Information Technology Reference
In-Depth Information
community. Messages do not disclose to communicating peers sender's internal struc-
ture and algorithms, but only behaviour choices.
Community behaviours are observed locally through message boxes. Processing of
messages in autonomic nodes is FCFS, it follows the arrivals of messages in node's
message box. We assume that a node is able to create a message box per concern; this
message box shall contain both sent and received messages pertaining to the concern.
There are no assumptions on reliability of message delivery.
To represent contents of message boxes and consequently behaviours reflected in
these messages we shall use and extend the notation of protocol expressions following
the seminal work on protocol validation by G. Holzmann [19]. Small Latin characters
represent received messages; characters, written as denominators of a fraction repre-
sent own sent messages; a dot represents FCFS ordering of messages; a plus sign
between two messages represents alternatives; bracketed message sequence taken to
the power of N represents N or more repetitions of the same message sequence; 1
stands for empty box, and ш — for a deadlock.
A cross operation ( B [] B 2 [⊗ ) applied to one or more message boxes verifies
the soundness of message exchange; the exchange is sound if it is deadlock free and
there are no residuals in message box[es]. As axiomatically suggested in [19] the
properties (re-write rules) of protocol expression as in (5) should hold.
1
ab
a
---
a
---
a
---
(5)
a
---
1
---
a
---
1
---
1
---
ab
+
c
b
---
a
bc
a
=
;
a
=
;
-----------
=
;
=
+
;
=
+
------------
------------
+
,
3 Autonomic Communication Models
3.1 An Example of Etiquette
Using the above models we show how autonomic node behaviours are induced by
certain rules reflecting common community concern. To distinguish these rules from
other rules (policies) we shall term them etiquette rules (e-rules), where etiquette is a
complete ruleset reflecting the concern in question. As an example of a shared con-
cern we consider trust establishment in ad hoc communication environment, where
nodes use/ donate each other's resources to relay media datagrams with no infrastruc-
ture. Etiquette can be used in parallel with e.g. reputation schemes [20], or with infer-
ring trust from control exchange, e.g. routing [21].
Consider the set of workflows (6) implemented by three nodes A, B, and C, and
expressed in terms of functionalities (3) as introduced in Fig. 1.
; bW b
=
F 14
; cW
=
F 13
F 34
F 14
(6)
aW
=
F 13
,
c
,
,
,
a
,
;
dW
=
F 14
F 43
F 13
d
,
,
,
,
Semantics of (6) and their distribution between nodes A, B, and C is represented in
Fig. 3, where dotted line is a boundary between IPv4 and IPv6.
Search WWH ::




Custom Search