mobile ip and mpls

7/23/2019 Mobile IP and MPLS

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Integration of Mobile IP and Multi-Protocol Label Switching

Zhong Ren Chen-Khong Tham Chun-Choong Foo Chi-Chung Ko

Department of Electrical and Computer Engineering

National University of Singapore

10 Kent Ridge Crescent, Singapore 119260

Tel: (65) 874 5095, Fax: (65) 779 1103

E-mail: engp9021, eletck, engp7643, [email protected]

Abstract —Multi-Protocol Label Switching is a technology that combines

the simplicity of IP routing with the high-speed switching of ATM. Mobile

IP is a protocol that allows users to move around and yet maintain continu-

ousIP network connectivity. In thispaper, we propose a schemeto integrate

the Mobile IP and MPLS protocols. The integration improves the scalabil-

ity of the Mobile IP data forwarding process by leveraging on the features

of MPLS which are fast switching, small state maintenance and high scal-

ability. In addition, we have removed the need for IP-in-IP tunneling from

HA to FA under this scheme. This paper covers some issues regarding Mo-

bile IP scalability and also defines the signaling and control mechanisms

required to integrate MPLS and Mobile IP.

Keywords—Multi-protocol Label Switching (MPLS),

Label Distribution Protocol (LDP), Mobile IP (MIP)

I. INTRODUCTION

MPLS is a packet forwarding scheme. Since labels have only

local significance between two adjacent LSRs on a route, MPLS

has high scalability. Mobile IP is designed to support mobile

computing over the Internet.

Currently there are proposals to incorporate IP-based tech-

nologies into the core networks of future wireless cellular sys-

tems such as Universal Mobile Telecommunications System

(UMTS) [1], Iceberg Project [2] and Cellular IP [3]. Mobile IP

could potentially provide host mobility solution in these future

networks. Since the number of users and terminals connected to

these future systems would be very large, the scalability of the

Mobile IP solution is of great concern and interest. There have

also been work in integrating ATM as the transport provider into

these core networks [4]. Since MPLS and ATM are very closely

related, it would be desirable to incorporate MPLS into these

core networks too.

In this paper, we propose a scheme to integrate the Mobile

IP and MPLS protocols. The integration improves the scalabil-

ity of the Mobile IP data forwarding process. Our work here

paves the way for the incorporation of both the Mobile IP and

MPLS protocols into these future IP-based core networks, and

also provide mobility support for MPLS.

The organization of the rest of the article is as follows. Sec-

tion II briefly presents the basics of MPLS. Section III gives a

short introduction to the Mobile IP basic operation scheme. Sec-

tion IV presents the potential scalability problem of Mobile IP.In Section V, we present our solution to integrate MPLS into

Mobile IP in details. Evaluation results are presented in Section

VI. Finally, our conclusion is presented in Section VII.

II. MULTI-PROTOCOL LABEL SWITCHING

MPLS is a technology that integrates the label-swapping

paradigm with network-layer routing [5]. Each MPLS packet

Shim

header

e.g.IPv6

e.g.

ATM

L2 Header Label

L3 Header

Label COS S TTL

20 3 1 8

L2 Header

Label / IPHeader L3 Data

Label/ L2

Header

L3 Data

Figure 1. Label Encoding

1

18 .181.0 .31 D a ta

2

0

1

1

18 .181.0 .31 D a ta

MPLS

Backbone

0

. .. . .. .. . . .. . ..

9 18.181 0 -

In

Lbl

Address

Prefix

Out

Port

Out

Lbl

7 1 28.197 1 -

Out

Port

Out

Lbl

0 7

... ...

1 6

In

Lbl

3

In

Port

2

...

5

...

2

0 942

In

Lbl

Address

Prefix

Out

port

Out

Lbl

- 128.197 1 3

- 164.67 1 5

- ...... 1 ...

- 18.181 1 4

LSR1 LSR2

LSR4

LSR3

0

18 .181.0 .31 D a ta9

18 .181.0 .31 D a ta4

...

1

In

Port

1

Figure 2. MPLS Operation Procedure

has a label. Depending on different Layer 2 and Layer 3 tech-

nologies involved, different label encoding schemes can be used.

They are illustrated in Figure 1.

