org.scion.jpan.internal

Class Segments

java.lang.Object

org.scion.jpan.internal.Segments

public class Segments
extends Object

This class gets segment information from a path service and constructs paths.

Assumption: When requesting CORE segments (inter-ISD or intra-ISD), the path service will return at least one segment for every AS in the src-ISD to connecting to every AS in the dst-ISD. Intra-ISD this is ensured by mutual registration, inter-ISD this is ensured by sending PCB to all other core-AS.
Source: ...

3.2. Core Path-Segment Registration
The core beaconing process creates path segments from core AS to core AS. These core-segments are then added to the control service path database of the core AS that created the segment, so that local and remote endpoints can obtain and use these core-segments. In contrast to the intra-ISD registration procedure, there is no need to register core-segments with other core ASes (as each core AS will receive PCBs originated from every other core AS).

Method Summary

Modifier and Type	Method and Description
static List<Daemon.Path>	getPaths(SegmentLookupServiceGrpc.SegmentLookupServiceBlockingStub service, ScionBootstrapper bootstrapper, long srcIsdAs, long dstIsdAs, boolean minimizeLookups) Lookup segments, construct paths, and return paths.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

getPaths

public static List<Daemon.Path> getPaths(SegmentLookupServiceGrpc.SegmentLookupServiceBlockingStub service,
                                         ScionBootstrapper bootstrapper,
                                         long srcIsdAs,
                                         long dstIsdAs,
                                         boolean minimizeLookups)

Lookup segments, construct paths, and return paths.

Implementation notes. The sequence diagrams Fig. 43. and 4.4 in the book (edition 2022) seems to suggest to always request UP, CORE and DOWN, even if paths without CORE are possible. The reference implementation (scionproto) optimizes this a bit by not requesting CORE iff there is only one CORE. Scionproto also uses prior knowledge of whether AS are CORE or not to determine which segments to request.

Here, we do things a bit differently because we may not have prior knowledge whether the destination is CORE or not.

Parameters:

service - Segment lookup service

bootstrapper - Bootstrapper

srcIsdAs - source ISD/AS

dstIsdAs - destination ISD/AS

minimizeLookups - If 'true', this attempts to reduce the number of segment request when constructing a paths. This comes at the cost of having less path variety to chose from, however, the shortest paths should always be available (unless there is a path with a CORE segment that is shorter than a pure UP and/or DOWN path). This is similar, but not equal to, depth-first search as proposed in the Scion book 2022, page 82.

Returns:

list of available paths (unordered)