Mobile IP Working Group Karim El Malki
INTERNET-DRAFT Hesham Soliman
Expires: May 2002 Ericsson Radio Systems
November 2001
Simultaneous Bindings for Mobile IPv6 Fast Handoffs
<draft-elmalki-mobileip-bicasting-v6-01.txt>
Status of this memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC 2026.
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This document is an individual submission to the IETF.
Abstract
Fast Handover for Mobile IPv6 [1] and Bidirectional Edge Tunnel
Handover [2] describe protocols to minimise the amount of service
disruption when performing layer-3 handoffs. This draft extends the
Fast Handover protocol with a simultaneous bindings function and the
BETH capabilities with a bicasting function to minimise packet loss
at the MN. Traffic for the MN is therefore bicast or n-cast for a
short period to its current location and to one or more locations
where the MN is expected to move to shortly. This removes the timing
ambiguity regarding when to start sending traffic for the MN to its
new point of attachment followng a Fast Handover and allows the
decoupling of layer-2 and layer-3 handoffs. It also saves the MN
periods of service disruption in the case of ping-pong movement.
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TABLE OF CONTENTS
1. Introduction.....................................................2
1.1 Terminology.....................................................3
2. Simultaneous Bindings............................................3
3. Fast Handovers in Mobile IPv6....................................4
4. Bidirectional Edge Tunnel Handover (BETH)........................5
5. Decoupling L3 Handoffs from L2 handoffs using Simultaneous
Bindings ...........................................................6
6. Avoiding service disruption due to ping-pong movement............7
7. Changes to the Fast Handover and BETH Operations.................7
7.1 MN Operation ................................................7
7.1 HA/MAP/AR Operation .........................................8
8. Simultaneous Bindings Flag in Fast Binding Update (F-BU) message.9
9. Simultaneous Bindings suboption for Fast Binding Acknowledgement.9
(F-BA) message......................................................9
10. Multiple copies of packets received at AR......................10
11. Reception of multiple copies in the MN.........................10
12. References.....................................................10
13. Authors' Addresses.............................................11
14. Full Copyright Statement.......................................12
1. Introduction
Fast Handover for Mobile IPv6 [1] and Bidirectional Edge Tunnel
Handover [2] describe protocols to minimise the amount of service
disruption when performing layer-3 handoffs. This draft extends the
Fast Handover protocol with a simultaneous bindings function and the
BETH capabilities with a bicasting function to minimise packet loss
at the MN. Traffic for the MN is therefore bicast or n-cast for a
short period to its current location and to one or more locations
where the MN is expected to move to shortly. This removes the timing
ambiguity regarding when to start sending traffic for the MN to its
new point of attachment followng a Fast Handover and allows the
decoupling of layer-2 and layer-3 handoffs. It also saves the MN
periods of service disruption in the case of ping-pong movement.
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Appendix A contains some calculations illustrating how to achieve
zero service disruption at L3 using [1] or [2] and bicasting.
1.1 Terminology
This section presents a few terms used throughout the document.
oAR _ old Access Router.
nAR - new Access Router.
L2 handoff - Movement of a MN's point of Layer 2 (L2)
connection from one wireless access point to another.
L3 handoff - Movement of a MN between ARs which involves
changing the on-link care-of address at Layer 3 (L3).
L2 trigger - Information from L2 that informs L3 of particular
events before and after L2 handoff. The descriptions of L2
triggers in this document are not specific to any particular
L2, but rather represent generalizations of L2 information
available from a wide variety of L2 protocols.
Bicasting/n-casting - The splitting of a stream of packets
destined for a MN via its current AR (the oAR) into two or
more streams, and the simultaneous transmission of the
streams to oAR and one or more nAR. Bicasting is a technique
used to reduce packet loss during handover.
ping-ponging - Rapid back and forth movement between two
wireless access points due to failure of L2 handoff. Ping-
ponging can occur if radio conditions for both the old and
new access points are about equivalent and less than optimal
for establishing a good, low error L2 connection.
