IETF Next Steps in Signaling C. Shen
Internet-Draft H. Schulzrinne
Intended status: Informational Columbia U.
Expires: June 6, 2010 S. Lee
J. Bang
Samsung AIT
December 3, 2009
NSIS Operation Over IP Tunnels
draft-ietf-nsis-tunnel-07.txt
Abstract
NSIS QoS signaling enables applications to perform QoS reservation
along a data flow path. When the data flow path contains IP tunnel
segments, NSIS QoS signaling has no effect within those tunnel
segments and the resulting QoS-untended tunnel segments could become
the weakest QoS link and invalidate the QoS efforts in the rest of
the end-to-end path. The problem with NSIS signaling within the
tunnel is caused by the tunnel encapsulation which masks packets'
original IP header fields. Those original IP header fields are
needed to intercept NSIS signaling messages and classify QoS data
packets. This document defines a solution to this problem by mapping
end-to-end QoS session requests to corresponding QoS sessions in the
tunnel, thus extending the end-to-end QoS signaling into the IP
tunnel segments.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on June 6, 2010.
Copyright Notice
Copyright (c) 2009 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
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described in the BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 5
3.1. IP Tunneling Protocols . . . . . . . . . . . . . . . . . . 5
3.2. NSIS QoS Signaling in the Presence of IP Tunnels . . . . . 7
4. Design Overview . . . . . . . . . . . . . . . . . . . . . . . 9
4.1. Design Requirements . . . . . . . . . . . . . . . . . . . 9
4.2. Overall Design Approach . . . . . . . . . . . . . . . . . 10
4.3. Tunnel Flow ID for Different IP Tunneling Protocols . . . 11
5. NSIS Operation over Tunnels with Pre-configured QoS
Sessions . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.1. Sender-initiated Reservation . . . . . . . . . . . . . . . 12
5.2. Receiver-initiated Reservation . . . . . . . . . . . . . . 13
6. NSIS Operation over Tunnels with Dynamically Created QoS
Sessions . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
6.1. Conveying Tunnel Flow ID Between Tunnel End-points . . . . 15
6.2. Sender-initiated Reservation . . . . . . . . . . . . . . . 15
6.3. Receiver-initiated Reservation . . . . . . . . . . . . . . 17
6.4. Timing Issues of End-to-end and Tunnel Signaling . . . . . 18
7. NSIS-Tunnel Signaling Capability Discovery . . . . . . . . . . 19
7.1. NODE_CHAR Object Format . . . . . . . . . . . . . . . . . 20
7.2. Using NODE_CHAR Object . . . . . . . . . . . . . . . . . . 20
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
9. Security Considerations . . . . . . . . . . . . . . . . . . . 21
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 22
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
11.1. Normative References . . . . . . . . . . . . . . . . . . . 22
11.2. Informative References . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24
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1. Introduction
IP tunneling is a technique that allows a packet to be encapsulated
and carried as payload within an IP packet. The resulting
encapsulated packet is called an IP tunnel packet, and the packet
being tunneled is called the original packet. In typical scenarios,
IP tunneling is used to exert explicit forwarding path control (e.g.,
in Mobile IP [RFC3220]), facilitate the secure IP delivery
architecture (e.g., in IPSEC [RFC2401]), and help packet routing in
IP networks of different characteristics (e.g., between IPv6 and IPv4
networks [RFC4213]).
This document considers the situation when the packet being tunneled
contains a Next Step In Signaling (NSIS) [RFC4080] message. NSIS is
an IP network layer signaling architecture consisting of a Generic
Internet Signaling Transport (GIST) [I-D.ietf-nsis-ntlp] sub-layer
for signaling transport, and an NSIS Signaling Layer Protocol (NSLP)
sub-layer customizable for different applications. We focus on the
Quality of Service (QoS) NSLP [I-D.ietf-nsis-qos-nslp] which provides
functionalities that extend those of the earlier RSVP [RFC2205]
signaling. In this document the term "NSIS" and "NSIS QoS" are used
interchangeably.
Without additional efforts, NSIS signaling does not work within IP
tunneling segments of a signaling path. The reason is that tunnel
encapsulation masks the original packet including its header and
payload. However, information from the original packet is required
both for NSIS peer node discovery and for QoS data flow packet
classification. Without access to information from the original
packet, an IP tunnel acts as an NSIS-unaware virtual link in the end-
to-end NSIS signaling path.
This document defines a mechanism to extend NSIS signaling for end-
to-end QoS reservation into IP tunnels. The NSIS-aware IP tunnel
end-points that support this mechanism is called NSIS-tunnel-aware
end-points. There are two main operation modes. On one hand, if the
tunnel already has pre-configured QoS sessions, the NSIS-tunnel-aware
end-points map end-to-end QoS signaling requests directly to existing
tunnel sessions as long as there are enough tunnel session resources;
on the other hand, if no pre-configured tunnel QoS sessions are
available, the NSIS-tunnel-aware end-points dynamically initiate and
maintain tunnel QoS sessions that are then associated with the
corresponding end-to-end QoS sessions. Note that whether the tunnel
pre-configures QoS sessions or not, and which pre-configured tunnel
QoS sessions a particular end-to-end QoS signaling request should be
matched to is a policy issue out of scope of this document.
The rest of this document is organized as follows, Section 2 defines
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terminology. Section 3 presents the problem statement including
common IP tunneling protocols, and existing behavior of NSIS QoS
signaling operating over IP tunnels. Section 4 introduces the design
requirements and overall approach of our mechanism. More details
about how NSIS QoS signaling operates with tunnels that use pre-
configured QoS and dynamic QoS signaling are provided in Section 5
and Section 6. Section 7 describes a method to automatically
discover whether a tunnel end-point node supports the NSIS-tunnel
interoperation mechanism defined in this document. Section 8
discusses IANA considerations and Section 9 considers security.
