Introduction to l3 movement detection and l3 link identifier
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Introduction to L3 Movement Detection and L3 Link Identifier. Xiaoyu Liu [email protected] 2004-05-07. Contents. Background Link ID in L3 Movement Detection Concept of “L2 Link” and “L3 Link” L3 Movement Detection (MD) Problems and Approaches of L3 MD

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Introduction to L3 Movement Detection and L3 Link Identifier

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Introduction to l3 movement detection and l3 link identifier

Introduction to L3 Movement Detection and L3 Link Identifier

Xiaoyu Liu

[email protected]

2004-05-07


Contents

Contents

  • Background

  • Link ID in L3 Movement Detection

    • Concept of “L2 Link” and “L3 Link”

    • L3 Movement Detection (MD)

    • Problems and Approaches of L3 MD

    • Link Identifier (Link ID) for “L3 Link”

    • Faster L3 MD

    • A Possible Solution

  • Final Remarks and Suggestions


Background 1

Background (1)

  • Link ID

    • “MIPv6: from hindsight to foresight?”, by Erik Nordmark, IETF mobileip WG

      draft-nordmark-mobileip-mipv6-hindsight-00.txt

    • “Router Advertisement Link Identification for Mobile IPv6 Movement Detection” by Brett Pentland et al, IETF mobileip WG

      draft-pentland-mobileip-linkid-00.txt

  • ARID

    • “Awareness of the handover to be distinguished from a L2 or L3”, by Soohong Park, IEEE 802.21 WG


Background 2

Background (2)

  • Key Point of Discussions in 802.21 Mailing List

    • Extension of L2 Management Frames to carry L3 Info

      • 802.11 Beacon

      • 802.16e NBR_ADV neighbor list

    • Possible Venues

      • 802.11r / 802.11 WIEN

      • 802.16e

      • 802.21

    • Potential Issues

      • Channel Utilization, etc.

  • Objective:

    • Reduce the L3 handover latency

    • Reduce the redundant message exchanges


Example scenario w multiple ar prefix

Example Scenario w/ Multiple AR & Prefix

  • Multiple AR, i.e. AR2/AR3 for redundancy or load balance

  • Each AR advertises different prefix


Concept of l2 link

AR1

AR2

AR3

AP1

AP2

AP3

Concept of “L2 Link”

“L2 Link” is Attachment Point to wireless/wired networks

Changes of “L2 Link” will result in a L2 handover

Three “L2 Links” (radio link ) in the shown example scenario

Internet

A::

B::

C::

“L2 Link” 1

“L2 Link” 2

“L2 Link” 3


Concept of l3 link

AR1

AR2

AR3

AP1

AP2

AP3

Concept of “L3 Link”

Changes of “L3 Link” will result in a L3 handover

STA changes its attachment from AP1 to AP2 and its IP address needs to change, i.e., “L3 link” changes.

STA changes its attachment from AP2 to AP3 but its IP address does not need to change, i.e. still remains at the same L3 link.

Only two “L3 Links” in the shown scenario.

Internet

A::

B::

C::

“L3 Link” 2

“L3 Link” 1

* L3 Link:

a communication facility or medium over which nodes can communicate at the link layer

Note: Assignment of ARID should take this scenario into consideration.


L3 movement detection

Internet

AR1

STA

AP1

AP2

L3 Movement Detection

  • STA is attached to AR1 via AP1.

  • STA changes its network attachment point to AP2, a new “L2 link” has been established.

    • STA should receive a hint that “L3 link” change may have occurred.

  • STA may or may not have a valid IP configuration (a default router and global IP address).

  • STA should validate its IP configuration; If not valid, STA initiates a new IP configuration immediately.

?


Two problems of l3 movement detection

Two Problems of L3 Movement Detection

  • How to Represent a L3 Movement Event?

    • Identifier or signal to indicate whether or not the IP address needs to change after the STA moves

  • How to Reduce the L3 Movement Detection Latency

    • Long latency: Roughly 3 secs for NUD

    • Random latency: RS/RA exchange


Approaches of l3 movement detection

Approaches of L3 Movement Detection

  • Representation a L3 movement

    • Link ID (Link Identifier)

  • Faster L3 Movement Detection

    • L3 MD info carried in L2 management frame

    • L3 MD info cached in L2 Attachment Points


L3 link identifier link id

L3 Link Identifier (Link ID)

  • An Identifier to Represent a “L3 Link”

    • Upon the receipt of a Link ID, a STA can determine whether a L3 link changes or not. Hence it can determine whether its IP address should be changed/re-configured or not.

    • Assumed to be carried in an RA; Might also be carried in an L2 frames such as beacons (e.g. ARID)

  • A Generic Notion with specific Implementations

    • Location Indication Option (Erik Nordmark)

    • Link ID Message (Brett Pentland et al)

  • All Routers on the same “L3 link” Advertise the same Link ID

    • Discovery procedure to guarantee the uniqueness of Link ID in the same “L3 Link”

    • Potential issues of Prefix and ARID to represent a “L3 Link”


Fast l3 movement detection

Fast L3 Movement Detection

  • L3 MD info Carried in extended L2 Management Frame

    • Reserved bits limit the length of the L3 MD info

      • ARID: 8 bits (sufficient?)

      • Link ID message: 32 bits or 128 bits (Proposals in IETF)

    • Performance issues, e.g. impacts on channel utilization

    • L2 & L3 handover procedures interleaved

  • L3 MD info Cached in Network Attachment Points

    • Get L3 MD info upon the L2 connection set up (Fast Router Discovery)

    • No channel utilization problem, but with slightly longer delay compared with above approach

    • Separate L2 & L3 H/O; Compatible with today’s paradigm

    • Might be used as a recommended practice


A possible solution

Internet

RA

RA

LinkID

LinkID

AR

AP

A Possible Solution

0. An AP caches an RA with a Link ID.

1. STA establishes a new “L2 link” association with AP.

2. After a new “L2 link” is connected, the AP immediately sends STA a cached RA with a Link ID.

3. STA receives a RA with a Link ID.

4. STA checks “L3 link” change using the received Link ID.

5. In case of “L3 link” change, STA initiates a new IP configuration.

Reduce the redundant message exchanges and random L3 MD delay; Solve the problems of the extension of L2 frames to include L3 MD info.

STA


Final remarks

Final Remarks

  • Two technical Issues for L3 MD

    • Problem1: How to identify a L3 movement event

    • Problem2: How to reduce the L3 Movement Detection Latency

  • Suggestions for 802.21 WG regarding above Technical Issues

    • Problem1

      • Collaborate with IETF DNA WG to refine the Link ID schemes (proposals in IETF and ARID in IEEE)

    • Problem2

      • Appendix in 802.21 standard to address the guideline for fast L3 Movement Detection

      • Specific schemes to carry L3 MD info should be discussed in other WG respectively, e.g., 802.11/802.16e

  • Comments?


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