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Stream Control Transmission Protocol (SCTP) Readdressing Retransmission Trigger draft-micchie-tsvwg-fastmsctp-01

Stream Control Transmission Protocol (SCTP) Readdressing Retransmission Trigger draft-micchie-tsvwg-fastmsctp-01. Michio Honda Keio University micchie@sfc.wide.ad.jp. SCTP Signaling on Migration between Different Access Networks.

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Stream Control Transmission Protocol (SCTP) Readdressing Retransmission Trigger draft-micchie-tsvwg-fastmsctp-01

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  1. Stream Control Transmission Protocol (SCTP) Readdressing Retransmission Triggerdraft-micchie-tsvwg-fastmsctp-01 Michio Honda Keio University micchie@sfc.wide.ad.jp

  2. SCTP Signaling on Migration between Different Access Networks • Dynamic Address Reconfiguration (ADDIP) [RFC5061] support mobility between different access network • ASCONF Chunk(s) signal a peer endpoint of addition and deletion of addresses in an SCTP Association • End-to-end mobility approach

  3. Connectivity Disruption on Migration to Another Wireless Network • Passing an area of bad wireless coverage • Overhead to switch the wireless network to connect • Layer 2 configuration • Scanning available base stations • Establishing link layer connectivity • Layer 3 configuration • DHCP, Stateless Address Autoconfiguration, DHCPv6

  4. Transmission Delay Caused by Retransmission Time Outs (RTOs) • During connectivity disruption on a mobile node, SCTP endpoints on the mobile node and the correspondent node fail to transmit packets • After connectivity revival, the lost packets are not retransmitted until the next RTO expires • The RTO value is doubled on each RTO expiration between 1 and 60 seconds [RFC 2988]

  5. New Retransmission Trigger based on Readdressing Events • In order to avoid extra transmission delay, immediate retransmission after the connectivity revival is required • Exchanging ASCONF and ASCONF-ACK Chunks indicates connectivity revival on the SCTP Association • On the other hand, ASCONFs are transmitted not only due to migration, but also due to other events • E.g., )Configuring new IP addresses on another wireless interface without deletion of existing IP addresses • Exchanging ASCONF and ASCONF-ACK due to migration should be distinguished from other events

  6. New Retransmission Trigger based on Readdressing Events (2) • New Retransmission Trigger • When following readdressing events occur, the endpoint MAY retransmit unacknowledged data without waiting for the next RTO expiration • Change of all local addresses • It occurs on the mobile node-side endpoint • Data transmitted from the previous addresses are never acknowledged by the peer • Previous addresses are already deleted by the ASCONF • Change of all destination addresses • It occurs on the correspondent node-side endpoint • Data transmitted to the previous destinations are never delivered • Previous destinations are already deleted by the ASCONF

  7. New Retransmission Trigger based on Readdressing Events (3) • A readdressing event means change of the communication path • Mobile node-side endpoint • SCTP congestion control is based on a destination • When at least 1 RTO expires during connectivity disruption • RTO has been doubled and cwnd has been decreased to 1 • When no RTO expires during connectivity disruption • RTO has not been doubled, but cwnd is increased • Correspondent node-side endpoint • RTO and cwnd are naturally reset due to change of the destination • Path parameters, such as cwnd and RTO should be reset and retransmission should be started with slow-start • RTO SHOULD be set to RTO.Initial on the retransmission • cwnd SHOULD be set to <= 2*MTU on the retransmission

  8. Examples of Experimental Results • 3.8 seconds disconnected period occurs before change of the IP address • Large improvement case • RTO expires long after connectivity revival • 6.8 seconds disconnected period occurs before change of the IP address • Small improvement case • RTO expires soon after connectivity revival

  9. Conclusion • A new retransmission trigger on SCTP • Migration to another access network often involves connectivity disruption • Passing an area of bad wireless coverage • Layer 2/3 configuration • During the connectivity disruption, SCTP endpoints fail to transmit data • After connectivity revival, SCTP endpoints do not retransmit lost packets until the next RTO expiration • The new retransmission trigger retransmits the packets based on readdressing event caused by migration • Connectivity revival is indicated by exchanging ASCONF Chunks • Change of all local addresses or all destination addresses indicates migration

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