1. ASN.1 Compiler for text-based protocols!
Raman Govindan
Software Consultant, Wipro Technologies

2. ITU-T and ITU-D Workshop - Bangalore (India), 30-31 August 2001
AGENDA
What is ASN.1 Compiler?
Components of ASN.1 Compiler
Example of ASN.1 Specification
Working of ASN.1 Compiler
Case Study
ITU-T and ITU-D Workshop - Bangalore (India), August 2001

3. ITU-T and ITU-D Workshop - Bangalore (India), 30-31 August 2001
What is ASN.1 Compiler?
ASN.1 Compiler is a tool to convert the data description in ASN.1 format to programming language dependent data structures and associated routines to encode/decode the same.
Two approaches to generate encode/decode routines
dedicated routines per message
generic routines (which is considered for the rest of the presentation)
ITU-T and ITU-D Workshop - Bangalore (India), August 2001

4. ASN.1 Compiler Components
specification
Input Validation
and Parsing
Header
Driving
File
Table
Front End
Back End
ASN.1 Encode
Decoded
Data
ASN.1 Decode
Network
Encoded
bytes
ITU-T and ITU-D Workshop - Bangalore (India), August 2001

5. ITU-T and ITU-D Workshop - Bangalore (India), 30-31 August 2001
ASN.1 Example
A ::= SEQUENCE {
b BOOLEAN
c C
d D
e INTEGER }
C ::= SEQUENCE {
c BOOLEAN
D ::= SEQUENCE {
e INTEGER
typedef struct {
char b;
C c;
D d;
int e;
} A;
char c;
} C;
} D;
- Illustrates one-to-one mapping of Abstract Syntax to Concrete Syntax
- Same example will be used to demonstrate working of ASN Compiler
ITU-T and ITU-D Workshop - Bangalore (India), August 2001

6. ITU-T and ITU-D Workshop - Bangalore (India), 30-31 August 2001
Wipro ASN.1 Compiler Front-End Working B
BOOLEAN A I
INTEGER C D I B
Graph is converted to table using Depth First Algorithm.
Info B; Info I; Info C; Info D; Info A;
&B, &I &I, &B, &C, &D, &I
ITU-T and ITU-D Workshop - Bangalore (India), August 2001

7. ITU-T and ITU-D Workshop - Bangalore (India), 30-31 August 2001
Wipro ASN.1 Compiler Back-End Working
Driving Table
typedef struct {
char b;(1)
C c;
D d;
int e;(5)
} A;
char c;(0)
int e;(2)
} C;
int e;(3)
} D; B
SEQUENCE 4 B C D I
SEQUENCE 4 B C D I
SEQUENCE 4 B C D I
SEQUENCE 4 B C D I I C D A
SEQUENCE 1 I
SEQUENCE 2 B I
SEQUENCE 2 B I
ROOT
BOOLEAN
BOOLEAN
Values within () indicate the value to be encoded.
Encoded Bit stream
INTEGER
INTEGER
INTEGER 1 2 3 5
ITU-T and ITU-D Workshop - Bangalore (India), August 2001

8. Footprint of various alternatives.
Units are in KB
160
140
120
100 80
Table Driven Approach
Dedicated Routines 60 40 20
RAS
Q.931
H.245
H.225
H.323
ITU-T and ITU-D Workshop - Bangalore (India), August 2001

9. ITU-T and ITU-D Workshop - Bangalore (India), 30-31 August 2001
Advantages of text-based protocols and how ASN.1 Tools help achieve the same.
easy implementation
easy debugging
similar parser implementation available
high extensibility
ASN.1 Compiler eases implementation
ASN.1 Compiler trace facility for debug
ASN.1 Compiler generates code.
ASN.1 support extension elements
ITU-T and ITU-D Workshop - Bangalore (India), August 2001

10. Case Study Text-based ASN.1-based
Case study is on a comparative study of text-based versus ASN.1-based protocol
extract of text-based protocol and its equivalent ASN.1 representation is taken as reference for the study.
ITU-T and ITU-D Workshop - Bangalore (India), August 2001

