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Friday, 27 March 2009

OFC 2009, Day 4

“An Offline Impairment Aware RWA Algorithm with Dedicated Path Protection Consideration”

The first author of this paper was Siamak Azodolmolky. He presented a novel offline physical layer impairment aware routing and wavelength assignment algorithm for various transparent all-optical networks, while considering dedicated path protection. He started by presenting a network planning and operation tool they’ve developed, focusing his presentation on a specific part of it, the impairment aware lightpath routing component of the tool. They consider several impairments, like node crosstalk, PMD, XPM, FWM, etc. and calculate a Q-factor. This is only for offline settings (used for network planning), but in an online setting they would have to change the way the Q factor is currently calculated, because it is very computationally intensive today.

“Impact of Topology and Traffic on Physical Layer Monitoring in Transparent Networks”

This was an invited talk by Dan Kilper, Bell Labs, Alcatel-Lucent, USA. He analysed the benefit of optical performance monitoring, with respect to network topology and traffic patterns. So in OEO networks we can monitor things in the regenerator sites.  But in optical nets this is more complicated. So the question is: where to place monitoring sites? They have tested some schemes, and shown that we can reduce costs significantly by placing monitoring sites in specific locations.

“Optical Multi Domain Routing”

This was also an invited talk. The speaker was Xavi Masip.

He reviewed the current limitations in multi-domain routing as well as some of the research lines in the optical area. Some notes:

1. Mixing routing, multi domain, and optics makes things very complex. Today it is known that all ISPs are being glued together with BGP. So to change it is very complicated – no one wants to lose connectivity. And BGP works.

2. Why multilayer? To optimise layers: we have one top IP layer, then a lower one for connection oriented packet networks, and finally the photonic transport layer. With multilayer optimisation we one can reduce costs and power needs.

3. Today we don’t have multidomain optical routing, BGP takes care of everything. There is some work on this area, but more research is needed.

4. Check work on Optical BGP (OBGP), and also OBGP+. Could be interesting.

5. Do we need multi domain optical routing? Answer by pure transport people (optical people): NO (upper layers can do that). Answer by IP layer people: definitely not (we can do that, just provide connectivity). Answer by carriers: are we supposed to share info?... (confidentiality is very important)

“PCE Communication Protocol for Resource Advertisement in Multi-Domain BGP-Based Networks”

The presenter was Francesco Peolucci. They propose new PCEP messages to announce inter-domain resource information typically not advertised by BGP because of scalability reasons. These enable effective PCE-based path computations and preserve network stability, scalability, and intra-domain information confidentiality. Some notes:

1. BGP doesn’t advertise alternative solutions. BGP applies tie breaking rules, and only advertises one route, no alternative paths – for scalability reasons.

2. Proposed solution – extend PCE protocol with one new message that carries route info that is not advertised by BGP. They also propose to include another message with bandwidth availability of interdomain traffic engineering.

3. This is limited to a set of domains (they consider only 20 domains), not to the entire internet… so no worries about scalability. But the fact is that I was still worried about scalability. They don’t address this, they only say “it is not a problem” because they limit themselves to 20 domains (not sure why).

“On Resource Provisioning for Dynamic Multi-Domain Networks”

Xiaolan J. Zhang gave an interesting talk where she studied the performance of multidomain resource dimensioning/routing techniques with limited information sharing, and provided motivation for considering fairness issues. Some notes:

1. Imagine your network is well dimensioned, but your “neighbour” network is underprovisioned. Your connections to that network are rejected because of them, so you don’t have a big incentive to have a well dimensioned net… One domain can hurt performance of other domains.

2. A global shortest path routing solution prefers larger domains – large domains have advantage over smaller domains.

3. So they propose a global SPF but they normalise the costs to the size of the network. They improve performance on smaller nets, without causing problems in the big network.

“Avoiding Path-Vectors in Multi-Domain Optical Networks”

Marcelo Yannuzzi showed that a modified version of a path vector protocol can drastically reduce the blocking and converge significantly faster, while exchanging less number of routingmessages both during failure-free conditions and during a convergence. More notes:

1. OBGP+: A modified Path Vector (ENAW), including a cost that is dependent on number of lambdas available.

2. OBGP+ performs way better than OBGP in terms of blocking, number of messages exchanged, convergence time in case of failure, routing advertisements (churn).

3. Conclusions: even minor modifications are sufficient to outperform a plain path vector like OBPP. Avoid plain path vector for the interdomain RWA protocol.

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