draft-ietf-rohc-sigcomp-user-guide-01.txt   draft-ietf-rohc-sigcomp-user-guide-02.txt 
Robust Header Compression A. Surtees Robust Header Compression A. Surtees
Internet-Draft M. West Internet-Draft M. West
Expires: August 19, 2005 Siemens/Roke Manor Research Expires: January 19, 2006 Siemens/Roke Manor Research
February 18, 2005 July 18, 2005
SigComp Users' Guide SigComp Users' Guide
draft-ietf-rohc-sigcomp-user-guide-01.txt draft-ietf-rohc-sigcomp-user-guide-02.txt
Status of this Memo Status of this Memo
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RFC 3668.
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2005). Copyright (C) The Internet Society (2005).
Abstract Abstract
This document provides an informational guide for users of the This document provides an informational guide for users of the
SigComp protocol. The aim of the document is to assist users when SigComp protocol. The aim of the document is to assist users when
making SigComp implementation decisions; for example the choice of making SigComp implementation decisions; for example the choice of
compression algorithm and the level of robustness against lost or compression algorithm and the level of robustness against lost or
misordered packets. misordered packets.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Overview of the User Guide . . . . . . . . . . . . . . . . . . 3 2. Overview of the User Guide . . . . . . . . . . . . . . . . . . 3
3. UDVM assembly language . . . . . . . . . . . . . . . . . . . . 4 3. UDVM assembly language . . . . . . . . . . . . . . . . . . . . 4
3.1 Lexical level . . . . . . . . . . . . . . . . . . . . . . 4 3.1 Lexical level . . . . . . . . . . . . . . . . . . . . . . 4
3.2 Syntactic level . . . . . . . . . . . . . . . . . . . . . 5 3.2 Syntactic level . . . . . . . . . . . . . . . . . . . . . 5
3.2.1 Expressions . . . . . . . . . . . . . . . . . . . . . 6 3.2.1 Expressions . . . . . . . . . . . . . . . . . . . . . 7
3.2.2 Instructions . . . . . . . . . . . . . . . . . . . . . 7 3.2.2 Instructions . . . . . . . . . . . . . . . . . . . . . 8
3.2.3 Directives . . . . . . . . . . . . . . . . . . . . . . 8 3.2.3 Directives . . . . . . . . . . . . . . . . . . . . . . 9
3.2.4 Labels . . . . . . . . . . . . . . . . . . . . . . . . 9 3.2.4 Labels . . . . . . . . . . . . . . . . . . . . . . . . 10
3.3 Uploading the bytecode to the UDVM . . . . . . . . . . . . 10 3.3 Uploading the bytecode to the UDVM . . . . . . . . . . . . 10
4. Compression algorithms . . . . . . . . . . . . . . . . . . . . 11 4. Compression algorithms . . . . . . . . . . . . . . . . . . . . 12
4.1 Simplified LZ77 . . . . . . . . . . . . . . . . . . . . . 11 4.1 Well-known Compression Algorithms . . . . . . . . . . . . 12
4.2 LZSS . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 4.1.1 Simplified LZ77 . . . . . . . . . . . . . . . . . . . 12
4.3 LZW . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 4.1.2 LZSS . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.4 DEFLATE . . . . . . . . . . . . . . . . . . . . . . . . . 20 4.1.3 LZW . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.5 LZJH . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 4.1.4 DEFLATE . . . . . . . . . . . . . . . . . . . . . . . 21
4.6 EPIC . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 4.1.5 LZJH . . . . . . . . . . . . . . . . . . . . . . . . . 24
4.2 Adapted Algorithms . . . . . . . . . . . . . . . . . . . . 28
4.2.1 Modified DEFLATE . . . . . . . . . . . . . . . . . . . 28
5. Additional SigComp mechanisms . . . . . . . . . . . . . . . . 31 5. Additional SigComp mechanisms . . . . . . . . . . . . . . . . 31
5.1 Acknowledging a state item . . . . . . . . . . . . . . . . 31 5.1 Acknowledging a state item . . . . . . . . . . . . . . . . 32
5.2 Static dictionary . . . . . . . . . . . . . . . . . . . . 33 5.2 Static dictionary . . . . . . . . . . . . . . . . . . . . 33
5.3 CRC checksum . . . . . . . . . . . . . . . . . . . . . . . 33 5.3 CRC checksum . . . . . . . . . . . . . . . . . . . . . . . 34
5.4 Announcing additional resources . . . . . . . . . . . . . 34 5.4 Announcing additional resources . . . . . . . . . . . . . 34
5.5 Shared compression . . . . . . . . . . . . . . . . . . . . 35 5.5 Shared compression . . . . . . . . . . . . . . . . . . . . 36
6. Security considerations . . . . . . . . . . . . . . . . . . . 38 6. Security considerations . . . . . . . . . . . . . . . . . . . 37
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 38 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 37
8. Intellectual Property Right Considerations . . . . . . . . . . 38 8. Intellectual Property Right Considerations . . . . . . . . . . 37
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 39 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 40 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 39
A. UDVM bytecode for the compression algorithms . . . . . . . . . 40 A. UDVM bytecode for the compression algorithms . . . . . . . . . 39
A.1 Simplified LZ77 . . . . . . . . . . . . . . . . . . . . . 40 A.1 Well-known Algorithms . . . . . . . . . . . . . . . . . . 39
A.2 LZSS . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 A.1.1 Simplified LZ77 . . . . . . . . . . . . . . . . . . . 39
A.3 LZW . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 A.1.2 LZSS . . . . . . . . . . . . . . . . . . . . . . . . . 39
A.4 DEFLATE . . . . . . . . . . . . . . . . . . . . . . . . . 41 A.1.3 LZW . . . . . . . . . . . . . . . . . . . . . . . . . 40
A.5 LZJH . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 A.1.4 DEFLATE . . . . . . . . . . . . . . . . . . . . . . . 40
A.6 EPIC . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 A.1.5 LZJH . . . . . . . . . . . . . . . . . . . . . . . . . 40
A.2 Adapted Algorithms . . . . . . . . . . . . . . . . . . . . 40
A.2.1 Modified DEFLATE . . . . . . . . . . . . . . . . . . . 40
Intellectual Property and Copyright Statements . . . . . . . . 42 Intellectual Property and Copyright Statements . . . . . . . . 42
1. Introduction 1. Introduction
This document provides an informational guide for users of the This document provides an informational guide for users of the
SigComp protocol RFC-3320 [4]. The idea behind SigComp is to SigComp protocol RFC-3320 [4]. The idea behind SigComp is to
standardize a Universal Decompressor Virtual Machine (UDVM) that can standardize a Universal Decompressor Virtual Machine (UDVM) that can
be programmed to understand the output of many well-known compressors be programmed to understand the output of many well-known compressors
including DEFLATE DEFLATE [10] and LZW LZW [9]. The bytecode for the including DEFLATE [10] and LZW [9]. The bytecode for the choice of
choice of compression algorithm is uploaded to the UDVM as part of compression algorithm is uploaded to the UDVM as part of the
the compressed data. compressed data.
The basic SigComp RFC describes the actions that an endpoint must The basic SigComp RFC describes the actions that an endpoint must
take upon receiving a SigComp message. However the entity take upon receiving a SigComp message. However the entity
responsible for generating new SigComp messages (the SigComp responsible for generating new SigComp messages (the SigComp
compressor) is left as an implementation decision; any compressor can compressor) is left as an implementation decision; any compressor can
be used provided that it generates SigComp messages that can be be used provided that it generates SigComp messages that can be
successfully decompressed by the receiving endpoint. successfully decompressed by the receiving endpoint.
This document offers a number of different compressors that can be This document offers a number of different compressors that can be
used by the SigComp protocol. It also describes how standard stream- used by the SigComp protocol. It also describes how standard stream-
skipping to change at page 3, line 42 skipping to change at page 3, line 42
algorithms to the receiving endpoint, arbitrary compression algorithms to the receiving endpoint, arbitrary compression
algorithms can be supported provided that bytecode has been written algorithms can be supported provided that bytecode has been written
for the corresponding decompressor. for the corresponding decompressor.