2. Terminology
This document uses terminology defined in [RFC2473],
[I-D.ietf-nsis-ntlp], and [I-D.ietf-nsis-qos-nslp]. In addition, the
following terms are used:
Tunnel IP Header: The IP header prepended to the original packet
during encapsulation. It specifies the tunnel end-points as
source and destination.
Tunnel Specific Header: The header fields inserted by the
encapsulation mechanism after the tunnel IP header and before the
original packet. These headers may or may not exist depending on
the specific tunnel mechanism used.
Tunnel Intermediate Node (Tmid): A node which resides in the middle
of the forwarding path between the tunnel entry-point node and the
tunnel exit-point node.
IP Tunnel: A tunnel configured as a virtual link between two IP
nodes, on which the encapsulating protocol is IP.
Flow Identifier (Flow ID): The set of header fields which is used to
identify a [Data] flow. For example, it may include flow sender
and receiver addresses, protocol and port numbers.
End-to-end [QoS] Signaling: The signaling process that manipulates
the QoS control information in the end-to-end path from the flow
sender to the flow receiver. When the end-to-end flow path
contains tunnel segments, this document uses end-to-end [QoS]
signaling to refer specially to the [QoS] signaling outside the
tunnel segments.
Tunnel [QoS] Signaling: The signaling process that manipulates the
QoS control information in the path inside a tunnel, between the
tunnel entry-point and the tunnel exit-point nodes.
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[Adjacent] NSIS Peer: The next node along the signaling path, in the
upstream or downstream direction, with which a NSIS node
explicitly interacts.
NSIS-aware Node: A node that supports NSIS signaling.
NSIS-aware Tunnel End-point Node: A tunnel end-point node which is
also an NSIS node.
NSIS-tunnel-aware [Tunnel] End-point Node: An NSIS-aware Tunnel End-
point node which also supports the NSIS operation over IP tunnels
mechanism defined in this document.
3. Problem Statement
3.1. IP Tunneling Protocols
The following definition of IP tunnel is derived from [RFC2473] and
adapted for both IPv4 and IPv6.
IP tunneling is a technique for establishing a "virtual link" between
two IP nodes for transmitting data packets as payloads of IP packets
(see Figure 1). From the point of view of the two nodes, this
"virtual link", called an IP tunnel, appears as a point-to-point link
on which IP acts like a link-layer protocol. The two IP nodes play
specific roles. One node encapsulates original packets received from
other nodes or from itself and forwards the resulting tunnel packets
through the tunnel. The other node decapsulates the received tunnel
packets and forwards the resulting original packets towards their
destinations, possibly itself. The encapsulating node is called the
tunnel entry-point node (Tentry), and it is the source of the tunnel
packets. The decapsulating node is called the tunnel exit-point node
(Texit), and it is the destination of the tunnel packets.
Tunnel from node B to node D
<---------------------->
Tunnel Tunnel Tunnel
Entry-Point Intermediate Exit-Point
Node Node Node
+-+ +-+ +-+ +-+ +-+
|A|-->--//-->--|B|=====>====|C|===//==>===|D|-->--//-->--|E|
+-+ +-+ +-+ +-+ +-+
Original Original
Packet Packet
Source Destination
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Node Node
Figure 1: IP Tunnel
An IP tunnel is a unidirectional mechanism - tunnel packet flow takes
place in one direction between the IP tunnel entry-point and exit-
point nodes (see Figure 1). Bi-directional tunneling is achieved by
combining two unidirectional mechanisms, that is, configuring two
tunnels, each in opposite direction to the other - the entry-point
node of one tunnel is the exit-point node of the other tunnel.
Figure 2 illustrates the original packet and the resulting tunnel
packet. In a tunnel packet, the original packet is encapsulated
within the tunnel header. The tunnel header contains two components,
the tunnel IP header and other tunnel specific headers. The tunnel
IP header specifies tunnel entry-point node as IP source address and
tunnel exit-point node as IP destination address, thus causing the
tunnel packet to be routed inside the tunnel. The tunnel specific
headers in between the tunnel IP header and the original packet in a
tunnel packet are optional, depending on the tunneling protocol in
use.
+----------------------------------//-----+
| Original | |
| | Original Packet Payload |
| Header | |
+----------------------------------//-----+
< Original Packet >
|
v
<Tunnel Headers> < Original Packet >
+---------+ - - - - - +-------------------------//--------------+
| Tunnel | Tunnel | |
| IP | Specific | Original Packet |
| Header | Headers | |
+---------+ - - - - - +-------------------------//--------------+
< Tunnel IP Packet >
Figure 2: IP Tunnel Encapsulation
Commonly used IP tunneling protocols include Generic Routing
Encapsulation (GRE) [RFC1701][RFC2784], Generic Routing Encapsulation
over IPv4 Networks (GREIPv4) [RFC1702] and IP Encapsulation within IP
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(IPv4INIPv4) [RFC1853][RFC2003], Minimal Encapsulation within IP
(MINENC) [RFC2004], IPv6 over IPv4 Tunneling (IPv6INIPv4) [RFC4213],
Generic Packet Tunneling in IPv6 Specification (IPv6GEN) [RFC2473]
and IPSEC tunneling mode (IPSEC) [RFC4301][RFC4303]. Among these
tunneling protocols, the tunnel headers in IPv4INIPv4, IPv6INIPv4 and
IPv6GEN contain only a tunnel IP header, and no tunnel specific
headers. All the other tunneling protocols have a tunnel header
consisting of both a tunnel IP header and a tunnel specific header.
The tunnel specific header is the GRE header for GRE and GREIPv4, the
minimum encapsulation header for MINENC and the Encapsulation
Security Payload (ESP) header for IPSEC tunneling mode. As will be
discussed in Section 4.3, some of the tunnel specific headers may be
used to identify a flow in the tunnel and facilitate NSIS operating
over IP tunnels.