2. Simultaneous Bindings
Simultaneous bindings are built into the Mobile IPv4 protocol [3]. To
enable multiple simultaneous bindings using Mobile IPv4 the MN simply
sends the first normal Registration Request for a care-of address and
then sends other Registration messages for another set of care-of
addresses having the `S' bit set. The receiver of the Registration
Requests (e.g. the HA) will then maintain all these care-of address
bindings for the MN contemporarily rather than only servicing the MN
at the care-of address in its most recent Registration Request (which
would be the case had the `S' bit not been set). This results in
bicasting or n-casting of packets to all the care-of addresses. This
draft extends the Mobile IPv6 protocol [4] with similar functionality
and describes a new Simultaneous Bindings flag for the Fast Binding
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Update in [1]. Although [2] is not based on MN Binding Updates, it is
possible to extend it with the same resulting bicasting capability.
Multiple simultaneous bindings and bicasting can be an important tool
to decouple L3 handoffs from L2 handoffs and to reduce packet loss.
In [1] this mechanism instructs the recipient of the F-BU with the
simultaneous bindings flag to make multiple copies of packets
destined to the MN and send them to multiple MN care-of addresses
before the MN actually moves there. In a similar way for [2] this
mechanism instructs the anchor FA (aFA), after receiving an L2
source-trigger (L2-ST) or target-triggered HRqst message, to make
multiple copies of packets destined to the MN and send them to
multiple MN care-of addresses before the MN actually moves there.
This allows a smoothing of the L3 handoff, meaning that packet loss
is minimised or even eliminated. Simultaneous bindings are also
useful to prevent service disruption due to ping-ponging as described
later.
3. Fast Handovers in Mobile IPv6
The mechanism to obtain fast L3 handoffs for Mobile IPv6 is described
in [1] and illustrated in Figure 1. This mechanism involves the use
of L2 triggers which allow the L3 handoff to be anticipated rather
than being performed after the L2 handoff completion as normal. Fast
Handoffs are required to ensure that the layer 3 (Mobile IP) handoff
delay is minimised, thus also minimising and possibly eliminating the
period of service disruption which normally occurs when a MN moves
between two ARs. This period of service disruption usually occurs due
to the time required by the MN to update its HA after it moves
between ARs. During this time period the MN cannot resume or continue
communications. Following is a short summary of the Fast Handover
mechanism described in [1].
+-----------+ 1a. HI +-----+
| | ---------------->| nAR |
| oAR | 1b. HAck | |
+-----------+ <----------------+-----+
^ | ^
(2a. RtSolPr) | | 2b |
| | Pr | 3. Fast BU (F-BU)
| | RtAdv | 4. Fast BA (F-BACK)
| v v
+------------+
| MN |
+------------+ - - - - - ->
Movement
Figure 1 _ Fast MIPv6 Handover Protocol
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While the MN is connected to its old Access Router (oAR) and is about
to move to a new Access Router (nAR), the Fast Handoffs in Mobile
IPv6 requires:
- the MN to obtain a new care-of address at the nAR while connected
to the oAR the MN to send a BU to its old anchor point (e.g. oAR) to
update its binding cache with the MN's new care-of address.
- the old anchor point (e.g. oAR) to start forwarding packets
destined for the MN to nAR.
The MN or oAR may initiate the Fast Handoff procedure by using
wireless link-layer information or link-layer _triggers_ which inform
that the MN will soon be handed off between two wireless access
points respectively attached to oAR and nAR. If the _trigger_ is
received at the MN, the MN will initiate the layer-3 handoff process
by sending a Proxy Router Solicitation message to oAR. Instead if the
_trigger_ is received at oAR then it will transmit a Proxy Router
Advertisement to the appropriate MN, without the need for
solicitations.
