said by bigdaddy:
So GPON's Max Upload Speed potential 1.244 Gbps split 32 way's is 38.875Mpbs. So how can VZ offer 65Mpbs Upload over GPON via the 150/65 and 300/65 Tiers isn't that a Recipe for Over Subscription ? Now XG-PON has a Max Upload Speed of 2.5Gbps split that 32 way's you come out with 78.125Mbps per user. Why doesn't VZ roll out XG-PON for the FiOS Quantum Tiers ?
Same go's for Down Speed GPON 2.448Gbps split 32 way's is 77.75Mbps. XG-PON split 32 way's is 312.5Mbps. The FiOS Quantum 300/65 should be on XG-PON Not GPON. So how in the World is VZ FiOS Going to offer 500/65 ? Like I said a Recipe for Over Subscription.
Contention and split ratios are the least worrisome point for passive optical networks(GPON and 10G XG-PON) on last mile connections.
They can be planned carefully from the start to limit the number per port according to how much bandwidth the operator intends to sell.
However it doesn't make much sense to go with very low contention with passive networks (1:8 or 1:4), instead operators prefer to do it with P2P since it does not justify for much cost savings to do so.
The 2 major concerns with GPON/XG-PON instead are:
1) How are you going to feed the monster OLT box backplane connection that connects it back to the core aggregation switches.
2) How to tame monster OLT box with the high number of connections and traffic it has to handle as subscriber rate scales to peak numbers. It requires a monster processing power to handle thousands of simultaneous users compared to dedicated ports for active Ethernet users?If each subscriber creates >64 connections, it's enough to cause massive congestion, thus causing huge spikes in latencies during peak hours.
Just to compare, this is one of the highest capacity and latest OLT product from Calix.[Note: Current present GPON OLTs on average only handles about 200Gbps for backplane connections]
»www.calix.com/systems/e-series/c···-20.htmlKey highlights to note(quoted from site):
-2 terabit backplane with 100 Gbps connection to each line card slot
-Serves 480 point-to-point GE or over 10,000 GPON subscribers, with the capacity to serve over 20,000 subscribers through higher density line cards in the future
So if you just do a simple calculation:
The latest GPON/XG-PON line cards have 8 ports today.
Assume they are selling a 1Gbps service.
If each card has ONLY a 100gbps to breath, while each port handles 30 lines(32 in theory with 2 often reserved) on a passive splitter,
8 x 32 lines/ONTs x 1Gbps = 256Gbps diet
[Compare this again to active ethernet, 480ports/20 line cards you get only around 24 ports to share the 100Gbps load on each line card - That'a nearly 10x more capacity for each line card (256/24)]
*Important note: In reality, many ISPs are only giving 1x-4x 10GE Ethernet lines to their OLTs backplane. Complains are already coming in mostly during peak hours.
Next comes switching speed and connection load handling between users. Cisco claims they can handle terabit speeds with their active switches with at most only caters around 400 dedicated ports , but how about a high capacity OLT that claims to handle 10k to 20k users simultaneously? That's quite a monster to tame.