Internet DRAFT - draft-lachos-multi-domain-sfc-alto
draft-lachos-multi-domain-sfc-alto
SFC WG D. Lachos
Internet-Draft Unicamp
Intended status: Informational Q. Xiang
Expires: September 10, 2020 Tongji/Yale University
C. Rothenberg
Unicamp
Y. Yang
Tongji/Yale University
March 9, 2020
Multi-domain Service Function Chaining with ALTO
draft-lachos-multi-domain-sfc-alto-01
Abstract
The delivery of network services often require service functions and
their specific order, called a service function chain (SFC). A SFC
request is usually composed by distributed resources which are
expected to available across multiple domains with different
technology and/or administration. This document describes different
standardization activities and research projects addressing the
challenges posed by SFC across multiple domains (specifically,
multiple administrative domains). In addition, this document
presents an initial approach to realize inter-domain service chains
leveraging the Application Layer Traffic Optimization (ALTO)
protocol. Finally, another important concern of this document is to
initiate a discussion (ALTO, SFC as well as other WGs) regarding if,
how, and under what conditions ALTO can be useful to improve the
multi-domain SFC process.
Status of This Memo
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This Internet-Draft will expire on September 10, 2020.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Context and Motivation . . . . . . . . . . . . . . . . . . . 4
3.1. Standardization Activities . . . . . . . . . . . . . . . 4
3.1.1. IETF . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1.2. ETSI . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1.3. MEF . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Research projects . . . . . . . . . . . . . . . . . . . . 5
4. ALTO for Multi-domain SFC . . . . . . . . . . . . . . . . . . 6
4.1. Advantages of using ALTO . . . . . . . . . . . . . . . . 7
4.1.1. Inter-domain info discovery with ALTO Property Map . 7
4.1.2. Inter-domain path computation with ALTO Cost Map . . 7
4.2. Motivating Use Cases . . . . . . . . . . . . . . . . . . 8
4.2.1. ALTO as part of the SFC eXchange Platform . . . . . . 8
4.2.2. Resource Orchestration for Multi-Domain, Geo-
Distributed Data Analytics . . . . . . . . . . . . . 10
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
6. Security Considerations . . . . . . . . . . . . . . . . . . . 12
7. Summary and Outlook . . . . . . . . . . . . . . . . . . . . . 13
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
9.1. Normative References . . . . . . . . . . . . . . . . . . 13
9.2. Informative References . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction
The delivery of end-to-end services often requires various Service
Functions (SFs). Service Function Chaining (SFC) is an abstracted
view of a service that defines a set of required SFs as well as the
order in which they must be executed [RFC7665]. Multi-domain SFC is
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the ability to deploy SFC across multiple domains with different
technology and/or administration. To do so, an inter-domain
communication process between different organizations is necessary in
order to (i) exchange abstract topology, resource and service
information, and then (ii) compute inter-domain service function
paths.
Nowadays, different standardization efforts (e.g., IETF, MEF, ETSI)
and research projects activities (e.g., 5GEx [H2020.5GEX], 5G-
Transformer [H2020-5G-TRANSFORMER], T-NOVA [T-NOVA]) have been
focused on multi-domain network service chaining. Standarization is
essential to provide recommendations to create interoperable
architectures with standardized protocols, and solutions (being
developed by different projects) are addressing a diverse range of
requirements to provide network services provided using multiple
administrative domains.
More recently, the ALTO WG started to discuss the uses of ALTO as an
information model for representing network resource and services in
multi-domain scenarios:
o [DRAFT-ALTO-BROKER-MDO] proposes an ALTO-based Broker-assisted
architecture where a broker plane works as a coordinator between a
set of top-level control planes, i.e., Multi-domain Orchestrator
(MdOs). The ALTO services (with the proposed extensions) provides
abstract maps with a simplified, yet enough information view about
MdOs involved in the federation. This information includes the
abstract network topology, resource availability (e.g., CPUs,
Memory, and Storage) and capabilities (e.g., supported NFs).
o The document [DRAFT-ALTO-UNICORN] presents Unicorn, a resource
orchestration framework for multi-domain, geo-distributed data
analytics. This work resorts in ALTO as the information model to
support the accurate, yet privacy-preserving resource discovery
across different domains. The key information to be provided by
the use of ALTO including different types of resources, e.g., the
computing, storage, and networking resources.
