1. Opportunistic Mobility with Multipath TCP
Costin Raiciu
Department of Computer Science
University Politehnica of Bucharest
Joint work with Dragos Niculescu, Marcelo Bagnulo (UC3M) and Mark Handley (UCL)

2. Mobile Devices Everywhere!
Smartphones
Tablets
Cars
Network connectivity is a requirement
Wifi, 3G, Bluetooth
Vastly different properties
Mention coverage, performance, range, etc.

3. Problem Statement Connectivity is transient for mobile nodes
A few seconds for Wifi at driving speeds [Bala2010]
TCP connections use one interface
When link goes down, connection dies
How can we utilize all these links to get the best performance?

4. What is a good mobility strategy?
3G celltower

5. What is a good mobility strategy?
3G celltower

6. What is a good mobility strategy?
3G celltower

7. What is a good mobility strategy?
3G celltower
Make Before Break

8. What is a good mobility strategy?
3G celltower
Make Before Break

9. What is a good mobility strategy?
3G celltower

10. What is a good mobility strategy?
3G celltower
Make Before Break

11. What is a good mobility strategy?
3G celltower

12. What is a good mobility strategy?
3G celltower
Actively Use Multiple Interfaces

13. What is a good mobility strategy?
3G celltower
Actively Use Multiple Interfaces

14. Mobility Solutions Current Mobile Stacks No Mobile IP Yes TCP-Migrate
Survive Connection
Make Before Break
Multiple Links
Current Mobile Stacks No
Mobile IP
Yes
TCP-Migrate

15. Mobility Solutions Current Mobile Stacks No Mobile IP Yes TCP-Migrate
Survive Connection
Make Before Break
Multiple Links
Current Mobile Stacks No
Mobile IP
Yes
TCP-Migrate
Multipath TCP

16. Multipath TCP: Overview
MPTCP uses multiple paths in the network for one transport connection
Opens multiple subflows which carry data over the different paths
Different paths are selected by using different addresses and/or ports
MPTCP is a drop in replacement for TCP
Works with unmodified apps
Works over the existing network

17. MPTCP Mobile Architecture
3G celltower

18. MPTCP Mobile Architecture
3G celltower
SYN
MP_CAPABLE X

19. MPTCP Mobile Architecture
3G celltower
SYN/ACK MP_CAPABLE Y

20. MPTCP Mobile Architecture
3G celltower

21. MPTCP Mobile Architecture
3G celltower
STATE
CWND
Snd.SEQNO
Rcv.SEQNO …

22. MPTCP Mobile Architecture
3G celltower
STATE
CWND
Snd.SEQNO
Rcv.SEQNO …

23. MPTCP Mobile Architecture
3G celltower
STATE
CWND
Snd.SEQNO
Rcv.SEQNO …

24. MPTCP Mobile Architecture
3G celltower
STATE
CWND
Snd.SEQNO
Rcv.SEQNO …
SYN
JOIN Y

25. MPTCP Mobile Architecture
3G celltower
STATE
CWND
Snd.SEQNO
Rcv.SEQNO …
SYN/ACK
JOIN X

26. MPTCP Mobile Architecture
3G celltower
STATE A
CWND
Snd.SEQNO
Rcv.SEQNO …
STATE B
CWND
Snd.SEQNO
Rcv.SEQNO …

27. MPTCP Mobile Architecture
3G celltower
STATE A
CWND
Snd.SEQNO
Rcv.SEQNO …
DATA
SEQ A DSEQ: 1
STATE B
CWND
Snd.SEQNO
Rcv.SEQNO …

28. MPTCP Mobile Architecture
3G celltower
STATE A
CWND
Snd.SEQNO
Rcv.SEQNO …
DATA
SEQ A DSEQ: 1
DATA
SEQ B
DSEQ: 2
STATE B
CWND
Snd.SEQNO
Rcv.SEQNO …

29. MPTCP Mobile Architecture
3G celltower
STATE A
CWND
Snd.SEQNO
Rcv.SEQNO …
DATA
SEQ B
DSEQ: 2
STATE B
CWND
Snd.SEQNO
Rcv.SEQNO …

30. MPTCP Mobile Architecture
3G celltower
STATE A
CWND
Snd.SEQNO
Rcv.SEQNO …
SEQNO A DSEQ: 2
DATA
DATA
SEQ B
DSEQ: 2
STATE B
CWND
Snd.SEQNO
Rcv.SEQNO …

31. What if the remote server is not MPTCP enabled?
This will be the case for initial deployment
Solution: use an MPTCP proxy
Will be deployed by the mobile operator
Phones will be configured with the proxy’s address via DHCP
The proxy can also help with:
Simultaneous move
Peer to peer operation

32. Proxy Functionality: Server Does Not Speak MPTCP
3G celltower
MPTCP
Proxy

33. Proxy Functionality: Server Does Not Speak MPTCP
3G celltower
MPTCP
Proxy

34. Proxy Functionality: Server Speaks MPTCP
3G celltower
MPTCP
Proxy

35. Proxy Functionality: Server Speaks MPTCP
3G celltower
MPTCP
Proxy

36. Evaluation
The benefits come from using multiple interfaces concurrently
We considered multiple scenarios:
Indoor mobility (trace)
Outdoor mobility (simulation)
3G and WIFI connectivity varies
Link speeds and variations taken from [Bala2010, Bychk2006]

37. Algorithms under test TCP 3G, TCP WiFi
WiFi First: switch to WiFi if available
Optimal TCP = Migrate TCP + Oracle
MPTCP

38. Outdoors Mobility, Walking

39. Outdoors Mobility, Walking

40. Outdoors Mobility, Walking

41. Outdoors Mobility, Walking

42. Outdoors Mobility, Walking

43. Outdoors Mobility, Walking

44. Similar Improvements in All Tests
MPTCP vs. Optimal TCP: %
MPTCP vs. WiFi First: %

45. Energy Experiments Bits/Joule varies for the same interface
How do we know which is the more efficient interface?
Periodically activate all interfaces
Measure Bits/Joule
Switch to the most efficient one
Compared to TCP WiFI MPTCP improves:
Energy efficiency by 7%
Throughput by 50%

46. MPTCP Overheads CPU overheads Network overheads Memory overheads
Depend on the number of subflows
Negligible for x86 and few subflows
Network overheads
20B in each segment ~ 1.5%
Memory overheads
Receive buffer grows as max(RTT)*sum(BW) across all paths

47. Conclusions MPTCP for mobility seems like a no-brainer
Its main advantage is overlapping the use of multiple interfaces
Gets best throughput and robustness
Might improve energy usage
Exciting things to do next
Test how real apps work with MPTCP on mobile phones
Study scenarios with two WiFi, two 3G interfaces

48. Backup Slides

49. Looking Beyond Throughput
For mobile phones energy matters!
MPTCP can shift connections to the more efficient interface