An Architecture for Internet Data Transfer Niraj Tolia, Michael Kaminsky, David G. Andersen, and Swapnil Patil NSDI ’ Eunsang Cho

2/23 Contents Motivation Data Oriented Transfer (DOT)‏  Architecture  Scenarios Evaluation  File Transfer  Postfix – production mail server Conclusion

3/23 Motivation Over 70% of Internet traffic is bulk data transfer.  Many efforts to improve this kind of transfer. Imagine that you have a novel data transfer – such as BitTorrent. How can you deploy it?  Update HTTP: Talk to IETF. Modify Apache, IIS, Firefox, IE,...  Update SMTP: Talk to IETF. Modify Sendmail, Postfix, Thunderbird, Outlook,...  Repeat... Give it up...

4/23 Motivation Innovation in data transfer is very difficult. Why?  Content negotiation and data transfer is tightly coupled.  Content negotiation: deciding what data to be sent. Naming, language, identification,...  Data transfer: actual data bits are exchanged. Solution Application Protocol SenderReceiver Xfer Service and Data Data

5/23 Data Oriented Transfer (DOT)‏

6/23 Architecture Applications perform content negotiation as before. And then, applications use transfer service for actual data exchange.

7/23 An unique OID (object identifier) refers to an object.  OID is generated with cryptographic hash. Hints inform the possible data locations. Data Exchange using DOT Xfer Service Sender Receiver Request File X OID, Hints put(X) OID, Hints get(OID, Hints) read() data Transfer Plugins

8/23 Data Exchange using DOT An unique OID (object identifier) refers to an object.  OID is generated with cryptographic hash. Hints inform the possible data locations. Generic Transfer Client Extra round trips

9/23 Extensibility Application Protocol SenderReceiver Xfer Service USB Keychain Xfer Service Local Cache USB Keychain Bittorrent Application-independent cache Non-networked transfers New network features Bittorrent Plugins

10/23 Plugins Plugins: add new features to DOT  Transfer plugins Transferring data between hosts  Storage plugins Providing access to local data Dividing data into chunks Computing the content hash of data

11/23 Plugin Examples Multi-path plugin  Acts as a load balancer between multiple transfer plugins Portable storage plugin  Supports portable storage device such as USB keychain DOT Network MultiPath Plugin Transfer Plugin Transfer Plugin

12/23 Scenarios Beneficial usages  Cross-application caching A user receives the same file through IM as well as .  Content delivery networks Akamai could extent their reach beyond just the Web.  Not bound to a particular network, layer, or technology Multi-path transfer over different types of network Portable storage to transfer data

13/23 Benefits Applications can reuse available transfer techniques. Easier deployment of new technologies. Cross-application sharing.

14/23 Limitations DOT is a receiver-pull, point-to-point service.  Not suitable for real-time communication such as telnet. Intended to large transfers.  Extra round trips are significant overhead for small transfers.

15/23 Evaluation

16/23 File Transfer gcp  Similar to scp  Bulk data transfer occurs via GTC-GTC communication Network Emulator  Evaluate various bandwidths and delays Network Emulator

17/23 Result of File Transfer Overhead: hashing, extra RTT No noticeable overhead with delay

18/23 Multi-path Plugin Link 1 (Mbps/ms) Link 2 (Mbps/ms) Single (s)Multipath (s)Savings 100/ % 10/ % Gigabit Link 1 Link 2 40MB over ideal 100Mbps: 3.2s Multi-path plugin nearly doubles throughput. TCP effects dominate. Link is not saturated. 100/ % 10/ % 1/ %

19/23 Portable Storage Plugin 255MB over emulated DSL  Based on Virtual Machine transfers at CMU Wait 5 minutes, and plug USB drive into receiver Two drive speeds  8MB/s  20MB/s 2 Mbit/s

20/23 Result of Portable Storage Plugin s (~ 19 min) Device Inserted

21/23 Postfix Trace Replay DOT is integrated with Postfix as an SMTP protocol extension.  for backward compatibility Based on recorded messages, messages were regenerated and used for replay.  Postfix is disk-bound, so DOT’s CPU overhead is negligible.  Savings are due to duplication within s. (caching) ProgramSecondsBytes Sent Postfix468172MB Postfix + DOT468117MB (68%)

22/23 Postfix Integration The cost of integrating DOT with the Postfix One week job for a graduate student, new to Postfix  Easy deployment ProgramLoCNew LoC% GTC Library-421- Postfix70, % smtpd6, % smtp3, %

23/23 Conclusion DOT separates content negotiation from data transfer.  With easier extending possibility DOT architecture has:  Relatively low overhead, especially for high delay  Benefits with caching and extensibility