Internet Engineering Task Force Q. Wang, Ed.
Internet-Draft ZTE Corporation
Intended status: Informational R. Valiveti, Ed.
Expires: December 16, 2021 Infinera Corp
H. Zheng, Ed.
Huawei
H. Helvoort
Hai Gaoming B.V
S. Belotti
Nokia
June 14, 2021
Applicability of GMPLS for B100G Optical Transport Network
draft-ietf-ccamp-gmpls-otn-b100g-applicability-07
Abstract
This document examines the applicability of using existing GMPLS
routing and signalling mechanisms to set up ODUk (e.g., ODUflex) LSP
over ODUCn links, as defined in the 2020 version of G.709.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. OTN terminology used in this document . . . . . . . . . . . . 3
3. Overview of the OTUCn/ODUCn in G.709 . . . . . . . . . . . . 3
3.1. OTUCn . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1.1. OTUCn-M . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. ODUCn . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.3. Time Slot Granularity . . . . . . . . . . . . . . . . . . 7
3.4. Structure of OPUCn MSI with Payload type 0x22 . . . . . . 7
3.5. Client Signal Mappings . . . . . . . . . . . . . . . . . 8
4. GMPLS Implications and Applicability . . . . . . . . . . . . 9
4.1. TE-Link Representation . . . . . . . . . . . . . . . . . 9
4.2. Implications and Applicability for GMPLS Signalling . . . 10
4.3. Implications and Applicability for GMPLS Routing . . . . 11
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
6. Authors (Full List) . . . . . . . . . . . . . . . . . . . . . 12
7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 13
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
9. Security Considerations . . . . . . . . . . . . . . . . . . . 14
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
10.1. Normative References . . . . . . . . . . . . . . . . . . 14
10.2. Informative References . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction
The current GMPLS routing [RFC7138] and signalling [RFC7139]
extensions support the control of OTN signals and capabilities that
were defined in the 2012 version of G.709 [ITU-T_G709_2012].
In 2016 a new version of G.709 was published: [ITU-T_G709_2016].
This version introduces new higher rate OTU and ODU signals, termed
OTUCn and ODUCn respectively, which have a nominal rate of n x 100
Gbit/s. According to the definition in [ITU-T_G709_2016], OTUCn and
ODUCn perform only section layer role and ODUCn supports only ODUk
clients. This document focuses on the use of existing GMPLS
mechanisms to set up ODUk (e.g., ODUflex) LSP over ODUCn links,
independently from how these links have been set up.
Since the [ITU-T_G709_2020] does not introduce any new features to
OTUCn and ODUCn comparing to [ITU-T_G709_2016], this document starts
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with [ITU-T_G709_2020] by first presenting an overview of the OTUCn
and ODUCn signals, and then analysing how the current GMPLS routing
and signalling mechanisms can be utilized to setup ODUk (e.g.,
ODUflex) LSPs over ODUCn links.
2. OTN terminology used in this document
a. OPUCn: Optical Payload Unit - Cn. Where Cn indicates that the
bit rate is approximately n*100G.
b. ODUCn: Optical Data Unit - Cn.
c. OTUCn: Fully standardized Optical Transport Unit - Cn.
d. OTUCn-M: This signal is an extension of the OTUCn signal
introduced above. This signal contains the same amount of
overhead as the OTUCn signal, but contains a reduced amount of
payload area. Specifically, the payload area consists of M 5G
tributary slots (where M is strictly less than 20*n).
e. PSI: OPU Payload Structure Indicator. This is a 256-byte signal
that describes the composition of the OPU signal. This field is
a concatenation of the Payload type (PT) and the Multiplex
Structure Indicator (MSI) defined below.
f. MSI: Multiplex Structure Indicator. This structure indicates the
grouping of the tributary slots in an OPU payload area that
realizes a client signal which is multiplexed into an OPU. The
individual clients multiplexed into the OPU payload area are
distinguished by the Tributary Port number (TPN).
Detailed description of these terms can be found in
[ITU-T_G709_2020].
3. Overview of the OTUCn/ODUCn in G.709
This section provides an overview of OTUCn/ODUCn signals defined in
[ITU-T_G709_2020].
