As per Relevance of the word encapsulation, we have this rfc below:
Network Working Group M.
Request for Comments: 1755
Category: Standards Track F.
FORE Systems, Inc
A.
E.
D.
Motorola
A.
Ascom Timeplex, Inc
February 1995
ATM Signaling Support for IP over
Status of this
This document specifies an Internet standards track protocol for
Internet community, and requests discussion and suggestions
improvements. Please refer to the current edition of the "
Official Protocol Standards" (STD 1) for the standardization
and status of this protocol. Distribution of this memo is unlimited
This memo describes the ATM call control signaling exchanges
to support Classical IP over ATM implementations as described in
1577 [LAUB94]. ATM endpoints will incorporate ATM signaling
as specified in the ATM Forum User-Network Interface (UNI
Specification Version 3.1 [ATMF94]. IP over ATM
utilize the services of local ATM signaling entities to establish
release ATM connections. This memo should be used to define
support required by IP over ATM implementations from their local
signaling entities
This document is an implementors guide intended to
interoperability among RFC 1577, RFC 1483, and UNI ATM signaling.
applies to IP hosts and routers which are also ATM endsystems
assumes ATM networks that completely implement the ATM Forum
Specification Version 3.1. Unless explicitly stated, no
is made between the Private and Public UNI
Perez, Liaw, Mankin, Hoffman, Grossman & Malis [Page 1]
RFC 1755 ATM Signaling Support for IP over ATM February 1995
UNI 3.1 is considered an erratum to the UNI 3.0 specification. It
been produced by the ATM Forum, largely for reasons of alignment
Recommendation Q.2931. Although UNI 3.1 is based on UNI 3.0 there
several changes that make the two versions incompatible.
description of how to support IP over ATM using UNI 3.0 is found
Appendix B
Table of
1. Conventions ............................................... 3
2. Overview .................................................. 3
3. Use of Protocol Procedures ................................ 4
3.1 VC Establishment ..................................... 4
3.2 Multiprotocol Support on VCs ........................ 4
3.3 Support for Multiple VCs ............................. 5
3.4 VC Teardown........................................... 6
4. Overview of UNI Call Setup Signaling ...................... 6
5. Overview of Call Establishment Message Content ............ 7
6. Information Elements with Endpoint Significance ........... 8
6.1 ATM Adaptation Layer Parameters ...................... 8
6.2 Broadband Low Layer Information ..................... 8
6.2.1 Framework for Protocol Layering ............... 9
7. Information Elements with Significance to the ATM Network . 11
7.1 ATM Traffic Descriptor ............................... 11
7.2 Broadband Bearer Capability .......................... 15
7.3 QoS Parameter......................................... 16
7.4 ATM Addressing Information ........................... 16
8. Dealing with Failure of Call Establishment................. 18
9. Security Considerations .................................... 18
10. Open Issues ............................................... 19
11. Acknowledgements........................................... 19
12. References ................................................ 19
13. Authors' Addresses ........................................ 20
Appendix A Sample Signaling Messages ......................... 22
Appendix B IP over ATM using UNI 3.0 Signaling ............... 25
Appendix C Combinations of Traffic Related Parameters ........ 27
Appendix D Frame Relay Interworking .......................... 28
Perez, Liaw, Mankin, Hoffman, Grossman & Malis [Page 2]
RFC 1755 ATM Signaling Support for IP over ATM February 1995
1.
The following language conventions are used in the items
specification in this document
o MUST, SHALL, or MANDATORY -- the item is an absolute
of the specification
o SHOULD or RECOMMEND -- this item SHOULD generally be followed
all but exceptional circumstances
o MAY or OPTIONAL -- the item is truly optional and MAY be
or ignored according to the needs of the implementor
2.
In a Switched Virtual Connection (SVC) environment, ATM
channel connections (VCCs) are dynamically established and
as needed. This is accomplished using the ATM call/connection
signaling protocol, which operates between ATM endsystems and the
network. The signaling entities use the signaling protocol
establish and release calls (association between ATM endpoints)
connections (VCCs). Signaling procedures include the use
addressing to locate ATM endpoints and allocation of resource in
network for the connection. It also provides indication
negotiation between ATM endpoints for selection of end-to-
protocols and their parameters. This memo describes how
signaling protocol is used in support of IP over ATM, and,
particular, the information exchanged in the signaling protocol
effect this support
IP address to ATM address resolution and routing issues are not
the scope of this memo, and are treated as part of IP in figure 1.
+--------------+ +------+ +----------+
| | | |<--->| IP / ARP |
| |<--->| This | | RFC 1577 |
| ATM | | Memo | +----------+
| signaling | | |<--->| RFC 1483 |
| | +------+ +----------+
| | -------------> | AAL 5 |
| | +----------+
| | -------------> | ATM |
+--------------+ +----------+
Figure 1.
Relationship of this memo to IP, RFC 1483,
ATM signaling, ATM and AAL
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RFC 1755 ATM Signaling Support for IP over ATM February 1995
3. Use of Protocol
The following requirements are motivated to provide
guidelines on how multiple ATM connections between peer
SHOULD be managed, to prevent connection thrashing and
problems
3.1. VC
The owner of an existing VCC is defined to be the entity within
ATM endsystem that establishes the connection. An ATM endsystem
establish an ATM call when it has a datagram to send and either
is no existing VCC that it can use for this purpose, it chooses
to use an existing VCC, (e.g., for reasons of route optimization
quality of service), or the VCC owner does not allow sharing
To reduce the latency of the address resolution procedure at
called station, the following procedure MAY be used
If a VCC is established using the LLC/SNAP encapsulation, the
endstation of the VCC MAY send an InARP_REQUEST to the
endstation after the connection is established (i.e. received
CONNECT message) and before the calling endstation sends the
data packet. In addition, the calling endstation MAY send its
packets without waiting for the InARP_REPLY. An endstation
respond, generate, and manage its ATMARP table according to
procedures specified in RFC1293 [BRAD92], Section 7, "
Operation", during the life time of the VCC
To avoid establishing multiple VCCs to the same endstation, a
endstation MAY associate the calling party number in the
message with the established VCC. This VCC MAY be used to
data packets destined to a endstation whose ATMARP resolution
in an ATM address that is the same as the associated calling
number. Sharing of VCCs is subject to the policies configured at
endstation as described in section 4.3 of this recommendation
3.2. Multiprotocol Support on
When two ATM endsystems run multiple protocols, an ATM connection
be shared among two or more datagram protocol entities, as long
the VCC owner allows sharing and if the encapsulation allows
multiplexing and demultiplexing (i.e. the LLC/SNAP encapsulation).
