OPSAWG Working Group N. Sambo
Internet-Draft M. Dallaglio
Intended status: Standards Track P. Castoldi
Expires: December 29, 2017 Scuola Superiore Sant'Anna
G. Fioccola
A. Di Giglio
Telecom Italia
F. Cugini
CNIT
G. Bernini
P. Giardina
Nextworks
June 27, 2017
Extending YANG for events, actions, and finite state machine
draft-sambo-opsawg-ccamp-supa-ext-yang-fsm-00
Abstract
Network operators and service providers are facing the challenge of
deployment of systems from different vendors while looking for a
trade-off among transmission performance, network device reuse, and
capital expenditure without the need of being tied to single vendor
equipment. The deployment and operation of more dynamic and
programmable transport optical network infrastructures can be driven
by adopting model-driven and software-defined control and management
paradigms. In this context, YANG enables to compile a set of
consistent vendor-neutral data models for optical networks and
components based on actual operational needs emerging from
heterogeneous use cases. This document extends YANG from data to
functional modeling in order to describe events, operations, and
finite state machine of YANG-defined network elements. The proposed
models can be applied in the context of optical networks to pre-
instruct data plane devices (e.g., an optical transponder) on the
actions to be performed (e.g., code adaptation) in case some events,
such as physical layer degradations, occur.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 29, 2017.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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publication of this document. Please review these documents
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions used in this document . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Example of application . . . . . . . . . . . . . . . . . . . 4
5. Extending YANG for events and reactions . . . . . . . . . . . 7
6. Extending YANG for finite state machine (FSM) . . . . . . . . 9
7. Implementation for the considered use case of application . . 9
8. Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.1. YANG model for events and actions - Tree . . . . . . . . 10
8.2. YANG model for FSM - Tree . . . . . . . . . . . . . . . . 11
8.3. YANG model for events and actions - Code . . . . . . . . 12
8.4. YANG model for FSM - Code . . . . . . . . . . . . . . . . 16
8.5. Example of values for the YANG model . . . . . . . . . . 19
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19
10. Security Considerations . . . . . . . . . . . . . . . . . . . 20
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
11.1. Normative References . . . . . . . . . . . . . . . . . . 20
11.2. Informative References . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
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1. Introduction
Networks are evolving toward more programmability, flexibility, and
multi-vendor interoperability. Multi-vendor interoperability can be
applied in the context of nodes, i.e. a node composed of components
provided by different vendors (named white box) is assembled under
the same control system. This way, operators can optimize costs and
network performance without the need of being tied to single vendor
equipment. NETCONF protocol RFC6241 [RFC6241] based on YANG data
modeling language RFC6020 [RFC6020] is emerging as a candidate
Software Defined Networking (SDN) enabled protocol. First, NETCONF
supports both control and management functionalities, thus permits
high programmability. Then, YANG enables data modeling in a vendor-
neutral way. Some recent works have provided YANG models to describe
attributes of links (e.g., identification), nodes (e.g., connectivity
matrix), media channels, and transponders (e.g., supported forward
error correction - FEC) of networks
([I-D.ietf-i2rs-yang-network-topo] [I-D.vergara-ccamp-flexigrid-yang]
[I-D.zhang-ccamp-l1-topo-yang]), also including optical technologies.
Such draft mainly refers to elastic optical networks (EONs), i.e.
optical networks based on flexible grid where circuits with different
bandwidth requirements are switched. EONs are expected to employ
flexible transponders, i.e. transponders supporting multiple bit
rates, multiple modulation formats, and multiple codes. Such
transponders permits the (re-) configuration of the bit rate value
based on traffic requirements, as well as the configuration of the
modulation format and code based on the physical characteristics of a
path (e.g., quadrature phase shift keying is more robust than 16
quadrature amplitude modulation). This document extends YANG from
data to functional modeling in order to describe events, operations,
and finite state machine of YANG-defined network elements. Such
models can be applied to a case of transponder reconfiguration in
EONs. In particular, the model enables a centralized remote network
controller (managed by a network operator) to instruct a transponder
controller about the actions to perform when certain events (e.g.,
failures) occur. The actions to be taken and the events can be re-
programmed on the device.
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC2119 [RFC2119].
