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Expressing Source Filters in SDP

Expressing Source Filters in SDP. Dave Thaler (Microsoft). Why?. Required for single-source sessions in 232/8 ~Required for other Include-mode sessions Exclusion list useful in some scenarios Want app getting SDP to be able to translate into API calls (draft-ietf-idmr-msfapi-00.txt).

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Expressing Source Filters in SDP

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  1. Expressing Source Filters in SDP Dave Thaler (Microsoft)

  2. Why? • Required for single-source sessions in 232/8 • ~Required for other Include-mode sessions • Exclusion list useful in some scenarios • Want app getting SDP to be able to translate into API calls (draft-ietf-idmr-msfapi-00.txt)

  3. Extensibility Mechanisms • Option A: new address type • c= line currently contains address family & group address • Option B: new attribute • a=<attribute>:<value> • Receivers ignore a= if not understood • (c=,a=)* prohibited by SDP syntax

  4. Option A: address type • Example: • c=IN IP4SF 224.2.17.12/127 excl 1.1.1.1 2.2.2.2 • Not backwards compatible • Existing SDP receivers can’t understand • Seems to be problematic for exclude mode

  5. Option B: attribute • Example: • c=IN IP4 224.2.17.12/127 • a=excl:IN IP4 224.2.17.12 1.1.1.1 2.2.2.2 • Backwards compatible • Existing SDP receivers ignore filter, join group • Result of ignoring unrecognized means legacy receivers may try to join 232/8 groups • No big deal?

  6. Choose one? • Prefer single mechanism for both include/exclude mode • consistency • code reuse • Proposal: option B • a={incl,excl}:<network type> <address type> <connection address> ( <source> )+

  7. Example 1: multi-source session, separate group address per source • c=IN IP4 232.2.17.12/127 • c=IN IP4 232.1.2.3/127 • a=incl:IN IP4 232.2.17.12 1.1.1.1 • a=incl:IN IP4 232.1.2.3 2.2.2.2

  8. Example 2: multiple address types • c=IN IP4 224.2.17.12/127 • c=IN IP6 FF0E::11A/127 • a=excl:IN IP4 224.2.17.12 1.1.1.1 • a=excl:IN IP6 FF0E::11A 2001:210:1:2:240:96ff:fe25:8ec9

  9. Example 3: multiple groups with same filter • Example 3a: group range • c=IN IP4 224.2.1.1/127/3 • a=incl:IN IP4 224.2.1.1 1.1.1.1 2.2.2.2 • Example 3b: independent groups, wildcard? • c=IN IP4 224.2.1.1/127 • c=IN IP4 224.2.2.2/63 • a=incl:IN IP4 * 1.1.1.1 2.2.2.2

  10. Limitations with used with SAP • “The text payload should be no greater than 1 Kbyte in length.” • 40 bytes per IPv6 address, 16 per IPv4 address • assuming ~400 bytes for other stuff, 15 IPv6 source addresses or 39 IPv4 addrs fit w/o compression

  11. Other source-specific considerations • Single-source session should have a=recvonly • CANNOT assume the reverse

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