This document provides bytecode for the following algorithms: This document provides bytecode for the following algorithms:
1. Simplified LZ77 1. Simplified LZ77
2. LZSS 2. LZSS
3. LZW 3. LZW
4. DEFLATE 4. DEFLATE
5. LZJH 5. LZJH
6. EPIC
Any of the above algorithms may be useful depending on the desired Any of the above algorithms may be useful depending on the desired
compression ratio, processing and memory requirements, code size, compression ratio, processing and memory requirements, code size,
implementation complexity and Intellectual Property (IPR) implementation complexity and Intellectual Property (IPR)
considerations. considerations.
As well as encoding the application messages using the chosen As well as encoding the application messages using the chosen
algorithm, the SigComp compressor is responsible for ensuring that algorithm, the SigComp compressor is responsible for ensuring that
messages can be correctly decompressed even if packets are lost or messages can be correctly decompressed even if packets are lost or
misordered during transmission. The SigComp feedback mechanism can misordered during transmission. The SigComp feedback mechanism can
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tokens optionally separated by whitespace. Each token can be a text tokens optionally separated by whitespace. Each token can be a text
name, an instruction opcode, a delimiter, or an integer (specified as name, an instruction opcode, a delimiter, or an integer (specified as
decimal, binary or hex). decimal, binary or hex).
The following ABNF description RFC-2234 [3] specifies the syntax of a The following ABNF description RFC-2234 [3] specifies the syntax of a
token: token:
token = (name / opcode / delimiter / dec / bin / hex) token = (name / opcode / delimiter / dec / bin / hex)
name = (lowercase / "_") 1*(lowercase / digit / "_") name = (lowercase / "_") 1*(lowercase / digit / "_")
opcode = uppercase *(uppercase / digit / "-") opcode = uppercase *(uppercase / digit / "-")
delimiter = "." / "!" / "$" / ":" / "(" / ")" / operator delimiter = "." / "," / "!" / "$" / ":" / "(" / ")" /
operator
dec = 1*(digit) dec = 1*(digit)
bin = "0b" 1*("0" / "1") bin = "0b" 1*("0" / "1")
hex = "0x" 1*(hex_digit) hex = "0x" 1*(hex_digit)
hex_digit = digit / %x41-46 / %x61-66 hex_digit = digit / %x41-46 / %x61-66
digit = %x30-39 digit = %x30-39
uppercase = %x41-5a uppercase = %x41-5a
lowercase = %x61-7a lowercase = %x61-7a
operator = "+" / "-" / "*" / "/" / "%" / "&" / "|" / operator = "+" / "-" / "*" / "/" / "%" / "&" / "|" /
"^" / "~" / "<<" / ">>" "^" / "~" / "<<" / ">>"
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from one or more lexical tokens. from one or more lexical tokens.
The following ABNF description specifies the syntax of the assembly The following ABNF description specifies the syntax of the assembly
language. Note that the lexical parsing step is assumed to have been language. Note that the lexical parsing step is assumed to have been
carried out, so in particular the boundaries between tokens are carried out, so in particular the boundaries between tokens are
already known and the comments and whitespace have been deleted: already known and the comments and whitespace have been deleted:
assembly = *(instruction / directive / label) assembly = *(instruction / directive / label)
instruction = opcode ["(" operand *("," operand) ")"] instruction = opcode ["(" operand *("," operand) ")"]
operand = [["$"] expression] operand = [["$"] expression]
; Operands can be left black if they can ; Operands can be left blank if they can
; be automatically inferred by the ; be automatically inferred by the
; compiler, e.g. a literal (#) operand ; compiler, e.g. a literal operand
; that specifies the total number of ; that specifies the total number of
; operands for the instruction. ; operands for the instruction.
; When "$" is prepended to an operand, ; When "$" is prepended to an operand,
; the corresponding integer is an ; the corresponding integer is an
; address rather than the actual operand ; address rather than the actual operand
; value. This symbol is mandatory for ; value. This symbol is mandatory for
; reference operands ($), optional for ; reference operands, optional for
; multitypes (%) and addresses (@), and ; multitypes and addresses, and
; disallowed for literals (#). ; disallowed for literals.
label = ":" name label = ":" name
directive = padding / data / set directive = padding / data / set / readonly
; note that directive names are ; note that directive names are
; syntactically of category <name>; all ; syntactically of category <name>; all
; directives are intended to syntactically ; directives are intended to syntactically
; match: name ["(" expression *("," ; match: name ["(" expression *(","
; expression) ")"] ; expression) ")"]
padding = ("pad" / "align" / "at") "(" expression ")" padding = ("pad" / "align" / "at") "(" expression ")"
data = ("byte" / "word") "(" expression *("," data = ("byte" / "word") "(" expression *(","
expression) ")" expression) ")"
readonly = "readonly" "(" "0" / "1" ")"
set = "set" "(" name "," expression ")" set = "set" "(" name "," expression ")"
expression = value / "(" expression operator expression ")" expression = value / "(" expression operator expression ")"
value = dec / bin / hex / name / "." / "!" value = dec / bin / hex / name / "." / "!"
; "." is the location of this ; "." is the location of this
; instruction/directive, whereas "!" is ; instruction/directive, whereas "!" is
; the location of the closest ; the location of the closest
; DECOMPRESSION-FAILURE ; DECOMPRESSION-FAILURE
The following sections define how to convert the instructions, labels The following sections define how to convert the instructions, labels
and directives into UDVM bytecode: and directives into UDVM bytecode:
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is encountered it is replaced by the location in the bytecode of the is encountered it is replaced by the location in the bytecode of the
closest DECOMPRESSION-FAILURE instruction (i.e. the closest zero closest DECOMPRESSION-FAILURE instruction (i.e. the closest zero
byte). This can be useful when writing UDVM instructions that call a byte). This can be useful when writing UDVM instructions that call a
decompression failure, for example: decompression failure, for example:
INPUT-BYTES (1, temp, !) INPUT-BYTES (1, temp, !)
The above instruction causes a decompression failure to occur if it The above instruction causes a decompression failure to occur if it
tries to input data from beyond the end of the compressed message. tries to input data from beyond the end of the compressed message.
N.B. When using "!" in the assembly language to generate bytecode,
care must be taken to ensure that the address of the zero used at
bytecode generation time will still contain zero when the bytecode is
run.
It is also possible to assign integer values to text names: when a It is also possible to assign integer values to text names: when a
text name is encountered in an expression it is replaced by the text name is encountered in an expression it is replaced by the
integer value assigned to it. Section 3.2.3 explains how to assign integer value assigned to it. Section 3.2.3 explains how to assign
integer values to text names. integer values to text names.
3.2.2 Instructions 3.2.2 Instructions
A UDVM instruction is specified by the instruction opcode followed by A UDVM instruction is specified by the instruction opcode followed by
zero or more operands. The instruction operands are enclosed in zero or more operands. The instruction operands are enclosed in
parentheses and separated by commas, for example: parentheses and separated by commas, for example:
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The missing operand should be given the value 4 because it is The missing operand should be given the value 4 because it is
followed by a total of 4 operands. followed by a total of 4 operands.
If the operand is a reference then as per Figure 9 of SigComp, the If the operand is a reference then as per Figure 9 of SigComp, the
parser inserts the shortest bytecode capable of encoding the supplied parser inserts the shortest bytecode capable of encoding the supplied
memory address. Note that reference operands will always be preceded memory address. Note that reference operands will always be preceded
by the symbol "$" in assembly because they always encode memory by the symbol "$" in assembly because they always encode memory
addresses rather than actual operand values. addresses rather than actual operand values.
