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IP over ATM WG M. Perez, F. Liaw, D. Grossman,
Internet-Draft A. Mankin, E. Hoffman, A. Malis
Expires September 6, 1994 April 1994
<draft-ietf-atm-sig-00.txt>
ATM Signaling Support for IP over ATM
1. Status of this Memo
This memo is an internet draft. Internet Drafts are working documents
of the Internet Engineering Task Force (IETF), its Areas, and its
Working Groups. Note that other groups may also distribute working
documents as Internet Drafts.
Internet Drafts are draft documents valid for a maximum of six
months. Internet Drafts may be updated, replaced, or obsoleted by
other documents at any time. It is not appropriate to use Internet
Drafts as reference material or to cite them other than as a "working
draft" or "work in progress". Please check the lid-abstracts.txt
listing contained in the internet-drafts shadow directories on
nic.ddn.mil, nnsc.nsf.net, nic.nordu.net, ftp.nisc.src.com, or
munnari.oz.au to learn the current status of any Internet Draft.
2. Abstract
This memo describes how implementations of IP over ATM should use ATM
call control signaling procedures to establish and release ATM
connections. It is intended to serve implementations of IP and
multiprotocol interconnection over ATM that use ATM signaling as
specified in the ATM Forum User-Network Interface (UNI) Specification
Version 3.0 [ATMF93]. In particular, during development of this
memo, the IP over ATM working group has focused its activities on the
Classical IP over ATM model, as described in RFC 1577 [LAUB94];
therefore particular attention is given to support RFC 1577.
This document is an implementors guide intended to foster
interoperability among RFC 1577, RFC 1483, and UNI ATM signaling. It
serves as an intermediary role between IP and ATM Call control
signaling which establishes and releases ATM calls/connections on
behalf of IP. Specifically, this memo details the coding of ATM
signaling messages when used to support IP.
This memo applies to IP hosts and routers which are also ATM
endsystems. It assumes ATM networks that completely implement the ATM
Forum UNI Specification Verion 3.0.
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Note: An erratum to the UNI 3.0 specification has been produced by
the ATM Forum Technical Committee, largely for reasons of alignment
with Recommendation Q.2931. The erratum will be published as the UNI
3.1 Specification in the summer of 1994. This memo assumes the
changes to the specification indicated in the erratum and attemps to
point out the relevant incompatibilities with UNI 3.0.
3. Overview
In a Switched Virtual Connection (SVC) environment, ATM virtual
channel connections (VCCs) are dynamically established and released
as needed. This is accomplished using the ATM call/connection control
signaling protocol, which operates between ATM endsystems and the ATM
network. The signaling entities use the signaling protocol to
establish and release calls (association between ATM endpoints) and
connections (VCCs). Signaling procedures include the use of
addressing to locate ATM endpoints and allocation of resource in the
network for the connection. It also provides indication and
negotiation between ATM endpoints for selection of end-to-end
protocols and their parameter. This memo describes how the signaling
protocol is used in support of IP over ATM, and, in particular, the
information exchanged in the signaling protocol to effect this
support.
IP address to ATM address resolution and routing issue are not in the
scope of this I-D, and is treated as part of IP in figure 1. These
issue depend on the subnet and end-to-end networking model being
used. A taxonomy of subnet and end-to-end networking models is pro-
vided in [COLE94]. The simplest case is the Classical IP over ATM
model described in RFC 1577.
+--------------+ +------+ +----------+
| | | |<--->| IP / ARP |
| |<--->| This | | RFC 1577 |
| ATM | | I-D | +----------+
| signalling | | |<--->| RFC 1483 |
| | +------+ +----------+
| | -------------> | AAL 5 |
| | +----------+
| | -------------> | ATM |
+--------------+ +----------+
Figure 1.
Relationship of this I-D to IP, RFC 1483,
ATM signalling, ATM and AAL5
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4. Use of protocol procedures
The following requirements are motivated to provide implementation
guidelines on how multiple ATM connections between peer systems
should be managed, to prevent connection thrashing and related
problems.