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3. Terminology
ABNO: Application-Based Network Operations
BER: Bit Error Rate
EON: Elastic Optical Network
FEC: Forward Error Correction
FSM: Finite State Machine
NETCONF: Network Configuration Protocol
OAM: Operation Administration and Maintenance
SDN: Software Defined Network
YANG: Yet Another Network Generator
4. Example of application
Flexible transponders enable several settings of transmission
parameters' configuration, through the support of multiple modulation
formats and forward error correction (FEC) schemes. This way,
transmission parameters can be (re-)configured based on the physical
layer conditions. The YANG model presented in this draft enables to
pre-program reconfiguration settings of data plane devices in case of
failures or physical layer degradations. In particular, soft
failures are assumed. Soft failures imply transmission performance
degradation, in turns a bit error rate (BER) increase, e.g. due to
the ageing of some network devices. Without loosing generality, the
ABNO architecture is assumed for the control and management of EONs
(RFC7491 [RFC7491]). Considering the state of the art, when pre-FEC
BER passes above a predefined threshold, it is expected that an alarm
is sent to the OAM Handler, which communicates with the ABNO
controller that may trigger an SDN controller (that could be the
Provisioning Manager of ABNO RFC7491 [RFC7491]) for computing new
transmission parameters. The involved ABNO modules are shown in the
simplified ABNO architecture of Fig. 1. Then, transponders are
reconfigured. When alarms related to several connections impacted by
the soft failure are generated, this procedure may be particularly
time consuming. The related workflow for transponder reconfiguration
is shown in Fig. 2. The proposed model enables an SDN controller to
instruct the transponder about reconfiguration of new transmission
parameters values if a soft failure occurs. This can be done before
the failure occurs (e.g., during the connection instantiation phase
or during the connection service), so that data plane devices can
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promptly reconfigure themselves without querying the SDN controller
to trigger an on-demand recovery. This is expected to speed up the
recovery process from soft failures. The related flow chart is shown
in Fig. 3.
___________ ___________
| ABNO | | OAM |
|controller | ------ | Handler |
|___________| |___________|
| |
| |
| |
____________ |
| SDN | |
| controller | |
|____________| |
|
| |
| |
| |
_____________________________
| Client |
| network |
|_____________________________|
Figure 1: Assumed ABNO functional modules
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_____________________
| 1 |
|Sending alarm to the |
| OAM Handler |
| |
|_____________________|
|
|
|
_____________________
| 2 |
| Trigger |
| SDN Controller |
| |
|_____________________|
|
|
|
_____________________
| 3 |
| Computation of |
| new transmission |
| parameters |
|_____________________|
|
|
|
_____________________
| 4 |
| Data plane |
| reconfiguration |
| |
|_____________________|
Figure 2: Flow chart of the expected state-of-the-art approach
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_______________________
| 1 |
| Instructing the local |
| controller of |
| data plane devices |
|_______________________|
|
|
|
_______________________
| 2 |
| Local reconfiguration |
| upon failure |
| detection |
|_______________________|
|
|
|
_______________________
| 3 |
| |
| notification |
| |
|_______________________|
Figure 3: Flow chart of the approach exploiting YANG models in this
draft
5. Extending YANG for events and reactions
The model extends YANG to define a list of events associated with
specific reactions. The related code and tree are shown in the
Appendix.
<event>: this element defines an event and it is composed by a set
of leaves' attributes as follows.
<name>: this attribute defines the name of the event.
<type>: this attribute defines the type of the event from
a pool of possible event types predefined inside
the YANG model. Together with the <name> attribute,
it uniquely identifies the event.
<description>: this optional attribute is a "string" describing
the event
<filters>: this leaf is a list that enhances the description
of an event. Given that an event does not necessary
means a particular degradation or faults, this list
can be used to define thresholds to express a measure
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of the event.
<filter>: this leaf of <filters> defines a threshold to
characterize the event.
<filter-id>: this leaf of <filters> define the
identifier number associated with the <filter>
attribute.
<reaction>: this attribute defines a list of operations to take
if the event occurs.
<operations>: this list defines the set of operations
that have to be taken if the event occurs.
<id>: this leaf of <operations> defines the
identifier number of an operation.
<type>: this leaf of <operations> defines
the type of an operation.
<simple>: this leaf defines (differently
from <conditional> detailed below) an
operation that has to be directly
executed.
<execute>: this attribute recalls an
RPC encapsulating the effective
task (operation) to be executed
by the data plane hardware.
<next-operation>: this attribute
defines the identification
number of a next operation that
has to be taken.
<conditional>: this leaf enables a check
("true" or "false") to be verified
before executing the operation. Based
on the check, the proper attributes
<execute> and <next-operation> are
considered.
