Merge branch 'anders/diameter/pool/OTP-12428' into maint

* anders/diameter/pool/OTP-12428:
  Fix SCTP match blunder in suites
  Be backwards compatible with diameter_sctp listener state
  Add gen_tcp testcase that fails sporadically
  Simplify transport suite
  Remove (ancient) dead code
  Don't orphan slave nodes in example suite
  Refresh example code
  Improve language consistency in diameter(1)
  Add pool suite to test transport_opt() pool_size
  Adapt tcp/sctp transport modules for pool_size > 1
  Add transport_opt() pool_size

22 files changed, 804 insertions, 497 deletions

diff --git a/lib/diameter/doc/src/diameter.xml b/lib/diameter/doc/src/diameter.xml
index 00b54ffbc4..638c1c4c2b 100644
--- a/lib/diameter/doc/src/diameter.xml
+++ b/lib/diameter/doc/src/diameter.xml
@@ -21,7 +21,7 @@
 
 <copyright>
 <year>2011</year>
-<year>2014</year>
+<year>2015</year>
 <holder>Ericsson AB. All Rights Reserved.</holder>
 </copyright>
 <legalnotice>
@@ -111,7 +111,7 @@ Defined in &dict_data_types;.</p>
 <tag><c>application_alias() = term()</c></tag>
 <item>
 <p>
-A name identifying a Diameter application in
+Name identifying a Diameter application in
 service configuration.
 Passed to &call; when sending requests
 defined by the application.</p>
@@ -129,7 +129,7 @@ ExtraArgs = list()
 </pre>
 
 <p>
-A module implementing the callback interface defined in &man_app;,
+Module implementing the callback interface defined in &man_app;,
 along with any
 extra arguments to be appended to those documented.
 Note that extra arguments specific to an outgoing request can be
@@ -156,7 +156,7 @@ Has one the following types.</p>
 <tag><c>{alias, &application_alias;}</c></tag>
 <item>
 <p>
-A unique identifier for the application in the scope of the
+Unique identifier for the application in the scope of the
 service.
 Defaults to the value of the <c>dictionary</c> option if
 unspecified.</p>
@@ -165,7 +165,7 @@ unspecified.</p>
 <tag><c>{dictionary, atom()}</c></tag>
 <item>
 <p>
-The name of an encode/decode module for the Diameter
+Name of an encode/decode module for the Diameter
 messages defined by the application.
 These modules are generated from files whose format is documented in
 &man_dict;.</p>
@@ -174,7 +174,7 @@ These modules are generated from files whose format is documented in
 <tag><c>{module, &application_module;}</c></tag>
 <item>
 <p>
-The callback module with which messages of the Diameter application are
+Callback module in which messages of the Diameter application are
 handled.
 See &man_app; for the required interface and semantics.</p>
 </item>
@@ -182,7 +182,7 @@ See &man_app; for the required interface and semantics.</p>
 <tag><c>{state, term()}</c></tag>
 <item>
 <p>
-The initial callback state.
+Initial callback state.
 The prevailing state is passed to some
 &man_app;
 callbacks, which can then return a new state.
@@ -192,7 +192,7 @@ Defaults to the value of the <c>alias</c> option if unspecified.</p>
 <tag><c>{call_mutates_state, true|false}</c></tag>
 <item>
 <p>
-Specifies whether or not the &app_pick_peer;
+Whether or not the &app_pick_peer;
 application callback can modify the application state.
 Defaults to <c>false</c> if unspecified.</p>
 
@@ -209,7 +209,7 @@ probably avoid it.</p>
 <tag><c>{answer_errors, callback|report|discard}</c></tag>
 <item>
 <p>
-Determines the manner in which incoming answer messages containing
+Manner in which incoming answer messages containing
 decode errors are handled.</p>
 
 <p>
@@ -233,7 +233,7 @@ Defaults to <c>discard</c> if unspecified.</p>
 <tag><c>{request_errors, answer_3xxx|answer|callback}</c></tag>
 <item>
 <p>
-Determines the manner in which incoming requests are handled when an
+Manner in which incoming requests are handled when an
 error other than 3007 (DIAMETER_APPLICATION_UNSUPPORTED, which cannot
 be associated with an application callback module), is detected.</p>
 
@@ -293,7 +293,7 @@ Multiple options append to the argument list.</p>
 <tag><c>{filter, &peer_filter;}</c></tag>
 <item>
 <p>
-A filter to apply to the list of available peers before passing it to
+Filter to apply to the list of available peers before passing it to
 the &app_pick_peer; callback for the application in question.
 Multiple options are equivalent a single <c>all</c> filter on the
 corresponding list of filters.
@@ -311,7 +311,7 @@ Defaults to 5000.</p>
 <tag><c>detach</c></tag>
 <item>
 <p>
-Causes &call; to return <c>ok</c> as
+Cause &call; to return <c>ok</c> as
 soon as the request in
 question has been encoded, instead of waiting for and returning
 the result from a subsequent &app_handle_answer; or
@@ -427,7 +427,7 @@ configuration passed to &start_service; or &add_transport;.</p>
 <tag><c>peer_filter() = term()</c></tag>
 <item>
 <p>
-A filter passed to &call; in order to select candidate peers for a
+Filter passed to &call; in order to select candidate peers for a
 &app_pick_peer; callback.
 Has one of the following types.</p>
 
@@ -1032,7 +1032,7 @@ case the corresponding callbacks are applied until either all return
 <tag><c>{capx_timeout, &dict_Unsigned32;}</c></tag>
 <item>
 <p>
-The number of milliseconds after which a transport process having an
+Number of milliseconds after which a transport process having an
 established transport connection will be terminated if the expected
 capabilities exchange message (CER or CEA) is not received from the peer.
 For a connecting transport, the timing of connection attempts is
@@ -1079,7 +1079,7 @@ transport.</p>
 
 <item>
 <p>
-A callback invoked prior to terminating the transport process of a
+Callback invoked prior to terminating the transport process of a
 transport connection having watchdog state <c>OKAY</c>.
 Applied to <c>application|service|transport</c> and the
 <c>&transport_ref;</c> and <c>&app_peer;</c> in question:
@@ -1095,7 +1095,7 @@ The return value can have one of the following types.</p>
 <tag><c>{dpr, [option()]}</c></tag>
 <item>
 <p>
-Causes Disconnect-Peer-Request to be sent to the peer, the transport
+Send Disconnect-Peer-Request to the peer, the transport
 process being terminated following reception of
 Disconnect-Peer-Answer or timeout.
 An <c>option()</c> can be one of the following.</p>
@@ -1104,7 +1104,7 @@ An <c>option()</c> can be one of the following.</p>
 <tag><c>{cause, 0|rebooting|1|busy|2|goaway}</c></tag>
 <item>
 <p>
-The Disconnect-Cause to send, <c>REBOOTING</c>, <c>BUSY</c> and
+Disconnect-Cause to send, <c>REBOOTING</c>, <c>BUSY</c> and
 <c>DO_NOT_WANT_TO_TALK_TO_YOU</c> respectively.
 Defaults to <c>rebooting</c> for <c>Reason=service|application</c> and
 <c>goaway</c> for <c>Reason=transport</c>.</p>
@@ -1113,7 +1113,7 @@ Defaults to <c>rebooting</c> for <c>Reason=service|application</c> and
 <tag><c>{timeout, &dict_Unsigned32;}</c></tag>
 <item>
 <p>
-The number of milliseconds after which the transport process is
+Number of milliseconds after which the transport process is
 terminated if DPA has not been received.
 Defaults to 1000.</p>
 </item>
@@ -1129,7 +1129,7 @@ Equivalent to <c>{dpr, []}</c>.</p>
 <tag><c>close</c></tag>
 <item>
 <p>
-Causes the transport process to be terminated without
+Terminate the transport process without
 Disconnect-Peer-Request being sent to the peer.</p>
 </item>
 
@@ -1156,7 +1156,7 @@ Defaults to a single callback returning <c>dpr</c>.</p>
 <tag><c>{length_errors, exit|handle|discard}</c></tag>
 <item>
 <p>
-Specifies how to deal with errors in the Message Length field of the
+How to deal with errors in the Message Length field of the
 Diameter Header in an incoming message.
 An error in this context is that the length is not at least 20 bytes
 (the length of a Header), is not a multiple of 4 (a valid length) or
@@ -1188,11 +1188,26 @@ See &man_tcp; for the behaviour of that module.</p>
 </note>
 </item>
 
+<tag><c>{pool_size, pos_integer()}</c></tag>
+<item>
+<p>
+Number of transport processes to start.
+For a listening transport, determines the size of the pool of
+accepting transport processes, a larger number being desirable for
+processing multiple concurrent peer connection attempts.
+For a connecting transport, determines the number of connections to
+the peer in question that will be attempted to be establshed:
+the &service_opt;: <c>restrict_connections</c> should also be
+configured on the service in question to allow multiple connections to
+the same peer.</p>
+
+</item>
+
 <marker id="spawn_opt"/>
 <tag><c>{spawn_opt, [term()]}</c></tag>
 <item>
 <p>
-An options list passed to &spawn_opt; when spawning a process for an
+Options list passed to &spawn_opt; when spawning a process for an
 incoming Diameter request.
 Options <c>monitor</c> and <c>link</c> are ignored.</p>
 
@@ -1205,7 +1220,7 @@ Defaults to the list configured on the service if not specified.</p>
 <tag><c>{transport_config, term(), &dict_Unsigned32; | infinity}</c></tag>
 <item>
 <p>
-A term passed as the third argument to the &transport_start; function of
+Term passed as the third argument to the &transport_start; function of
 the relevant &transport_module; in order to
 start a transport process.
 Defaults to the empty list if unspecified.</p>
@@ -1233,7 +1248,7 @@ To listen on both SCTP and TCP, define one transport for each.</p>
 <tag><c>{transport_module, atom()}</c></tag>
 <item>
 <p>
-A module implementing a transport process as defined in &man_transport;.
+Module implementing a transport process as defined in &man_transport;.
 Defaults to <c>diameter_tcp</c> if unspecified.</p>
 
 <p>
@@ -1253,7 +1268,7 @@ corresponding timeout (see below) or all fail.</p>
 <tag><c>{watchdog_config, [{okay|suspect, non_neg_integer()}]}</c></tag>
 <item>
 <p>
-Specifies configuration that alters the behaviour of the watchdog
+Configuration that alters the behaviour of the watchdog
 state machine.
 On key <c>okay</c>, the non-negative number of answered DWR
 messages before transitioning from REOPEN to OKAY.
@@ -1308,7 +1323,7 @@ in predicate functions passed to &remove_transport;.</p>
 <tag><c>transport_ref() = reference()</c></tag>
 <item>
 <p>
-An reference returned by &add_transport; that
+Reference returned by &add_transport; that
 identifies the configuration.</p>
 </item>
 
