Exacte cijfers ga je niet vinden, de telecom wereld gaat een hoop geld in om en is zeer geheimzinnig.
Verder mis je blijkbaar mijn punt. Het punt is niet of kabel een gedeeld systeem is of niet, het punt is dat je niet de specificatie van snelheid per cable modem moet gaan gebruiken om iets te zeggen over de backend capaciteit van het netwerk. Puur logisch nadenken zou al genoeg moeten zijn om te releasieren dat je dan de mist in gaat. Immers als een klant 400 Mbit kan krijgen (zelfs 500 Mbit bij ZZP) en je gaat beweren dat het backend 816 a 1600 Mbit maximaal kan verwerken dan zul je zelf begrijpen dat je dan na een klant of 3 enorme schommelingen in je netwerk gaat krijgen. Die schommelingen zijn er niet*. Die waren er vroeger overigens wel, maar nu zijn we 20 jaar verder en werkt het hele systeem heel anders.
*Kan natuurlijk altijd zo zijn dat iemand in een flat gebouw andere ervaringen heeft omdat daar bijvoorbeeld te veel kabels naar dezelfde verdeler lopen. Maar dat zegt niets over de haalbaarheid van 10 Gbps per cable modem in algemene zin.
Feitelijk loopt de kabel eigenlijk al een jaar of 10 vooruit op xDSL. Bij xDSL loopt elke koper kabel namelijk naar de hoofdcentrale, dit zijn kabels die kilometers lang kunnen zijn. Je overboeking daarachter zit in de apparatuur om dat signaal om te zetten naar je hoofdnetwerk. We zijn allemaal bekend met het fenomeen dat xDSL niet snel wil wanneer je ver van de centrale woont. Daarom kwam KPN meer dan 10 jaar geleden al met het idee om street cabinets te plaatsen. DAarbij gaat de koper kabel voortaan naar een wijkverdeeler die zelf verglaasd op het hoofdnetwerk zit. Dat plan heeft echter jaren lang op een zeer laag pitje gedraaid. De kabel heeft dat systeem echter al lang en breed geimplementeerd. Vanaf jouw huis gaat er een individuele kabel naar het kleine verdeelertje. Per kabel zit er een aparte versterking op (afhankelijk van de lengte). De verdeler zet alles gezamenlijk door naar de grotere unit. Die grotere unit is reeds verglaasd aangesloten. Alleen dat geeft al aan dat alle zorgen over de haalbaarheid van 1 Gbps+ over de kabel eigenlijk onzinnig zijn.
Beste startpunt naar de waarheid over hoe het wel zit is echt gaan zoeken wat een CMTS doet:
https://www.google.nl/sea...o+docsis+3.0+cmts&ie=&oe= .
Pakken we even wat documentatie uit 2006:
Broadband CMTS Routers
The three models of Cisco broadband CMTS router that this document discusses are the:
uBR7223
uBR7246
uBR7246-VXR
All three are based on a Peripheral Component Interconnect (PCI) bus architecture.
The first two are based on a single PCI backplane that is rated at 1 Gbps, however it will normally operate at 600-800 Mbps due to PCI arbitration overhead.
The VXR uses two PCI backplanes, at 600 Mbps each to give 1.2 Gbps throughput. This is a conservative estimate, and true performance may exceed this figure.
The uBR and uBR-VXR models support the Data over Cable System Interface Specification (DOCSIS) 1.0/1.1 protocol and are meant to inter operate with DOCSIS based Cable Modems. A software upgrade is all that is required in a Cisco CMTS to enable DOCSIS 1.1 capability. The hardware is fully DOCSIS 1.1 compliant.
The DOCSIS 1.0 Radio Frequency Interface (RFI) Specification SP-RFI-I05-991105 specifies that there shall be support for 8191 Service IDentifiers (SID) per downstream CMTS transmitter, but that 16 are reserved for future use. This yields 8175 usable SIDs per downstream on the uBR CMTS. In the case of the 4 slot 7246 this means there is a theoretical limit of 32,700 SIDs. Each Cable Modem will require at least one SID but can have multiple SIDs allocated to it for various types of transmission such as Data or Voice, as an example.
There is no implementation restriction in the Cisco uBR7200 MAC code that would put any further limit on the number of CMs per line card. The DOCSIS protocol limit of 8175 (max unicast SID limit) will be limited in a real HFC network by: HFC/RF plant quality(return path quality), #'s of HHP in the combining plan, and DHCP/ToD/TFTP performance capability.
Number of CMs per Upstream Port
It is strongly recommended that the provider keep the number of CMs per upstream port reasonable. This again is not a Cisco implementation restriction. A DOCSIS upstream channel is a multiple access time-aligned contention based communication channel. We do not want the contention level on any single upstream to be so high as to cause excessive multiplicity of collisions with ill effects of laser clipping, etc. Another by product of excessive collisions are latency of recovery times for Cable Modems when contending for a small amount of ranging opportunities when a large number of Cable Modems are already transmitting data. The Cisco CMTS uses dynamic ranging to ensure modems will always get a chance to register, but the number of opportunities decreases as the load detected on the upstream increases to ensure we are granting the data requests.
If the upstream is excessively loaded with too many modems then it may take longer for modems to recover to online state which can impact customer satisfaction.
Note: It is also extremely important to traffic engineer the number of simultaneously active subscribers on each upstream (US) channel/line card such that service remains consistent and adequate during peak busy hour.
