Initial Congestion Exposure (ConEx) Deployment Examples
draft-briscoe-conex-initial-deploy-02
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draft-briscoe-conex-initial-deploy-02
ConEx B. Briscoe, Ed.
Internet-Draft BT
Intended status: Informational D. Kutscher
Expires: September 14, 2012 NEC
March 13, 2012
Initial Congestion Exposure (ConEx) Deployment Examples
draft-briscoe-conex-initial-deploy-02
Abstract
This document gives examples of how ConEx deployment might get
started, focusing on unilateral deployment by a single network.
Status of This Memo
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This Internet-Draft will expire on September 14, 2012.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Recap: Incremental Deployment Features of the ConEx
Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. ConEx Components . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Recap of Basic ConEx Components . . . . . . . . . . . . . 4
3.2. Per-Network Deployment Concepts . . . . . . . . . . . . . 4
4. Example Initial Deployment Arrangements . . . . . . . . . . . 5
4.1. Single Receiving Network Scenario . . . . . . . . . . . . 5
4.1.1. ConEx Functions in the Single Receiving Network
Scenario . . . . . . . . . . . . . . . . . . . . . . . 7
4.1.2. Incentives to Unilaterally Deploy ConEx in a
Receiving Network . . . . . . . . . . . . . . . . . . 8
4.2. Mobile Network Scenario . . . . . . . . . . . . . . . . . 9
4.2.1. CONEX Functions in a Mobile Network Scenario . . . . . 12
4.2.2. Incentives to Unilaterally Deploy CONEX in a
Mobile Operator Network . . . . . . . . . . . . . . . 13
4.3. Scenario Internal to a Multi-Tenant Data Centre . . . . . 13
4.3.1. Incremental Deployment of ConEx Scenario in a
Multi-Tenant Data Centre . . . . . . . . . . . . . . . 15
5. Security Considerations . . . . . . . . . . . . . . . . . . . 15
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
7. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 15
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16
9. Informative References . . . . . . . . . . . . . . . . . . . . 16
Appendix A. Summary of Changes between Drafts . . . . . . . . . . 17
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1. Introduction
This document gives examples of how ConEx deployment might get
started, focusing on unilateral deployment by a single network.
2. Recap: Incremental Deployment Features of the ConEx Protocol
The ConEx mechanism document [ConEx-Abstract-Mech] goes to great
lengths to design for incremental deployment in all the respects
below. It should be referred to for precise details on each of these
points:
o The ConEx mechanism is essentially a change to the source, in
order to re-insert congestion feedback into the network.
o Source-host-only deployment is possible without any negotiation
required, and individual transport protocol implementations within
a source host can be updated separately.
o Receiver modification may optionally improve ConEx for some
transport protocols with feedback limitations (TCP being the main
example), but it is not a necessity
o Proxies for the source and/or receiver are feasible (though not
necessarily straightforward)
o Queues and network forwarding do not require any modification for
ConEx.
o ECN is not required in the network for ConEx. If some network
nodes support ECN, it can be used by ConEx.
o ECN is not required at the receiver for ConEx. The sender should
nonetheless attempt to negotiate ECN-usage with the receiver,
given some aspects of ConEx work better the more ECN is deployed,
particularly auditing and border measurement.
o Given ConEx exposes information for IP-layer policy devices to
use, the design does not preclude possible innovative uses of
ConEx information by other IP-layer devices, e.g. forwarding
itself
o Packets indicate whether or not they support ConEx.
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3. ConEx Components
3.1. Recap of Basic ConEx Components
[ConEx-Abstract-Mech] introduces the following components:
o The ConEx Wire Protocol
o Forwarding devices (unmodified)
o Sender (modified for ConEx)
o Receiver (optionally modified)
o Audit
o Policy Devices:
* Rest-of-Path Congestion Monitoring Devices
* Congestion Policers
[ConEx-Abstract-Mech] should be referred to for definitions of each
of these components and further explanation.
3.2. Per-Network Deployment Concepts
Network deployment-related definitions:
Internet Ingress: The first IP node a packet traverses that is
outside the source's own network. In a domestic network that will
be the first node downstream from the home access equipment. In
an enterprise network this is the provider edge router.
Internet Egress: The last IP node a packet traverses before reaching
the receiver's network.