This indication of sharing a VCC MAY be by configuration or via
API. Similarly, the Internet layer supports multiplexing of
end-to-end transport sessions. To properly detect idle
while sharing a VCC among more than one higher layer
entities, the ATM endsystem MUST monitor the traffic at the
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RFC 1755 ATM Signaling Support for IP over ATM February 1995
multiplexing layer
3.3. Support for Multiple
An ATMARP server or client MAY establish an ATM call when it has
datagram to send and either there is no existing VCC that it can
for this purpose, it chooses not to use an existing VCC, or the
of the VCC does not allow sharing. Note that there might be VCCs
the destination which are used for IP, but an ARP server might
to use a separate VCC for ARP only. The ATMARP server or client
maintain or release the call as specified in RFC 1577. However,
the VCC is shared among several protocol entities, the ATMARP
or server SHALL NOT disconnect the call as suggested in RFC 1577.
Systems MUST be able to support multiple connections between
systems (without regard to which peer system initiated
connection). They MAY be configured to only allow one
connection at a time
If a receiver accepts more than one call from a single source,
receiver MUST then accept incoming PDUs on the
connection(s), and MAY transmit on the additional connections
Receivers SHOULD NOT accept the incoming call, only to close
connection or ignore PDUs from the connection
Because opening multiple connections is specifically allowed
algorithms to prevent connection call collision, such as the
found in section 8.4.3.5 of ISO/IEC 8473 [ISO8473], MUST NOT
implemented
While allowing multiple connections is specifically desired
allowed, implementations MAY choose (by configuration) to permit
a single connection to some destinations. Only in such a case, if
colliding incoming call is received while a call request is pending
the incoming call MUST be rejected. Note that this MAY result in
failure to establish a connection. In such a case, each system
wait at least a configurable collision retry time in the range 1
10 seconds before retrying. Systems MUST add a random increment
with exponential backoff
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RFC 1755 ATM Signaling Support for IP over ATM February 1995
3.4. VC
Either endsystem MAY close a connection. If the connection is
or reset while a datagram is being transmitted, the datagram is lost
Systems SHOULD be able to configure a minimum holding time
connections to remain open as long as the endpoints are up. (
that holding time, the time the connection has been open,
from idle time.) A suggested default value for the minimum
time is 60 seconds
Because some public networks MAY charge for connection holding time
and connections MAY be a scarce resource in some networks
endsystems, each system implementing a Public ATM UNI interface
support the use of a configurable inactivity timer to
connections that are idle for some period of time. The timer's
SHOULD include a range from a small number of minutes to "infinite".
A default value of 20 minutes is RECOMMENDED. Systems which
implement a Private ATM UNI interface SHOULD support the
timer. If implemented, the inactivity timer MUST monitor traffic
both directions of the connection
4. Brief Overview of UNI Call Setup Signaling Procedures and
This section provides a summary of point-to-point
procedures. Readers are referred to [ATMF93].
UNI signaling messages used for point-to-point call/
control are the following
Call Setup Call
---------- ------------
SETUP
CALL PROCEEDING RELEASE
CONNECT
An ATM endpoint initiates a call request by sending a SETUP
to the network. The network processes the call request to
if the call can be progressed. If so, the network indicates the
of the newly allocated VPCI/VCI in its first response to the
SETUP message, which is either a CALL PROCEEDING or CONNECT message
If a call cannot be accepted, by the network or destination ATM end
point, a RELEASE COMPLETE is sent. At the destination ATM endpoint
the network offers the call using the SETUP message. If
destination endpoint is able to accept the call, it responds with
CONNECT message (which MAY be preceded by a CALL PROCEEDING);
otherwise, it sends a RELEASE COMPLETE message. See Appendix A
Section 2 for guidance on the use of the CALL PROCEEDING message
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RFC 1755 ATM Signaling Support for IP over ATM February 1995
Call release can be initiated by either endpoint or (rarely) by
network. When an endpoint wishes to release a call, it sends
RELEASE message to the network. The network responds with a
COMPLETE message, frees up resources associated with the call,
initiates clearing toward the other endpoint. The network
clearing by sending a RELEASE message to the ATM endpoint,
reponds by sending a RELEASE COMPLETE message. Upon receipt of
RELEASE COMPLETE message, the network frees any resources
with the call
5. Overview of Call Establishment Message
Signaling messages are structured to contain mandatory and
variable length information elements (IEs). IEs are
subdivided into octet groups, which in turn are divided into fields
IEs contain information related to the call, which is relevant to
network, the peer endpoint or both. Selection of optional IEs
the content of mandatory and optional IEs in a call
message determines the parties to and nature of the
over the ATM connection. For example, the call establishment
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
over AAL 5.
A SETUP message which establishes an ATM connection to be used for
and multiprotocol interconnection calls MUST contain the
IEs
AAL
ATM Traffic
Broadband Bearer
Broadband Low Layer
QoS
Called Party
Calling Party
and MAY, under certain circumstance contain the following IEs
Calling Party
Called Party
Transit Network
In UNI 3.1, the AAL Parameters and the Broadband Low
Information IEs are optional in a SETUP message. However, in
of IP over ATM these two IEs MUST be included. Appendix A shows
example SETUP message coded in the manner indicated in this memo
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RFC 1755 ATM Signaling Support for IP over ATM February 1995
6. Information Elements with Endpoint to Endpoint
This section describes the coding of, and procedures surrounding
information elements in a SETUP message with significance only to
endpoints of an ATM call supporting IP
6.1. ATM Adaptation Layer
The AAL Parameters IE (see section 5.4.5.5 and Annex F of [ATMF93])
carries information about the ATM Adaptation Layer (AAL) to be
on the connection. RFC 1483 specifies encapsulation of IP over AAL 5.
