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Implementing DCCP

Implementing DCCP. Experience so far… Tom Phelan tphelan@sonusnet.com. DCCP-TP. Fresh start implementation optimized for portability Thinking embedded systems No code from Linux implementation – all original Current release R0.00 – early stage

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Implementing DCCP

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  1. Implementing DCCP Experience so far… Tom Phelan tphelan@sonusnet.com

  2. DCCP-TP • Fresh start implementation optimized for portability • Thinking embedded systems • No code from Linux implementation – all original • Current release R0.00 – early stage • Supports core DCCP (RFC 4340, but with DCCP-NAT encap) and CCID 2 (RFC 4341). • Doesn’t support every feature of DCCP, but a lot • Good effort made to ensure supported features are responsibly implemented • Corners cut mostly in API at this stage • Includes Linux user-space port • DCCP service and apps run as single Linux process (with Pthreads)

  3. DCCP-TP (more) • Near-term next steps: • I’m working on CCID 3 • Jawad Shafi working on Windows user-space port • Documentation (wiki), source code and discussion forum at: • http://www.phelan-4.com/dccp-tp/ • Anyone who wants to contribute, see http://www.phelan-4.com/dccp-tp/tiki-index.php?page=Todo+List and jump in 

  4. Observations • The specs present a number of difficulties for implementers • Gerrit Renker’s recent post on rfc3448bis hits the nail on the head • Almost all features have relevant text scattered about • Often need to read multiple sections of two or three different RFCs to get full sense of a feature • Many features interact with other features • To implement a single feature you need to first understand several other features • Difficult to tell normative from informative • Conflicting text about optionality/desirability of features • Reducing oscillations in rfc3448bis good example

  5. Observations (2) • Much of the suggested implementation text didn’t work for me • Issues with fuzziness, memory use, complexity, efficiency often led me to pursue other solutions • Coming to an understanding of the suggested implementation helped • Pseudo-code was great • One, shows you how to do it, all in one place • Two, getting to understand it teaches that you need to look all over for relevant text • But does it really work? • I haven’t found any problems yet

  6. Observations (3) • Ack Vectors are difficult • Biggest problem is unbounded memory needs • Second is complexity • One of the features where relevant text is most scattered about • And what does all this cost buy you? • Knowledge of which packets were lost • What good is that?

  7. Conclusions • DCCP is feature-rich • Some features are highly complex • Easy to go down wrong path if you aren’t careful • Interop between independent implementations will be work

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