ConEx-Enabled Network: A network whose edge nodes implement ConEx
policy functions.
Each network can unilaterally choose to use any ConEx information
given by those sources using ConEx, independently of whether other
networks use it.
Typically, a network will use ConEx information by deploying a policy
function at the ingress edge of its network to monitor arriving
traffic and to act in some way on the congestion information in those
packets that are ConEx-enabled. Actions might include policing,
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altering the class of service, or re-routing. Alternatively, less
direct actions via a management system might include triggering
capacity upgrades, triggering penalty clauses in contracts or levying
charges between networks based on ConEx measurements.
Typically, a network using ConEx info will deploy a ConEx policy
function near the ingress edge and a ConEx audit function near the
egress edge. The segment of the path between a ConEx policy function
and a ConEx audit function can be considered to be a ConEx-protected
segment of the path. Assuming a network covers all its ingresses and
egresses with policy functions and audit functions respectively, the
network within this ring will be a ConEx-protected network.
Of course, because each edge device usually serves as both an ingress
and an egress, the two functions are both likely to be present in
each edge device.
4. Example Initial Deployment Arrangements
In all the deployment scenarios below, we assume that deployment
starts with some data sources being modified with ConEx code. The
rationale for this is that the developer of a scavenger transport
protocol like LEDBAT has a strong incentive to tell the network how
little congestion it is causing despite sending large volumes of
data. In this case the developer makes the first move expecting it
will prompt at least some networks to move in response--so that they
use the ConEx information to reward users of the scavenger protocol.
4.1. Single Receiving Network Scenario
The name 'Receiving Network' for this scenario merely emphasises that
most data is arriving from connected networks and data centres and
being consumed by residential customers on this access network. Some
data is of course also travelling in the other direction.
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DSLAMs __
/|/ ,-.Home-a
__/__| |-----( )
,-----. / \ | |--- `-'
,---. / \ ,------P/ \|\__
/ \ ' Core '/| BRAS | __
( Peer )-->-|P | '------' /|/
\ / | | _____| |---
'---` ' '\,------./ | |---
\ M / |BRAS | \|\__
`-----' '------A\ __
| P| \ /|/
/|\ /|\ \__\_| |--- ,-.
,---. ,---. / | |-----( )
/Data \ / \ \|\__ `-'Home-b
( Centre) ( CDN )
\ / \ / Access Network
'---` '---` <------------->
P=Congestion-Policer; M=Congestion-Monitor; A=Audit function
Figure 1: Single Receiving Network Scenario
Figure Figure 1 is an attempt to show the salient features of a ConEx
deployment in a typical broadband access provider's network (within
the constraints of ASCII art). Broadband remote access servers
(BRASs) control access to the core network from the access network
and vice versa. Home networks (and small businesses) connect to the
access network, but only two are shown.
In this diagram, all data is travelling towards the access network of
Home-b, from the Peer network, the Data centre, the CDN and Home-a.
Data actually travels in both directions on all links, but only one
direction is shown.
The data centre, core and access network are all run by the same
network operator, but each is the responsibility of a different
department with internal accounting between them. The content
distribution network (CDN) is operated by a third party CDN provider,
and of course the peer network is also operated by a third party.
This operator of the data centre, core and access network is the only
one in the diagram to have deployed ConEx monitoring and policy
devices at the edges of its network. However, it has not enabled ECN
on any of its network elements and neither has any other network in
the diagram. The operator has deployed a congestion policing
function (P) on the provider-edge router where the peer attaches to
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its core, on the BRAS where the CDN attaches and on the other BRAS
where each of the residential customers like Home-a attach. On the
provider-edge router where the data centre attaches it has deployed a
congestion monitoring function (M). Each of these policing and
monitoring functions handles the aggregate of all traffic traversing
it, for all destinations.
The operator has deployed an audit function on each logical output
port of the BRAS for each end-customer site like Home-b. The Audit
function handles the aggregate of all traffic for that end-customer
from all sources. For traffic in the opposite direction (e.g. from
Home-b to Home-a, there would be equivalent policing (P) and audit
(A) functions in the converse locations to those shown.
Some content sources in the CDN and in the data centre are using the
ConEx protocol, but others are not. There is a similar situation for
hosts attached to the Peer network and hosts in home networks like
Home-a: some are sending ConEx packets at least for bulk data
transports, while others are not.