Thus, AAL 5 MUST be indicated in the "AAL type" field
Coding and procedure related to the 'Forward and Backward
CPCS-SDU Size' fields are discussed in [ATKI94]. Values may
from zero to 65,535. Although the default IP over AAL 5/ATM is 9188
bytes, endstations are encouraged to support MTU sizes up to
including 64k
Ordinarily, no Service Specific Convergence Sublayer (SSCS) will
used for multiprotocol interconnect over AAL5. Therefore, the
'type' field SHOULD be absent or, if present, coded to Null SSCS
Format and field values of AAL Parameters
----------------------------------------------------------
| aal_parameters |
----------------------------------------------------------
| aal_type 5 (AAL 5) |
| fwd_max_sdu_size_identifier 140 |
| fwd_max_sdu_size 65,535 (desired IP MTU) |
| bkw_max_sdu_size_identifier 129 |
| bkw_max_sdu_size 65,535 (desired IP MTU) |
| sscs_type identifier 132 |
| sscs_type 0 (null SSCS) |
----------------------------------------------------------
6.2. Broadband Low Layer
Selection of an encapsulation to support IP over an ATM VCC is
using the Broadband Low Layer Information (B-LLI) IE, along with
AAL Parameters IE, and the B-LLI negotiation procedure
RFC 1577 specifies LLC/SNAP as the default encapsulation.
encapsulation MUST be implemented by all endstations.
encapsulation MUST be signaled in the B-LLI as shown below
Signaling indication of other encapsulations is discussed in
D, Section 4. Note that only LLC is indicated in the B-LLI. It is
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RFC 1755 ATM Signaling Support for IP over ATM February 1995
to the LLC layer to look into the encapsulation header of the
following call setup. A B-LLI specifying both LLC and a layer_3_
SNAP layer is not recommended. If in those packets, the SNAP
indicates IP, it is the LLC layer's job to hand the packets up to IP
Format of B-LLI IE indicating LLC/SNAP
----------------------------------------------------------
| bb_low_layer_information |
----------------------------------------------------------
| layer_2_id 2 |
| user_information_layer 12 (lan_llc - ISO 8802/2) |
----------------------------------------------------------
6.2.1. Framework for Protocol
The support of connectionless services from a connection
link layer exposes general problems of connection management
specifically the problems of connection acceptance, assignment
quality of service, and connection shutdown. For a connection to
associated with the correct protocol on the called host, it
necessary for information about one or more layers of
identification to be associated with a connection "management entity
or "endpoint". This association is what we call a binding in
memo. In this section we attempt to describe a framework for
usable binding or service architecture given the available IEs in
ATM call control messages
It is important to distinguish between two basic uses of
identification elements present in the UNI setup message. The
is the description of the protocol encapsulation that will be used
the data packet over the virtual connection, the second is the
that will be responsible for managing the call. All protocols
in various IEs MUST be used to encapsulate the call, but the
specific, or highest, layer specified SHOULD manage the call.
defines a hierarchy of services and provides a framework
applications, including LLC and IP, to terminate calls.
hierarchy provides a clear mechanism for support of higher
protocol and application bindings, when their use and
is defined in the appropriate standards bodies
In general, it would be desirable to allow data packets to be
directly into an application's address space after connection
established. This is possible only if we have both encapsulation
managing entity indications in the signaling message
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RFC 1755 ATM Signaling Support for IP over ATM February 1995
The B-LLI is the only information element currently available in
3.1 for designating protocol endpoints. It contains codepoints
describe layer 2 and layer 3 protocol entities associated with
call. There are other information elements under consideration in
ATM Forum and ITU, which could come to play a significant role in
description of application to connection binding, but their use
not yet defined, and they are not part of the framework described
RFC 1577. They include B-HLI, for containing information for a
layer protocol, Network Layer Information (NLI) to
information for the network layer, and UUI, which is meant to
information for use by the top level application
The following figure shows a B-LLI that MAY be used for specifying
call setup that IP will manage the call and that this VC will be
only for IP traffic. Called parties MUST accept this B-LLI.
caller using VC MUST use LLC-SNAP encapsulation on all IP datagrams
despite the fact that the caller views the VC as dedicated to IP
The reason for this requirement is that while we require receivers
accept this form of call setup, they may choose whether or not
multiplex the call through LLC, in other words to ignore the Layer 3
information. This choice is dependent on the receiver'
implementation's protocol architecture and is local to the receiver
Format of B-LLI IE indicating VC ownership by
(NOTE: LLC/SNAP encapsulation is still used
----------------------------------------------------------
| bb_low_layer_information |
----------------------------------------------------------
| layer_2_id 2 |
| user_information_layer 12 (lan_llc - ISO 8802/2) |
| layer_3_id 3 |
| ISO/IEC TR 9577 IPI 204 (0xCC) |
----------------------------------------------------------
Null-encapsulated VCs are described in RFC 1483. Such a VC
result in the most direct form of binding a VC to IP. However,
method of signaling for this type of VC has not yet been
into the IP over ATM context. For completeness, we mention that
signaling would use a B-LLI containing the layer 3 identifier
the ISO/IEC TR-9577 protocol codepoint and omitting the layer 2
identifier [ATMF93]. Since no layer 2 is specified, frames
by AAL processing would be given directly to IP. Processing of
B-LLI is not required at this time
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RFC 1755 ATM Signaling Support for IP over ATM February 1995
7. Information Elements with Significance to the ATM
This section describes the coding of, and procedures surrounding
information elements with significance to the ATM network, as well
the endpoints of an ATM call supporting multiprotocol operation
The standards, implementation agreements, research and
surrounding such issues as traffic management, quality of service
bearer service description are still evolving. Much of this
is cast to give the greatest possible latitude to ATM
implementation and service offerings. ATM endsystems need to
the traffic contract and bearer service they request from the
to the capabilities offered by the network. Therefore, this memo
only offer what, at the present time, are the most appropriate
efficient coding rules to follow for setting up IP and ATMARP VCCs
Future revisions of this memo may take advantage of ATM services
capabilities that are not yet available
7.1. ATM Traffic
The ATM traffic descriptor characterizes the ATM virtual
in terms of peak cell rate (PCR), sustainable cell rate (SCR),
maximum burst size. This information is used to allocate
(e.g., bandwidth, buffering) in the network. In general, the
traffic descriptor for supporting multiprotocol interconnection
ATM will be driven by factors such as the capacity of the network
conformance definition supported by the network, performance of
ATM endsystem and (for public networks) cost of services
The most convenient model of IP behavior corresponds to the
Effort Capability (see section 3.6.2.4 of [ATMF93]). If
capability is offered by the ATM network(s), it MAY be requested
including the Best Effort Indicator, the peak cell rate
(CLP=0+1) and peak cell rate backward (CLP=0+1) fields in the
Traffic Descriptor IE. When the Best Effort Capability is used,
guarantees are provided by the network, and in fact, throughput
be zero at any time. This type of behavior is also described by
1633 [BRAD94].
