ALTO S. Kiesel
Internet-Draft University of Stuttgart
Intended status: Informational M. Stiemerling
Expires: January 5, 2015 H-DA
July 4, 2014
Application Layer Traffic Optimization (ALTO) Cross-Domain Server
Discovery
draft-kiesel-alto-xdom-disc-00
Abstract
The goal of Application-Layer Traffic Optimization (ALTO) is to
provide guidance to applications that have to select one or several
hosts from a set of candidates capable of providing a desired
resource. ALTO is realized by a client-server protocol. Before an
ALTO client can ask for guidance it needs to discover one or more
ALTO servers that can provide suitable guidance.
In some deployment scenarios, in particular if the information about
the network topology is partitioned and distributed over several ALTO
servers, an ALTO client may need to discover an ALTO server outside
of its own network domain, in order to get appropriate guidance.
This document details applicable scenarios, itemizes requirements,
and analyzes existing solution approaches for such ALTO cross-domain
server discovery. However, the specification of a procedure is
beyond the scope of this document. Note, that in earlier versions of
this document, ALTO cross-domain server discovery was referred to as
"third-party discovery", but it has been renamed to avoid naming
ambiguities.
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Terminology and Requirements Language
This document makes use of the ALTO terminology defined in RFC 5693
[RFC5693].
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 RFC 2119 [RFC2119].
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/.
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 January 5, 2015.
Copyright Notice
Copyright (c) 2014 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
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Document History . . . . . . . . . . . . . . . . . . . . . 4
1.2. Feedback . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. The Need for ALTO Cross-Domain Server Discovery . . . . . . . 5
2.1. Partitioned ALTO Knowledge . . . . . . . . . . . . . . . . 5
2.2. ALTO Queries on behalf of a Third Party . . . . . . . . . 6
2.3. Partitioned Knowledge and Queries for a a Third Party . . 7
2.4. Example . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Requirements for ALTO Cross-Domain Server Discovery . . . . . 9
3.1. Discovery Client Application Programming Interface . . . . 9
3.2. Data Storage and Authority Requirements . . . . . . . . . 9
3.3. Cross-Domain Operations Requirements . . . . . . . . . . . 9
3.4. Protocol Requirements . . . . . . . . . . . . . . . . . . 10
3.5. Further Requirements . . . . . . . . . . . . . . . . . . . 10
4. Related IETF Protocols and Activities . . . . . . . . . . . . 11
5. Security Considerations . . . . . . . . . . . . . . . . . . . 12
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
7.1. Normative References . . . . . . . . . . . . . . . . . . . 14
7.2. Informative References . . . . . . . . . . . . . . . . . . 14
Appendix A. ALTO and Tracker-based Peer-to-Peer Applications . . 16
Appendix B. Contributors List and Acknowledgments . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22
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1. Introduction
Application-Layer Traffic Optimization (ALTO) [RFC5693] is realized
by an HTTP-based client-server protocol [RFC7285]. Before an ALTO
client can issue ALTO queries, it needs to discover a suitable ALTO
server. During the design phase of the overall ALTO solution, two
different server discovery scenarios have been identified and
documented in the ALTO requirements document [RFC6708].
In the first scenario, documented in Req. AR-32, it is sufficient for
a given ALTO client to discover a single ALTO server (or a small
number of ALTO servers with identical knowledge, for reasons of
reliability), usually the nearest one, as recommended by the operator
of the access network. A discovery mechanism for this scenario,
based on DHCP and DNS, is specified in [RFC7286]. An alternative
approach, based on IP anycast, is documented in
[I-D.kiesel-alto-ip-based-srv-disc].
In the second scenario, documented in Req. AR-33, an ALTO client may
need to discover many different ALTO servers, depending on the
queries it wants to issue. These ALTO servers may be located in
other network domains than the client is. This document details
applicable scenarios, itemizes requirements, and analyzes existing
solution approaches for such ALTO cross-domain server discovery.
