The Network Simulator NS-2 & SCTP Module Student ： Kuo-Lun Lu Advisor ： Dr. Jen-Yi Pan

Outline SCTP - what ' s is SCTP - important features SCTP module - multi-interface - set nodes - configuration parameters

What is SCTP ? SCTP ( Stream Control Transmission Protocol ) - PSTN signaling messages over IP Networks Similar to TCP and UDP - transport layer - reliable / unreliable transmission - congestion control - ordered / unordered transmission

Important Features Multi-homing Multiple Streams SACK reliable / unreliable transmission ordered / unordered

SCTP Multi-homing More than one IP address. - one of the IP addresses is set to be the primary address  primary path - other IP addresses  secondary path

Multi-homing – change path

SCTP Multiple Stream The streams within an SCTP association allow the endpoints to transfer multiple sequences of messages at the same time.

Acknowledgment chunk SCTP detects packet losses by checking the blocking gaps in its Selective Acknowledgment (SACK) chunks.

SCTP module Base SCTP Agent 在撰寫的過程中，主要遵循 RFC2960 與其相關的後續推出的 draft 。包括有： –Normal Establishment of an Association (rudimentary handshake) –Transmission of DATA Chunks –Acknowledgment on Reception of DATA Chunks –Management Retransmission Timer –Multi-homed SCTP Endpoints –Stream Identifier and Stream Sequence Number –Ordered and Unordered Delivery –Report Gaps in Received DATA TSNs –SCTP Slow-Start and Congestion Avoidance –Endpoint Failure Detection –Path Failure Detection –Path Heartbeat (without upper layer control) –Partial Reliability (draft-ietf-tsvwg-usctp-01.txt)

Multi-interface NS2's architecture, a node can't actually be multihomed.  Each multihomed node is actually made up of more than one node. - core node - interface node

建立多網路介面節點方法 -- command Where to find?  in sctp.cc set-multihome-core : 建立核心節點 multihome-add-interface : 核心節點與網路介面 Link $ns node-config-multihome-core \ -wiredRouting OFF \ -macTrace OFF set host1_core [$ns node 1.0.1] set host1_if0 [$ns node 1.0.2] set host1_if1 [$ns node 2.0.1] $ns multihome-add-interface $host1_core $host1_if0 $ns multihome-add-interface $host1_core $host1_if1

在節點加上 SCTP agent multihome-attach-agent : 將 SCTP agent 加到節點上 – 若 SCTP 僅有單一網路介面則用 attach-agent set sctp0 [new Agent/SCTP] $ns attach-agent $host0 $sctp0 – 若 SCTP 有多個網路介面則用 multihome-attach-agent set sctp1 [new Agent/SCTP] $ns multihome-attach-agent $host1_core $sctp1

設定路徑 set-primary-destination: 目的端有多個介面, 設定要到達的 Destination 位置 –$sctp0 set-primary-destination $host1_if0 不指定 ?  force-source: 設定多界面節點的主用 interface –$ns at 0 "$sctp1 force-source $host1_if0“

主要參數設定 Where to find?  in sctp.cc PathMaxRetrans_ 5 – 當路徑的錯誤計數器超過此參數值時，會將此路徑的狀態設為 INACTIVE 並改由其他路徑傳輸。 maxInitRetransmits 8 – 是 INIT Chunk 的最大重傳次數 heartInterval_ 30 – 當路徑超過此參數時間沒有資料傳送時，將路徑視為是 idle path ，並開始 透過 HEARTBEAT 機制偵測路徑的狀態 ( 以秒為單位 ) 。

主要參數設定 (cont.) mtu_ 1500 – 是指每條路徑的最大傳輸單位 initialSsthresh_ –Ssthresh( 以 Byte 為單位 ) InitialCwnd_ 2 –Cwnd ( 以 MTU - SCTP/IP headers 為單位 ) numOutStreams_ 1 – 指由傳送端到接收端有幾條 outbound stream unordered_ 0 – 所傳輸的資料是有序或無序傳輸，預設 0 指 ordered ipHeaderSize_ 20 –IP header 的長度

主要參數設定 (cont.) dataChunkSize_ 512 –Data chunk 的長度 useDelayedSacks_ 1 – 是否使用 Delay SACK rtxToAlt_ 1 …. 其餘參數設定可參閱 NS2 使用手冊

rtxToAlt_ – 重傳的資料是否要使用其他路徑傳輸 0 = same, 1 = alt, 2 = fast rtx to same + timeouts to alt