@@ -1737,6 +1752,14 @@ connection might look as follows.</p>
 The information presented here is as in the <c>connect</c> case except
 that the client connections are grouped under an <c>accept</c> tuple.</p>
 
+<p>
+Whether or not the &transport_opt; <c>pool_size</c> affects the format
+of the listing in the case of a connecting transport, since a value
+greater than 1 implies multiple transport processes for the same
+<c>&transport_ref;</c>, as in the listening case.
+The format in this case is similar to the listening case, with a
+<c>pool</c> tuple in place of an <c>accept</c> tuple.</p>
+
 </item>
 
 <tag><c>connections</c></tag>
diff --git a/lib/diameter/examples/code/GNUmakefile b/lib/diameter/examples/code/GNUmakefile
index 98e36a99e3..81f1da5a39 100644
--- a/lib/diameter/examples/code/GNUmakefile
+++ b/lib/diameter/examples/code/GNUmakefile
@@ -1,7 +1,7 @@
 #
 # %CopyrightBegin%
 #
-# Copyright Ericsson AB 2010-2012. All Rights Reserved.
+# Copyright Ericsson AB 2010-2015. All Rights Reserved.
 #
 # The contents of this file are subject to the Erlang Public License,
 # Version 1.1, (the "License"); you may not use this file except in
@@ -20,7 +20,7 @@
 EXAMPLES  = client server relay # redirect proxy
 
 CALLBACKS = $(EXAMPLES:%=%_cb)
-MODULES   = peer $(EXAMPLES) $(EXAMPLES:%=%_cb)
+MODULES   = node $(EXAMPLES) $(EXAMPLES:%=%_cb)
 
 BEAM = $(MODULES:%=%.beam)
 
diff --git a/lib/diameter/examples/code/client.erl b/lib/diameter/examples/code/client.erl
index 46eb4a55db..be5b4cbba5 100644
--- a/lib/diameter/examples/code/client.erl
+++ b/lib/diameter/examples/code/client.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %%
-%% Copyright Ericsson AB 2010-2014. All Rights Reserved.
+%% Copyright Ericsson AB 2010-2015. All Rights Reserved.
 %%
 %% The contents of this file are subject to the Erlang Public License,
 %% Version 1.1, (the "License"); you may not use this file except in
@@ -38,7 +38,7 @@
 -module(client).
 
 -include_lib("diameter/include/diameter.hrl").
--include_lib("diameter/include/diameter_gen_base_rfc3588.hrl").
+-include_lib("diameter/include/diameter_gen_base_rfc6733.hrl").
 
 -export([start/1,     %% start a service
          connect/2,   %% add a connecting transport
@@ -50,17 +50,14 @@
 %% both the record and list encoding here, one detached and one not,
 %% is just for demonstration purposes.
 
-%% Convenience functions using the default service name, ?SVC_NAME.
+%% Convenience functions using the default service name.
 -export([start/0,
          connect/1,
          stop/0,
          call/0,
          cast/0]).
 
--define(SVC_NAME,     ?MODULE).
--define(APP_ALIAS,    ?MODULE).
--define(CALLBACK_MOD, client_cb).
-
+-define(DEF_SVC_NAME, ?MODULE).
 -define(L, atom_to_list).
 
 %% The service configuration. As in the server example, a client
@@ -70,27 +67,27 @@
                         {'Origin-Realm', "example.com"},
                         {'Vendor-Id', 0},
                         {'Product-Name', "Client"},
-                        {'Auth-Application-Id', [?DIAMETER_APP_ID_COMMON]},
-                        {application, [{alias, ?APP_ALIAS},
-                                       {dictionary, ?DIAMETER_DICT_COMMON},
-                                       {module, ?CALLBACK_MOD}]}]).
+                        {'Auth-Application-Id', [0]},
+                        {application, [{alias, common},
+                                       {dictionary, diameter_gen_base_rfc6733},
+                                       {module, client_cb}]}]).
 
 %% start/1
 
 start(Name)
   when is_atom(Name) ->
-    peer:start(Name, ?SERVICE(Name)).
+    node:start(Name, ?SERVICE(Name)).
 
 start() ->
-    start(?SVC_NAME).
+    start(?DEF_SVC_NAME).
 
 %% connect/2
 
 connect(Name, T) ->
-    peer:connect(Name, T).
+    node:connect(Name, T).
 
 connect(T) ->
-    connect(?SVC_NAME, T).
+    connect(?DEF_SVC_NAME, T).
 
 %% call/1
 
@@ -99,10 +96,10 @@ call(Name) ->
     RAR = #diameter_base_RAR{'Session-Id' = SId,
                              'Auth-Application-Id' = 0,
                              'Re-Auth-Request-Type' = 0},
-    diameter:call(Name, ?APP_ALIAS, RAR, []).
+    diameter:call(Name, common, RAR, []).
 
 call() ->
-    call(?SVC_NAME).
+    call(?DEF_SVC_NAME).
 
 %% cast/1
 
@@ -111,15 +108,15 @@ cast(Name) ->
     RAR = ['RAR', {'Session-Id', SId},
                   {'Auth-Application-Id', 0},
                   {'Re-Auth-Request-Type', 1}],
-    diameter:call(Name, ?APP_ALIAS, RAR, [detach]).
+    diameter:call(Name, common, RAR, [detach]).
 
 cast() ->
-    cast(?SVC_NAME).
+    cast(?DEF_SVC_NAME).
 
 %% stop/1
 
 stop(Name) ->
-    peer:stop(Name).
+    node:stop(Name).
 
