OSP Module for Secure, Multi-Lateral Peering

  Ulrich Abend

   FhG Fokus

    Edited by

  Di-Shi Sun

   Copyright (c) 2003 FhG Fokus


   Table of Contents

   [1]User's Guide



                [4]Exported Parameters

                             [5]sp1_uri, sp2_uri



                             [8]private_key, local_certificate,

                             [9]sp1_weight, sp2_weight










                [19]Exported Functions








   [27]Developer's Guide

   [28]Frequently Asked Questions


                                  User's Guide


   The OSP module enables SER to support secure, multi-lateral peering using
   the OSP standard defined by ETSI (TS 101 321 V4.1.1). This module will
   enable your SER to:

     * Send a peering authorization request to a peering server.

     * Validate a digitally signed peering authorization token received in a
       SIP INVITE message.

     * Report usage information to a peering server.



   The OSP module depends on the following modules which must be loaded
   before the OSP module.

     * textops -- text based operation

     * OSP Toolkit -- The OSP Toolkit, available from www.sipfoundry.org/OSP,
       must be built before building SER with the OSP Module. See the
       document "Multi-lateral Peering with SER", located at
       http://developer.berlios.de/docman/?group_id=3799 for build


Exported Parameters

  sp1_uri, sp2_uri

   These string parameters define peering servers to be used for requesting
   peering authorization and routing information. sp1_uri must be configured.
   sp2_uri is required only if there are two peering servers. Each peering
   server address takes the form of a standard URL, and consists of up to
   four components:

     * An optional indication of the protocol to be used for communicating
       with the peering server. Both HTTP and HTTP secured with SSL/TLS are
       supported and are indicated by "http://" and "https://" respectively.
       If the protocol is not explicitly indicated, the SER defaults to HTTP
       secured with SSL.

     * The Internet domain name for the peering server. An IP address may
       also be used, provided it is enclosed in square brackets such as

     * An optional TCP port number for communicating with the peering server.
       If the port number is omitted, the SER defaults to port 1080 (for
       HTTP) or port 1443 (for HTTP secured with SSL).

       The uniform resource identifier for requests to the peering server.
       This component is not optional and must be included.

   Example 1. Setting the OSP servers

   modparam ("osp", "sp1_uri", "http://osptestserver.transnexus.com:1080/osp") 
   modparam ("osp", "sp2_uri", "https://[]:1443/osp")                   



   device_ip (string) is a recommended parameter that explicitly defines the
   IP address of SER in an peering request message (as SourceAlternate
   type=transport). The IP address must be in brackets as shown in the
   example below.

   Example 2. Setting the device IP address

   modparam ("osp", "device_ip", "[]")                                 



   When SER receives a SIP INVITE with a peering token, the OSP Module will
   validate the token to determine whether or not the call has been
   authorized by a peering server. Peering tokens may, or may not, be
   digitally signed. The token format (integer) parameter defines if SER will
   validate signed or unsigned tokens or both. The values for token format
   are defined below. The default value is 2.

   0 - Validate only signed tokens. Calls with valid signed tokens are

   1 - Validate only unsigned tokens. Calls with valid unsigned tokens are

   2 - Validate both signed and unsigned tokens are allowed. Calls with valid
   tokens are allowed.

   Example 3. Setting the token format

   modparam ("osp", "token_format", 2)                                        


  private_key, local_certificate, ca_certificates

   These parameters identify files are used for validating peering
   authorization tokens and establishing a secure channel between SER and a
   peering server using SSL. The files are generated using the 'Enroll'
   utility from the OSP Toolkit. By default, the proxy will look for
   pkey.pem, localcert.pem, and cacart_0.pem in the default configuration
   directory. The default config directory is set at compile time using
   CFG_DIR and defaults to /usr/local/etc/ser/. The files may be copied to
   the expected file location or the parameters below may be changed.

   Example 4. Set authorization files

   If the default CFG_DIR value was used at compile time, the files will be
   loaded from:

   modparam ("osp", "private_key", "/usr/local/etc/ser/pkey.pem")             
   modparam ("osp", "local_certificate", "/usr/local/etc/ser/localcert.pem")  
   modparam ("osp", "ca_certificates", "/usr/local/etc/ser/cacert.pem")       


  sp1_weight, sp2_weight

   These sp_weight (integer) parameters are used for load balancing peering
   requests to peering servers. These parameters are most effective when
   configured as factors of 1000. For example, if sp1_uri should manage twice
   the traffic load of sp2_uri, then set sp1_weight to 2000 and sp2_weight to
   1000. Shared load balancing between peering servers is recommended.
   However, peering servers can be configured as primary and backup by
   assigning a sp_weight of 0 to the primary server and a non-zero sp_weight
   to the back-up server. The default values for sp1_weight and sp2_weight
   are 1000.

