and natural ones, no attempt has been made to be exhaustive and
comprehensive.
We have investigated delay bounds, throughput bounds, reliability
bounds, and other requirements. We have studied how the requirements
should be translated from the client's level into forms suitable (and
correct) for lower levels, described some examples of requirement
specification, and discussed some of the objections that may be
raised.
The material in this paper covers only part of the first phase in the
design of a real-time service: that during which the various
requirements are assembled and examined to extract useful suggestions
for the design of the server. Server needs and design principles
will be the subject of the subsequent paper mentioned several times
above.
Acknowledgments
Ralf Herrtwich and Dinesh Verma contributed ideas to, and corrected
mistakes in, a previous version of the manuscript. The author is
deeply indebted to them for their help and for the many discussions
he had with them on the topics dealt with in this paper. The
comments of Ramesh Govindan and Riccardo Gusella are also gratefully
acknowledged.
References
[Brad64] Brady, P., "A Technique for Investigating On-Off Patterns
of Speech", Bell Systems Technical Journal, Vol. 44,
Pgs. 1-22, 1964.
[Ferr89a] Ferrari, D., "Real-Time Communication in
Packet-Switching Wide-Area Networks", Technical Report
TR-89-022, International Computer Science Institute,
Berkeley, May 1989.
[Ferr89b] Ferrari D., and D. Verma, "A Scheme for Real-Time Channel
Establishment in Wide-Area Networks", IEEE J. Selected
Areas Communications SAC-8, April 1990.
[Gait90] Gaitonde, S., D. Jacobson, and A. Pohm, "Bounding Delay on
a Multifarious Token Ring Network", Communications of the
ACM, Vol. 33, No. 1, Pgs. 20-28, January 1990.
[Herr89] Herrtwich R., and U. Brandenburg, "Accessing and
Customizing Services in Distributed Systems", Technical
Report TR-89-059, International Computer Science Institute,
Berkeley, October 1989.
[Herr90] Herrtwich, R, personal communication, February 1990.
[Verm90] Verma, D., personal communication, February 1990.
Table Ia
Examples of Client Requirements
Interactive Non-Interactive
Voice Video
Delay Bounds
deterministic:Dmax [ms] 200 - (1000) -
statistical:Dmax [ms] - 200 - (1000)
Zmin - (*) - (*)
jitter:Jmax [ms] 1 5
Throughput Bounds
deterministic:Tmin [kby/s] 8.834 4140
average:Tave [kby/s] 3.933 4140
I [s] 100 100
Reliability Bound:Wmin 0.98 (*) (0.90) (*)
Delay&Reliability:ZminWmin - 0.98 - 0.90
Sequencing yes yes
Absence of Duplications yes yes
Failure Recovery:
max.repair time [s] 10 100
Max.Setup Time [s] 0.8 (o) 15 (o)
----------------------------------
(*) To be chosen by the server
(o) Could be much longer if advance reservations were required
(+) Could be achieved by using a preexisting connection
Table Ib
Examples of Client Requirements
Real-Time File
Datagram Transfer
Delay Bounds
deterministic:Dmax [ms] 50 - (1500)
statistical:Dmax [ms] - (1000) -
Zmin - (0.95) -
jitter:Jmax [ms] - -
Throughput Bounds
deterministic:Tmin [kby/s] - 728
average:Tave [kby/s] - 700
I [s] - 100
Reliability Bound:Wmin 0.98 1
Delay&Reliability:ZminWmin - -
Sequencing - yes
Absence of Duplications yes yes
Failure Recovery:
max.repair time [s] - 100
Max.Setup Time [s] 0 (+) 5 (o)
----------------------------------
(*) To be chosen by the server
(o) Could be much longer if advance reservations were required
(+) Could be achieved by using a preexisting connection
Table II
Translation of the Requirements in Table I
Non-Interactive File
Video Transfer
Delay Bounds
deterministic:Dmax' [ms] (966) - - (1482)
statistical:Dmax' [ms] - (966) (982) -
Zmin' - (*) (0.95) -
jitter:Jmax' [ms] 5 -
Reliability Bound:Wmin' 0.90-1 (*) 1
Delay&Reliability:(ZminWmin)' - 0.90-1 -
_____________________________________
(*) To be chosen by the server
Security Considerations
Security considerations are not discussed in this memo.
Author's Address
Domenico Ferrari
University of California
Computer Science Division
EECS Department
Berkeley, CA 94720
Phone: (415) 642-3806
EMail: ferrari@UCBVAX.BERKELEY.EDU