 stop() ->
-    stop(?SVC_NAME).
+    stop(?DEF_SVC_NAME).
diff --git a/lib/diameter/examples/code/node.erl b/lib/diameter/examples/code/node.erl
new file mode 100644
index 0000000000..4fe9007059
--- /dev/null
+++ b/lib/diameter/examples/code/node.erl
@@ -0,0 +1,174 @@
+%%
+%% %CopyrightBegin%
+%%
+%% Copyright Ericsson AB 2010-2015. All Rights Reserved.
+%%
+%% The contents of this file are subject to the Erlang Public License,
+%% Version 1.1, (the "License"); you may not use this file except in
+%% compliance with the License. You should have received a copy of the
+%% Erlang Public License along with this software. If not, it can be
+%% retrieved online at http://www.erlang.org/.
+%%
+%% Software distributed under the License is distributed on an "AS IS"
+%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
+%% the License for the specific language governing rights and limitations
+%% under the License.
+%%
+%% %CopyrightEnd%
+%%
+
+%%
+%% A library module used by the example Diameter nodes. Does little
+%% more than provide an alternate/simplified transport configuration.
+%%
+
+-module(node).
+
+-export([start/2,
+         listen/2,
+         connect/2,
+         stop/1]).
+
+-type protocol()
+   :: tcp | sctp.
+
+-type ip_address()
+   :: default
+    | inet:ip_address().
+
+-type server_transport()
+   :: protocol()
+    | {protocol(), ip_address(), non_neg_integer()}.
+
+-type server_opts()
+   :: server_transport()
+    | {server_transport(), [diameter:transport_opt()]}
+    | [diameter:transport_opt()].
+
+-type client_transport()
+   :: protocol() | any
+    | {protocol() | any, ip_address(), non_neg_integer()}
+    | {protocol() | any, ip_address(), ip_address(), non_neg_integer()}.
+
+-type client_opts()
+   :: client_transport()
+    | {client_transport(), [diameter:transport_opt()]}
+    | [diameter:transport_opt()].
+
+%% The server_transport() and client_transport() config is just
+%% convenience: arbitrary options can be specifed as a
+%% [diameter:transport_opt()].
+
+-define(DEFAULT_PORT, 3868).
+
+%% ---------------------------------------------------------------------------
+%% Interface functions
+%% ---------------------------------------------------------------------------
+
+%% start/2
+
+-spec start(diameter:service_name(), [diameter:service_opt()])
+   -> ok
+    | {error, term()}.
+
+start(Name, Opts)
+  when is_atom(Name), is_list(Opts) ->
+    diameter:start_service(Name, Opts).
+
+%% connect/2
+
+-spec connect(diameter:service_name(), client_opts())
+   -> {ok, diameter:transport_ref()}
+    | {error, term()}.
+
+connect(Name, Opts)
+  when is_list(Opts) ->
+    diameter:add_transport(Name, {connect, Opts});
+
+connect(Name, {T, Opts}) ->
+    connect(Name, Opts ++ client_opts(T));
+
+connect(Name, T) ->
+    connect(Name, [{connect_timer, 5000} | client_opts(T)]).
+
+%% listen/2
+
+-spec listen(diameter:service_name(), server_opts())
+   -> {ok, diameter:transport_ref()}
+    | {error, term()}.
+
+listen(Name, Opts)
+  when is_list(Opts) ->
+    diameter:add_transport(Name, {listen, Opts});
+
+listen(Name, {T, Opts}) ->
+    listen(Name, Opts ++ server_opts(T));
+
+listen(Name, T) ->
+    listen(Name, server_opts(T)).
+
+%% stop/1
+
+-spec stop(diameter:service_name())
+   -> ok
+    | {error, term()}.
+
+stop(Name) ->
+    diameter:stop_service(Name).
+
+%% ---------------------------------------------------------------------------
+%% Internal functions
+%% ---------------------------------------------------------------------------
+
+%% server_opts/1
+%%
+%% Return transport options for a listening transport.
+
+server_opts({T, Addr, Port}) ->
+    [{transport_module, tmod(T)},
+     {transport_config, [{reuseaddr, true},
+                         {ip, addr(Addr)},
+                         {port, Port}]}];
+
+server_opts(T) ->
+    server_opts({T, loopback, ?DEFAULT_PORT}).
+
+%% client_opts/1
+%%
+%% Return transport options for a connecting transport.
+
+client_opts({T, LA, RA, RP})
+  when T == all;   %% backwards compatibility
+       T == any ->
+    [[S, {C,Os}], T] = [client_opts({P, LA, RA, RP}) || P <- [sctp,tcp]],
+    [S, {C,Os,2000} | T];
+
+client_opts({T, LA, RA, RP}) ->
+    [{transport_module, tmod(T)},
+     {transport_config, [{raddr, addr(RA)},
+                         {rport, RP},
+                         {reuseaddr, true}
+                         | ip(LA)]}];
+
+client_opts({T, RA, RP}) ->
+    client_opts({T, default, RA, RP});
+
+client_opts(T) ->
+    client_opts({T, loopback, loopback, ?DEFAULT_PORT}).
+
+%% ---------------------------------------------------------------------------
+
+tmod(tcp)  -> diameter_tcp;
+tmod(sctp) -> diameter_sctp.
+
+ip(default) ->
+    [];
+ip(loopback) ->
+    [{ip, {127,0,0,1}}];
+ip(Addr) ->
+    [{ip, Addr}].
+
+addr(loopback) ->
+    {127,0,0,1};
+addr(A) ->
+    A.
diff --git a/lib/diameter/examples/code/peer.erl b/lib/diameter/examples/code/peer.erl
deleted file mode 100644
index 7519abfb2c..0000000000
--- a/lib/diameter/examples/code/peer.erl
+++ /dev/null
@@ -1,150 +0,0 @@
-%%
-%% %CopyrightBegin%
-%%
-%% Copyright Ericsson AB 2010-2013. All Rights Reserved.
-%%
-%% The contents of this file are subject to the Erlang Public License,
-%% Version 1.1, (the "License"); you may not use this file except in
-%% compliance with the License. You should have received a copy of the
-%% Erlang Public License along with this software. If not, it can be
-%% retrieved online at http://www.erlang.org/.
-%%
-%% Software distributed under the License is distributed on an "AS IS"
-%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
-%% the License for the specific language governing rights and limitations
-%% under the License.
-%%
-%% %CopyrightEnd%
-%%
-
-%%
-%% A library module that factors out commonality in the example
-%% Diameter peers.
-%%
-
--module(peer).
-
--include_lib("diameter/include/diameter.hrl").
--include_lib("diameter/include/diameter_gen_base_rfc3588.hrl").
-
--export([start/2,
-         listen/2,
-         connect/2,
-         stop/1]).
-
--type service_name()
-   :: term().
-
--type protocol()
-   :: tcp | sctp.
-
--type ip_address()
-   :: default
-    | inet:ip_address().
-
--type server_config()
-   :: protocol()
-    | {protocol(), ip_address(), non_neg_integer()}.
-
--type client_config()
-   :: protocol()
-    | {protocol(), ip_address(), non_neg_integer()}
-    | {protocol(), ip_address(), ip_address(), non_neg_integer()}.
-
--define(DEFAULT_PORT, 3868).
-
-%% ---------------------------------------------------------------------------
-%% Interface functions
-%% ---------------------------------------------------------------------------
-
-%% start/2
-
--spec start(service_name(), list())
-   -> ok
-    | {error, term()}.
-
-start(Name, Opts)
-  when is_atom(Name), is_list(Opts) ->
-    diameter:start_service(Name, Opts).
-
-%% connect/2
-
--spec connect(service_name(), client_config())
-   -> {ok, reference()}
-    | {error, term()}.
-
-connect(Name, T) ->
-    diameter:add_transport(Name, {connect, [{connect_timer, 5000}
-                                            | client(T)]}).
-
-%% listen/2
-
--spec listen(service_name(), server_config())
-   -> {ok, reference()}
-    | {error, term()}.
-
-listen(Name, T) ->
-    diameter:add_transport(Name, {listen, server(T)}).
-
-%% stop/1
-
--spec stop(service_name())
-   -> ok
-    | {error, term()}.
-
-stop(Name) ->
-    diameter:stop_service(Name).
-
-%% ---------------------------------------------------------------------------
-%% Internal functions
-%% ---------------------------------------------------------------------------
-
-%% server/1
-%%
-%% Return config for a listening transport.
-
-server({T, Addr, Port}) ->
-    [{transport_module, tmod(T)},
-     {transport_config, [{reuseaddr, true},
-                         {ip, addr(Addr)},
-                         {port, Port}]}];
-
-server(T) ->
-    server({T, loopback, ?DEFAULT_PORT}).
-
-%% client/1
-%%
-%% Return config for a connecting transport.
-
-client({all, LA, RA, RP}) ->
-    [[M,{K,C}], T]
-        = [client({P, LA, RA, RP}) || P <- [sctp,tcp]],
-    [M, {K,C,2000} | T];
-
-client({T, LA, RA, RP}) ->
-    [{transport_module, tmod(T)},
-     {transport_config, [{raddr, addr(RA)},
-                         {rport, RP},
-                         {reuseaddr, true}
-                         | ip(LA)]}];
-
-client({T, RA, RP}) ->
-    client({T, default, RA, RP});
-
-client(T) ->
-    client({T, loopback, loopback, ?DEFAULT_PORT}).
-
-tmod(tcp)  -> diameter_tcp;
-tmod(sctp) -> diameter_sctp.
-
-ip(default) ->
-    [];
-ip(loopback) ->
-    [{ip, {127,0,0,1}}];
-ip(Addr) ->
-    [{ip, Addr}].
-
-addr(loopback) ->
-    {127,0,0,1};
-addr(A) ->
-    A.
diff --git a/lib/diameter/examples/code/relay.erl b/lib/diameter/examples/code/relay.erl
index d3438f83f3..0aa3cd06d3 100644
--- a/lib/diameter/examples/code/relay.erl
+++ b/lib/diameter/examples/code/relay.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %%
-%% Copyright Ericsson AB 2010-2012. All Rights Reserved.
+%% Copyright Ericsson AB 2010-2015. All Rights Reserved.
 %%
 %% The contents of this file are subject to the Erlang Public License,
 %% Version 1.1, (the "License"); you may not use this file except in
@@ -31,9 +31,6 @@
 
 -module(relay).
 
--include_lib("diameter/include/diameter.hrl").
--include_lib("diameter/include/diameter_gen_base_rfc3588.hrl").
-
 -export([start/1,
          listen/2,
          connect/2,
@@ -44,49 +41,47 @@
          connect/1,
          stop/0]).
 
--define(APP_ALIAS,    ?MODULE).
--define(SVC_NAME,     ?MODULE).
--define(CALLBACK_MOD, relay_cb).
+-define(DEF_SVC_NAME, ?MODULE).
 
 %% The service configuration.
 -define(SERVICE(Name), [{'Origin-Host', atom_to_list(Name) ++ ".example.com"},
                         {'Origin-Realm', "example.com"},
                         {'Vendor-Id', 193},
                         {'Product-Name', "RelayAgent"},
-                        {'Auth-Application-Id', [?DIAMETER_APP_ID_RELAY]},
-                        {application, [{alias, ?MODULE},
-                                       {dictionary, ?DIAMETER_DICT_RELAY},
-                                       {module, ?CALLBACK_MOD}]}]).
+                        {'Auth-Application-Id', [16#FFFFFFFF]},
+                        {application, [{alias, relay},
+                                       {dictionary, diameter_relay},
+                                       {module, relay_cb}]}]).
 
 %% start/1
 
 start(Name)
   when is_atom(Name) ->
-    peer:start(Name, ?SERVICE(Name)).
+    node:start(Name, ?SERVICE(Name)).
 
 start() ->
-    start(?SVC_NAME).
+    start(?DEF_SVC_NAME).
 
 %% listen/2
 
 listen(Name, T) ->
-    peer:listen(Name, T).
+    node:listen(Name, T).
 
 listen(T) ->
-    listen(?SVC_NAME, T).
+    listen(?DEF_SVC_NAME, T).
 
 %% connect/2
 
 connect(Name, T) ->
-    peer:connect(Name, T).
+    node:connect(Name, T).
 
 connect(T) ->
-    connect(?SVC_NAME, T).
+    connect(?DEF_SVC_NAME, T).
 
 %% stop/1
 
 stop(Name) ->
-    peer:stop(Name).
+    node:stop(Name).
 
 stop() ->
-    stop(?SVC_NAME).
+    stop(?DEF_SVC_NAME).
diff --git a/lib/diameter/examples/code/server.erl b/lib/diameter/examples/code/server.erl
index 3959461cec..8c91e68895 100644
--- a/lib/diameter/examples/code/server.erl
+++ b/lib/diameter/examples/code/server.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %%
-%% Copyright Ericsson AB 2010-2012. All Rights Reserved.
+%% Copyright Ericsson AB 2010-2015. All Rights Reserved.
 %%
 %% The contents of this file are subject to the Erlang Public License,
 %% Version 1.1, (the "License"); you may not use this file except in
@@ -34,21 +34,16 @@
 
 -module(server).
 
--include_lib("diameter/include/diameter.hrl").
--include_lib("diameter/include/diameter_gen_base_rfc3588.hrl").
-
 -export([start/1,    %% start a service
          listen/2,   %% add a listening transport
          stop/1]).   %% stop a service
 
-%% Convenience functions using the default service name, ?SVC_NAME.
+%% Convenience functions using the default service name.
 -export([start/0,
          listen/1,
          stop/0]).
 
--define(SVC_NAME,     ?MODULE).
--define(APP_ALIAS,    ?MODULE).
--define(CALLBACK_MOD, server_cb).
+-define(DEF_SVC_NAME, ?MODULE).
 
 %% The service configuration. In a server supporting multiple Diameter
 %% applications each application may have its own, although they could all
@@ -57,32 +52,32 @@
                         {'Origin-Realm', "example.com"},
                         {'Vendor-Id', 193},
                         {'Product-Name', "Server"},
-                        {'Auth-Application-Id', [?DIAMETER_APP_ID_COMMON]},
-                        {application, [{alias, ?APP_ALIAS},
-                                       {dictionary, ?DIAMETER_DICT_COMMON},
-                                       {module, ?CALLBACK_MOD}]}]).
+                        {'Auth-Application-Id', [0]},
+                        {application, [{alias, common},
+                                       {dictionary, diameter_gen_base_rfc6733},
+                                       {module, server_cb}]}]).
 
 %% start/1
 
 start(Name)
   when is_atom(Name) ->
-    peer:start(Name, ?SERVICE(Name)).
+    node:start(Name, ?SERVICE(Name)).
 
 start() ->
-    start(?SVC_NAME).
+    start(?DEF_SVC_NAME).
 
 %% listen/2
 
 listen(Name, T) ->
-    peer:listen(Name, T).
+    node:listen(Name, T).
 
 listen(T) ->
-    listen(?SVC_NAME, T).
+    listen(?DEF_SVC_NAME, T).
 
 %% stop/1
 
 stop(Name) ->
-    peer:stop(Name).
+    node:stop(Name).
 
 stop() ->
-    stop(?SVC_NAME).
+    stop(?DEF_SVC_NAME).
diff --git a/lib/diameter/examples/code/server_cb.erl b/lib/diameter/examples/code/server_cb.erl
index 9d8d395d06..071e152493 100644
--- a/lib/diameter/examples/code/server_cb.erl
+++ b/lib/diameter/examples/code/server_cb.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %%
-%% Copyright Ericsson AB 2010-2014. All Rights Reserved.
+%% Copyright Ericsson AB 2010-2015. All Rights Reserved.
 %%
 %% The contents of this file are subject to the Erlang Public License,
 %% Version 1.1, (the "License"); you may not use this file except in
@@ -24,7 +24,7 @@
 -module(server_cb).
 
