NW's Carolyn Duffy Marsan posed a couple of more technical questions to SAIC spokeswoman Melissa Koskovich on the new offerings:
Marsan: Does Ethernet run directly over the fiber optic network? Is that a service that requires extra equipment that we didn't talk about?
SAIC: Yes, the PON technologies we are implementing allow for very efficient Ethernet transport. Under the ITU specification (GPON), any Ethernet traffic is encapsulated at the optical level using either ATM or a protocol called GEM (GPON encapsulating method). GEM provides for highly efficient packetizing of typically very sensitive traffic such as voice or video. Whether it is an enterprise or government network deployment, SAIC can administer the OLT to ONT communication with carrier-class capabilities for VLAN separation (i.e., 802.1ad or “QnQ”). Alternatively, we can administer a more traditional VLAN separation to mirror existing network transport schemes. SAIC can also implement a PON network using a more recent IEEE standard called EPON. EPON uses standard 802.3 Ethernet frames without the encapsulation method used in the GPON implementation. The EPON standard also allows for symmetrical bandwidth delivery at 1 Gigabit or even 10 Gigabit speeds to each ONT. Regardless of which PON technology or encapsulation method is used, the OLTs and ONTs will interface with any device that has a standard 1 gigabit or 10 gigabit Ethernet interface and can be integrated into an existing core infrastructure.
Marsan: If all the workgroup switches are removed and all the gear in the wiring closets eliminated, where does a network administrator do traffic shaping, deep packet inspection, etc.?
SAIC: The administrative consideration one would give an Ethernet switch does not apply in a PON distribution system. We instead administer a policy within the OLT located in the data center for each Ethernet port on the ONT. Parameters such as committed information rate (CIR) and VLAN configurations are centrally controlled and can be imported to the OLT as a batch or controlled on an individual user basis. You can set system wide policies or configure work groups or tenants with a high degree of granularity. As a security precaution, ONTs are not configurable by the end user. When powered on, the ONT initializes a secure handshake with the OLT and downloads all configuration data. Any other requirements for traffic shaping or packet inspection remain unchanged since SCS does not replace data center architectures such as servers, routers, or firewalls. SCS is not just a powerful replacement for legacy Layer 2 architectures, it is a means for expanding service delivery to the end user while eliminating significant overhead costs.
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It's about time FTTD is being addressed (again)!
Great article. Bravo! The principals, however, have only begun to describe the extent of disruption that will undoubtedly result from neutralizing the LAN/MAN diameter through the transparency of glass, but it's a great start, nonetheless, to reviving discussion about a technology whose time is long overdue.
Given my druthers, I'd have liked reading more about physical media issues that are almost certain to arise during every customer evaluation, given the absence of single-mode fiber (SMF) at the LAN level, since multi-mode (MMF) has heretofore been specified almost exclusively in those rare situations where enterprise fiber-based LANs in ordinary workplaces have been installed, at all.
And while it's true that MMF could be used in lieu of SMF in satisfying PON requirements, that would be very much like volunteering to the same distance limitations imposed by Category x cabling, only a couple of hundred meters longer.
PoE, too, in my opinion could stand more discussion, since the technique has become the tail that wags the dog, in some respects, and it will not be overcome easily unless it is addressed properly with solutions that can solve a range of terminal device power requirement contingencies. There are several alternative- and emerging- methods at this time that can be used for delivering low-voltage d.c. to desktops and APs that don't entail massive investments in GbE switches and the copper cages they sit in, and in some cases the PoE requirement could be obviated entirely without incurring operational or safety penalties.
I should note that this issue has been near and dear to me for over twenty years now, first having been involved with PONs during the mid-Eighties when passive splitters from Codenoll and CanSTAR, and Ethernet electronics from primarily Ungermann-Bass and 3Comm, were used. I recently posted a message to the CR-4 Forum (URL: http://tinyurl.com/6y49zu ) that some readers here may find of interest, since I covered many of the same issues as the reference article above, and then some. Enjoy!
frank@fttx.org
Bandwidth
Yet another PON's article that doesn't explain that the bandwidth is essentially shared. 2.4Gig sounds like a lot, but if you're sharing it between 32 ONT's, you're only getting 75Mbps per ONT.
Real World
While true the fact that 2.4Gbps is shared download bandwidth for 32 users, real-world data suggests that never is the case. Access users seldom if ever decide to do the same thing all at once. This is very much like how ethernet switches share bandwidth for upstream access. New standards for faster PONs are being testing which will enable even faster bandwidth.
There is no rule that says the bandwidth need be shared among 32
There is no rule that says the bandwidth need be shared among 32 users. Splitter configuration can be implemented on a smaller scale as well as ports being un-terminated.
> There is no rule that says
> There is no rule that says the bandwidth need be
> shared among 32 users. Splitter configuration can
> be implemented on a smaller scale as well as
> ports being un-terminated.
Absolutely correct. However, every cost model I've
seen is totally reliant on close to a 100% 'take up'
of the OLT. If this doesn't happen costs sky rocket.
That's true if you're a
That's true if you're a carrier deploying this technology in a typical provider/subscriber model. But this story is talking about the ability for a business to own the PON infrastructure and manage it themselves. It's therefore not the same scale and cost consideration that a carrier would be looking at.
2.4 Gig never sounded like a lot.
Think services: voice, video, data,
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