1. 4.1.5 multi-homing

2. 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.

3. 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.

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

5. 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

6. IP reference model(From Stewart/Xie)

7. 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)

8. 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

9. 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

10. 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

11. 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.

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

14. 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

15. architecture

16. 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 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.