TPOT Translucent Proxying of TCP Pablo Rodriguez, Sandeep Sibal, Oliver Spatscheck AT&T Labs - Research

2 The Problem Intermediate proxy SYN DATA Router Destination Source proxy ACK

3 The Solution Intermediate proxy SYN Router Destination Source proxy ACK + tunneling info DATA

4 The Protocol Source Translucent Proxy (S,S_p) Intermediate Translucent Proxy (P,P_p) Destination (D,D_p) SYN: (S,S_p,D,D_p) (tcp_option: SET) ACK: (D,D_p,S,S_p) (tcp_option: P,P_p) DATA: (S,S_p,D,D_p) (IP-Tunneled via: P, P_p) SYN: (P,P_p,D,D_p) (tcp_option: SET) ACK: (D,D_p,P,P_p) DATA: (P,P_p,D,D_p)

5 TPOT: Benefits n Proxies can be placed and cascaded u Anywhere in the network u Without configuration u Without additional signalling n Graceful overload handling and fault tolerance u Fall back to plain IP routing u Late commitment: Proxy decides to proxy a connection during connection establishment not during signaling n Smaller RTTs and drop rates improve throughput n TPOT enables connection pooling

6 TPOT: Costs n Enabling TPOT requires either: u Changing TCP/IP stack of client, or u Using an explicit proxy on the client, or u Placing the access proxy at a focal point n Extra processing on TPOT machine u Scales using TPARTY - farm of TPOT machines close to router n Extra bandwidth for IP tunnel u Decreased by header compression for inner headers n TPOT-hierarchy fixed for the lifetime of a TCP connection u Might lead to sub-optimal routing of traffic (unlikely for current rate of route changes) n TPOT does not discover proxies not on the route to the original source

7 TPOT Example: Cable Access n Problem u Provide caching for a cable access network n Requirements u Low investment u Easy management u Multiple routes u Fault tolerant u Low overhead n Solution u TPOT enabled cable access modem which allows the use of caches in aggregation points

8 TPOT Example: Cable Access Origin Server Client PROXY Origin Server Client Cable Modem PROXY

9 TPOT Example: Cable Access - Benefits n Low Investment u Cable modem can be used to TPOT enable client n Easy Management u No client site configuration n Multiple Routes u Use of TPOT provides IP tunnel n Fault Tolerance u Failure of any cache in the network does not impact client n Low Overhead u No signaling overhead

10 Performance n Measurement of TCP throughput u different RTTs u 10MBits/sec Ethernet u with two TPOT machine or two Router n TPOT has been implemented on Scout n TPOT is currently being ported to Linux n Extensive performance testing and analysis is reported in AT&T TR

11 TPOT: Related Work n Transparent Proxies u have to be on a focal point n Active Networks u require a new networking infrastructure u are difficult to deploy incrementally n Transformer Tunnels u require additional signalling and/or configuration n Proxy Autodiscovery Protocols u requires additional signaling

12 Conclusion n TPOT provides scalable proxy cache discovery u without additional signaling u without configuration u with incremental deployment u with fault tolerance