Mixed Networks Using the ANSI/ITUMTP Gateway Feature

The optional ANSI/ITUMTP Gateway feature, now also available for IP networks, and the addition of the iplimi and ipgwi applications enables the EAGLE to act as an interface between nodes that support ANSI, ITU-I, and ITU-N protocols. For more information on the ANSI/ITUMTP Gateway feature, contact your Oracle Sales Representative.

Figure 2-11 shows an example of a complex network that includes all these types of nodes. Table 2-8 provides more detail about the nodes, network types, and point codes used in this example.

The following SS7 protocol constraints determine how the network must be configured:

• A linkset is a group of links that terminate into the same adjacent point code. All links in the linkset can transport compatible MSU formats. The network type of the linkset is the same as the network type of the adjacent point code assigned to the linkset.
• When nodes in different networks need to communicate, each node must have either a true point code or an alias point code for each of the network types. For example, if Node 1 (in an ANSI network) needs to communicate to Node 7 (in an ITU-N network), Node 1 must have an ANSI true point code and an ITU-N alias point code, while Node 7 must have an ITU-N true point code and an ANSI alias point code.
• The systems are usually deployed as mated pairs. The links connecting the EAGLE to its mate are C links. Each EAGLE must have a C linkset for each network type that the EAGLE connects to. Therefore, in Figure 2-11, Nodes 5 and 6 are connected with three linksets, one each for ANSI traffic, ITU-I traffic, and ITU-N traffic.
• To perform routing, the EAGLE must convert the routing labels in MSUs. To perform this conversion, every destination point code (DPC), originating point code (OPC), and concerned point code must be defined in the Routing table. Even if the EAGLE does not route MSUs to these nodes, they must be provisioned in the Routing table to provision the alias point codes required in the conversion process.

  Figure 2-11 Complex Network with ANSI, ITU-I, and ITU-N Nodes

  

  Table 2-8 Nodes and Point Codes in Complex Network Example

  Node	Node Type	Network Types Supported	True Point Codes1	Alias Point Codes2
  1	SSP	ANSI	A1	N1, I1
  2	SSP	ANSI	A2	I2
  3	SSP	ANSI	A3	N3, I3
  4	SSP	ANSI	A4	N4
  5	STP (with IP7 Secure Gateway functionality)	ANSI, ITU-N, ITU-I	A5, N5, I5
  6	STP (with IP7 Secure Gateway functionality)	ANSI, ITU-N, ITU-I	A6, N6, I6
  7	STP (with IP7 Secure Gateway functionality)	ITU-N, ITU-I	N7, I7	A7
  8	STP (with IP7 Secure Gateway functionality)	ITU-N, ITU-I	N8, I8	A8
  9	STP (with IP7 Secure Gateway functionality)	ITU-N, ITU-I	N9, I9	A9
  10	STP (with IP7 Secure Gateway functionality)	ITU-N, ITU-I	N10, I10	A10
  11	SSP	ITU-N	N11	I11, A11
  12	SSP	ITU-I	I12	N12, A12
  13	SSP	ITU-I	I13	N13, A13
  14	SSP	ITU-N	N14	I14, A14
  15	SSP	ITU-I	I15	N15, A15
  16	SSP	ITU-I	I16	N16, A16
  Notes: 1. A true point code (TPC) defines a destination in the EAGLE’s destination point code table.A TPC is a unique identifier of a node in a network. An STP (with IP7 Secure Gateway functionality) must have a TPC for each network type that the EAGLE connects to. An SSP connects to only one type of network, so it has only one TPC. 2. An alias point code is used to allow nodes in other networks to send traffic to and from a EAGLE when that EAGLE does not have a TPC for the same network type.

The configured links and point codes in the complex network shown in Figure 2-11 allows most nodes to communicate with other nodes. However, note that Node 2 cannot communicate with Node 13 or Node 16, or with any node in the ITU-N network because Node 2 does not have an ITU-N alias point code.