If the operand is a multitype then the parser first checks whether If the operand is a multitype then the parser first checks whether
the symbol "$" is present. If so then as per Figure 10 of SigComp, the symbol "$" is present. If so then, as per Figure 10 of SigComp,
it inserts the shortest bytecode capable of encoding the supplied it inserts the shortest bytecode capable of encoding the supplied
integer as a memory address. If not then it inserts the shortest integer as a memory address. If not then, as per Figure 10 of
bytecode that encodes the supplied integer as an operand value. SigComp, it inserts the shortest bytecode that encodes the supplied
integer as an operand value.
If the operand is an address then the parser checks whether the If the operand is an address then the parser checks whether the
symbol "$" is present. If so then the supplied integer is encoded as symbol "$" is present. If so then the supplied integer is encoded as
a memory address, just as for the multitype instruction above. If a memory address, just as for the multitype instruction above. If
not then the byte position of the opcode is subtracted from the not then the byte position of the opcode is subtracted from the
supplied integer modulo 16, and the result is encoded as an operand supplied integer modulo 16, and the result is encoded as an operand
value as per Figure 10 of SigComp. value as per Figure 10 of SigComp.
3.2.3 Directives 3.2.3 Directives
skipping to change at page 9, line 33 skipping to change at page 9, line 51
evaluate to give integers n[0],..., n[k-1] from 0 to 255. evaluate to give integers n[0],..., n[k-1] from 0 to 255.
The directive "word (n[0],..., n[k-1])" appends k consecutive 2-byte The directive "word (n[0],..., n[k-1])" appends k consecutive 2-byte
words to the bytecode. The word string is supplied as expressions words to the bytecode. The word string is supplied as expressions
which evaluate to give integers n[0],..., n[k-1] from 0 to 65535. which evaluate to give integers n[0],..., n[k-1] from 0 to 65535.
The directive "set (name, n)" assigns an integer value n to a The directive "set (name, n)" assigns an integer value n to a
specified text name. The integer value can be supplied in the form specified text name. The integer value can be supplied in the form
of an expression. of an expression.
The directive "readonly (n)" where n is 0 or 1 can be used to
indicate that an area of memory could be changed (0) or will not be
changed (1) during the execution of the UDVM. This directive could
be used, for example, in conjunction with "!" to ensure that the
address of the nearest zero will still contain zero when the bytecode
is executed.
3.2.4 Labels 3.2.4 Labels
A label is a special directive used to assign memory addresses to A label is a special directive used to assign memory addresses to
text names. text names.
Labels are specified by giving a single colon followed by the text Labels are specified by giving a single colon followed by the text
name to be defined. The (absolute) position of the byte immediately name to be defined. The (absolute) position of the byte immediately
following the label is evaluated and assigned to the text name. For following the label is evaluated and assigned to the text name. For
example: example:
skipping to change at page 11, line 28 skipping to change at page 12, line 14
(destination + code_len - 1) inclusive. (destination + code_len - 1) inclusive.
4. Compression algorithms 4. Compression algorithms
This chapter describes a number of compression algorithms that can be This chapter describes a number of compression algorithms that can be
used by a SigComp compressor. In each case the document provides used by a SigComp compressor. In each case the document provides
UDVM bytecode for the corresponding decompression algorithm, which UDVM bytecode for the corresponding decompression algorithm, which
can be uploaded to the receiving endpoint as part of a SigComp can be uploaded to the receiving endpoint as part of a SigComp
message. message.
Section 4.1 covers a simple algorithm in some detail, including the Section 4.1.1 covers a simple algorithm in some detail, including the
steps required to compress and decompress a SigComp message. The steps required to compress and decompress a SigComp message. The
remaining sections cover well-known compression algorithms that can remaining sections cover well-known compression algorithms that can
be adapted for use in SigComp with minimal modification. be adapted for use in SigComp with minimal modification.
4.1 Simplified LZ77 4.1 Well-known Compression Algorithms
4.1.1 Simplified LZ77
This section describes how to implement a very simple compression This section describes how to implement a very simple compression
algorithm based on LZ77 LZ77 [7]. algorithm based on LZ77 [7].
A compressed message generated by the simplified LZ77 scheme consists A compressed message generated by the simplified LZ77 scheme consists
of a sequence of 4-byte characters, where each character contains a of a sequence of 4-byte characters, where each character contains a
2-byte position value followed by a 2-byte length value. Each pair 2-byte position value followed by a 2-byte length value. Each pair
of integers identifies a byte string in the UDVM memory; when of integers identifies a byte string in the UDVM memory; when
concatenated these byte strings form the decompressed message. concatenated these byte strings form the decompressed message.
When implementing a bytecode decompressor for the simplified LZ77 When implementing a bytecode decompressor for the simplified LZ77
scheme, the UDVM memory is partitioned into five distinct areas as scheme, the UDVM memory is partitioned into five distinct areas as
shown below: shown below:
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The next 256 bytes are initialized by the bytecode to contain the The next 256 bytes are initialized by the bytecode to contain the
integers 0 to 255 inclusive. The purpose of this memory area is to integers 0 to 255 inclusive. The purpose of this memory area is to
provide a dictionary of all possible uncompressed characters; this is provide a dictionary of all possible uncompressed characters; this is
important to ensure that the compressor can always generate a important to ensure that the compressor can always generate a
sequence of position/length pairs that encode a given message. For sequence of position/length pairs that encode a given message. For
example, a byte with value 0x41 (corresponding to the ASCII character example, a byte with value 0x41 (corresponding to the ASCII character
"A") can be found at Address 0x0141 of the UDVM memory, so the "A") can be found at Address 0x0141 of the UDVM memory, so the
compressed character 0x0141 0001 will decompress to give this ASCII compressed character 0x0141 0001 will decompress to give this ASCII
character. Note that encoding each byte in the application message character. Note that encoding each byte in the application message
as a separate 4-byte compressed character is not recommended however, as a separate 4-byte compressed character is not recommended,
as the resulting "compressed" message is four times as large as the however, as the resulting "compressed" message is four times as large
original uncompressed message. as the original uncompressed message.
The compression ratio of LZ77 is improved by the remaining UDVM The compression ratio of LZ77 is improved by the remaining UDVM
memory, which is used to store a history buffer containing the memory, which is used to store a history buffer containing the
previously decompressed messages. Compressed characters can point to previously decompressed messages. Compressed characters can point to
strings that have previously been decompressed and stored in the strings that have previously been decompressed and stored in the
buffer; so the overall compression ratio of the LZ77 algorithm buffer; so the overall compression ratio of the LZ77 algorithm
improves as the decompressor "learns" more text strings and is able improves as the decompressor "learns" more text strings and is able
to encode longer strings using a single compressed character. The to encode longer strings using a single compressed character. The
buffer is circular, so older messages are overwritten by new data buffer is circular, so older messages are overwritten by new data
when the buffer becomes full. when the buffer becomes full.
Note that the actual size of this circular buffer depends on the Note that the actual size of this circular buffer depends on the
total amount of memory available to the UDVM. The minimum size of total amount of memory available to the UDVM. The minimum size of
the the UDVM memory is 1K, so the circular buffer will always contain at
UDVM memory is 1K, so the circular buffer will always contain at
least 512 bytes. least 512 bytes.