However, the specification of a procedure is beyond the scope of this
document. An experimental discovery procedure, which fulfills the
requirements documented here, but which is currently not recommended
for usage in the Internet, is documented in
draft-kiesel-alto-xdom-disc-alg-00.txt.
1.1. Document History
This document is a direct successor of [I-D.kiesel-alto-3pdisc] and
[I-D.kist-alto-3pdisc]. The scenario and mechanisms described here
and in these documents have been referred to as "third-party server
discovery" in the past. However, to avoid ambiguities with a
completely different scenario, it has been renamed to "ALTO Cross-
Domain Server Discovery".
1.2. Feedback
Comments and discussions about this document should be directed to
the ALTO working group: alto@ietf.org.
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2. The Need for ALTO Cross-Domain Server Discovery
ALTO Cross-Domain Server discovery is needed, if two independent
effects appear at the conjunction: partitioned knowledge and clients
sending queries on behalf of other hosts. The following two
subsections will discuss these effects separately, before the next
subsection will discuss the combination of both.
2.1. Partitioned ALTO Knowledge
ALTO is realized by an HTTP-based client-server protocol. Basically,
this protocol allows ALTO clients to download "cost maps", which
indicate costs or other properties (according to various metrics) of
the data path between endpoints. Furthermore, ALTO clients may
access only parts of a cost map through the "map filtering service",
and they may query endpoint properties through the "endpoint property
service". Further similar services exist; for details refer to
[RFC7285]. The endpoints are usually identified through their IP
addresses. For efficiency reasons, endpoints may be grouped by using
IP address prefixes and the "network map" with provider-defined
identifiers (PIDs) defined within the ALTO protocol.
Conceptually, the ALTO protocol allows to query for path costs
between arbitrary IP addresses from the whole IP address range, i.e.,
a full 2^32 x 2^32 matrix for IPv4 and a 2^128 x 2^128 matrix for
IPv6 (The "PID" mechanism introduced in the ALTO protocol makes
storage and transmission more efficient but does not alter that basic
principle). And in fact, there may be deployment scenarios where a
single ALTO server (or a cluster of servers operated by a single
organization) has this "Internet-wide view", e.g., a community
project collecting end-to-end measurements.
However, a very important class of scenarios is, when guiding
information actually originates from the (access) network operators,
such as Internet Service Providers (ISPs), IT departments of large
companies or universities, etc. The information available at each of
these providers will not be a full NxN matrix, but more like a 1xN
vector, i.e., indicating cost "from us to anywhere" while cost "from
anywhere to anywhere" is unknown. Several options exist how these
pieces of information could be exposed to the ALTO clients, at least
in theory:
1. The individual 1xN vectors could be aggregated to a virtual
network-wide NxN matrix. This virtual matrix could be exposed
through a single ALTO server or through a cluster of ALTO servers
with identical information. However, no back-end protocol and
process for this aggregation is currently defined.
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2. Each (access) network operator could operate their own ALTO
server, which only has this partial knowledge available there.
Requests for unknown (source,destination)-pairs would be
redirected to another ALTO server. The idea has been discussed
[I-D.kiesel-alto-alto4alto] but no complete specification exists.
A related option would be to establish something similar to a web
search engine, which would do the redirecting. But again, no
detailed specification exists.
3. Each (access) network operator could operate their own ALTO
server, which only has this partial knowledge available there.
It would be the duty of the client-side ALTO server discovery
mechanism to directly find an ALTO server that can reasonably
answer a given query. This option will be considered in more
detail in the remainder of this memo.
2.2. ALTO Queries on behalf of a Third Party
An ALTO client may be co-located with or embedded into the resource
consumer, i.e., the entity that seeks to access the desired resource
and that will be one endpoint of the data transmission to be
optimized. This kind of ALTO client will most often only be
interested in "cost from me to somewhere else" queries, i.e., in an
1xN matrix.
In contrast, the ALTO client may also be located at some kind of
directory server, P2P tracker, CDN redirect server, etc., i.e., at
some entity that takes part in the application signaling but is not
the endpoint of the actual user data transmission to be optimized.
