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Session Border Controllers – use with caution

This presentation by Henning Schulzrinne at the SIP Summit 2005 provides an in-depth look at Session Border Controllers (SBCs) and their implications in modern networking. It discusses the transient nature of SBCs, their motivations, and the cost of convenience in network evolution. Key concerns include the limitations of transparency, security, and scalability of SBCs, as well as the need for careful application-layer considerations in SIP. Schulzrinne emphasizes the delicate balance between media session inspection and maintaining session privacy, revealing potential pitfalls for users and services alike.

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Session Border Controllers – use with caution

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Presentation Transcript

  1. Session Border Controllers – use with caution Henning Schulzrinne Dept. of Computer Science Columbia University (SIP Summit 2005, Honolulu, Hawaii)

  2. Overview • SBCs as transient phenomena? • Motivations • SBC – the cost of convenience

  3. Network evolution earlier: email, IM SBC only IP-level (with filter)

  4. High-level motivations • Why application-layer elements in SIP that are not quite proxies? • SMTP has various MTAs, but they are just MTAs (e.g., spam filter) • Guesses: • media vs. control separation • good idea in theory, harder in today’s limited-functionality Internet • see Asterix, Skype • proxy model of no content (SDP) inspection or modification too limited • CALEA (needs to be invisible) • charging for services • not an issue for email and web

  5. Motivations • Short term (hopefully) • SIP “fix up” or “dumbing down” • brute-force NAT traversal • Long term needs • fire wall control • billing enforcement

  6. The dangers • May not be present in all instances • SBCs are a box description, not a function description • Lack of visibility • cannot tell where SBC is located • hard to diagnose failures • see HTTP “transparent proxy” experience • one example: TP thought SIP was HTTP • hard to address content cryptographically to such box • Lack of transparency • not all features make it through SBC • header support • copying content • routing loops • Lack of security • Inherent conflict between need for media session inspection and session privacy • Session description modification removes accountability • Lack of scalability

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