The MN obtains a new care-of address while connected to oAR by means
of router advertisements containing information from the nAR (Proxy
Router Advertisement, PrRtAdv, which may be sent due to a Proxy
Router Solicitation, RtSolPr). The oAR will validate the MN's new
COA by sending a Handoff Initiate (HI) message to the nAR. Based on
the response generated in the Handoff Acknowledge (HAck) message, the
oAR will either generate a tunnel to the MN's new COA (if the address
was valid) or generate a tunnel to the nAR's address (if the address
was already in use on the new subnet). If the address was already in
use on the new subnet, the nAR will generate a host route for the MN
using its old COA. The new COA sent in the HI message is formed by
appending the MN's _current_ interface identifier to the nAR's
prefix. Note that the HI/HAck exchange is decoupled from the handoff
procedure and should be performed in advance so as not to add latency
to the protocol exchange.
4. Bidirectional Edge Tunnel Handover (BETH)
The following figure is taken from [2].
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+------+ HRqst +------+
| oAR |<-------->| nAR |
+------+ HRply +------+
^ ^
old L2 | | new L2
+-------+ +-----+
| |
| |
V V
+------+ movement
| MN | --------->
+------+
Figure 2 - BETH Handover
BETH describes a way to implement fast handoffs without involving
messages from the MN. Upon receipt of L2 triggers, which communicate
the upcoming movement of a MN between two ARs, the oAR will establish
a bidirectional tunnel between itself and the nAR (or viceversa). As
soon as the oAR detects that the MN has disconnected as described in
[2], the oAR will start forwarding traffic it receives for the MN
over to nAR. In the opposite direction the nAR will reverse tunnel
traffic sent by the MN on its new link back to oAR.
5. Decoupling L3 Handoffs from L2 handoffs using Simultaneous Bindings
The mechanisms described in [1] and [2] allow the anticipation of the
layer 3 handoff such that data traffic can be redirected to the MN's
new location before it moves there. However it is not simple to
determine the correct time to start forwarding between oAR and nAR,
which has an impact on how smooth the handoff will be. Packet loss
will occur if this is performed too late or too early with respect to
the time in which the MN detaches from oAR and attaches to nAR. Also,
some measure is needed to support the case in which the MN moves
quickly back-and-forth between ARs (ping-pong).
In many wireless networks it is not possible to know in advance
precisely when a MN will detach from the wireless link to oAR and
attach to the one connected to nAR. Therefore determining the time
when to start forwarding packets between oAR and nAR is not possible.
Certain wireless technologies involve layer-2 messages which instruct
the MN to handoff immediately or simply identify that the MN has
already detached/attached. Even if the ARs could extract this
information, there may not be sufficient time for the oAR to detect
the MN's detachment and start getting packets tunnelled over to nAR
before the MN attached to nAR. This is because wireless layer-2
handoff times are quite small (i.e. range from 10's to 100's ms).
Thus a period of service disruption may occur due to this timing
uncertainty unless further enhancements are made to the handoff
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mechanism. If the L3 handoff is anticipated and the oAR starts
forwarding data to nAR upon receipt of the Fast BU in [1] or upon
receipt of the L2-LD trigger in [2], then the period of service
disruption will be according to the following:
A = L3 handoff anticipation (time difference between the start of the
L3 fast handoff and the moment in which the L2 handoff occurs)
h = L2 handoff time (disconnection time due to L2 handoff)
Approximate period before MN receives packets again = A + h
It is therefore necessary to decouple layer-3 handoff timing from
layer-2 handoff timing. One solution is to bicast or n-cast packets
destined to the MN for a short period from the old anchor point (e.g.
oAR) to one or more potential future MN locations (e.g. nAR/s) before
the MN actually moves there. This means that the handoff procedure
described previously would be enhanced by having the old anchor point
(e.g. oAR) send one copy of packets to the MN's old on-link care-of
address and another copy of the packets to the MN's new care-of
address (or addresses) connected to nAR. The MN is thus able to
receive traffic independently of the exact layer-2 handoff timing
during the handoff period.