3.2. NSIS QoS Signaling in the Presence of IP Tunnels
Typically, applications use NSIS QoS signaling to reserve resources
for a flow along the flow path. NSIS QoS signaling can be initiated
by either the flow sender or flow receiver. Figure 3 shows an
example scenario with five NSIS nodes, including flow sender node A,
flow receiver node E, and intermediate NSIS nodes B, C and D. Nodes
which are not NSIS QoS capable are not shown.
NSIS QoS NSIS QoS NSIS QoS NSIS QoS NSIS QoS
Node Node Node Node Node
+-+ +-+ +-+ +-+ +-+
|A|-->--//-->--|B|----->----|C|---//-->---|D|-->--//-->--|E|
+-+ +-+ +-+ +-+ +-+
Flow Flow
Sender Receiver
Node Node
Figure 3: Example Scenario of Sender-initiated NSIS QoS Signaling
Node A Node B Node C Node D Node E
| | | | |
| RESERVE | | | |
+--------->| | | |
| | RESERVE | | |
| +--------->| | |
| | | RESERVE | |
| | +--------->| |
| | | | RESERVE |
| | | +--------->|
| | | | RESPONSE |
| | | |<---------+
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| | | RESPONSE | |
| | |<---------+ |
| | RESPONSE | | |
| |<---------+ | |
| RESPONSE | | | |
|<---------+ | | |
| | | | |
| | | | |
Figure 4: Example Scenario of Sender-initiated NSIS QoS Reservation
Figure 4 illustrates a sender-initiated signaling sequence in the
scenario of Figure 3. Sender node A sends a RESERVE message towards
receiver node E. The RESERVE message gets forwarded by intermediate
NSIS Nodes B, C, and D and finally reaches receiver node E. Receiver
node E then sends back a RESPONSE message confirming the QoS
reservation, again through the previous intermediate NSIS nodes in
the data flow path.
There are two important aspects in the above signaling process that
are worth mentioning. First, the flow sender does not initially know
exactly which intermediate nodes are NSIS-aware and should be
involved in the signaling process for a flow from node A to node E.
Discovery of those nodes, namely node B, C and D is accomplished by a
separate NSIS peer discovery process (not shown above, see
[I-D.ietf-nsis-ntlp]). The NSIS peer discovery messages contain
special IP header and payload format or include a Router Alert Option
(RAO) [RFC2113] [RFC2711]. The special formats of NSIS discovery
messages allow node B, C and D to intercept them and subsequently
insert themselves into the signaling path for the flow in question.
After formation of the signaling path, all signaling messages
corresponding to this flow will be passed to these nodes for
processing. Other nodes which are not NSIS-aware simply forward all
signaling messages like any other IP packets without additional
handling.
Second, the goal of QoS signaling is to install control information
to give QoS treatment for the flow being signaled. Basic QoS control
information includes the data flow ID for packets classification and
type of QoS treatment those packets are entitled to. The flow ID
contains a set of header fields such as flow sender and receiver
addresses, protocol and port numbers.
Now consider Figure 5 where nodes B, C and D are end-points and
intermediate nodes of an IP tunnel. During the signaling path
discovery process, node B might still be able to intercept and
process NSIS peer discovery messages if it recognizes them before
performing tunnel encapsulation; node D might be able to identify
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NSIS peer discovery messages after performing tunnel decapsulation.
A tunnel intermediate node such as node C, however, only sees the
tunnel header of the packets and will not be able to identify the
original NSIS peer discovery message or insert itself in the flow
signaling path. Furthermore, the flow ID of the original flow is
based on IP header fields of the original packet. Those fields are
also hidden in the payload of the tunnel packet. So there is no way
node C can classify packets belonging to that flow in the tunnel. In
summary, the problem is that tunnel intermediate nodes are unable to
intercept original NSIS signaling messages and unable to classify
original data flow packets as a result of tunnel encapsulation. An
IP tunnel segment appears just like a QoS-unaware virtual link.
Since the best QoS of an end-to-end path is judged based on its
weakest segment, leaving the tunnel path "untended" risks voiding
other efforts to provide QoS in the rest of the path.
Tunnel from node B to node D
<---------------------->
Tunnel Tunnel Tunnel
Entry-Point Intermediate Exit-Point
NSIS QoS NSIS QoS NSIS QoS NSIS QoS NSIS QoS
Node Node Node Node Node
+-+ +-+ +-+ +-+ +-+
|A|-->--//-->--|B|=====>====|C|===//==>===|D|-->--//-->--|E|
+-+ +-+ +-+ +-+ +-+
Flow Flow
Sender Receiver
Node Node
Figure 5: Example Scenario of NSIS QoS Signaling with IP Tunnel
4. Design Overview
4.1. Design Requirements
We identify the following design requirements for NSIS operating over
IP tunnels.
o The mechanism should work with all common IP tunneling protocols
listed in Section 3.1.
o Some IP tunnels maintain pre-configured QoS sessions inside the
tunnel. The mechanism should work for IP tunnels both with and
without pre-configured tunnel QoS sessions.
o The mechanism should minimize the required upgrade to existing
infrastructure in order to facilitate its deployment.
Specifically, we limit the necessary upgrade to NSIS-aware tunnel
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end-points. Only tunnel end-points needs to support the mechanism
defined in this document. Such tunnel end-points are called NSIS-
tunnel-aware end-points. All other nodes, both inside and outside
the tunnel should be transparent to this mechanism.
o The mechanism should facilitate its incremental deployment by
providing a method for one NSIS-tunnel-aware end-point to discover
whether the other end-point is also NSIS-tunnel-aware.
o The mechanism should learn from design experience of previous work
on RSVP over IP tunnels (RSVP-TUNNEL) [RFC2746], while also
addressing the following major differences of NSIS from RSVP.
