Internet DRAFT - draft-ahn-manet-multigateway
draft-ahn-manet-multigateway
MANET Working Group Sanghyun Ahn
INTERNET-DRAFT Youngmin Kim
Expired: April 2006 University of Seoul
Yujin Lim
University of Suwon
Jaehwoon Lee
Dongguk University
October 2005
Load Balancing in MANET with Multiple Internet Gateways
draft-ahn-manet-multigateway-00.txt
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Copyright (C) The Internet Society (2005).
Abstract
In MANET, nodes wishing to communicate with nodes in the wired
Internet, the global Internet connectivity is required and this
functionality can be achieved with the help of the Internet gateway
(IGW). For the support of reliability and flexibility, multiple IGWs
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can be provisioned for a MANET. In this case, load-balancing becomes
one of the important issues since the network performance such as
the network throughput can be improved if the load of the IGW is
well-balanced. In this draft, we categorize the load-balancing
mechanisms for the IPv6-based MANET with multiple IGWs and define
a new load-balancing metric computed from the hop distance and
the number of routing table entries.
Table of Contents:
1. Introduction...................................................3
2. Terminology....................................................3
3. Categorization of Load Balancing Mechanisms....................4
3.1 SMN........................................................4
3.2 SIGW.......................................................5
4. Message Format.................................................5
4.1 Message Format for SMN.....................................5
4.2 Message Format for SIGW....................................6
5. Security Considerations........................................8
References........................................................9
Author's Addresses................................................9
Intellectual Property Statement..................................10
Disclaimer of validity...........................................10
Copyright Statement..............................................10
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1. Introduction
The Internet gateway (IGW) in an access network can provide the
global Internet connectivity for nodes in a MANET. The IGW belongs
to both the wired Internet and the MANET and connects them. For the
support of reliability and flexibility, multiple IGWs can be
provisioned for a MANET.
It is important for MNs to discover available IGWs for the Internet
connectivity. There are two major approaches, reactive and
proactive [1]:
- Reactive discovery
A MN broadcasts a message which solicits the information on IGWs
for the global connection within the MANET. IGWs receiving the
message reply the MN with there IP prefix addresses.
- Proactive discovery
Each IGW periodically broadcasts its service and IP prefix
information within the MANET. A MN receiving the message decides
an IGW to connect to the Internet.
These two approaches can be combined into a hybrid gateway discovery
scheme [2].
Load-balancing is one of the important issues when MNs access the
Internet via multiple gateways. The network performance can be
improved if the load is balanced well among the gateways.
In this draft, Internet gateway discovery mechanisms to improve the
network throughput with balancing the load among multiple IGWs are
categorized for the IPv7-based MANET, and a new metric to select
an IGW and modified/new message formats for this metric are defined.
2. Terminology
In this draft, we use the terms defined in [1], except for the term
described below.
IGW signaling message
A message to announce the IPv6 address of an IGW's wired
interface and the IGW load information to other IGWs
via the wired Internet.
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3. Categorization of Load-Balancing Mechanisms
We assume that a MANET has fixed multiple gateways for the Internet
connectivity and mobile nodes move within a limited area. The basic
IGW operation for the global connectivity is adopted from [1].
Load-balancing mechanisms for multiple gateways are categorized as
shown in table 1. The factors considered for the categorization are
the chooser of the IGW for the Internet connectivity (the chooser
can be a MN or an IGW) and whether the flooding of a control message
is limited or not (i.e., the expanding ring search or the
maximum TTL flooding). The expanding ring search scheme selects
the locally optimal IGW among nearby IGWs and, on the other hand,
the maximum TTL flooding scheme selects the globally optimal IGW
among all IGWs.
Table 1. Categories of load-balancing mechanisms
+-----------------------+-------------------+-------------------+
| + Selection of an IGW | Selected by a MN | Selected by a IGW |
| +---------------+ | | |
| Flooding Scheme + | (SMN) | (SIGW) |
+-----------------------+-------------------+-------------------+
| Expanding Ring Search | SMN-ERS | SIGW-ERS |
| (ERS) | | |
+-----------------------+-------------------+-------------------+
| Maximum TTL Flooding | SMN-MTF | SIGW-MTF |
| (MTF) | | |
+-----------------------+-------------------+-------------------+
3.1 SMN
In order to provide a MN with the load-balancing information which
can be used for the optimal IGW selection, additional information is
included in the IGW advertisement. The IGW advertisement may be
disseminated proactively or reactively.
A MN may receive more than one advertisement during a certain period
(TIMER_MN). The MN selects the IGW with the minimum value of IGW_i^c
computed according to equation 1. When two or more IGWs have the same
value, the first received advertisement is chosen. Let i_in_G be any
IGW. IGW_i^c is defined as:
IGW_i^c = k*H + R, i_in_G (1)
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where H is the hop distance between the IGW and the MN and k is the
weighting factor. R is defined as the number of valid routing table
entries. Under the low-load condition, H dominates IGW_i^c. When
traffic is concentrated on a certain IGW, R gets increased and
becomes the dominating part of IGW_i^c. Thus, the MN newly accessing
the Internet selects the IGW with light load so that the traffic
load can be distributed among IGWs.
3.2 SIGW
In this mechanism, all IGWs in a MANET share the IGW_i^c
information, and the only IGW with the minimum value can send an
IGW advertisement message. To compute IGW_i^c, each IGW should
receive the IGW solicitation message with the hop count information
from the soliciting MN.
The IGW calculates IGW_i^c based on the number of its routing table
entries and the hop count from the IGW solicitation, and shares the
calculated information with other IGWs over the wired Internet.