The owner of an existing VCC is defined to be the entity within the
ATM endsystem that establishes the connection. An ATM endsystem may
establish an ATM call when it has a datagram to send and either there
is no existing VCC that it can use for this purpose, it chooses not
to use an existing VCC, (e.g., for reasons of route optimization or
quality of service), or the VCC owner does not allow sharing.
When two ATM endsystems run multiple protocols, an ATM connection may
be shared among two or more datagram protocol entities, as long as
the VCC owner allows sharing, as well as if the encapsulation allows
proper multiplexing and demultiplexing, (i.e., the LLC/SNAP
encapsulation or RFC 1490 over FRSSCS). This indication of sharing a
VCC MAY be by configuration or via an API. Similarly, the Internet
layer supports multiplexing of multiple end-to-end transport session.
To properly detect idle connection while sharing a VCC among more
than one higher layer protocol entities, the ATM endsystem SHALL
monitor the traffic at the lowest multiplexing layer.
An ATMARP server or client may establish an ATM call when it has a
datagram to send and either there is no existing VCC that it can use
for this purpose, it chooses not to use an existing VCC, or the
owner of the VCC does not allow sharing. Note that there might be
VCCs to the destination which are used for IP, but an ARP server
might prefer to use a separate VCC for ARP only. The ATMARP server or
client may maintain or release the call as specified in RFC1577.
However, if the VCC is shared among several protocol entities, the
ATMARP client or server SHALL not disconnect the call as suggested in
RFC1577.
Systems MUST be able to support multiple connections between peer
systems (without regard to which peer system initiated each
connection). They MAY be configured to only allow one such
connection at a time.
If a receiver accepts more than one call from a single source, that
receiver MUST then accept incoming PDUs on the additional
connection(s), and MAY transmit on the additional connections.
Receivers SHOULD NOT accept the incoming call, only to close the
connection or ignore PDUs from the connection.
Because opening multiple connections is specifically allowed,
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algorithms to prevent connection call collision, such as the one
found in section 8.4.3.5 of ISO/IEC 8473 [ISO8473], MUST NOT be
implemented.
While allowing multiple connections is specifically desired and
allowed, implementations MAY choose (by configuration) to permit only
a single connection to some destinations. Only in such a case, if a
colliding incoming call is received while a call request is pending,
the incoming call shall be rejected. Note that this may result in a
failure to establish a connection. In such a case, each system shall
wait at least a configurable collision retry time in the range 1 to
10 seconds before retrying. Systems SHOULD add a random increment,
with exponential backoff.
Either endsystem MAY close a connection. If the connection is closed
or reset while a datagram is being transmitted, the datagram is lost.
Systems SHOULD be able to configure a minimum holding time for
connections to remain open as long as the endpoints are up. (Note
that holding time, the time the connection has been open, differs
from idle time.) A suggested default value for the minimum holding
time is 60 seconds.
Because some public networks may charge for connection holding time,
and connections may be a scarce resource in some networks or
endsystems, each system implementing a Public ATM UNI interface MUST
support the use of a configurable inactivity timer to clear
connections that are idle for some period of time. The timer's range
SHOULD include a range from a small number of minutes to "infinite",
and the default value SHOULD be "infinite". Systems which only
implement a Private ATM UNI interface SHOULD, but are not required
to, support the inactivity timer. If implemented, the inactivity
timer shall monitor traffic of both receiving and transmiting
activities.
5. Brief Overview of UNI Call Setup Signaling Procedures and Messages
This section provides a summary of point-to-point signaling
procedures. Readers are referred to [ATMF93] and [Q2931].
