Internet DRAFT - draft-nagami-mpls-vcid-atm
draft-nagami-mpls-vcid-atm
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Network Working Group Ken-ichi Nagami (Toshiba Corp.)
INTERNET DRAFT Noritoshi Demizu (SonyCSL/NAIST)
Hiroshi Esaki (Toshiba Corp.)
Paul Doolan (Ennovate Networks)
February 1998
Expires August 1998
VCID Notification over ATM link
<draft-nagami-mpls-vcid-atm-00.txt>
Status of this memo
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Abstract
Several label switching schemes have been proposed to integrate Layer
2 and Layer 3. The ATM Label Switching Router (ATM-LSR) is one of
the major applications of label switching. Because the ATM layer
labels (VPI and VCI) associated with a VC may change on each VC of
that VCC, it is not possible to use them to identify a VCC in label
binding messages. The concept of Virtual Connection Identifier (VCID)
is introduced to solve this problem. VCID has the same value at both
ends of a VCC and at all the intermediate ATM-LSRs through which the
VCC passes. This document specifies the procedures for the
communication of VCID values between neighboring ATM-LSRs that must
occur in order to ensure this property.
1. Introduction
Several label switching schemes have been proposed to integrate Layer
2 and Layer 3. The ATM Label Switching Router (ATM-LSR) is one of the
major applications of label switching.
In the case of ATM VCCs, the VPI and VCI labels are, in the general
case, rewritten with new values at every switch node through which
the VCC passes and cannot be used to provide end to end
identification of a VCC.
In the context of MPLS 'flows', which are classes of packets that
have some common charachteristic that may be deduced by examination
of the layer 3 header in the packets, are bound to layer 2 'labels'.
We speak of flows being 'bound' to l abels. These bindings are
conveyed between peer LSRs by means of a Label Distributi on Protocol
[LDP].
In order to apply MPLS to ATM links, we need some way to identify ATM
VCCs in LDP binding messages. In [VCID], an identifier called a
Virtual Connection ID (VCID) is introduced. VCID has the same value
at both ends of a VCC. This document specifies the procedures for
the communication of VCID values between neighboring ATM-LSRs that
must occur in order to ensure this property.
2. Overview of VCID Notification Procedures
2.1 VCID Notification procedures
The ATM has several types of VCCs (transparent point-to-point
link/VP/PVC/SVC). A transparent point-to-point link is defined as one
that has the same VPI/VCI label at both ends of a VCC. For example,
two nodes are directly connected (i.e., without intervening ATM
switches) or are connected through a VP with the same VPI value at
both ends of the VP.
There are two broad categories of VCID notification procedures;
inband and out of band. The categorisation refers to the connection
over which the messages of the VCID notification procedure are
forwarded. In the case of the inband procedures, those messages are
forwarded over the VCC to which they refer. In contrast the out of
band procedures transmit the messages over some other connection
(than the VCC to which they refer).
We list below the various types of link and briefly mention the VCID
notification procedures employed and the rational for that
choice. The procedures themselves are discussed in detail in later
sections.
Transparent point-to-point link : no VCID notification
VCID notification procedure is not necessary because the label
(i.e., VPI/VCI) is the same at each end of the VC.
VP : inband notification (as a default mechanism)
- Inband notification
VCID notification is needed because the VPI at each end of the VC
may not be the same. Inband VCID notification [VCID] is used in
this case.
- No notification
If a node has only one VP to a neighboring node, VCID notification
procedure is not mandatory. The VCI can be used as the VCID. This
is because the VCI value is the same at each end of the VP.
[Note] For easier implementation, using inband notification even
in the case of a single VP is recommended.
PVC : inband notification
Inband VCID notification [VCID] is used in this case because the
labels at each end of the VC may not be the same.
SVC : there are three possibilities
- Out of band notification
If a signaling message has a field which is large enough to carry
a VCID value (e.g., UUS [UUS]), then the VCID is carried directly
in it.
- Outband notification using a small-sized field
If a signaling message has a field which is not large enough to
carry a VCID value, this procedure is used.
- Inband notification
If a signaling message can not carry user information, this
procedure is used.
When an LSP is a point-to-multipoint VC and an ATM switch in an
LSR is not capable of VC merge, it may cause problems in
performance and quality of service. When the LSR wants to add a
new leaf to the LSP, it needs to split the active LSP temporarily
to send an inband notification message.
2.2 VCID Assignment
A VCID value is assigned by either an upstream node or a downstream
node depending on the type of VC. For a point-to-point VC, either
the upstream node or the downstream node could assign a VCID
value. For a point-to-multipoint VC, only an upstream (root) node can
assign a VCID value.
3. VCID Notification Procedures
3.1 Inband Notification Procedures
3.1.1 Inband Notification for Point-to-point VC
VCID notification is performed by transmitting a control message
through the VCC newly established (by signalling or management) for
use as an label switched path (LSP) [ARCH], The procedure for VCID
notification between two nodes A and B is detailed below.
0. Node A establishes a VCC to the destination LSR B. (by signalling
or management)
1. Node A selects a VCID value.
2. Node A sends a message which contains the VCID value through the
newly established VCC to Node B.