11. Extract of Text-based protocol
time-fields = 1*( "t=" start-time space stop-time
*(CRLF repeat-fields) CRLF)
[zone-adjustments CRLF]
repeat-fields = "r=" repeat-interval space typed-time
1*(space typed-time)
zone-adjustments = time space ["-"] typed-time
*(space time space ["-"] typed-time)
start-time = time | "0"
stop-time = time | "0"
time = POS-DIGIT 9*(DIGIT)
;sufficient for 2 more centuries
repeat-fields = "r=" repeat-interval space typed-time
repeat-interval = typed-time
typed-time = 1*(DIGIT) [fixed-len-time-unit]
fixed-len-time-unit = "d" | "h" | "m" | "s"
ITU-T and ITU-D Workshop - Bangalore (India), August 2001

12. Equivalent ASN.1 Representation
TimeFields ::= SEQUENCE {
timeFields SEQUENCE OF TimeField
zoneAdjustments ZoneAdjustments OPTIONAL }
TimeField ::= SEQUENCE {
startTime NTPTimeStamp Optional -- Optional means 0
stopTime NTPTimeStamp Optional -- Optional means 0
repeatFields SEQUENCE OF RepeatField OPTIONAL
NTPTimeStamp ::= INTEGER( )
positiveNegativeNTPTimeStamp ::= INTEGER( )
repeatFields ::= SEQUENCE {
repeatInterval typedTime
duration typedTime
offset SEQUENCE OF typedTime
ITU-T and ITU-D Workshop - Bangalore (India), August 2001

13. Equivalent ASN.1 Representation . . .
zoneAdjustements ::= SEQUENCE {
time NTPTimeStamp
adjust positiveNegativetypedTime }
typedTime ::= CHOICE {
ntpTimeStamp NTPTimeStamp
days INTEGER ( ) Two centuries
hours INTEGER ( ) One year
minutes INTEGER ( ) One year
seconds INTEGER ( ) -- One year
positiveNegativetypedTime ::= CHOICE {
ntpTimeStamp positiveNegativeNTPTimeStamp
days INTEGER( )
hours INTEGER( )
minutes INTEGER( )
seconds INTEGER( )
ITU-T and ITU-D Workshop - Bangalore (India), August 2001

14. Benchmark Results Text-based ASN.1-based
2800 Encoding - 1micro-seconds
280 Decoding - 1micro- seconds
Is there a tool to optimize parser-generated code?
Footprint is 100KB for entire grammar which includes the one in this case study.
Text compression can be used for efficient bandwidth at the expense of performance
23000 Encoding - 1micro-seconds
22000 Decoding - 1micro-seconds
Optimized ASN.1 Compiler leads to easier development
Footprint is 45KB
PER can be used for efficient bandwidth
Encoding Text-based performance is slow due to text processing like string concatenation
Encoding/Decoding of text-based protocol accounts to around .004 micro-seconds as compared to just micro-seconds
ITU-T and ITU-D Workshop - Bangalore (India), August 2001

15. Hurdles to ASN.1-based protocol
Availability of limited free ASN.1 tools
Contribute more and more tools in public domain.
Tool to convert BNF to ASN.1 representation will promote text-based evangelists to consider ASN.1-based protocols.
ITU-T and ITU-D Workshop - Bangalore (India), August 2001

16. ITU-T and ITU-D Workshop - Bangalore (India), 30-31 August 2001
One Application of ASN.1
VoiceEngine for RG
VoiceEngine for RG
ASN.1 is used here
Bluetooth
Wipro
VoiceEngine
H323-NCS GW
Cable
Modem
E’net /
USB
Home LAN
SIP
H.323
HFC out
Settop Box, C
Home Gateway, M
HFC OUT
LAN Access Point
visit us at
VoiceEngine Software provides the Voice Over Cable Capability to the device
ITU-T and ITU-D Workshop - Bangalore (India), August 2001

17. ITU-T and ITU-D Workshop - Bangalore (India), 30-31 August 2001
Thank You
visit us at
ITU-T and ITU-D Workshop - Bangalore (India), August 2001