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New conference paper: “Bounding Mobile Latency from Network Interconnections” at AINTEC 2026

Our new paper “Bounding Mobile Latency from Network Interconnections” will appear at the 2026 Asian Internet Engineering Conference (AINTEC ’26), being held from December 1–3, 2026 in Taipei, Taiwan.

Observed exit points and additional latency relative to an ideal direct path for AT&T (left), T-Mobile (center), and Verizon (right), based on measurements from 2021. Marker locations identify exit points, while line heights show additional latency to a destination in San Diego and line colors identify the exit used. See Sections 4.1 and 4.2 of the paper for details. (Figure 3 from the paper.)
Cumulative distributions of additional latency for AT&T, T-Mobile, and Verizon. Solid lines show latency above an ideal direct path; dashed lines show latency above an ideal path through an operator’s exit point. Substantial additional latency remains even after accounting for the geographic detour through exit points. See Sections 4.2 and 4.3 for details. (Figure 4 from the paper.)

From the abstract:

Mobile latency is determined by how Mobile Network Operators (MNOs) route traffic: from phones, across the MNO’s network to exit points where it enters the public Internet. Exit points are few, and MNOs are quiet about details, but their role prompts us to ask: What is the latency cost to send traffic through an exit point? We develop a new method to evaluate this question, and demonstrate it on the three largest U.S. MNOs, although in principle it can apply globally. Our new analysis of existing traceroutes shows that AT&T, T-Mobile, and Verizon funnel nationwide traffic through only 9, 5, and 9 exits, and the geographic detour they incur adds up to 62.1 ms compared to an ideal, direct-path. We show that even assuming speed-of-light paths through the exit points, up to 46.9 ms of additional latency remains. To understand if these costs can be overcome we compare actual to theoretically optimal placements, finding that latency of current placements is 18–66% above the population and 32–72% above the market-share weighted optimum with the same number of exits. However, we show this gap is small in absolute terms: perfect placement would recover only a few milliseconds of the tens remaining. Geographic optimization offers little: the inflation users experience comes from routing and other overhead.

This paper is joint work of Shefali Tushar Kulkarni and John Heidemann from USC/ISI. This work was supported by DARPA through the SABRES project and by the NSF through the BRIPOD and TEPPIT projects.

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Congratulations to the cohort of students in the 2026 ISI Research Experience for Undergraduates

We recently completed the Summer 2026 Research Experience for Undergraduates program at USC/ISI.

Congratulations to our students from around the U.S.: Anirvan Bagchi, from University of Georgia; Zoe Fingleton, from Smith College; Andrew Gutierrez, from U. California-Davis; Samchan Lee, from Swarthmore; Marlena Pegolo, from George Washington University; Jaisen Soundar, from Georgia Tech; Kristelle Widjaja, from University of Illinois Urbana-Champaign; Eric Wu, from Brown University; Brian Zhang, from Carnegie Mellon University; and Patrick Zheng, from University of Maryland!

The 2026 ISI REU cohort of students, and some mentors.

Thanks to our mentors: Jose-Luis Ambite, Andrea Belz, Michael Collins, Emilio Ferrara, Itay Hen, Mayank Kejriwal, Deborah Khider, Erik Kline, Luca Luceri, Shrikanth Narayanan, and Alexey Tregubov, and PI and mentor Jelena Mirkovic with co-PI and mentor John Heidemann.

We wish our summer undergraduate students the best as they continue their undergraduate programs this fall!

SRAII, the ISI REU program, is supported by the National Science Foundation, and the mentors have diverse support from USC/ISI, NSF, DARPA, NIH, and industry.

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New conference paper: “Understanding Partial Reachability in the Internet Core” at NINeS 2026

Our new paper “Understanding Partial Reachability in the Internet Core” will appear at the 2026 New Ideas in Networked Systems (NINeS), a virtual meeting on February 10, 2026.

Durations of peninsulas (regions with partial Internet reachability) as seen in 2017q4, showing that most peninsulas are brief, but some persist for days or months (Figure 4 from [Baltra26a]). We see similar results in 2020.