4.1.1. ConEx Functions in the Single Receiving Network Scenario
Within the BRAS there are logical ports that model the rate of each
access line from the DSLAM to each home network [TR-059]. They are
fed by a shared queue that models the rate of the downstream link
from the BRAS to the DSLAM (sometimes called the backhaul network).
If there is congestion anywhere in the set of networks in Figure
Figure 1 it is nearly always:
o either self-congestion in the queues into the logical ports
representing the access lines
o or shared congestion in the shared queue on the BRAS that feeds
them.
Any ConEx sources sending data through this BRAS will receive
feedback about these losses from the destination and re-insert it as
ConEx markings into the data. Figure 2 shows an example plot of the
loss levels that might be seen at different monitoring points along a
path between the data centre and home-b, for instance. The top half
of the figure shows the loss probability within the BRAS consists of
0.1% at the shared queue and 0.2% self-congestion in the logical
output port that models the access line, making 0.3% in total. This
upper diagram also shows whole path congestion as signalled by the
ConEx sender, which remains unchanged along the whole path at 0.3%.
The lower half of the figure shows (downstream congestion) = (whole
path) - (upstream congestion). Upstream congestion can only be
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monitored locally where the loss actually happens (within the BRAS
output queues). Nonetheless, given there is rarely loss anywhere
else but within the BRAS, this limitation is not significant in this
scenario. The lower half of the figure also shows the location of
the policing and audit functions. Policing anywhere within or
upstream ofthe BRAS will be based on the downstream congestion level
of 0.3%. While Auditing within the BRAS but after all the queues can
check that the whole path congestion signalled by ConEx is no less
than the loss levels experienced within the BRAS itself.
Data centre-->|<--core-->|<------BRAS--------->|<--Home--
| |
^loss |<-Shared->|<-Access->|
|probability backhaul
|
0.3%|- - - - - - - - - - - - - - - - - - - - +-----------------
| whole path congestion |
| |
| |upstream
0.1%| +---------+congestion
| |
-O==============================+----------------------------->
monitoring point
^loss
|probability Policing Audit
| | |
| V |
0.3%|----------------O-------------+ |
| |downstream |
0.2%| +---------+ |
| congestion| |
| | |
| | V
-O----------------------------------------+====O============-->
monitoring point
Figure 2: Example plot of loss levels along a path
4.1.2. Incentives to Unilaterally Deploy ConEx in a Receiving Network
Even a sending application that is modified to use ConEx can choose
whether to send ConEx or Not-ConEx packets. Nonethelss, ConEx
packets bring information to a policer about congestion expected on
the rest of the path beyond the policer. Not-ConEx packets bring no
such information. Therefore a network that has deployed ConEx
policers will tend to rate-limit not-ConEx packets conservatively in
order to manage the unknown risk of congestion. In contrast, a
network doesn't normally need to rate-limit ConEx-enabled packets
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unless they reveal a persistently high contribution to congestion.
This natural tendency for networks to favour senders that provide
ConEx information encourages senders to choose to use the ConEx
protocol whenever they can.
{ToDo: complete this section}
4.2. Mobile Network Scenario
Mobile networks (in general, but we focus on 3GPP EPS here) are
another type of network that is generally amenable to initial CONEX
deployment because of its need to make congestion visible to the
network:
Congestion management is highly important: mobile network operators
have traditionally gone to great extent to detect and act upon
congestion at different locations in their networks. Capacity
investments are high, (especially) wireless resources have been
comparatively scarce, and many physical resources (wireless links,
backhaul links, core networks) are shared.
Evolving from highly differentiated services to 'best-effort'
communication: The conversion to IP-based communication and to
ubiquitous Internet access services has rendered traditional
models of fine-granular differentiated services too inefficient
and complicated. The majority of flows are mapped onto best-
effort bearers -- which calls for appropriate resource sharing and
accounting models for such flows.