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RFC 1755 ATM Signaling Support for IP over ATM February 1995
Format and field values of ATM Traffic Descriptor
----------------------------------------------------------
| traffic_descriptor |
----------------------------------------------------------
| fwd_peak_cell_rate_0+1_identifier 132 |
| fwd_peak_cell_rate_0+1 (link rate) |
| bkw_peak_cell_rate_0+1_identifier 133 |
| bkw_peak_cell_rate_0+1 (link rate) |
| best_effort_indication 190 |
----------------------------------------------------------
When the network does not support Best Effort Capability or
predictable ATM service is desired for IP, more specific
parameters MAY be specified and the Best Effort capability not used
Doing so includes use of two other traffic-related IEs and
discussed in the following paragraphs and sections
The Traffic Descriptor IE is accompanied by the Broadband
Capability IE and the QoS Parameter IE. Together these define
signaling view of ATM traffic management. In this memo, we
an agreed-on, required subset of traffic management capabilities,
specified by using the three IEs. The figure immediately below
the set of the allowable combinations of traffic parameters which
IP over ATM endsystems MUST support in their ATM signaling.
subset includes Best Effort in the form of a non-guaranteed
combination (the rightmost column of the table below); a type
traffic description that is intended for ATM "pipes", for
between two routers (the middle column); and a type of
description that will allow initial use of token-bucket
characterizations of the source, as presented in RFC 1363 [PART92]
and RFC 1633, for example (the leftmost column).
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RFC 1755 ATM Signaling Support for IP over ATM February 1995
Combinations of Traffic Related
that MUST be supported in the SETUP
|---------------------------------|
|Broadband Bearer |
|Capability |
|---------------------------------|
|Broadband Bearer | C | X | X |
|---------------------|---|---|---|
|Traffic Type | | | |
|(CBR,VBR) | |CBR| & |
|---------------------|---|---|---|
|Timing Required | |YES| &&|
|---------------------------------|
|Traffic Descriptor |
|Parameter |
|---------------------------------|
|PCR (CLP=0) | | | |
|---------------------|---|---|---|
|PCR (CLP=0+1) | S | S | S |
|---------------------|---|---|---|
|SCR (CLP=0) | | | |
|---------------------|---|---|---|
|SCR (CLP=0+1) | S | | |
|---------------------|---|---|---|
|MBS (CLP=0) | | | |
|---------------------|---|---|---|
|MBS (CLP=0+1) | S | | |
|---------------------|---|---|---|
|Best Effort | | | S |
|---------------------|---|---|---|
|Tagging | NO| NO| NO
|---------------------------------|
|---------------------------------|
|QOS Classes | 0 | 0 | 0 |
-----------------------------------
S =
& = Parameter is coded to either "no indication" or VBR or octet 5
(Traffic Type/Timing Required) is absent; these three codings
treated as
&& = Parameter is coded to either "no indication" or "No" or octet 5
is absent; these three codings are treated as
Use of other allowable combinations of traffic parameters listed
the large table in Appendix C may work, since they are allowed
[ATMF94], but this will depend on the the calling endsystem,
network, and the called endsystem
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RFC 1755 ATM Signaling Support for IP over ATM February 1995
If Best Effort service is not use, link rate SHOULD not be
as the peak cell rate. Without any knowledge of the application,
is RECOMMENDED that a fraction, such as 1/10th, of the the
bandwidth be requested
[ATMF93] does not provide any capability for negotiation of the
traffic descriptor paramenters. This means that
a) the calling endsystem SHOULD have some prior knowledge as
the traffic contract that will be acceptable to both
called endsystem and the network
b) if, in response to a SETUP message, a calling
receive a RELEASE COMPLETE message, or a CALL
message followed by a RELEASE COMPLETE message, with
#37, User Cell Rate Unavailable, it MAY examine
diagnostic field of the Cause IE and reattempt the call
selecting smaller values for the parameter(s) indicated.
the RELEASE COMPLETE or RELEASE message is received with
#73, Unsupported combination of traffic parameter, it
try other combinations from table 5-7 and 5-8 of [ATMF93].
c) the called endsystem SHOULD examine the ATM traffic
IE in the SETUP message. If it is unable to process cells
the Forward PCR indicated, it SHOULD clear the call with
#37, User Cell Rate Unavailable
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RFC 1755 ATM Signaling Support for IP over ATM February 1995
7.2. Broadband Bearer
Broadband Bearer Connection Oriented Service Type X (BCOB-X) or
C (BCOB-C) are both applicable for multiprotocol interconnection
depending on the service(s) provided by the ATM network and
capabilities (e.g., for traffic shaping) of the ATM endsystem.
