I-D: draft-rahman-mipshop-mih-transport-01.txt

1
Transport of Media Independent Handover Messages
Over IP

• I-D draft-rahman-mipshop-mih-transport-01.txt

67th IETF Annual Meeting MIPSHOP Working Group
2
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

3
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
WLAN Network
WiMAX Network
Cellular Network
Contains MIH Proxy Function
WLANAP
WiMAX BS
MIH Proxy
Cellular BS
L2 Signaling
MN contains MIH application multiple access
technologies
Mobile Node
Mobility
4
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

5
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
Cellular
Cellular Interface
WLAN Interface
6
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

7
MIH Application Retransmission Timers

• Three retransmission timers defined for
  Information Service (IS), Event Service (ES), and
  Command Service (ES)

Message Content Associated Retransmission Timer Example Value Notes
IS Information Timer (T1) 1000 ms T1 gt T2 Least time Sensitive
ES Event Timer (T2) 500 ms T3 lt T2 lt T1
CS Command Timer (T3) 100 ms T3 lt T2 Most time sensitive
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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
Retransmit request for IS and re-set application
timer T1
3
Send IS response (with piggy backed ACK) and set
application timer T1
4
Send ACK
5
MN then decides to move to cellular (based on
radio conditions)
6
Send Link Up ES to inform about HO completion
(no ACK required)
Session continues over cellular
7
9
MIH Signaling Example 1 Via WLAN MIH Proxy
WLAN (Proxy)
Mobile Node
Cellular
Mobility Manager
1
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
Retransmit IS request
5
Send ACK
6
Send IS response
7
Send ACK
Inter-work UDP/IP message to L2 message
8
Forward IS response
10
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

11
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