UNI signaling messages used for point-to-point call connection
control are the following:
Call Setup Call Release
---------- ------------
SETUP RELEASE
CALL PROCEEDING RELEASE COMPLETE
CONNECT
CONNECT ACKNOWLEDGE
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An ATM endpoint initiates a call request by sending a SETUP message
to the network. The network processes the call request to determine
if the call can be progressed. If so, the network indicates the value
of the newly allocated VPI/VCI in its first response to the the SETUP
message, which may either be a CALL PROCEEDING or CONNECT message. If
a call cannot be accepted, by the network or destination ATM
endpoint, a RELEASE COMPLETE is sent. At the destination ATM
endpoint, the network offers the call using the SETUP message. If
the destination endpoint is able to accept the call, it responds with
a CONNECT message; otherwise, it sends a RELEASE COMPLETE message.
Release can be initiated by either endpoint or (rarely) by the
network. When an endpoint wishes to release a call, it sends a
RELEASE message to the network. The network responds with a RELEASE
COMPLETE message, frees up resources associated with the call, and
initiates clearing toward the other endpoint. The network initiates
clearing by sending a RELEASE message to the ATM endpoint, which
reponds by sending a RELEASE COMPLETE message. Upon receipt of the
RELEASE COMPLETE message, the network frees any resources associated
with the call.
6. Overview of call establishment message content
Signalling messages are structured to contain mandatory and optional
variable length information elements (IEs). IEs are further
subdivided into octet groups, which in turn are divided into fields.
IEs contain information related to the call, which may be relevant to
the network, the peer endpoint or both. Selection of optional IEs
and the content of mandatory and optional IEs in call establishment
message determines the parties to and nature of the communication
over the ATM connection. For example, the call establishment message
for a call which will be used for constant bitrate video over AAL 1
will have different contents than a call which will be used for IP
over AAL 5.
A SETUP message which establishes an ATM connection to be used for IP
and multiprotocol interconnection calls SHALL contain the following
IE:
AAL Parameters
ATM Traffic Descriptor (ATM User Cell Rate)
Broadband Bearer Capability
Broadband Low Layer Information
QoS Parameter
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Called Party Number
Calling Party Number
and may, under certain circumstance contain the following IEs :
Calling Party Subaddress
Called Party Subaddress
Transit Network Selection
In UNI 3.0 the AAL Parameters and the Broadband Low Layer Information
IEs are optional in a SETUP message. However, in support of IP over
ATM these two IEs MUST be included. Annex A shows an example SETUP
message coded in the manner indicated in this draft.
7. Information Elements with Endpoint to Endpoint Significance
This section describes the coding of, and procedures surrounding,
information elements in a SETUP message with significance only to the
endpoints of an ATM call supporting IP and multiprotocol operation.
7.1. ATM Adaption Layer Parameters
The AAL Parameters IE (see section 5.4.5.5 and Annex F of [ATMF93])
carries information about the ATM Adaption Layer (AAL) to be used on
the connection. RFC 1483 specifies encapsulation of IP over AAL 5.
Thus, AAL 5 SHALL be indicated in the "AAL type" field.
Coding and procedure related to the Forward and Backward Maximum
CPCS-SDU Size fields are discussed in [ATKI94].
Streaming mode is not applicable to IP and multiprotocol interconnect
over AAL5. The mode field SHOULD be omitted from the AAL Parameters
IE. If present it SHALL be set to "message" mode and SHALL be
ignored by the destination endsystem.
Ordinarily, no Service Specific Convergence Sublayer (SSCS) will be
used for multiprotocol interconnect over AAL5. Therefore, the SSCS
Type field SHOULD be absent or, if present, coded to Null SSCSS. The
exception will occur in the event that the network provide
interworking between ATM and Frame Relay. In this case, the ATM
endsystem will receive a SETUP or CONNECT message containing an AAL
Parameters IE with the SSCS Type field coded as Frame relay SSCSS.
The call SHALL be cleared with cause #93, AAL Parameters not
supported unless the ATM endsystem supports RFC 1490 encapsulation
over FRSSCS, and a Broadband Low-layer Information IE is coded to
indicate RFC 1490 encapsulation (see below).