From an ALTO perspective, this kind of ALTO client does not issue
ALTO queries for its own optimization needs, but instead it issues
queries on behalf of remote third parties.
One motivation for this second type of configuration is faster
deployment, as only some central servers would have to be equipped
with an ALTO client and not all the clients. Furthermore, only these
central servers (e.g., servers of a CDN) would need to access the
ALTO servers, while the less-trusted clients could be denied to
access the topology and cost maps. Another important reason is, that
in some scenarios, much better optimization results can be achieved,
if the ALTO guidance is considered at a central resource directory.
See Appendix A for a detailed case study and analysis of such a
scenario.
In the second scenario, ALTO queries may be interested in the path
costs from an arbitrary point in the network topology (where the
third party is, on behalf of which the query is sent) to other
arbitrary points in the topology (where the candidate resource
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providers are located). That is, such ALTO clients might want to
access the full (virtual) NxN matrices.
A more detailed discussion of various options where to place the
functional entities comprising the overall ALTO architecture can be
found in [I-D.ietf-alto-deployments].
2.3. Partitioned Knowledge and Queries for a a Third Party
As long as all ALTO servers store identical information, an ALTO
client can send its queries to any server. A procedure for finding
an ALTO server by means of DHCP is specified in [RFC7286].
If ALTO knowledge is partitioned and distributed over several ALTO
servers and the ALTO client is co-located with a resource consumer,
the DHCP based discovery procedure [RFC7286] will most likely work as
well. The reason is, that this kind of ALTO client will only issue
queries for "costs from me to anywhere", and the network operator can
configure via DHCP an ALTO server that can answer these types of
query.
If, however, ALTO knowledge is partitioned and distributed over
several ALTO servers and the ALTO client issues ALTO queries on
behalf of third parties, a different kind of server discovery
mechanism is needed. These ALTO queries will ask for the "costs from
X to anywhere" (where X is the IP address or PID of the third party).
For each of these queries a suitable ALTO server has to be found and
X will be the parameter for the discovery mechanism.
2.4. Example
The following, non-normative example illustrates the discovery
procedure envisioned in this document.
Assume a peer-to-peer tracker is located in the network operated by
ISP A. Some peer, which is located in ISP B's network, asks the
tracker for an ALTO-optimized list of other peers that take part in a
specific swarm. The tracker can observe the source address X of this
message, which is the peer's IP address.
Assume that there is no omniscient ALTO server that knows the whole
Internet topology. Therefore, the ALTO client in the tracker does a
"back-connect" to the ALTO server operated by ISP B, which knows path
costs from said peer (i.e., IP address X) to anywhere. The ALTO
client retrieves this information and the tracker sorts the peer list
according to it, before returning it to the peer.
Before this "back-connect" can occur, the server ALTO discovery
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mechanism needs to map from the peer's IP address X to the ALTO
server of ISP B, i.e., the network operator that controls IP address
X and has assigned it to the peer.
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3. Requirements for ALTO Cross-Domain Server Discovery
A solution for the problem described in the previous section would be
an ALTO Cross-Domain Server Discovery system. This section itemizes
requirements.
3.1. Discovery Client Application Programming Interface
The discovery client would be called through some kind of application
programming interface (API) and the parameters would be an IP address
and, for purposes of extensibility, a service identifier such as
"ALTO". It would return an URI that offers the requested service
("ALTO") for the given IP address.
In other words, the client would be used to retrieve a mapping:
(IP address, "ALTO") -> IRD-URI
where IRD-URI is the URI of the Information Resource Directory (IRD,
see Section 9 of [RFC7285]) of an ALTO server that can give
reasonable guidance to a resource consumer with the indicated IP
address.
3.2. Data Storage and Authority Requirements
The information for mapping IP addresses and service parameters to
URIs should be stored in a - preferably distributed - database. It
must be possible to delegate administration of parts of this
database. Usually, the mapping from a specific IP address to an URI
is defined by the authority that has administrative control over this
IP address, e.g., the ISP in residential access networks or the IT
department in enterprise, university, or similar networks.