   Example 5. Setting the OSP server weights

   modparam ("osp", "sp1_weight", 1000)                                       



   The device_port (string) parameter is an optional field which includes the
   SIP port being used by SER in the peering request (as SourceAlternate
   type=network) to the peering server. If is not configured, this
   information is not included in the peering request. This field is useful
   if multiple SERs are running on the same Linux computer since it enables
   the peering server to administer different peering policies based on
   different SIP proxies.

   Example 6. Setting the device port

   modparam ("osp", "device_port", "5060")                                    



   The enable_crypto_hardware_support (integer) parameter is used to set the
   cryptographic hardware acceleration engine in the openssl library. The
   default value is 0 (no crypto hardware is present). If crypto hardware is
   used, the value should be set to 1.

   Example 7. Setting the hardware support

   modparam ("osp", "enable_crypto_hardware_support", 0)                      



   The ssl_lifetime (integer) parameter defines the lifetime, in seconds, of
   a single SSL session key. Once this time limit is exceeded, the OSP Module
   will negotiate a new session key. Communication exchanges in progress will
   not be interrupted when this time limit expires. This is an optional field
   with default value is 200 seconds.

   Example 8. Setting the ssl lifetime

   modparam ("osp", "ssl_lifetime", 200)                                      



   The persistence (integer) parameter defines the time, in seconds, that an
   HTTP connection should be maintained after the completion of a
   communication exchange. The OSP Module will maintain the connection for
   this time period in anticipation of future communication exchanges to the
   same peering server.

   Example 9. Setting the persistence

   modparam ("osp", "persistence", 1000)                                      



   The retry_delay (integer) parameter defines the time, in seconds, between
   retrying connection attempts to an OSP peering server. After exhausting
   all peering servers the OSP Module will delay for this amount of time
   before resuming connection attempts. This is an optional field with
   default value is 1 second.

   Example 10. Setting the retry delay

   modparam ("osp", "retry_delay", 1)                                         



   The retry_limit (integer) parameter defines the maximum number of retries
   for connection attempts to an peering server. If no connection is
   established after this many retry attempts to all peering servers, the OSP
   Module will cease connection attempts and return appropriate error codes.
   This number does not count the initial connection attempt, so that a
   retry_limit of 1 will result in a total of two connection attempts to
   every peering server. The default value is 2.

   Example 11. Setting the retry limit

   modparam ("osp", "retry_limit", 2)                                         



   The timeout (integer) parameter defines the maximum time in milliseconds,
   to wait for a response from an peering server. If no response is received
   within this time, the current connection is aborted and the OSP Module
   attempts to contact the next peering server. The default value is 10

   Example 12. Setting the timeout

   modparam ("osp", "timeout", 10)                                            



   The max_destinations (integer) parameter defines the maximum number of
   destinations that SER requests the peering server to return in a peering
   response. The default value is 5.

   Example 13. Setting the number of destination

   modparam ("osp", "max_destinations", 5)                                    



   The validate_call_id (integer) parameter instructs the OSP module to
   validate call id in the peering token. If this value is set to 1, the OSP
   Module validates that the call id in the SIP INVITE message matches the
   call id in the peering token. If they do not match the INVITE is rejected.
   If this value is set to 0, the OSP Module will not validate the call id in
   the peering token. The default value is 1

   Example 14. Instructing the module to validate call id

   modparam ("osp", "validate_call_id", 1)                                    


Exported Functions


   This function checks for the existence of the OSP-Auth-Token header field.

   Example 15. checkospheader usage

   if (checkospheader()) {                                                    
     log("OSP header field found.\n");                                        
   } else {                                                                   
     log("no OSP header field present\n");                                    



   This function validates an OSP-Token specified in the OSP-Auth-Tokenheader
   field of the SIP message. If a peering token is present, it will be
   validated locally. If no OSP header is found or the header token is
   invalid or expired, -1 is returned; on successful validation 1 is

   Example 16. validateospheader usage

   if (validateospheader()) {                                                 
     log("valid OSP header found\n");                                         
   } else {                                                                   
     log("OSP header not found, invalid or expired\n");                       



   This function launches a query to the peering server requesting the IP
   address of one or more destination peers serving the called party. If
   destination peers are available, the peering server will return the IP
   address and a peering authorization token for each destination peer. The
   OSP-Auth-Token Header field is inserted into the SIP message and the SIP
   uri is rewritten to the IP address of destination peer provided by the
   peering server.