To share the information, the IGW can multicast using the
ALL_MANET_GW_MULTICAST address [1] or other dedicated multicast
address, or can unicast to each IGW in the same MANET.
4. Message Format
4.1 Message Format for SMN
Figure 1 shows the modified prefix information option of the IGW
advertisement for the inclusion of the information needed for the
defined load-balancing metric [1, 3].
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Prefix Length |L|A|M|H| Resv. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Valid Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| Preferred Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| Hop Count |# of Rout. Ent.| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| |
+- -+
| |
+- Prefix -+
| |
+- -+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Modified prefix information option of the IGW
advertisement message
M: A flag bit to indicate that the Hop Count and the Number of
Routing Entry field are valid.
H: A flag bit to indicate that the Hop Count field needs to be
increased by one whenever the message is processed by each
intermediate MN on the path toward the MN.
Hop Count: The number of hops from the IGW to a MN.
No. of Routing Entry: The number of routing table entries that
the IGW is currently maintaining.
As explained previously, an IGW advertisement is sent out
periodically or as a response to an IGW solicitation. In the case of
a response to the solicitation, the Hop Count field has the number
of hops that the IGW solicitation message has been forwarded.
In the case of the periodic advertisement, the field is increased by
one by each intermediate MN.
4.2 Message Format for SIGW
Figure 2 shows the modified IGW solicitation message format for the
inclusion of the hop count information.
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|M|H| Reserved | Hop Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++++++++++++++++++++++++++++++++|
| |
. .
. Options .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Modified format of the IGW solicitation message
H: A flag bit to indicate that the Hop Count field is valid and
the Hop Count needs be increased by one whenever the message
is processed by each intermediate MN on the path towards the
IGW.
Hop Count: The number of hops from the soliciting MN to the IGW.
Figure 3 shows the format of the IGW signaling message defined to
share IGW_i^c among all IGWs. By exchanging this message, each IGW
can know the wireless and the wired interface address of other IGWs
in the same MANET.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Hop Count |# of Rout. Ent.| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++++++++++++++++++++++++++++++++|
| |
+- -+
| |
+- IPv6 Address -+
| |
+- -+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Format of the IGW signaling message
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Type: A value to identify the type of the IGW signaling message.
Type = 1 means that this message is for the distribution of
the IGW address to other IGWs. Type = 2 means that this
message has the information on the hop count and the number
of routing table entries of the IGW. Type = 3 means that the
IGW has already sent out an IGW advertisement to the
soliciting MN.
Hop Count: The number of hops from the IGW to a MN.
No. of Routing Entry: The number of routing table entries that
the IGW is currently maintaining.
IPv6 Address: For Type = 1, the IPv6 address of the IGW's wired
network and, for Type = 2 or 3, the IPv6 address of the
soliciting MN.
Using the type-1 message (with Type = 1), each IGW disseminates its
address to other IGWs. The source and the destination address of the
type-1 IGW signaling message are the IPv6 address of the IGW's
wireless network interface and the ALL_MANET_GW_MULTICAST address,
respectively.
Once an IGW receives an IGW solicitation message, the IGW sends to
the wired Internet a type-2 IGW signaling message with setting valid
values in the Hop count and the Number of Routing Entry field.
After receiving an IGW solicitation, the IGW waits for the IGW
signaling messages from other IGWS for a certain period (TIMER_IGW).
After the certain period, if its IGW_i^c is smaller than the
received IGW_i^cs, the IGW sends an IGW advertisement to the
soliciting MN. Otherwise, the IGW drops the solicitation without
sending an IGW advertisement. If no IGW signaling message is
received during the period, the IGW sends an advertisement to the
soliciting MN.
When the IGW sends the IGW advertisement to the soliciting MN,
it also sends a type-3 message to all IGWs through the Internet.
The IGW receiving the type-3 message just drops the solicitation
message. If the soliciting MN receives more than one advertisement,
it selects the first one received.
The type-2 or type-3 IGW signaling message are sent through the
wired Internet to the IGWs in the same MANET using some kind of
wired Internet multicast mechanism or unicast. And this is out of
the scope of this draft.
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5. Security Considerations
There are no security considerations in this draft.
References
[1] R. Wakikawa, J. T. Malinen, C. E. Perkins, A. Nilsson and
A. J. Tuominen, "Global connectivity for IPv6 mobile ad hoc
networks", draft-wakikawa-manet-globalv6-04.txt, work in progress.
[2] P. Ratanchandani and R. Kravets, "A hybrid approach to
internet connectivity for mobile ad hoc networks", WCNC 2003,
pp. 1522-1527, March 2003.
[3] T. Narten, E. Nordmark and W. Simpson, "Neighbor Discovery
for IP Version 6 (ipv6)", RFC 2461.
Authors' Addresses
Sanghyun Ahn
University of Seoul
90, Cheonnong-dong, Tongdaemun-gu
Seoul 130-743, KOREA
Email: ahn@venus.uos.ac.kr
Youngmin Kim
University of Seoul
90, Cheonnong-dong, Tongdaemun-gu
Seoul 130-743, KOREA
Email: blhole@venus.uos.ac.kr
Yujin Lim
University of Suwon
San 2-2, Wawoo-ri, Bongdam-eup, Hwaseong-si
Kyeongi-do 445-743, Korea
Email: yujin@suwon.ac.kr
Jaehwoon Lee
Dongguk University
26, 3-ga Pil-dong, Chung-gu
Seoul 100-715, KOREA
Email: jaehwoon@dongguk.edu
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