From the abstract:

Routing strives to connect all the Internet, but compete: political pressure threatens routing fragmentation; architectural changes such as private clouds, carrier-grade NAT, and firewalls make connectivity conditional; and commercial disputes create partial reachability for days or years. This paper suggests persistent, partial reachability is fundamental to the Internet and an underexplored problem. We first derive a conceptual definition of the Internet core based on connectivity, not authority. We identify peninsulas: persistent, partial connectivity; and islands: when computers are partitioned from the Internet core. Second, we develop algorithms to observe each across the Internet, and apply them to two existing measurement systems: Trinocular, where 6 locations observe 5M networks frequently, and RIPE Atlas, where 13k locations scan the DNS roots frequently. Cross-validation shows our findings are stable over three years of data, and consistent with as few as 3 geographically-distributed observers. We validate peninsulas and islands against CAIDA Ark, showing good recall (0.94) and bounding precision between 0.42 and 0.82. Finally, our work has broad practical impact: we show that peninsulas are more common than Internet outages. Factoring out peninsulas and islands as noise can improve existing measurement systems; their “noise” is 5x to 9.7x larger than the operational events in RIPE’s DNSmon. We show that most peninsula events are routing transients (45%), but most peninsula-time (90%) is due to a few (7%) long-lived events. Our work helps inform Internet policy and governance, with our neutral definition showing no single country or organization can unilaterally control the Internet core.

A technical report with additional appendices is available from our website and arXiv.

This paper is joint work of Guillermo Baltra, Tarak Saluja, Yuri Pradkin, and John Heidemann, building on work begun when Guillermo was a PhD student at USC and Tarak was a summer undergraduate researcher visiting USC from Swarthmore College.

The work is supported by NSF via the EIEIO, MINCEQ, Internet Map, and BRIPOD projects, and by DARPA via AQUARIUS.

Data created from the work is available at ANT, and the input and validation data is available from ANT, RIPE Atlas, and CAIDA.

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large Internet outage across Pakistan

Starting shortly before 2025-08-19t17:05Z (10:05pm August 19 local time in Pakistan), a very large Internet outage occurred across all of Pakistan. Although not affecting all networks, in many areas 50% or more fo the networks are down, as shown in the following map:

Internet outages across Pakistan, shown here at 2025-08-19t17:38Z.
Internet outages across Pakistan, shown here at 2025-08-19t17:38Z.

We saw the first outages at 16:30Z, and they quickly ramped up to about half of the networks in most of the country. Since the network outages closely follow the country’s borders, it seems unlikely that this is a weather-related event. As of the time of this post (t20:00Z), the outage appears to be ongoing. We’ll post an update here when we learn more.

Some reports are suggesting it’s a backbone outage caused due to flooding.

These outage were detected using Trinocular, our Internet outage detection system and the large change resulted in an alert.

Update 2025-08-20t00:20Z: It looks like Pakistan’s Internet began recovering around 20:45Z, and is basically back to normal by 2025-08-19t22:30Z (3am local time in Pakistan).

Here’s an “after” picture at 22:24Z:

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Recent Graduate ASM Rizvi Featured in ISI News

Recent PhD graduate ASM Rizvi was featured in an ISI News story, sharing his thoughts about joining USC and ISI and what he plans to do after graduation.

Congratulations again, Rizvi!

ASM Rizvi (photograph by Angel Itua).
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Huge Power Outage in Chile as Seen in Internet Outages

Today around 3:30pm local time (around 2025-02-25 T18:30Z), Chile suffered a major power outage. News reports suggest 8 million or more are without power.

We can see the effects of this power outage on Internet access as measured by Trinocular, our internet outage detection system. Outages start around 18:30Z and increase steadily to 20:30Z, the most recent data we have.

We wish Chile the best at a rapid recovery!

Update on Wed 2025-02-26: Our observations show the Chilean Internet starting coming back online around 2025-02-26t02:00Z (which is 2025-02-25t23:00 Chilean time), with most if it back around t06:00Z (2025-02-26t03:00 Chilean time).