 -include_lib("diameter/include/diameter.hrl").
--include_lib("diameter/include/diameter_gen_base_rfc3588.hrl").
+-include_lib("diameter/include/diameter_gen_base_rfc6733.hrl").
 
 %% diameter callbacks
 -export([peer_up/3,
diff --git a/lib/diameter/src/base/diameter.erl b/lib/diameter/src/base/diameter.erl
index d74e091e11..1bbdf6e34d 100644
--- a/lib/diameter/src/base/diameter.erl
+++ b/lib/diameter/src/base/diameter.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %%
-%% Copyright Ericsson AB 2010-2013. All Rights Reserved.
+%% Copyright Ericsson AB 2010-2014. All Rights Reserved.
 %%
 %% The contents of this file are subject to the Erlang Public License,
 %% Version 1.1, (the "License"); you may not use this file except in
@@ -337,6 +337,7 @@ call(SvcName, App, Message) ->
    :: {transport_module, atom()}
     | {transport_config, any()}
     | {transport_config, any(), 'Unsigned32'() | infinity}
+    | {pool_size, pos_integer()}
     | {applications, [app_alias()]}
     | {capabilities, [capability()]}
     | {capabilities_cb, evaluable()}
diff --git a/lib/diameter/src/base/diameter_config.erl b/lib/diameter/src/base/diameter_config.erl
index dd1c9b73bb..270faa9542 100644
--- a/lib/diameter/src/base/diameter_config.erl
+++ b/lib/diameter/src/base/diameter_config.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %%
-%% Copyright Ericsson AB 2010-2014. All Rights Reserved.
+%% Copyright Ericsson AB 2010-2015. All Rights Reserved.
 %%
 %% The contents of this file are subject to the Erlang Public License,
 %% Version 1.1, (the "License"); you may not use this file except in
@@ -554,6 +554,9 @@ opt({watchdog_config, L}) ->
 opt({spawn_opt, Opts}) ->
     is_list(Opts);
 
+opt({pool_size, N}) ->
+    is_integer(N) andalso 0 < N;
+
 %% Options that we can't validate.
 opt({K, _})
   when K == transport_config;
diff --git a/lib/diameter/src/base/diameter_lib.erl b/lib/diameter/src/base/diameter_lib.erl
index b5f1ae3937..cd88619b66 100644
--- a/lib/diameter/src/base/diameter_lib.erl
+++ b/lib/diameter/src/base/diameter_lib.erl
@@ -31,6 +31,8 @@
          spawn_opts/2,
          wait/1,
          fold_tuple/3,
+         fold_n/3,
+         for_n/2,
          log/4]).
 
 %% ---------------------------------------------------------------------------
@@ -292,6 +294,35 @@ ft(Value, {Idx, T}) ->
     setelement(Idx, T, Value).
 
 %% ---------------------------------------------------------------------------
+%% # fold_n/3
+%% ---------------------------------------------------------------------------
+
+-spec fold_n(F, Acc0, N)
+   -> term()
+ when F    :: fun((non_neg_integer(), term()) -> term()),
+      Acc0 :: term(),
+      N    :: non_neg_integer().
+
+fold_n(F, Acc, N)
+  when is_integer(N), 0 < N ->
+    fold_n(F, F(N, Acc), N-1);
+
+fold_n(_, Acc, _) ->
+    Acc.
+
+%% ---------------------------------------------------------------------------
+%% # for_n/2
+%% ---------------------------------------------------------------------------
+
+-spec for_n(F, N)
+   -> non_neg_integer()
+ when F :: fun((non_neg_integer()) -> term()),
+      N :: non_neg_integer().
+
+for_n(F, N) ->
+    fold_n(fun(M,A) -> F(M), A+1 end, 0, N).
+
+%% ---------------------------------------------------------------------------
 %% # log/4
 %%
 %% Called to have something to trace on for happenings of interest.
diff --git a/lib/diameter/src/base/diameter_service.erl b/lib/diameter/src/base/diameter_service.erl
index f4afa6eb94..e1cc7bdfc9 100644
--- a/lib/diameter/src/base/diameter_service.erl
+++ b/lib/diameter/src/base/diameter_service.erl
@@ -766,8 +766,9 @@ reason(failure) ->
 start(Ref, {T, Opts}, S)
   when T == connect;
        T == listen ->
+    N = proplists:get_value(pool_size, Opts, 1),
     try
-        {ok, start(Ref, type(T), Opts, S)}
+        {ok, start(Ref, type(T), Opts, N, S)}
     catch
         ?FAILURE(Reason) ->
             {error, Reason}
@@ -785,11 +786,16 @@ type(connect = T) -> T.
 
 %% start/4
 
-start(Ref, Type, Opts, #state{watchdogT = WatchdogT,
-                              peerT = PeerT,
-                              options = SvcOpts,
-                              service_name = SvcName,
-                              service = Svc0})
+start(Ref, Type, Opts, State) ->
+    start(Ref, Type, Opts, 1, State).
+
+%% start/5
+
+start(Ref, Type, Opts, N, #state{watchdogT = WatchdogT,
+                                 peerT = PeerT,
+                                 options = SvcOpts,
+                                 service_name = SvcName,
+                                 service = Svc0})
   when Type == connect;
        Type == accept ->
     #diameter_service{applications = Apps}
@@ -797,14 +803,19 @@ start(Ref, Type, Opts, #state{watchdogT = WatchdogT,
         = merge_service(Opts, Svc0),
     {_,_} = Mask = proplists:get_value(sequence, SvcOpts),
     RecvData = diameter_traffic:make_recvdata([SvcName, PeerT, Apps, Mask]),
-    Pid = s(Type, Ref, {{spawn_opts([Opts, SvcOpts]), RecvData},
-                        Opts,
-                        SvcOpts,
-                        Svc}),
-    insert(WatchdogT, #watchdog{pid = Pid,
-                                type = Type,
-                                ref = Ref,
-                                options = Opts}),
+    T = {{spawn_opts([Opts, SvcOpts]), RecvData}, Opts, SvcOpts, Svc},
+    Rec = #watchdog{type = Type,
+                    ref = Ref,
+                    options = Opts},
+    diameter_lib:fold_n(fun(_,A) ->
+                                [wd(Type, Ref, T, WatchdogT, Rec) | A]
+                        end,
+                        [],
+                        N).
+
+wd(Type, Ref, T, WatchdogT, Rec) ->
+    Pid = wd(Type, Ref, T),
+    insert(WatchdogT, Rec#watchdog{pid = Pid}),
     Pid.
 
 %% Note that the service record passed into the watchdog is the merged
@@ -817,7 +828,7 @@ spawn_opts(Optss) ->
           T /= link,
           T /= monitor].
 
-s(Type, Ref, T) ->
+wd(Type, Ref, T) ->
     {_MRef, Pid} = diameter_watchdog:start({Type, Ref}, T),
     Pid.
 
@@ -1719,31 +1730,43 @@ info_transport(S) ->
               [],
               PeerD).
 
-%% Only a config entry for a listening transport: use it.
-transport([[{type, listen}, _] = L]) ->
-    L ++ [{accept, []}];
-
-%% Only one config or peer entry for a connecting transport: use it.
-transport([[{type, connect} | _] = L]) ->
-    L;
+%% Single config entry. Distinguish between pool_size config or not on
+%% a connecting transport for backwards compatibility: with the option
+%% the form is similar to the listening case, with connections grouped
+%% in a pool tuple (for lack of a better name), without as before.
+transport([[{type, Type}, {options, Opts}] = L])
+  when Type == listen;
+       Type == connect ->
+    L ++ [{K, []} || [{_,K}] <- [keys(Type, Opts)]];
 
 %% Peer entries: discard config. Note that the peer entries have
 %% length at least 3.
 transport([[_,_] | L]) ->
     transport(L);
 
-%% Possibly many peer entries for a listening transport. Note that all
-%% have the same options by construction, which is not terribly space
-%% efficient.
-transport([[{type, accept}, {options, Opts} | _] | _] = Ls) ->
-    [{type, listen},
+%% Multiple tranports. Note that all have the same options by
+%% construction, which is not terribly space efficient.
+transport([[{type, Type}, {options, Opts} | _] | _] = Ls) ->
+    transport(keys(Type, Opts), Ls).
+
+%% Group transports in an accept or pool tuple ...
+transport([{Type, Key}], [[{type, _}, {options, Opts} | _] | _] = Ls) ->
+    [{type, Type},
      {options, Opts},
-     {accept, [lists:nthtail(2,L) || L <- Ls]}].
+     {Key, [tl(tl(L)) || L <- Ls]}];
+
+%% ... or not: there can only be one.
+transport([], [L]) ->
+    L.
+
+keys(connect = T, Opts) ->
+    [{T, pool} || lists:keymember(pool_size, 1, Opts)];
+keys(_, _) ->
+    [{listen, accept}].
 
 peer_dict(#state{watchdogT = WatchdogT, peerT = PeerT}, Dict0) ->
     try ets:tab2list(WatchdogT) of
-        L ->
-            lists:foldl(fun(T,A) -> peer_acc(PeerT, A, T) end, Dict0, L)
+        L -> lists:foldl(fun(T,A) -> peer_acc(PeerT, A, T) end, Dict0, L)
     catch
         error: badarg -> Dict0  %% service has gone down
     end.
diff --git a/lib/diameter/src/modules.mk b/lib/diameter/src/modules.mk
index a2a7a51892..c9dd4e683a 100644
--- a/lib/diameter/src/modules.mk
+++ b/lib/diameter/src/modules.mk
@@ -1,7 +1,7 @@
 
 # %CopyrightBegin%
 #
-# Copyright Ericsson AB 2010-2014. All Rights Reserved.
+# Copyright Ericsson AB 2010-2015. All Rights Reserved.
 #
 # The contents of this file are subject to the Erlang Public License,
 # Version 1.1, (the "License"); you may not use this file except in
@@ -94,7 +94,7 @@ BINS = \
 # Released files relative to ../examples.
 EXAMPLES = \
 	code/GNUmakefile \
-	code/peer.erl \
+	code/node.erl \
 	code/client.erl \
 	code/client_cb.erl \
 	code/server.erl \
diff --git a/lib/diameter/src/transport/diameter_sctp.erl b/lib/diameter/src/transport/diameter_sctp.erl
index 32e7aaca39..66cffa41c0 100644
--- a/lib/diameter/src/transport/diameter_sctp.erl
+++ b/lib/diameter/src/transport/diameter_sctp.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %%
-%% Copyright Ericsson AB 2010-2014. All Rights Reserved.
+%% Copyright Ericsson AB 2010-2015. All Rights Reserved.
 %%
 %% The contents of this file are subject to the Erlang Public License,
 %% Version 1.1, (the "License"); you may not use this file except in
@@ -37,7 +37,8 @@
          code_change/3,
          terminate/2]).
 
