1. SCTP as a transport for Diameter
draft-pascual-dime-sctp-00
vpascual@acmepacket.com
gonzalo.camarillo@ericsson.com
IETF 79 - DIME WG
November 2010, Beijing, China

2. Motivation
• Clarify/specify the usage of Diameter over
SCTP and its associated security mechanisms

3. draft-ietf-dime-rfc3588bis-25
• The base protocol is defined to run over TCP,
SCTP or TLS
– assuming that TLS is run on top of TCP when it is used
• The use of a secured transport for exchanging
Diameter messages is mandatory
– being TLS the primary method and IPsec a secondary
alternative
• A TLS-like mechanism for Diameter over SCTP is
desired

4. TLS over SCTP has some serious
limitations
• These are documented in draft-ietf-tsvwg-dtls-
for-sctp-06
• Examples:
– It does not support the unordered delivery of SCTP
user messages
– It uses a TLS connection for every bidirectional
stream, which requires a substantial amount of
resources and message exchanges if a large number of
streams is used
• TLS over SCTP has seen very little deployment, if
any

5. DTLS over SCTP overcomes the
limitations of TLS over SCTP
• DTLS over SCTP supports all features SCTP supports.
Examples:
– It does support the unordered delivery of SCTP user
messages
– It uses one DTLS connection per SCTP association
• The IESG has recently approved it as a Proposed
Standard and it will be published as a Standards Track
RFC
• Proposal: adopt DTLS over SCTP as a security
mechanism for Diameter

6. Mapping of Diameter messages into
SCTP streams
• Diameter messages need to be mapped into SCTP streams
in a way that avoids Head Of the Line (HOL) blocking
– Mapping diameter messages into different SCTP streams could
fulfill this requirement but some increase of processing delay
might be incurred
– Sending every Diameter message via the SCTP Stream ID zero
with the “unordered” flag set leads to improved performance
and simplicity
– Proposal: “a Diameter entity SHOULD send every Diameter
message over stream zero with the unordered flag set. On the
receiving side, a Diameter entity MUST be ready to receive
Diameter messages over any stream”

7. Questions to the WG
• Is this something we should work on?
• Where?
– rfc3588bis vs. separate document