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7.2. Broadband Low Layer Information
Selection of an encapsulation to support IP and multiprotocol
interconnection over an ATM VCC is done using the Broadband Low Layer
Information (B- LLI) IE, along with the AAL Parameters IE, and the
B-LLI negotiation procedure.
Protocol encapsulation for multiprotocol interconnection over ATM and
AAL5 are specified in RFC 1483. Three encapsulation are provided;
these are:
(a) LLC/SNAP encapsulation
(b) VC-multiplexing (null encapsulation)
(c) Use of RFC 1490 over the Frame Relay Service Specific Sublayer
(FRSSCS)
The example codings for the B-LLI IE provided in Appendix D of the
ATM Forum UNI 3.0 specification were selected to correspond to the
RFC 1483 encapsulations.
RFC 1577 specifies LLC/SNAP as the default encapsulation. Therefore
LLC encapsulation MUST be indicated in the B-LLI as shown in figure
D.3.1 of [ATMF93]. Signaling indication of other encapsulations is
discussed in next section. Note that in this case only LLC is
indicated in the B-LLI. It is up to the LLC layer to look into the
encapsulation header of the packet. If the SNAP header indicates IP,
it is the LLC layer's job to hand the packet up to IP.
7.2.1. Encapsulation negotiation
The call/connection control signaling protocols include a mechanism
to support negotiation of encapsulation for endsystems that support
more than one. This section describes the procedures for negotiation
of an encapsulation.
As stated in the previous section, this I-D requires that hosts and
router which are ATM endsystems implement LLC/SNAP encapsulation.
Nevertheless, RFC 1483 also specifies VC-multiplexing and recognizes
use of RFC 1490 over FRSSCS. VC-multiplexing SHOULD be implemented to
achieve maximum interoperability. Implementation of RFC 1490
encapsulation over FRSSCS is also recommended for interworking with
Frame Relay networks.
The B-LLI negotiation procedures (see Annex C of [ATMF93]) are
initiated by the calling ATM endsystem by including up to three
instance of the B-LLI IE in the SETUP message in descending order of
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preference (following the rule for repeating IE in section 5.4.5.1 of
[ATMF93]).
The following is the list of the four possible combinations that B-
LLI IE instances may be included in the SETUP message. Each instance
is referred to by its encapsulation name as it appears in RFC 1483,
and corresponding section labels from ATM Forum UNI 3.0
sepcification.
a) LLC/SNAP encapsulation (D.3.1)
In this case, the calling ATM endsystem can only send and receive
packets preceded by an LLC/SNAP identification.
b) VC-multiplexing (D.3.2) and LLC/SNAP (D.3.1)
The calling ATM endsystem prefers to use VC multiplexing, but is
willing to agree to use LLC/SNAP encapsulation instead, if the called
ATM endsytem only supports LLC/SNAP.
c) LLC/SNAP (D.3.1) and VC-multiplexing (D.3.2)
The calling ATM endsystem prefers to use LLC/SNAP encapsulation,
but is willing to agree to use VC multiplexing instead, if the called
ATM endsystem only supports VC multiplexing.
d) RFC 1490 encapsulation over FRSSCS (D.3.2, omitting octets 7a
and 7b and MUST have FR-SSCS in SSCS type of AAL Parameters IE.)
The calling ATM endsystem can only send and receive packets using
RFC 1490 over FRSSCS. Use of RFC 1490 encapsulation presently cannot
be negotiated as an alternative to LLC encapsulation or VC-
multiplexing because the procedures for frame relay to ATM signalling
interworking have not yet been specified by ITU-T and the ATM Forum.
If the B-LLI IE is encoded to indicate RFC 1490 encapsulation, the
SSCS type field of the AAL Parameters IE SHALL coded to indicate
FRSSCS. Note that the AAL Parameters IE can not be coded to indicate
both NULL and FR-SSCS and neither LLC encapsulation nor VC-
multiplexing will be interoperable when used over FR-SSCS.