--export([info/1]).  %% service_info callback
+-export([listener/1,%% diameter_sync callback
+         info/1]).  %% service_info callback
 
 -export([ports/0,
          ports/1]).
@@ -99,22 +100,31 @@
 -record(listener,
         {ref       :: reference(),
          socket    :: gen_sctp:sctp_socket(),
-         count = 0 :: uint(),
+         count = 0 :: uint(),  %% attached transport processes
          tmap = ets:new(?MODULE, []) :: ets:tid(),
              %% {MRef, Pid|AssocId}, {AssocId, Pid}
          pending = {0, ets:new(?MODULE, [ordered_set])},
          tref      :: reference(),
          accept    :: [match()]}).
 %% Field tmap is used to map an incoming message or event to the
-%% relevent transport process. Field pending implements a queue of
-%% transport processes to which an association has been assigned (at
-%% comm_up and written into tmap) but for which diameter hasn't yet
-%% spawned a transport process: a short-lived state of affairs as a
-%% new transport is spawned as a consequence of a peer being taken up,
-%% transport processes being spawned by the listener on demand. In
-%% case diameter starts a transport before comm_up on a new
-%% association, pending is set to an improper list with the spawned
-%% transport as head and the queue as tail.
+%% relevant transport process. Field pending implements two queues:
+%% the first of transport-to-be processes to which an association has
+%% been assigned (at comm_up and written into tmap) but for which
+%% diameter hasn't yet spawned a transport process, a short-lived
+%% state of affairs as a new transport is spawned as a consequence of
+%% a peer being taken up, transport processes being spawned by the
+%% listener on demand; the second of started transport processes that
+%% have not yet been assigned an association.
+%%
+%% When diameter calls start/3, the transport process is either taken
+%% from the first queue or spawned and placed in the second queue
+%% until an association is established. When an association is
+%% established, a controlling process is either taken from the second
+%% queue or spawned and placed in the first queue. Thus, there are
+%% only elements in one queue at a time, so share an ets table queue
+%% and tag it with a positive length if it contains the first queue, a
+%% negative length if it contains the second queue. The case -1 is
+%% handled differently for backwards compatibility reasons.
 
 %% ---------------------------------------------------------------------------
 %% # start/3
@@ -139,9 +149,9 @@ ip(T) ->
     T.
 
 %% A listener spawns transports either as a consequence of this call
-%% when there is not yet an association to associate with it, or at
-%% comm_up on a new association in which case the call retrieves a
-%% transport from the pending queue.
+%% when there is not yet an association to assign it, or at comm_up on
+%% a new association in which case the call retrieves a transport from
+%% the pending queue.
 s({accept, Ref} = A, Addrs, Opts) ->
     {LPid, LAs} = listener(Ref, {Opts, Addrs}),
     try gen_server:call(LPid, {A, self()}, infinity) of
@@ -226,7 +236,7 @@ i({connect, Pid, Opts, Addrs, Ref}) ->
     {LAs, Sock} = open(Addrs, Rest, 0),
     putr(?REF_KEY, Ref),
     proc_lib:init_ack({ok, self(), LAs}),
-    erlang:monitor(process, Pid),
+    monitor(process, Pid),
     #transport{parent = Pid,
                mode = {connect, connect(Sock, RAs, RP, [])},
                socket = Sock};
@@ -236,8 +246,8 @@ i({accept, Pid, LPid, Sock, Ref})
   when is_pid(Pid) ->
     putr(?REF_KEY, Ref),
     proc_lib:init_ack({ok, self()}),
-    erlang:monitor(process, Pid),
-    erlang:monitor(process, LPid),
+    monitor(process, Pid),
+    monitor(process, LPid),
     #transport{parent = Pid,
                mode = {accept, LPid},
                socket = Sock};
@@ -246,7 +256,7 @@ i({accept, Pid, LPid, Sock, Ref})
 i({accept, Ref, LPid, Sock, Id}) ->
     putr(?REF_KEY, Ref),
     proc_lib:init_ack({ok, self()}),
-    MRef = erlang:monitor(process, LPid),
+    MRef = monitor(process, LPid),
     %% Wait for a signal that the transport has been started before
     %% processing other messages.
     receive
@@ -270,15 +280,23 @@ close(Sock, Id) ->
 
 %% listener/2
 
+%% Accepting processes can be started concurrently: ensure only one
+%% listener is started.
 listener(LRef, T) ->
+    diameter_sync:call({?MODULE, listener, LRef},
+                       {?MODULE, listener, [{LRef, T}]},
+                       infinity,
+                       infinity).
+
+listener({LRef, T}) ->
     l(diameter_reg:match({?MODULE, listener, {LRef, '_'}}), LRef, T).
 
-%% Existing process with the listening socket ...
+%% Existing listening process ...
 l([{{?MODULE, listener, {_, AS}}, LPid}], _, _) ->
-    {LAs, _Sock} = AS,
-    {LPid, LAs};
-
-%% ... or not: start one.
+     {LAs, _Sock} = AS,
+     {LPid, LAs};
+ 
+%% ... or not.
 l([], LRef, T) ->
     {ok, LPid, LAs} = diameter_sctp_sup:start_child({listen, LRef, T}),
     {LPid, LAs}.
@@ -347,11 +365,17 @@ type(T) ->
 %% # handle_call/3
 %% ---------------------------------------------------------------------------
 
+handle_call(T, From, #listener{pending = L} = S)
+  when is_list(L) ->
+    handle_call(T, From, upgrade(S));
+
 handle_call({{accept, Ref}, Pid}, _, #listener{ref = Ref,
-                                               count = N}
+                                               pending = {N,Q},
+                                               count = K}
                                      = S) ->
-    {TPid, NewS} = accept(Ref, Pid, S),
-    {reply, {ok, TPid}, NewS#listener{count = N+1}};
+    TPid = accept(Ref, Pid, S),
+    {reply, {ok, TPid}, downgrade(S#listener{pending = {N-1,Q},
+                                             count = K+1})};
 
 handle_call(_, _, State) ->
     {reply, nok, State}.
@@ -370,8 +394,46 @@ handle_cast(_, State) ->
 handle_info(T, #transport{} = S) ->
     {noreply, #transport{} = t(T,S)};
 
+handle_info(T, #listener{pending = L} = S)
+  when is_list(L) ->
+    handle_info(T, upgrade(S));
+
 handle_info(T, #listener{} = S) ->
-    {noreply, #listener{} = l(T,S)}.
+    {noreply, downgrade(#listener{} = l(T,S))}.
+
+%% upgrade/1
+
+upgrade(#listener{pending = [TPid | {0,Q}]} = S) ->
+    ets:insert(Q, {TPid, now()}),
+    S#listener{pending = {-1,Q}}.
+%% Prior to the possiblity of setting pool_size on in transport
+%% configuration, a new accepting transport was only started following
+%% the death of a predecessor, so that there was only at most one
+%% previously started transport process waiting for an association.
+%% This assumption no longer holds with pool_size > 1, in which case
+%% several accepting transports are started concurrently. Deal with
+%% this by placing the started transports in a new queue of transport
+%% processes waiting for an association.
+%%
+%% Since only one of this queue and the existing queue of controlling
+%% processes waiting for a transport to be started can be non-empty at
+%% any given time, implement both queues in the same ets table. The
+%% absolute value of the first element of the 2-tuple is the queue
+%% length, the sign says which queue it is.
+
+%% downgrade/1
+%%
+%% Revert to the pre-pool_size representation when possible, for
+%% backwards compatibility in the case that the pool_size option
+%% hasn't been used.
+
+downgrade(#listener{pending = {-1,Q}} = S) ->
+    TPid = ets:first(Q),
+    ets:delete(Q, TPid),
+    S#listener{pending = [TPid | {0,Q}]};
+
+downgrade(S) ->
+    S.
 
 %% ---------------------------------------------------------------------------
 %% # code_change/3
@@ -436,54 +498,46 @@ l({sctp, Sock, _RA, _RP, Data} = Msg, #listener{socket = Sock} = S) ->
         setopts(Sock)
     end;
 
-%% Transport is asking message to be sent. See send/3 for why the send
-%% isn't directly from the transport.
-l({send, AssocId, StreamId, Bin}, #listener{socket = Sock} = S) ->
-    send(Sock, AssocId, StreamId, Bin),
-    S;
+l({'DOWN', MRef, process, TPid, _}, #listener{pending = {_,Q}} = S) ->
+    down(ets:member(Q, TPid), MRef, TPid, S);
+
+%% Timeout after the last accepting process has died.
+l({timeout, TRef, close = T}, #listener{tref = TRef,
+                                        count = 0}) ->
+    x(T);
+l({timeout, _, close}, #listener{} = S) ->
+    S.
+
+%% down/4
 
 %% Accepting transport has died. One that's awaiting an association ...
-l({'DOWN', MRef, process, TPid, _}, #listener{pending = [TPid | Q],
-                                              tmap = T,
-                                              count = N}
-                                    = S) ->
+down(true, MRef, TPid, #listener{pending = {N,Q},
+                                 tmap = T,
+                                 count = K}
+     = S)
+  when N < 0 ->
+    ets:delete(Q, TPid),
     ets:delete(T, MRef),
     ets:delete(T, TPid),
-    start_timer(S#listener{count = N-1,
-                           pending = Q});
-
-%% ... ditto and a new transport has already been started ...
-l({'DOWN', _, process, _, _} = T, #listener{pending = [TPid | Q]}
-                                  = S) ->
-    #listener{pending = NQ}
-        = NewS
-        = l(T, S#listener{pending = Q}),
-    NewS#listener{pending = [TPid | NQ]};
-
-%% ... or not.
-l({'DOWN', MRef, process, TPid, _}, #listener{socket = Sock,
-                                              tmap = T,
-                                              count = N,
-                                              pending = {P,Q}}
-                                    = S) ->
+    start_timer(S#listener{count = K-1,
+                           pending = {N+1,Q}});
+
+%% ... or one that already has one.
+down(B, MRef, TPid, #listener{socket = Sock,
+                              tmap = T,
+                              count = K,
+                              pending = {N,Q}}
+                        = S) ->
     [{MRef, Id}] = ets:lookup(T, MRef),  %% Id = TPid | AssocId
     ets:delete(T, MRef),
     ets:delete(T, Id),
     Id == TPid orelse close(Sock, Id),
-    case ets:lookup(Q, TPid) of
-        [{TPid, _}] -> %% transport in the pending queue ...
+    if B ->     %% Waiting for attachment in the pending queue ...
             ets:delete(Q, TPid),
-            S#listener{pending = {P-1, Q}};
-        [] ->           %% ... or not
-            start_timer(S#listener{count = N-1})
-    end;
-
-%% Timeout after the last accepting process has died.
-l({timeout, TRef, close = T}, #listener{tref = TRef,
-                                        count = 0}) ->
-    x(T);
-l({timeout, _, close}, #listener{} = S) ->
-    S.
+            S#listener{pending = {N-1,Q}};
+       true ->  %% ... or already attached
+            start_timer(S#listener{count = K-1})
+    end.
 