Label swapping is done by associating labels with routes and

using the label value in the packet forwarding process. Packets

are classified and routed at the ingress Label Switching Routers

(LSRs) of an MPLS-capable domain. The mapping between IP

packets and a Label Switched Path (LSP) is done by providing

a Forwarding Equivalence Class (FEC) specification for each

LSP. MPLS labels are then inserted. When an LSR receives a

labeled packet, it will use the label as an index to look up the

forwarding table. This is faster than the process of parsing the

routing table and search for the longest match done in IP rout-

ing. The packet is processed as specified by the forwarding tableentry. The incoming label is replaced by the outgoing label, and

the packet is switched to the next LSR. Before a packet leaves

an MPLS domain, its MPLS label is removed. The MPLS oper-

ation procedure in a sample network is shown in Figure 2.

MPLS uses the Label Distribution Protocol (LDP) [6] to dis-

tribute the labels and set up LSPs. LSP setup can be traffic,

request or topology-driven. In the case of a topology-driven

scheme the labels are pre-assigned according to existing rout-

ing protocol information.

III. MOBILE IP

Mobile IP is a protocol to support mobile computing over the

Internet. A Mobile IP scheme has been adopted by the IETF for

standardization in IP version 4 (IPv4) [7]. A Mobile Node (MN)

is identified by the IP address it has when it is in its home net-

work, called its home address. When a MN movesaway from its

home network to a foreign network, it obtains a temporary Care-

Of-Address (COA) from the Foreign Agent (FA) in the foreign

network. The MN registers with a Home Agent (HA), which is

typically a router, in its home network, informing the latter of

its COA. Any Correspondent Node (CN) wishing to communi-



1

2 3

4

Home Agent Foreign AgentGlobal

Interne

t

Mobile

Node

IP Host

Figure 3. Mobile IP DatagramFlow

1 3 1

2

2 1

2

3

13 1 2CN1

LSR1

1

LSR2

LSR3

LSR4

FA

HA

MN

MN

MPLS

Network

Figure 4. Sample Architecture

cate with the MN need not be aware that the MN has moved; it

simply sends IP packets addressed to the MN’s home address.

These packets are routed via normal IP routing to the MN’s

home network, where they are intercepted by the HA. The latter

encapsulates each such packet in another IP packet which con-

tains the MN’s COA as destination address. Thus these packets

are delivered to the MN’s new location by a tunneling process.

Figure 3 illustrates the routing of datagram to and from a MN

away from home.

IV. MOBILE IP SCALABILITY ISSUES

The operation of Mobile IP involves three different activities,

which are the agent advertisement process, the registration pro-cess and the data forwarding process. It is crucial that these three

different activities operate efficiently in order for the Mobile IP

protocol to be scalable to systems consisting of huge numbers

of mobile hosts.

The data forwarding process of a Mobile IP HA works as fol-

lows. For every IP packet that the HA receives, it needs to check

if the destination IP address of the packet matches any MNs that

are currently registered in a foreign network. If yes, the HA will

perform IP tunneling of the packet by adding an IP header to

the packet and then sending it out to the routing process for for-

warding. If no match is found, the HA just sends the packet out

to the routing process for forwarding.

The amount of processing required by the HA in this forward-

ing process depends on the number of MNs belonging to thehome network that are currently registered in a foreign network.

If there are many such kind of MNs, the forwarding process will

take very long. Considering that every packet forwarded by the

HA has to undergo this forwarding process, the overhead of this

packet forwarding process may be too high even after optimiza-

tion through the use of appropriate data structures and lookup

algorithms [8]. This poses a scalability concern that affects the

use of the Mobile IP protocol in future wireless mobile systems.

V. MPLS AN D MOBILE IP

In this section we will present our solution to integrate both

MPLS and Mobile IP in details.

A. Single MPLS Domain

A.1 Architecture

As shown in Figure 4, HA and FA are edge LSRs and belong

to the same MPLS domain. They support both MPLS and Mo-

bile IP functionality. We assume that the MN home address is

a.b.c.d and the HA address is a.b.c.e. In addition, we assume

that FA COA is w.x.y.z.

MN FA HAMIP agent

advertisement

MIP registrationrequest

MIP registrationrequest

LSP Setup

MIP registrationreplyMIP registration

reply

Modify Label

Table

Modify Routing

Table

Figure 5. Registration Procedure

MN FA HACN

Datagram

Datagram

Datagram

Looks Up

Label Table

Looks Up

Label Table

Looks Up

Routing Table

Figure 6. Datagram Delivery

A.2 Registration Procedure

1. MN determines whether it is at home when it receives agent

advertisement messages broadcast by the mobility agents.

2. If the MN is in a foreign network, it acquires a temporary

COA from FA and sends registration request to FA.

3. Since FA is an edge LSR, it will analyze the incoming regis-

tration request message and get the destination address of it.