table in the previous section showed the use of BCOB-X and BCOB-
with other parameters. The figure below shows format and
values for a BCOB-X when the Traffic Descriptor IE indicates
Effort
Format and field values of Broadband Bearer Capability
----------------------------------------------------------
| bb_bearer_capability |
----------------------------------------------------------
| spare 0 |
| bearer_class 16 (BCOC-X) |
| spare 0 |
| traffic_type 0 (no indication) |
| timing_reqs 0 (no indication) |
| susceptibility_to_clipping 0 (not suscept) |
| spare 0 |
| user_plane_configuration 0 (point_to_point) |
----------------------------------------------------------
IP over ATM signaling MUST permit BCOB-C and BCOB-X, in
combinations shown in the previous section. It MAY also permit
of the allowable combinations shown in Appendix C
Currently, there is no capability for negotiation of the
bearer capability. This means that
a) the calling endsystem SHOULD have some prior knowledge as
the broadband bearer capability that will be acceptable
both the called endsystem and the network
b) if, in response to a SETUP message, a calling
receives a RELEASE COMPLETE message, or a CALL
message followed by a RELEASE COMPLETE message, with
#57, bearer capability not authorized or #58 bearer
not presently available, it MAY reattempt the call
selecting another bearer capability
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RFC 1755 ATM Signaling Support for IP over ATM February 1995
7.3. QoS
The Unspecified QoS class (Class 0) is the only QoS class that
be supported by all networks and the only QoS class allowed
using the Best Effort service. The Specified QoS Class for
Oriented Data Transfer (Class 3) or the Specified QoS Class
Connectionless Data Transfer (Class 4) may be applicable
multiprotocol over ATM, but their use has to be negotiated with
network provider. The combinations of QoS parameters with the
Traffic Descriptor and the Broadband Bearer Capability are
in the Traffic Descriptor section and in Appendix C
Format and field values of QoS Parameters
----------------------------------------------------------
| qos_parameter |
----------------------------------------------------------
| qos_class_fwd 0 (class 0) |
| qos_class_bkw 0 (class 0) |
----------------------------------------------------------
[ATMF93] does not provide any capability for negotiation of
of Service parameters. This means that
a) the calling endsystem SHOULD have some prior knowledge as
the QoS classes offered by the ATM network in conjunction
the requested Broadband Bearer Service and Traffic Descriptor
b) if, in response to a SETUP message, a calling
receives a RELEASE COMPLETE message, or a CALL
message followed by a RELEASE COMPLETE message, with
#49, Quality of Service Unavailable, it MAY reattempt the
after selecting another QoS class
Note: The two-bit 'coding standard' field of the General
octet in the IE header, SHOULD be set to '00' now that the ITU-T
standardized QoS class 0. Endsystems SHOULD treat either value ('11'
or '00') as requesting the ITU-T QoS class
7.4. ATM Addressing
ATM addressing information is carried in the Called Party Number
Calling Party Number, and, under certain circumstance, Called
Subaddress, and Calling Party Subaddress IE. Section 5.8 of [ATMF93]
provides the procedure for an ATM endsystem to learn its own
address from the ATM network, for use in populating the Calling
Number IE. Section 5.4.5.14 [ATMF94] describes the syntax
semantics of the calling party subaddress IE
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RFC 1755 ATM Signaling Support for IP over ATM February 1995
RFC 1577 RECOMMENDS that a router be able to provide multiple
support with a single physical ATM interface that may have one
more individual ATM endsystem addresses. Use of the Selector
in the NSAPAs and E.164 addresses (in the NSAP format) is
as a way to differentiate up to 256 different LISs for the same ESI
Therefore, an IP router MAY associate the IP addresses of the
LISs it supports with distinct ATM addresses differentiated only
the SEL field. If an IP router does this association, then
signaling entity MUST carry in the SETUP message the ATM
corresponding to the particular IP entity requesting the call,
the IP entity it is requesting a call to. These ATM addresses
carried in the Calling and Called Party Number IEs respectively
Native E.164 addresses do not support a SEL field. For IP
residing in a Public UNI where native E.164 addresses are used it
RECOMMENDED that multiple E.164 addresses be used to support
LISs. Note: multiple LIS support is the only recommended use of
SEL field. Use of this field is not recommended for selection
higher level applications
Resolution of IP addresses to ATM addresses is required of hosts
routers which are ATM endsystems that use ATM SVCs. RFC 1577
a mechanism for doing IP to ATM address resolution in the
IP model
Format and field values of Called and Calling Party Number
----------------------------------------------------------
| called_party_number |
----------------------------------------------------------
| type_of_number (international number / unknown) |
| addr_plan_ident (ISDN / ATM Endsystem Address) |
| addr_number (E.164 / ATM Endsystem Address) |
----------------------------------------------------------
----------------------------------------------------------
| calling_party_number |
----------------------------------------------------------
| type_of_number (international number / unknown) |
| addr_plan_ident (ISDN / ATM Endsystem Address) |
| presentation_indic (presentation allowed) |
| spare 0 |
| screening_indic (user provided verified & passed) |
| addr_number (E.164 / ATM Endsystem Address |
----------------------------------------------------------
Perez, Liaw, Mankin, Hoffman, Grossman & Malis [Page 17]
RFC 1755 ATM Signaling Support for IP over ATM February 1995
8. Dealing with Failure of Call
If an ATM call attempt fails with any of the following causes,
situation SHOULD be treated as Network Unreachable (if the called
endsystem is a router) or Host Unreachable (if the called
endsystem is a host). See the treatment of Network and
Unreachable conditions in RFC 1122 [BRAD89].
# 1 unallocated (unassigned)
# 3 no route to
# 17 user
# 18 no user
# 27 destination out of
# 38 network out of
# 41 temporary
# 47 resource unavailable,
If an ATM call attempt fails with any of the following causes,
ATM endsystem MAY retry the call, changing (or adding) the IE(s
indicated by the cause code and diagnostic
# 2 no route to specified transit
# 21 call
# 22 number
# 23 user rejects call with
# 37 user cell rate
# 49 quality of service
# 57 bearer capability not
# 58 bearer capability not presently
# 65 bearer capability not
# 73 unsupported combination of traffic
# 88 incompatible
# 91 invalid transmit network
# 78 AAL parameter cannot be
9. Security
Not all of the security issues relating to IP over ATM are
understood at this time, due to the fluid state of
specifications, newness of the technology, and other factors.
revisions of this specification will address the
capabilities that future signaling standards may offer to IP over
signaling
Perez, Liaw, Mankin, Hoffman, Grossman & Malis [Page 18]
RFC 1755 ATM Signaling Support for IP over ATM February 1995
10. Open
o This document version is specifically an RFC 1577/RFC 1483
implementation document. Although RFC 1577 and RFC 1483
specify an LLC/SNAP encapsulation, which is inherently
multiprotocol encapsulation, it is beyond to scope of
document to go into any multiprotocol specifications other
to point out some examples (see Appendix D for an example
NLPID encapsulation).
