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
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
|
Network Working Group W. Simpson
Request for Comments: 1619 Daydreamer
Category: Standards Track May 1994
PPP over SONET/SDH
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.
Abstract
The Point-to-Point Protocol (PPP) [1] provides a standard method for
transporting multi-protocol datagrams over point-to-point links.
This document describes the use of PPP over Synchronous Optical
Network (SONET) and Synchronous Digital Heirarchy (SDH) circuits.
This document is the product of the Point-to-Point Protocol Working
Group of the Internet Engineering Task Force (IETF). Comments should
be submitted to the ietf-ppp@merit.edu mailing list.
Applicability
This specification is intended for those implementations which desire
to use the PPP encapsulation over high speed private point-to-point
links, such as intra-campus single-mode fiber which may already be
installed and unused. Because the PPP encapsulation has relatively
low overhead, it is anticipated that significantly higher throughput
can be attained compared to other SONET/SDH payload mappings, at a
significantly lower cost for line termination equipment.
Simpson [Page i]
^LRFC 1619 PPP over SONET/SDH May 1994
Table of Contents
1. Introduction .......................................... 1
2. Physical Layer Requirements ........................... 1
3. Framing ............................................... 2
4. Configuration Details ................................. 3
SECURITY CONSIDERATIONS ...................................... 3
REFERENCES ................................................... 3
ACKNOWLEDGEMENTS ............................................. 3
CHAIR'S ADDRESS .............................................. 4
AUTHOR'S ADDRESS ............................................. 4
Simpson [Page ii]
^LRFC 1619 PPP over SONET/SDH May 1994
1. Introduction
PPP was designed as a standard method of communicating over point-
to-point links. Initial deployment has been over short local lines,
leased lines, and plain-old-telephone-service (POTS) using modems.
As new packet services and higher speed lines are introduced, PPP is
easily deployed in these environments as well.
This specification is primarily concerned with the use of the PPP
encapsulation over SONET/SDH links. Since SONET/SDH is by definition
a point-to-point circuit, PPP is well suited to use over these links.
The Synchronous Optical Network (SONET) [3] is an octet-synchronous
multiplex scheme that defines a family of standard rates and formats.
Despite the name, it is not limited to optical links. Electrical
specifications have been defined for single-mode fiber, multi-mode
fiber, and CATV 75 ohm coaxial cable. The transmission rates are
integral multiples of 51.840 Mbps, which may be used to carry T3/E3
bit-synchronous signals. The allowed multiples are currently
specified as
STS-1 51.840 STS-18 933.120
STS-3 155.520 STS-24 1,244.160
STS-9 466.560 STS-36 1,866.240
STS-12 622.080 STS-48 2,488.320
The CCITT Synchronous Digital Heirarchy (SDH) defines a subset of
SONET transmission rates beginning at 155.520 Mbps [5].
SONET SDH equivalent
STS-3c STM-1
STS-12c STM-4
STS-48c STM-16
2. Physical Layer Requirements
PPP treats SONET/SDH transport as octet oriented synchronous links.
SONET/SDH links are full-duplex by definition.
Interface Format
PPP presents an octet interface to the physical layer. There is
no provision for sub-octets to be supplied or accepted.
Simpson [Page 1]
^LRFC 1619 PPP over SONET/SDH May 1994
The octet stream is mapped into the SONET/SDH Synchronous Payload
Envelope (SPE), with the octet boundaries aligned with the SPE
octet boundaries.
No scrambling is needed during insertion into the SPE.
The Path Signal Label (C2) is intended to indicate the contents of
the SPE. The experimental value of 207 (cf hex) is used to
indicate PPP.
The Multiframe Indicator (H4) is currently unused, and MUST be
zero.
Transmission Rate
The basic rate for PPP over SONET/SDH is that of STS-3c/STM-1 at
155.520 Mbps. The available information bandwidth is 149.760
Mbps, which is the STS-3c/STM-1 SPE with section, line and path
overhead removed. This is the same super-rate mapping that is
used for ATM and FDDI [4].
Lower signal rates MUST use the Virtual Tributary (VT) mechanism
of SONET/SDH. This maps existing signals up to T3/E3 rates
asynchronously into the SPE, or uses available clocks for bit-
synchronous and byte-synchronous mapping.
Higher signal rates SHOULD conform to the SDH STM series, rather
than the SONET STS series, as equipment becomes available. The
STM series progresses in powers of 4 (instead of 3), and employs
fewer steps, which is likely to simplify multiplexing and
integration.
Control Signals
PPP does not require the use of control signals. When available,
using such signals can allow greater functionality and
performance. Implications are discussed in [2].
3. Framing
The framing for octet-synchronous links is described in "PPP in HDLC
Framing" [2].
The PPP frames are located by row within the SPE payload. Because
frames are variable in length, the frames are allowed to cross SPE
boundaries.
Simpson [Page 2]
^LRFC 1619 PPP over SONET/SDH May 1994
4. Configuration Details
The standard LCP sync configuration defaults apply to SONET/SDH
links.
The following Configuration Options are recommended:
Magic Number
No Address and Control Field Compression
No Protocol Field Compression
32-bit FCS
Security Considerations
Security issues are not discussed in this memo.
References
[1] Simpson, W., Editor, "The Point-to-Point Protocol (PPP)", RFC
1548, Daydreamer, December 1993.
[2] Simpson, W., Editor, "PPP in HDLC Framing", RFC 1549,
Daydreamer, December 1993.
[3] "American National Standard for Telecommunications - Digital
Hierarchy - Optical Interface Rates and Formats Specification",
ANSI T1.105-1991.
[4] "American National Standard for Telecommunications -
Synchronous Optical Network (SONET) Payload Mappings", ANSI
T1.105.02-1993 draft.
[5] CCITT Recommendation G.707, "Synchronous Digital Hierarchy Bit
Rates", June 1992.
Simpson [Page 3]
^LRFC 1619 PPP over SONET/SDH May 1994
Acknowledgments
PPP over SONET was first proposed by Craig Partridge (BBN). Some
information was obtained from the good folks at Bellcore.
Technical assistance and information was also provided by Victor
Demjanenko (SUNY Buffalo).
Special thanks to Morning Star Technologies for providing computing
resources and network access support for writing this specification.
Chair's Address
The working group can be contacted via the current chair:
Fred Baker
Advanced Computer Communications
315 Bollay Drive
Santa Barbara, California 93117
EMail: fbaker@acc.com
Author's Address
Questions about this memo can also be directed to:
William Allen Simpson
Daydreamer
Computer Systems Consulting Services
1384 Fontaine
Madison Heights, Michigan 48071
EMail: Bill.Simpson@um.cc.umich.edu
bsimpson@MorningStar.com
Simpson [Page 4]
|