First, NSIS is designed as a generic framework to accommodate
various signaling application needs, and therefore is split into a
signaling transport layer and a signaling application layer; RSVP
does not have a layer split and is designed only for QoS
signaling. Second, NSIS QoS NSLP allows both sender-initiated and
receiver-initiated reservations; RSVP only supports receiver-
initiated reservations. Third, NSIS deals only with unicast; RSVP
also supports multicast. Fourth, NSIS integrates a new session ID
feature which is different from the session identification concept
in RSVP.
4.2. Overall Design Approach
The overall design of this NSIS signaling and IP tunnel interworking
mechanism draws similar concepts from RSVP-TUNNEL [RFC2746], but is
tailored and extended for NSIS operation.
Since a flow is considered uni-directional, to accommodate flows in
both directions of a tunnel, we require both tunnel entry-point and
tunnel exit-point to be NSIS-tunnel-aware. If an NSIS-tunnel-aware
end-point needs to know whether the other tunnel end-point is also
NSIS-tunnel-aware, it uses the NSIS-tunnel capability discovery
mechanism defined in Section 7.
Tunnel end-points need to always intercept NSIS peer discovery
messages and insert themselves into the NSIS signaling path so they
can receive all NSIS signaling messages and coordinate their
interaction within tunnel QoS.
For tunnels that maintain pre-configured QoS sessions, upon receiving
a request to reserve resources for an end-to-end session, an NSIS-
tunnel-aware entry-point will try to map the end-to-end QoS session
to an existing tunnel session. To simplify the design, the mapping
decision is always made by the tunnel entry-point regardless of
whether the end-to-end session uses sender-initiated or receiver-
initiated NSIS signaling mode. The details about which end-to-end
session can be mapped to which pre-configured tunnel session depend
on policy mechanisms outside the scope of this document.
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For tunnels that do not maintain pre-configured QoS sessions, the
NSIS-tunnel-aware end-points dynamically initiate and manage a
corresponding tunnel QoS session for each end-to-end session. To
keep the handling mechanism consistent with the case for tunnels with
pre-configured QoS sessions, the tunnel entry-point always initiates
the mapping between the tunnel session and the end-to-end session.
An important characteristics of a tunnel QoS session is its tunnel
flow ID which identifies the end-to-end data flow within the tunnel.
In both tunnels with and without pre-configured QoS sessions, the
tunnel flow ID is assigned based on information available in the
tunnel header, therefore solving the tunnel-intermediate node flow
packet classification problem in Section 3.2. An example tunnel flow
ID contains the tunnel entry-point and exit-point IP addresses and a
tunnel inserted UDP port number. We discuss more details about
recommended choices of tunnel flow ID for different IP tunneling
protocols in Section 4.3.
Ultimately QoS handling needs to be enforced in the data plane. To
achieve that, NSIS-tunnel-aware entry-point nodes not only
encapsulate data flow packets according to the specific tunnel
protocol, but also insert any necessary header fields according to
the chosen tunnel flow ID. All those header fields are visible to
tunnel intermediate nodes. Tunnel intermediate nodes then classify
those data flow packets and apply appropriate QoS treatment. At the
tunnel exit-point, the data flow packet is decapsulated accordingly
and forwarded as usual.
4.3. Tunnel Flow ID for Different IP Tunneling Protocols
A tunnel flow ID identifies the end-to-end flow for packet
classification within the tunnel. The tunnel flow ID is based on a
set of tunnel header fields. Different tunnel flow ID can be chosen
for different tunneling mechanisms in order to minimize the
classification overhead. This document specifies the following flow
ID formats for the respective tunneling protocols.
o For IPv6 tunneling protocols (IPv6GEN), the tunnel flow ID
consists of the tunnel entry-point IPv6 address and the tunnel
exit-point IPv6 addresses plus a unique IPv6 flow label [RFC3697].
o For IPSEC tunnel mode (IPSEC), the tunnel flow ID contains tunnel
the entry-point IP address and the tunnel exit-point IP address
plus the Security Parameter Index (SPI).
o For all other tunneling protocols (GRE, GREIPv4, IPv4INIPv4,
MINENC, IPv6INIPv4), the tunnel entry-point inserts an additional
UDP header between the tunnel header and the original packet. The
flow ID consists of the tunnel entry-point and tunnel exit-point
IP addresses and the source port number in the additional UDP
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header. In this case, it is especially important that the tunnel
exit-point also understands the additional UDP encapsulation, and
therefore can correctly decapsulate both the normal tunnel header
and the additional UDP header. This requires both tunnel end-
points to be NSIS-tunnel-aware.
The above recommendations about choosing tunnel flow ID apply to
dynamically created QoS tunnel sessions. For pre-configured QoS
tunnel sessions, the corresponding flow ID is determined by the
configuration mechanism itself. For example, if the tunnel QoS is
DiffServ based, the DiffServ Code Point (DSCP) field value may be
used to identify the corresponding tunnel session.
5. NSIS Operation over Tunnels with Pre-configured QoS Sessions
When tunnel QoS is managed by pre-configured QoS sessions, both the
tunnel entry-point and tunnel exit-point also need to be configured
with the flow ID of the tunnel QoS session. This is to enable the
tunnel end-points to correctly perform matching encapsulating and
decapsulating operations. The procedures of NSIS operating over
tunnels with pre-configured QoS sessions are slightly different
depending on whether the end-to-end NSIS signaling is sender-
initiated or receiver-initiated. But in either case, it is the
tunnel entry-point that first creates the mapping between a tunnel
session and an end-to-end session.