Demand for congestion exposure at different levels: The demand for
more appropriate resource sharing in heavy usage scenarios has led
to an increased deployment of Deep-Packet Inspection (DPI) --
there is an obvious demand for informing the network about
congestion on roundtrip time scales. Moreover, 3GPP mobile
network operators require congestion information at different
time-scales, specifically on network-management time scales:
Identifying hot-spots, analyzing overload situations and assisting
network planning is routinely done by "drive tests" -- which could
be simplified with a CONEX approach. Congestion and base station
load information is also exchanged in Self-Organized Networking
(SON) to assist cell capacity optimization and hand-over decisions
(at smaller time-scales).
Mobile networks are also amenable to initial CONEX deployment because
they already provide many prerequisites:
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Elaborate and flexible policy and charging architecture: Mobile
networks today employ an elaborate and flexible policy and
charging infrastructure that can easily be advanced to account for
congestion contribution (instead of data volume as in many current
deployments) and that could thus provide incentives for CONEX
adoption and sender behavior.
Well integrated overall system: 3GPP specification cover many parts
of the overall system, including (for example) ECN usage by mobile
terminals. It would thus be quite feasible to introduce CONEX to
such networks (without requiring CONEX support in non-3GPP
networks) by specifying its detailed usage in the corresponding
specifications.
Frequent usage of gateways and proxies It is quite common that
actual deployments employ proxy caches, TCP proxies etc., which
introduces additional options for an initial deployment (for
instance by only modifying proxy TCP senders at a very early
phase).
The EPS architecture and its standardized interfaces are depicted in
Figure 3. The EPS provides IP connectivity to UEs (user equipment,
i.e., mobile nodes) and access to operator services, such as global
Internet access and voice communications. The EPS comprises the
access (evolved UMTS Terrestrial Radio Access Network, E-UTRAN) and
the core network (Evolved Packet Core, EPC -- all network elements
except the E-UTRAN). QoS is supported through an EPS bearer concept,
providing hierarchical bindings within the network. Please see
[conex-mobile] for a detailed description of the individual elements.
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+-------+
+-------+ | PCRF |
| HSS | /+-------+\
+-------+ Gx/ \Rx
| / \
| / \
| +-------+ SGi +-------+
| | P-GW |=========|IP Svr |
| +-------+ +-------+
HPLMN | |
------------------------------|--------------|----------------------
VPLMN | |
+-------+ |
| MME | |
/+-------+\ |S8
S1-MME / \ |
/ \S11 |
/ \ |
+-----------+ \ |
+----+ LTE-Uu | | \ |
| UE |========| | S1-U +-------+
+----+ | E-UTRAN |==============| S-GW |
| (eNBs) | +-------+
| |
+-----------+
Figure 3: EPS Architecture Overview
Figure 3 does not only depict data path elements but also mobility
management, home subscriber servers (HSS) etc, distinguishing home
networks and visited networks. Figure 4 depicts a simplified
network, focusing on data path elements only.
In Figure 4 depicts a fairly simple deployment scenario, where CONEX
is supported by servers for sending data (here: web servers in the
Internet and caches in an operator's network) but not by UEs (neither
for receiving nor sending). An operator who chooses to run a
policing function on the network ingress (e.g., on the P-GW) can
still benefit from congestion exposure without requiring any change
on UEs.
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+------------+
| Web server |
| w/ CONEX |
+------------+
|
|
|
-----------------------
| | |
| Internet | |
| | |
-----------------------
|
--------------------------------------------|--------
| | |
| +-----------+ |
| | Web cache | |
| | w/ CONEX | |
| +-----------+ |
| | |
| +----+ +-------+ +-------+ +-------+ |
| | UE |=====| eNB |=====| S-GW |=====| P-GW | |
| +----+ +-------+ +-------+ +-------+ |
| |
| Operator B |
-----------------------------------------------------
Figure 4: CONEX support on servers and caches
Logical CONEX functions would be mapped to network elements as
follows:
CONEX sender: Web cache
(Unmodified) receiver: UE
Policer: P-GW
Audit function: eNB (optional, since operator controls sender)
4.2.1. CONEX Functions in a Mobile Network Scenario
In a mobile network, shared congestion can occur at different places,
i.e., in the radio access network, on backhaul links, and in the core
network.
In this specific scenario, we assume that not all downlink traffic is
CONEX-enabled, but that all (TCP) traffic that originates from the
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operators web cache is.
