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modules-new-design:lcr-module-design [2010/05/31 18:54] – 87.93.31.28modules-new-design:lcr-module-design [2010/06/09 08:41] (current) – 87.95.129.219
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 +====== New LCR Module Design (proposal) ======
  
 +A new design for Kamailio's LCR module making it simpler, more powerful, and easier to manage via an admin interface.
 +===== Introduction =====
 +
 +Current LCR module lacks some useful features and it's hard to manage via an admin interface due to the complexity and not good relationship between its DB tables.
 +
 +Some of the current design issues are:
 +  * LCR rule definitions are mixed with rule steps/targets in same 'lcr' table.
 +  * In order to reuse some gateway in two different groups it's required to duplicate all the information for the given gateway (ip, port, flags, ping...).
 +  * Summarizing, making an admin interface for LCR tables is difficult as the current design doesn't follow a good pattern.
 +
 +Some desired features would be:
 +  * There si no way to make a rule stop if it fails to handle the request and we don't want other matching rules to be loaded (i.e: "I want calls to 001 just to use gw3 and not to use default gateways, those belonging to rule with NULL prefix, if gw3 is down).
 +  * Rules should be disabled without having to delete them.
 +
 +In order to simplify implementation and use, gateway groups are no longer supported.  Instead, gateways are directly specified as rule targets, where each rule target has a priority and weight.
 +
 +
 +===== New DB schema =====
 +==== lcr_rule ====
 +
 +^ Column           ^ Description                                   ^ Possible values   ^ Default value ^
 +| id               | Primary key: identifier of this rule        | Integer | |
 +| lcr_id           | Identifier of LCR instance                  | Integer | |
 +| prefix           | Prefix of Request URI user part             | NULL / String | NULL |
 +| from_uri         | Regular expression to match the From URI (or given pseudo-variable) | NULL / String (regular expression) | NULL |
 +| stopper          | If it's 1 no other rules would be inspected after finding this one | Integer (1=on / 0=off) | 0 |
 +| enabled          | Is it this rule active so it can be loaded?   | Integer (1=on / 0=off) | 1 |
 +
 +Keys:
 +  * PRIMARY KEY: //id//
 +  * UNIQUE: //lcr_id// + //prefix// + //from_uri//
 +==== lcr_rule_target table ====
 +
 +^ Column           ^ Description                                   ^ Possible values   ^ Default value ^
 +| id               | Primary key                                 | Integer | |
 +| rule_id          | Integer pointing to the //id// of an entry in //lcr_rule// table | Integer | |
 +| gw_id            | Gateway for this rule target (points to //id// in //lcr_gw// table) | Integer | |
 +| priority         | Priority of this rule target within all targets for the same rule | Integer (0-255) | |
 +| weight           | Weight of this rule target within all equal priority targets for the same rule | Integer (1-254) | |
 +
 +Keys:
 +  * PRIMARY KEY: //id//
 +  * UNIQUE: //rule_id// + //gw_id//
 +  * INDEX: //rule_id//
 +==== lcr_gw table ====
 +
 +^ Column           ^ Description                                   ^ Possible values   ^ Default value ^
 +| id               | Primary key, identifier of the gateway        | Integer | |
 +| lcr_id           | Identifier of LCR instance                    | Integer | |
 +| gw_name          | Name of the gateway (only for documentation)  | String | NULL |
 +| ip_addr          | IP of the gateway                             | NULL / String | NULL |
 +| port             | Port of the gateway                           | NULL (no port is added) / Integer (5060=sip / 5061=sips) | NULL |
 +| uri_scheme       | Scheme of the Request URI                     | NULL / Integer (NULL and 1 = sip / 2=sips) | NULL |
 +| transport        | Transport used for this gateway               | NULL (no transport is added) / Integer (0=udp / 1=tcp / 2=tls / 3=sctp) | NULL |
 +| params           | URI params to be added to Request URI         | NULL / String | NULL |
 +| hostname         | Hostname to set in Request URI host part      | NULL / String | NULL |
 +| strip            | Number of characters to be stripped from the front of Request URI user | NULL / Integer | NULL |
 +| tag              | Prefix to be added to Request URI user part after removing //strip// characters | NULL / String | NULL |
 +| flags            | Flags enabled when loading this gateway       | Integer | 0 |
 +| defunct          | Gateway is defunct until this Linux timestamp time            | NULL (= 0) / Integer | NULL |
 +
 +Keys:
 +  * PRIMARY KEY: //id//
 +  * UNIQUE: //lcr_id// + //ip_addr// + //port// + //transport// + //hostname//
 +
 +
 +===== New module parameters, functions and flags =====
 +==== flag(DONT_STRIP_OR_TAG) ====
 +
 +When calling //next_gw()// function the value of //flag(DONT_STRIP_OR_TAG)// is inspected. If it is set then //strip// and //tag// values of the selected gateway are ignored so the Request URI user part is not modified.
 +
 +This is an optional module parameter. If it's not defined then //strip// and //tag// are always applied for each gateway.
 +
 +An use case in which this flag is useful:
 +
 +  * The PSTN gateway allows national format (NNNNNNNNN) and international format with "00" (00NNNNNNNNNNNN).
 +  * Kamailio is configured to normalize destination numbers to E.164 (+NNNNNNNNN) if the call is international, or leave it in national format (no E.164).
 +  * In this case it's required to replace "+" with "00" when such gateway is selected by LCR module.
 +  * But it's also required not to modify the RURI user part if the number format is national.
 +
 +The following configuration would do the job:
 +
 +  * //lcr_gw// entry for the PSTN gateway:
 +    * **strip:** 1
 +    * **tag:** 00
 +
 +  * Script configuration:<code bash>
 +# This route ensures that the dialed number is in the form +XXXXXX
 +# (international E164) or national (XXXXXXX without + or 00):
 +route(NORMALIZE_NUMBER);
 +
 +# Load gateways as usual.
 +load_gws(...);
 +
 +# If the dialed number is national then enable the flag(DONT_USE_STRIP_TAG)
 +# to avoid the RURI user part being striped and tagged with gw values.
 +if !(starts_with("$rU", "+"))
 +  setflag(DONT_STRIP_OR_TAG);
 +  
 +next_gw();
 +</code>

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