<statement>: this leaf of
<conditional> defines the
condition to be verified before
executing the operation.
<true>: this leaf of <conditional>
defines a result of the check
associated to <statement>.
Proper <execute> and
<next-operation> attributes are
associated with this result of
the check.
<false>: this leaf of <conditional>
defines a result of the check
associated to <statement>.
Proper <execute> and
<next-operation> attributes are
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associated with this result of
the check.
6. Extending YANG for finite state machine (FSM)
This model extends the one of the events and reactions by adding the
state information and state transition. More precisely, the model
defines a list of states associated with events. Each state has a
description attribute and it is identified through an id. Each state
includes a list of events as defined in the event model, with the
additional next-state attribute, which points to the next state. The
related code and tree are shown in the Appendix.
<current-state>: it defines the current state of the FSM.
<states>: this element defines the FSM as follows.
<state>: this list defines all the FSM states.
<id>: this leaf attribute of <state> defines the
identifier of the state
<name>: this leaf attribute of <state> defines the name of
the state
<description>: this leaf is a "string" describing the
state
<events>: this attribute is the one described in the
previous section. In particular, this attribute
defines a list of events that may induce a
transition to another state in the FSM.
<next-state>: this attribute is included in the
model <events> and defines the next state
of FSM when an operation is executed.
7. Implementation for the considered use case of application
The models defined in this document are an extension of YANG through
functions, events, and FSM, besides data modeling. These models can
be used to enable a centralized network controller, managed by a
network operator, to instruct data plane hardware on its
reconfiguration if some events, such as a failure or physical layer
degradation, occur. As an example, an optical signal impacted by a
soft failure (i.e., a physical layer degradation inducing a pre
forward error correction bit error rate increase - pre-FEC) can be
maintained by adapting the FEC of the signal itself. This action to
be taken and, more in general operations to be executed depending on
critical events, can be (re-) programmed on the transponder by (re-)
sending a NETCONF <edit-config> message to the device controller
including a FSM defined by the YANG model. Such a system has the
main goal to speed up the reaction of the network to certain events/
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faults and to alleviate the workload of the centralized controller.
The speed up derives from the fact that the centralized controller is
able to pre-compute and pre-configure on the network devices the
actions to take when an event occurs taking into account a global
view and knowledge of the network. In this way, the device is
already aware of the actions to be locally applied to reconfigure a
connection, avoiding to inform the controller and to wait for the
response indicating what to do. Consequently, part of the workload
is also removed from the centralized controller. When the reaction
is successfully completed in the data plane, the centralized
controller can be notified about the faults and the taken action. A
flexible transponder supporting two FEC types, 7% and 20%, is
considered. A two-states FSM is also assumed. The states have
<name> attribute set to "Steady" and "Fec-Baud-Adapt", respectively.
In the "Steady" state, the signal is in a healthy condition, adopting
a 7% FEC, with a pre-FEC BER below an assigned threshold of 9 x 10-4.
A transition from this state can be triggered by the event with
<name>=BER_CHANGE and <filter-type>=9 x 10-4, thus expressing a
change of the pre-FEC BER above the threshold. In case the pre-FEC
BER exceeds 9 x 10-4 due to a soft failure, the state machine evolves
to the "Fec-Baud-Adapt" state and an adaptation to a more robust FEC
of 20% (executed by the attribute <execute>) is performed. The
system can return to the "Steady" state if the pre-FEC BER goes below
another pre-defined threshold and the FEC is reconfigured to 7%.
8. Appendix
This appendix reports the YANG models code and the related tree.
