MPLS Working Group Ken-ichi Nagami (Toshiba Corp.)
INTERNET DRAFT Noritoshi Demizu (NAIST)
Hiroshi Esaki (Toshiba Corp.)
Paul Doolan (Ennovate Networks)
August 1998
Expires February 1999
VCID Notification over ATM link
<draft-ietf-mpls-vcid-atm-01.txt>
Status of this memo
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Abstract
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 VC, it is
not possible to use them to identify a VC 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 VC. 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 VCs, the VPI and VCI labels are, in the general
case, rewritten with new values at every switch node through which
the VC passes and cannot be used to provide end to end
identification of a VC.
In the context of MPLS 'stream', 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 stream being 'bound' to labels. These bindings are
conveyed between peer LSRs by means of a Label Distribution Protocol
[LDP].
In order to apply MPLS to ATM links, we need some way to identify ATM
VCs 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 VC. 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 VCs (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 VC. 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 VC to which they refer. In contrast the out of
band procedures transmit the messages over some other connection
(than the VC 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.
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., GIT [GIT]), 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 VC newly established (by signalling or management) for
use as an label switched path (LSP) [FRAME], The procedure for VCID
notification between two nodes A and B is detailed below.
0. Node A establishes a VC 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 VC to Node B.
3. Node A establishes an association between the outgoing label
(VPI/VCI) for the VC and the VCID value.
4. Node B receives the message from the VC and establishes an
association between the VCID in the message and the incomming
label(VPI/VCI) for the VC.
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 VC.
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 VC 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 VC is created
or a new leaf is added to the VC.
First, the procedure for establishing the first VC is described.
1. The upstream node assigns a VCID value for the VC. When the VCID
value is already assigned to a VC, 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 VC used for a
label switched path. This message is transferred to all leaf
nodes.
3. The upstream node establishes an association between the outgoing
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 its 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 VC is used.
2. The upstream node sends a message which contains the VCID value
and the address of the upstream node through the VC 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 its 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 an ATM
signaling message and the message has a field which is not large
enough to carry a VCID value.
SETUP message of the 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
the 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 may
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 VC 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 VC 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.
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 associated with some other VC
between the upstream and downstream LSRs, that old VC is removed
from service.
4. After the upstream 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.
The procedure employed when a downstream LSR assigns a VCID is
as follows:
1. An upstream LSR establishes a VC 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.
3. The upstream LSR establishes the association between the VC with
the BLLI value and the VCID and sends an ACK message to the
downstream LSR. If the VCID is associated with some other VC
between the upstream and downstream LSRs, that old VC 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 VC
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 the 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.
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 the 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 ATM
signaling message and the message has a field (e.g., GIT [GIT]) which
is large enough to carry a VCID value. Message format is described in
[GIT].
Node A Node B
| |
|<-------------->|
| ATM Signaling |
| with VCID |
4 VCID Message Format
4.1 VCID Class Messages
VCID class messages are added to the LDP specification [LDP]. An LDP
VCID PDU consists of an LDP common header followed by one or more
objects. VCID PROPOSE inband message is sent as a null encapsulation
packet through a VC to be used as an LSP. A label value in the label
stack entry for VCID PROPOSE inband message is 4, that should be
added as a reserved label value to the section 2.1 of [ENCAPS].
Other messages are sent as TCP packets.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version | Msg Class | PDU Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LDP Identifier |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Msg Type | Reserved | Msg Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mandatory Objects |
| (Variable Length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Objects |
| (Variable Length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Version
One octet unsigned integer containing the version number of the
protocol. This version of the specification specifies protocol
Version = 0x01.
Msg Class
One octet integer defining the class of the LDP message.
VCID Class = 0x04
PDU Length
Two octet integer specifying the total length of this PDU in
bytes, excluding the common header.
LDP Identifier
Six octet field that uniquely identifiers the label space for
which this PDU applies. The first four octets encode an IP
address assigned to the LSR. This address should be the router-
id, also used in LSR-path-vector loop detection/prevention
objects. The last two octets identify a label space within the
LSR. For a platform-wide label space, these should both be
zero.
Reserved
This field is reserved. It must be set to zero on transmission
and must be ignored on receipt.
Msg Type
The MsgType field identifies the type of message. The following
discovery messages are supported:
VCID Propose inband Message = 0x01
VCID Propose Message = 0x02
VCID ACK Message = 0x02
VCID NACK Message = 0x03
Msg Length
Two octet integer specifying the total length of all objects
associated with the message type.