In summary, this document offers (i) an overview reference of several
initiatives (standardization efforts and projects) behind building a
complete multi-domain SFC, and (ii) concrete use case examples of how
ALTO can be incorporated in the multi-domain SFC architecture.
The overall rationale of this document is to begin a discussion
between the SFC and the ALTO WG (other WGs are welcome) concerning
if, how, and under which conditions ALTO will be helpful in the SFC
traversing different administrative domains.
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2. Terminology
This document makes use of the terminology defined
in [DRAFT-HH-MDSFC], [DRAFT-ALTO-UNICORN], [DRAFT-ALTO-BROKER-MDO],
and [RFC7665].
3. Context and Motivation
In order to offer a complete end-to-end network service, the multi-
domain approach involves two different aspects: multiple
administrations or multi-domain single
administrations [DRAFT-MD-VIRT].
o Multiple Administrations: Market fragmentation results from having
different operators focused on a specific region. This makes
difficult to deploy new services, for example, virtual
connectivity spanning multiple countries.
o Multi-domain Single Administrations: Technology fragmentation
creates multi-domain single administration. For example,
different parts of a network could be created as different domains
using separate technologies.
This section summarizes, on the one hand, main standardization
efforts delivering collections of norms and recommendations
(architectures, frameworks, protocols), while on the other hand it
also provides an overview of several projects formed to develop
network services across multiple domains.
3.1. Standardization Activities
3.1.1. IETF
SFC that span domains owned by single or multiple administrative
entities are being proposed. The Hierarchical Service Function
Chaining (hSFC) [RFC8459], for example, defines an architecture to
deploy SFC in large networks. This RFC proposes to decompose the
network into smaller domains (domains under the control of a single
organization). Another proposed initiative is [DRAFT-HH-MDSFC] that
describes SFC crossing different domains owned by various
organizations (e.g., ISPs) or by a single organization with
administration partitions. The proposed architecture uses a SFC
eXchange Platform (SXP) to collect and exchange information
(topology, service states, policies, etc.) between different
organizations and it works both in centralized (Multiple SFC domains
connected by a logical SXP) and distributed (SXP server as a broker)
environments.
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Another initiative is the Network Function Virtualization Research
Group (NFVRG). The draft "Multi-domain Network Virtualization"
[DRAFT-MD-VIRT] envisions a complete end-to-end logical network as
stitching services offered by multiple domains from multiple
providers. It also points to the need for creating solutions that
enable the exchange of relevant information (resources and
topologies) across different providers.
3.1.2. ETSI
The ETSI NFV ISG is paving the way toward viable architectural
options supporting the efficient placement of functions in different
administrative domains. More specifically, the document
[ETSI-NFV-IFA028] reports different NFV MANO architectural approaches
with use cases related to network services provided using multiple
administrative domains. Besides, it gives a non-exhaustive list of
key information to be exchanged between administrative domains
(monitoring parameters, topology view, resource capabilities, etc.)
and recommendations related to security to permit the correct and
proper operation of the final service.
3.1.3. MEF
With its work on the Service Operations Specification MEF
55 [MEF-SOE-MEF55], MEF has defined a reference architecture and
framework for describing functional management entities (and
interfaces between them) needed to support Lifecycle Service
Orchestration (LSO). This LSO architecture enables automated
management and control of E2E connectivity services across multiple
operator networks. The automated service management includes
fulfillment, control, performance, assurance, usage, security,
analytics, and policy capabilities that make it possible, for
example, expanding the footprint of service providers to interact
with potentially several operators to manage and control the access
portions of E2E services.
3.2. Research projects
Several projects include an architectural model integrating NFV
management with SDN control capabilities to address the challenges
towards flexible, dynamic, cost-effective, and on-demand service
chaining.
[H2020.5GEX] aims to integrate multiple administrations and
technologies through the collaboration between operators in the
context of emerging 5G networking. [VITAL][T-NOVA] follow a
centralized approach where each domain advertises its capabilities to
a federation layer which will act as a broker. In order to avoid one
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network operator per country or regions, [H2020-5G-NORMA] proposes
the use of management and control into a single virtual domain.