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Adam Russell Interviews Wes Hardaker about Internet Standardization

On a recent episode of the ISI/nsiders podcast, host Adam Russell interviewed ANT lab member Wes Hardaker about the creation of the DNS at ISI, his history in making software of the Internet interoperate better, research usability and his general desire to promote life long learning.

See https://www.isi.edu/isi-insiders-podcast/ for the series, and https://rss.com/podcasts/isi-nsiders/1904285/ for Season 1, Episode 7 (about 20 minutes) for the interview with Wes Hardaker.

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Adam Russell Interviews John Heidemann about Network Research

As part of the ISI/nsiders podcast, Adam Russell, anthropologist and director of ISI’s AI division is interviewing a number of researchers at ISI.

He recently interviewed John Heidemann about John’s work in networking research about measuring the Internet.

See https://www.isi.edu/isi-insiders-podcast/ for the series, and https://rss.com/podcasts/isi-nsiders/1804707/ for Season 1, Episode 3 (about 20 minutes) for his interview of John Heidemann.

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new technical report “Auditing for Bias in Ad Delivery Using Inferred Demographic Attributes”

We have released a new technical report: “Auditing for Bias in Ad Delivery Using Inferred Demographic Attributes”, available at https://arxiv.org/abs/2410.23394.

From the abstract:

[Imana23c, figure 3]: Detecting racial skew with BISG-based inference is less sensitive (shown by the lower test statistic Z) than either knowing true-race, or using our improved version that reflects potential inference error. More samples and larger underlying skew make the range of confusion smaller, but do not eliminate it.
[Imana23c, figure 3]: Detecting racial skew with BISG-based inference is less sensitive (shown by the lower test statistic Z) than either knowing true-race, or using our improved version that reflects potential inference error. More samples and larger underlying skew make the range of confusion smaller, but do not eliminate it.

Auditing social-media algorithms has become a focus of public-interest research and policymaking to ensure their fairness across demographic groups such as race, age, and gender in consequential domains such as the presentation of employment opportunities. However, such demographic attributes are often unavailable to auditors and platforms. When demographics data is unavailable, auditors commonly infer them from other available information. In this work, we study the effects of inference error on auditing for bias in one prominent application: black-box audit of ad delivery using paired ads. We show that inference error, if not accounted for, causes auditing to falsely miss skew that exists. We then propose a way to mitigate the inference error when evaluating skew in ad delivery algorithms. Our method works by adjusting for expected error due to demographic inference, and it makes skew detection more sensitive when attributes must be inferred. Because inference is increasingly used for auditing, our results provide an important addition to the auditing toolbox to promote correct audits of ad delivery algorithms for bias. While the impact of attribute inference on accuracy has been studied in other domains, our work is the first to consider it for black-box evaluation of ad delivery bias, when only aggregate data is available to the auditor.

This technical report is joint work of Basilial Imana and Aleksandra Korolova (both of Princeton) and John Heidemann (USC/ISI). This work was supported by the NSF via CNS-1956435, CNS-2344925, and CNS-2319409 (the InternetMap project).

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Hurricane Helene Croses the Southeast U.S. as Seen in Internet Outages

Hurricane Helene made landfall in the U.S. at 11:10pm EDT Sept. 26 (2024-09-27t03:10Z) near Tallahassee, Florida, and we’ve been watching it in the Trinocular Internet Outage system.

Flordia Internet infrasructure appears to have done quite well, with relatively few Internet outages. Here is the view 4.5 hours after landfall, at 3:40am EDT Sept. 27 (2024-09-27t07:40Z), when the eye was already over southern Georgia:

However, storm damange resulted in many outages across Georgia at daybreak. Here is 11 hours after landfall, at 6am EDT Sept 27 (2024-09-27t10:00):

The Carolinas seem particularly strongly effected. Here is a zoom from Georgia to Kentucky as of 9am EDT Sat. Sept. 28 (2024-09-28t13:41Z):

Fortunately the Internet infrastructure in Georgia was quick to recover, suggesting most Internet outages were power loss. We wish the best for those in Kentucky, and for those with physical storm damage and coping with flooding.

The most recent outage data is always visible on our outage website.