4. Then FA updates its routing table and adds a host specific

row with the value of MN home address. In addition, it sets the

outgoing port value of this entry to be the incoming port number

from which it received the registration request.

5. Based on the IP routing table, FA forwards the registration

request message toward HA.

6. The packet is forwarded to HA hop-by-hop using IP routing.

7. When HA gets the registration request message and learns

the COA, it searches its label table to find the row with the MN

home address as FEC. The second row in Table I is that one.

8. Then, it will send a label request using LDP to FA with the

COA as FEC. FA replies with an LDP label mapping message to

HA. When this label mapping message arrives at HA, the LSP

would have been established (the first row in Table I is created

by LDP). In the case of the topology-driven scheme, the besteffort LSPs from FA to HA and from HA to FA would have

already been established using conventional IP routing. So, for

best effort traffic, we can use that best effort LSP in order to

reduce the registration time.

9. HA changes the row in its label table that uses the MN home

address as FEC. It sets the empty out label and outgoing port

entries to the values of out label and outgoing port of the LSP

from HA to FA. In this way, HA can relay the packets destined to

MN home address to its current location in the foreign network.

10. After that, HA sends a registration reply to FA along the

LSP from HA to FA.

11. When FA receives the registration reply, it records the in-

coming port number and in label value of the reply message.

Then it adds a new row in its label table. Table ?? illustrates theexample label table of FA after receiving the registration reply.

Figure 5 illustrates the procedure of Mobile IP registration.

Table I is an example label table of HA after registration. The

out label value and outgoing port number of LSP from HA to

FA are 5 and 1 respectively. The first row of Table I is the label

binding for the LSP from HA to FA. Since HA is the ingress

LSR, the in label value entry is empty. The second row is the la-



bel binding for the LSP from CN to MN. Since HA is the egress

LSR of this LSP, originally the outgoing port and out label en-

tries are both empty. But HA has set these two entries to the

values of out label and outgoing port of the LSP from HA to FA

after receiving registration request.

TABLE I

EXAMPLE LABEL TABLE OF HA AFTER REGISTRATION

Incoming In FEC Outgoing OutPort Label Port Label

2 - w.x.y.z 1 51 9 a.b.c.d 1 5

... ... ... ... ...

A.3 Datagram Delivery

1. Packets from a CN to the MN are addressed to the MN home

address and intercepted by the HA.

2. HA uses the incoming label value as an index to look up its

label table. According to Table I, HA inserts the label value in

the second row of the label table into packet and sends it out

through the port indicated in the same row. If MN is still in the

home network, out label and outgoing port entries are empty.The packet will be sent to the IP layer and sent out based on the

corresponding routing table entry to MN.

3. The packet is delivered from HA to FA along the LSP by

label swapping.

4. FA receives the packet and looks up its label table. Since it is

the egress of the LSP from HA to FA, the out label and outgoing

port entries are empty. FA strips off the label and sends the

packet to the IP layer.

5. Finally, FA forwards the packet to MN based on the informa-

tion in the newly-added host specific row of the routing table.

6. MN receives the packet sent by CN.

Figure 6 illustrates the procedure of Mobile IP registration.

As noted above, integrating MPLS and Mobile IP makes IP-

in-IP tunneling unnecessary in the data forwarding process. In-stead we use MPLS to switch the packet to the foreign network.

Switching is much faster than conventional IP forwarding. The

whole forwarding process is done at the MPLS layer and HA

doesn’t need to involve the IP layer. This improves the scalabil-

ity of the Mobile IP protocol. In addition, since label header is

much smaller than IPheader, the traffic overhead from HA to FA

is also reduced. Moreover, with Constraint-Based Label Distri-

bution Protocol (CR-LDP) [9] we can setup an LSP satisfying

the QoS requirements of the traffic and do traffic engineering

[10].

A.4 Multiple Foreign Agents

In this section, we will discuss the registration and data deliv-

ery schemes for MN movement from one FA to another FA. We

assume that the new FA COA is a.s.d.f .

Once the MN moves to a new FA:

1. The registration procedure described in the previous section

is repeated once between the HA and new FA.

