1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
|
Network Working Group A. Malis
Request for Comments: 4816 Verizon
Category: Standards Track L. Martini
Cisco Systems
J. Brayley
ECI Telecom
T. Walsh
Juniper Networks
February 2007
Pseudowire Emulation Edge-to-Edge (PWE3)
Asynchronous Transfer Mode (ATM) Transparent Cell Transport Service
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
The document describes a transparent cell transport service that
makes use of the "N-to-one" cell relay mode for Pseudowire Emulation
Edge-to-Edge (PWE3) Asynchronous Transfer-Mode (ATM) cell
encapsulation.
1. Introduction
This transparent cell transport service allows migration of ATM
services to a PSN without having to provision the ATM subscriber or
customer edge (CE) devices. The ATM CEs will view the ATM
transparent cell transport service as if they were directly connected
via a Time Division Multiplexer (TDM) leased line. This service is
most likely to be used as an internal function in an ATM service
provider's network as a way to connect existing ATM switches via a
higher-speed PSN, or to provide ATM "backhaul" services for remote
access to existing ATM networks.
Malis, et al. Standards Track [Page 1]
^L
RFC 4816 PWE3 ATM Transparent Cell Transport Service February 2007
1.1. Specification of Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [1].
2. Transparent Cell Transport Definition
The transparent port service is a natural application of the "N-to-
one" Virtual Circuit Connection (VCC) cell transport mode for PWE3
ATM encapsulation described in [2], and MUST be used with pseudowires
of type 0x0003, "ATM transparent cell transport" [4].
The ATM transparent port service emulates connectivity between two
remote ATM ports. This service is useful when one desires to connect
two CEs without processing or switching at the Virtual Path
Connection (VPC) or VCC layer. The ingress PE discards any
idle/unassigned cells received from the ingress ATM port, and maps
all other received cells to a single pseudowire.
The egress PE does not change the Virtual Path Identifier (VPI),
Virtual Circuit Identifier (VCI), Payload Type Identifier (PTI), or
Cell Loss Priority (CLP) bits when it sends these cells on the egress
ATM port. Therefore, the transparent port service appears to emulate
an ATM transmission convergence layer connection between two ports.
However, since the ingress PE discards idle/unassigned cells, this
service benefits from statistical multiplexing bandwidth savings.
In accordance with [2], cell concatenation MAY be used for
transparent cell-relay transport in order to save the PSN bandwidth.
If used, it MUST be agreed between the ingress and egress PEs. In
particular, if the Pseudo Wire has been set up using the PWE3 control
protocol [3], the ingress PE MUST NOT exceed the value of the
"Maximum Number of concatenated ATM cells" Pseudowire Interface
Parameter Sub-TLV (Interface Parameter ID = 0x02 [4]) received in the
Label Mapping message for the Pseudo Wire, and MUST NOT use cell
concatenation if this parameter has been omitted by the egress PE.
ATM Operations and Management (OAM) cells MUST be transported
transparently, and the PEs do not act on them. If the PEs detect a
PSN or pseudowire failure between them, they do not generate any OAM
cells, but rather bring down the ATM interfaces to the CEs (e.g.,
generating LOS on the ATM port), just as if it were a transmission
layer failure.
Malis, et al. Standards Track [Page 2]
^L
RFC 4816 PWE3 ATM Transparent Cell Transport Service February 2007
Similarly, ATM Integrated Local Management Interface (ILMI) signaling
from the CEs, if any, MUST be transported transparently, and the PEs
do not act on it. However, the PEs must act on physical interface
failure by either withdrawing the PW labels or by using pseudowire
status signaling to indicate the interface failure. The procedures
for both alternatives are described in [3].
3. Security Considerations
This document does not introduce any new security considerations
beyond those in [2] and [3]. This document defines an application
that utilizes the encapsulation specified in [2], and does not
specify the protocols used to carry the encapsulated packets across
the PSN. Each such protocol may have its own set of security issues,
but those issues are not affected by the application specified
herein. Note that the security of the transported ATM service will
only be as good as the security of the PSN. This level of security
might be less rigorous than a native ATM service.
4. Congestion Control
Since this document discusses an application of the "N-to-one" VCC
cell transport mode for PWE3 ATM encapsulation described in [2], the
congestion control considerations are identical to those discussed in
section 15 of [2]. The PWE3 Working Group is also undertaking
additional work on ATM-related congestion issues, and implementers
should anticipate that an RFC will be published describing additional
congestion control techniques that should be applied to ATM emulation
over pseudowires.
5. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Martini, L., Jayakumar, J., Bocci, M., El-Aawar, N., Brayley, J.,
and G. Koleyni, "Encapsulation Methods for Transport of
Asynchronous Transfer Mode (ATM) over MPLS Networks", RFC 4717,
December 2006.
[3] Martini, L., Rosen, E., El-Aawar, N., Smith, T., and G. Heron,
"Pseudowire Setup and Maintenance Using the Label Distribution
Protocol (LDP)", RFC 4447, April 2006.
[4] Martini, L., "IANA Allocations for Pseudowire Edge to Edge
Emulation (PWE3)", BCP 116, RFC 4446, April 2006.
Malis, et al. Standards Track [Page 3]
^L
RFC 4816 PWE3 ATM Transparent Cell Transport Service February 2007
Acknowledgments
The authors would like to thank the members of the PWE3 working group
for their assistance on this document, and Sasha Vainshtein of Axerra
in particular for his comments and suggestions.
Author's Addresses
Andrew G. Malis
Verizon Communications
40 Sylvan Road
Waltham, MA
EMail: andrew.g.malis@verizon.com
Luca Martini
Cisco Systems, Inc.
9155 East Nichols Avenue, Suite 400
Englewood, CO, 80112
EMail: lmartini@cisco.com
Jeremy Brayley
ECI Telecom
Omega Corporate Center
1300 Omega Drive
Pittsburgh, PA 15205
EMail: jeremy.brayley@ecitele.com
Tom Walsh
Juniper Networks
1194 N Mathilda Ave
Sunnyvale, CA 94089
EMail: twalsh@juniper.net
Malis, et al. Standards Track [Page 4]
^L
RFC 4816 PWE3 ATM Transparent Cell Transport Service February 2007
Full Copyright Statement
Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Malis, et al. Standards Track [Page 5]
^L
|
