As per Relevance of the word information, we have this rfc below:
Network Working Group K.
Request for Comments: 2171 M.
Category: Informational NTT
June 1997
MAPOS - Multiple Access Protocol over SONET/SDH Version 1
Status of this
This memo provides information for the Internet community. This
does not specify an Internet standard of any kind. Distribution
this memo is unlimited
Authors'
This memo documents a multiple access protocol for transmission
network-protocol datagrams, encapsulated in High-Level Data
Control (HDLC) frames, over SONET/SDH. This document is NOT
product of an IETF working group nor is it a standards
document. It has not necessarily benefited from the widespread
in depth community review that standards track documents receive
This document describes the protocol MAPOS, Multiple Access
over SONET/SDH, for transmitting network-protocol datagrams
SONET/SDH. It focuses on the core protocol -- other documents
in the bibliography may be referenced in conjunction with
document to provide support and services for protocols at
layers
1.
1.1 SONET/
The Synchronous Optical Network/Synchronous Digital
(SONET/SDH) [1][2][3][4] family of ITU-T standard protocols
designed to provide common, simple, and flexible interface
broadband optical fiber transmission systems. It enables
octet-synchronous multiplexing of lower rate tributaries
SONET/SDH-compliant transmission systems are widely deployed
telephone carriers world wide
This document defines the MAPOS protocol -- a method for
HDLC frames over SONET/SDH. The protocol provides multiple
capability to SONET/SDH, an inherently point-to-point link.
enables construction of seamless networking environment
SONET/SDH as transmission media for both LAN and WAN
Murakami & Maruyama Informational [Page 1]
RFC 2171 MAPOS June 1997
1.2 Possible
The MAPOS protocol provides multiple access, broadcast / multicast
capable switched LAN environment using SONET/SDH lines
transmission media. Possible configurations of MAPOS system
shown in the following diagrams. In (a), two end nodes are
to each other. Figure (b) shows a star-topology "SONET-LAN"
multiple end nodes are connected to an HDLC frame switch. The
switch forwards packets between nodes and provides multiple
capability. In (c), multiple frame switches are linked together
creating a switching cluster
+------+ +------+
| Node +--------------------------------+ Node |
+------+ +------+
(a) Point-to-Point
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RFC 2171 MAPOS June 1997
+------+ +---------------+
| Node +--------------------------------+ |
+------+ | |
| |
+------+ | |
| Node +--------------------------------+ |
+------+ | |
| Frame Switch |
+------+ | |
| Node +--------------------------------+ |
+------+ | |
| |
+------+ | |
| Node +--------------------------------+ |
+------+ +---------------+
(b) Point-to-Multipoint
+--------+ +--------+
| Frame +----------------------+ Frame |
| Switch +--------+ +--------+ Switch |
+--+-----+ +-+----+-+ +--------+
| | Frame | +--------+
+--+-----+ | Switch | +--------+ | Frame |
| Frame | +-----+--+ | Frame +------+ Switch |
| Switch | +---------+ Switch | ++-------+
+-------++ +--------+ |
|________________________________________|
(c) Switching cluster
Figure 1. Possible
Each port on a switch has an unique identifier within the switch.
node connected to a switch port must inherit the address of the port
That is, the node address is equal to the port identifier and
unique within the switch
In a switch cluster, a node address is subnetted. The high-
bits, the part where the corresponding bits in the "subnet mask"
1, indicate the switch address. The remaining low-order
indicate the unique node address within the switch. The two
form an unique address for a given node
In either case, the address may be configured manually into a
interface, or automatically by the address assignment
described in [5].
Murakami & Maruyama Informational [Page 3]
RFC 2171 MAPOS June 1997
Note that any two components may be connected either directly, or
a long-haul SONET/SDH leased line
1.3 Packet
The protocol is connection-less -- when a node wish to
with some other node, it simply fills-in the destination address
an HDLC frame, places it in one or more SONET/SDH payloads, and
it over a SONET/SDH link
The switch forwards the frame to its destination based on
destination address. In a switch cluster, the frame may be
by multiple switches and is eventually delivered to the
node. Broadcast and multicast are also supported. Frames with
invalid destination address are silently discarded
Like ethernet, the multiple access capability is provided by a
or a switch cluster. Since MAPOS is a link layer protocol, it
independent of the upper layer protocols. That is, it can support
network layer protocols such as IP. MAPOS IPv4 support is
in [6].