The called ATM endsystem SHALL select the encapsulation method it is
able to support from the B-LLI IE present in SETUP message. If it
supports more than one of the encapsulations indicated in the SETUP
message, it MUST select the one which appears first in the SETUP
message. The called ATM endsystem then includes the B-LLI IE content
corresponding to the selected encapsulation in the CONNECT message.
If the called endsystem does not support any encapsulation indicated
in the incoming SETUP message, it SHALL clear the call with cause
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#88, incompatible destination. If the received SETUP message does
not include the B-LLI IE, the call SHALL be cleared with cause #21,
"call rejected", with diagnostics indicating rejection reason =
information element missing and the B-LLI IE identifier. As
described in Annex C of [ATMF93], if the calling ATM endpoint
receives a CONNECT message that does not contain a B-LLI IE, it SHALL
assume the encapsulation indicated in the first BLLI IE that it
included in the SETUP message.
7.2.2. Framework for Protocol Layering
The support of connectionless services from a connection oriented
link layer exposes general problems of connection management,
specifically the problems of connection acceptance, assignment of
quality of service, and connection shutdown. For a connection to be
associated with the correct protocol on the called host, it is
necessary for information about one or more layers of protocol
identification to be associated with a connection "management entity"
or "endpoint". This association is what we call a binding in this
draft. In this section we attempt to describe a framework for a
usable binding or service architecture given the available IEs in the
ATM call control messages.
It is important to distinguish between two basic uses of protocol
identification elements present in the UNI setup message. The first
is the description of the protocol encapsulation that will be used on
the data packet over the virtual connection, the second is the entity
that will be responsible for managing the call. All protocols present
in various IEs should be used to encapsulate the call, but the most
specific, or highest, layer specified should manage the call. This
defines a hierarchy of services and provides a framework for
applications, including LLC and IP, to terminate calls. The hierarchy
provides a clear mechanism for support of higher level protocol and
application bindings, when their use and specification is defined in
the appropriate standards bodies.
The B-LLI is the only information element currently available in UNI
3.0 for designating the application endpoint. It contains codepoints,
which describe layer 2 and layer 3 protocols entities associated with
the call. There are other information elements under consideration in
the ATM Forum and ITU, which could come to play a significant role in
the description of application to connection binding, but their use
is not currently sanctioned by the Forum, and they are not part of
the framework described by RFC1577. They include B-HLI, for
containing information for a higher layer protocol, Network Layer
Information (NLI) to contain information for the network layer, and
UUI, which is meant to carry information for use by the top level
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application.
In general, it would be desirable to allow data packets to be stored
directly into applications address space after connection is
established. This is possible only if we have both forward and
backward encapsulation indication in the signaling message.
To support multiprotocol encapsulation, the LLC protocol management
entity should accept all connections directed specifically to it. For
each connection that is terminated at LLC, all protocols that are
intended to be supported by this host through that interface should
be made available. Termination of the call is at the discretion of
the LLC connection management entity, based on the information it has
available to it, specifically the perceived packet traffic and
administrative policies of the host.
VC-multiplexed IP is specified by using only the layer 3 identifier
in B-LLI using an ISO-TR-9577 protocol codepoint. Since no layer 2
is specified, frames produced by AAL processing will be given
directly to IP. Since IP is highest specified protocol, it will be
responsible for managing the connection.
8. Information Elements with Significance to the ATM Network
This section describes the coding of, and procedures surrounding,
information elements with significance to the ATM network, as well as
the endpoints of an ATM call supporting multiprotocol operation.
The standards, implementation agreements, research and experience
surrounding such issues as traffic management, quality of service and
bearer service description are still evolving. Much of this material
is cast so as to give the greatest possible latitude to ATM network
implementation and service offerings. ATM endsystems need to match
the traffic contract and bearer service they request from the network
to the capabilities offered by the network. Therefore, this memo can
only offer what, at the present time, are the most appropriate and
efficient coding rules to follow for setting up IP and ATMARP VCCs.