5.1. Sender-initiated Reservation
Sender Tentry Tmid Texit Receiver
| | | | |
| RESERVE | | | |
+--------->| | | |
| | RESERVE | |
| +-------------------->| |
| | | | RESERVE |
| | | +--------->|
| | | | RESPONSE |
| | | |<---------+
| | RESPONSE | |
| |<--------------------+ |
| RESPONSE | | | |
|<---------+ | | |
| | | | |
| | | | |
Figure 6: Sender-initiated End-to-end Session with Pre-configured
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Tunnel QoS Sessions
Figure 6 illustrates the signaling sequence when end-to-end signaling
outside the tunnel is sender-initiated. Upon receiving a RESERVE
message from the sender, Tentry checks tunnel QoS configuration,
determines whether and how this end-to-end session can be mapped to a
pre-configured tunnel session. The mapping criteria are part of the
pre-configuration and outside the scope of this document. Tentry
indicates success or failure of the mapping between the end-to-end
session and a tunnel session in the RESERVE message being tunneled to
Texit. The signaling proceeds as usual until a RESPONSE message
arrives at Texit, Tentry and finally the sender. If the RESPONSE
message that Tentry received confirms that the overall signaling is
successful, Tentry starts to encapsulate all incoming packets of the
data flow using the tunnel flow ID corresponding to the mapped tunnel
session. Texit knows how to decapsulate the tunnel packets because
it recognizes the mapped tunnel flow ID based on information supplied
during tunnel session pre-configuration.
5.2. Receiver-initiated Reservation
Figure 7 shows the signaling sequence when end-to-end signaling
outside the tunnel is receiver-initiated. Upon receiving the first
end-to-end Query message, Tentry examines the tunnel QoS
configuration, updates the Query message accordingly, and tunnel the
Query message to Texit. Texit decapsulates the QUERY message,
processes it and forwards it toward the receiver. Later the receiver
sends back a RESERVE message passing through Texit and reaches
Tentry. Tentry decides on whether and how the QoS request for this
end-to-end session can be mapped to a pre-configured tunnel session,
again based on an algorithm outside the scope of this document, and
then indicates the outcome in the outgoing RESERVE message. The
signaling continues until a RESPONSE message arrives at Tentry, Texit
and finally the receiver. If the RESPONSE message that Tentry
received confirms that the overall signaling is successful, Tentry
starts to encapsulate all incoming packets of the data flow using the
tunnel flow ID corresponding to the mapped tunnel session.
Similarly, Texit knows how to decapsulate the tunnel packets because
it recognizes the mapped tunnel flow ID based on information supplied
during tunnel session pre-configuration.
Sender Tentry Tmid Texit Receiver
| | | | |
| QUERY | | | |
+--------->| | | |
| | QUERY | |
| +-------------------->| |
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| | | | QUERY |
| | | +--------->|
| | | | RESERVE |
| | | |<---------+
| | RESERVE | |
| |<--------------------+ |
| RESERVE | | | |
|<---------+ | | |
| RESPONSE | | | |
+--------->| | | |
| | RESPONSE | |
| +-------------------->| |
| | | | RESPONSE |
| | | +--------->|
| | | | |
| | | | |
Figure 7: Receiver-initiated End-to-end Session with Pre-configured
Tunnel QoS Sessions
Since tunnel QoS signaling is not involved in pre-configured QoS
tunnels, Figure 6 and Figure 7 look as if the tunnel is a single
virtual link. The signaling path simply skips all tunnel
intermediate nodes. However, both Tentry and Texit need to deploy
NSIS-tunnel related functionalities described above, including acting
on the end-to-end NSIS signaling messages based on tunnel QoS status,
mapping end-to-end and tunnel QoS sessions, and correctly
encapsulating and decapsulating tunnel packets according to the
tunnel protocol and the configured tunnel flow ID.
6. NSIS Operation over Tunnels with Dynamically Created QoS Sessions
When there are no pre-configured tunnel QoS sessions, a tunnel can
apply the same NSIS QoS signaling mechanism used for the end-to-end
path to manage the QoS inside the tunnel. The tunnel NSIS signaling
involves only those NSIS nodes in the tunnel forwarding path. The
flow IDs for the tunnel signaling are based on tunnel header fields.
NSIS peer discovery messages inside the tunnel also distinguish
themselves using the tunnel header fields, which solves the problem
for tunnel intermediate NSIS nodes to intercept signaling messages as
described in Section 3.2.
When tunnel end-points dynamically create tunnel QoS sessions, they
need to determine whether the tunnel NSIS signaling is sender-
initiated or receiver-initiated. In order to reduce complexity, we
decide that the end-to-end session and the tunnel session should
share the same signaling initiation mode. Since the end-to-end
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session is the originator that causes the establishment of the tunnel
session, the tunnel session always follows the initiation mode of the
end-to-end session. Specifically, when the end-to-end session is
sender-initiated, the tunnel session should also be sender-initiated;
when the end-to-end session is receiver-initiated, the tunnel session
should also be receiver-initiated.
6.1. Conveying Tunnel Flow ID Between Tunnel End-points
Depending on what type of tunnel flow ID in Section 4.3 is used,
dynamically created tunnel QoS sessions may involve packet
encapsulation other than standard tunneling mechanisms. For example,
when a particular tunnel session inserts an additional UDP header for
its flow ID, that additional UDP header added by the NSIS-tunnel-
aware entry-point is not part of the standard tunnel encapsulation
process. In these cases, the NSIS-tunnel-aware exit-point needs to
be notified about the special encapsulation so it can perform correct
decapsulation by removing both the standard tunnel header and the
additional UDP header. The NSIS-tunnel-aware exit-point can learn
about the tunnel flow ID through the NSIS signaling process inside
the tunnel that creates the tunnel QoS sessions. However, it needs
to further understand that the specific tunnel QoS session is
associated with an end-to-end session and therefore needs to be
decapsulated based on the corresponding tunnel flow ID. This is
achieved by using one of the objects in QoS NSLP messages called
BOUND_SESSION_ID [I-D.ietf-nsis-qos-nslp]. When used for NSIS
signaling over tunnels, the BOUND_SESSION_ID object carries the
session ID of the corresponding tunnel session and a Binding Code of
value 0x01 indicating tunnel handling. The NSIS-tunnel-aware entry-
point includes this tunnel binding object in appropriate end-to-end
signaling messages. The NSIS-tunnel-aware exit-point that receives
this tunnel session binding object then records the association
between the tunnel QoS session and the end-to-end session. With this
association, the NSIS-tunnel-aware exit-point can perform correct
decapsulation for the data packets belonging to the end-to-end
session.