2. Physical
This protocol treats the underlying end-to-end SONET/SDH
link as if it was a plain, transparent channel. It sends HDLC
in SONET/SDH payloads, and expects them to arrive at the other
unaltered
Each node and switch should terminate SONET/SDH overhead such
section overhead, line overhead, and path overhead according to
specification of SONET/SDH. Unfortunately, SONET and SDH
interpretations are not identical. In addition, some SONET/
implementations utilize some overhead bytes in proprietary manner
The detail of the interpretation is beyond the scope of
document. Appendix A describes some of the most
differences among SONET, SDH, and their implementations that
causes interoperability problems. Implementors of SONET/
interfaces are strongly encouraged to be aware of such differences
and provide workaround options in their products
Murakami & Maruyama Informational [Page 4]
RFC 2171 MAPOS June 1997
3. Data Link
3.1 HDLC Frame
MAPOS uses the same HDLC-like framing as used in PPP-over-SONET
described in RFC-1662[7]. Figure 2 shows the frame format.
Link Control (LLC), and Sublayer/Sub-Network Access Protocol (SNAP
are not used. It does not include the bytes for transparency.
fields are transmitted from left to right
+----------+----------+----------+----------+
| | | | |
| Flag | Address | Control | Protocol |
| 01111110 | 8bits | 00000011 | 16 bits |
+----------+----------+----------+----------+
+-------------+------------+----------+-----------
| | | | Inter-
| Information | FCS | Flag | fill or
| | 16/32 bits | 01111110 |
+-------------+------------+----------+------------
Figure 2. Frame
Flag
Flag sequence is used for frame synchronization. Each frame
and ends with a flag sequence 01111110 (0x7E). If a
immediately follows another, one flag sequence may be treated
the end of the preceding frame and the beginning of the
following frame. When the line is idle, the flag sequence is to
transmitted continuously on the line
The address field contains the destination HDLC address. A
is forwarded by a switch based on this field. It is 8 bits wide
The LSB indicates the end of this field, and must always be 1.
MSB is used to indicate if the frame is a unicast or a
frame. The MSB of 0 means unicast, with the remaining six
indicating the destination node address. MSB of 1 means multicast
with the remaining six bits indicating the group address.
address 11111111 (0xFF) means that the frame is a broadcast frame
The address 00000001 (0x01) is reserved to identify the
processor inside a switch. Frames with an invalid address
be silently discarded
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RFC 2171 MAPOS June 1997
+-------------+-+
| | | | | | | | |
| | node addr |1|
+-+-----------+-+
^ ^
| |
| +------- EA bit (always 1)
|
1 : broadcast,
0 :
Figure 3 Address
The control field contains single octet 00000011 (0x03) which,
HDLC nomenclature, means that the frame is an
Information (UI) with the Poll/Final (P/F) bit set to zero.
with any other control field values should be silently discarded
The protocol field indicates the protocol to which the
encapsulated in the information field belongs. It conforms to
ISO 3309 extension mechanism, and the value for this field may
obtained from the most recent "Assigned Numbers" [8] and "
Version 1 Assigned Numbers" [9].
The information field contains the datagram for the
specified in the protocol field. The length of this field
vary, but shall not exceed 65,280 (64K - 256) octets
Frame Check Sequence (FCS
By default, the frame check sequence (FCS) field is 16-bits long
Optionally, 32 bit FCS may be used instead. The FCS is
over all bits of the address, control, protocol, and
fields prior to escape conversions. The least significant octet
the result is transmitted first as it contains the coefficient
the highest term
Inter-frame
A sending station must continuously transmit the flag sequence
inter-frame fill after the FCS field. The inter-frame
sequences must be silently discarded by the receiving station
Murakami & Maruyama Informational [Page 6]
RFC 2171 MAPOS June 1997
When an under-run occurs during DMA in the sending station, it
abort the frame transfer and continuously send the flag sequence
indicate the error
3.2 Octet-Synchronous
MAPOS uses an octet stuffing procedure because it treats SONET/SDH
a byte-oriented synchronous link. Since SONET/SDH
transparency, Async-Control-Character-Map (ACCM) is not used.