3. Node A establishes an association between the label for the VC and
the VCID value.
4. Node B receives the message from the VCC and establishes an
association between the VCID in the message and that VCC.
5. Node B sends an ACK message to node A.
6. After Node A receives the ACK message, node A and node B both
associate the VCID with the same VCC.
Node A Node B
| |
|--------------->|
| VCID |
| |
|<---------------|
| ACK |
3.1.2 Inband notification for point-to-multipoint VC
VCID notification is performed by sending a control message through
the VCC to be used as an LSP. The upstream node must assign the VCID
value, the procedure by which it notifies the downstream node of that
value is given below. The procedure is used when a new VCC is created
or a new leaf is added to the VCC.
First, the procedure for establishing the first VC is described.
1. The upstream node assigns a VCID value for the VCC. When the VCID
value is already assigned to a VCC, it is used for VCID.
2. The upstream node sends a message which contains the VCID value
and the address of the upstream node through the VCC used for a
label switched path. This message is transferred to all leaf
nodes.
3. The upstream node establishes an association between the label for
the VC and the VCID value.
4. The downstream nodes receiving the message check the address of
the upstream node. If the address is not the same network prefix
as own address, the message is discarded. Otherwise, the
downstream nodes establish an association between the VCID in the
message and the VC from which the message is received.
5. The downstream nodes send an ACK message to the upstream node.
6. After the upstream node receives the ACK messages, the upstream
node and the downstream nodes share the VCID.
Upstream Downstream 1 Downstream 2
| | |
|-----------+--->| |
| VCID +------------------->|
| | |
|<---------------| |
| ACK | |
|<-------------------------------|
| ACK |
Second, the procedure for adding a leaf to the existing
point-to-multipoint VC is described.
0. The upstream node adds the downstream node, using the ATM
signaling.
1. The VCID value which already assigned to the VCC is used.
2. The upstream node sends a message which contains the VCID value
and the address of the upstream node through the VCC used for a
label switched path. This message is transferred to all leaf
nodes.
3. The downstream nodes receiving the message check the address of
the upstream node. If the address is not the same network prefix
as own address, the message is discarded. Otherwise, the
downstream nodes establish an association between the VCID in the
message and the VC from which the message is received.
4. After the upstream node receives the ACK messages, the upstream
node and the downstream nodes share the VCID.
3.2 Outband Notification using a small-sized field
This method can be applied when a VC is established using a signaling
message and the message has a field which is not large enough to
carry a VCID value.
The signaling SETUP message of ATM Forum UNI 3.1/4.0 has a 7-bit
mandatory field for the user. This is a user specific field in the
Layer 3 protocol field in the BLLI IE (Broadband Low Layer
Information Information Element).
The BLLI value is used as a temporary identifier for a VC during a
VCID notification procedure. This mechanism is defined as "Outband
Notification using a small-sized field" described in [VCID]. The BLLI
value of a new VC must not be assigned to other VCs during the
procedure to avoid identifier conflict. When the association among
the BLLI value, a VCID value, and the corresponding VC is
established, the BLLI value can be reused for a new VC. VCID values
can be assigned independently from BLLI values.
Node A Node B
| |
|<-------------->|
| ATM Signaling |
| with BLLI |
| |
|--------------->|
| BLLI & VCID |
| |
|<---------------|
| ACK |
A point-to-multipoint VC can also be established using ADD_PARTY of
ATM Forum Signaling. ADD_PARTY adds a new VC leaf to an existing VC
or an existing VC tree. In this procedure, the BLLI value of
ADD_PARTY has to be the same value as that used to establish the
first point-to-point VC of the tree. The same BLLI value can be used
in different VC trees only when these VC trees can not add a leaf at
the same time. As a result, the BLLI value used in the signaling must
be determined by the root node of the multicast tree.
[note]
BLLI value is unique at the sender node. But BLLI value is not
unique at the reciever node because multiple sender nodes allocate
the same BLLI value. So, the receiver node must recognize BLLI
value and the sender address. ATM Signaling messages(SETUP and
ADD_PARTY) carry both the BLLI and the sender ATM address. The
receiver node can realize which node sends the BLLI message.
3.2.1 Outband notification using a small-sized field for point-to-point VC
This subsection describes procedures for establishing a VCC and for
notification of its VCID between neighboring LSRs for unicast
traffic. VC pool [VCPOOL] can be applied.
For point-to-point VC, either an upstream LSR or a downstream LSR can
allocate a VCID for a new VC.
The procedure employed when the upstream LSR assigns a VCID is as
follows.
1. An upstream LSR establishes a VCC to the downstream LSR using ATM
signaling and supplies a value in the BLLI field that it is not
currently using for any other (incomplete) VCID notification
transaction with this peer.
2. The upstream LSR notifies the downstream LSR of the association
between the BLLI and VCID values. The precise form of the message
used is outside the scope of this document but it could be
dedicated to this purpose or a modified LDP BIND message.