4.1.1 VCID Propose inband Message
This message is sent as a null encapsulation packet with a label
value 4 through a VC to be used as an LSP.
Mandatory Objects
At least one of each mandatory object with associated object headers.
+-----------------------+----------+
| MANDATORY OBJECT | Type |
+-----------------------+----------+
| VCID | 0x01 |
+-----------------------+----------+
| Address | 0x03 |
+-----------------------+----------+
4.1.2 VCID Propose Message
Mandatory Objects
At least one of each mandatory object with associated object headers.
+-----------------------+----------+
| MANDATORY OBJECT | Type |
+-----------------------+----------+
| VCID | 0x01 |
+-----------------------+----------+
| Temporary ID | 0x02 |
+-----------------------+----------+
4.1.3 VCID ACK Message
Mandatory Objects
At least one of each mandatory object with associated object headers.
+-----------------------+----------+
| MANDATORY OBJECT | Type |
+-----------------------+----------+
| VCID | 0x01 |
+-----------------------+----------+
4.1.4 VCID NACK Message
Mandatory Objects
At least one of each mandatory object with associated object headers.
+-----------------------+----------+
| MANDATORY OBJECT | Type |
+-----------------------+----------+
| VCID | 0x01 |
+-----------------------+----------+
4.2 VCID Class Objects
4.2.1 Object Header
All objects in a VCID message must begin with the following object
header. This header is the same as LDP specification.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Obj Type | Sub Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Object Type
VCID_OBJECT = 0x01
TEMPORARY_ID_OBJECT = 0x02
ADDRESS_OBJECT = 0x03
4.2.2 VCID Object
+-----------------------+-------+--------------------------+----------+
| OBJECT | Type | Subtype(s) | Length |
+-----------------------+-------+--------------------------+----------+
| VCID | 0x01 | 0x01 Default | 4 |
+-------------------------------+--------------------------+----------+
Subtype = 0x01 Default
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| VCID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4.2.3 Temporary ID Object
+-----------------------+-------+--------------------------+----------+
| OBJECT | Type | Subtype(s) | Length |
+-----------------------+-------+--------------------------+----------+
| Temporary ID | 0x02 | 0x01 BLLI | 1 |
+-------------------------------+--------------------------+----------+
Subtype = 0x01 Default
0
0 1 2 3 4 5 6 7 8
+-+-+-+-+-+-+-+-+-+
| BLLI |
+-+-+-+-+-+-+-+-+-+
4.2.4 Address Object
+-----------------------+-------+--------------------------+----------+
| OBJECT | Type | Subtype(s) | Length |
+-----------------------+-------+--------------------------+----------+
| Address | 0x02 | 0x01 Default | variable |
+-------------------------------+--------------------------+----------+
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address List Family |Source Address (variable length)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Address (variable length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Address Family
This 16 bit quantity contains a value from ADDRESS FAMILY NUM-
BERS in Assigned Numbers [RFC1700] that encodes the address family
that the network layer addresses in the Addresses field are from.
Addresses
Two addresses encoded according to the Address Family Field,
padded to a 16-bit boundary. First address is a source address of
this object. Second address is a destination address of this
object.
4.3 Mapping messages
4.3.1 Label Object
An VCID subtype is added to label object of an advertisment class
message in the LDP specification. This object is used for a label
mapping between SMD and VCID.
+-----------------------+-------+--------------------------+----------+
| OBJECT | Type | Subtype(s) | Length |
+-----------------------+-------+--------------------------+----------+
| Label | 0x03 | 0x03 VCID | 4 |
+-------------------------------+--------------------------+----------+
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 Shigeo Matsuzawa, Akiyoshi Mogi, Yasuhiro Katsube, Muneyoshi
Suzuki, George Swallow and 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
[FRAME] R. Callon, et al., "A Framework for Multiprotocol Label
Switching", draft-ietf-mpls-framework-02.txt, Nov. 1997
[GIT] 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-ietf-mpls-git-uus-assignment-00.txt, June 1998
[ENCAPS] E. Rossen, et al., "MPLS Label Stack Encoding",
draft-ietf-mpls-label-encaps-02.txt, July 1998
[rfc1700] J. Reynolds, J. Postel, "Assigned Numbers", RFC 1700, ISI,
October 1994
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
Graduate School of Information Science,
Nara Institute of Science and Technology
8916-5 Takayama, Ikoma, Nara 630-0101, Japan
Phone: +81-743-72-5348
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
Datatracker
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