Also, the 5G-Transformer project [H2020-5G-TRANSFORMER] is defining
flexible slicing and federation of transport networking and computing
resources across multiple domains.
4. ALTO for Multi-domain SFC
A "dialogue" between potential domains that will provide multi-domain
SFC could be beneficial for a more efficient use of resources and
increasing the SFC performance. However, constrained knowledge of
the network services and underlying network topology based only on
localized views from the point of view of a single domain limits the
potential and scope for multi-domain SFC.
Note: The examples used in this document are based on architectures
and assumptions currently being proposed in the SFC
WG [DRAFT-HH-MDSFC] and in the ALTO
WG [DRAFT-ALTO-BROKER-MDO] [DRAFT-ALTO-UNICORN].
To enable a highly customized multi-domains SFC, [DRAFT-HH-MDSFC]
proposes a SFC eXchange Platform to realize inter-domain
communication between top-level control planes. The SXP is a logical
entity deployed in future Software-defined IXP (as a trusted third-
party platform) or built by a single owner between different
networks.
On a high level, the scope of the SXP contains two main tasks:
o Provide end-to-end visibility through the collection of topology
information, service states, and policies from different domains.
o Compute inter-domain service function path to select the service
function location from multiple candidate domains.
The ALTO protocol [RFC7285] provides abstract network information in
the form of map services that can be consumed by applications in
order to become network-aware and to take optimized decisions
regarding traffic flows. Recently, ALTO is also being considered in
multi-domain orchestration scenarios [DRAFT-ALTO-UNICORN]
[DRAFT-ALTO-BROKER-MDO], in which an ALTO server can convey inter-
domain network resource and topology information.
In this context, the SXP can take advantage of multi-domain ALTO
services to obtain important inter-domain information to "guide" the
resource/service provider selection process in that the "best" domain
or candidate domains (according to established policies) can be
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intelligently selected. The following ALTO services can be
identified:
4.1. Advantages of using ALTO
ALTO (and customized ALTO extensions) can be used to offer
aggregated/abstracted views on various types of information including
domain-level topology, storage resources, computation resources,
networking resources and PNF/VNF capabilities. This generic
representation contributing to a more simple and scalable solution
for resource and service discovery in multi-domain, multi-technology
environments.
In case of Multi-domain SFC, the following ALTO services could be
identified:
4.1.1. Inter-domain info discovery with ALTO Property Map
Each domain needs a global view of other potential candidate domains
to know who can provide part of the SF in the SFC. A brief list of
information to be exchanged between different domains includes:
o Resource capabilities, applicable to both IT (computing and
storage) and networking resources participant of the multi-domain
SFC, to assist on the decision of SFs placement.
o Access information (e.g., URL) to the orchestrator entry points
and Service Access Points (SAPs) for a corresponding network/
domain.
The ALTO Property Map Service [DRAFT-ALTO-PM] can provide a clear
global view of the resource information offered by other domains.
This information allows discovering which candidate domains may be
contacted to deliver the remaining requirements of a requested end-
to-end service deployment.
4.1.2. Inter-domain path computation with ALTO Cost Map
Once the candidate domains are discovered, it is necessary to compute
inter-domain service function path to select the service function
location from those different candidate domains.
The connectivity information among discovered domains can be
retrieved by an ALTO Cost Map service, responding, for instance, a
path vector with the AS-level topology distance between the source
domain and candidate domains. Moreover, path vector constraints (as
described in the Multi-Cost Map [RFC8189]) can be applied to filter
out the list of unqualified domains.
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In case of the Hybrid Hierarchical SFC architecture [DRAFT-HH-MDSFC],
the SXP (or the Path Calculation Element in the top-level control
plane) could use this information to compute multi-domain service
function paths.
4.2. Motivating Use Cases
4.2.1. ALTO as part of the SFC eXchange Platform
As mentioned earlier, [DRAFT-HH-MDSFC] defines a multi-domain SFC
architecture that combines control planes to be deployed either into
a large domain consisting of smaller sub-domains owned by the same
organization or into multiple large domains with different ownership.