2. After registration, the third row in Table II is new: it is the

label binding for the LSP from HA to new FA. The outgoing

port number and out label value in the second row are changed

13 1

2

2 1

2

3

13 1 2CN1

LSR1

1

LSR2

LSR3

LSR4

Old FA

HA

MN

MNMPLS

Network

NewFA

2

1 2

2MN

Figure 7. Multiple FA Sample Ar-chitecture

13 1

2

2 1

2

3

13 1 2CN1

LSR1

1

LSR2

LSR3

LSR4

FA

HA

MN

MNMPLS

Network

CN3

CN2

LSR6

LSR5

12

2

1 2

2

Figure 8. Multiple CN Sample Ar-chitecture

to the corresponding values of the third one so that the packets

destined to MN home address can be relayed to the new foreign

network. At the New FA, it adds a host specific row with the

value of MN home address in its routing table.

TABLE II

EXAMPLE LABEL TABLE OF HA AFTER MN M OVES TO A NEW FOREIGN

NETWORK


2 - w.x.y.z 1 5

1 9 a.b.c.d 1 6

2 - a.s.d.f 1 6... ... ... ... ...

3. The datagram delivery procedure described in the previous

section is repeated once between the HA and new FA.

4. Finally MN receives the packet sent by CN.

A.5 Mobile Node Homing

In this section we will discuss the registration and data deliv-

ery schemes for MN movement from the foreign network back

to its home network:

1. MN finds it is back to home network after receiving agent

advertisement messages broadcast by its home agent.

2. It sends a deregistration request message to the home agentwith registration lifetime field equal to zero. The COA in this

message is the COA of the HA.

3. HA deletes the out label value and outgoing port number

from the second row of its label table that are added during the

last registration with the FA. As illustrated in Table III, these

two entries are left empty.

4. When packets destined to MN home address arrive at HA, it

strips off the label and sends the packets to the IP layer.

5. Then it searches the IP routing table. The packets are sent

out to MN based directly on the information in the routing table.

6. MN receives the packet sent by CN.

TABLE III

EXAMPLE LABEL TABLE OF HA AFTER MN MOVES BACK TO HOME

NETWORK


2 - w.x.y.z 1 51 9 a.b.c.d - -

... ... ... ... ...



A.6 Multiple Correspondent Nodes

If there are multiple CNs communicating with MN, once the

MN moves to a foreign network, all traffic from those CNs need

to be relayed to the current location of MN. In Figure 8, there

are three CNs communicating with the MN.

In best effort case, the registration procedure is the same as

the procedure in the case of one CN. The sample label table of

HA after registration is illustrated in Table IV. The first row is

the label binding for the LSP from HA to FA. The second, third

and fourth rows are the label bindings for the LSPs from each

CN to HA. Outgoing port and out label in these rows have been

set to the out label value and outgoing port number of the first

row. So packets arriving along these three LSPs are all sent out

from the same port with the same label value to foreign network.

TABLE IV

EXAMPLE LABEL TABLE OF HA AFTER REGISTRATION IN MULTIPLE CN

CASE


2 - w.x.y.z 1 5

1 9 a.b.c.d 1 51 8 a.b.c.d 1 5

1 7 a.b.c.d 1 5... ... ... ... ...

If the traffic from different CNs have different QoS require-

ments, HA needs to establish a new LSP from HA to FA for each

class of service. That means that HA must know the number of

CoS of the traffic destined to MN home address. When pack-

ets arrive at HA, it needs to classify the packets to identify its

CoS and destination. Then, HA maps them to the correspond-

ing LSP based on the combination of the CoS and destination

address of the packets. Using such mechanism, we can support

differentiated services in MPLS networks [11].

B. Multiple Domains

Multiple domain connectivity needs to be considered in our

scheme as there is a possibility of mobile nodes moving between

different domains. There are some specific requirements on the

border routers of these domains depending on the nature of the

inter-domain connections as described in the following subsec-

tions.

CN1

LSR1 LSR2

LSR3

LSR4

LSR5

HA

MN

MN

MPLS

Network

MPLS

Network

FA

LSR6

Figure 9. Multiple MPLS Domains

CN1

LSR1

LSR2

LSR3

LSR4

LSR5

HA

MN

MN

MPLS

Network

MPLS

Network

FA

Router1 IP

Network

FA

MN

Figure 10. AnIP Cloud in Between

B.1 Multiple MPLS Domains

As shown in Figure 9, HA and FA are edge LSRs and belong

to two different MPLS domains which are directly connected.

They support both MPLS and Mobile IP functionality.

Here the two edge LSRs (LSR3 and LSR5) are LDP Border

Gateway Protocol (BGP) peers [12]. That means they can ex-

change label information between them. So in this case, we can

establish a LSP from HA to FA across the link connecting these

two different MPLS domains. Our registration and data deliveryschemes described in previoussections can be used here without

any modification.