3. The downstream LSR establishes the association between the VCC
with the BLLI value and the VCID and sends an ACK message to the
upstream LSR. If the VCID is associated with some other VCC
between the upstream and downstream LSRs, that old VCC is removed
from service.
4. After the upstream LSR receives the ACK message, it establishes
the association between the VCC and the VCID. The VCC is ready to
be used. At this time the BLLI value employed in this transaction
is free for reuse.
The procedure employed when a downstream LSR assigns a VCID is
as follows:
1. An upstream LSR establishes a VCC by ATM signaling between the
downstream LSR with a unique BLLI value at this time.
2. The downstream LSR notifies the upstream LSR of a paired BLLI
value and VCID using a message dedicated for this purpose or
together within a BIND message.
3. The upstream LSR establishes the association between the VCC with
the BLLI value and the VCID and sends an ACK message to the
downstream LSR. If the VCID is associated with some other VCC
between the upstream and downstream LSRs, that old VCC is removed
from service.
4. After the downstream LSR receives the ACK message, it establishes
the association between the VC and the VCID. The VC is ready to
be used.At this time the BLLI value employed in this transaction
is free for reuse.
3.2.2 Outband notification using a small-sized field
for point-to-multipoint VC
This subsection describes procedures for establishing the first VC
for a multicast tree and for adding a new VC leaf to an existing VCC
tree including the notification of its VCID for a multicast stream
using point-to-multipoint VCs.
In this procedure, an upstream LSR determines both the VCID and BLLI
value in the multicast case. The reason that the BLLI value is
determined by an upstream LSR is described above.
First, the procedure for establishing the first VC is described.
1. An upstream LSR establishes a VC by ATM Forum Signaling between
the downstream LSR with a unique BLLI value at this time.
2. The upstream LSR notifies the downstream LSR of a paired BLLI
value and VCID using a message dedicated for this purpose or
together within a BIND message.
3. The downstream LSR establishes the association between the VC with
the BLLI value and the VCID and sends an ACK message to the
upstream LSR. If the VCID is used by some other VC between the
upstream and downstream LSRs, the old VC is discarded.
4. After the upstream LSR receives the ACK message, the VC is ready
to be used and the BLLI value can be used for another VC.
Second, the procedure for adding a leaf to the existing
point-to-multipoint VC is described.
1. The upstream LSR establishes a VC by ATM Forum Signaling between
its downstream LSR with the BLLI value that was used during the
first signaling procedure. If another VC is using the BLLI value
at the same time, the upstream waits for the completion of the
signaling procedure that is using this BLLI value.
2. Go to step 2 of the procedure for the first VC.
3.3 Outband notification
This method can be applied when a VC is established using a signaling
message and the message has a field (e.g., UUS [UUS]) which is large
enough to carry a VCID value.
Node A Node B
| |
|<-------------->|
| ATM Signaling |
| with VCID |
Security Considerations
Security issues are not discussed in this document.
Intellectual Property Considerations
Toshiba Corporation and Ennovate Networks may seek patent or other
intellectual property protection for some of the aspects of the
technology discussed in this document. If any standards arising from
this document are or become protected by one or more patents assigned
to Toshiba Corporation, Toshiba intends to license them on reasonable
and non- discriminatory terms.
Acknowledgments
The authors would like to acknowledge the valuable technical comments
of the members of the LAST-WG of the WIDE Project.
References
[VCID] N. Demizu, et al., "VCID: Virtual Connection Identifier",
draft-demizu-mpls-vcid-01.txt, Oct. 1997
[VCPOOL] N. Demizu, et al., "VC pool",
draft-demizu-mpls-vcpool-00.txt, Oct. 1997
[ARCH] R. Callon, et al., "A Framework for Multiprotocol Label
Switching", draft-ietf-mpls-framework-02.txt, Nov. 1997
[UUS] M. Suzuki, "The Assignment of the Information Field and
Protocol Identifier in the Q.2941 Generic Identifier and Q.2957
User-to-user Signaling for the Internet Protocol",
draft-suzuki-git-uus-assignment-00.txt, Nov. 1997
Authors Information
Ken-ichi Nagami
R&D Center, Toshiba Corporation,
1 Komukai-Toshiba-cho, Saiwai-ku,
Kawasaki, 210, Japan
Phone: +81-44-549-2231
Email: nagami@isl.rdc.toshiba.co.jp
Noritoshi Demizu
Sony Computer Science Laboratory, Inc.
Takanawa Muse Bldg.
3-14-13, Higashigotanda,
Shinagawa-ku, Tokyo, 141 Japan
Phone: +81-3-5448-4380
E-mail: demizu@csl.sony.co.jp
E-mail: nori-d@is.aist-nara.ac.jp
Hiroshi Esaki
Computer and Network Division,
Toshiba Corporation,
1-1-1 Shibaura,
Minato-ku, 105-01, Japan
Email: hiroshi@isl.rdc.toshiba.co.jp
Paul Doolan
Ennovate Networks
330 Codman Hill Road
Boxborough, MA
Phone: 978-263-2002 x103
Email: pdoolan@ennovatenetworks.com