 %% t/2
 %%
@@ -582,29 +636,24 @@ accept(Opts) ->
 %% No pending associations: spawn a new transport.
 accept(Ref, Pid, #listener{socket = Sock,
                            tmap = T,
-                           pending = {0,_} = Q}
-                 = S) ->
+                           pending = {N,Q}})
+  when N =< 0 ->
     Arg = {accept, Pid, self(), Sock, Ref},
     {ok, TPid} = diameter_sctp_sup:start_child(Arg),
-    MRef = erlang:monitor(process, TPid),
+    MRef = monitor(process, TPid),
     ets:insert(T, [{MRef, TPid}, {TPid, MRef}]),
-    {TPid, S#listener{pending = [TPid | Q]}};
-%% Placing the transport in the pending field makes it available to
-%% the next association. The stack starts a new accepting transport
-%% only after this one brings the connection up (or dies).
-
-%% Accepting transport has died. This can happen if a new transport is
-%% started before the DOWN has arrived.
-accept(Ref, Pid, #listener{pending = [TPid | {0,_} = Q]} = S) ->
-    false = is_process_alive(TPid),  %% assert
-    accept(Ref, Pid, S#listener{pending = Q});
+    ets:insert(Q, {TPid, now()}),
+    TPid;
+%% Placing the transport in the second pending table makes it
+%% available to the next association.
 
 %% Pending associations: attach to the first in the queue.
-accept(_, Pid, #listener{ref = Ref, pending = {N,Q}} = S) ->
+accept(_, Pid, #listener{ref = Ref,
+                         pending = {_,Q}}) ->
     TPid = ets:first(Q),
     TPid ! {Ref, Pid},
     ets:delete(Q, TPid),
-    {TPid, S#listener{pending = {N-1, Q}}}.
+    TPid.
 
 %% send/2
 
@@ -718,34 +767,12 @@ up(#transport{parent = Pid,
 find(Id, Data, #listener{tmap = T} = S) ->
     f(ets:lookup(T, Id), Data, S).
 
-%% New association and a transport waiting for one: use it.
+%% New association ...
 f([],
-  {_, #sctp_assoc_change{state = comm_up,
-                         assoc_id = Id}},
-  #listener{tmap = T,
-            pending = [TPid | {_,_} = Q]}
+  {_, #sctp_assoc_change{state = comm_up, assoc_id = Id}},
+  #listener{pending = {N,Q}}
   = S) ->
-    [{TPid, MRef}] = ets:lookup(T, TPid),
-    ets:insert(T, [{MRef, Id}, {Id, TPid}]),
-    ets:delete(T, TPid),
-    {TPid, S#listener{pending = Q}};
-
-%% New association and no transport start yet: spawn one and place it
-%% in the queue.
-f([],
-  {_, #sctp_assoc_change{state = comm_up,
-                         assoc_id = Id}},
-  #listener{ref = Ref,
-            socket = Sock,
-            tmap = T,
-            pending = {N,Q}}
-  = S) ->
-    Arg = {accept, Ref, self(), Sock, Id},
-    {ok, TPid} = diameter_sctp_sup:start_child(Arg),
-    MRef = erlang:monitor(process, TPid),
-    ets:insert(T, [{MRef, Id}, {Id, TPid}]),
-    ets:insert(Q, {TPid, now()}),
-    {TPid, S#listener{pending = {N+1, Q}}};
+    {find(Id, S), S#listener{pending = {N+1,Q}}};
 
 %% Known association ...
 f([{_, TPid}], _, S) ->
@@ -755,6 +782,31 @@ f([{_, TPid}], _, S) ->
 f([], _, _) ->
     false.
 
+%% find/2
+
+%% Transport waiting for an association: use it.
+find(Id, #listener{tmap = T,
+                   pending = {N,Q}})
+  when N < 0 ->
+    TPid = ets:first(Q),
+    [{TPid, MRef}] = ets:lookup(T, TPid),
+    ets:insert(T, [{MRef, Id}, {Id, TPid}]),
+    ets:delete(T, TPid),
+    ets:delete(Q, TPid),
+    TPid;
+
+%% No transport start yet: spawn one and queue.
+find(Id, #listener{ref = Ref,
+                   socket = Sock,
+                   tmap = T,
+                   pending = {_,Q}}) ->
+    Arg = {accept, Ref, self(), Sock, Id},
+    {ok, TPid} = diameter_sctp_sup:start_child(Arg),
+    MRef = monitor(process, TPid),
+    ets:insert(T, [{MRef, Id}, {Id, TPid}]),
+    ets:insert(Q, {TPid, now()}),
+    TPid.
+
 %% assoc_id/1
 
 assoc_id({[#sctp_sndrcvinfo{assoc_id = Id}], _}) ->
diff --git a/lib/diameter/src/transport/diameter_tcp.erl b/lib/diameter/src/transport/diameter_tcp.erl
index 4d1b8bec51..0b26f429fb 100644
--- a/lib/diameter/src/transport/diameter_tcp.erl
+++ b/lib/diameter/src/transport/diameter_tcp.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %%
-%% Copyright Ericsson AB 2010-2013. All Rights Reserved.
+%% Copyright Ericsson AB 2010-2015. All Rights Reserved.
 %%
 %% The contents of this file are subject to the Erlang Public License,
 %% Version 1.1, (the "License"); you may not use this file except in
@@ -37,7 +37,8 @@
          code_change/3,
          terminate/2]).
 
--export([info/1]).  %% service_info callback
+-export([listener/1,%% diameter_sync callback
+         info/1]).  %% service_info callback
 
 -export([ports/0,
          ports/1]).
@@ -191,7 +192,7 @@ init(T) ->
 i({T, Ref, Mod, Pid, Opts, Addrs})
   when T == accept;
        T == connect ->
-    erlang:monitor(process, Pid),
+    monitor(process, Pid),
     %% Since accept/connect might block indefinitely, spawn a process
     %% that does nothing but kill us with the parent until call
     %% returns.
@@ -218,8 +219,8 @@ i({T, Ref, Mod, Pid, Opts, Addrs})
 %% A monitor process to kill the transport if the parent dies.
 i(#monitor{parent = Pid, transport = TPid} = S) ->
     proc_lib:init_ack({ok, self()}),
-    erlang:monitor(process, Pid),
-    erlang:monitor(process, TPid),
+    monitor(process, Pid),
+    monitor(process, TPid),
     S;
 %% In principle a link between the transport and killer processes
 %% could do the same thing: have the accepting/connecting process be
@@ -235,7 +236,7 @@ i({listen, LRef, APid, {Mod, Opts, Addrs}}) ->
     LAddr = laddr(LAddrOpt, Mod, LSock),
     true = diameter_reg:add_new({?MODULE, listener, {LRef, {LAddr, LSock}}}),
     proc_lib:init_ack({ok, self(), {LAddr, LSock}}),
-    erlang:monitor(process, APid),
+    monitor(process, APid),
     start_timer(#listener{socket = LSock}).
 
 laddr([], Mod, Sock) ->
@@ -336,17 +337,25 @@ accept(Opts) ->
 
 %% listener/2
 
+%% Accepting processes can be started concurrently: ensure only one
+%% listener is started.
 listener(LRef, T) ->
-    l(diameter_reg:match({?MODULE, listener, {LRef, '_'}}), LRef, T).
+    diameter_sync:call({?MODULE, listener, LRef},
+                       {?MODULE, listener, [{LRef, T, self()}]},
+                       infinity,
+                       infinity).
 
-%% Existing process with the listening socket ...
-l([{{?MODULE, listener, {_, AS}}, LPid}], _, _) ->
-    LPid ! {accept, self()},
+listener({LRef, T, TPid}) ->
+    l(diameter_reg:match({?MODULE, listener, {LRef, '_'}}), LRef, T, TPid).
+
+%% Existing listening process ...
+l([{{?MODULE, listener, {_, AS}}, LPid}], _, _, TPid) ->
+    LPid ! {accept, TPid},
     AS;
 
-%% ... or not: start one.
-l([], LRef, T) ->
-    {ok, _, AS} = diameter_tcp_sup:start_child({listen, LRef, self(), T}),
+%% ... or not.
+l([], LRef, T, TPid) ->
+    {ok, _, AS} = diameter_tcp_sup:start_child({listen, LRef, TPid, T}),
     AS.
 
 %% get_addr/1
@@ -502,7 +511,7 @@ m({'DOWN', _, process, Pid, _}, #monitor{parent = Pid,
 
 %% Another accept transport is attaching.
 l({accept, TPid}, #listener{count = N} = S) ->
-    erlang:monitor(process, TPid),
+    monitor(process, TPid),
     S#listener{count = N+1};
 
 %% Accepting process has died.
diff --git a/lib/diameter/test/diameter_examples_SUITE.erl b/lib/diameter/test/diameter_examples_SUITE.erl
index aef4bc35ef..dc0b466b59 100644
--- a/lib/diameter/test/diameter_examples_SUITE.erl
+++ b/lib/diameter/test/diameter_examples_SUITE.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %%
-%% Copyright Ericsson AB 2013-2014. All Rights Reserved.
+%% Copyright Ericsson AB 2013-2015. All Rights Reserved.
 %%
 %% The contents of this file are subject to the Erlang Public License,
 %% Version 1.1, (the "License"); you may not use this file except in
@@ -397,4 +397,4 @@ stop(Name)
 
 stop(Config) ->
     Prot = proplists:get_value(group, Config),
-    [] = [RC || N <- ?NODES, RC <- [stop(concat(Prot, N))], RC /= ok].
+    [] = [RC || N <- ?NODES, RC <- [catch stop(concat(Prot, N))], RC /= ok].
diff --git a/lib/diameter/test/diameter_gen_sctp_SUITE.erl b/lib/diameter/test/diameter_gen_sctp_SUITE.erl
index 51ccb1e6ec..25017272b5 100644
--- a/lib/diameter/test/diameter_gen_sctp_SUITE.erl
+++ b/lib/diameter/test/diameter_gen_sctp_SUITE.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %%
-%% Copyright Ericsson AB 2010-2013. All Rights Reserved.
+%% Copyright Ericsson AB 2010-2015. All Rights Reserved.
 %%
 %% The contents of this file are subject to the Erlang Public License,
 %% Version 1.1, (the "License"); you may not use this file except in
@@ -119,10 +119,10 @@ send_not_from_controlling_process(_) ->
 
 send_not_from_controlling_process() ->
     FPid = self(),
-    {L, MRef} = spawn_monitor(fun() -> listen(FPid) end),%% listening process
+    {L, MRef} = spawn_monitor(fun() -> listen(FPid) end),
     receive
         {?MODULE, C, S} ->
-            erlang:demonitor(MRef, [flush]),
+            demonitor(MRef, [flush]),
             [L,C,S];
         {'DOWN', MRef, process, _, _} = T ->
             error(T)
@@ -137,13 +137,7 @@ listen(FPid) ->
     LPid = self(),
     spawn(fun() -> connect1(PortNr, FPid, LPid) end), %% connecting process
     Id = assoc(Sock),
-    ?SCTP(Sock, {[#sctp_sndrcvinfo{assoc_id = Id}], _Bin})
-        = recv(). %% Waits with this as current_function.
-
-%% recv/0
-
-recv() ->
-    receive T -> T end.
+    recv(Sock, Id).
 