6. Avoiding service disruption due to ping-pong movement
It is possible that the layer-2 handoff procedure may fail or
terminate abruptly in wireless systems. Therefore a MN which expects
to move between oAR and nAR may unexpectedly never complete the
layer-2 handoff and find itself connected to oAR. Another undesired
effect is that the MN could ping-pong between ARs due to layer-2
mobility issues. Both these cases would leave the MN unable to resume
communication and have to transmit a new F-BU in [1] or wait for a
new bidirectional tunnel setup in [2] before resuming communications.
This may be solved through the use of simultaneous bindings which
allow the MN to maintain layer-3 connectivity with the oAR during the
affected handoff period, thus smoothing the handoff. This eliminates
the need for continuous transmission of Fast Binding Updates in [1]
or continuous bidirectional tunnel setups in [2]. It also prevents
the period of service disruption from being extended due to the
effect of the above link-layer issues on L3 handoff.
7. Changes to the Fast Handover and BETH Operations
7.1 MN Operation
The MN operation in [1] is affected by the changes introduced by this
document. The addition to [1] is that a MN with an existing active
binding which receives a new router advertisement (PrRtAdv) MUST be
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"eager" to establish new bindings. When a MN has at least one
existing binding and receives a new PrRtAdv it MUST send a Fast
Binding Update (F-BU) with the Simultaneous Bindings flag set (_B_
flag). The new flag is described in section 8. In addition the MN
MUST be able to process the new simultaneous bindings suboption in
the Fast Binding Acknowledgement message described in section 9. The
lifetime field returned in this suboption MUST be used by the MN to
identify the lifetime of the simultaneous binding requested. Two BU
lifetime values will be returned: Bicasting lifetime (in the
simultaneous bindings suboption) and new CoA lifetime (in the BA
option) as described in the following sections. The new CoA lifetime
(placed in the BA option as specified in [4]) runs in parallel with
the Bicasting lifetime. Hence, when the bicasting lifetime ends, the
MN will remove this entry from the Binding Update list and simply
keep one entry for the new CoA with the remaining new CoA lifetime.
7.1 HA/MAP/AR Operation
The HA [4], MAP [5] and AR [1] are the possible recipients of a F-BU
message. Upon receiving a F-BU message having the _B_ flag set (see
section 8), the HA/MAP/oAR MUST create a new binding cache sub-entry
(linked to the original entry for the old CoA) for the MN's new CoA.
This sub-entry contains the same fields as normal binding cache
entries but it MUST not replace any existing entries for the MN. The
new sub-entry will have two lifetimes instead of one: the normal new
CoA BU lifetime (sent in the BA) and a Bicasting lifetime set to
SHORT_BINDING_LIFETIME (sent in the BA sub-option). The new CoA
lifetime runs in parallel with the Bicasting lifetime. Until the
Bicasting lifetime expires, the HA/MAP/oAR MUST send a copy of the
data destined for the MN to the old CoA and to the new CoA/s in the
linked binding cache sub-entry or sub-entries. When the Bicasting
lifetime expires, the MAP/HA/oAR MUST remove the bicasting lifetime
field and replace the old binding cache entry for the old CoA with
the new CoA sub-entry. As a result, the HA/MAP/AR will end up with
one entry for the MN's new CoA with the remaining new CoA lifetime.
In [2] the F-BU messages are not used. When a bidirectional tunnel is
established for the first time (i.e. not renewed) between oAR and
nAR, the oAR MUST maintain two lifetime entries for the tunnel:
normal tunnel lifetime (already described in [2]) and a Bicasting
lifetime set to SHORT_BINDING_LIFETIME. Until the Bicasting lifetime
expires the oAR MUST copy data destined to the MN both to its on-link
CoA and through the tunnel to nFA. When the Bicasting lifetime
expires, the oAR MUST stop bicasting and only forward traffic for the
MN through the tunnel to nFA until the tunnel lifetime itself
expires.
The default value for SHORT_BINDING_LIFETIME is 2s. This parameter
MUST be configurable as it my vary depending on the type of radio
link in the system.