3.3. Cross-Domain Operations Requirements
The cross-domain server discovery mechanism should be designed in
such a way that it works across the public Internet and also in other
IP-based networks. This in turn means that such mechanisms cannot
rely on protocols that are not widely deployed across the Internet or
protocols that require special handling within participating
networks. An example is multicast, which is not generally available
across the Internet.
The ALTO Cross-Domain Server Discovery protocol must support gradual
deployment without a network-wide flag day. If the mechanism needs
some kind of well-known "rendezvous point", re-using an existing
infrastructure (such as the DNS root servers or the WHOIS database)
should be preferred over establishing a new one.
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3.4. Protocol Requirements
The protocol must be able to operate across middleboxes, especially
across NATs and firewalls.
The protocol will specify an algorithm that determines the service
parameters to be used when queries and responses are exchanged. This
service parameter will specify 'ALTO' for the ALTO cross-domain
service discovery. Potentially, it also specifies other required
parameters needed for the service discovery, such as to be used
transport or application level protocol.
The protocol will support the query with the above mentioned service
parameters and allow that the response contains one or more URI(s).
The protocol shall not require any pre-knowledge from the client
other than any information that is known to a regular IP host on the
Internet.
3.5. Further Requirements
The ALTO cross domain server discovery cannot assume that the server
discovery client and the server discovery responding entity are under
the same administrative control.
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4. Related IETF Protocols and Activities
TBD. Survey. In particular, the ECRIT WG has specified a reverse-
DNS-based procedure [RFC7216] to solve a similar problem; TBD:
analyze whether we can re-use or adapt it.
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5. Security Considerations
A high-level discussion of security issues related to ALTO is part of
the ALTO problem statement [RFC5693]. A classification of unwanted
information disclosure risks, as well as specific security-related
requirements can be found in the ALTO requirements document
[RFC6708].
The remainder of this section focuses on security threats and
protection mechanisms for the third-party ALTO server discovery
procedure as such. Once the ALTO server's URI has been discovered
and the communication between the ALTO client and the ALTO server
starts, the security threats and protection mechanisms discussed in
the ALTO protocol specification [RFC7285] apply.
TBD
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6. IANA Considerations
This document does not require any IANA action.
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7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
7.2. Informative References
[I-D.ietf-alto-deployments]
Stiemerling, M., Kiesel, S., Previdi, S., and M. Scharf,
"ALTO Deployment Considerations",
draft-ietf-alto-deployments-09 (work in progress),
February 2014.
[I-D.kiesel-alto-3pdisc]
Kiesel, S., Stiemerling, M., Schwan, N., Scharf, M.,
Tomsu, M., and H. Song, "ALTO Server Discovery Protocol",
draft-kiesel-alto-3pdisc-05 (work in progress),
March 2011.
[I-D.kiesel-alto-alto4alto]
Kiesel, S., "Using ALTO for ALTO server selection",
draft-kiesel-alto-alto4alto-00 (work in progress),
July 2010.
[I-D.kiesel-alto-ip-based-srv-disc]
Kiesel, S. and R. Penno, "Application-Layer Traffic
Optimization (ALTO) Anycast Address",
draft-kiesel-alto-ip-based-srv-disc-03 (work in progress),
July 2014.
[I-D.kist-alto-3pdisc]
Kiesel, S., Krause, K., and M. Stiemerling, "Third-Party
ALTO Server Discovery (3pdisc)", draft-kist-alto-3pdisc-05
(work in progress), January 2014.
[RFC5693] Seedorf, J. and E. Burger, "Application-Layer Traffic
Optimization (ALTO) Problem Statement", RFC 5693,
October 2009.
[RFC6708] Kiesel, S., Previdi, S., Stiemerling, M., Woundy, R., and
Y. Yang, "Application-Layer Traffic Optimization (ALTO)
Requirements", RFC 6708, September 2012.
[RFC7216] Thomson, M. and R. Bellis, "Location Information Server
(LIS) Discovery Using IP Addresses and Reverse DNS",
RFC 7216, April 2014.