 %% connect1/3
 
@@ -154,7 +148,7 @@ connect1(PortNr, FPid, LPid) ->
     FPid ! {?MODULE,
             self(),
             spawn(fun() -> send(Sock, Id) end)}, %% sending process
-    MRef = erlang:monitor(process, LPid),
+    MRef = monitor(process, LPid),
     down(MRef).  %% Waits with this as current_function.
 
 %% down/1
@@ -277,7 +271,8 @@ acc(N, Acc) ->
 
 loop(Sock, MRef, Bin) ->
     receive
-        ?SCTP(Sock, {[#sctp_sndrcvinfo{assoc_id = Id}], B}) ->
+        ?SCTP(Sock, {[#sctp_sndrcvinfo{assoc_id = Id}], B})
+          when is_binary(B) ->
             Sz = size(Bin),
             {Sz, Bin} = {size(B), B},  %% assert
             ok = send(Sock, Id, mark(Bin)),
@@ -291,7 +286,7 @@ loop(Sock, MRef, Bin) ->
 %% connect2/3
 
 connect2(Pid, PortNr, Bin) ->
-    erlang:monitor(process, Pid),
+    monitor(process, Pid),
 
     {ok, Sock} = open(),
     ok = gen_sctp:connect_init(Sock, ?ADDR, PortNr, []),
@@ -311,9 +306,14 @@ connect2(Pid, PortNr, Bin) ->
 
 recv(Sock, Id) ->
     receive
-        ?SCTP(Sock, {[#sctp_sndrcvinfo{assoc_id = Id}], Bin}) ->
+        ?SCTP(Sock, {[#sctp_sndrcvinfo{assoc_id = I}], Bin})
+          when is_binary(Bin) ->
+            Id = I,   %% assert
             Bin;
-        T ->  %% eg. 'DOWN'
+        ?SCTP(S, _) ->
+            Sock = S, %% assert
+            recv(Sock, Id);
+        T ->
             exit(T)
     end.
 
diff --git a/lib/diameter/test/diameter_gen_tcp_SUITE.erl b/lib/diameter/test/diameter_gen_tcp_SUITE.erl
index 7e232edb44..4b542e0156 100644
--- a/lib/diameter/test/diameter_gen_tcp_SUITE.erl
+++ b/lib/diameter/test/diameter_gen_tcp_SUITE.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %%
-%% Copyright Ericsson AB 2013. All Rights Reserved.
+%% Copyright Ericsson AB 2014-2015. All Rights Reserved.
 %%
 %% The contents of this file are subject to the Erlang Public License,
 %% Version 1.1, (the "License"); you may not use this file except in
@@ -18,10 +18,10 @@
 %%
 
 %%
-%% Some gen_sctp-specific tests demonstrating problems that were
+%% Some gen_tcp-specific tests demonstrating problems that were
 %% encountered during diameter development but have nothing
-%% specifically to do with diameter. At least one of them can cause
-%% diameter_traffic_SUITE testcases to fail.
+%% specifically to do with diameter. These can cause testcases in
+%% other suites to fail.
 %%
 
 -module(diameter_gen_tcp_SUITE).
@@ -30,7 +30,8 @@
          all/0]).
 
 %% testcases
--export([send_long/1]).
+-export([send_long/1,
+         connect/1]).
 
 -define(LOOPBACK, {127,0,0,1}).
 -define(GEN_OPTS, [binary, {active, true}, {ip, ?LOOPBACK}]).
@@ -41,7 +42,8 @@ suite() ->
     [{timetrap, {minutes, 2}}].
 
 all() ->
-    [send_long].
+    [connect,     %% Appears to fail only when run first.
+     send_long].
 
 %% ===========================================================================
 
@@ -87,15 +89,6 @@ connect(PortNr, LPid) ->
     LPid ! {self(), fun(B) -> send(Sock, B) end},
     down(LPid).
 
-%% down/1
-
-down(Pid)
-  when is_pid(Pid) ->
-    down(erlang:monitor(process, Pid));
-
-down(MRef) ->
-    receive {'DOWN', MRef, process, _, Reason} -> Reason end.
-
 %% send/2
 %%
 %% Send from a spawned process just to avoid sending from the
@@ -104,3 +97,47 @@ down(MRef) ->
 send(Sock, Bin) ->
     {_, MRef} = spawn_monitor(fun() -> exit(gen_tcp:send(Sock, Bin)) end),
     down(MRef).
+
+%% ===========================================================================
+
+%% connect/1
+%%
+%% Test that simultaneous connections succeed. This fails sporadically
+%% on OS X at the time of writing, when gen_tcp:connect/2 returns
+%% {error, econnreset}.
+
+connect(_) ->
+    {ok, LSock} = gen_tcp:listen(0, ?GEN_OPTS),
+    {ok, {_,PortNr}} = inet:sockname(LSock),
+    Count = lists:seq(1,8),  %% 8 simultaneous connects
+    As = [gen_accept(LSock) || _ <- Count],
+    %% Wait for spawned processes to have called gen_tcp:accept/1
+    %% (presumably).
+    receive after 2000 -> ok end,
+    Cs = [gen_connect(PortNr) || _ <- Count],
+    [] = failures(Cs),
+    [] = failures(As).
+
+failures(Monitors) ->
+    [RC || {_, MRef} <- Monitors, RC <- [down(MRef)], ok /= element(1, RC)].
+
+gen_accept(LSock) ->
+    spawn_monitor(fun() ->
+                          exit(gen_tcp:accept(LSock))
+                  end).
+
+gen_connect(PortNr) ->
+    spawn_monitor(fun() ->
+                          exit(gen_tcp:connect(?LOOPBACK, PortNr, ?GEN_OPTS))
+                  end).
+
+%% ===========================================================================
+
+%% down/1
+
+down(Pid)
+  when is_pid(Pid) ->
+    down(monitor(process, Pid));
+
+down(MRef) ->
+    receive {'DOWN', MRef, process, _, Reason} -> Reason end.
diff --git a/lib/diameter/test/diameter_pool_SUITE.erl b/lib/diameter/test/diameter_pool_SUITE.erl
new file mode 100644
index 0000000000..a59cd66a2e
--- /dev/null
+++ b/lib/diameter/test/diameter_pool_SUITE.erl
@@ -0,0 +1,133 @@
+%%
+%% %CopyrightBegin%
+%%
+%% Copyright Ericsson AB 2015. All Rights Reserved.
+%%
+%% The contents of this file are subject to the Erlang Public License,
+%% Version 1.1, (the "License"); you may not use this file except in
+%% compliance with the License. You should have received a copy of the
+%% Erlang Public License along with this software. If not, it can be
+%% retrieved online at http://www.erlang.org/.
+%%
+%% Software distributed under the License is distributed on an "AS IS"
+%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
+%% the License for the specific language governing rights and limitations
+%% under the License.
+%%
+%% %CopyrightEnd%
+%%
+
+%%
+%% Test of the pool_size option in connecting nodes with multiple
+%% connections.
+%%
+
+-module(diameter_pool_SUITE).
+
+-export([suite/0,
+         all/0,
+         init_per_testcase/2,
+         end_per_testcase/2,
+         init_per_suite/1,
+         end_per_suite/1]).
+
+%% testcases
+-export([tcp_connect/1,
+         sctp_connect/1,
+         any_connect/1]).
+
+%% ===========================================================================
+
+-define(util, diameter_util).
+
+%% Config for diameter:start_service/2.
+-define(SERVICE(Host),
+        [{'Origin-Host', Host ++ ".ericsson.com"},
+         {'Origin-Realm', "ericsson.com"},
+         {'Host-IP-Address', [{127,0,0,1}]},
+         {'Vendor-Id', 12345},
+         {'Product-Name', "OTP/diameter"},
+         {'Auth-Application-Id', [0]},  %% common
+         {'Acct-Application-Id', [3]},  %% accounting
+         {restrict_connections, false},
+         {application, [{alias, common},
+                        {dictionary, diameter_gen_base_rfc6733},
+                        {module, diameter_callback}]},
+         {application, [{alias, accounting},
+                        {dictionary, diameter_gen_acct_rfc6733},
+                        {module, diameter_callback}]}]).
+
+%% ===========================================================================
+
+suite() ->
+    [{timetrap, {seconds, 30}}].
+
+all() ->
+    [tcp_connect,
+     sctp_connect,
+     any_connect].
+
+init_per_testcase(_Name, Config) ->
+    Config.
+
+end_per_testcase(_Name, _Config) ->
+    diameter:stop().
+
+init_per_suite(Config) ->
+    [{sctp, ?util:have_sctp()} | Config].
+
+end_per_suite(_Config) ->
+    ok.
+
+%% ===========================================================================
+
+tcp_connect(_Config) ->
+    connect(tcp, tcp).
+
+sctp_connect(Config) ->
+    case lists:member({sctp, true}, Config) of
+       true  -> connect(sctp, sctp);
+       false -> {skip, no_sctp}
+    end.
+
+any_connect(_Config) ->
+    connect(any, tcp).
+
+%% connect/2
+
+%% Establish multiple connections between a client and server.
+connect(ClientProt, ServerProt) ->
+    ok = diameter:start(),
+    [] = [{S,T} || S <- ["server", "client"],
+                   T <- [diameter:start_service(S, ?SERVICE(S))],
+                   T /= ok],
+    %% Listen with a single transport with pool_size = 4. Ensure the
+    %% expected number of transport processes are started.
+    LRef = ?util:listen("server", ServerProt, [{pool_size, 4}]),
+    {4,0} = count("server", LRef, accept), %% 4 transports, no connections
+    %% Establish 5 connections.
+    Ref = ?util:connect("client", ClientProt, LRef, [{pool_size, 5}]),
+    {5,5} = count("client", Ref, pool),    %% 5 connections
+    %% Ensure the server has started replacement transports within a
+    %% reasonable time. Sleepsince there's no guarantee the
+    %% replacements have been started before the client has received
+    %% 'up' events. (Although it's likely.)
+    sleep(),
+    {9,5} = count("server", LRef, accept), %% 5 connections + 4 accepting
+    %% Ensure ther are still the expected number of accepting transports
+    %% after stopping the client service.
+    ok = diameter:stop_service("client"),
+    sleep(),
+    {4,0} = count("server", LRef, accept), %% 4 transports, no connections
+    %% Done.
+    ok = diameter:stop_service("server").
+
+count(Name, Ref, Key) ->
+    [{transport, [[{ref, Ref} | T]]},
+     {connections, Cs}]
+        = diameter:service_info(Name, [transport, connections]),
+    {Key, Ps} = lists:keyfind(Key, 1, T),
+    {length(Ps), length(Cs)}.  %% number of processes, connections
+
+sleep() ->
+    receive after 1000 -> ok end.
diff --git a/lib/diameter/test/diameter_transport_SUITE.erl b/lib/diameter/test/diameter_transport_SUITE.erl
index fcffa69c24..84ab6cbdc4 100644
--- a/lib/diameter/test/diameter_transport_SUITE.erl
+++ b/lib/diameter/test/diameter_transport_SUITE.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %%
-%% Copyright Ericsson AB 2010-2013. All Rights Reserved.
+%% Copyright Ericsson AB 2010-2015. All Rights Reserved.
 %%
 %% The contents of this file are subject to the Erlang Public License,
 %% Version 1.1, (the "License"); you may not use this file except in
@@ -104,7 +104,7 @@ tc() ->
      reconnect].
 