The steps required to implement an LZ77 compressor and decompressor The steps required to implement an LZ77 compressor and decompressor
are similar, although compression is more processor-intensive as it are similar, although compression is more processor-intensive as it
requires a searching operation to be performed. Assembly for the requires a searching operation to be performed. Assembly for the
simplified LZ77 decompressor is given below: simplified LZ77 decompressor is given below:
; Variables that do not need to be stored after decompressing each ; Variables that do not need to be stored after decompressing each
; SigComp message are stored here: ; SigComp message are stored here:
skipping to change at page 15, line 16 skipping to change at page 15, line 48
to give the desired application message. As an example, a message to give the desired application message. As an example, a message
compressed using the simplified LZ77 algorithm is given below: compressed using the simplified LZ77 algorithm is given below:
0x0154 0001 0168 0001 0165 0001 0120 0001 0152 0001 0165 0001 0173 0x0154 0001 0168 0001 0165 0001 0120 0001 0152 0001 0165 0001 0173
0x0002 0161 0001 0175 0001 0172 0001 0161 0001 016e 0001 0174 0001 0x0002 0161 0001 0175 0001 0172 0001 0161 0001 016e 0001 0174 0001
0x0120 0001 0161 0001 020d 0002 0174 0001 0201 0003 0145 0001 016e 0x0120 0001 0161 0001 020d 0002 0174 0001 0201 0003 0145 0001 016e
0x0001 0164 0001 0120 0001 016f 0001 0166 0001 0211 0005 0155 0001 0x0001 0164 0001 0120 0001 016f 0001 0166 0001 0211 0005 0155 0001
0x016e 0001 0169 0001 0176 0001 0165 0001 0172 0002 0165 0001 010a 0x016e 0001 0169 0001 0176 0001 0165 0001 0172 0002 0165 0001 010a
0x0001 0x0001
The uncompressed message is "The Restaurant at the End of the
Universe\n".
The bytecode for the LZ77 decompressor can be uploaded as part of the The bytecode for the LZ77 decompressor can be uploaded as part of the
compressed message as specified in Section 3.3. However, in order to compressed message as specified in Section 3.3. However, in order to
improve the overall compression ratio it is important to avoid improve the overall compression ratio it is important to avoid
uploading bytecode in every compressed message. For this reason uploading bytecode in every compressed message. For this reason
SigComp allows the UDVM to save an area of its memory as a state item SigComp allows the UDVM to save an area of its memory as a state item
between compressed messages. Once a state item has been created it between compressed messages. Once a state item has been created it
can be retrieved by sending the corresponding state identifier using can be retrieved by sending the corresponding state identifier using
the following SigComp message format: the following SigComp message format:
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
skipping to change at page 15, line 46 skipping to change at page 16, line 35
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| | | |
: remaining SigComp message : : remaining SigComp message :
| | | |
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
The partial_state_identifier field must contain the first 6 bytes of The partial_state_identifier field must contain the first 6 bytes of
the state identifier for the state item to be accessed (see [RFC- the state identifier for the state item to be accessed (see [RFC-
3320] for details of how state identifiers are derived). 3320] for details of how state identifiers are derived).
4.2 LZSS 4.1.2 LZSS
This section provides UDVM bytecode for the simple but effective LZSS This section provides UDVM bytecode for the simple but effective LZSS
compression algorithm LZSS [8]. compression algorithm [8].
The principal improvement offered by LZSS over LZ77 is that each The principal improvement offered by LZSS over LZ77 is that each
compressed character begins with a 1-bit indicator flag to specify compressed character begins with a 1-bit indicator flag to specify
whether the character is a literal or an offset/length pair. A whether the character is a literal or an offset/length pair. A
literal value is simply a single uncompressed byte that is appended literal value is simply a single uncompressed byte that is appended
directly to the decompressed message. directly to the decompressed message.
An offset/length pair contains a 12-bit offset value from 1 to 4096 An offset/length pair contains a 12-bit offset value from 1 to 4096
inclusive, followed by a 4-bit length value from 3 to 18 inclusive. inclusive, followed by a 4-bit length value from 3 to 18 inclusive.
Taken together these values specify one of the previously received Taken together these values specify one of the previously received
skipping to change at page 17, line 40 skipping to change at page 18, line 29
returned_parameters_location, state_length, 64, returned_parameters_location, state_length, 64,
decompress_sigcomp_message, 6, 0) decompress_sigcomp_message, 6, 0)
:circular_buffer :circular_buffer
An example message compressed using the LZSS algorithm is given An example message compressed using the LZSS algorithm is given
below: below:
0x279a 0406 e378 b200 6074 1018 4ce6 1349 b842 0x279a 0406 e378 b200 6074 1018 4ce6 1349 b842
4.3 LZW The uncompressed message is "Oh no, not again!".
4.1.3 LZW
This section provides UDVM bytecode for the well-known LZW This section provides UDVM bytecode for the well-known LZW
compression algorithm LZW [9]. This algorithm is used in a number of compression algorithm LZW [9]. This algorithm is used in a number of
standards including the GIF image format. standards including the GIF image format.
LZW compression operates in a similar manner to LZ77 in that it LZW compression operates in a similar manner to LZ77 in that it
maintains a circular buffer of previously received decompressed data, maintains a circular buffer of previously received decompressed data,
and each compressed character references exactly one byte string from and each compressed character references exactly one byte string from
the circular buffer. However, LZW also maintains a "codebook" the circular buffer. However, LZW also maintains a "codebook"
containing 1024 position/length pairs that point to byte strings containing 1024 position/length pairs that point to byte strings
skipping to change at page 20, line 4 skipping to change at page 20, line 43
; position/length pair: ; position/length pair:
OUTPUT ($position_value, $length_value) OUTPUT ($position_value, $length_value)
JUMP (next_character) JUMP (next_character)
:end_of_message :end_of_message
END-MESSAGE (requested_feedback_location, END-MESSAGE (requested_feedback_location,
returned_parameters_location, state_length, 64, returned_parameters_location, state_length, 64,
decompress_sigcomp_message, 6, 0) decompress_sigcomp_message, 6, 0)
:static_dictionary pad (256) :static_dictionary pad (256)
:circular_buffer :circular_buffer
at (4492) at (4492)
:codebook :codebook
An example message compressed using the LZW algorithm is given below: An example message compressed using the LZW algorithm is given below:
0x14c6 f080 6c1b c6e1 9c20 1846 e190 201d 0684 206b 1cc2 0198 6f1c 0x14c6 f080 6c1b c6e1 9c20 1846 e190 201d 0684 206b 1cc2 0198 6f1c
0x9071 b06c 42c6 8195 111a 4731 a021 02bf f0 0x9071 b06c 42c6 8195 111a 4731 a021 02bf f0
4.4 DEFLATE The uncompressed message is "So long and thanks for all the fish!\n".
4.1.4 DEFLATE
This section provides UDVM bytecode for the DEFLATE compression This section provides UDVM bytecode for the DEFLATE compression
algorithm. DEFLATE is the algorithm used in the well-known "gzip" algorithm. DEFLATE is the algorithm used in the well-known "gzip"
file format. file format.
The following bytecode will decompress the DEFLATE compressed data The following bytecode will decompress the DEFLATE compressed data
format DEFLATE [10] with the following modifications: format DEFLATE [10] with the following modifications:
1. The DEFLATE compressed data format separates blocks of compressed 1. The DEFLATE compressed data format separates blocks of compressed
data by transmitting 7 consecutive zero bits. Each SigComp data by transmitting 7 consecutive zero bits. Each SigComp
message is assumed to contain a separate block of compressed message is assumed to contain a separate block of compressed
data, so the end-of-block bits are implicit and do not need to be data, so the end-of-block bits are implicit and do not need to be
transmitted at the end of a SigComp message. transmitted at the end of a SigComp message.
2. The bytecode supports only DEFLATE block type 01 (data compressed 2. This bytecode supports only DEFLATE block type 01 (data
with fixed Huffman codes). compressed with fixed Huffman codes).