With above points in mind, Cisco recommends two numbers.
Recommended max CMs per line card = approximately 1000-1200 modems per line card primarily dictated by worst case download speeds customer wishes to tolerate for its subscribers during peak activity time.
Recommended max CMs per US receiver = Not greater than 200 per upstream port primarily dictated by return path Noise,SNR, collision level control.
To calculate we assume the following are TRUE (Please see Cisco's traffic engineering white paper Multimedia Traffic Engineering for HFC Networks. This is a 1.27MB pdf file.)
Example
Out of the given pool of subscribers, 40% are logged on during busy hour.
Out of the 40% subscribers that are logged-on during busy hour, only 25% might be downloading data simultaneously and contributing to the peak activity.
Thus, peak data demand during busy hour is 10% (.4 *.25) of the subscriber base.
Let us assume that a service provider wishes to limit the worst case data throughput per user at peak busy hour to not less than 256 Kbps. Thus it means that for a given line card with a single one 27 Mbps usable 64QAMdownstream channel bandwidth, the total number of simultaneously active subscribers has to be limited to 27000000/256000 ~= 100.
Since simultaneously active subscribers are assumed to be 10% of total subscriber base, we end up with a number of around 1000 subscribers per line card. Cisco strongly recommends this number not be stretched beyond 1500 subscribers per line card, since service will be severely degraded during the busy hour. This could lead to disconnection, offline status, extremely erratic performance from the cable modem customer point of view, longer than average ranging time for modems attempting to re-register, as well as other system and performance anomalies.
Given a fairly uniform distribution of these subscribers across all 6 upstreams, assuming the use of a MC16c card, the customer will end up with a total of about 200-250 subscribers per US port.
Another way to look at it is to try to limit the number of contending users per US port during peak activity time. Cisco recommends the average number of simultaneously active/contending CMs per US be kept around 10-20. These recommendations are also based on how the multiplicity factor of colliding modems on each US receiver can lead to saturation and clipping on the HFC network. Once we have a limit on max contending CMs per US port, we can get total max CMs per US port by roughly multiplying the number by 10 (10% peak demand assumption). Cisco has thousands of DOCSIS CMTS units operating world wide. Using engineering data combined with real world field experience Cisco has proven that, based upon the DOCSIS protocol and how it operates, deployments enjoy maximum success when subscribers per US does not exceed 250.
Of course every service offering is different and the customer must determine, based upon techniques discussed here as well as other traffic engineering sources, what the proper number of modems for their situation should be. Cisco can only make recommendations as determining the maximum or proper number of cable modems per upstream/linecard is highly subjective based upon a multitude of factors.
Homes Passed and Penetration
Cisco has found that customers who wish to successfully deploy data over cable networks based upon the DOCSIS standard must take into account many factors for success. One fundamental point that will ensure success is keeping customer return domains within reason. Cisco has found that keeping the homes passed (HHP) per upstream port to a reasonable level can significantly improve deployment success, maintenance costs, and improve customer satisfaction. Cisco has found that 2,000 homes passed per US port with ~10% penetration. Using 2000 homes as a threshold for maximum HHP per US port is a cost effective design guideline which allows the operator to deploy rapidly while keeping maintenance areas reasonable. The operator needs to remember that combining large areas, such as 4,000-10,000 Homes Passed means that any one section of that return path network that induces noise will funnel to the given US receiver and affect service for ALL subscribers. The above information must be looked at under even more scrutiny when considering Voice deployments. A network wishing to run Voice will have a much greater chance for success when deployment thresholds are maintained under those recommended in this document.
Given the previous information, Cisco highly recommends 2,000 homes passed per US receiver port as a maximum with ~10% penetration. Cost of adding upstream ports is far cheaper than regular outages and unexplainable or irregular network behavior due to return path over utilization. This recommendation would be further reduced and the provider highly encouraged to use the HFC design White Paper above to lay out their return path HHP based upon the specific network parameters they expect/observe in their network.
Dit gaat over 2006 en destijds was het snelste abonnement circa 20 Mbit. Toen kon je dus al een CMTS krijgen (de tegenhanger van de CM of cable modem) met dual PCI en een minimale bandbreedte van 1.2 Gbps. Dat is dan ook de reden dat Cisco weg wil komen met 1000 subscribers per line card. De achterliggende capaciteit was namelijk gigantisch veel groter dan de maximale snelheid van een enkele modem. Combineer dat met overboeking en je kunt duizenden aansluitingen combineren. Je zult hopelijk zelf begrijpen dat in deze context de schatting van Archie in 2015 met 816 Mbps backend capaciteit echt kant nog wal raakt. Verder is de ISP vrij om simpelweg meer hardware in te zetten, dus minder cable modems per CMTS. Het heeft natuurlijk wel jaren geduurd voor we modems kregen die de huidige 400+ Mbit kunnen halen. Logischerwijze is het aan de achterkant ook niet 12 jaar lang stil blijven staan...
[
Voor 183% gewijzigd door
sdk1985 op 23-08-2018 00:22
]
:strip_icc():strip_exif()/u/379464/crop5aa19fab1f77b_cropped.jpeg?f=community)
:strip_icc():strip_exif()/u/234177/what-carrot.jpg?f=community)
/u/212961/Alfred%2520Max%2520Headroom.png?f=community)
:strip_icc():strip_exif()/u/326331/crop5a11862143866_cropped.jpeg?f=community)
