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LUF vs. LRF

LUF vs. LRF. draft-schumacher-drinks-luf-lrf-diff-01.txt Greg Schumacher, Hadriel Kaplan. What’s an LUF?. From Speermint-Terminology: “The Look-Up Function (LUF) provides a mechanism for determining for a given request the target domain to which the request should be routed.”

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LUF vs. LRF

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  1. LUF vs. LRF draft-schumacher-drinks-luf-lrf-diff-01.txt Greg Schumacher, Hadriel Kaplan

  2. What’s an LUF? • From Speermint-Terminology: “The Look-Up Function (LUF) provides a mechanism for determining for a given request the target domain to which the request should be routed.” • The question is: what does “target domain” mean? • Option A: terminating domain • Option B: next-domain Of course sometimes they are the same domain • Option C: next-hop/next-trunk? Note: this isn’t a question about what a specific box does – it can do LUF and LRF in one transaction

  3. Proposal • Change terminology to define LUF as: “The Look-Up Function (LUF) provides a mechanism for determining for a given request the target terminating domain to which the request should be routed.” • Change terminology to define LRF as: “The Location Routing Function (LRF) determines for the target terminating domain of a given request the location of the SF in that domain and optionally develops other SED required to route the request to that domain, possibly through transit SSPs.“

  4. Background slides from DRINKs presentation

  5. Example 1: Bilateral peer 1: Where is +1234567890? 2: <sip:+1234567890@b.com> 3: INVITE sip:+1234567890@b.com LUF 1 2 3 SSP-A SSP-B

  6. Example 1: The real world Even bi-lateral peering in the real world is not one trunk, not all trunks are created equal, and it often depends on where the request came from SSP-A SSP-B

  7. Why LUF answer is not next-hop • SF addressing is not static - they change due to dynamic, temporary topology changes, or operator control • SF address availability/reachability is not global • SF addresses overlap - some SSP's use RFC-1918 addresses • SF addresses are private - many SSPs do not wish to publish the SBE addresses they use for all peering connections with all peers

  8. Example 2: Transit peering LUF 1: Where is +1234567890? 2: <sip:+1234567890@b.com> 3: INVITE sip:+1234567890@b.com 1 2 SSP-C SSP-A SSP-B SSP-E SSP-F 3 How do I get to b.com?

  9. Why LUF is not next-domain • Transit SSP connections are not static • Transit SSP connections are not globally routable - some SSP peering connections only service direct bi-lateral traffic, while others are usable for transit traffic but only for specific regions or national codes • Transit SSP connection details are private • Loops can happen – the LUF in subsequent domains does not know the routing history of the request

  10. So what is LRF? 1: Where is +1234567890? 2: <sip:+1234567890@b.com> 3: INVITE sip:+1234567890@b.com • LRF determines how to reach b.com • Currently through static provisioning (retrieved on-box or through ENUM/SIP-redir queries) • Resulting SIP request example: INVITE sip:+1234567890@b.com SIP/2.0Route: <sip:sbe1.e.com;lr> • Or another, in request-uri:sip:+1234567890;tgrp=trunk1.e.com;trunk-context=a.com@b.com

  11. Why split them out? • LUF can be easily centralized, should be centralized • LRF may be centralized, distributed, or both • LUF rules/decisions/answers are not typically different based on who’s asking • LRF almost always is different for that • LUF security/privacy properties are very different from LRF

  12. Example 2: Real world SSP-C SSP-A SSP-B SSP-E SSP-F

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