Configuring X.25 8-27Configuring X.25 Address Translation TemplatesThe X.25 address translation function in the FRM provides automatic translation ofselected fields within a Call Request packet, according to a previously defined "tem-plate." You can change the called address, calling address, user data, and/or facilitiesfields of a Call Request packet as it passes into or out of the node.There are various uses for this feature; for example:l For security reasons, a translation of the calling address might enable routing ofall Call Request packets with certain addresses, while all others are cleared.l Translation of user data can allow rerouting of all packets with the same calledaddress, with all those containing one type of information going to one location,while those with another type go elsewhere.The translation template has two parts: the template ID and the translation formula.The Call Request packet can be modified (using the translation formula) to replaceparts of it with characters specified by the formula and/or with parts of the templateID.Each port has two sets of translation templates associated with it, one for incomingpackets and one for outgoing packets. When an incoming packet enters the node, it isimmediately checked against any incoming template defined for that port. If thepacket matches the template, a translation is carried out and the packet continuestoward its destination, using the routing tables defined by SVC Subscriber configu-ration. If the packet does not match the template, it is not accepted.An outgoing packet is checked just before it leaves the node. If it matches the tem-plate, a translation is carried out; if it does not match, it continues unchanged.The hunt group function is performed within the routing table process, so to handleoutbound packets, a port that is part of a hunt group needs a set of templates that isspecific to that port. This allows a different set of outbound translations for each port.Address translation is especially useful in providing backup routing via a public datanetwork (PDN), as represented in the following example.Figure 8-8 Backup Using Address TranslationPrimary route failedNode 1 Node 2Backup route over PDN
