Critical Infrastructure Analysis of Telecom for Natural Disasters

  --------------------------------- -------- ----------------------------
  Gerard O'Reilly, Ahmad Jrad,      and      Theresa Brown, Stephen
  Ramesh Nagarajan\                          Conrad\
  *{goreilly, jrad,                          *{tbrown,
  rameshn}@lucent.com*\                      sconrad,}@sandia.gov*\
  Bell Laboratories Research,                Sandia National
  Lucent Technologies, 101                   Laboratories\
  Crawfords Corner Rd.\                      Albuquerque, NM
  Holmdel, NJ 07733                          

  --------------------------------- -------- ----------------------------

ABSTRACT

Critical national infrastructures for power, emergency services,
finance, and other basic industries rely heavily on information and
telecommunications networks (voice, data, Internet) to provide services
and conduct business. While these networks tend to be highly reliable,
severe, large scale outages do occur, especially at times of unfolding
disasters, which can lead to cascading effects on other dependent
infrastructures. This paper describes recent natural disasters in the
USA, namely hurricanes Katrina, Rita, and Wilma, and the impacts they
have had on power outages and flooding leading to failures on the
dependent critical infrastructure. In particular we consider the impact
of these disasters on the affected telecommunication networks. We
quantify the level of availability of wireline and wireless services
during these network failures. We also discuss studies that were
performed in preparation for a hurricane impact. The studies have been
performed using the Network Simulation Modeling and Analysis Research
Tool (N-SMART), which has been developed to support detailed wireline
and wireless network simulations under varying network conditions and
degrees of failures. We analyze the levels of outages and recovery times
for these disaster events as well as possible mitigations to prepare in
advance for these and other potential future disasters.

INTRODUCTION

Network outages are usually small in comparison to those large-scale
outages which occur only once in many decades. The impact of three major
hurricanes hitting the same region (Southeast USA) in a single year in
2005 is an example of just such a large impact event (See Figure 1):

-   **Hurricane Katrina**, first hit Florida as a category 1 hurricane
    on 25 August 2005. Then Katrina crossed the Gulf of Mexico and rose
    gradually to a category 5 hurricane on 28 August. Katrina weakened
    slightly before it made landfall on 29 August 2005 and struck
    Louisiana, Mississippi, and the southwest part of Alabama, as a
    strong Category 4 with maximum sustained winds of 140 mph.

-   **Hurricane Rita**, hit southeast Texas, and Louisiana on 24
    September 2005 as a category 3 hurricane.

-   **Hurricane Wilma**, a category 3 hurricane, hit Florida on 24
    October 2005.

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Figure 1. Overview of the three hurricanes

These hurricanes caused several billions of dollars of damages to
telecom networks and other critical infrastructure in the impacted
areas.

Communications systems were disabled because of the following:

-   Direct storm damage

-   Resultant flooding

-   Major and widespread power outages

-   Repair crews\' inability to access communication equipment.

Figure 2 shows the percent of wirelines and wireless out of service in
the affected areas, derived from public references \[6\] through \[11\].
The major wireline carrier in the area, BellSouth, together with the
major wireless carriers, suffered approximately 3 millions lines out of
service at the peak. This is estimated to be about 50% of the total
lines and wireless subscribers in the affected area. Many lines were
down due to loss of power, access lines on poles were blown down, and
wireless towers were blow over due to high winds. Recovery was fairly
rapid, over a period of weeks to most customers whose homes and
businesses were still standing. There remain some uninhabitable areas,
so a couple of hundred thousand "potential" lines remain out of service.
Also, flooding, especially in New Orleans and surrounding areas,
destroyed central office buildings.

![](media/image3.wmf){width="3.2840277777777778in" height="1.725in"}

**Figure 2 - % of wirelines and wireless out of service**

After Hurricane Katrina hit and caused devestating damage, there was
great fear that the next hurricane, called Rita, would cause the same
level of damage to the Houston area where it was directly headed. This
paper describes some of the planning of possible damage scenarios for
Rita and the use of simulations for predicting possible outcomes. We
first introduce our simulation that represents a metropolitan area
telecommunications network. Then, we describe the disruption scenarios
and simulation results. Finally, we conclude with possible mitigations
in advance of a hurricane.

The Houston /Galveston area, where Rita was headed, is shown on Figure 3
with all the wirecenter boundaries. This area serves approximately 4.1
million wireline and mobile subscribers.