Figure 1 shows a SXP connecting three different domains (AS1, AS2,
AS3). Each domain provides different SFs: AS1 -> SF1; AS2 -> SF2 and
SF3; AS3 -> SF3. The SXP includes an ALTO server component to
provide abstract topology, resource, and service information for the
high-level control plane in each domain.
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SFC eXchange
Platform
+--------------------+
| +--------+ |
| | ALTO | |
| | Server | |
| +--------+ |
+----> <-----+
| +----------^---------+ |
| | |
| | |
| | |
+----v---+ +-----v--+ +------v-+
|Control | |Control | |Control |
|Plane | |Plane | |Plane |
+--------+ +--------+ +--------+
| | |
| | |
| | |
+--------+ +--------+ +--------+
|Data | |Data | |Data |
|Plane -------Plane -------Plane |
+--------+ +--------+ +--------+
SF1 SF2 SF3
SF3
[----AS1----][-----AS2-----][-----AS3-----]
Figure 1: ALTO as part of the SFC eXchange Platform
Every domain has a local Information Base Element; this component can
be used by the SXP to create hierarchical databases containing inter-
domain resource and topology information. This information source is
used by the ALTO server to create two different ALTO Map Services:
(i) Property Map and (ii) Cost Map.
The Property Map includes a property value grouped by Autonomous
System (AS), this value contains the supported network functions.
Additional properties could be considered such as resource
availability (e.g., CPUs, Memory, and Storage), orchestrator entry
points, etc. An example of the Property Map in our basic scenario
is:
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+-----+--------------+-------------+-----+-----+---------+-----+
| | Capabilities | Entry Point | CPU | MEM | Storage | ... |
+-----+--------------+-------------+-----+-----+---------+-----+
| AS1 | {SF1} | http://... | ... | ... | ... | ... |
| AS2 | {SF2, SF3} | http://... | ... | ... | ... | ... |
| AS3 | {SF3} | http://... | ... | ... | ... | ... |
+-----+--------------+-------------+-----+-----+---------+-----+
Table 1: ALTO Property Map
The Cost Map defines a path vector as an array of ASes, representing
the AS-level topological distance for a given SFC request. Table 2
below shows a brief example of a service request and its inter-domain
service function path response containing a list of potential domains
to be traversed to deliver such service.
+---------------+---------------------------------------+
| SFC Request | Multi-domain Service Function Path(s) |
+---------------+---------------------------------------+
| SF1->SF2->SF3 | 1:{AS1:SF1->AS2:SF2->AS2:SF3} |
| | 2:{AS1:SF1->AS2:SF2->AS3:SF3} |
+---------------+---------------------------------------+
Table 2: ALTO Cost Map
4.2.2. Resource Orchestration for Multi-Domain, Geo-Distributed Data
Analytics
In addition to commercial SFC, ALTO is also used as a core
information model for collaborative data science networks. The
document [DRAFT-ALTO-UNICORN] presents the design of Unicorn, a
unified resource orchestration framework for multi-domain, geo-
distributed data analytics, currently being developed and deployed in
the CMS network, one of the largest scientific experiments in the LHC
network.
ALTO is well suited as a fundamental component in Unicorn for
providing a generic representation that (1) allows different types of
data analytics jobs to accurately describe their resource
requirements and (2) allows member networks to provide accurate
information on different types of resources they own and at the same
time maintain their privacies.
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.-------------. .-------------.
|Application 1| ... |Application N|
'-------------' '-------------'
\ /
.- - - - - - - -\- - - - - - - - - - - -/- - - - - - - - - - - - - - -.
| Unicorn \ / |
| .-----------------------. |
| | Resource Orchestrator | .----------------------.|
| | | |Distributed Hash Table||
| | .-----------. |---- | of Computing and ||
| | |ALTO Client| | | Storage Resources ||
| | '-----------' | '----------------------'|
| '-----------------------' |
| / | \ |
| / | \ |
| .-------------. .-----------. .-------------. |
| |ALTO Server 1| | Execution | |ALTO Server M| |
| '-------------' | Agents | '-------------' |
| | '-----------' | |
| | / \ | |
| .----------------./ \ .----------------. |
| | Site 1 | . . | Site N | |
| '----------------' '----------------' |
'- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -'
Figure 2: Architecture of Unicorn.