 init_per_suite(Config) ->
-    [{sctp, have_sctp()} | Config].
+    [{sctp, ?util:have_sctp()} | Config].
 
 end_per_suite(_Config) ->
     ok.
@@ -127,7 +127,10 @@ tcp_accept(_) ->
     accept(tcp).
 
 sctp_accept(Config) ->
-    if_sctp(fun accept/1, Config).
+    case lists:member({sctp, true}, Config) of
+        true  -> accept(sctp);
+        false -> {skip, no_sctp}
+    end.
 
 %% Start multiple accepting transport processes that are connected to
 %% with an equal number of connecting processes using gen_tcp/sctp
@@ -157,7 +160,10 @@ tcp_connect(_) ->
     connect(tcp).
 
 sctp_connect(Config) ->
-    if_sctp(fun connect/1, Config).
+    case lists:member({sctp, true}, Config) of
+        true  -> connect(sctp);
+        false -> {skip, no_sctp}
+    end.
 
 connect(Prot) ->
     T = {Prot, make_ref()},
@@ -251,28 +257,6 @@ abort(SvcName, LRef, Ref)
 %% ===========================================================================
 %% ===========================================================================
 
-%% have_sctp/0
-
-have_sctp() ->
-    case gen_sctp:open() of
-        {ok, Sock} ->
-            gen_sctp:close(Sock),
-            true;
-        {error, E} when E == eprotonosupport;
-                        E == esocktnosupport -> %% fail on any other reason
-            false
-    end.
-
-%% if_sctp/2
-
-if_sctp(F, Config) ->
-    case proplists:get_value(sctp, Config) of
-        true ->
-            F(sctp);
-        false ->
-            {skip, no_sctp}
-    end.
-
 %% init/2
 
 init(accept, {Prot, Ref}) ->
@@ -381,37 +365,14 @@ start_connect(tcp, T, Svc, Opts) ->
     diameter_tcp:start(T, Svc, Opts).
 
 %% start_accept/2
-%%
-%% Start transports sequentially by having each wait for a message
-%% from a job in a queue before commencing. Only one transport with a
-%% pending accept is started at a time since diameter_{tcp,sctp}
-%% currently assume (and diameter currently implements) this.
 
 start_accept(Prot, Ref) ->
-    Pid = sync(accept, Ref),
     {Mod, Opts} = tmod(Prot),
-
-    try
-        {ok, TPid, [?ADDR]} = Mod:start({accept, Ref},
-                                        ?SVC([?ADDR]),
-                                        [{port, 0} | Opts]),
-        ?RECV(?TMSG({TPid, connected})),
-        TPid
-    after
-        Pid ! Ref
-    end.
-
-sync(What, Ref) ->
-    ok = diameter_sync:cast({?MODULE, What, Ref},
-                            [fun lock/2, Ref, self()],
-                            infinity,
-                            infinity),
-    receive {start, Ref, Pid} -> Pid end.
-
-lock(Ref, Pid) ->
-    Pid ! {start, Ref, self()},
-    erlang:monitor(process, Pid),
-    Ref = receive T -> T end.
+    {ok, TPid, [?ADDR]} = Mod:start({accept, Ref},
+                                    ?SVC([?ADDR]),
+                                    [{port, 0} | Opts]),
+    ?RECV(?TMSG({TPid, connected})),
+    TPid.
 
 tmod(sctp) ->
     {diameter_sctp, [{sctp_initmsg, ?SCTP_INIT}]};
@@ -463,7 +424,11 @@ gen_send(tcp, Sock, Bin) ->
 
 gen_recv(sctp, Sock) ->
     {_OS, _IS, Id} = getr(assoc),
-    ?RECV(?SCTP(Sock, {[#sctp_sndrcvinfo{assoc_id = Id}], Bin}), Bin);
+    receive
+        ?SCTP(Sock, {[#sctp_sndrcvinfo{assoc_id = Id}], Bin})
+          when is_binary(Bin) ->
+            Bin
+    end;
 gen_recv(tcp, Sock) ->
     tcp_recv(Sock, <<>>).
 
diff --git a/lib/diameter/test/diameter_util.erl b/lib/diameter/test/diameter_util.erl
index 92c72c84e7..e95cbfceb5 100644
--- a/lib/diameter/test/diameter_util.erl
+++ b/lib/diameter/test/diameter_util.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %%
-%% Copyright Ericsson AB 2010-2013. All Rights Reserved.
+%% Copyright Ericsson AB 2010-2015. All Rights Reserved.
 %%
 %% The contents of this file are subject to the Erlang Public License,
 %% Version 1.1, (the "License"); you may not use this file except in
@@ -29,7 +29,8 @@
          run/1,
          fold/3,
          foldl/3,
-         scramble/1]).
+         scramble/1,
+         have_sctp/0]).
 
 %% diameter-specific
 -export([lport/2,
@@ -184,6 +185,19 @@ s(Acc, L) ->
     s([T|Acc], H ++ Rest).
 
 %% ---------------------------------------------------------------------------
+%% have_sctp/0
+
+have_sctp() ->
+    case gen_sctp:open() of
+        {ok, Sock} ->
+            gen_sctp:close(Sock),
+            true;
+        {error, E} when E == eprotonosupport;
+                        E == esocktnosupport -> %% fail on any other reason
+            false
+    end.
+
+%% ---------------------------------------------------------------------------
 %% eval/1
 %%
 %% Evaluate a function in one of a number of forms.
@@ -254,13 +268,12 @@ path(Config, Name) ->
 %%
 %% Lookup the port number of a tcp/sctp listening transport.
 
-lport(M, {Node, Ref}) ->
-    rpc:call(Node, ?MODULE, lport, [M, Ref]);
+lport(Prot, {Node, Ref}) ->
+    rpc:call(Node, ?MODULE, lport, [Prot, Ref]);
 
 lport(Prot, Ref) ->
-    Mod = tmod(Prot),
     [_] = diameter_reg:wait({'_', listener, {Ref, '_'}}),
-    [N || {listen, N, _} <- Mod:ports(Ref)].
+    [N || M <- tmod(Prot), {listen, N, _} <- M:ports(Ref)].
 
 %% ---------------------------------------------------------------------------
 %% listen/2-3
@@ -292,13 +305,17 @@ connect(Client, Prot, LRef, Opts) ->
     Ref = add_transport(Client, {connect, opts(Prot, PortNr) ++ Opts}),
     true = transport(Client, Ref),                 %% assert
 
-    ok = receive
-             {diameter_event, Client, {up, Ref, _, _, _}} -> ok
-         after 10000 ->
-                 {Client, Prot, PortNr, process_info(self(), messages)}
-         end,
+    diameter_lib:for_n(fun(_) -> ok = up(Client, Ref, Prot, PortNr) end,
+                       proplists:get_value(pool_size, Opts, 1)),
     Ref.
 
+up(Client, Ref, Prot, PortNr) ->
+    receive
+        {diameter_event, Client, {up, Ref, _, _, _}} -> ok
+    after 10000 ->
+            {Client, Prot, PortNr, process_info(self(), messages)}
+    end.
+
 transport(SvcName, Ref) ->
     [Ref] == [R || [{ref, R} | _] <- diameter:service_info(SvcName, transport),
                    R == Ref].
@@ -327,13 +344,15 @@ add_transport(SvcName, T) ->
     Ref.
 
 tmod(tcp) ->
-    diameter_tcp;
+    [diameter_tcp];
 tmod(sctp) ->
-    diameter_sctp.
+    [diameter_sctp];
+tmod(any) ->
+    [diameter_sctp, diameter_tcp].
 
 opts(Prot, T) ->
-    [{transport_module, tmod(Prot)},
-     {transport_config, [{ip, ?ADDR}, {port, 0} | opts(T)]}].
+    [{transport_module, M} || M <- tmod(Prot)]
+        ++ [{transport_config, [{ip, ?ADDR}, {port, 0} | opts(T)]}].
 
 opts(listen) ->
     [{accept, M} || M <- [{256,0,0,1}, ["256.0.0.1", ["^.+$"]]]];
diff --git a/lib/diameter/test/modules.mk b/lib/diameter/test/modules.mk
index 4fea62461c..6da96bd676 100644
--- a/lib/diameter/test/modules.mk
+++ b/lib/diameter/test/modules.mk
@@ -1,8 +1,7 @@
-#-*-makefile-*-   ; force emacs to enter makefile-mode
 
 # %CopyrightBegin%
 #
-# Copyright Ericsson AB 2010-2013. All Rights Reserved.
+# Copyright Ericsson AB 2010-2015. All Rights Reserved.
 #
 # The contents of this file are subject to the Erlang Public License,
 # Version 1.1, (the "License"); you may not use this file except in
@@ -40,6 +39,7 @@ MODULES = \
 	diameter_gen_sctp_SUITE \
 	diameter_gen_tcp_SUITE \
 	diameter_length_SUITE \
+	diameter_pool_SUITE \
 	diameter_reg_SUITE \
 	diameter_relay_SUITE \
 	diameter_stats_SUITE \