![](media/image4.wmf){width="3.2020833333333334in"
height="2.0388888888888888in"}

**Figure 3 - Houston, Texas Area**

We will be using the following terms and abbreviations throughout the
rest of the paper:

-   Traffic: used to refer to actual telecom calls

-   LE -- Local Exchange: this is a switch serving wireline customers

-   MSC -- Mobile Switching Center: this is a switch serving wireless
    customers

-   LD -- Long Distance: a switch that serves no actual lines but
    provides long distance service

-   LT -- Local Tandem switch

-   AT- Access Tandem switch

-   ISP -- Internet Service Provider: receives and processes modem calls
    to the Internet. ISPs do not originate calls, they only receive them

-   Intra-LE traffic: traffic that originates and terminates on LEs

-   LE traffic: traffic that uses an LE at either end. This also
    includes the Intra-LE traffic as well but it also has the LE-LD,
    LE-MSC, LE-ISP traffic.

The same terms above apply to MSC & LD traffic.

Traditional TELEPHONY Simulation

The Network-Simulation Modeling and Analysis Research Tool (N-SMART) has
been developed to support detailed wireline and wireless network
simulations \[1\]. It studies telecom network readiness and traffic
behavior on various disaster scenarios. It can create scenarios that
demonstrate the pattern of telecom traffic loads and user behavior
during the time of disaster, such as physical line disconnection and
switching system failure.

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  ![](media/image5.wmf){width="3.623611111111111in"
  height="1.9993055555555554in"}

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Figure 4. N-SMART-Voice Model

N-SMART is a discrete event (call level) telecom model that simulates
capacities, blocking levels, retrials, and time to complete calls for
both wireline and wireless networks. Figure 4 depicts the building
blocks of the N-SMART-Voice simulation model, information input, and
model output \[1\]\[2\]\[3\]\[4\]\[5\].

Various simulation scenarios analyze how different traffic patterns,
traffic loads, user behaviors, and disaster severities impact network
performance and recovery. By analyzing the results of simulations, the
tool shows how different telecom elements, such as bandwidth deficiency,
switch processor overload, and user behavior, impact the performance of
the network and its robustness.

The simulation engine employs of algorithms to generate events related
to calls, re-attempts, network failures, switch processor overloads, and
collects session data in the form of simulation output. See \[2-4\] for
details on N-SMART.

The traffic pattern in a telecommunications network changes as a
function of the time-of-day. During certain hours of the day, the
traffic is at a maximum while at some other hours there is a very small
amount of traffic in the network. This is represented by a traffic
profile, as shown in Figure 5 (e.g., 4 PM to 8 PM is the busy hours of
traffic). This traffic profile is used in N-SMART to drive the traffic
generation throughput during the simulation day.

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  ![](media/image6.wmf){width="3.6180555555555554in"
  height="1.6159722222222221in"}

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Figure 5. 24-Hour Traffic Profile

Disruption Scenarios

We describe three simulation scenarios as follows:

1.  Baseline scenario without any disruption.

2.  Wide scale power outage. This is a power infrastructure outage
    cascading into the telecom infrastructure.

3.  Wide scale power outage AND disrupt many buildings in the South East
    region due to flooding, that is both a power infrastructure and a
    telecom outage.

Using the traffic profile from Figure 5 for the baseline scenario,
Figure 6 shows the simulation results.

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  ![](media/image7.wmf){width="3.6166666666666667in"
  height="1.8194444444444444in"}

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Figure6. Baseline Calls

There are nine statistics on Figure 6 as follows:

1.  FATT - first attempts of calls

2.  GEN - total calls generated

3.  ADM - admitted calls which complete

4.  SWBL - switch blocked calls

5.  TRBL - trunk blocked calls

6.  BSY - calls which end to busy line

7.  ABDN - calls which are abandoned

8.  ANSM - calls routed to an answering machine

9.  ACTIVE - total active calls across the network

All of these statistics, with the exception of ACTIVE, are cumulative
call counts over 5-minute intervals. The ACTIVE measure is a snapshot of
the total number of active calls at the sampling instant (end of every 5
minute interval). Figure shows call statistics for the baseline
scenario, also representing the 24-hour traffic profile for our
metropolitan area. The busy hour is from 16:00 (4 PM) to 20:00 (8 PM).
Under normal conditions (no disruptions), most first attempts (FATT) are
admitted (ADM) and complete except for a small fraction encountering
busy. But most of them are retried and complete on subsequent attempts
if the user doesn't abandon.

Scenario 2 Discussion

In advance of the impending hurricane Rita, the storm track was
identified as heading straight for Houston, Texas as shown in Figure 7.