11.
The authors wish to thank the work of their colleagues who attend
IP over ATM working group; the ATM Forum Technical Committee; the
Signaling Subworking Group in ANSI-Accredited Technical
T1S1; the ATM Access Signaling experts in ITU-T (formerly CCITT
Study Group 11. Rao Cherukuri (IBM) and Jeff Kiel (formerly
Bellcore, presently with BellSouth) were particularly valuable
coordinating among T1S1, ITU-T and the ATM Forum to make sure
the needs of multiprotocol over ATM could be expressed in the
signaling protocol
[ATKI94] Atkinson, R., "Default IP MTU over ATM AAL5", RFC 1626,
Naval Research Laboratory, May 1994.
[ATMF94] ATM Forum, "ATM User-Network Interface Specification
3.1", 1994.
[ATMF93] ATM Forum, "ATM User-Network Interface Specification
3.0", (Englewood Cliffs, NJ: Prentice Hall, 1993).
[BRAD89] Braden, R., Editor, "Requirements for Internet Hosts --
Communication Layers", STD 3, RFC 1122, USC/Information
Institute, October 1989.
[BRAD94] Braden, R., Clark, D., and S. Shenker, "Integrated
in the Internet Architecture: An Overview", RFC 1633,
USC/Information Science Institute, June 1994.
[BRAD92] Bradley, T., and C. Brown, "Inverse Address
Protocol", RFC 1293, Wellfleet Communications, Inc.,
1992.
[HEIN93] Heinanen, J., "Multiprotocol Encapsulation over
Adaptation Layer 5", RFC 1483, Telecom Finland, July 1993.
Perez, Liaw, Mankin, Hoffman, Grossman & Malis [Page 19]
RFC 1755 ATM Signaling Support for IP over ATM February 1995
[ISO8473] ISO/IEC 8473, Information processing systems -
communications - Protocol for providing the connectionless-
network service, 1988.
[ISO9577] Information Technology - Telecommunication and
exchange between systems - Protocol identification in the
layer ISO/IEC TR9577 (International Standards Organization
Geneva, 1990).
[LAUB93] Laubach, M., "Classical IP and ARP over ATM", RFC 1577,
Hewlett-Packard Laboratories, December 1993.
[PART92] Partridge, C., "A Proposed Flow Specification", RFC 1363,
BBN, September 1992.
[Q.2931] Broadband Integrated Service Digital Network (B-ISDN
Digital Subscriber Signaling System No.2 (DSS2) User
Interface Layer 3 Specification for Basic Call/Connection
ITU-T Recommendation Q.2931, (International
Union: Geneva, 1994)
Authors'
Maryann Perez
USC/Information Sciences
4350 N. Fairfax Drive Suite 400
Arlington, VA 22203
Phone: 703-807-0132
EMail: perez@isi.
Fong-Ching
FORE Systems, Inc
174 Thorn Hill
Warrendale, PA 15086-7535
Phone: (412) 772-8668
EMail: fong@fore.
Allison
USC/Information Sciences
4350 N. Fairfax Drive Suite 400
Arlington, VA 22203
Phone: 703-807-0132
EMail: mankin@isi.
Perez, Liaw, Mankin, Hoffman, Grossman & Malis [Page 20]
RFC 1755 ATM Signaling Support for IP over ATM February 1995
Eric
USC/Information Sciences
4350 N. Fairfax Drive Suite 400
Arlington, VA 22203
Phone: 703-807-0132
EMail: hoffman@isi.
Dan
Motorola
Phone: 617-821-7333
EMail: dan@merlin.dev.cdx.mot.
Andrew G.
Ascom Timeplex, Inc
Advanced Products Business
289 Great Road Suite 205
Acton, MA 01720
Phone: (508) 266-4522
EMail: malis@maelstrom.timeplex.
Perez, Liaw, Mankin, Hoffman, Grossman & Malis [Page 21]
RFC 1755 ATM Signaling Support for IP over ATM February 1995
Appendix A. Sample Signaling
1. SETUP and CONNECT
This appendix shows sample codings of the SETUP and CONNECT
messages. The fields in the IE header are not shown
+--------------------------------------------------------------------+
Information Elements
Fields Value/(Meaning
-------------------- ---------------
aal_
aal_type 5 (AAL 5)
fwd_max_sdu_size_ident 140
fwd_max_sdu_size (send IP MTU value
bkw_max_sdu_size_ident 129
bkw_max_sdu_size (recv IP MTU value
sscs_type identifier 132
sscs_type 0 (null SSCS
user_cell_
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_
spare 0
bearer_class 16 (BCOC-X
spare 0
traffic_type 0 (no indication
timing_reqs 0 (no indication
susceptibility_to_clipping 0 (not susceptible
clipping
spare 0
user_plane_configuration 0 (point_to_point
bb_low_layer_
layer_2_id 2
user_information_layer 12 (lan_llc (ISO 8802/2)
qos_
qos_class_fwd 0 (class 0)
qos_class_bkw 0 (class 0)
Perez, Liaw, Mankin, Hoffman, Grossman & Malis [Page 22]
RFC 1755 ATM Signaling Support for IP over ATM February 1995
called_party_
type_of_number (international number / unknown
addr_plan_ident (ISDN / ATM Endsystem Address
number (E.164 / ATM Endsystem Address
calling_party_
type_of_number (international number / unknown
addr_plan_ident (ISDN / ATM Endsystem Address
presentation_indic (presentation allowed
spare 0
screening_indic (user_provided verified and passed
number (E.164 / ATM Endsystem Address
+--------------------------------------------------------------------+
Figure 1.
