GST Billing from which State

Company A is in the business of Infrastructure Provider (i e. Having IP-1 license from DOT) . It has gst registration in Delhi and UP. Company A leases out the underground Opticle fibre cable(OFC) to company B (company b is registered in UP). There are two end points of OFC, one in Delhi another in UP. 

Now questions is for GST Billing , from which States CompanyA should issue tax invoice in the name of CompanyB  and how to decide whether cgst/sgst to be charged or igst to be charged.