Assembly for the DEFLATE decompressor is given below: Assembly for the DEFLATE decompressor is given below:
at (32) at (32)
:index pad (2) :index pad (2)
:extra_length_bits pad (2) :extra_length_bits pad (2)
:length_value pad (2) :length_value pad (2)
:extra_distance_bits pad (2) :extra_distance_bits pad (2)
:distance_value pad (2) :distance_value pad (2)
skipping to change at page 23, line 7 skipping to change at page 23, line 46
END-MESSAGE (requested_feedback_location, END-MESSAGE (requested_feedback_location,
returned_parameters_location, state_length, 64, returned_parameters_location, state_length, 64,
decompress_sigcomp_message, 6, 0) decompress_sigcomp_message, 6, 0)
:circular_buffer :circular_buffer
An example message compressed using the DEFLATE algorithm is given An example message compressed using the DEFLATE algorithm is given
below: below:
0xf3c9 4c4b d551 28c9 4855 08cd cb2c 4b2d 2a4e 5548 cc4b 5170 0532 0xf3c9 4c4b d551 28c9 4855 08cd cb2c 4b2d 2a4e 5548 cc4b 5170 0532
0x2b4b 3232 f3d2 b900 0000 00ff ff00 0x2b4b 3232 f3d2 b900
4.5 LZJH The uncompressed message is "Life, the Universe and Everything\n".
4.1.5 LZJH
This section provides UDVM bytecode for the LZJH compression This section provides UDVM bytecode for the LZJH compression
algorithm. LZJH is the algorithm adopted by the International algorithm. LZJH is the algorithm adopted by the International
Telecommunication Union (ITU-T) Recommendation V.44 LZJH [11]. Telecommunication Union (ITU-T) Recommendation V.44 LZJH [11].
Assembly for the LZJH decompressor is given below: Assembly for the LZJH decompressor is given below:
at (32) at (32)
; The following 2-byte variables are stored in the scratch-pad memory ; The following 2-byte variables are stored in the scratch-pad memory
skipping to change at page 27, line 21 skipping to change at page 28, line 16
decompress_sigcomp_message, 6, 0) decompress_sigcomp_message, 6, 0)
:circular_buffer :circular_buffer
An example message compressed using the LZJH algorithm is given An example message compressed using the LZJH algorithm is given
below: below:
0x5c09 e6e0 cadc c8d2 dcce 40c2 40f2 cac2 e440 c825 c840 ccde 29e8 0x5c09 e6e0 cadc c8d2 dcce 40c2 40f2 cac2 e440 c825 c840 ccde 29e8
0xc2f0 40e0 eae4 e0de e6ca e65c 1403 0xc2f0 40e0 eae4 e0de e6ca e65c 1403
4.6 EPIC The uncompressed message is "...spending a year dead for tax
purposes.\n".
This section provides bytecode for a version of the Efficient
Protocol Independent Compression (EPIC) scheme.
The basic EPIC scheme is designed to compress protocol headers such
as TCP/IP, but the underlying algorithm (known as Hierarchical
Huffman) can be applied to the compression of arbitrary data. In
particular the compression algorithm used by EPIC obtains a very high
compression ratio on data with a known structure, so it is ideally
suited for compressing the messages generated by SIP or other
signaling protocols.
Note however that in its basic form the EPIC algorithm does not have
the ability to detect and adapt to new patterns in the uncompressed
data; instead it relies on a fixed pre-programmed description of how
the protocol to be compressed is expected to behave.
The application messages encountered by SigComp will typically
contain segments of generic text that cannot be compressed using the
basic EPIC scheme. Fortunately however, EPIC can easily be upgraded
to cope with generic data by adding the ability to store a circular
buffer of previously received text strings as per LZ77 or DEFLATE.
The resulting hybrid algorithm offers the best of both worlds: a very
high compression ratio for the "well-behaved" parts of the
application message, and a good compression ratio even for the
portions of the message that cannot be pre-programmed into the
compression algorithm.
The following bytecode implements a decompressor for a hybrid of EPIC
and DEFLATE. The tables of compressed characters are generated using
the Hierarchical Huffman algorithm from EPIC, and are designed to
give a very high compression ratio for a typical SIP/SDP message.
The ability to store and retrieve text strings from a buffer of
previously received messages is taken from DEFLATE.
To illustrate the performance of the hybrid algorithm, the following 4.2 Adapted Algorithms
results have been generated for the call flow in Section 3.2.1 of
"SIP Call Flow Examples" FLOWS [1]. Note that to improve the overall
compression ratio, all algorithms employ a static dictionary (see
Section 5.2) and the shared compression mechanism (see Section 5.5):
Algorithm: Total compressed message size: 4.2.1 Modified DEFLATE
DEFLATE with static Huffman codes 660 bytes Alternative algorithms can also be used with SigComp. This section
DEFLATE with adaptive Huffman codes 625 bytes shows a modified version of the DEFLATE [10] algorithm. The two-
EPIC 560 bytes stage encoding of DEFLATE is replaced by a single step with a
discrete Huffman code for each symbol. The literal/length symbol
probabilities are dependent upon whether the previously symbol was a
literal or a match. Bit-handling is also simpler, in that all bits
are input using the INPUT-HUFFMAN instruction and the value of the H
bit does not change so all bits are input, read and interpreted in
the same order.
Assembly for the EPIC algorithm is given below. A compressor to Assembly for the algorithm is given below. String matching rules are
generate messages for this algorithm can be adapted from an ordinary the same as for the other LZ-based algorithms, with the alternative
DEFLATE compressor; the string matching rules should be left encoding of the literals and length/distance pairs.
unchanged but the tables of Huffman codes used by DEFLATE should be
replaced by those used in the following assembly:
at (32) at (32)
:index pad (2) :index pad (2)
:distance_value pad (2) :distance_value pad (2)
:old_pointer pad (2) :old_pointer pad (2)
at (42) at (42)
set (requested_feedback_location, 0) set (requested_feedback_location, 0)
skipping to change at page 30, line 44 skipping to change at page 31, line 4
LOAD (old_pointer, $decompressed_pointer) LOAD (old_pointer, $decompressed_pointer)
COPY-OFFSET ($distance_value, $index, $decompressed_pointer) COPY-OFFSET ($distance_value, $index, $decompressed_pointer)
OUTPUT ($old_pointer, $index) OUTPUT ($old_pointer, $index)
JUMP (character_after_match) JUMP (character_after_match)
:end_of_message :end_of_message
END-MESSAGE (requested_feedback_location, END-MESSAGE (requested_feedback_location,
returned_parameters_location, state_length, 64, returned_parameters_location, state_length, 64,
decompress_sigcomp_message, 6, 0) decompress_sigcomp_message, 6, 0)
:circular_buffer :circular_buffer
An example message compressed using the EPIC algorithm is given An example message compressed using the modified DEFLATE algorithm is
below: given below:
0xd956 b132 cd68 5424 c5a9 6215 8a70 a64d af0a 5499 3621 509b 3e4c 0xd956 b132 cd68 5424 c5a9 6215 8a70 a64d af0a 5499 3621 509b 3e4c
0x28b4 a145 b362 653a d0a6 498b 5a6d 2970 ac4c 930a a4ca 74a4 c268 0x28b4 a145 b362 653a d0a6 498b 5a6d 2970 ac4c 930a a4ca 74a4 c268
0x0c 0x0c
The uncompressed message is "Arthur leapt to his feet like an author
hearing the phone ring".
5. Additional SigComp mechanisms 5. Additional SigComp mechanisms
The following chapter covers the additional mechanisms that can be The following chapter covers the additional mechanisms that can be
employed by SigComp to improve the overall compression ratio; employed by SigComp to improve the overall compression ratio;
including the acknowledgment of SigComp state over an unreliable including the acknowledgment of SigComp state over an unreliable
link, sharing state between two directions of a compressed message link, sharing state between two directions of a compressed message
flow etc. flow etc.
When each of the compression algorithms described in Chapter 4 has When each of the compression algorithms described in Chapter 4 has
successfully decompressed the current SigComp message, the contents successfully decompressed the current SigComp message, the contents
skipping to change at page 34, line 30 skipping to change at page 34, line 44
found in SigComp RFC-3320 [4]. found in SigComp RFC-3320 [4].
5.4 Announcing additional resources 5.4 Announcing additional resources
If a particular endpoint is able to offer more processing or memory If a particular endpoint is able to offer more processing or memory
resources than the mandatory minimum, the SigComp feedback mechanism resources than the mandatory minimum, the SigComp feedback mechanism
can be used to announce that these resources are available to the can be used to announce that these resources are available to the
remote endpoint. This may help to improve the overall compression remote endpoint. This may help to improve the overall compression
ratio between the two endpoints. ratio between the two endpoints.
