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A Receiver-Centric Transport Protocol for Mobile Hosts with Heterogeneous Wireless Interfaces. H. Hsieh, K. Kim, Y. Zhu and R. Sivakumar ACM Mobicom 2003. Addressed Issues. Loss discrimination/recovery Power management Seamless handoffs Server migration Bandwidth aggregation.
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A Receiver-Centric Transport Protocol for Mobile Hosts with Heterogeneous Wireless Interfaces H. Hsieh, K. Kim, Y. Zhu and R. Sivakumar ACM Mobicom 2003
Addressed Issues • Loss discrimination/recovery • Power management • Seamless handoffs • Server migration • Bandwidth aggregation Wired-wireless Network
Proposed Solution • A receiver-centric TCP clone – RCP (Reception Control Protocol) • A multi-state extension of RCP – Radial RCP (R2CP) for multi-homed hosts
Core Thesis Behind Proposal • The wireless last link is crucial • Receiver has accurate knowledge of channel conditions • Receiver has knowledge of all its interfaces • Receiver can handle functionality without making changes at the sender
RCP Protocol Overview • Data Transfer: • REQ-DATA instead of DATA-ACK • REQ in 2 modes • Cumulative • Pull In CUM or PULL mode REQ DATA 3 out-of-order DATA segments-> Fast Retransmit Receiver Sender
RCP Protocol Overview • Congestion Window maintained at Receiver • Receiver can react to packet loss based on its knowledge of channel conditions Window moves forward on DATA receipt
RCP Performance Analysis • Comparison with improved TCP-SACK as well as TCP-NewReno • TCP friendly • Performs much better than TCP in a wired-wireless scenario with optimizations • RCP-ELN better than TCP-ELN • RCP-STP better than STP Simulated Topology
Misc. Discussions • Overhead not prohibitive • For reverse direction data-flow e.g. mobile server, recommend a TCP-RCP hybrid • Extending RCP for rate-controlled traffic is an option • Receiver can switch between reliable/unreliable mode of delivery
Critical Review • All decisions relegated to mobile host but is the mobile host always equipped to make the right decision? • How is channel state accurately monitored? • Requires an intelligent application (and possibly an effective Service Location Protocol) to make good use of RCP/R2CP • Security Implications: • What if receiver misbehaves? • Sender flooded with REQs • Undesirable as sender is a Server!