1. Feature Guide
  2. DSR Features and Functions
  3. Diameter Core Routing

2.5 Diameter Core Routing

The DSR application provides a Diameter Routing Agent to forward messages to the appropriate destination based on information contained within the message including header information and applicable Attribute Value Pairs (AVP). As per the core Diameter specification, the DSR provides the capability to route Diameter messages based on any combination, or presence/absence, of Destination-Host, Destination-Realm, and Application-ID. In addition DSR optionally provides the capability to look at Command-Code and origination information, namely Origin-Realm and Origin-Host for advanced routing functionality. The average diameter message size supported is 2K bytes with a maximum message size of 60K bytes.

DSR high level message processing and routing is shown below. The numbers show the message flow through the system.

Figure 2-6 High Level Message Processing and Routing in DSR


High Level Message Processing and Routing in DSR

DSR supports the following routing functions:

  • Message routing to Diameter peers based upon user-defined message content rules.
  • Message routing to Diameter peers based upon user-defined priorities and weights.
  • Message routing to Diameter peers with multiple transport connections.
  • Alternate routing on connection failures.
  • Alternate routing on Answer timeouts.
  • Alternate routing on user-defined Answer responses.
  • Route management based on peer transport connection status changes.
  • Route management based on OAM configuration changes.

Routing rules and rule actions are used to implement the routing behavior required by the operator. Routing rules are defined using combinations of the following data elements:

  • Destination-Realm (leading, trailing characters, exact match, contains, not equal or always true).
  • Destination-Host (leading, trailing characters, exact match, contains, always true, present and not equal, or presence/absence).
  • Application-ID (exact match, not equal, or always true).
  • Command-Code (exact match, not equal or always true).
  • Origin-Realm (leading, trailing characters, exact match, contains, not equal or always true.
  • Origin-Host (leading, trailing characters, exact match, contains, not equal or always true).

A set of configurable timers (100 – 180,000 milliseconds) control the length of time the DSR waits to receive an answer to an outstanding request. The maximum number of times a request can be rerouted upon connection failure or timeout is configurable from 0 – 4 retries.

DSR supports the concepts of routes, peer route tables, peer route groups, connection route groups, route lists, and peer node groups to provide a very powerful and flexible load balancing solution. A Route Group is comprised of a prioritized list of peers or connections used for routing messages. A route list is comprised of multiple route groups – only one of which is designated as active at any one time. Each route list supports the following configurable information:

  • Route List ID.
  • Up to five Route Groups with associated Route Group Priority level (1-5).
  • Minimum Route Group Availability Weight to control which Route Group in the Route List is actively used for routing requests.
  • 0-10 optional Traffic Throttle Groups with associated Max Loss % Threshold for use with IETF Diameter Overload Indicator Conveyance (DOIC) feature.

Each Route Group supports the following configurable information:

  • Route Group ID.
  • Up to 160 Peer IDs -OR- 512 Connection IDs.
  • Weight (1-64K) for each Peer ID or Connection ID.

When peers or connections have the same priority level a weight is assigned to each peer/connection which defines the weighted distribution of messages amongst the peers/connections. For example, if two peers with equal priority have weights 100 and 150 respectively then 40% of the messages will be forward to peer-1 (100/(100+150)) and 60% of the messages will be forward to peer-2 (150/(100+150)).

Peer Route Tables can be assigned to Peer Nodes or Application IDs. Each Peer Route Table has its own set of Peer Route Rules.

A set of peers with equal priority within a Route List is called a “Peer Route Group”. Multiple connections to the same peer can be assigned to a Connection Route Group (CRG). The use of CRGs allows for prioritized routing between connections to the same peer. An example use case would be connecting to Peers across different sites which share the same hostname. The peer within the site would be contacted for any traffic originated within the site and the remote peer should be contacted only if the local peer is unavailable.

Figure 2-7 Connection Route Group


Connection Route Group

When multiple Route Groups are assigned to a Route List, only one of the Route Groups is designated as the "Active Route Group" for routing messages for that Route List. The remaining Route Groups within the Route List are referred to as "Standby Route Groups". DSR designates the "Active Route Group" within each Route List based on the Route Group's priority and available capacity relative to the provisioned minimum capacity (described below) of the Route List. When the "Operational Status" of peers change or the configuration of either the Route List or Route Groups within the Route List change, then DSR may need to change the designated "Active Route Group" for the Route List. An example of Route List and Route Group relationships is shown below.

Figure 2-8 Route List, Route Group, Peer Relationship Example


Route List, Route Group, Peer Relationship Example

Showing a different set of route lists and route groups, an example of peer routing based on route groups with a route list is shown in the figure below.

Figure 2-9 Load Balancing Based on Route Groups and Peer Weights


Load Balancing Based on Route Groups and Peer Weights

DSR supports provisioning up to 160 routes in a route group (same priority) and allows for provisioning of 3 route groups per route list.

To further enhance the load balancing scheme, the DSR allows the operator to provision a “minimum route list capacity” threshold for each route list. This provisioned “minimum route list capacity” is compared against the route group capacity. The route group capacity is dynamically computed based on the availability status of each route within the route group and is the sum of all the weights of “available” routes in a route group. If the route group capacity is higher than the threshold, the route group is considered “available” for routing messages. If the route group capacity is lower (due to one of more failures on certain routes in the route group), the route group is not considered “available” for routing messages. DSR uses the highest priority (lowest value) “available” route group within a route list when routing messages over the route list. If none of the route groups in the route list are “available”, DSR will use the route group with the most “available” capacity, also honoring route group priority, when routing messages over the route list.

A peer node group is a configuration managed object that provides a container for a collection of DSR peer nodes with like attributes (Example: same network element or same capacity requirement). The user configures DSR peer nodes with their IP addresses in the peer node group container. Applications can use this IP address grouping for various functions such as IPFE for a distribution algorithm.