6.2. Sender-initiated Reservation
Sender Tentry Tmid Texit Receiver
| | | | |
| RESERVE | | | |
+--------->| | | |
| | RESERVE' | | |
| +=========>| | |
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| | | RESERVE' | |
| | +=========>| |
| | RESERVE | |
| | w/ BOUND_SESSION_ID | |
| +-------------------->| |
| | | RESPONSE'| |
| | |<=========+ |
| | | | RESERVE |
| | | +--------->|
| | RESPONSE'| | |
| |<=========+ | |
| | | | RESPONSE |
| | | |<---------+
| | RESPONSE | |
| |<--------------------+ |
| RESPONSE | | | |
|<---------+ | | |
| | | | |
| | | | |
Figure 8: Sender-initiated Reservation for both End-to-end and Tunnel
Signaling
Figure 8 shows the messaging sequence of how NSIS operates over IP
tunnels when both end-to-end session and tunnel session are sender-
initiated. Tunnel signaling messages are distinguished from end-to-
end messages by a prime symbol after the message name. The sender
first sends an end-to-end RESERVE message which arrives at Tentry.
Tentry chooses the tunnel flow ID, creates the tunnel session and
associates the end-to-end session with the tunnel session. Tentry
then sends a tunnel RESERVE' message matching the request of the end-
to-end session towards Texit to reserve tunnel resources. Tentry
also appends a tunnel BOUND_SESSION_ID object to the original RESERVE
message containing the session ID of the tunnel session and sends it
towards Texit using normal tunnel encapsulation.
The tunnel RESERVE' message is processed hop-by-hop inside the tunnel
for the flow identified by the chosen tunnel flow ID. When Texit
receives the tunnel RESERVE' message, a reservation state for the
tunnel session is created. Texit also sends a tunnel RESPONSE'
message to Tentry. On the other hand, the end-to-end RESERVE message
passes through the tunnel intermediate nodes (Tmid) just like other
tunneled packets. When Texit receives the end-to-end RESERVE
message, it notices the binding of a tunnel session and updates the
end-to-end RESERVE message based on the result of the tunnel session
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reservation. Then Texit removes the tunnel BOUND_SESSION_ID object
and forwards the end-to-end RESERVE message further along the path
towards the receiver. When the receiver receives the end-to-end
RESERVE message, it sends an end-to-end RESPONSE message back to the
sender.
6.3. Receiver-initiated Reservation
Figure 9 shows the messaging sequence of how NSIS signaling operates
over IP tunnels when both end-to-end and tunnel sessions are
receiver-initiated. Tentry first receives an end-to-end QUERY
message from the sender, it chooses the tunnel flow ID, creates the
tunnel session and sends a tunnel QUERY' message matching the request
of the end-to-end session towards Texit. Tentry also appends a
tunnel BOUND_SESSION_ID object containing the session ID of the
tunnel session to the original QUERY message and sends it toward
Texit using normal tunnel encapsulation.
The tunnel QUERY' message is processed hop-by-hop inside the tunnel
for the flow identified by the chosen tunnel flow ID. When Texit
receives the tunnel QUERY' message, it creates a reservation state
for the tunnel session without sending a tunnel RESERVE' message
immediately.
The end-to-end QUERY message passes along tunnel intermediate nodes
like other tunneled packets. When Texit receives the end-to-end
QUERY message, it notices the binding of a tunnel session and checks
the state information for the tunnel session. When the tunnel
session state is available, Texit updates the end-to-end QUERY
message with information from tunnel session state (e.g., QoS
availability in the tunnel), removes the tunnel BOUND_SESSION_ID
object and forwards the end-to-end QUERY message further along the
path.
Sender Tentry Tmid Texit Receiver
| | | | |
| QUERY | | | |
+--------->| | | |
| | QUERY' | | |
| +=========>| | |
| | | QUERY' | |
| | +=========>| |
| | QUERY | |
| | w/ BOUND_SESSION_ID | |
| +-------------------->| |
| | | | QUERY |
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| | | +--------->|
| | | | RESERVE |
| | | |<---------+
| | | RESERVE' | |
| | |<=========+ |
| | RESERVE' | | |
| |<=========+ | |
| | RESERVE | |
| |<--------------------+ |
| RESERVE | | | |
|<---------+ | | |
| | RESPONSE'| | |
| +=========>| | |
| | | RESPONSE'| |
| | +=========>| |
| RESPONSE | | | |
+--------->| | | |
| | RESPONSE | |
| +-------------------->| |
| | | | RESPONSE |
| | | +--------->|
| | | | |
| | | | |
Figure 9: Receiver-initiated Reservation for Both End-to-end and
Tunnel Signaling
When Texit receives the first end-to-end RESERVE message issued by
the receiver, it finds the reservation state of the tunnel session
and triggers a tunnel RESERVE' message for that session. Meanwhile
Texit forwards the end-to-end RESERVE message towards Tentry. When
Tentry receives the tunnel RESERVE' message, it creates the
reservation state for the tunnel session and sends a tunnel RESPONSE'
message back to Texit. When Tentry receives the end-to-end RESERVE
message, it updates the end-to-end RESERVE message with the result of
the corresponding tunnel session reservation. Then Tentry forwards
the end-to-end RESERVE message upstream toward the sender. When the
sender receives the end-to-end RESERVE message, it sends an end-to-
end RESPONSE message back to the receiver.