Sample contents of SETUP
[* : optional, ignored if present
Perez, Liaw, Mankin, Hoffman, Grossman & Malis [Page 23]
RFC 1755 ATM Signaling Support for IP over ATM February 1995
In IP over ATM environments the inclusion of the "AAL parameters"
is *mandatory* to allow for MTU size negotiation between the
and destination. The "Broadband Low Layer Information" IE is
mandatory for specifying the IP encapsulation scheme
+--------------------------------------------------------------------+
Information Elements
Fields
-------------------- -----
aal_
aal_type 5 (AAL 5)
fwd_max_sdu_size_ident 140
fwd_max_sdu_size (send IP MTU value
bkw_max_sdu_size_ident 129
bkw_max_sdu_size (recv IP MTU value
sscs_type identifier 132
sscs_type 0 (null SSCS
bb_low_layer_
layer_2_id 2
user_information_layer 12 (lan_llc (ISO 8802/2)
connection
spare 0
vp_assoc_signaling 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
As in the SETUP message, IP over ATM environments demand
inclusion of the "AAL parameters" IE so that the destination
specify the MTU size that it is willing to receive
2. Hints on Use of CALL PROCEEDING
Use of the CALL PROCEEDING message is beneficial in
where the called party's ATM signaling entity and AAL Users
decoupled. An arriving SETUP may result in an immediate
PROCEEDING response from the called party's ATM signaling entity
while it locally queries the called IP-ATM entity to see if
SETUP's conditions are acceptable. The acceptance of the SETUP'
conditions would then cause the ATM signaling entity to issue
CONNECT back to the switch. The two possible refusal modes at
Perez, Liaw, Mankin, Hoffman, Grossman & Malis [Page 24]
RFC 1755 ATM Signaling Support for IP over ATM February 1995
called party then become
a) Called party has no IP-ATM entity resident. Issue
COMPLETE in response to SETUP
b) Called party has a resident IP-ATM entity, so CALL
was issued. The IP-ATM entity rejects the call request, so
RELEASE is issued instead (to be acknowledged by the
with RELEASE COMPLETE).
Appendix B. IP over ATM using UNI 3.0
This appendix describes how to support IP over ATM using UNI 3.0
signalling. Differences in the coding or semantics of each
IE is given
1. AAL
Values for maximum SDU size may range from one (not zero) to 64K
A 'mode' field is an allowable field in UNI 3.0. Nevertheless,
'mode' field SHOULD be omitted from the AAL Parameters IE and MUST
ignored by the destination endsystem
2. Traffic Management Related
In UNI 3.0 issues of traffic management were less understood than
UNI 3.1. UNI 3.0 does not contain a guide to coordinating the use
the User Cell Rate IE (Traffic Descriptor IE in UNI 3.1),
Bearer Capability IE, and QoS parameters IE. Therefore,
recommendation for specifying parameters in these IEs is the same
that given above when using UNI 3.1. The following section
describes relevant differences in names and code values
2.1 ATM User Cell Rate (instead of ATM Traffic Descriptor
The ATM Traffic Descriptor IE is refered to as 'ATM User Cell Rate
IE in UNI 3.0. Also, the value for the cause 'user cell
unavailable' is #51.
2.3 QoS
The two-bit 'coding standard' field of the General Information
in the IE header, should be set to '11' inidicating that the IE is
standard defined for the network (as opposed to an ITU-TS standard
present on the network side of the interface
Perez, Liaw, Mankin, Hoffman, Grossman & Malis [Page 25]
RFC 1755 ATM Signaling Support for IP over ATM February 1995
3. ATM Addressing
In UNI 3.1, the 'ATM Endsystem Address' type was introduced
differentiate ATM addresses from OSI NSAPs. In UNI 3.0, '
Endsystem Address' is not a valid type. Therefore, in the called
calling party subaddress IEs the three-bit 'type of subaddress'
MUST specify 'NSAP' (value = 001) when using the subaddress IE
carry ATM addresses
4. Dealing with Failure of Call
In UNI 3.0 the there are certain cause values which are
than UNI 3.1. Two relevant differences are the following
'AAL Parameter Cannot Be Supported' is #93 (#78 in UNI 3.1),
'User Cell Rate Unavailable' is #51 (#37 in UNI 3.1).
Perez, Liaw, Mankin, Hoffman, Grossman & Malis [Page 26]
RFC 1755 ATM Signaling Support for IP over ATM February 1995
Appendix C
Combinations of Traffic Related
tha MAY be supported in the SETUP
|-----------------------------------------------------------------|
|Broadband Bearer |
|Capability |
|-----------------------------------------------------------------|
|Broadband Bearer |A,C| X |X |C | X |C| X |A,C| X | X |C| X |
|---------------------|---|---|---|---|---|-|---|---|---|---|-|---|
|Traffic Type | | | | | | | | | | | | |
|(CBR,VBR) | |CBR| & | |& | |& | |CBR|& |&| & |
|---------------------|---|---|---|---|---|-|---|---|---|---|-|---|
|Timing Required | | Y |&& | |&& | |&& | | Y |&& | |&& |
|-----------------------------------------------------------------|
|Traffic Descriptor |
|Parameter |
|-----------------------------------------------------------------|
|PCR (CLP=0) | S | S | S | | | | | | | | | |
|---------------------|---|---|---|---|---|-|---|---|---|---|-|---|
|PCR (CLP=0+1) | S | S | S | S | S |S| S | S | S | S |S| S |
|---------------------|---|---|---|---|---|-|---|---|---|---|-|---|
|SCR (CLP=0) | | | | | S |S| | | | | | |
|---------------------|---|---|---|---|---|-|---|---|---|---|-|---|
|SCR (CLP=0+1) | | | | | | | S | S | | | | |
|---------------------|---|---|---|---|---|-|---|---|---|---|-|---|
|MBS (CLP=0) | | | | | S |S| | | | | | |
|---------------------|---|---|---|---|---|-|---|---|---|---|-|---|
|MBS (CLP=0+1) | | | | | | | S | S | | | | |
|---------------------|---|---|---|---|---|-|---|---|---|---|-|---|
|Best Effort | | | | | | | | | | |S| S |
|---------------------|---|---|---|---|---|-|---|---|---|---|-|---|
|Tagging |Y/N|Y/N|Y/N|Y/N|Y/N|N| N | N | N | N |N| N |
|-----------------------------------------------------------------|
|-----------------------------------------------------------------|
|QOS Classes | * | * | * | * | * |*| * | * | * | * |0| 0 |
|-----------------------------------------------------------------|
(Table 2 is a reproduction of Table F-1 of Appendix F in [ATMF 94].)