8.1. YANG model for events and actions - Tree
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+--rw events
+--rw event [name type]
+--rw name string
+--rw type event-type
+--rw description? string
+--rw filters
| +--rw filter [filter-id]
| +--rw filter-id yp:filter-id
+--rw reaction
+--rw operation [id]
+--rw id event-id-type
+--rw type enumeration
+--rw conditional
| +--rw statement string
| +--rw true
| | +--rw execute
| | +--rw next-operation? event-id-type
| +--rw false
| +--rw execute
| +--rw next-operation? event-id-type
+--rw simple
+--rw execute
+--rw next-operation? event-id-type
8.2. YANG model for FSM - Tree
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+--rw current-state? leafref
+--rw states
+--rw state [id]
+--rw id state-id-type
+--rw name string
+--rw description? string
+--rw events
+--rw event [name type]
+--rw name string
+--rw type event-type
+--rw description? string
+--rw filters
| +--rw filter [filter-id]
| +--rw filter-id yp:filter-id
+--rw reaction
+--rw operation [id]
+--rw id event-id-type
+--rw type enumeration
+--rw conditional
| +--rw statement string
| +--rw true
| | +--rw execute
| | +--rw next-operation? event-id-type
| | +--rw next-state? leafref
| +--rw false
| +--rw execute
| +--rw next-operation? event-id-type
| +--rw next-state? leafref
+--rw simple
+--rw execute
+--rw next-operation? event-id-type
+--rw next-state? leafref
8.3. YANG model for events and actions - Code
module events {
namespace "http://sssup.it/events";
prefix ev;
import ietf-yang-push {
prefix yp;
}
organization
"Scuola Superiore Sant'Anna Network and Services Laboratory";
contact
" Editor: Matteo Dallaglio
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<mailto:m.dallaglio@sssup.it>
";
description
"This module contains a YANG definitions of events and generic
reactions.";
revision 2016-03-15 {
description "Initial Revision.";
reference
"RFC xxxx: A YANG data model for the description of events and
reactions";
}
// identity statements
identity EVENT {
description "Base for all types of event";
}
identity ON_CHANGE {
base EVENT;
description
"The event when the database changes.";
}
// typedef statements
typedef event-type {
type identityref {
base EVENT;
}
}
typedef event-id-type {
type uint32;
}
// grouping statements
grouping operation-block {
leaf id {
type event-id-type;
}
leaf type {
type enumeration {
enum CONDITIONAL_OP;
enum SIMPLE_OP;
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}
mandatory true;
}
grouping execution-top {
anyxml execute {
description "Represent the action to perform";
}
leaf next-operation {
type event-id-type;
description "the id of the next operation to execute";
}
}
container conditional {
when "../type = 'CONDITIONAL_OP'";
leaf statement {
type string;
mandatory true;
description
"The statement to be evaluated before execution.
E.g. if a=b";
}
container true {
uses execution-top;
}
container false {
uses execution-top;
}
}
container simple {
when "../type = 'SIMPLE_OP'";
description
"Simple execution of an action without checking any condition";
uses execution-top;
}
}
grouping operation-top {
list operation {
key "id";
ordered-by user;
uses operation-block;
}
}
grouping on-change {
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description
"Event occuring when a modification of one or more
objects occurs";
container filters {
description
"This container contains a list of configurable filters
that can be applied to subscriptions. This facilitates
the reuse of complex filters once defined.";
list filter {
key "filter-id";
description
"A list of configurable filters that can be applied to
subscriptions.";
leaf filter-id {
type yp:filter-id;
description
"An identifier to differentiate between filters.";
}
uses yp:datatree-filter;
}
}
}
grouping event-top {
leaf name {
type string;
mandatory true;
}
leaf type {
type event-type;
mandatory true;
}
leaf description {
type string;
}
// list of all possible events
uses on-change {
when "type = 'ON_CHANGE'";
}
container reaction {
uses operation-top;
}
}
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grouping events-top {
container events {
list event {
key "name type";
uses event-top;
}
}
}
// data definition statements
uses events-top;
// extension statements
// feature statements
// augment statements
// rpc statements
// notification statements
}//module events
8.4. YANG model for FSM - Code
module finite-state-machine {
namespace "http://sssup.it/fsm";
prefix fsm;
import events {
prefix ev;
}
organization
"Scuola Superiore Sant'Anna Network and Services Laboratory";
contact
" Editor: Matteo Dallaglio
<mailto:m.dallaglio@sssup.it>
";
description
"This module contains a YANG definitions of a generic finite state
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machine.";
revision 2016-03-15 {
description "Initial Revision.";
reference
"RFC xxxx:";
}
// identity statements
// typedef statements
typedef state-id-type {
type uint32;
}
// grouping statements
grouping state-top {
leaf id {
type state-id-type;
}
leaf name {
type string;
}
leaf description {
type string;
}
grouping next-state-top {
leaf next-state {
type leafref {
path "../../../../../../../../../states/state/id";
}
description "Id of the next state";
}
}
uses ev:events-top {
augment "events/event/reaction/operation/conditional/true" {
uses next-state-top;
}
augment "events/event/reaction/operation/conditional/false" {
uses next-state-top;
}
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augment "events/event/reaction/operation/simple" {
//uses next-state-top;
leaf next-state {
type leafref {
path "../../../../../../../../states/state/id";
}
description "Id of the next state";
}
}
}
}
grouping states-top {
leaf current-state {
type leafref {
path "../states/state/id";
}
}
container states {
list state {
key "id";
uses state-top;
}
}
}
// data definition statements
uses states-top;
// extension statements
// feature statements
// augment statements.