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[RFC7285] Alimi, R., Penno, R., and Y. Yang, "Application-Layer
Traffic Optimization (ALTO) Protocol", RFC 7285,
June 2014.
[RFC7286] Kiesel, S., Stiemerling, M., Schwan, N., Scharf, M., and
H. Song, "Application-Layer Traffic Optimization (ALTO)
Server Discovery", RFC 7286, June 2014.
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Appendix A. ALTO and Tracker-based Peer-to-Peer Applications
The ALTO protocol specification [RFC7285] details how an ALTO client
can query an ALTO server for guiding information and receive the
corresponding replies. However, in the considered scenario of a
tracker-based P2P application, there are two fundamentally different
possibilities where to place the ALTO client:
1. ALTO client in the resource consumer ("peer")
2. ALTO client in the resource directory ("tracker")
In the following, both scenarios are compared in order to explain the
need for third-party ALTO queries.
In the first scenario (see Figure 2), the resource consumer queries
the resource directory for the desired resource (F1). The resource
directory returns a list of potential resource providers without
considering ALTO (F2). It is then the duty of the resource consumer
to invoke ALTO (F3/F4), in order to solicit guidance regarding this
list.
In the second scenario (see Figure 4), the resource directory has an
embedded ALTO client, which we will refer to as 3PAC (Third-Party
ALTO Client) in this document. After receiving a query for a given
resource (F1) the resource directory invokes the 3PAC to evaluate all
resource providers it knows (F2/F3). Then it returns a, possibly
shortened, list containing the "best" resource providers to the
resource consumer (F4).
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............................. .............................
: Tracker : : Peer :
: ______ : : :
: +-______-+ : : k good :
: | | +--------+ : P2P App. : +--------+ peers +------+ :
: | N | | random | : Protocol : | ALTO- |------>| data | :
: | known |====>| pre- |*************>| biased | | ex- | :
: | peers, | | selec- | : transmit : | peer |------>| cha- | :
: | M good | | tion | : n peer : | select | n-k | nge | :
: +-______-+ +--------+ : IDs : +--------+ bad p.+------+ :
:...........................: :.....^.....................:
|
| ALTO
| client protocol
__|___
+-______-+
| |
| ALTO |
| server |
+-______-+
Figure 1: Tracker-based P2P Application with random peer preselection
Peer w. ALTO cli. Tracker ALTO Server
--------+-------- --------+-------- --------+--------
| F1 Tracker query | |
|======================>| |
| F2 Tracker reply | |
|<======================| |
| F3 ALTO client protocol query |
|---------------------------------------------->|
| F4 ALTO client protocol reply |
|<----------------------------------------------|
| | |
==== Application protocol (i.e., tracker-based P2P app protocol)
---- ALTO client protocol
Figure 2: Basic message sequence chart for resource consumer-
initiated ALTO query
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............................. .............................
: Tracker : : Peer :
: ______ : : :
: +-______-+ : : :
: | | +--------+ : P2P App. : k good peers & +------+ :
: | N | | ALTO- | : Protocol : n-k bad peers | data | :
: | known |====>| biased |******************************>| ex- | :
: | peers, | | peer | : transmit : | cha- | :
: | M good | | select | : n peer : | nge | :
: +-______-+ +--------+ : IDs : +------+ :
:.....................^.....: :...........................:
|
| ALTO
| client protocol
__|___
+-______-+
| |
| ALTO |
| server |
+-______-+
Figure 3: Tracker-based P2P Application with ALTO client in tracker
Peer Tracker w. 3PAC ALTO Server
--------+-------- --------+-------- --------+--------
| F1 Tracker query | |
|======================>| |
| | F2 ALTO cli. p. query |
| |---------------------->|
| | F3 ALTO cli. p. reply |
| |<----------------------|
| F4 Tracker reply | |
|<======================| |
| | |
==== Application protocol (i.e., tracker-based P2P app protocol)
---- ALTO client protocol
Figure 4: Basic message sequence chart for third-party ALTO query
Note: the message sequences depicted in Figure 2 and Figure 4 may
occur both in the target-aware and the target-independent query mode
(c.f. [RFC6708]). In the target-independent query mode no message
exchange with the ALTO server might be needed after the tracker
query, because the candidate resource providers could be evaluated
using a locally cached "map", which has been retrieved from the ALTO
server some time ago.