frames are mapped into the SONET/SDH payload as follows
Each HDLC frame is separated from another frame by one or more
sequence, 01111110 (0x7E). An escape sequence is defined to
the flag sequence and itself. Prior to sending the frame, but
the FCS computation, every occurrence of 01111110 (0x7E) other
the flags is to be converted to the sequence 01111101 01011110 (0x7
0x5E), and the sequence 01111101 (0x7D) is to be converted to
sequence 01111101 01011101 (0x7D 0x5D). Upon receiving a frame,
conversion must be reversed prior to FCS computation
4. Further
To fully utilize MAPOS protocol, it is useful to reference
documents[5][6][9][10] in conjunction with this document
5. Security
Security issues are not discussed in this memo
[1] CCITT Recommendation G.707: Synchronous Digital Hierarchy
Rates (1990).
[2] CCITT Recommendation G.708: Network Node Interface
Synchronous Digital Hierarchy (1990).
[3] CCITT Recommendation G.709: Synchronous Multiplexing
(1990).
[4] American National Standard for Telecommunications -
Hierarchy - Optical Interface Rates and Formats Specification
ANSI T1.105-1991.
[5] Murakami, K. and M. Maruyama, "A MAPOS version 1 Extension -
Node Switch Protocol," RFC2173, June, 1997.
Murakami & Maruyama Informational [Page 7]
RFC 2171 MAPOS June 1997
[6] Murakami, K. and M. Maruyama, "IPv4 over MAPOS Version 1,"
RFC2176, June, 1997.
[7] Simpson, W., editor, "PPP in HDLC-like Framing," RFC1662,
1994.
[8] IANA, "IANA-Assignments,"
http://www.iana.org/iana/assignments.
[9] Maruyama, M. and K. Murakami, "MAPOS Version 1
Numbers," RFC2172, June 1997.
[10] Murakami, K. and M. Maruyama, "A MAPOS version 1 Extension -
Switch Switch Protocol," RFC2174, June, 1997.
The authors would like to acknowledge the contributions
thoughtful suggestions of John P. Mullaney, Clark Bremer,
Kobayashi, Paul Francis, Toshiaki Yoshida, and Takahiro Sajima
Author's
Ken
NTT Software
3-9-11, Midori-
Musashino-
Tokyo-180,
E-mail: murakami@ntt-20.ecl.
Mitsuru
NTT Software
3-9-11, Midori-
Musashino-
Tokyo-180,
E-mail: mitsuru@ntt-20.ecl.
Murakami & Maruyama Informational [Page 8]
RFC 2171 MAPOS June 1997
APPENDIX A. Differences among SONET, SDH, and their
This section briefly describes the major differences among
which is an ANSI standard, SDH, an ITU-T standard, and
implementations
AU pointer (H1, H2, H3)
The AU pointer consists of bytes H1, H2, and H3. The bits 5 and 6
of the H1 byte are called "SS bits," and are used to indicate
offset into the payload where the beginning of a SPE is located
(Note that "SPE" is a SONET term -- SDH calls it "VC.") In
case of OC-3c, SONET sets the SS bits of the second and the
H1 bytes to 0, whereas SDH sets them to 10 for AU-4, and 01
AU-31. Although the SS bits may be ignored at the
station, some transmission systems discards SONET/SDH frames
SS bits that it doesn't expect -- the sending station should
aware of this, and include a configuration option to handle it
Z1 and Z
The Z bytes are reserved in SONET/SDH. Some transmission systems
however, use them in a proprietary manner. SONET uses Z1 for
Error Monitoring. NTT, a carrier in Japan, utilized Z1
Automatic Protection Switching (APS.)
DCC
The D bytes are called the Data Communication channel (DCC),
are defined for maintenance and operations. However, some
and vendors use them in a proprietary manner. For example, NTT'
STM-1 UNI uses the D4, D5, and D6 bytes to transfer section
path maintenance information
Murakami & Maruyama Informational [Page 9]
if you see any problems within the linking, don't worry be happy,
this is version 0.1 of the Relevance System and you gotta expect some crappy subroutines sometimes,
just be content we did not write this in Java, which would have made this "bigger and better" HAHAHHA.
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