LUF%20vs.%20LRF

1
LUF vs. LRF

• draft-schumacher-drinks-luf-lrf-diff-01.txt
• Greg Schumacher, Hadriel Kaplan

2
Whats 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 isnt a question about what a specific
  box does it can do LUF and LRF in one
  transaction

3
Example 1 Bilateral peer
LUF
1
2
3
SSP-A
SSP-B

• 1 Where is 1234567890?
• 2 ltsip1234567890_at_b.comgt
• 3 INVITE sip1234567890_at_b.com

4
Example 1 The real world
SSP-A
SSP-B

• 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

5
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

6
Example 2 Transit peering
LUF
1
2
SSP-C
SSP-A
SSP-B
SSP-E
SSP-F
3

• 1 Where is 1234567890?
• 2 ltsip1234567890_at_b.comgt
• 3 INVITE sip1234567890_at_b.com

How do I get to b.com?
7
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

8
So what is LRF?

• 1 Where is 1234567890?
• 2 ltsip1234567890_at_b.comgt
• 3 INVITE sip1234567890_at_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
  sip1234567890_at_b.com SIP/2.0Route
  ltsipsbe1.e.comlrgt
• Or another, in request-urisip1234567890tgrpt
  runk1.e.comtrunk-contexta.com_at_b.com

9
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 whos asking
• LRF almost always is different for that
• LUF security/privacy properties are very
  different from LRF

10
Example 2 Real world
SSP-C
SSP-A
SSP-B
SSP-E
SSP-F