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8. Simultaneous Bindings Flag in Fast Binding Update (F-BU) message
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Option Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Rsv |B|Rsv| Prefix Length | Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Options...
+-+-+-+-+-+-+-+-+-+-+-+-
Description of the flag added to the F-BU option already defined in
[1]:
B When set indicates a request for bicasting all
packets to both COAs of the MN (in the source
address field and the alternate-CoA suboption).
This BU will add another COA to the Binding
Cache.
9. Simultaneous Bindings suboption for Fast Binding Acknowledgement
(F-BA) message
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Sub-Option Type| Sub-Option Len|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| status | Reserved | Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Sub-Option Type TBD
Sub-Option Len
Status Indicates success (0) or failure (128
and above).
Lifetime The bicasting lifetime for the
simultaneous binding requested in the
F-BU.
The alignment requirement for this sub-option is 2n+2.
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10. Multiple copies of packets received at AR
If the MN has simultaneous active bindings with HA/MAP/AR, it could
(but preferably should not) receive multiple copies of the same
traffic directed to it. The use of simultaneous bindings does not
mean that the MN is receiving packets contemporarily from multiple
sources. This depends on the characteristics of the access (L2)
technology. The bicasting of packets involves sending a copy of the
data to the AR which the MN is moving to (the nAR). Until the MN
actually completes the L2 handoff to the nAR and fully establishes
the new L2 link, the nAR MAY receive packets for a MN to which it
does not have a direct link layer connection. If the new AR is aware
that the MN is performing a handover (due to earlier reception of the
HI message) The AR MAY:
- drop all packets for the MN, or
- buffer packets for the MN.
The choice of which action to take may depend on the type of traffic
involved (e.g. real-time or non real-time), but this is outside the
scope of this document. The AR MAY also in parallel attempt to
establish a link-layer connection with the MN. However an AR MUST NOT
send ICMP Destination Unreachable messages if it drops packets or is
unable to deliver the received IP packets due to unavailability of
direct layer connection with the MN. This is because the MN will be
receiving one copy of the packets.
11. Reception of multiple copies in the MN
In some rare scenarios it may be possible that the MN receives more
than one copy of the same packet. Generally the Internet routing
mechanisms can not guarantee a delivery of a single copy of an IP
packet to a node. However some TCP congestion avoidance
implementations are known to react negatively to the reception of 3
duplicate acknowledgements. The algorithm in [6] addresses this
problem. When using [6] bicasting should not cause any negative
performance impacts for TCP.
12. References
[1] G. Dommety (Editor) et al, _Fast Handovers for Mobile IPv6_,
draft-ietf-mobileip-fast-mipv6-02.txt, work in progress, July 2001.
[2] J. Kempf et al., "Bidirectional Edge Tunnel Handover for IPv6",
draft-kempf-beth-ipv6-02, work in progress, September 2001.
[3] C. Perkins (Editor), _IP Mobility Support for IPv4, revised_,
draft-ietf-mobileip-rfc2002-bis-08, work in progress, September 2001.
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[4] D. Johnson and C. Perkins, "Mobility Support in IPv6", draft-
ietf-mobileip-ipv6-14.txt, work in progress, July 2000.
[5] H. Soliman, C. Castelluccia, K. El Malki and L. Bellier,
_Hierarchical MIPv6 mobility management_, draft-ietf-mobileip-hmipv6-
05.txt, work in progress, November 2001.
[6] R. Ludwig, _The Eifel algorithm for TCP_, draft-ietf-tsvwg-tcp-
eifel-alg-01.txt, work in progress, November 2001.
13. Authors' Addresses
The authors may be contacted at the addresses below:
Karim El Malki
Ericsson Radio Systems AB
LM Ericssons Vag. 8
126 25 Stockholm
SWEDEN
Phone: +46 8 7195803
Fax: +46 8 7190170
E-mail: Karim.El-Malki@era.ericsson.se
Hesham Soliman
Ericsson Radio Systems
Torshamnsgatan 23, Kista
Stockholm
SWEDEN
Phone: +46 8 4046619
Fax: +46 8 4043630
E-mail: Hesham.Soliman@era.ericsson.se
The working group can be contacted via the current chairs:
Basavaraj Patil Phil Roberts
Nokia Corporation Megisto Systems Inc.
