Some of the topology data is very old. TopologyZoo lists a "last updated" date which does not correspond to when the network looked the way it did in the update. For example, networks that look to be from the late 1980s or 1990s have dates in 2011 or 2012.
NSF looks to be NSFNET circa late 1980s (the AS number would have helped as the DSO, T1, and T3 NSFNET and vBNS all had differenct AS). InternetMCI went out of existance in the mid-1990s. Sprintlink (AS1239) looks to be same era. These show the network cores for provider networks. Some have about 1,000 nodes in their edge network but a small core. Back in the late 1990s a lot of US networks had a flat ISIS IGP with 600 to 1,200 nodes, according to claims made in NANOG presentations at the time or claims made outside of meetings at NANOG or IETF. The data therefore may be real world but a lot of it is about 20 years old and may not reflect the present. Curtis In message <[email protected]> Levente Csikor writes: > Dear All, > since our previous works in remote LFA analysis (papers already sent to > these mailing lists) assumed unit cost networks, therefore as I > promised, I calculated the corresponding LFA and rLFA coverages in those > networks with their original link costs. > These networks were inferred from Rocketfuel dataset (/Mahajan, R., > Spring, N., Wetherall, D., Anderson, T.:// > //Inferring link weights using end-to-end measurements. In: ACM IMC, pp. > 231â236 (2002)/), SNDLib (http://sndlib.zib.de), and > TopologyZoo(http://www.topology-zoo.org). The found coverages and some > details are found in the table below, where /n/ and /m/ denote the > number of nodes and the number of links, respectively. The other columns > mark the different coverages obrtained by simple LFA and remote LFA, > where LP indicates the link-protecting case, while NP notes the case of > node protection. > Topologies marked with an asterisk(*) did not have inferred real link > costs from the datasets, so their costs were initially set to 1 (unit > costs). > > I believe that these results computed on real-world networks could > significantly improve the rlfa draft, especially Sec. 9.3., and the > advantages of remote LFA over simple LFA would be more emphasized. > > > +==============+====+====+==========+===========+============+============+ > | Topology | n | m | LFA_LP | LFA_NP | rLFA_LP | rLFA_NP | > +==============+====+====+==========+===========+============+============+ > | AS1221 | 7 | 9 | 0.809 | 0.25 | 0.809 | 0.25 | > +--------------+----+----+----------+-----------+------------+------------+ > | AS1239 | 30 | 69 | 0.8735 | 0.7554 | 1 | 0.9795 | > +--------------+----+----+----------+-----------+------------+------------+ > | AS1755 | 18 | 33 | 0.8725 | 0.7741 | 0.9967 | 0.9959 | > +--------------+----+----+----------+-----------+------------+------------+ > | AS3257 | 27 | 64 | 0.923 | 0.7186 | 0.99 | 0.8472 | > +--------------+----+----+----------+-----------+------------+------------+ > | AS3967 | 21 | 36 | 0.7857 | 0.6460 | 1 | 0.9325 | > +--------------+----+----+----------+-----------+------------+------------+ > | AS6461 | 17 | 37 | 0.9338 | 0.6933 | 0.9963 | 0.7075 | > +--------------+----+----+----------+-----------+------------+------------+ > | Abilene* | 12 | 15 | 0.5606 | 0.6078 | 0.9090 | 0.8725 | > +--------------+----+----+----------+-----------+------------+------------+ > | Arnes* | 41 | 57 | 0.6225 | 0.3518 | 0.7487 | 0.4562 | > +--------------+----+----+----------+-----------+------------+------------+ > | AT&T | 22 | 38 | 0.8225 | 0.5647 | 1 | 0.8497 | > +--------------+----+----+----------+-----------+------------+------------+ > | Deltacom | 113| 161| 0.5771 | 0.4910 | 0.8539 | 0.8148 | > +--------------+----+----+----------+-----------+------------+------------+ > | Gambia | 28 | 28 | 0.037 | 0.04 | 0.1851 | 0.12 | > +--------------+----+----+----------+-----------+------------+------------+ > | Geant | 37 | 55 | 0.6906 | 0.3977 | 0.8303 | 0.6582 | > +--------------+----+----+----------+-----------+------------+------------+ > | Germ_50 | 50 | 88 | 0.9004 | 0.8381 | 1 | 0.9995 | > +--------------+----+----+----------+-----------+------------+------------+ > | Germany* | 27 | 32 | 0.6948 | 0.599 | 1 | 0.9549 | > +--------------+----+----+----------+-----------+------------+------------+ > | InternetMCI | 19 | 33 | 0.9035 | 0.6798 | 0.9415 | 0.9136 | > +--------------+----+----+----------+-----------+------------+------------+ > | Italy* | 33 | 56 | 0.784 | 0.5741 | 1 | 0.9269 | > +--------------+----+----+----------+-----------+------------+------------+ > | NSF* | 26 | 43 | 0.86 | 0.6347 | 1 | 1 | > +--------------+----+----+----------+-----------+------------+------------+ > > > Furthermore, after reading the draft again-and-again, I have found that > it should be more emphasized in the draft that calculating or seeking > for a remote LFA staging point should be done IF AND ONLY IF no simple > LFA were found. This is important, since normally people obviously think > and observe that the failure coverage of remote LFA should be greater > than or equal to the coverage obtained by simple LFA. Moreover, people > also think that LFAs produce a subset of remote LFAs. However, if after > a failure only P-spaces and Q-spaces are taken into account in order to > seek a (remote) loop-free alternate, then it is possible that a simple > LFA would not be found resulting unprotected node-pairs. But, this case > could only happen when link costs are not unit costs. For an easier > understanding, consider the network depicted below: > 1 1 > F--------S-----------X--------E > \ / \ > 10 \ / 4 \ 1 > \ / 1 \ > N ---------------------------C > | | > 1 | | 1 > | | > | 1 1 | > A--------------B-------------D > > Assume that S wishes to send a packet to D, and the shortest path goes > through E, therefore it is S-E-C-D. Suppose that the link (s,e) > fails, or even the node e itself fails. In this case, since LFA (and its > calculation) only consider all other neighbors of s, then node N would > be an easy LFA for this failure, since dist(N,D) < dist(N,S)+dist(S,D). > However, if we only seek possible remote LFAs, than according to the > (r)SPF calculations, or taking into account our distance-function > conditions will result that D's Q-space will contain node N (besides > some other nodes), but S's P-space won't (it will only contain node F > and what is more, if node F does not exist, then S's P-space would be > empty), therefore no intersection of the two spaces will exist, leaving > this network vulnerable to the failure of link (s,e). > > This results that a neighbor should be always reached by the neighboring > link, even if there exists a shorter, but definitely bigger in hop-count > path to it. > According to this case (when seeking simple LFA is missed), the > condition of extended P-space described by our distance functions, > should be modified a bit: > For source /s/, destination /d/, and next-hop /e/, some node /n != s,d/ > is an extended link-protecting remote LFA for the /s-d/ pair if and only if > /âv â neigh(s) : dist(v, n) < dist(v, s) + dist(s, e) + dist(e, n)//*&& > dist(s,v) < dist(s,e) + dist(e**,v)*/** > /dist(n, d) < dist(n, s) + dist(s, d) . / > > One can easily observe that emphasizing more that remote LFA seeking > process is only "executed" after no simple LFA is found could much more > ease the understanding and won't result a headache to the reader who > accidentally wants to calculate rLFA coverage in such network. > > Please let me know, if my interpretation is not correct. > Thanks. > > Best, > Levente
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