PCR = Peak Cell Rate, SCR = Sustainable Cell Rate
MBS = Maximum Burst
Y = Yes, N = No, S =
Y/N = either "Yes" or "No" is
Perez, Liaw, Mankin, Hoffman, Grossman & Malis [Page 27]
RFC 1755 ATM Signaling Support for IP over ATM February 1995
* = allowed QoS class values are a network option. Class 0
always supported for alignment with ITU-
& = parameter is coded to either "no indication" or VBR
octet 5a(Traffic Type/Timing Required) is absent; these
codings are treated as
&& = parameter is coded to either "no indication" or "No"
octet 5a(Traffic Type/Timing Required) is absent; these
codings are treated as
A blank entry in the table indicates that the parameter is
present
Appendix D. Frame Relay
1. RFC 1490 over FR-SSCS vs. RFC 1483 over null-
Procedures for Frame Relay to ATM signaling interworking have not
been specified by ITU-T, the ATM Forum, or the Frame Relay Forum.
an ATM endsystem wishes to use FR-SSCS, FR-SSCS and RFC 1490
encapsulation must both be be specified in the SETUP message
Nevertheless, since neither LLC encapsulation nor VC-
will interoperate when used over FR-SSCS, these two
cannot be negotiated as alternatives to RFC 1490 encapsulation (
Section 4, Encapsulation Negotiation).
In ATM environments the SSCS layer is part of the AAL functionality
The SSCS serves to coordinate the needs of a protocol above with
requirements of next lower layer, the Common Part
Sublayer (CPCS). For example, the UNI ATM signaling protocol runs
top of a signaling SSCS which among other things provides an
transfer service for signaling messages. Since the SSCS is
part of the AAL, the SSCS type is specified as one of the
in the AAL Parameters IE. To date there has not been an SSCS
for data transmission in ATM and this type field is usually set
'null'.
The exception occurs when doing FR interworking where an
endsystem may choose to use the FR-SSCS over AAL 5 in order
communicate with a FR endsystem. In that case the SSCS type in
AAL Parameters IE of the SETUP message is set to 'FR-SSCS'.
Also included in a SETUP message is an indication in the B-LLI IE
the protocol layers to be used above the AAL. In particular,
connections established to carry connectionless network
traffic require a layer above the AAL for multiplexing
protocols over a single VC [HEIN 93]. As mentioned above, RFC 1577
Perez, Liaw, Mankin, Hoffman, Grossman & Malis [Page 28]
RFC 1755 ATM Signaling Support for IP over ATM February 1995
defines LLC as default multiplexing layer for IP over AAL5.
Specification of the SSCS restricts the encapsulation protocol
over it, since RFC 1483 (in addition to applicable ITU standards
defines the use of RFC 1490 encapsulation over the FR-SSCS, and
or null encapsulation otherwise. The fact that it is not possible
in the UNI 3.0 signaling specification, to negotiate between the FR
SSCS and null-SSCS can result in interoperability
between stations that implement and wish to use the FR-SSCS and
that do not, even though they both are using IP. The guidelines
the following section were developed to decrease the chance that
interoperability restrictions occur
2. Scenarios for
The following discussion uses the terms "network interworking"
"service interworking". "Network interworking" uses FR-SSCS
AAL5 between the InterWorking Unit (IWU) and the ATM endsystem,
the ATM endsystem is aware that the other endpoint is a FR/
Network IWU. "Service interworking" aims to make the
transparent to the ATM endsystem by adding encapsulation
and other payload processing in the FR/ATM Service IWU to allow
ATM endsystem to operate as if it were talking to another
endsystem
The most common scenario where FR-SSCS could be negotiated is
an ATM endsystem and a FR/ATM network IWU to allow connectivity
an ATM endsystem and a FR endsystem residing behind a FR/ATM
IWU
-------- --------
------- | | | | -------
| A | | FR/ATM | | ATM | | B |
| (FR) |----->| IWU |----->| switch |----->| (ATM) |
------- | | | | -------
-------- --------
| | | |
-----> --------------------->
FR call ATM
A network IWU can place a call to an ATM host (on behalf of a
host) by signaling for FR-SSCS and assuming that the ATM
supports FR-SSCS. The B-LLI IE SHALL be encoded to indicate RFC 1490
encapsulation and the SSCS type field of the AAL Parameters IE
be coded to indicate FR-SSCS. If the FR-SSCS negotiation
because the called ATM host does not support FR-SSCS, the IWU
retry the call negotiating for LLC encapsulation or VC-multiplexing
Perez, Liaw, Mankin, Hoffman, Grossman & Malis [Page 29]
RFC 1755 ATM Signaling Support for IP over ATM February 1995
However, the IWU can only attempt the retry if it is able to do FR
ATM service interworking. Such service interworking adds
processing overhead during the call
The even more problematic case occurs when a call is requested in
opposite direction, i.e. when an ATM host places a call to a
residing behind an IWU
-------- --------
------- | | | | -------
| B | | FR/ATM | | ATM | | A |
| (FR) |<-----| IWU |<-----| switch |<-----| (ATM) |
------- | | | | -------
-------- --------
| | | |
<----- <---------------------
FR call ATM
Not knowing that the destination resides behind an IWU, the
host will negotiate for the default LLC encapsulation (
requesting VC-multiplexing as an alternative). In this situation
IWU can accept the call and do the necessary service interworking
reject the call specifying 'AAL Parameters not supported'. If the
rejects the call it risks the possibility that calling host does
support FR-SSCS or simply does not retry and the call will never
established
3. Possible
While Frame Relay interworking is possible, it is not possible
negotiate FR-SSCS with LLC encapsulation or VC-multiplexing,
decreases the chances of completing an ATM call. However