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The problem with the first approach is, that while the resource
directory might know thousands of peers taking part in a swarm, the
list returned to the resource consumer is usually shortened for
efficiency reasons. Therefore, the "best" (in the sense of ALTO)
potential resource providers might not be contained in that list
anymore, even before ALTO can consider them.
For illustration, consider a simple model of a swarm, in which all
peers fall into one of only two categories: assume that there are
"good" ("good" in the sense of ALTO's better-than-random peer
selection, based on an arbitrary desired rating criterion) and "bad'
peers only. Having more different categories makes the maths more
complex but does not change anything to the basic outcome of this
analysis. Assume that the swarm has a total number of N peers, out
of which are M "good" and N-M "bad" peers, which are all known to the
tracker. A new peer wants to join the swarm and therefore asks the
tracker for a list of peers.
If, according to the first approach, the tracker randomly picks n
peers from the N known peers, the result can be described with the
hypergeometric distribution. The probability that the tracker reply
contains exactly k "good" peers (and n-k "bad" peers) is:
/ m \ / N - m \
\ k / \ n - k /
P(X=k) = ---------------------
/ N \
\ n /
/ n \ n!
with \ k / = ----------- and n! = n * (n-1) * (n-2) * .. * 1
k! (n-k)!
The probability that the reply contains at most k "good" peers is:
P(X<=k)=P(X=0)+P(X=1)+..+P(X=k).
For example, consider a swarm with N=10,000 peers known to the
tracker, out of which M=100 are "good" peers. If the tracker
randomly selects n=100 peers, the formula yields for the reply:
P(X=0)=36%, P(X<=4)=99%. That is, with a probability of approx. 36%
this list does not contain a single "good" peer, and with 99%
probability there are only four or less of the "good" peers on the
list. Processing this list with the guiding ALTO information will
ensure that the few favorable peers are ranked to the top of the
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list; however, the benefit is rather limited as the number of
favorable peers in the list is just too small.
Much better traffic optimization could be achieved if the tracker
would evaluate all known peers using ALTO, and return a list of 100
peers afterwards. This list would then include a significantly
higher fraction of "good" peers. (Note, that if the tracker returned
"good" peers only, there might be a risk that the swarm might
disconnect and split into several disjunct partitions. However,
finding the right mix of ALTO-biased and random peer selection is out
of the scope of this document.)
Therefore, from an overall optimization perspective, the second
scenario with the ALTO client embedded in the resource directory is
advantageous, because it is ensured that the addresses of the "best"
resource providers are actually delivered to the resource consumer.
An architectural implication of this insight is that the ALTO server
discovery procedures must support third-party discovery. That is, as
the tracker issues ALTO queries on behalf of the peer which contacted
the tracker, the tracker must be able to discover an ALTO server that
can give guidance suitable for that respective peer.
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Appendix B. Contributors List and Acknowledgments
The initial version of this document was co-authored by Marco Tomsu
(Alcatel-Lucent).
This document borrows some text from [RFC7286], as it was
historically part of that memo. Special thanks to Michael Scharf and
Nico Schwan.
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Authors' Addresses
Sebastian Kiesel
University of Stuttgart Information Center
Allmandring 30
Stuttgart 70550
Germany
Email: ietf-alto@skiesel.de
URI: http://www.rus.uni-stuttgart.de/nks/
Martin Stiemerling
University of Applied Sciences Darmstadt, Computer Science Dept.
Haardtring 100
Darmstadt 64295
Germany
Phone: +49 6151 16 7938
Email: mls.ietf@gmail.com
URI: http://ietf.stiemerling.org
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