Additionally, if an endpoint has any pieces of state that may be
useful for the remote endpoing to reference, it can advertise the
identifiers for the states. The remote endpoint can then make use of
any that it also knows about (i.e. knows the contents of) e.g. a
dictionary or shared mode state (see Section 5.5).
The values of the following SigComp parameters can be announced using The values of the following SigComp parameters can be announced using
the SigComp feedback mechanism: the SigComp advertisement mechanism:
cycles_per_bit decompression_memory_size state_memory_size cycles_per_bit
decompression_memory_size
state_memory_size>
SigComp_version SigComp_version
state identifiers
As explained in SigComp, in order to announce the values of these As explained in SigComp, in order to announce the values of these
parameters the following fields must be reserved in the UDVM memory: parameters the following fields must be reserved in the UDVM memory:
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| cpb | dms | sms | returned_parameters_location | cpb | dms | sms | returned_parameters_location
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| SigComp_version | | SigComp_version |
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
| length_of_partial_state_ID_1 |
+---+---+---+---+---+---+---+---+
| |
: partial_state_identifier_1 :
| |
+---+---+---+---+---+---+---+---+
: :
+---+---+---+---+---+---+---+---+
| length_of_partial_state_ID_n |
+---+---+---+---+---+---+---+---+
| |
: partial_state_identifier_n :
| |
+---+---+---+---+---+---+---+---+
These fields can be reserved in any of the algorithms of Chapter 4 by These fields can be reserved in any of the algorithms of Chapter 4 by
replacing the line "set (returned_parameters_location, 0)" with the replacing the line "set (returned_parameters_location, 0)" with the
following piece of assembly: following piece of assembly:
:adverts_len pad (1)
:adverts_len_lsb pad (1)
:returned_parameters_location pad (1) :returned_parameters_location pad (1)
:returned_sigcomp_version pad (1) :returned_sigcomp_version pad (1)
:state_ids pad (x)
where x is enough space for the number state identifiers that the
endpoint wishes to advertise.
When a SigComp message is successfully decompressed and saved as When a SigComp message is successfully decompressed and saved as
state, the following bytecode announces to the receiving endpoint state, the following bytecode announces to the receiving endpoint
that additional resources are available at the sending endpoint: that additional resources and pieces of state are available at the
sending endpoint:
:end_of_message :end_of_message
LOAD (returned_parameters_location, N) LOAD (returned_parameters_location, N)
INPUT-BYTES (1, adverts_len_lsb, done)
INPUT-BYTES ($adverts_len, state_ids, done)
:done
Note that the integer value "N" should be set equal to the amount of Note that the integer value "N" should be set equal to the amount of
resources available at the sending endpoint. N should be expressed resources available at the sending endpoint. N should be expressed
as a 2-byte integer with the most significant bits corresponding to as a 2-byte integer with the most significant bits corresponding to
the cycles_per_bit parameter and the least significant bits the cycles_per_bit parameter and the least significant bits
corresponding to the SigComp_version parameter. corresponding to the SigComp_version parameter.
The length of the state identifiers, followed by the state
identifiers in the format shown are appended to the end of the
compressed message.
5.5 Shared compression 5.5 Shared compression
This section provides bytecode for implementing the SigComp shared This section provides bytecode for implementing the SigComp shared
compression mechanism RFC-3321 [5]. If two endpoints A and B are compression mechanism RFC-3321 [5]. If two endpoints A and B are
communicating via SigComp, shared compression allows the messages communicating via SigComp, shared compression allows the messages
sent from Endpoint A to Endpoint B to be compressed relative to the sent from Endpoint A to Endpoint B to be compressed relative to the
messages sent from Endpoint B to Endpoint A (and vice versa). This messages sent from Endpoint B to Endpoint A (and vice versa). This
may improve the overall compression ratio by reducing the need to may improve the overall compression ratio by reducing the need to
transmit the same information in both directions. transmit the same information in both directions.
As described in RFC-3321 [5], two steps must be taken to implement As described in RFC-3321 [5], two steps must be taken to implement
shared compression at an endpoint. Firstly, it is necessary to shared compression at an endpoint.
announce to the remote endpoint that shared compression is available.
Secondly, assuming that such an announcement is received from the
remote endpoint, then the state created by shared compression must be
accessed to improve the overall compression ratio.
In order to announce that shared compression is available the
following fields must be reserved in the UDVM memory:
0 1 2 3 4 5 6 7 Firstly, it is necessary to announce to the remote endpoint that
+---+---+---+---+---+---+---+---+ shared compression is available. This is done by announcing the
| cpb | dms | sms | returned_parameters_location state identifier as an available piece of state. This can be done
+---+---+---+---+---+---+---+---+ using the returned_parameters_location announcement as in
| SigComp_version | Section 5.4.
+---+---+---+---+---+---+---+---+
| length_of_partial_state_ID_1 |
+---+---+---+---+---+---+---+---+
| |
: partial_state_identifier_1 :
| |
+---+---+---+---+---+---+---+---+
: :
+---+---+---+---+---+---+---+---+
| length_of_partial_state_ID_n |
+---+---+---+---+---+---+---+---+
| |
: partial_state_identifier_n :
| |
+---+---+---+---+---+---+---+---+
These fields can be reserved in any of the algorithms of Chapter 4 by Secondly, assuming that such an announcement is received from the
replacing the line "set (returned_parameters_location, 0)" with the remote endpoint, then the state created by shared compression needs
following piece of assembly: to be accessed by the message sent in the opposite direction. This
can be done in a similar way to accessing the static dictionary (see
Section Section 5.2), but using the appropriate state identifier, for
example, by using the INPUT-BYTES instruction as below:
:returned_parameters_location pad (1)
:returned_sigcomp_version pad (1)
:length_of_partial_state_id_a pad (1)
:partial_state_identifier_a pad (6)
:length_of_partial_state_id_b pad (1)
:partial_state_identifier_b pad (20)
:extended_flags pad (2)
:shared_state_id pad (6) :shared_state_id pad (6)
:padding pad (6)
:minimum_access_length pad (2)
:announcement_location pad (2)
:decompressed_start pad (2)
:decompressed_length pad (2)
:shared_hash_length pad (2)
In Figure 5 of [RFC-3321], an example SigComp message format is
provided to carry the shared compression information between the two
endpoints. This message format can be decompressed at the receiving
endpoint by inserting the following assembly after the label
":decompress_sigcomp_message" in one of the algorithms of Chapter 4:
:decompress_sigcomp_message
INPUT-BYTES (1, extended_flags, !)
COMPARE ($extended_flags, 32768, initialize_state_announcement,
access_shared_state, access_shared_state)
:access_shared_state :access_shared_state
INPUT-BYTES (6, shared_state_id, !) INPUT-BYTES (6, shared_state_id, !)
STATE-ACCESS (shared_state_id, 6, 0, 0, $decompressed_start, 0) STATE-ACCESS (shared_state_id, 6, 0, 0, $decompressed_start, 0)
:initialize_state_announcement
MULTILOAD (minimum_access_length, 4, 6, length_of_partial_state_id_a,
$decompressed_pointer, 5120)
COPY-LITERAL (padding, 8, $decompressed_pointer)
LSHIFT ($extended_flags, 1)
COMPARE ($extended_flags, 32768, algorithm_start,
announce_acked_state_id, announce_acked_state_id)
:announce_acked_state_id
LOAD (length_of_partial_state_id_a, 1536)
INPUT-BYTES (6, partial_state_identifier_a, !)