8.1. ATM Traffic Descriptor
The ATM Traffic descriptor is contained in the ATM Traffic Descriptor
IE (called ATM User Cell Rate IE in [ATMF93] prior to the erratum).
It characterizes the ATM virtual connection in terms of peak cell
rate (PCR), sustainable cell rate (SCR), and maximum burst size.
This information is used to allocate resources (e.g., bandwidth,
buffering) in the network. In general, the ATM traffic descriptor
for supporting multiprotocol interconnection over ATM will be driven
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by factors such as the capacity of the network, conformance
definition supported by the network, performance of the ATM endsystem
and (for public networks) cost of services.
The most convenient model of IP behavior corresponds to the Best
Effort Capability (see section 3.6.2.4 of [ATMF93]). If this
capability is offered by the ATM network(s), it SHOULD be requested
by including the Best Effort Indicator, the peak cell rate forward
(CLP=0+1) and peak cell rate backward (CLP=0+1) fields in the ATM
Traffic Descriptor IE.
[ATMF93] does not provide any capability for negotiation of the ATM
Traffic Descriptor. This means that:
a) the calling endsystem SHOULD have a "pretty good idea" as to the
traffic contract that will be acceptable to both the called endsystem
and the network.
b) if, in response to a SETUP message, a calling endsystem receive
a RELEASE COMPLETE message, or a CALL PROCEEDING message followed by
a RELEASE COMPLETE message, with cause #51, User cell rate
unavailable, it MAY examine the diagnostic field of the Cause IE and
reattempt the call after selecting smaller values for the
parameter(s) indicated. If the RELEASE COMPLETE or RELEASE message
is received with cause #73, Unsupported combination of traffic
parameter, it MAY try other combinations from table 5-7 and 5-8 of
[ATMF93].
c) the called endsystem SHOULD examine the ATM traffic descriptor
IE in the SETUP message. If it is unable to process cells at the
Forward PCR indicated, it should clear the call cause #51, User cell
rate unavailable.
8.2. Broadband Bearer Capability
Broadband Bearer Connection Oriented Service Type X (BCOB-X) or Type
C (BCOB-C) are applicable for multiprotocol interconnection,
depending on the service(s) provided by the ATM network and the
capabilities (e.g. for traffic shaping) of the ATM endsystem. The
example coding of Broadband Bearer Capability in figure D.2.1 of
[ATMF93] applies for BCOB-C. When BCOB-X is specified, the "traffic
type" and "timing requirements" fields SHALL be set to "no
indication" and "no indication", respectively. The susceptibility to
clipping and User plane traffic configuration SHALL be set to "not
susceptible to clipping" and "point-to-point", respectively.
[ATMF93] does not provide any capability for negotiation of the
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broadband bearer capability. This means that:
a) the calling endsystem SHOULD have a "pretty good idea" as to the
broadband bearer capability that will be acceptable to both the
called endsystem and the network.
b) if, in response to a SETUP message, a calling endsystem receives
a RELEASE COMPLETE message, or a CALL PROCEEDING message followed by
a RELEASE COMPLETE message, with cause #57, bearer capability not
authorized or #58 bearer capability not presently available, it MAY
reattempt the call after selecting another bearer capability.
8.3. QoS Parameters
The Unspecified QoS class (Class 0), the Specified QoS Class for
Connection Oriented Data Transfer (Class 3) or the Specified QoS
Class for Connectionless Data Transfer (Class 4) may be applicable
to multiprotocol over ATM. The available combination of QoS
parameters with the ATM Traffic Descriptor and the Broadband Bearer
Capability is specific to the ATM network.
