4.1.5 multi-homing

introduction Multi-homing A host is said to be multihomed if it has multiple network interfaces or IP address. To increase the reliability of the network applications.

Some issues in using multi-homing path failure detection How to know the link condition? path exploration path selection Which link is better to transmit data? path handover Handover scenario.

Transport layer multi-homing SCTP, Stream Control Transmission Protocol SCTP was originally designed for transmitting PSTN signaling messages across the Internet. TCP + multi-homing

SCTP overview SCTP is a new IETF standard transport protocol (RFC2960) Stream Control Transmission Protocol Originally used in Signaling transport as like SS7 doing telephone switching over IP networks highly reliable, timely delivery, high availability Why ? TCP and UDP lacked some features that were needed

IP reference model(From Stewart/Xie)

Stream Control Transmission Protocol (SCTP) All about SCTP… Connection-oriented, reliable transport protocol combination with TCP & UDP Security features (4-way handshake, tags) Message oriented (streams of messages/chunks) Reliable in-sequence or out-of-sequence delivery to upper layer TCP-friendly flow/congestion control with selective ack. Supports Multi-streaming and Multi-homing one association can contain many logical streams multiple physical or logical interfaces Monitors peer and path reachability (heartbeats) Reasonable overhead (typical 28 bytes for data)

SCTP multi-homing Endpoints of a connection can consist of more than one IP address Data chunks are transmitted over primary path and idle paths are alternative Separate congestion control parameters for different paths

SCTP multi-homing Multiple src/dest ip addresses Use of different physical paths not guaranteed Peer reachability and path status are monitored (heartbeat) One selectable default path Parameters per path (cwnd, RTT, RTO, PRL) IP network IP A2 IP B2 IP B1 IP B3 IP A1

SCTP Multihoming Internet Host A A1 A2 Host B B1 B2 Internet ISP hosts choose 1 of 4 possible TCP connections: (A1,B1) or (A1,B2) or (A2,B1) or (A2,B2) one SCTP association ({A1,A2}, {B1,B2}) concept of “primary” destination Let B1 be Host A’s primary destination Let A1 be Host B’s primary destination network state (RTT, cwnd, ssthresh, …) maintained per destination

Network layer multi-homing IPv4 multi-homing Network must have its own public IP address range and an AS number The routing over these connections is normally controlled by a BGP enabled router. In the case where one outgoing link from the multihomed network fails, outgoing traffic will automatically be routed via one of the remaining links.

Data link multi-homing 802.21 IEEE 802.21 is developing standards to enable handover and interoperability between heterogeneous network types including both 802 and non 802 networks.

IEEE 802.21 Media Independent Handover(HIM) Three mobility service Optimization of handovers between heterogeneous IEEE 802 system as well as between 802 and cellular systems Three mobility service Event Service 換手事件觸發 Command Service 相對應命令下達 Information Service 蒐集interface資訊 14

802.21 architecture

Session Initiation Protocol (SIP) + IEEE 802.21 A mobile node with 2 WLAN interfaces. A session is running on one WLAN connection initially. SIP uses IEEE 802.21 Media Independent Information Service (MIIS) to acquire network information and to configure the other WLAN interface. When the first WLAN fails, SIP sends Re-Invite and Registration message to switch the session to the second WLAN interface.