Assuming unmodified receivers (UEs) the main CONEX function that is
of interest in this scenario is congestion accountability for web
traffic: a policing entity on the P-GW would be able to account for
congestion contribution for downlink web traffic per user -- and
possibly transfer corresponding information to charging. (Different
operator policies are possible -- for instance, it is also possible
to police traffic more strictly, after a certain congestion
contribution budget has been used in a accounting period.)
Congestion exposure could also be used for traffic offload decisions,
for example when downstream entities detect upstream congestion (in
the core network).
Moreover, congestion exposure could also be used in longer timer
frame network management applications, i.e., downstream nodes in the
network access network could report on upstream vs downstream
congestion statistics on aggregated flows to assist performance
optimizations, network planning etc.
4.2.2. Incentives to Unilaterally Deploy CONEX in a Mobile Operator
Network
In mobile networks, both mobile terminals and mobile network
equipment are standardised by the 3GPP. This represents a much more
centralised standardisation model, where if the 3GPP were to adopt
the ConEx protocol, it might mandate ConEx implementation for
compliant equipment. Initially 3GPP might mandate ConEx only in user
equipment, then each operator could choose (or not) to use ConEx
information for traffic management. This would also have the
interesting side-effect of making ConEx mode widely available outside
cellular networks, given 3GPP user equipment roams elsewhere.
The comparatively non-invasive addition of CONEX support described in
the previous section enables operators to add CONEX-based congestion
accountability for a considerable fraction of the traffic (all
cacheable web traffic). It is independent of other operators and
independent of other forms of congestion management (DPI-based for
example). But compared to other forms of congestion management, this
approach does not require DPI, and it can be extended to other
traffic types (in addition to HTTP) in a later deployment phase. The
existing policy and charging infrastructure can be leveraged.
4.3. Scenario Internal to a Multi-Tenant Data Centre
A number of companies offer hosting of virtual machines on their data
centre infrastructure--so-called infrastructure as a service (IaaS).
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A set amount of processing power, memory, storage and network are
offered. Although processing power, memory and storage are
relatively simple to allocate on the 'pay as you go' basis that has
become common, the network is less easy to allocate given it is a
naturally distributed system.
The design involves the following elements, all involving changes
solely in the hypervisor or operating systems, not network switches:
o A bulk congestion policing function to police all the traffic from
a VM into the network (similar to [CongPol]), implemented as a
shim in the hypervisor;
A customer may run virtual machines on multiple physical nodes, in
which case the data centre operator would ensure that it deployed
a policer in the hypervisor on each node where the customer was
running a VM, at the time the each VM was instantiated.The DC
operator would arrange for them to collectively enforce the per-
customer congestion allowance, as a distributed policer.
o A function to distribute a customer's tokens to the policer
associated with each of the customer's VMs. This could be similar
to the distributed rate limiting of [DRL]]), or a logically
centralised bucket of congestion tokens could be used with simple
1-1 communication between it and the local token bucket in the
hypervisor under each VM. Importantly, traditional bit-rate
tokens cannot simply be reassigned from one VM to another without
implications on the balance of network loading (requiring operator
intervention each time), whereas congestion tokens can be freely
reassigned between different VMs, because a congestion token is
equivalent at any place or time in a network;
o Reinsertion of congestion feedback at the sending side, which may
be implemented:
* either as a shim in both sending and receiving hypervisors
using edge-to-edge feedback (as in Seawall [Seawall]).
* or in the sending operating system using the congestion
exposure protocol (ConEx [ConEx-Abstract-Mech]);
If the Seawall option is used, a feedback proxy will also be
required as a shim in the hypervisor at the receiver. This passes
congestion feedback that the network operator can trust to the
sending hypervisor, by creating a tunnel between the hypervisors.
Seawall uses a local variant of the Internet Protocol within the
data centre to implement this tunnel.
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If the ConEx option is used, a congestion audit function will also
be required as a shim in the hypervisor (or container) layer where
data leaves the network and enters the receiving host. The ConEx
option is only applicable if the guest OS at the sender has been
modified to send ConEx markings in IPv6 using [conex-destopt]. In
addition, the ConEx options could be encoded in the IPv4 header by
hiding them within the packet ID field as described in
[intarea-ipv4-id-reuse].
o Network switches would not need any modification. However, audit
would be easier if switches supported ECN. Ideally data centre
TCP could be used as well, although not essential. DCTCP is based
on ECN and designed for data centres. DCTCP involves a more
aggressive AQM in layer 3 switches with a shallow step threshold
for ECN marking. DCTCP also requires modified sender and receiver
TCP algorithms.