3.1. OTUCn
In order to carry client signals with rates greater than 100 Gbit/s,
[ITU-T_G709_2020] takes a general and scalable approach that
decouples the rates of OTU signals from the client rate. The new OTU
signal is called OTUCn, and this signal is defined to have a rate of
(approximately) n*100G. The following are the key characteristics of
the OTUCn signal:
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a. The OTUCn signal contains one ODUCn. The OTUCn and ODUCn signals
perform digital section roles only (see
[ITU-T_G709_2020]:Section 6.1.1)
b. The OTUCn signals can be viewed as being formed by interleaving n
OTUC signals (which are labeled 1, 2, ..., n), each of which has
the format of a standard OTUk signal without the FEC columns (per
[ITU-T_G709_2020] Figure 7-1). The ODUCn have a similar
structure, i.e. they can be seen as being formed by interleaving
n instances of ODUC signals (respectively). The OTUC signal
contains the ODUC signals, just as in the case of fixed rate OTUs
defined in [ITU-T_G709_2020].
c. Each of the OTUC "slices" have the same overhead as the standard
OTUk signal in [ITU-T_G709_2020]. The combined signal OTUCn has
n instances of OTUC overhead, ODUC overhead.
d. The OTUC signal has a slightly higher rate compared to the OTU4
signal (without FEC); this is to ensure that the OPUC payload
area can carry an ODU4 signal.
As explained above, within [ITU-T_G709_2020], the OTUCn, ODUCn and
OPUCn signal structures are presented in a (physical) interface
independent manner, by means of n OTUC, ODUC and OPUC instances that
are marked #1 to #n. Specifically, the definition of the OTUCn
signal does not cover aspects such as FEC, modulation formats, etc.
These details are defined as part of the adaptation of the OTUCn
layer to the optical layer(s). The specific interleaving of
OTUC/ODUC/OPUC signals onto the optical signals is interface specific
and specified for OTN interfaces with standardized application codes
in the interface specific recommendations (G.709.x).
OTUCn interfaces can be categorized as follows, based on the type of
peer network element (see Figure 1):
a. inter-domain interfaces: These types of interfaces are used for
connecting OTN edge nodes to (a) client equipment (e.g. routers)
or (b) hand-off points from other OTN networks. ITU-T has
standardized the Flexible OTN (FlexO) interfaces to support these
functions. For example, Recommendation [ITU-T_G709.1] specifies
a flexible interoperable short-reach OTN interface over which an
OTUCn (n >=1) is transferred, using bonded FlexO interfaces which
belong to a FlexO group.
b. intra-domain interfaces: In these cases, the OTUCn is transported
using a proprietary (vendor specific) encapsulation, FEC etc. It
may also be possible to transport OTUCn for intra-domain links
using FlexO.
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==================================================================
+--------------------------------------------------------+
| OTUCn signal |
+--------------------------------------------------------+
| Inter+Domain | Intra+Domain | Intra+Domain |
| Interface (IrDI)| Interface (IaDI)| Interface |
| FlexO (G.709.1) | FlexO (G.709.x) | Proprietary |
| | (Future) | Encap, FEC etc. |
+--------------------------------------------------------+
==================================================================
Figure 1: OTUCn transport possibilities
3.1.1. OTUCn-M
The standard OTUCn signal has the same rate as that of the ODUCn
signal as shown in Table 1. This implies that the OTUCn signal can
only be transported over wavelength groups which have a total
capacity of multiples of (approximately) 100G. Modern DSPs support a
variety of bit rates per wavelength, depending on the reach
requirements for the optical path. In other words, it is possible to
extend the reach of an optical path (i.e. increase the physical
distance covered) by lowering the bitrate of the digital signal that
is modulated onto the optical signals. If the total rate of the ODUk
LSPs planned to be carried over an ODUCn link is smaller than n*100G,
it is possible to "crunch" the OTUCn not to transmit some of unused
timeslots. With this in mind, ITU-T supports the notion of a reduced
rate OTUCn signal, termed the OTUCn-M. The OTUCn-M signal is derived
from the OTUCn signal by retaining all the n instances of overhead
(one per OTUC slice) but with only M (M is less than 20*n) OPUCn
tributary slots available to carry ODUk LSPs.
