network protocols handbook.pdf

147Protocols GuideVoice Over IP(VOIP) - Other ProtocolsProtocol NameSCTP: Stream Control TransmissionProtocolof this Verification tag must be set to the value of theInitiate tag received from the peer endpoint duringthe association initialization.• Checksum - This field contains an Adler-32 checksumon this SCTP datagram.Protocol DescriptionStream Control Transmission Protocol (SCTP) is designed totransport PSTN signalling messages (SS7/C7) over IP networks,but is capable of broader applications. SCTP is a reliabletransport protocol operating on top of a connectionless packetnetwork such as IP. SCTP is designed to address the limitationsand complexity of TCP while transporting real time signaling anddata such as PSTN signaling over an IP network. SCTP canalso run on top of the UDP layer.SCTP offers the following services:• acknowledged error-free non-duplicated transfer of userdata;• data fragmentation to conform to discovered path MTUsize;• sequenced delivery of user messages within multiplestreams, with an option for order-of-arrival delivery ofindividual user messages;• optional bundling of multiple user messages into a singleSCTP packet; and• network-level fault tolerance through supporting of multihoming at either or both ends of an association.Related protocolsUDP, TCP, IP, SS7/C7Sponsor SourceSCTP is defined by IETF (www.ietf.org ) in RFC 2960.Referencehttp://www.javvin.com/protocol/rfc2960.pdfStream Control Transmission ProtocolThe design of SCTP includes appropriate congestion avoidancebehavior and resistance to flooding and masquerade attacks.The SCTP datagram is comprised of a common header andchunks. The chunks contain either control information or userdata.Protocol Structure16 32bitSource Port NumberDestination Port NumberVerification TagChecksum• Source Port Number - SCTP sender’s port number.It can be used by the receiver, in combination withthe source IP Address, to identify the association towhich this datagram belongs.• Destination Port Number – Destination port numberwhere SCTP datagram is intended to go. The receivinghost will use this port number to de-multiplex theSCTP datagram to the correct receiving endpoint/application.• Verification Tag - The receiver uses the Verificationtag to identify the association. On transmit, the value