Routing and Conversion Within a Single Network Type

The following steps demonstrate how an EAGLE routes and converts when an ITU-N node sends an MSU to another ITU-N node. For example, assume that Node 11 in Figure 2-11 sends an MSU to Node 14. The MSU is routed from Node 11 to Node 7 to Node 5 to Node 9 to Node 14. The following steps describe the actions performed at Node 5 (an STP with IP⁷ Secure Gateway functionality):

1. An ITU-N formatted MSU (which has a network identifier=01b and a 14-bit destination point code/originating point code) is received on an iplimi card (for this example at location 1103).
2. MSU discrimination is performed with the following substeps:
   1. Compare the received network identifier (NI) to the list of valid NIs. (Each configured linkset for a receiving link has a defined list of valid NIs.) If the comparison fails, the MSU is discarded and an STP measurement is logged. In this example, the received NI (01b) is valid for an iplimi card.
   2. Extract the NI and destination point code (DPC) from the received MSU.
   3. Determine whether the destination of the received MSU is this STP. If not (as is the case in this example), the MSU is passed to the STP’s routing function.
3. The routing function selects which outgoing link to use by searching a routing table for an entry for the DPC (N14 in this example). The routing table identifies another iplimi card (for this example at location 1107) to be used for the outgoing link.
4. Determine whether MSU conversion is required (required when the source network type is not the same as the destination network type). In this example, both Node 11 and Node 14 are ITU-N nodes, so conversion is not required.
5. Forward the MSU across the Interprocessor Message Transport (IMT) bus from location 1103 to location 1107, where the MSU is transmitted out the link towards Node 14.

Routing and Conversion Between Different Network Types

The routing and conversion steps performed by a EAGLE when an ITU-N node sends an MSU to an ITU-I node are the same as the steps shown in the Routing and Conversion Within a Single Network Type section, except for the conversion step.

For example, assume that Node 11 in Figure 2-11 sends an MSU to Node 16. The MSU is routed from Node 11 to Node 7 to Node 5 to Node 9 to Node 16. The following steps describe the actions performed at Node 5 (an EAGLE with IP⁷ Secure Gateway functionality):

1. Perform step 1 through step 3 as shown in the Routing and Conversion Within a Single Network Type section. In this example, assume that the routing function determines that the outgoing link is configured on the IP card at location 1203.
2. Determine whether MSU conversion is required (required when the source network type is not the same as the destination network type). In this example, Node 11 is an ITU-N node and Node 16 is an ITU-I node, so conversion is required. Conversion consists of two phases: Message Transfer Part (MTP) conversion and user part conversion.
3. Perform MTP conversion (also known as routing label conversion). The following parts of the MSU can be affected by MTP conversion:
   • Length indicator — for ITU-N to ITU-I conversion, the length of the MSU does not change
   • Service Information Octet (SIO), Priority — for conversion to ITU, the priority is set to 0. For conversion to ANSI, the priority is set to a default of 0, which can later be changed based on user part conversion.
   • Service Information Octet (SIO), Network Indicator — the NI bits are set to the NI value for the destination node. In this example, NI is set to 00b.
   • Routing Label, Destination Point Code (DPC) — the DPC is replaced with the destination’s true point code. In this example, N16 is replaced by I16.
   • Routing Label, Originating Point Code (OPC) — the OPC is replaced with the appropriate network type’s alias point code for the originating node. In this example, N11 is replaced with I11.
   • Routing Label, Signaling Link Selector (SLS) — no SLS conversion is required between ITU-I and ITU-N nodes. However, if one of the nodes were an ANSI node, conversion would be required between a 5-bit or 8-bit SLS for ANSI nodes and a 4-bit SLS for ITU nodes.
4. Perform user part conversion, if necessary. Currently, only SCCP traffic and only network management messages have the Message Transfer Part (MTP) converted. All other user parts have their data passed through unchanged.
5. Forward the MSU across the Interprocessor Message Transport (IMT) bus from location 1103 to location 1203, where the MSU is transmitted out the link towards Node 16.