6.4. Timing Issues of End-to-end and Tunnel Signaling
NSIS operation over tunnels that dynamically create QoS sessions
involves two correlated but separate signaling sessions, the end-to-
end session and the corresponding tunnel session. The outcome of the
tunnel signaling session directly affects the outcome of the end-to-
end signaling session. Since the two signaling sessions overlap in
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time, there are circumstances when a tunnel end-point has to decide
whether it should proceed with the end-to-end signaling session while
it is still waiting for results of the tunnel session. Sequential
mode and parallel mode are two basic options for this problem. In
sequential mode, end-to-end signaling pauses when it is waiting for
results of tunnel signaling, and resumes upon receipt of the tunnel
signaling outcome. In parallel mode, end-to-end signaling continues
outside the tunnel while tunnel signaling is still in process and its
outcome is unknown. Our design in Section 6 adopts a hybrid mode in
order to strike a balance between speed and efficiency. The rule is
that end-to-end signaling should wait for tunnel signaling if it is
expecting information that is required to initiate the end-to-end
reservation; but end-to-end signaling does not need to wait for
tunnel signaling if the end-to-end QoS reservation is already in
progress.
An example of end-to-end signaling having to wait for tunnel
signaling outcome is the end-to-end QUERY message from Texit to the
receiver in Figure 9. That Query message needs to wait for the
QUERY' message about the tunnel QoS information and then be forwarded
toward the receiver. The tunnel QoS information learned from the
QUERY' message supplies important information needed to initiate the
end-to-end reservation. This timing rule ensures that the first end-
to-end RESERVE message originated from the receiver will have the
correct view of the whole path, both inside and outside the tunnel.
An example of end-to-end signaling not having to wait for tunnel
signaling outcome is a RESERVE message which is about to leave the
tunnel, such as the RESERVE message from Texit to the receiver in
Figure 8 and the RESERVE message from Tentry to sender in Figure 9.
Those RESERVE messages can be forwarded immediately even if the
tunnel QoS reservation outcome is still unknown. However, the tunnel
end-point should try to learn about results of the corresponding
tunnel session reservation either through proactive polling after a
specific amount of time, or before a refresh message is scheduled to
be sent. Once the tunnel session reservation information is
available, the tunnel end-point should immediately trigger an end-to-
end RESERVE message subject to the results of the tunnel reservation.
That is, if the tunnel reservation is successful, the message would
be a normal RESERVE refresh; otherwise, the RESERVE message should
indicate that some error has occurred in the reservation path.
7. NSIS-Tunnel Signaling Capability Discovery
As discussed in Section 6.1, when operating over a tunnel, NSIS-
tunnel-aware end-points may need to perform special encapsulation and
decapsulation such as inserting and removal of an extra UDP header.
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Therefore, before the NSIS-tunnel-aware end-point decides to initiate
such encapsulation, it needs to know whether the other entry-point is
also NSIS-tunnel-aware and thus capable of performing matching
decapsulation. This section defines a mechanism to enable this
capability discovery for tunnels using dynamically created tunnel QoS
sessions. For tunnels with pre-configured QoS sessions, an end-point
can learn the NSIS-tunnel capability information of the other end-
point during the pre-configuration process.
7.1. NODE_CHAR Object Format
A GIST NODE_CHAR object is defined to discover the NSIS-tunnel
handling capability of a tunnel end-point. The format of the
NODE_CHAR object follows the general object definition in GIST. The
object contains a fixed header specifying the object type and object
length, followed by the object value.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|A|B|r|r| Type |r|r|r|r| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|T| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: NODE_CHAR Object Format
Type: NODE_CHAR
Length: 1, measured in units of 32-bit word
Value: Value contains a single 'T' bit, indicating the node supports
the NSIS-tunnel handling mechanisms defined in this document. The
reserved bits in the value field can be used to signal other node
characteristics in the future.
The bits marked 'A' and 'B' define the desired behavior for objects
whose Type field is not recognized. If a node does not recognize the
NODE_CHAR object, the desired behavior is "Ignore". That is, the
object must be deleted and the rest of the message processed as
usual. This can be satisfied by setting 'AB' to '01' according to
Appendix A.2 of the GIST specification [I-D.ietf-nsis-ntlp].
7.2. Using NODE_CHAR Object
The NODE_CHAR object is included in a QUERY or RESERVE message by a
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tunnel end-point that needs to learn about the other end-point's NSIS
tunnel handling capability. If the receiving tunnel end-point is
indeed NSIS-tunnel-aware, it recognizes this object and knows that
the sending end-point is NSIS-tunnel-aware. The receiving tunnel
end-point places the same object in a RESPONSE message to inform the
sending end-point that it is also NSIS-tunnel-aware. Example
procedures of how to use the NODE_CHAR object over tunnels that
dynamically creates QoS sessions are further detailed below.
First, assume that both end-to-end and tunnel session are sender-
initiated (Section 6.2) and an NSIS-tunnel-aware Tentry wants to
discover the NSIS-tunnel capability of Texit before starting the
tunnel signaling. Tentry includes a Request Identification
Information (RII) object (see [I-D.ietf-nsis-qos-nslp]) and a
NODE_CHAR object with T bit set in the first end-to-end RESERVE
message sent to Texit. When Texit receives this RESERVE message, if
it is also NSIS-tunnel-aware, it learns that Tentry is NSIS-tunnel-
aware and includes the same object with T bit set in the following
end-to-end RESPONSE message sent back to Tentry. Otherwise, Texit
ignores the NODE_CHAR object. When Tentry receives the RESPONSE
message, it knows whether Texit is NSIS-tunnel-aware by checking the
existence of the NODE_CHAR object and its T bit. If both tunnel
endpoints are NSIS-tunnel-aware, the rest of the procedures follows
those defined in Section 6.2.