6000 Connection Drive Suite 120, 20251 Century Blvd
Irving, TX 75039 Germantown MD 20874
USA USA
Phone: +1 972-894-6709 Phone: +1 847-202-9314
EMail: Raj.Patil@nokia.com EMail: proberts@megisto.com
Fax : +1 972-894-5349
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14. Full Copyright Statement
Copyright (C) The Internet Society (2001). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in anyway, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English. The limited permissions granted above are perpetual and will
not be revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided onan
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."
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Appendix A - Timing Calculations for bicasting
Example 1
---------
+--------+
+------| MAP/HA |------+
| +--------+ |
| |
v v
+-----+ +-----+
| oAR | | nAR |
+-----+ +-----+
+-----+
| MN |
+-----+ - - - - - >
Movement
This is the case specified by [1] with the extension of using the MAP
from [5].
A = anticipation time (F-BU is sent from MN at time t-A, where t is
the time when the MN actually hands-off at L2)
h = handoff time (L2 only)
D1 = MN to MAP delay (through oAR)
D2 = MN to MAP delay (through nAR)
p = F-BU and routing table processing time in the MAP and MN
To achieve zero L3 service disruption it is necessary for the time
period between starting the fast handoff and the MN completing the L2
handoff to be greater than or equal to the tiem it take for traffic
to reach the MN at its new link (through nAR). This is represented by
the following formula:
(A+h)>=((D1+D2)+p)
Assuming that p<<(D1+D2) this can be simplified to:
(A+h)>=(D1+D2)
To achieve maximum performance from simultaneous bindings it is
necessary for the above relation to hold.
The Anticipation time (A) is important and needs to be calculated
appropriately for the link-layer being used. Depending on the L2 this
may need engineering to synchronise the L2 and L3 handoffs.
Once the MN has moved to nAR, it will be receiving traffic delayed by
(D2-D1) with respect to when it was attached to oAR. To smooth this
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delay variation (jitter), which may be a problem for real-time
services, it may be necessary to implement a smoothing buffer at nAR.
Example 2
---------
+-----+ +-----+
| oAR | -------------->| nAR |
+-----+ +-----+
|
|
|
v
+-----+
| MN |
+-----+ - - - - - >
Movement
When the MAP/HA/oAR are one entity (as considered in [1]), the
following calculations apply.
A = anticipation time (F-BU is sent from MN at time t-A, where t is
the time when the MN actually hands-off at L2)
h = handoff time (L2 only)
d = MN to AR delay (assume constant as MN moves ARs)
L = oAR to nAR delay
As previously, the following must be true for the simultaneous
bindings to yield zero L3 disruption:
(A+h)>=(d+L+d)
=> (A+h)>=(2d+L)
The Anticipation time (A) is important and needs to be calculated
appropriately for the link-layer being used. Depending on the L2 this
may need engineering to synchronise the L2 and L3 handoffs.
Once the MN has moved to nAR, it will be receiving traffic delayed by
an amount L with respect to when it was attached to oAR. To smooth
this delay variation (jitter), which may be a problem for real-time
services, it may be necessary to implement a smoothing buffer at nAR.
Example 3
---------
In [2], a similar calculation applies as that in Example 2 but there
is no need for the MN-AR communication. Therefore the following
formula must be true to achieve zero service disruption at L3:
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(A+h)>=(L+d)
The Anticipation time (A) is important and needs to be calculated
appropriately for the link-layer being used.
Once the MN has moved to nAR, it will be receiving traffic delayed by
an amount L with respect to when it was attached to oAR. To smooth
this delay variation (jitter), which may be a problem for real-time
services, it may be necessary to implement a smoothing buffer at nAR.
El Malki and Soliman [Page 15]