This read-only OCTET STRING (1 to 20 bytes) holds a prefix associated with this specific port, using the same E.164 (1-15 ASCII octets) or ATM-endsystem (1-20 binary octets) encoding as the node-level prefix object, but the description adds that for ATM DCE ports specifically, only ATM-endsystem prefixes of exactly 104 bits (13 octets) and all E.164 prefixes are eligible for ILMI address registration. This extra constraint matters because ILMI (Integrated Local Management Interface) auto-registration has stricter length requirements than general prefix matching, so a prefix configured outside those bounds on a DCE port simply won't be usable for ILMI purposes even though it might work for other routing functions. An engineer troubleshooting why a customer's ATM endsystem address isn't being auto-registered via ILMI would check whether svcPrefixPrefix on the relevant DCE port is exactly 13 octets (104 bits), since anything else silently fails ILMI eligibility.