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1.1 root 1: % run this through LaTeX with the appropriate wrapper
2:
3: \chapter {Defining New Services}\label{services}
4: There are several components which are manipulated when a service is invoked.
5: Briefly,
6: let us consider how to define a new service.
7: There are three databases to be managed:
8: \begin{describe}
9: \item[isoentities:] which maintains the mappings between application-entity
10: information and presentation addresses
11: (described in Chapter~\ref{isoentities});
12:
13: \item[isobjects:] which maintains the mappings between object descriptors and
14: object identifiers
15: (described in Chapter~\ref{isobjects});
16: and,
17:
18: \item[isoservices:] which maintains the mappings between textual descriptions
19: of services, service selectors, and local programs
20: (described in Chapter~\ref{isoservices} of \voltwo/).
21: \end{describe}
22:
23: For the remainder of this chapter,
24: consider any fictitious service
25: with suffix \verb"servicestore"
26: (e.g., for the host \verb"gremlin",
27: the service might be known as \verb"gremlin-servicestore"),
28: and with an application context name of \verb*"local service".
29:
30: There are many ways in which the mappings can be performed.
31: Two approaches are described in this chapter.
32: If you wish to use a different variation,
33: then presumably you know enough about what you are doing not to need
34: additional documentation here!
35:
36: \section {Standard Services}\label{service:standard}
37: The ``standard'' approach is the simplest and most straight-forward mapping
38: strategy.
39:
40: First,
41: the abstract syntax {\em presentation context information\/} (PCI) of
42: the service,
43: along with the {\em application context\/} of the service should be defined.
44: These are object identifiers (as described in Section~\ref{psap:oid} on
45: page~\pageref{psap:oid}).
46: The object identifier tree \verb"1.17.2" has been usurped for
47: defining local services using {\em The ISO Development Environment}.
48: Choose \verb"n",
49: where \verb"n" is the lowest unassigned number in the \verb"1.17.2.n" subtree,
50: for use by the service
51: (\verb"n" should be an integer greater than \verb"0").
52: Now edit the \man isobjects(5) file thusly:
53: \begin{quote}\small\begin{verbatim}
54: "local service pci" 1.17.2.n.1
55: "local service" 1.17.2.n.2
56: \end{verbatim}\end{quote}
57:
58: Next,
59: the template for the {\em application-entity information\/} and
60: {\em presentation address\/} of the service should be defined.
61: These are used for outgoing connections.
62: The application-entity information portion is currently an object identifier,
63: from the \verb"1.17.4.1" subtree.
64: The presentation address portion is a presentation selector,
65: a session selector, a transport selector, and a set of network addresses.
66: Currently, the convention is to use empty presentation and session selectors,
67: a unique transport selector,
68: and a simple default template for the network addresses
69: (the templates will be filled-in during connection establishment).
70: The choice of a transport selector is troublesome;
71: for the present,
72: a 16--bit binary selector space is suggested.
73: Choose \verb"p",
74: where \verb"p" is the lowest unassigned TSAP ID between \verb"1024" and
75: \verb"2047" inclusive.
76: Now edit the \man isoentities(5) file thusly:
77: \begin{quote}\small\begin{verbatim}
78: default servicestore 1.17.4.1.n "" "" #p/
79: \end{verbatim}\end{quote}
80:
81: Finally,
82: the program on the local system implementing the service should be defined.
83: This is used for incoming connections.
84: Given the strategy used for allocating presentation addresses above,
85: one need only map between a transport selector and a program.
86: Edit the \man isoservices(5) thusly:
87: \begin{quote}\small\begin{verbatim}
88: "tsap/servicestore" #p program arg1 arg2 ... argN
89: \end{verbatim}\end{quote}
90:
91: \section {GOSIP Services}\label{service:gosip}
92: The U.S.~Government OSI Profile\cite{US.GOSIP} specifies a somewhat different
93: mapping strategy.
94: Rather than list the differences,
95: the entire process is described here.
96:
97: First,
98: the abstract syntax {\em presentation context information\/} (PCI) of the
99: service,
100: along with the {\em application context\/} of the service should be defined.