![](media/image8.png){width="3.2847222222222223in"
height="2.627083333333333in"}

**Figure 7 - Rita Unfolding (as of 21 Sept 2005)**

Predictions were made by Los Alamos National Laboratory on the potential
power outage in the area (Figure 8).

![](media/image9.png){width="3.2041666666666666in"
height="2.3722222222222222in"}

**Figure 8 - Possible Power Outage map**

![](media/image10.wmf){width="2.4034722222222222in"
height="2.4340277777777777in"}

**Figure 9 - Scenario 2: Traffic Impacted by wide scale power outage**

In a wide scale power outage, most mobile traffic will be out of service
after a few hours when the cell towers batteries run out. i.e., about
36% of overall traffic in the area as shown on Figure 9. Note: wireline
and mobile switching offices with diesel back-up generators should
survive power outages.

Scenario 3 RESULTS

This scenario considers failure of the entire mobile network due to
power outage of base stations + telecom office failures in the Southeast
region due to flooding.

-   12 total Mobile Switch Centers are failed because their cell towers
    failed.

-   18 total Local Exchanges (LEs) are failed

-   No Access Tandem, Local Tandem, or Long Distance offices are failed

The failure lasts for just 24 hours (in reality flooding would cause the
failure to potentially last much longer). The failure occurs from 12:00
noon of the first day of impact to 12 noon of the second day.

Figure 10 shows the level of call build-up, because of re-attempts
across the wireline and mobile networks. Generated calls at the peak can
be more than 20 times normal.

![](media/image11.wmf){width="3.3666666666666667in"
height="1.9305555555555556in"}

**Figure 10 - Scenario 3 -- power outage and SE Region flooded**

Figure 11 shows the blocking levels for all calls during the disruption
which was greater than 95% for many hours of the simulation.

![](media/image12.wmf){width="3.2840277777777778in"
height="1.8659722222222221in"}

**Figure 11 - Scenario 3 -- blocking levels**

Figure 12 shows a network snapshot at the height of blocking where red
shows the highest level of blocking (greater than 75%).

![](media/image13.png){width="3.1972222222222224in"
height="2.076388888888889in"}

**Figure 12 - Scenario 3 during the height of failure**

Figure 13 shows the network starting to recover 30 minutes after the
failure ends. It takes several hours for the substantial blocking levels
to subside.

![](media/image14.wmf){width="3.203472222222222in"
height="1.9402777777777778in"}

**Figure 13 - Scenario 3 - 30 minutes after the failure ended**

There are many potential uses for simulations of this type as follows:

-   Pre-Evaluate Susceptible Regions

-   Set Requirements and Practices for Mitigation

-   Network Design Changes for Redundancy

-   Pre-Deploy Spares and Material

-   Real-Time Deployment of Emergency Staff

##### In addition, special scenarios can be simulated to assess the impact of various evacuation scenarios on the telecommunication network. This can help in finding and employing the scenario, which would maintain the maximum connectivity between the affected residents and the local authorities and emergency services.

Mitigating Strategies

Communications companies, both wireline and wireless, have mitigating
strategies to prepare for disasters and to restore service after
disasters.

In general, restorations are prioritized along these general guidelines:

-   TSP (Telephone Service Priority - Ordered list of critical
    facilities to restore)

-   Critical Services

-   High priority business sites

    Mitigating Power Disruptions

Many telephone service interruptions result from widespread power
outages. In anticipation of electrical outages during severe weather
conditions, telcos maintain generators in all central offices and
back-up power sources to remote terminals. The back-up power to remote
terminals lasts approximately 8 to 10 hours. If it is depleted, Telco
crews enter the area as soon as it safe and accessible to deploy
generators or replace back-up power sources.

Some wireless operators adopt a strategy to get their cell sites back in
operation without the support of commercial power.

-   First, some wireless networks are \"hardened\" with the installation
    of permanent generators for cell sites serving critical public
    sector clients such as hospitals, airports and military
    installations.

-   Second, hundreds of portable generators are ready to be deployed to
    cell sites that have lost power. They have also pre-planned
    deliveries of fuel to these emergency generators and high priority
    status for additional deliveries during an emergency.

    Mitigating Strategies for HURRICANES

Telcos prepare in many ways for disaster situations. For example, they

-   Move vehicles and equipment away from the coast, and deploy crews to
    staging sites where they can enter the affected areas after the
    storm ends.

-   Put controls in place to manage network traffic flow.

-   Survey remote terminals near the coast so they can be repaired
    quickly as needed.

-   Make plans to assess damage after the storm abates.

-   Put employees in other regions on stand-by to assist as needed, and
    arrange for local emergency housing.

