RCP & R 2 CP: Receiver-Centric Transport Protocols for Mobile Hosts

1. RCP & R2CP: Receiver-Centric Transport Protocols for Mobile Hosts Jonathan Levitt James Michaels

2. Presentation Outline • Introduction • Receiver-Centric Advantages • Reception Control Protocol (RCP) • RCP Performance • Radial RCP (R2CP) • R2CP Functionality Gains • R2CP Performance • Critique • Related Work • Summary

3. Introduction • TCP: Sender-Centric Protocol • Data sender performs all important tasks • TCP’s Issues with Wireless Connections • Assumes all losses are due to congestion • Congestion control mechanisms are designed for wired connections • A packet retransmission after a wireless loss is likely to be lost again, thus wasting energy

4. Receiver-Centric Advantages • Loss Recovery • Ability to avoid the feedback overheads and latency • Changes are needed only to the mobile host • Congestion Control • Moves responsibility of congestion control to receiver • Power Management • Efficient power-conserving decisions made at receiver without involving sender

5. Time Server Mobile Host Send SYN seq=x Receive SYN Send SYN seq=y, ACK x+1 Receive SYN + ACK Send ACK y+1 Receive ACK { Sends REQ seq=z Receives REQ RTT Sends DATA Receives DATA Reception Control Protocol (RCP) REQ-DATA Handshake Connection Management

6. Reception Control Protocol (RCP) • Congestion Control • Since RCP is a TCP clone, it adopts the window based congestion control used in TCP • Slow start, congestion avoidance, fast retransmit, and fast recovery are triggered in the same fashion as in TCP

7. 1 1 2 2 3 3 4 4 DATA REQ (4) 1 2 REQ (2) Reception Control Protocol (RCP) Flow Control Reliability The receiver determines which data the sender should send The receiver determines how much data the sender can send

8. RCP Performance What are the three advantages of receiver-centric protocols? Loss Recovery, Congestion Control, and Power Management

9. Radial RCP (R2CP) • Consists of one receiver, and one or multiple senders • Virtual connections exist between the R2CP receiver and the RCP pipes • Principles of Design: • Receiver-Centric Operation • Maintaining Multiple States • Decoupling Functionalities • Effective Packet Scheduling

10. Radial RCP (R2CP) Architecture

11. R2CP Functionality Gains • Seamless Handoffs • Receiver controls which and how much data is sent through each interface • Server Migration • Minimization of overheads incurred in transferring protocol states • Bandwidth Aggregation • Receiver can internally coordinate the transmission of multiple senders

12. R2CP Performance

13. Critique • RCP could possibly add weights to each flow • RCP is most useful when only the mobile host link is wireless

14. Related Work • WTCP (Wireless TCP) • Receiver controls the send rate, but still depends on the sender for reliability • WebTP • Receiver-driven protocol, but overly aggressive compared to TCP

15. Summary • RCP is a receiver-centric protocol • Mobile host is more knowledgeable about local wireless channel conditions • Advantages include intelligent loss recovery, congestion control, and power management • R2CP controls multiple RCP pipes • Advantages includes seamless handoffs, server migration, and bandwidth aggregation

16. Questions?