LOAD (announcement_location, length_of_partial_state_id_b)
:algorithm_start
Additionally, the following piece of assembly should be inserted
following the label ":end_of_message" in the chosen algorithm:
:end_of_message
LSHIFT ($extended_flags, 1)
COMPARE ($extended_flags, 32768, end, announce_shared_state,
announce_shared_state)
:announce_shared_state
; The following instructions calculate the shared state identifier:
COPY-LITERAL (decompressed_length, 1, $announcement_location)
set (buffer_size, (udvm_memory_size - circular_buffer))
MULTILOAD (decompressed_length, 2, 65528, $decompressed_pointer)
SUBTRACT ($shared_hash_length, $decompressed_start)
REMAINDER ($shared_hash_length, buffer_size)
ADD ($decompressed_length, $shared_hash_length)
LOAD ($decompressed_start, $decompressed_length)
SHA-1 ($decompressed_start, $shared_hash_length,
$announcement_location)
:end
6. Security considerations 6. Security considerations
This draft describes implementation options for the SigComp protocol This draft describes implementation options for the SigComp protocol
RFC-3320 [4]. Consequently the security considerations for this RFC-3320 [4]. Consequently the security considerations for this
draft match those of SigComp. draft match those of SigComp.
7. Acknowledgements 7. Acknowledgements
Thanks to Thanks to
Richard Price
Carsten Bormann Carsten Bormann
Adam Roach Adam Roach
Lawrence Conroy Lawrence Conroy
Christian Schmidt Christian Schmidt
Max Riegel Max Riegel
Lars-Erik Jonsson Lars-Erik Jonsson
Jonathan Rosenberg Jonathan Rosenberg
Stefan Forsgren Stefan Forsgren
Krister Svanbro Krister Svanbro
Miguel Garcia Miguel Garcia
skipping to change at page 39, line 5 skipping to change at page 38, line 5
for valuable input and review. for valuable input and review.
8. Intellectual Property Right Considerations 8. Intellectual Property Right Considerations
The IETF has been notified of intellectual property rights claimed in The IETF has been notified of intellectual property rights claimed in
regard to some or all of the specification contained in this regard to some or all of the specification contained in this
document. For more information consult the online list of claimed document. For more information consult the online list of claimed
rights. rights.
9 References 9. References
[1] Johnston, A., Donovan, S., Sparks, R., Cunningham, C. and K. [1] Johnston, A., Donovan, S., Sparks, R., Cunningham, C., and K.
Summers, "Session Initiation Protocol (SIP) Basic Call Flow Summers, "Session Initiation Protocol (SIP) Basic Call Flow
Examples", RFC 3665, December 2003. Examples", RFC 3665, December 2003.
[2] Bradner, S., "The Internet Standards Process -- Revision 3", [2] Bradner, S., "The Internet Standards Process -- Revision 3",
RFC 3667, February 2004. RFC 3667, February 2004.
[3] Crocker, D. and P. Overell, "Augmented BNF for Syntax [3] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997. Specifications: ABNF", RFC 2234, November 1997.
[4] Price, R., Borman, C., Christoffersson, J., Hannu, H., Liu, Z. [4] Price, R., Borman, C., Christoffersson, J., Hannu, H., Liu, Z.,
and J. Rosenberg, "Signaling Compression (SigComp)", RFC 3320, and J. Rosenberg, "Signaling Compression (SigComp)", RFC 3320,
January 2003. January 2003.
[5] Hannu, H., Christoffersson, J., Forsgren, S., Leung, K., Liu, [5] Hannu, H., Christoffersson, J., Forsgren, S., Leung, K., Liu,
Z. and R. Price, "Signaling Compression (SigComp)", RFC 3321, Z., and R. Price, "Signaling Compression (SigComp) - Extended
January 2003. Operations", RFC 3321, January 2003.
[6] Garcia-Martin, M., Borman, C., Ott, J., Price, R. and A. Roach, [6] Garcia-Martin, M., Borman, C., Ott, J., Price, R., and A.
"The Session Initiation Protocol (SIP) and Session Description Roach, "The Session Initiation Protocol (SIP) and Session
Protocol (SDP) Statc Dictionary for Signaling Compression Description Protocol (SDP) Statc Dictionary for Signaling
(SigComp)", RFC 3485, February 2003. Compression (SigComp)", RFC 3485, February 2003.
[7] Ziv, J. and A. Lempel, "A universal algorithm for sequential [7] Ziv, J. and A. Lempel, "A universal algorithm for sequential
data compression", IEEE 23:337-343, 1977. data compression", IEEE 23:337-343, 1977.
[8] Storer, J., "Data Compression: Methods and Theory", Computer [8] Storer, J., "Data Compression: Methods and Theory", Computer
Science Press ISBN 0-88175-161-8, 1998. Science Press ISBN 0-88175-161-8, 1998.
[9] Nelson, M., "LZW Data Compression", Dr Dobb's Journal, October [9] Nelson, M., "LZW Data Compression", Dr Dobb's Journal,
1989. October 1989.
[10] Deutsch, P., "DEFLATE Compressed Data Format Specification [10] Deutsch, P., "DEFLATE Compressed Data Format Specification
version 1.3", RFC 1951, May 1996. version 1.3", RFC 1951, May 1996.
[11] "Data Compression Procedures", ITU-T Recommendation V.44, [11] "Data Compression Procedures", ITU-T Recommendation V.44,
November 2000. November 2000.
Authors' Addresses Authors' Addresses
Abigail Surtees Abigail Surtees
Siemens/Roke Manor Research Siemens/Roke Manor Research
Roke Manor Research Ltd. Roke Manor Research Ltd.
Romsey, Hants SO51 0ZN Romsey, Hants SO51 0ZN
UK UK
Phone: +44 (0)1794 833131 Phone: +44 (0)1794 833131
EMail: abigail.surtees@roke.co.uk Email: abigail.surtees@roke.co.uk
URI: http://www.roke.co.uk URI: http://www.roke.co.uk
Mark A. West Mark A. West
Siemens/Roke Manor Research Siemens/Roke Manor Research
Roke Manor Research Ltd. Roke Manor Research Ltd.
Romsey, Hants SO51 0ZN Romsey, Hants SO51 0ZN
UK UK
Phone: +44 (0)1794 833311 Phone: +44 (0)1794 833311
EMail: mark.a.west@roke.co.uk Email: mark.a.west@roke.co.uk
URI: http://www.roke.co.uk URI: http://www.roke.co.uk
Appendix A. UDVM bytecode for the compression algorithms Appendix A. UDVM bytecode for the compression algorithms
The following sections list the UDVM bytecode generated for each The following sections list the UDVM bytecode generated for each
compression algorithm of Section 4. compression algorithm of Section 4.
Note that the different assemblers can output different bytecode for Note that the different assemblers can output different bytecode for
the same piece of assembly code, so a valid assembler can produce the same piece of assembly code, so a valid assembler can produce
results different from those presented below. However, the following results different from those presented below. However, the following
bytecode should always generate the same decompressed messages on any bytecode should always generate the same decompressed messages on any
UDVM. UDVM.