After a natural disaster like a hurricane occurs, a Telco's efforts
proceed in an orderly manner designed to ensure the safety of employees.
Restoration begins in the central offices and moves outward toward the
customers' premises. As soon as the affected area is declared safe for
entry, Telco employees survey and assess the damage to company
facilities. Once the downed power lines are cleared, Telco employees can
begin restoration work. The facility restoration/sweep process focuses
on repairing damage to large feeder cables first, followed by smaller
distribution cables next. These facilities must be restored before
restoring service to local areas and replacing facilities into each
customer\'s home or business. Unlike power companies that can usually
repair a common line serving many people in an area, the
telecommunications network features a dedicated pair of wires in each
cable for each customer. As a result, telecom restoration can
potentially be far more complex to achieve and service must be restored
one customer connection at a time.

Wireless MITIGATIONS

Wireless telcos have much the same procedures as wireline operators,
except that their "access plant" is different, i.e., wireless cell phone
to cell tower. They prepare in many ways, For example, they

-   Tow or drive self-contained mobile cell sites called Cellular on
    Wheels, or \"COWs,\" into an area to provide extra call capacity or
    to restore communications following a disaster.

-   Drive \"COLTs,\" (Cellular on Light Trucks), which are smaller than
    COWs, wherever a mobile cell site is needed and include two masts
    for microwave antennas.

-   Prepare a \"RAT,\" or Remote Antenna Trailers, to provide back-up
    antenna service if a tower is out of service.

-   Send portable electrical generators in from across the country to
    provide emergency power to cell sites without permanent generators.

-   Ready thousands of loaner wireless phones and extra batteries for
    distribution and use by local emergency personnel.

-   Finally, since high winds and falling limbs cause much of the damage
    during storms, some telcos place a high percentage of their lines in
    underground facilities (Buried Cable and Conduit) instead of aerial
    cable on poles. For example, Table 1 shows the % aerial cable by
    State, the lower number the better for telecommunications survival.
    This is more costly but increases telecommunications survival of
    both the access plant for wireline and cell tower connectivity for
    wireless.

*Table 1- % Aerial cable by State*

  ------------------------------ ----------------------------------------
  **State**                      **% aerial cable**

  Texas                          19%

  Florida                        22%

  Louisiana                      26%

  Mississippi                    33%

  Alabama                        39%
  ------------------------------ ----------------------------------------

References

1.  David J. Houck, Eunyoung Kim, Gerard P. O'Reilly, David D.
    Picklesimer, Huseyin Uzunalioglu, "A Network Survivability Model For
    Critical National Infrastructure," Bell Labs Technical Journal,
    Volume 8, Number 4, 2003.

2.  Ahmad Jrad, Huseyin Uzunalioglu, David J. Houck, Gerard O'Reilly,
    Stephen Conrad, Walt Beyeler "Wireless and Wireline Network
    Interactions in Disaster Scenarios, presented at MILCOM 2005,
    September 2005.

\[3\] Gerard P. O'Reilly, David J. Houck, Eunyoung Kim, Thomas B.
Morawski, David Picklesimer, Huseyin Uzunalioglu, "Infrastructure
Simulations of Disaster Scenarios," Networks 2004, Vienna, Austria,
June, 2004.

\[4\] Walt Beyeler, Stephen Conrad, Thomas Corbet, Gerard P. O'Reilly,
David D. Picklesimer, "Inter- Infrastructure Modeling - Ports and
Telecommunications," Bell Labs Technical Journal, Volume 9, Number 2,
2004, 91-105.

\[5\] Gerard O'Reilly, Huseyin Uzunalioglu, Stephen Conrad, Walt
Beyeler, "Inter-Infrastructure Simulations across Telecom, Power, and
Emergency Services," 2005 Design of Reliable Communication Networks -
5th International Workshop, Ischia, Italy, October 2005,

\[6\] BellSouth Press Releases, http://bellsouthcorp.com/emergency.

\[7\] Cingular Wireless Releases. http://cingular.mediaroom.com

\[8\] SBC Press Releases. http://www.sbc.com/gen

\[9\] Sprint Nextel Releases http://www2.sprint.com/mr/newsrelease

\[9\] Verizon Press Release news.vzw.com

\[10\] Mobile Pipeline
[http://www.mobilepipeline.com](http://www.mobilepipeline.com/news/170700146;jsessionid=SXCRRTQQYHV12QSNDBCCKHSCJUMEKJVN)

\[11\] Cellular South
[www.cellularsouth.com](http://www.cellularsouth.com/)