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Transport of Media Independent
Handover Messages Over IP
I-D: draft-rahman-mipshop-mih-transport-01.txt
67th IETF Annual Meeting
MIPSHOP Working Group
Key Concepts
• Re-use existing well proven Internet protocols for
–
–
–
–
Discovery of MIH nodes
Transport of MIH messages
Security
Etc.
• Use functionalities already provided by MIH (IEEE
802.21) & focus on transport mechanism
• Define new functionality at MIH application layer
where needed
Network Model
An MIH application
enabled node that
supports and/or
manages MNs for
seamless HO
Mobility
Manager #1
Mobility
Manager #N
Internet
Signaling
over IP
Signaling
over IP
Cellular
Network
WiMAX
Network
WiMAX BS
Cellular BS
WLAN
Network
WLAN
AP
MIH Proxy
L2 Signaling
MN contains MIH
application & multiple
access technologies
Mobile
Node
Mobility
Contains
MIH Proxy
Function
Summary of Proposal
• Hard coding or DHCP to discover Mobility Manager (MM)
– Mobile Node (MN) discovers MM at initialization
– Depends on number of MMs
– DHCP as per draft-daniel-dhc-mihis-opt-02.txt (Park, et al.)
• UDP as MIH transport mechanism between MM and MN
– Easy to implement, simple & fast, used by many other control protocols
e.g. SIP
• IPSec for security mechanism
• Existing MIH functionalities in order to
– Setup and keep track of MIH node identifiers, session and transaction
identifiers
– Discover capabilities of MIH peers
– Provide reliability with optional ACK bit fields
• Retransmission timers at MIH application layer to complement UDP for
reliability
– And associated congestion control mechanism
An MIH Enabled Mobile Node
• The MIH application shall have a newly defined port
number (from IANA)
New
Port
Number
MIH App.
Other App.
UDP
IP
WLAN
WLAN Interface
Cellular
Cellular Interface
Transport Mechanism for Reliable MIH Message
Delivery
• Sender of MIH message may request an
acknowledgement
– Done by setting ACK Request bit in MIH message
• Sender sets retransmission timer based on type of MIH
message (i.e. Information, Event, Command)
– If ACK does not arrive within timeout period then retransmit
– If ACK arrives within timeout then assume message delivered
correctly
• If ACK Request bit was set, the receiver shall send an
ACK message
– Done by setting ACK Respond bit in MIH message
– ACK can be piggy backed with data
MIH Application Retransmission Timers
• Three retransmission timers defined for Information
Service (IS), Event Service (ES), and Command Service
(ES)
Message
Content
IS
Associated
Retransmission
Timer
Information Timer
(T1)
ES
Event
Timer
(T2)
CS
Command
Timer
(T3)
Example
Value
Notes
1000 ms
T1 > T2
Least time
Sensitive
500 ms
T3 < T2 < T1
100 ms
T3 < T2
Most time
sensitive
MIH Signaling Example 1: Directly Over UDP/IP
Mobile Node
Cellular
WLAN
Mobility Manager
Power up: connect to WLAN
1
Obtain
Neighbor List
2
Send a request for IS (e.g. NL) and set application timer T1
ACK not received
timeout after T1
3
4
5
Retransmit request for IS and re-set application timer T1
Send IS response (with piggy backed ACK) and set application timer T1
Send ACK
MN then decides to
move to cellular
(based on radio conditions)
6
7
Send ‘Link Up’ ES to inform about HO completion (no ACK required)
Session continues
over cellular
MIH Signaling Example 1: Via WLAN MIH Proxy
Mobile Node
1
Cellular
WLAN
(Proxy)
Mobility Manager
Power up: connect to WLAN
Obtain
Neighbor List
2
Send a request for IS (e.g. NL)
Inter-work L2 message
to UDP/IP message
3
Forward IS request
ACK not received
timeout after T1
4
5
6
7
Retransmit IS request
Send ACK
Send IS response
Send ACK
Inter-work UDP/IP
message to L2 message
8
Forward IS response
NAT Traversal, Fragmentation, & Security
• MNs can be behind NATs
– If MNs behind NATs initiate sessions with MM then there
will be no NAT traversal problems
• Trend in IEEE 802.21 is to use small MIH messages
– ES and CS: small and will not require fragmentation
– IS can be large: use IP fragmentation when needed
together with retransmission timers for reliability
• Use relevant IPSec features i.e. Encapsulated
Security Payload and/or Authentication Header for
secure messaging
Conclusions
• Re-use existing protocols as much as possible and
define new functionalities only where needed
• Use UDP: existing, fast, & simple to use transport
protocol
– Used by other protocols e.g. SIP commonly uses UDP,
CAPWAP also uses UDP, & the IETF NETLMM Working
Group also considers UDP for transport
• Use existing MIH (IEEE 802.21) functionalities:
– Provides options for ACKs, sessions & transactions
management
• Use MIH Application Retransmission timers for
reliability