1. User's Guide
  2. SIP HMR (Header Manipulation Rules)

21 SIP HMR (Header Manipulation Rules)

SIP header manipulation can also be configured in a way that makes it possible to manipulate the headers in SIP messages both statically and dynamically. Using this feature, you can edit response headers or the Request-URI in a request, and change the status code or reason phrase in SIP responses.

Static SIP Header and Parameter Manipulation allows you to set up rules in your Oracle Enterprise Communications Broker configuration that remove and/or replace designated portions of specified SIP headers. SIP HMR allows you to set up dynamic header manipulation rules, meaning that the Oracle Enterprise Communications Broker has complete control over alterations to the header value. More specifically:

  • The Oracle Enterprise Communications Broker can search header for dynamic content or patterns with the header value. It can search, for example, for all User parts of a URI that begin with 617 and end with 5555 (e.g., 617...5555).
  • The Oracle Enterprise Communications Broker can manipulate any part of a patterns match with any part of a SIP header. For example, 617 123 5555 can become 617 231 5555 or 508 123 0000, or any combination of those.

To provide dynamic header manipulation, the Oracle Enterprise Communications Broker uses regular expressions to provide a high degree of flexibility for this feature. This allows you to search a specific URI when you do not know that value of the parameter, but want to use the matched parameter value as the header value. It also allows you to preserve matched sections of a pattern, and change what you want to change.

You can apply header manipulation to session agents, SIP interfaces, and realms. You do so by first setting up header manipulations rules, and then applying them in the configurations where they are needed. Within the header manipulation rules, there are sets of element rules that designate the actions that need to be performed on a given header.

Each header rule and each element rule (HMR) have a set of parameters that you configure to identify the header parts to be manipulated, and in what way the Oracle Enterprise Communications Broker is to manipulate them. These parameters are explained in detail, but the parameter that can take regular expression values is match-value. This is where you set groupings that you want to store, match against, and manipulate.

Generally, you set a header rule that will store what you want to match, and then you create subsequent rules that operate on this stored value. Because header rules and element rules are applied sequentially, it is key to note that a given rule performs its operations on the results of all the rules that you have entered before it. For example, if you want to delete a portion of a SIP header, you would create Rule 1 that stores the value for the purpose of matching, and then create Rule 2 that would delete the portion of the header you want removed. This prevents removing data that might be used in the other header rules.

Given that you are using regular expression in this type of configuration, this tightly sequential application of rules means that you must be aware of the results to be yielded from the application of the regular expressions you enter. When you set a regular expression match value for the first rule that you enter, the Oracle Enterprise Communications Broker takes the results of that match, and then a second rule might exist that tells the Oracle Enterprise Communications Broker to use a new value if it the second rule’s match value finds a hit (and only 10 matches, 0-9, are permitted) for the results (yield) from applying the first rule.

Consider the example of the following regular expression entry made for a match-value parameter:‘Trunk(.+)’, which might be set as that match value in the first rule you configure. Given a SIP element rule called uri-param and the param-name tgid, it can yield two values:

  • Grouping 0—The entire matching string (Trunk1)
  • Grouping 1—The grouping (1)

In turn, these groupings can be referenced in an element rule by using this syntax: 

$<header rule name >.$<element rule name.$<value>

Additional syntax options that can be used with this feature are:

  • $headerName[‘[‘index’]’]
  • $headerName[‘[‘index’]’][.$index]
  • $headerName[‘[‘index’]’][.$elementName]
  • $headerName[‘[‘index’]’][.$elementName][.$index]