As the "crunching" algorithm is not standardized, knowing the value
of M is not enough to decide the timeslot availability.
3.2. ODUCn
The ODUCn signal defined in [ITU-T_G709_2020] can be viewed as being
formed by the appropriate interleaving of content from n ODUC signal
instances. The ODUC frames have the same structure as a standard ODU
-- in the sense that it has the same Overhead area, and the payload
area -- but has a higher rate since its payload area can embed an
ODU4 signal.
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The ODUCn signals have a rate that is captured in Table 1.
+----------+--------------------------------------------------------+
| ODU Type | ODU Bit Rate |
+----------+--------------------------------------------------------+
| ODUCn | n x 239/226 x 99,532,800 Kbit/s = n x 105,258,138.053 |
| | Kbit/s |
+----------+--------------------------------------------------------+
Table 1: ODUCn rates
The ODUCn is a multiplex section ODU signal, and is mapped into an
OTUCn signal which provides the regenerator section layer. In some
scenarios, the ODUCn, and OTUCn signals will be co-terminated, i.e.
they will have identical source/sink locations. [ITU-T_G709_2020]
allows for the ODUCn signal to pass through a digital regenerator
node which will terminate the OTUCn layer, but will pass the
regenerated (but otherwise untouched) ODUCn towards a different OTUCn
interface where a fresh OTUCn layer will be initiated (see Figure 2).
In this case, the ODUCn is carried by 3 OTUCn segments.
Specifically, the OPUCn signal flows through these regenerators
unchanged. That is, the set of client signals, their TPNs, trib-slot
allocation remains unchanged. The ODUCn Overhead might be modified
if TCM sub-layers are instantiated in order to monitor the
performance of the regenerator hops. In this sense, the ODUCn should
NOT be seen as a general ODU which can be switched via an ODUk cross-
connect.
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==================================================================
+--------+ +--------+
| +-----------+ |
| OTN |-----------| OTN |
| DXC +-----------+ DXC +
| | | |
+--------+ +--------+
<--------ODUCn------->
<-------OTUCn------>
+--------+ +--------+ +--------+ +--------+
| +--------+ | | +----------+ |
| OTN |--------| OTN | | OTN |----------| OTN |
| DXC +--------+ WXC +--------+ WXC +----------+ DXC |
| | | 3R | | 3R | | |
+--------+ +--------+ +--------+ +--------+
<-------------------------ODUCn-------------------------->
<---------------> <---------------> <------------------>
OTUCn OTUCn OTUCn
==================================================================
Figure 2: ODUCn signal
3.3. Time Slot Granularity
[ITU-T_G709_2012] has introduced the support for 1.25G granular
tributary slots in OPU2, OPU3, and OPU4 signals. With the
introduction of higher rate signals, it is not practical for the
optical networks (and the data plane hardware) to support a very
large number of connections at such a fine granularity. [ITU-
T_G709_2012] has defined the OPUC with a 5G tributary slot
granularity. This means that the ODUCn signal has 20*n tributary
slots (of 5 Gbit/s capacity). It is worthwhile considering that the
range of tributary port number (TPN) is 10*n instead of 20*n, which
restricts the maximum client signals that could be carried over one
single ODUC1.
3.4. Structure of OPUCn MSI with Payload type 0x22
As mentioned above, the OPUCn signal has 20*n 5G tributary slots.
The OPUCn MSI field has a fixed length of 40*n bytes and indicates
the availability and occupation of each TS. Two bytes are used for
each of the 20*n tributary slots, and each such information structure
has the following format ([ITU-T_G709_2020]:Section 20.4.1):
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a. The TS availability bit indicates if the tributary slot is
available or unavailable
b. The TS occupation bit indicates if the tributary slot is
allocated or unallocated
c. The tributary port number (14 bits) of the client signal that is
being carried in this specific TS. A flexible assignment of
tributary port to tributary slots is possible. Numbering of
tributary ports is from 1 to 10*n.