Figure 2 presents the architecture of Unicorn. Specifically, for
each member network, one or more ALTO servers are deployed to provide
accurate, yet privacy-preserving information of different types of
resources owned by the corresponding network. Examples of such
information include the link bandwidth between endpoints, the memory
I/O bandwidth and the CPU utilization at computing endpoints and the
storage space at storage endpoints. In addition to the basic ALTO
services defined in [RFC7285], The ALTO servers in Unicorn also
provide ALTO extension services such as the ALTO Multi-Cost Service
[RFC8189], the ALTO Server-Sent Event Service [DRAFT-ALTO-INCR-UPD]
and the ALTO Path Vector Service [DRAFT-ALTO-PV] to provide fine-
grained resource information.
Because the ALTO Path Vector service may expose additional private
information of each network, Unicorn develops an obfuscating protocol
which ensures that nor the orchestrator or any member networks can
associate any path vector information with a corresponding network.
To better address the scalability issue of multi-domain resource
discovery, Unicorn also develops a proactive full-mesh discovery
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mechanism, which precomputes network-level ALTO path vector
information and performs projection using such information to compute
the fine-grained resource information in response to orchestrator's
resource discovery requests.
Details of the obfuscating protocol and the proactive full-mesh
discovery mechanism developed in Unicorn can be found in the
[DRAFT-ALTO-UNICORN] document.
5. IANA Considerations
This document includes no request to IANA.
6. Security Considerations
The ALTO base protocol has an extensive discussion on potential
security and privacy issues. Using the ALTO base protocol to support
multi-domain SFC will not raise new security and privacy issue.
However, the information provided by the ALTO base protocol are
considered coarse-grained in several recent use cases. As a result,
several ALTO extension services have been designed to provide fine-
grained network information to the application. Using these ALTO
extension services for multi-domain SFC would raise new security and
privacy concerns. Next we list these issues on a per extension
basis.
The ALTO unified property extension [DRAFT-ALTO-PM] generalizes the
concept of endpoint properties to other entity domains, such as
abstract network element. The properties of these entities may
contain sensitive service-function-specific information. Exposing
such information may discourage networks to provide fine-grained
information to support multi-domain SFC.
The ALTO performance cost metrics extension [DRAFT-ALTO-METRICS]
proposes a set of ALTO cost metrics derived from traffic engineering
tools and protocols. It is stated in this extension that "sharing
network TE metric values in numerical mode requires full mutual
confidence between the entities managing the ALTO Server and Client."
In multi-domain SFC use case, such mutual confidence is needed not
only between ALTO server and client, but also among all networks, and
third-parties such as broker and a global orchestrator. How to
achieve such mutual confidence in multi-domain SFC use case requires
further investigation.
The ALTO path vector extension [DRAFT-ALTO-PV] allows ALTO clients to
query network information such as capacity region for a given set of
flows. Several related studies have shared concerns that this
extension may reveal more network internal structures than the more
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abstract single-node abstraction used in the ALTO base protocol. In
multi-domain SFC, this concern will further be amplified as third-
party participants may access such information. The recent designed
Unicorn system proposes an obfuscating protocol that prevent the
receiver of the capacity region information from associating this
region to any network. This protocol sheds light for addressing the
privacy issue brought by the ALTO path vector extension.
The ALTO cost calendar [DRAFT-ALTO-CALENDAR] and the ALTO incremental
update [DRAFT-ALTO-INCR-UPD] extensions allows the ALTO client to get
temporal network information. The intention of these extensions is
to allow applications to make flexible decisions on when to use
network information. However, both extensions expose temporal policy
and traffic information of network so that a user may know when the
network is most vulnerable for overloading. This issue need to be
carefully addressed in order for both extensions to be used for
multi-domain SFC.
7. Summary and Outlook
This document introduced initiatives and solutions being proposed in
the context of SFC traversing different domains. It is also provided
initial arguments why ALTO is a meaningful protocol in such multi-
domain scenario, and it presented use case examples about the how
ALTO can be used to advertise and discover abstract topology,
resource and service information from different domains, and then
compute inter-domain service function paths.
