1. IEEE 802.21 MEDIA INDEPENDENT HANDOVER DCN:21-06-0681-00-0000
Title: Congestion and Flow Control for MIH Protocol
Date Submitted: July 14, 2006
Presented at IEEE session in San Diego
Authors or Source(s):
Yoshihiro Ohba and Subir Das
Abstract: This document proposes text for LB1 comment # 708.

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3. LB1 Comment #708 on Section 8.3.1
“The protocol does not seem to include any capability to react to or avoid congestion events except as provided by the underlying transport. In particular, there is no mechanism to prevent the initiation of large numbers of parallel transactions, and the retransmission timeout is not adaptive (there is no backoff). This may be acceptable for operation of the MIHF protocol between nodes which directly connected over a single link which has native overload control; however, it would not be an acceptable approach for operation over IP networks in which congestion in intermediate nodes is not visible. The lack of rate limitation and the non-adaptiveness of the retransmit timer means that the protocol has no way to avoid causing congestion events.”
Resolution of the WG: need text for such a comprehensive issue, see 32

4. Investigation of the issues
There are two issues indicated in the comment:
Prevention of a large number of retransmissions in a short time
Prevention of a large number of transactions in parallel
1) is related to congestion control (controlling the flow of data during congestion)
2) can be solved with RFC 2988 which defines RTO (Retransmission Timeout) computation algorithm used for TCP
RFC 2988 is generally applicable to any protocol, including MIH protocol
2) is related to flow control (controlling the flow of data)
Closed-loop flow control (i.e., flow control with explicit feedback on network congestion sent from receiving node) might be too much for MIH protocol as it is not a data plane protocol
Open-loop flow control might be sufficient for MIH protocol
NSIS GIST (draft-ietf-nsis-ntlp-09.txt) uses open-loop flow control with a single rate limiter. MIH protocol can follow the GIST approach.
Congestion and flow control at MIH protocol layer should be turned off it is provided by transport protocol

5. Proposed Text Append the following text in Section 8.3.1:
“For congestion control, retransmission timer for MIH packet is computed based on the algorithm defined in RFC For flow control, a single rate limiter applies to all traffic (for all interfaces and message types). It applies to retransmissions as well as new messages, although an implementation may choose to prioritize one over the other. When the rate limiter is in effect, MIH packets are queued until transmission is re-enabled, or an error condition may be indicated back to local signaling applications. The rate limiting mechanism is implementation defined, but it is recommended that a token bucket limiter as described in RFC 4443 be used. The congestion and flow control provided by the MIH protocol layer is turned off in the case where the MIH transport protocol provides congestion and flow control.”
Add the following references in Section 2:
IETF RFC 2988, “Computing TCP's Retransmission Timer”, V. Paxson and M. Allman, November 2000.
IETF RFC 4443, “Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification”, A. Conta, S. Deering and M Gupta, March 2006.