101: These are object identifiers (as described in Section~\ref{psap:oid} on
102: page~\pageref{psap:oid}).
103: As previously described,
104: the object identifier tree \verb"1.17.2" is used to define local services.
105: Choose \verb"n",
106: where \verb"n" is the lowest unassigned number in the \verb"1.17.2.n" subtree,
107: for use by the service
108: (\verb"n" should be an integer greater than \verb"0").
109: Now edit the \man isobjects(5) file thusly:
110: \begin{quote}\small\begin{verbatim}
111: "local service pci" 1.17.2.n.1
112: "local service" 1.17.2.n.2
113: \end{verbatim}\end{quote}
114:
115: Next,
116: the template for the {\em application-entity information\/} and
117: {\em presentation address\/} of the service should be defined.
118: These are used for outgoing connections.
119: The application-entity information portion is currently an object identifier,
120: from the \verb"1.17.4.1" subtree.
121: The presentation address portion is a presentation selector,
122: a session selector, a transport selector, and a set of network addresses.
123: Currently, the convention is to use a unique presentation selector,
124: along with standard values for the session and transport selectors,
125: and a simple default template for the network addresses
126: (the templates will be filled-in during connection establishment).
127: The choice of the selectors is mandated by GOSIP:
128: a 16--bit binary selector space is used.
129: Choose \verb"p",
130: where \verb"p" is the lowest unassigned PSAP ID between \verb"1024" and
131: \verb"2047" inclusive.
132: Now edit the \man isoentities(5) file thusly:
133: \begin{quote}\small\begin{verbatim}
134: default servicestore 1.17.4.1.n #p/#1/#1/
135: \end{verbatim}\end{quote}
136:
137: Finally,
138: the program on the local system implementing the service should be defined.
139: This is used for incoming connections.
140: Given the strategy used for allocating presentation addresses above,
141: one need only map between a presentation selector and a program.
142: Edit the \man isoservices(5) thusly:
143: \begin{quote}\small\begin{verbatim}
144: "psap/servicestore" #p program arg1 arg2 ... argN
145: \end{verbatim}\end{quote}
146:
147: This strategy is less efficient than the first approach as it requires the
148: \man tsapd(8c) daemon to parse more information from the remote peer prior to
149: invoking the program which implements desired application context.
150:
151: \section {Static Servers}\label{static:services}
152: In Section~\ref{acs:server},
153: two different server disciplines,
154: the dynamic and the static approaches,
155: were described.
156: Thus far,
157: this chapter has described the dynamic approach.
158: The distinguishing mechanism of this discipline is that the entry in the
159: \man isoentities(5) file specifies \verb"default" for the host portion of the
160: service, e.g.,
161: \begin{quote}\small\begin{verbatim}
162: default servicestore 1.17.4.1.n #p/#1/#1/
163: \end{verbatim}\end{quote}
164:
165: To implement the static server discipline,
166: as described in Section~\ref{acs:server},
167: one defines the service for a particular host and specifies the non-standard
168: network (sub)address that the service exists on.
169: For example:
170: \begin{quote}\small\begin{verbatim}
171: gremlin imagestore 1.17.4.1.n \
172: #p/#1/#1/Internet=gremlin+17000
173: \end{verbatim}\end{quote}
174: Indicates that the service \verb"gremlin-imagestore" is available only by
175: using the TCP network service to the host \verb"gremlin" and then using TCP
176: port \verb"17000".
177: Similar definitions may be made for hosts using an X.25 service.
178: Further,
179: as is the case with any entry in the \man isoentities(5) file,
180: multiple network address may be present for a single service.
181: In these cases,
182: the server listens on all of these addresses.
183:
184: After making a suitable definition in the \man isoentities(5) file,
185: the server program must be started
186: (either by hand or automatically from some system startup file,
187: e.g., \file{/etc/rc.local}) without any arguments.
188: The server program,
189: using the \verb"isodeserver" routine described on page~\pageref{isodeserver}
190: will then perform the appropriate actions to start listening on the desired
191: addresses.
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