SC216 An Introduction to Optical Network Design and Planning, Jane M. Simmons; Monarch Network Architects, USA
This was a very interesting course. It started by explaining the most important optical network elements, and then it moved to algorithms - for routing, regeneration, and wavelength assignment - which was very interesting and I was not expecting in an OFC course. Then it also talked about traffic grooming. With all these things mixed, there is really a great need of good algorithms and protocols to make the network as efficient as possible. Some notes:
1. Long haul networks use roughly 80 lambdas per fibre, and regional/metro-core use roughly 40 lambdas. These are US figures, I guess, but I was impressed with these high values. Some of the networks I am aware of (from network providers) have only something between 10 and 40 Gbps, which means probably use only 1 to 4 lambdas... I guess maybe these are normal values for walled networks from a single network provider alone.
2. Today there is no wavelength conversion on optical add drop multiplexers. Wavelength conversion is only possible on OEO (Optical - Electrical - Optical) architectures. So it makes all sense the assumption we've used in the paper I will present here. We assumed there was no wavelength conversion in our all optical network scenario...
3. The optical reach (distance an optical signal can travel before necessitating regeneration) of legacy networks is between 500-600km. Today we can have 2000-4000km.
4. Having or not regeneration has immense cost implications in a long haul network. For this reason, the best routing mechanism to find the best path between two nodes should: a) from all available paths, check the one that has fewer number of regenerations, and b) then check for the shortest path in terms of number of hops.
5. Dynamic path routing may not be the best option in a long haul network - it can lead to too much "wavelength interference".
6. Using the noise figure instead of number of hops or distance as the metric for shortest path algorithms is probably the best option.
7. When a node performs regeneration, it is possible to have wavelength conversion in that node (because there is OEO conversion in that node, so we can make use of that).
8. Routing and Wavelength Assignment: doing it in separate steps (run shortest path, check if we have wavelengths available that satisfy the wavelength continuity constraint) is probably better than doing all in a single step.
9. Grooming (bundling of sub-wavelength traffic to form well-packed wavelengths) switches should be deployed in the edge, not core. And we probably don't need all nodes to be grooming-sites (maybe 20 to 40% is enough).
10. In a metro network you usually have a lot of fibres, so it's different from a long haul one, where you have less fibres but several lambdas.
SC243 Next Generation Transport Networks: The Evolution from Circuits to Packets, Ori A. Gerstel; Cisco Systems, USA
This was the course I was more interested in, but unfortunately it was the less interesting. There were two main reasons, I think, for that. The first was that most of the subject was not new to me, and since it was all just a superficial touch in the matter, I learned nothing new. The second was that the speaker wasn't particularly inspired, and the way he approached the subject was just not interesting (although one could see he really was an expert on the issue...).
Mainly Ori Gerstel talked about the two types of multiplexing used in transport networks: time division (SDH and related), wavelength (WDM) and packet (MPLS). He talked about the possible paths of evolution of all these technologies, and how they are somehow being put closer together. I was hoping he would talk more in-depth of MPLS and GMPLS, but he didn't say much rather than the very generic stuff.
There was, however, a very interesting point. He mentioned a study that looked at the household needs in 2010, in the US. In this study they consider these services would be offered to every household soon: HDTV, SDTV, PVRs, and VoIP. And they concluded that twenty such homes would generate more traffic than what traveled the entire Internet backbone in 1995! And he finished this slide using the same words I have recently used in my talks: "the bottleneck is moving to the aggregation and core parts of the network".
SC114 Passive Optical Networks (PONs), Paul Shumate; IEEE Lasers & Electro-Optics Society, USA
This was an excellent course by Paul Shumate. The objective of the course was to explain why PONs are becoming the key network approach to deliver Fiber to the Home (FTTH). Some notes:
1. The normal splitting ratio in current PONs is between 8 and 32. Although in the US they are satisfied with these values, n Europe there is a growing interest in much larger ratios, up to 2048 (European SuperPON).
2. The US seems more interested in this technology than Europe. The main reason is that in Europe the copper distances are shorter, and the copper is better (due to the reconstruction after World War II), so VDSL is seen as a good option.
3. The speaker showed the nice picture from Claffy et al. paper "the nature of the beast: recent traffic measurements from an Internet backbone", where the authors got to the conclusion that most packets in the Internet where 1500 bytes-long or less.
4. FTTH status: a) 4M homes already connected in the US (2008); b) highly successful in Asia, with 3M new subscriber each year in Japan (40-50M users in 2010/2011, probably); c) growing interest in Europe, especially Scandinavia, but also France, UK, Spain, etc.
5. How much bandwidth is necessary to the home? A: In the near future, with HDTV, many channels, TiVo, etc., at least 50-100Mbps.
6. Studies are now sugesting that symmetry is needed (asymmetric connections will be a thing of the past soon).
7. Average broadband speeds: Japan = 60 Mbps, Korea = 45 Mbps, Finland = 20 Mbps (the top three). Further below the US = 5Mbps, and the UK = 3Mbps. Portugal is in between these, with 8Mbps.