Can alternate cities be specified globally (which applies to all segments in the request) or separately for each segment in the request?

You can specify alternate cities either globally or for each segment.

How do I search for an alternate city by specifying a mileage radius for the entire journey versus specifying by leg?

For requesting alternate mileage globally, use the following XML request snippet:

</TravelerInfoSummary>
<TPA_Extensions>
   <IntelliSellTransaction Debug="0">
        <RequestType Name="50Itins"/>
   </IntelliSellTransaction Debug="0">
   <AlternateAirportMileage Number="50"/>
</TPA_Extensions>

For requesting alternate mileage by leg, use the following XML request snippet:

OriginDestinationInformation RPH="1">
     <DepartureDateTime>2008-09-01T11:00:00</DepartureDateTime>
     <OriginLocation LocationCode="DFW"/>
     <DestinationLocation LocationCode="PHL"/>
     <TPA_Extensions>
          <SisterDestinationMileage Number="50"/>
          <SisterOriginMileage Number="50"/>
          <SegmentType Code="O"/>
     <TPA_Extensions>
</OriginDestinationInformation>

How do I specify alternate cities for each segment in my XML request?

Use the following XML request snippet:

OriginDestinationInformation RPH="1">
     <DepartureDateTime>2007-07-01T03:00:00</DepartureDateTime>
     <OriginLocation LocationCode="PHL"/>
     <DestinationLocation LocationCode="SFO"/>
     <TPA_Extensions>
          <SisterDestinationLocation LocationCode="SJC"/>
          <SisterOriginMileage LocationCode="BWI"/>
          <SegmentType Code="O"/>
     <TPA_Extensions>
</OriginDestinationInformation>

How do I specify alternate cities globally in my XML request?

You can specify up to three alternate cities for a specified location. Use the following XML request snippet:

TPA_Extensions>
     <IntelliSellTransaction Debug="0">
          <RequestType Name="50ITINS"/>
     </IntelliSellTransaction
     <AlternateAirportCities
     <SpecifiedLocation LocationCode="PHL">
     <AlternateLocation LocationCode="BWI">
     </AlternateAirportCities
     <AlternateAirportCities
     <SpecifiedLocation LocationCode="SFO">
     <AlternateLocation LocationCode="SJC">
     </AlternateAirportCities
</TPA_Extensions>

How do I specify the alternate city mileage radius for both the departing and returning airports?

You can apply the radius option to both departing and returning airports globally or by leg. Use the following XML request snippets for each:

<TravelerInfoSummary>
<TPA_Extensions>
     <IntelliSellTransaction Debug="0">
          <RequestType Name="50ITINS"/>
     </IntelliSellTransaction>
     <AlternateAirportMileage Number="50"/>
</TPA_Extensions>

<OriginDestinationInformation RPH="1">
     <DepartureDateTime2008-09-01T11:00:00</DepartureDateTime>
     <OriginLocation LocationCode="DFW"/>
     <DestinationLocation LocationCode="PHL"/>
     <TPA_Extensions>
          <SisterDestinationMileage  Number="50"/>
          <SisterOriginMileage  Number="50"/>
          <SegmentType Code="O"/>
     </TPA_Extensions>
</OriginDestinationInformation>