3.5. Client Signal Mappings
The approach taken by the ITU-T to map non-OTN client signals to the
appropriate ODU containers is as follows:
a. All client signals are mapped into an ODUk (e.g., ODUflex) as
specified in clause 17 of [ITU-T_G709_2020].
b. ODU Virtual Concatenation has been deprecated. This simplifies
the network, and the supporting hardware since multiple different
mappings for the same client are no longer necessary. Note that
legacy implementations that transported sub-100G clients using
ODU VCAT shall continue to be supported.
c. ODUflex signals are low-order signals only. If the ODUflex
entities have rates of 100G or less, they can be transported over
either an ODUk (k=1..4) or an ODUCn. For ODUflex connections
with rates greater than 100G, ODUCn is required.
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==================================================================
Clients (e.g. SONET/SDH, Ethernet)
+ + +
| | |
+------------------+-------+------+------------------------+
| OPUk |
+----------------------------------------------------------+
| ODUk |
+-----------------------+---------------------------+------+
| OTUk, OTUk.V, OTUkV | OPUk | |
+----------+----------------------------------------+ |
| OTLk.n | | ODUk | |
+----------+ +---------------------+-----+ |
| OTUk, OTUk.V, OTUkV | OPUCn |
+----------+-----------------------+
| OTLk.n | | ODUCn |
+----------+ +------------+
| OTUCn |
+------------+
==================================================================
Figure 3: Digital Structure of OTN interfaces (from G.709:Figure 6-1)
4. GMPLS Implications and Applicability
4.1. TE-Link Representation
Section 3 of RFC7138 describes how to represent G.709 OTUk/ODUk with
TE-Links in GMPLS. Similar to that, ODUCn links can also be
represented as TE-Links, which can be seen in the figure below.
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==================================================================
+-----+ +-----+
| | | |
| A |<-OTUCn Link->| B |
| | | |
+-----+ +-----+
|<--- ODUCn Link -->|
|<---- TE-Link ---->|
3R 3R
+-----+ +-----+ +-----+ +-----+
| | | | | | | |
| A |<-OTUCn Link->| B |<-OTUCn Link->| C |<-OTUCn Link->| D |
| | | | | | | |
+-----+ +-----+ +-----+ +-----+
|<----------------------- ODUCn Link ------------------------>|
|<------------------------ TE-Link -------------------------->|
==================================================================
Figure 4: ODUCn TE-Links
Two endpoints of a TE-Link are configured with the supported resource
information, which may include whether the TE-Link is supported by an
ODUCn or an ODUk or an OTUk, as well as the link attribute
information (e.g., slot granularity, list of available tributary
slot).
4.2. Implications and Applicability for GMPLS Signalling
Once the ODUCn TE-Link is configured, the GMPLS mechanisms defined in
RFC7139 can be reused to set up ODUk/ODUflex LSP with no/few changes.
As the resource on the ODUCn link which can be seen by the client
ODUk/ODUflex is a set of 5G slots, the label defined in RFC7139 is
able to accommodate the requirement of the setup of ODUk/ODUflex over
ODUCn link. In [RFC7139], the OTN-TDM GENERALIZED_LABEL object is
used to indicate how the LO ODUj signal is multiplexed into the HO
ODUk link. In a similar manner, the OTN-TDM GENERALIZED_LABEL object
is used to indicate how the ODUk signal is multiplexed into the ODUCn
link. The ODUk Signal Type is indicated by Traffic Parameters. The
IF_ID RSVP_HOP object provides a pointer to the interface associated
with TE-Link and therefore the two nodes terminating the TE-link know
(by internal/local configuration) the attributes of the ODUCn TE
Link.
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Since the TPN currently defined in G.709 for ODUCn link has 14 bits,
while this field in RFC7139 only has 12 bits, some extension work is
needed. Given that a 12-bit TPN field can support ODUCn links with
up to n=400 (i.e. 40Tbit/s links), this extension is not urgently
needed.
An example is given below to illustrate the label format defined in
RFC7139 for multiplexing ODU4 onto ODUC10. One ODUC10 has 200 5G
slots, and twenty of them are allocated to the ODU4. Along with the
increase of "n", the label may become lengthy, an optimized label
format may be needed.
==================================================================
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TPN = 3 | Reserved | Length = 200 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 1 1 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 0 0| Padding Bits(0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
==================================================================
Figure 5: Label format
4.3. Implications and Applicability for GMPLS Routing
For routing, it is deemed that no extension to current mechanisms
defined in RFC7138 are needed. Because, once an ODUCn link is up,
the resources that need to be advertised are the resources that
exposed by this ODUCn link and the multiplexing hierarchy on this
link. Since the ODUCn link is the lowest layer of the ODU
multiplexing hierarchy, there is no need to explicitly define a new
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value to represent the ODUCn signal type in the OSPF-TE routing
protocol.