// rpc statements
// notification statements
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}//module fsm
8.5. Example of values for the YANG model
FIELD NAME | YANG DATA TYPE | VALUE
_________________|_____________________|________________________
Current State | leafref | "an existing state id
| | in the FSM"
| |
State | |
id | uint32 | 1
name | string | Steady
description | string | "whatever string"
| |
event | |
name | string | "whatever string"
type | enum | BER_CHANGE
description | string | "whatever string"
| |
filter | |
filter-id | uint32 | 2
filter-type | anyxml or xpath | BER>0.0009
| |
reaction | |
id | uint32 | 3
type | enum | SIMPLE
statement | string | "whatever string"
execute | anyxml | "this recalls an RPC
| | where the FEC value
| | is expressed"
next-operation | uint32 | NULL
next-state | leafref | "an existing state id
| | in the FSM"
9. Acknowledgements
This work has been partially supported by the European Commission
through the H2020 ORCHESTRA (Optical peRformanCe monitoring enabling
dynamic networks using a Holistic cross-layEr, Self-configurable
Truly flexible approach, grant agreement no: H2020-645360) project.
The views expressed here are those of the authors only. The European
Commission is not liable for any use that may be made of the
information in this document.
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10. Security Considerations
TBD
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
the Network Configuration Protocol (NETCONF)", RFC 6020,
DOI 10.17487/RFC6020, October 2010,
<http://www.rfc-editor.org/info/rfc6020>.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<http://www.rfc-editor.org/info/rfc6241>.
[RFC7491] King, D. and A. Farrel, "A PCE-Based Architecture for
Application-Based Network Operations", RFC 7491,
DOI 10.17487/RFC7491, March 2015,
<http://www.rfc-editor.org/info/rfc7491>.
11.2. Informative References
[I-D.ietf-i2rs-yang-network-topo]
Clemm, A., Medved, J., Varga, R., Bahadur, N.,
Ananthakrishnan, H., and X. Liu, "A Data Model for Network
Topologies", draft-ietf-i2rs-yang-network-topo-13 (work in
progress), June 2017.
[I-D.vergara-ccamp-flexigrid-yang]
Madrid, U., Perdices, D., Lopezalvarez, V., Dios, O.,
King, D., Lee, Y., and G. Galimberti, "YANG data model for
Flexi-Grid Optical Networks", draft-vergara-ccamp-
flexigrid-yang-04 (work in progress), March 2017.
[I-D.zhang-ccamp-l1-topo-yang]
zhenghaomian@huawei.com, z., Fan, Z., Sharma, A., and X.
Liu, "A YANG Data Model for Optical Transport Network
Topology", draft-zhang-ccamp-l1-topo-yang-07 (work in
progress), April 2017.
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Authors' Addresses
Nicola Sambo
Scuola Superiore Sant'Anna
Via Moruzzi 1
Pisa 56124
Italy
Email: nicola.sambo@sssup.it
Matteo Dallaglio
Scuola Superiore Sant'Anna
Via Moruzzi 1
Pisa 56124
Italy
Email: matteo.dallaglio@sssup.it
Piero Castoldi
Scuola Superiore Sant'Anna
Via Moruzzi 1
Pisa 56124
Italy
Email: piero.castoldi@sssup.it
Giuseppe Fioccola
Telecom Italia
Via Reiss Romoli, 274
Torino 10148
Italy
Email: giuseppe.fioccola@telecomitalia.it
Andrea Di Giglio
Telecom Italia
Via Reiss Romoli, 274
Torino 10148
Italy
Email: andrea.digiglio@telecomitalia.it
Sambo, et al. Expires December 29, 2017 [Page 21]
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Filippo Cugini
CNIT
Via Moruzzi 1
Pisa 56124
Italy
Email: filippo.cugini@cnit.it
Giacomo Bernini
Nextworks
Via Livornese 1027
Pisa 56122
Italy
Email: g.bernini@nextworks.it
Pietro G. Giardina
Nextworks
Via Livornese 1027
Pisa 56122
Italy
Email: p.giardina@nextworks.it
Sambo, et al. Expires December 29, 2017 [Page 22]