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

Transport of Media Independent Handover Messages Over IP

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

Cellular Network

WLAN Network

WiMAX Network

Internet

Mobility Manager #1

Cellular BS

WLANAP

WiMAX BS

Mobile Node

Mobility

MN contains MIH application & multiple access technologies

An MIH application enabled node that supports and/or

manages MNs for seamless HO

Mobility Manager #N

MIH Proxy

Contains MIH Proxy Function

Signaling over IP

Signaling over IP

L2 Signaling

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)

WLAN Cellular

IP

UDP

MIH App. Other App.New Port

Number

WLAN Interface 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)

MessageContent

Associated Retransmission

Timer

Example Value

Notes

ISInformation Timer

(T1) 1000 msT1 > T2

Least timeSensitive

ESEventTimer(T2)

500 ms T3 < T2 < T1

CSCommand

Timer(T3)

100 msT3 < T2

Most timesensitive

MIH Signaling Example 1: Directly Over UDP/IP

Mobile Node Cellular WLAN Mobility Manager

Power up: connect to WLAN

Send a request for IS (e.g. NL) and set application timer T1

ACK not receivedtimeout after T1

Retransmit request for IS and re-set application timer T1

Send IS response (with piggy backed ACK) and set application timer T1

Send ACK

Send ‘Link Up’ ES to inform about HO completion (no ACK required)

Session continues over cellular

1

2

34

5

6

7

MN then decides to move to cellular

(based on radio conditions)

Obtain Neighbor List

MIH Signaling Example 1: Via WLAN MIH Proxy

Mobile Node CellularWLAN (Proxy) Mobility Manager

Power up: connect to WLAN

Send a request for IS (e.g. NL) Inter-work L2 message

to UDP/IP message

1

2

3

4567

ObtainNeighbor List

Forward IS requestACK not receivedtimeout after T1

Retransmit IS request

Send ACK

Send IS response

Send ACK

Inter-work UDP/IPmessage to L2 message

Forward IS response 8

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