[ATMF93] does not provide any capability for negotiation of Quality
of Service parameters. This means that:
a) the calling endsystem SHOULD have a "pretty good idea" as to the
QoS classes offered by the ATM network in conjunction with the
requested Broadband Bearer Service and traffic descriptor.
b) if, in response to a SETUP message, a calling endsystem receives
a RELEASE COMPLETE message, or a CALL PROCEEDING message followed by
a RELEASE COMPLETE message, with cause #49, Quality of Service
unavailable, it MAY reattempt the call after selecting another QoS
class.
Note: In UNI 3.1 a new code point of '00' has been added to the
coding standard field in the IE header. This code point has been
added for compatability with Q.2931 and is to be used when indicating
the Unspecified QoS class (class 0). Therefore, the coding standard
field SHALL be set to '00' when indicating QoS class 0, as is
suggested for IP.
8.4. ATM Addressing information
ATM addressing information is carried in the Called Party Number,
Calling Party Number, and, under certain circumstance, Called Party
Subaddress, and Calling Party Subaddress IE. Section 5.1.3 and Annex
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A of [ATMF93] describes the syntax and semantics of ATM addressing
information, including use of the subaddress IE. Section 5.8 of
[ATMF93] provides the procedure for an ATM endsystem to learn its own
ATM address from the ATM network, for use in populating the Calling
Party Number IE.
Resolution of IP address to an ATM address is required of hosts and
router which are ATM endsystems that use ATM SVCs. RFC 1577 provides
a mechanism for doing IP to ATM address resolution in the classical
IP model.
9. Dealing with Failure of Call Establishment
If an ATM call attempt fails with any of the following cause, the
situation SHALL be treated as "network unreachable" (if the called
ATM endsystem is a router) or "host unreachable" (if the called ATM
endsystem is a host).
# 1 unallocated (unassigned) number
# 3 no route to destination
# 17 user busy
# 18 no user reponding
# 27 destination out of order
# 38 network out of order
# 41 temporary failure
# 47 resource unavailable, unspecified
If an ATM call attempt fails with any of the following causes, the
ATM endpoint may retry the call, changing (or adding) the IE(s)
indicated by the cause code and diagnostic.
# 2 no route to specified transit network
# 21 call rejected
# 22 number changed
# 23 user rejects call with CLIR
# 49 quality of service unavailable
# 51 user cell rate unavailable
# 57 bearer capability not authorized
# 58 bearer capability not presently available
# 65 bearer capability not implemented
# 73 unsupported combination of traffic parameter
# 88 incompatible destination
# 91 invalid transmit network selection
# 93 AAL parameter cannot be supported
Any cause in the protocol error class (value 96 to 111) where the
location is either private network serving the local user or public
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network serving the local user
10. Security Consideration
Security consideration are not addressed in this memo.
11. Acknowledgments
The authors wish to thank the work of their colleagues who attend the
IP over ATM working group; the ATM Forum Technical Committee; the
ATM Signalling Subworking Group in ANSI-Accredited Technical
Subcommittee T1S1; the ATM Access Signalling experts in ITU-T
(formerly CCITT) Study Group 11. Rao Cherukuri (IBM) and Jeff Kiel
(formerly with Bellcore, presently with BellSouth) were particularly
valuable in coordinating among T1S1, ITU-T and the ATM Forum to make
sure that the needs of multiprotocol over ATM could be expressed in
the ATM signaling protocol.
References
[ATKI93] Atkinson, R., "Internet-Draft: IP MTU over ATM AAL5", Naval
Research Laboratory, November 1993
[ATMF93] ATM Forum, "ATM User-Network Interface Specification Version
3.0", (Englewood Cliffs, NJ: Prentice Hall, 1993)
[COLE94] IP over ATM: A Framework Document Internet Draft
[HEIN93] Heinanen, J., "Multiprotocol Encapsulation over ATM Adaption
Layer 5", RFC 1483, USC/Information Science Institute, July 1993.
[ISO8473] ISO/IEC 8473, Information processing systems - Data
communications - Protocol for providing the connectionless-mode
network service, 1988.