4.3.1. Incremental Deployment of ConEx Scenario in a Multi-Tenant Data
Centre
The Seawall option above is a more processing intensive change to the
hypervisors, but it can be deployed unilaterally by the data centre
operator in al hypervisors (or containers).
The ConEx option above is only applicable if a particular guest OS
supports the marking of outgoing packets with ConEx markings.
A simple filter could be installed in each hypervisor to allow ConEx
packets through into the data centre network without going through
the SeaWall tunnel structure, while non-ConEx packets could be
tunnelled as per SeaWall. This would provide an incremental
deployment scenario with the best of both worlds: it would work for
unmodified guest OSs, but for guest OSs with ConEx support, it would
require less processing (therefore being faster) and not require a
duplicate feedback channel between hypervisors.
5. Security Considerations
6. IANA Considerations
This document does not require actions by IANA.
7. Conclusions
{ToDo}
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8. Acknowledgments
9. Informative References
[ConEx-Abstract-Mech] Mathis, M. and B. Briscoe, "Congestion
Exposure (ConEx) Concepts and Abstract
Mechanism",
draft-ietf-conex-abstract-mech-03 (work in
progress), October 2011.
[CongPol] Jacquet, A., Briscoe, B., and T. Moncaster,
"Policing Freedom to Use the Internet
Resource Pool", Proc ACM Workshop on Re-
Architecting the Internet (ReArch'08) ,
December 2008, <http://bobbriscoe.net/
projects/refb/#polfree>.
[DRL] Raghavan, B., Vishwanath, K., Ramabhadran,
S., Yocum, K., and A. Snoeren, "Cloud
control with distributed rate limiting", ACM
SIGCOMM CCR 37(4)337--348, 2007,
<http://doi.acm.org/10.1145/
1282427.1282419>.
[Seawall] Shieh, A., Kandula, S., Greenberg, A., and
C. Kim, "Seawall: Performance Isolation in
Cloud Datacenter Networks", Proc 2nd USENIX
Workshop on Hot Topics in Cloud Computing ,
June 2010, <http://research.microsoft.com/
en-us/projects/seawall/>.
[TR-059] Anschutz, T., Ed., "DSL Forum Technical
Report TR-059: Requirements for the Support
of QoS-Enabled IP Services", September 2003.
[conex-destopt] Krishnan, S., Kuehlewind, M., and C. Ucendo,
"IPv6 Destination Option for Conex",
draft-ietf-conex-destopt-01 (work in
progress), October 2011.
[conex-mobile] Kutscher, D., Mir, F., Winter, R., Krishnan,
S., and Y. Zhang, "Mobile Communication
Congestion Exposure Scenario",
draft-kutscher-conex-mobile-00 (work in
progress), March 2011.
[intarea-ipv4-id-reuse] Briscoe, B., "Reusing the IPv4
Identification Field in Atomic Packets",
Briscoe & Kutscher Expires September 14, 2012 [Page 16]
Internet-Draft Initial ConEx Deployment Examples March 2012
draft-briscoe-intarea-ipv4-id-reuse-01 (work
in progress), March 2012.
Appendix A. Summary of Changes between Drafts
Detailed changes are available from
http://tools.ietf.org/id/draft-briscoe-conex-initial-deploy-00.txt
From draft-briscoe-01 to draft-briscoe-02:
* Added Mobile Scenario section, and Dirk Kutscher as co-author;
*
From draft-briscoe-00 to draft-briscoe-01: Re-issued without textual
change. Merely re-submitted to correct a processing error causing
the whole text of draft-00 to be duplicated within the file.
Authors' Addresses
Bob Briscoe (editor)
BT
B54/77, Adastral Park
Martlesham Heath
Ipswich IP5 3RE
UK
Phone: +44 1473 645196
EMail: bob.briscoe@bt.com
URI: http://bobbriscoe.net/
Dirk Kutscher
NEC
Kurfuersten-Anlage 36
Heidelberg,
Germany
Phone:
EMail: kutscher@neclab.eu
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