated (or limited) to a resolution of +/- 12k bits at a time. -Tk
Re: SLA for voice and video over IP/MPLS
On Mon, Feb 28, 2011 at 9:08 PM, Anton Kapela tkap...@gmail.com wrote: On Mon, Feb 28, 2011 at 5:23 PM, William Herrin b...@herrin.us wrote: Who uses BER to measure packet switched networks? I do, some 'packet' test gear can, bitstream oriented software often will, etc. Hi Anton, So... Not really, no. You get a bit error on an Ethernet in the middle, the next router flunks the Ethernet CRC and you never see the packet. You get congestion in the middle, the router drops the packet and you never see it. You get a bit error on a 802.11 link in the middle, it retransmits and you get a clean packet with a little jitter and maybe out of order. Point is, you don't get a measurement that looks like Bit Error Rate because you don't have access to layer 1 and you see a very incomplete layer 2. Evaluating an MPLS virtual circuit, you want metrics that make sense for layer 3 in a packet switched network: loss at various sizes, delay, jitter, packet order. Don't take this the wrong way, but someone starts asking me about BER rates in the SLA on a packet switched network and the message I hear is that they're asking to be lied to. Like when I describe DSL quality in terms of the birds perched pooping on the lines. His mental model for datacom is stuck in the '80s and I'll have to accommodate that if I want to do business. And when he calls to complain that we owe him a day's credit because of a high BER, he'll be the nice gentleman who we humor because he pays his bills on time and the occasional service credits are built in to our price. Loss. Delay. Jitter. Not BER. BER is the wrong tool for even attempting to evaluate the end to end performance of an MPLS virtual circuit. For example, if we have 1 bit lost in 100, that'd be ~1 packet lost every 82 packets we receive, If you're losing 1 packet in 82, you're fired. Seriously, that's an order of magnitude off even for tasks less demanding than VoIP and streaming video. Doesn't matter if you flipped 1 bit or 20, 1.2% packet loss one way (2.4% round trip) is way excessive. That's at the level where you start to notice sluggish web browsing because of TCP's congestion control algorithms. -Bill -- William D. Herrin her...@dirtside.com b...@herrin.us 3005 Crane Dr. .. Web: http://bill.herrin.us/ Falls Church, VA 22042-3004
Re: SLA for voice and video over IP/MPLS
On Thu, Feb 24, 2011 at 6:10 PM, Diogo Montagner diogo.montag...@gmail.com wrote: Hello, I am looking for industry standard parameters to base the SLA of one network regarding to voice, video and data application. One won't find many, but a common rule of thumb is most apps will be 'fine' with networks that provide 10E-6 BER or lower loss rates. Which are the the accepted values for jiiter, delay, latency and packet loss for voice, video and data in a IP/MPLS ? This question is being framed backwards -- an engineer should ask ask what the particular codecs can tollerate, then seek out networks which can deliver on those needs. If the a/v equipment vendor can't tell the customer or user what sort of network is required, I recommend selecting a new a/v vendor. In any event, audio codecs such as ILBC, g729, and 722 are well positioned for 'loss concealment' mechanisms in the decoders, masking some reasonable amount of loss. This has been exhaustively tested, and the data is readily available [0]. Video codecs that degrade gracefully are also fairly common, though the industry focus seems to be on concealing loss for generic real-time data, and offloading this work onto a different abstraction. One example would be packetized 'forward error correction' schemes, which can be configured or adapted to nearly arbitrarily 'high' loss rates (eg. ProMPEG [1] and related work). If the a/v system in question can support FEC of any sort, then this should substantially reduce ones transport-layer loss rate concerns. -Tk [0]: http://www.vocal.com/speech_coders/psqm_data.html [1]: http://www.ispa-sat.ru/info/Inside%20Pro-MPEG%20FEC%20(IBC)%20.pdf
Re: SLA for voice and video over IP/MPLS
For video, the SCTE 168 doc covers this.. (first hit on google) Its fairly strict, but in depth. On Feb 24, 2011 6:12 PM, Diogo Montagner diogo.montag...@gmail.com wrote:
Re: SLA for voice and video over IP/MPLS
On Sun, Feb 27, 2011 at 4:20 PM, Anton Kapela tkap...@gmail.com wrote: On Thu, Feb 24, 2011 at 6:10 PM, Diogo Montagner diogo.montag...@gmail.com wrote: Hello, I am looking for industry standard parameters to base the SLA of one network regarding to voice, video and data application. One won't find many, but a common rule of thumb is most apps will be 'fine' with networks that provide 10E-6 BER or lower loss rates. out of pure curiosity, have you ever gotten a reasonable answer when asking a carrier about this? I can imagine a sale-rep's brain essentially exploding upon asking it. Additionally 'the network' is not 'the path my packets take' ... so what number are you really getting here? -Chris
Re: SLA for voice and video over IP/MPLS
Hi Chris, I never got this answer. Chris, Tim, Anton and Martin, thank you for all inputs. Really appreciate them. Thanks ./diogo -montagner On Mon, Feb 28, 2011 at 9:42 AM, Christopher Morrow morrowc.li...@gmail.com wrote: On Sun, Feb 27, 2011 at 4:20 PM, Anton Kapela tkap...@gmail.com wrote: On Thu, Feb 24, 2011 at 6:10 PM, Diogo Montagner diogo.montag...@gmail.com wrote: Hello, I am looking for industry standard parameters to base the SLA of one network regarding to voice, video and data application. One won't find many, but a common rule of thumb is most apps will be 'fine' with networks that provide 10E-6 BER or lower loss rates. out of pure curiosity, have you ever gotten a reasonable answer when asking a carrier about this? I can imagine a sale-rep's brain essentially exploding upon asking it. Additionally 'the network' is not 'the path my packets take' ... so what number are you really getting here? -Chris
Re: SLA for voice and video over IP/MPLS
On Sun, Feb 27, 2011 at 9:33 PM, Diogo Montagner diogo.montag...@gmail.com wrote: Hi Chris, I never got this answer. I suspect you won't... at least not a reasonable/usrful answer.
SLA for voice and video over IP/MPLS
Hello, I am looking for industry standard parameters to base the SLA of one network regarding to voice, video and data application. Which are the the accepted values for jiiter, delay, latency and packet loss for voice, video and data in a IP/MPLS ? Thanks ./diogo -montagner
Re: SLA for voice and video over IP/MPLS
I'd be looking at packet ordering perhaps for voice and esp video, having the packets arrive in order makes a huge difference for video On Friday, 25 February 2011, Diogo Montagner diogo.montag...@gmail.com wrote: Hello, I am looking for industry standard parameters to base the SLA of one network regarding to voice, video and data application. Which are the the accepted values for jiiter, delay, latency and packet loss for voice, video and data in a IP/MPLS ? Thanks ./diogo -montagner -- -- Martin Hepworth Oxford, UK