Second, assume that both end-to-end and tunnel sessions are receiver-
initiated (Section 6.3) and the NSIS-tunnel-aware Tentry wants to
discover the NSIS-tunnel capability of Texit before creating a tunnel
session. Tentry includes an RII object and a NODE_CHAR object with T
bit set in the first end-to-end QUERY message sent towards Texit. If
Texit is NSIS-tunnel-aware, it learns from the NODE_CHAR object that
Tentry is also NSIS-tunnel-aware. In the later end-to-end RESPONSE
message to this QUERY message, Texit includes a NODE_CHAR object with
T bit set to notify Tentry of its NSIS-tunnel capability. If both
tunnel end-points are NSIS-tunnel-aware, the rest of the procedures
follows those in Section 6.3.
8. IANA Considerations
This document defines a new object type called NODE_CHAR for GIST.
Its OType value needs to be assigned by IANA. The object format and
the setting of the extensibility bits are defined in Section 7.
9. Security Considerations
This draft does not raise new security threats. Security
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considerations for NSIS NTLP and QoS NSLP are discussed in
[I-D.ietf-nsis-ntlp] and [I-D.ietf-nsis-qos-nslp], respectively.
General threats for NSIS can be found in [RFC4081].
10. Acknowledgements
The authors would like to thank Tannes Tschofenig and other members
of the NSIS working group for comments to this work.
11. References
11.1. Normative References
[I-D.ietf-nsis-ntlp]
Schulzrinne, H. and M. Stiemerling, "GIST: General
Internet Signalling Transport", draft-ietf-nsis-ntlp-20
(work in progress), June 2009.
[I-D.ietf-nsis-qos-nslp]
Manner, J., Karagiannis, G., and A. McDonald, "NSLP for
Quality-of-Service Signaling", draft-ietf-nsis-qos-nslp-17
(work in progress), October 2009.
11.2. Informative References
[I-D.ietf-nsis-applicability-mobility-signaling]
Sanda, T., Fu, X., Jeong, S., Manner, J., and H.
Tschofenig, "Applicability Statement of NSIS Protocols in
Mobile Environments",
draft-ietf-nsis-applicability-mobility-signaling-13 (work
in progress), July 2009.
[I-D.ietf-nsis-nslp-natfw]
Stiemerling, M., Tschofenig, H., Aoun, C., and E. Davies,
"NAT/Firewall NSIS Signaling Layer Protocol (NSLP)",
draft-ietf-nsis-nslp-natfw-20 (work in progress),
November 2008.
[I-D.ietf-nsis-qspec]
Bader, A., Ash, G., Kappler, C., and D. Oran, "QoS NSLP
QSPEC Template", draft-ietf-nsis-qspec-22 (work in
progress), November 2009.
[RFC1701] Hanks, S., Li, T., Farinacci, D., and P. Traina, "Generic
Routing Encapsulation (GRE)", RFC 1701, October 1994.
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[RFC1702] Hanks, S., Li, T., Farinacci, D., and P. Traina, "Generic
Routing Encapsulation over IPv4 networks", RFC 1702,
October 1994.
[RFC1853] Simpson, W., "IP in IP Tunneling", RFC 1853, October 1995.
[RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003,
October 1996.
[RFC2004] Perkins, C., "Minimal Encapsulation within IP", RFC 2004,
October 1996.
[RFC2113] Katz, D., "IP Router Alert Option", RFC 2113,
February 1997.
[RFC2205] Braden, B., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", RFC 2205, September 1997.
[RFC2207] Berger, L. and T. O'Malley, "RSVP Extensions for IPSEC
Data Flows", RFC 2207, September 1997.
[RFC2401] Kent, S. and R. Atkinson, "Security Architecture for the
Internet Protocol", RFC 2401, November 1998.
[RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in
IPv6 Specification", RFC 2473, December 1998.
[RFC2711] Partridge, C. and A. Jackson, "IPv6 Router Alert Option",
RFC 2711, October 1999.
[RFC2746] Terzis, A., Krawczyk, J., Wroclawski, J., and L. Zhang,
"RSVP Operation Over IP Tunnels", RFC 2746, January 2000.
[RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
March 2000.
[RFC3220] Perkins, C., "IP Mobility Support for IPv4", RFC 3220,
January 2002.
[RFC3697] Rajahalme, J., Conta, A., Carpenter, B., and S. Deering,
"IPv6 Flow Label Specification", RFC 3697, March 2004.
[RFC4080] Hancock, R., Karagiannis, G., Loughney, J., and S. Van den
Bosch, "Next Steps in Signaling (NSIS): Framework",
RFC 4080, June 2005.
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[RFC4081] Tschofenig, H. and D. Kroeselberg, "Security Threats for
Next Steps in Signaling (NSIS)", RFC 4081, June 2005.
[RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms
for IPv6 Hosts and Routers", RFC 4213, October 2005.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, December 2005.
Authors' Addresses
Charles Shen
Columbia University
Department of Computer Science
1214 Amsterdam Avenue, MC 0401
New York, NY 10027
USA
Phone: +1 212 854 3109
Email: charles@cs.columbia.edu
Henning Schulzrinne
Columbia University
Department of Computer Science
1214 Amsterdam Avenue, MC 0401
New York, NY 10027
USA
Phone: +1 212 939 7004
Email: hgs@cs.columbia.edu
Sung-Hyuck Lee
SAMSUNG Advanced Institute of Technology
San 14-1, Nongseo-ri, Giheung-eup
Yongin-si, Gyeonggi-do 449-712
KOREA
Phone: +82 31 280 9552
Email: starsu.lee@samsung.com
Jong Ho Bang
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SAMSUNG Advanced Institute of Technology
San 14-1, Nongseo-ri, Giheung-eup
Yongin-si, Gyeonggi-do 449-712
KOREA
Phone: +82 31 280 9585
Email: jh0278.bang@samsung.com
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