The overall objective of this document is to arouse discussions in
the SFC WG in order to assess the suitability of the ALTO as a useful
protocol for multi-domain SFC scenarios. The result of such
discussions will be captured in future versions of this draft.
8. Acknowledgments
This work is supported by the Innovation Center of Ericsson S.A.,
Brazil (grant agreement UNI.64).
Many thanks to Sabine Randriamasy, and Lyle Bertz for their feedback
on this draft.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997,
<http://xml.resource.org/public/rfc/html/rfc2119.html>.
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[RFC7285] Alimi, R., Ed., Penno, R., Ed., Yang, Y., Ed., Kiesel, S.,
Previdi, S., Roome, W., Shalunov, S., and R. Woundy,
"Application-Layer Traffic Optimization (ALTO) Protocol",
RFC 7285, DOI 10.17487/RFC7285, September 2014,
<https://www.rfc-editor.org/info/rfc7285>.
[RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
Chaining (SFC) Architecture", RFC 7665,
DOI 10.17487/RFC7665, October 2015,
<https://www.rfc-editor.org/info/rfc7665>.
[RFC8189] Randriamasy, S., Roome, W., and N. Schwan, "Multi-Cost
Application-Layer Traffic Optimization (ALTO)", RFC 8189,
DOI 10.17487/RFC8189, October 2017,
<https://www.rfc-editor.org/info/rfc8189>.
9.2. Informative References
[DRAFT-ALTO-BROKER-MDO]
Perez, D. and C. Rothenberg, "ALTO-based Broker-assisted
Multi-domain Orchestration", draft-lachosrothenberg-alto-
brokermdo-00 (work in progress), March 2018.
[DRAFT-ALTO-CALENDAR]
Randriamasy, S., Yang, Y., Wu, Q., Lingli, D., and N.
Schwan, "ALTO Cost Calendar", draft-ietf-alto-cost-
calendar-05 (work in progress), June 2018.
[DRAFT-ALTO-INCR-UPD]
Roome, W., Yang, Y., and S. Chen, "ALTO Incremental
Updates Using Server-Sent Events (SSE)", draft-ietf-alto-
incr-update-sse-11 (work in progress), June 2018.
[DRAFT-ALTO-METRICS]
Wu, Q., Yang, Y., Lee, Y., Dhody, D., and S. Randriamasy,
"ALTO Performance Cost Metrics", draft-ietf-alto-
performance-metrics-04 (work in progress), June 2018.
[DRAFT-ALTO-PM]
Roome, W., Chen, S., Randriamasy, S., Yang, Y., and J.
Zhang, "Unified Properties for the ALTO Protocol", draft-
ietf-alto-unified-props-new-03 (work in progress), March
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[DRAFT-ALTO-PV]
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[DRAFT-ALTO-UNICORN]
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[DRAFT-HH-MDSFC]
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Hierarchical Multi-Domain Service Function chaining",
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[DRAFT-MD-VIRT]
Bernardos, C., Contreras, L., Vaishnavi, I., Szabo, R.,
Li, X., Paolucci, F., Sgambelluri, A., Martini, B.,
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[MEF-SOE-MEF55]
Metro Ethernet Forum, "Lifecycle Service Orchestration
(LSO): Reference Architecture and Framework", Mar 2016,
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Authors' Addresses
Danny Alex Lachos Perez
University of Campinas
Av. Albert Einstein 400
Campinas, Sao Paulo 13083-970
Brazil
Email: dlachosp@dca.fee.unicamp.br
URI: https://intrig.dca.fee.unicamp.br/danny-lachos/
Qiao Xiang
Tongji/Yale University
51 Prospect Street
New Haven, CT
USA
Email: qiao.xiang@cs.yale.edu
Christian Esteve Rothenberg
University of Campinas
Av. Albert Einstein 400
Campinas, Sao Paulo 13083-970
Brazil
Email: chesteve@dca.fee.unicamp.br
URI: https://intrig.dca.fee.unicamp.br/christian/
Lachos, et al. Expires September 10, 2020 [Page 16]
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Y. Richard Yang
Tongji/Yale University
51 Prospect St
New Haven, CT
USA
Email: yang.r.yang@gmail.com
Lachos, et al. Expires September 10, 2020 [Page 17]