The OSPF-TE extension defined in section 4 of RFC7138 can be reused
to advertise the resource information on the ODUCn link to help
finish the setup of ODUk/ODUflex.
5. Acknowledgements
6. Authors (Full List)
Qilei Wang (editor)
ZTE
Nanjing, China
Email: wang.qilei@zte.com.cn
Radha Valiveti (editor)
Infinera Corp
Sunnyvale, CA, USA
Email: rvaliveti@infinera.com
Haomian Zheng (editor)
Huawei
CN
EMail: zhenghaomian@huawei.com
Huub van Helvoort
Hai Gaoming B.V
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EMail: huubatwork@gmail.com
Sergio Belotti
Nokia
EMail: sergio.belotti@nokia.com
Iftekhar Hussain
Infinera Corp
Sunnyvale, CA, USA
Email: IHussain@infinera.com
Daniele Ceccarelli
Ericsson
Email: daniele.ceccarelli@ericsson.com
7. Contributors
Rajan Rao, Infinera Corp, Sunnyvale, USA, rrao@infinera.com
Fatai Zhang, Huawei,zhangfatai@huawei.com
Italo Busi, Huawei,italo.busi@huawei.com
Dieter Beller, Nokia, Dieter.Beller@nokia.com
Yuanbin Zhang, ZTE, Beiing, zhang.yuanbin@zte.com.cn
Zafar Ali, Cisco Systems, zali@cisco.com
Daniel King, d.king@lancaster.ac.uk
Manoj Kumar, Cisco Systems, manojk2@cisco.com
Antonello Bonfanti, Cisco Systems, abonfant@cisco.com
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Yuji Tochio, Fujitsu, tochio@fujitsu.com
8. IANA Considerations
This memo includes no request to IANA.
9. Security Considerations
None.
10. References
10.1. Normative References
[ITU-T_G709_2020]
ITU-T, "ITU-T G.709: Optical Transport Network Interfaces;
06/2020", https://www.itu.int/rec/T-REC-
G.709-202006-I/en, June 2020.
[RFC7138] Ceccarelli, D., Ed., Zhang, F., Belotti, S., Rao, R., and
J. Drake, "Traffic Engineering Extensions to OSPF for
GMPLS Control of Evolving G.709 Optical Transport
Networks", RFC 7138, DOI 10.17487/RFC7138, March 2014,
<https://www.rfc-editor.org/info/rfc7138>.
[RFC7139] Zhang, F., Ed., Zhang, G., Belotti, S., Ceccarelli, D.,
and K. Pithewan, "GMPLS Signaling Extensions for Control
of Evolving G.709 Optical Transport Networks", RFC 7139,
DOI 10.17487/RFC7139, March 2014,
<https://www.rfc-editor.org/info/rfc7139>.
10.2. Informative References
[ITU-T_G709.1]
ITU-T, "ITU-T G.709.1: Flexible OTN short-reach interface;
2018", , 2018.
[ITU-T_G709_2012]
ITU-T, "ITU-T G.709: Optical Transport Network Interfaces;
02/2012", http://www.itu.int/rec/T-REC-
G..709-201202-S/en, February 2012.
[ITU-T_G709_2016]
ITU-T, "ITU-T G.709: Optical Transport Network Interfaces;
07/2016", http://www.itu.int/rec/T-REC-
G..709-201606-P/en, July 2016.
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Authors' Addresses
Qilei Wang (editor)
ZTE Corporation
Nanjing
China
Email: wang.qilei@zte.com.cn
Radha Valiveti (editor)
Infinera Corp
Sunnyvale
USA
Email: rvaliveti@infinera.com
Haomian Zheng (editor)
Huawei
China
Email: zhenghaomian@huawei.com
Huub van Helvoort
Hai Gaoming B.V
Almere
Netherlands
Email: huubatwork@gmail.com
Sergio Belotti
Nokia
Email: sergio.belotti@nokia.com
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