A.1 Simplified LZ77 A.1 Well-known Algorithms
A.1.1 Simplified LZ77
0x0f86 0389 8d89 1588 8800 011c 0420 0d13 5051 2222 5051 16f5 2300 0x0f86 0389 8d89 1588 8800 011c 0420 0d13 5051 2222 5051 16f5 2300
0x00bf c086 a08b 06 0x00bf c086 a08b 06
A.2 LZSS A.1.2 LZSS
0x0f86 04a0 c48d 00a0 c41e 2031 0209 00a0 ff8e 048c bfff 0117 508d 0x0f86 04a0 c48d 00a0 c41e 2031 0209 00a0 ff8e 048c bfff 0117 508d
0x0f23 0622 2101 1321 0123 16e5 1d04 22e8 0611 030e 2463 1450 5123 0x0f23 0622 2101 1321 0123 16e5 1d04 22e8 0611 030e 2463 1450 5123
0x2252 5116 9fd2 2300 00bf c086 a089 06 0x2252 5116 9fd2 2300 00bf c086 a089 06
A.3 LZW A.1.3 LZW
0x0f86 06a1 ce8d 00b1 8f01 a0ce 13a0 4903 2313 2501 2506 1201 1752 0x0f86 06a1 ce8d 00b1 8f01 a0ce 13a0 4903 2313 2501 2506 1201 1752
0x88f4 079f 681d 0a24 2508 1203 0612 b18f 1252 0321 0ea0 4801 0624 0x88f4 079f 681d 0a24 2508 1203 0612 b18f 1252 0321 0ea0 4801 0624
0x5013 a049 0323 1351 5025 2251 5016 9fde 2300 00bf c086 a09f 06 0x5013 a049 0323 1351 5025 2251 5016 9fde 2300 00bf c086 a09f 06
A.4 DEFLATE A.1.4 DEFLATE
0x0f86 7aa2 528d 05a2 5200 0300 0400 0500 0600 0700 0800 0900 0a01 0x0f86 7aa2 528d 05a2 5200 0300 0400 0500 0600 0700 0800 0900 0a01
0x0b01 0d01 0f01 1102 1302 1702 1b02 1f03 2303 2b03 3303 3b04 a043 0x0b01 0d01 0f01 1102 1302 1702 1b02 1f03 2303 2b03 3303 3b04 a043
0x04a0 5304 a063 04a0 7305 a083 05a0 a305 a0c3 05a0 e300 a102 0001 0x04a0 5304 a063 04a0 7305 a083 05a0 a305 a0c3 05a0 e300 a102 0001
0x0002 0003 0004 0105 0107 0209 020d 0311 0319 0421 0431 05a0 4105 0x0002 0003 0004 0105 0107 0209 020d 0311 0319 0421 0431 05a0 4105
0xa061 06a0 8106 a0c1 07a1 0107 a181 08a2 0108 a301 09a4 0109 a601 0xa061 06a0 8106 a0c1 07a1 0107 a181 08a2 0108 a301 09a4 0109 a601
0x0aa8 010a ac01 0bb0 010b b801 0c80 2001 0c80 3001 0d80 4001 0d80 0x0aa8 010a ac01 0bb0 010b b801 0c80 2001 0c80 3001 0d80 4001 0d80
0x6001 1d03 229f b41e 20a0 6504 0700 1780 4011 0130 a0bf 0000 a0c0 0x6001 1d03 229f b41e 20a0 6504 0700 1780 4011 0130 a0bf 0000 a0c0
0xa0c7 8040 2901 a190 a1ff a090 1750 8040 1109 a046 1322 2101 1321 0xa0c7 8040 2901 a190 a1ff a090 1750 8040 1109 a046 1322 2101 1321
0x0123 169f d108 1004 1250 0422 1d51 229f d706 1251 1e20 9fcf 0105 0x0123 169f d108 1004 1250 0422 1d51 229f d706 1251 1e20 9fcf 0105
0x001f 2f08 1004 1250 0426 1d53 26f6 0614 530e 2063 1454 5223 2250 0x001f 2f08 1004 1250 0426 1d53 26f6 0614 530e 2063 1454 5223 2250
0x5216 9f9e 2300 00bf c086 a1de 06 0x5216 9f9e 2300 00bf c086 a1de 06
A.5 LZJH A.1.5 LZJH
0x0f86 08a1 5b8d 0700 a15b 0706 b18f 1d01 24a0 c317 5201 1a31 311e 0x0f86 08a1 5b8d 0700 a15b 0706 b18f 1d01 24a0 c317 5201 1a31 311e
0x24a0 b802 0101 0102 0100 0100 1752 0107 a04e 1e1d 6524 f822 2501 0x24a0 b802 0101 0102 0100 0100 1752 0107 a04e 1e1d 6524 f822 2501
0x0ea0 4602 13a0 4703 2713 2501 2416 9fcd 1d66 24e1 1752 03a0 639f 0x0ea0 4602 13a0 4703 2713 2501 2416 9fcd 1d66 24e1 1752 03a0 639f
0xb808 0812 0306 12b1 8312 5203 210e a046 0106 2350 0e28 6713 a047 0xb808 0812 0306 12b1 8312 5203 210e a046 0106 2350 0e28 6713 a047
0x0327 1351 5024 2251 5016 9fa8 1e24 9fb1 0401 0101 0102 0103 0201 0x0327 1351 5024 2251 5016 9fa8 1e24 9fb1 0401 0101 0102 0103 0201
0x0101 0d03 0007 0517 520d 0d06 061d 0826 f706 1253 1351 5011 1351 0x0101 0d03 0007 0517 520d 0d06 061d 0826 f706 1253 1351 5011 1351
0x5224 2251 5206 1250 1225 0154 169f 6617 5201 9fdb 070f 1c00 009e 0x5224 2251 5206 1250 1225 0154 169f 6617 5201 9fdb 070f 1c00 009e
0xce16 9f57 1d01 24fa 1752 0107 0d9e c206 2501 169f 6506 2601 169f 0xce16 9f57 1d01 24fa 1752 0107 0d9e c206 2501 169f 6506 2601 169f
0x7623 0000 bfc0 86a0 8e06 0x7623 0000 bfc0 86a0 8e06
A.6 EPIC A.2 Adapted Algorithms
A.2.1 Modified DEFLATE
0x0f86 04a1 d38d 00a1 d31e 20a1 4010 0500 0b2e 000c 0c88 011a 20a1 0x0f86 04a1 d38d 00a1 d31e 20a1 4010 0500 0b2e 000c 0c88 011a 20a1
0x0101 a042 a044 2000 a045 a05e a061 00a0 5fa0 66a1 0800 a067 a067 0x0101 a042 a044 2000 a045 a05e a061 00a0 5fa0 66a1 0800 a067 a067
0xa1ff 02a1 a0a1 aa23 00a1 aba1 d13a 00a1 d2a1 e1a1 1001 a3c4 a3e3 0xa1ff 02a1 a0a1 aa23 00a1 aba1 d13a 00a1 d2a1 e1a1 1001 a3c4 a3e3
0xa120 03bf 20bf 34a0 7b00 bf35 bfb3 a180 0180 3f68 803f 8700 0080 0xa120 03bf 20bf 34a0 7b00 bf35 bfb3 a180 0180 3f68 803f 8700 0080
0x3f88 803f c7a1 4001 807f 9080 7fff a090 1750 88a0 79a0 83a0 831e 0x3f88 803f c7a1 4001 807f 9080 7fff a090 1750 88a0 79a0 83a0 831e
0x20a0 c810 0400 00a1 ff01 0209 8801 1416 2000 171e a108 013e a049 0x20a0 c810 0400 00a1 ff01 0209 8801 1416 2000 171e a108 013e a049
0x2e00 a04a a059 a110 02a1 68a1 81a0 6100 a182 a1a1 a120 01a3 44a3 0x2e00 a04a a059 a110 02a1 68a1 81a0 6100 a182 a1a1 a120 01a3 44a3
0x6a3a 00a3 6ba3 aaa1 4001 a756 a760 2300 a761 a7df a180 01af c0af 0x6a3a 00a3 6ba3 aaa1 4001 a756 a760 2300 a761 a7df a180 01af c0af
0xd4a0 7b01 bfaa bfc9 0001 803f 9480 3ffb a090 0180 7ff8 807f ffa0 0xd4a0 7b01 bfaa bfc9 0001 803f 9480 3ffb a090 0180 7ff8 807f ffa0
skipping to change at page 42, line 50 skipping to change at page 42, line 50
Copyright (C) The Internet Society (2005). This document is subject Copyright (C) The Internet Society (2005). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights. except as set forth therein, the authors retain all their rights.
Acknowledgment Acknowledgment
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is currently provided by the
Internet Society. Internet Society.
This Internet-Draft will expire on August 19, 2005. This Internet-Draft will expire on January 19, 2006.
 End of changes. 

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