The Network Simulator NS-2 & SCTP Module

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_ 65536 • 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

The Network Simulator NS-2 & SCTP Module