SCTP: A new networking protocol for super-computing Mohammed Atiquzzaman Shaojian Fu Department of Computer Science University of Oklahoma.

Networking Characteristics in Supercomputing High bandwidth links between upercomputers; High bandwidth links between upercomputers; Requires low delay in packet delivery; Requires low delay in packet delivery; Many applications are based on message passing; Many applications are based on message passing; Multimedia applications becoming popular. Multimedia applications becoming popular.

SCTP: A new Transport Protocol is the most popular transport protocol to connect supercomputers. TCP is the most popular transport protocol to connect supercomputers. Supercomputer applications can take advantage of many Supercomputer applications can take advantage of many SCTP features: Support for multiple logical streams to improve data transmission throughput;Support for multiple logical streams to improve data transmission throughput; Support for multiple network interfaces to achieve high availability;Support for multiple network interfaces to achieve high availability; More secure mechanisms to prevent threats such as Denial of Service (DoS) attack.More secure mechanisms to prevent threats such as Denial of Service (DoS) attack.

What is SCTP? Stream Control Transmission Protocol; Stream Control Transmission Protocol; Originally designed to support Telephone signaling messages over IP Networks; Originally designed to support Telephone signaling messages over IP Networks; Currently supports most of the features of TCPCurrently supports most of the features of TCP Standardized by IETF RFC 2960; Standardized by IETF RFC 2960; Reliable transport protocol on top of IP Reliable transport protocol on top of IP

SCTP and TCP Features Both of them are reliable transport protocols; Both of them are reliable transport protocols; Similar Congestion Control algorithms Similar Congestion Control algorithms ( slow start,congestion avoidance); ( slow start, congestion avoidance); TCP, UDP, SCTP IP Link Layer Physical Layer Upper layer applications Slow start Congestion avoidance Slow start threshold

SCTP and TCP Differences  SCTP has the concept of an association instead of a connection;  Multiple Logical Streams in a Association;  Support for Multihoming;  SCTP is message oriented while TCP is byte stream oriented;  Protection against DoS attacks;

Where does SCTP fit? SCTP User Application SCTP Transport Layer IP Network Service SCTP User Application SCTP Transport Layer IP Network Service Multiple IP interfaces SCTP association Streams in an association internet

SCTP Multistreaming Multiple streams per association;  Multiple streams per association;  Multiple streams prevent head-of-line blocking that occurs in a single stream scenario;  Stream properties can be individually tailored to fit application requirements.

SCTP Multistreaming Multiple logical streams Head-of-line blocking

Benefit of Multistreaming Allows application to send multiple objects (text, images, audio) simultaneously. An object can delay the delivery of other objects;  Allows application to send multiple objects (text, images, audio) simultaneously. An object can delay the delivery of other objects;  Improve the data transmission throughput under packet losses;  Can help supercomputing applications involving multimedia objects.

Multihoming----Supports multiple IP addresses in an association. Super- computer 1 Super- computer 2 Network Path1 Network Path2 Network Path2 Interface1 Interface2 Interface1 Interface2 Association

Message-oriented feature Communication between supercomputer is often message-oriented;  Communication between supercomputer is often message-oriented;  TCP’s stream-oriented nature is often an inconvenience for applications based on message passing;  SCTP is message oriented: SCTP saves the programmers from doing SCTP saves the programmers from doing framing at the application layer manually. framing at the application layer manually.

High bandwidth delay links Supercomputers are usually connected by high bandwidth-delay product links; Supercomputers are usually connected by high bandwidth-delay product links; For optimal performance keep link full For optimal performance keep link full maximum TCP window size is 64KBmaximum TCP window size is 64KB a 192KB bandwidth-delay product line is empty more than 60% of the timea 192KB bandwidth-delay product line is empty more than 60% of the time ACK Data Supercomputer 1 Supercomputer 2

SCTP Large window support TCP supports windows up to TCP supports windows up to 2 16 bytes; TCP requires window scaling option TCP requires window scaling option (RFC 1323) to support large windows; (RFC 1323) to support large windows; SCTP has a natural support for large windows up to SCTP has a natural support for large windows up to 2 32 bytes to fill out the pipe. ACK Data Supercomputer 2 Supercomputer 1

Current SCTP implementations Linux ( FreeBSD/NetBSD/OpenBSD ( Solaris (

Summary SCTP is now an Internet standard track protocol (RFC 2960) Advantages over TCP: Multistreaming; Multihoming; Multihoming; Message oriented; Message oriented; Unordered data delivery; Unordered data delivery; Large window; Large window; Secure mechanisms. Secure mechanisms.