   The address of the called party must be a valid E164 number, otherwise
   this function returns -1. If the transaction was accepted by the peering
   server, the uri is being rewritten and 1 returned, on errors (peering
   servers are not available, authentication failed or there is no route to
   destination or the route is blocked) -1 is returned.

   Example 17. requestosprouting usage

   if (requestosprouting()) {                                                 
     log("successfully queried OSP server, now relaying call\n");             
   } else {                                                                   
     log("Authorization request was rejected from OSP server\n");             



   This function tries to prepare the INVITE to be forwarded or redirected
   using the first destination in the list returned by the peering server. If
   the route could not be prepared, the function returns 'FALSE' back to the
   script, which can then decide how to handle the failure.

   Example 18. preparefirstosproute usage

   if (preparefirstosproute ()) {                                             
     log("successfully prepared the first route, now relaying call\n");       
   } else {                                                                   
     log("could not prepare the route. The first destination was blocked\n"); 



   Once the call could not be completed through the first destination, this
   function tries to prepare the INVITE message using the next destination in
   the list returned by the peering Server. If it succeeds in preparing the
   route, the message is either redirected or relayed on (using the t_relay
   call), or else the function returns 'FALSE' back to the script, which can
   then decide how to handle the failure.

   Example 19. preparenextosproute usage

   if (preparenextosproute ()) {                                              
     log("successfully prepared the next route, now relaying call\n");        
   } else {                                                                   
     log("could not prepare the route. No next destination available\n");     



   This function tries to prepare all the routes in the list returned by the
   peering server. The message is then either forked off or redirected to the
   destination. If unsuccessful in preparing the routes a SIP 500 is sent
   back and a trace message is logged.

   Example 20. prepareallosproute usage

if (prepareallosproute ()) {                                                             
  log("successfully prepared the routes, now either forking or redirecting the call\n"); 
} else {                                                                                 
  log("could not prepare the route. No destination available\n");                        



   This function should be called after receiving a BYE message. If the
   message contains an OSP cookie, the function will forward originating
   and/or terminating duration usage information to a peering server. The
   function returns TRUE if the BYE includes an OSP cookie. The actual usage
   message will be send on a different thread and will not delay BYE
   processing. The function should be called before relaying the message.

   Example 21. reportospusage usage

if (reportospusage ()) {                                                                             
  log("OSP call duration usage will be reported\n");                                                 
} else {                                                                                             
  log("The BYE message does not include OSP information, it was not authorized by an OSP server\n"); 


                               Developer's Guide

   The functions of the OSP modules are not used by other SER modules.


                           Frequently Asked Questions

   Q: [29]What platforms does this module work on?

   Q: [30]Where can I get more information on this module?

   Q: [31]Where can I get more information on OSP?

   Q: [32]How do I obtain an OSP server for testing?

   Q: [33]How are the exported functions used by the OSP module?

   Q: What platforms does this module work on?

   A: The module has been implemented using Linux, the underlying toolkit and
   the module code itself should compile and work on Solaris, *BSD, and
   probably most other unix platforms with ssl and pthreads available, but
   the OSP Module has only been tested Linux.

   Q: Where can I get more information on this module?

   A: Please see the document "Multi-Lateral Peering with SER" located at
   http://developer.berlios.de/docman/?group_id=3799 or post a message on the
   SER mailing list. You may also send an e-mail to support@transnexus.com.

   Q: Where can I get more information on OSP?

   A: The OSP technical specification (ETSI TS 101 321) may be obtained from
   www.etsi.org. Additional documentation on OSP is available from

   Q: How do I obtain an OSP server for testing?

   A: OSP peering servers are available from the following sources:

     * OpenOSP server from www.sipfoundry.org is a complete OSP server

     * RAMS from www.sipfoundry.org is a new java based open source OSP

     * TransNexus provides free access to a hosted OSP peering server on the
       Internet for testing. Contact support@transnexus.com.

   Q: How are the exported functions used by the OSP module?

   A: See sample-osp-ser.cfg in modules/osp/etc for examples