[ISO9577] Information Technology - Telecommuncation and information
exchange between systems - Protocol identification in the network
layer ISO/IEC TR9577 (International Standards Organization: Geneva,
1990)
[LAUB93] Laubach, M., "Classical IP and ARP over ATM", RFC1577,
Hewlett-Packard Laboratories, December 1993
[Q.2931] Broadband Integrated Service Digital Network (B-ISDN)
Digital Subscriber Signalling System No.2 (DSS2) User Network
Interface Layer 3 Specification for Basic Call/Connection Control
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DRAFT April 1994
ITU-T Recommendation Q.2931, (International Telecommunication Union:
Geneva, 1994) (to be published March, 1994)
[Page 15]
ANNEX A
This annex shows sample codings of the SETUP and CONNECT signalling messages.
The fields in the IE header are not shown.
+--------------------------------------------------------------------+
SETUP
Information Elements/
Fields Value/(Meaning)
-------------------- ---------------
aal_params
aal_type 5 (AAL 5)
fwd_max_sdu_size_ident 140
fwd_max_sdu_size 9188 (default, send IP MTU value)
bkw_max_sdu_size_ident 129
bkw_max_sdu_size 9188 (default, recv IP MTU value)
mode identifier 131 *
mode message *
sscs_type identifier 132
sscs_type 0 (null SSCS)
user_cell_rate
fwd_peak_cell_rate_0_1_ident 132
fwd_peak_cell_rate_0_1 (link rate)
bkw_peak_cell_rate_0_1_ident 133
bkw_peak_cell_rate_0_1 (link rate)
best_effort_indication 190
bb_bearer_capab
spare 0
bearer_class 16 (BCOC-X)
spare 0
traffic_type 0 (no indication)
susceptibility_to_clipping 0 (not_susceptible_to_clipping)
timing_reqs 0 (no indication)
bb_low_layer_info
layer_2_id 2
user_information_layer 12 (lan_llc (ISO 8802/2)
qos_params
qos_class_fwd 0 (class_0)
qos_class_bkw 0 (class_0)
called_party_number
type_of_number (international_number / unknown)
addr_plan_ident (ISDN / ISO NSAPA)
number (E.164 / OSI NSAPA)
calling_party_number
type_of_number (international_number / unknown)
addr_plan_ident (ISDN / ISO NSAPA)
presentation_indic (presentation_allowed)
spare 0
screening_indic (user_provided_verified_and_passed)
number (E.164 / OSI NSAPA)
+--------------------------------------------------------------------+
Figure 1. Sample contents of SETUP message
[* : optional, ignored if present]
In IP over ATM environments the inclusion of the "AAL parameters" IE
is *mandatory* to allow for MTU size negotiation between the source
and destination. The "Broadband Low Layer Information" IE is also
mandatory for specifying the IP encapsualtion scheme.
+--------------------------------------------------------------------+
CONNECT
Information Elements/
Fields Value
-------------------- -----
aal_params
aal_type 5 (AAL 5)
fwd_max_sdu_size_ident 140
fwd_max_sdu_size 9188 (default, send IP MTU value)
bkw_max_sdu_size_ident 129
bkw_max_sdu_size 9188 (default, recv IP MTU value)
mode identifier 131 *
mode message *
sscs_type identifier 132
bb_low_layer_info
layer_2_id 2
user_information_layer 12 (lan_llc (ISO 8802/2)
connection identifier
spare 0
vp_assoc_signalling 1 (explicit_indication_of VPCI)
preferred_exclusive 0 (exclusive_vpci_vci)
vpci (assigned by network)
vci (assigned by network)
+--------------------------------------------------------------------+
Figure 2.
Sample contents of CONNECT message
As in the SETUP message, IP over ATM environments demand the inclusion
of the "AAL parameters" IE so that the destination may specify the
MTU size that it is willing to receive.
Authors' Addresses
perez@cmf.nrl.navy.mil (mankin, hoffman)
fong@fore.com
dan@merlin.dev.cdx.mot.com
malis@timeplex.com