B.2 An IP Cloud In-between

When there is an IP cloud between the HA domain and the FA

(Figure 10), an IP tunnel is needed to carry the data packets to

the FA. In this case, LSR3 will act as an interchange between the

LSP and the IP tunnel, acting as the FA from the viewpoint of

the HA. Packet is switched from the HA to LSR3 and tunneled

from LSR3 to the FA. Here the hierarchical FA management

scheme can be a solution [13], where every edge router has to

be a hierarchical FA. Slight modification can be made if the FA

is in a MPLS domain. The IP tunnel can be terminated at LSR5.

A LSP will continue the data forwarding task from LSR5 to the

FA. This modification requires LSR5 to be Mobile IP enabled.

In this case, the performance of the proposed scheme become

worse than all previous cases. But in any case, the IP tunnel is

shorten in the proposed scheme. Since switching is faster than

conventional IP forwarding, the transmission delay is improved.

C. Implication of Schemes

We have considered the case where the whole network in

question is a single MPLS domain, multiple MPLS domains and

the case where there are non-MPLS cloudspresent. Here the key

of different inter domain connectivity is whether the HA packet

processing needs to go up to the IP layer. If it does, then IP

tunneling has to be used to extend the LSP to FA. Our schemeworks in all these possible cases. However, our scheme works

best in the case where the whole network is MPLS capable.

VI. EVALUATION

To evaluate the MPLS and Mobile IP integration scheme per-

formance, we built a testbed and designed a set of experiments

to analyze the scheme.

A. Testbed

The single domain case has been implemented and evaluated

on Linux 2.3.30 software platform. The experimental results re-

ported in this paper are based on measurements taken from the

testbed illustrated in Figure 11. It consists of four PC routers

based on multi-homed 133MHz Pentium PCs hardware. They

are CN, HA, FA and one intermediate LSR between the HA and

FA. CN sends the packet destined to MN to HA and the HA for-

wards it to the FA through the intermediate LSR between them.

All of them are interconnected using 100Mbps full duplex links.

MN is a 133 MHz Pentium PC. HA and FA runs Mobile IP im-

plementation [14] in user space. The MPLS switching function

is implemented in Linux kernel.



Subnet 2

CN

HA FA

LSR

MN

Subnet 1

137.132.153.117

137.132.153.113

137.132.153.249

137.132.153.57

137.132.153.114

137.132.153.241

137.132.153.250

137.132.153.248

137.132.153.240

Ethernet

Figure 11. Testbed

0 1000 2000 3000 4000 5000 6000 7000 80000

100

200

300

400

500

600HAProcessingDelay withNumberof TableEntries

Numberof RoutingEntries

H A P r o c e s s i n g D e l a y ( u s e c )

PureMobileIP

MobileIPoverMPLS

MobileIP andMPLS Integration

Figure 12. Processing Delay at HA

B. Processing Delay at HA

During this experiment, we increase the routing and label ta-

ble size from 5 entries to 8000 entries. The measurements are

plotted in Figure 12. Each point on the graph was obtained by

averaging 50 consecutive measurements. From Figure 12, we

can find that the HA processing delays in Mobile IP and Mo-

bile IP over MPLS schemes increase with the increasing routing

table size. But in the MPLS-Mobile IP integration scheme, the

HA processing delay is almost constant. It is much lower than

the values in Mobile IP and Mobile IP over MPLS schemes. The

lower value is the result of having the entire HA data forward-

ing process executed in the MPLS layer after MPLS-Mobile IP

integration. So no IP routing table search is executed. Since

label table search is much faster than longest-bit-matching rout-

ing table search and IP tunneling needs to search routing table

twice, much processing time is saved and HA performance is

much improved. We also can find that Mobile IP over MPLS

has poorer performance than pure Mobile IP. This is caused by

the additional processing at MPLS layer before the packet goes

up to the IP layer.

0 1000 2000 3000 4000 5000 6000 7000 8000450

455

460

465

470

475

480

485Throughput Decrease with HA Entries Increasing

HA Table Entries

T h r o u g h t p u t ( K B y t e s / s e c )

Pure Mobile IPMIP and MPLS Integration

Figure 13. TCP Performance

0 1000 2000 3000 4000 5000 6000 7000 800012

12.2

12.4

12.6

12.8

13

13.2Roundtrip Delay Increase with HA Entries Increasing

HA Table Entries

R o u n d t r i p D e l a y ( m s e c )

Pure Mobile IP

MIP and MPLS Integration

Figure 14. Roundtrip Delay

C. TCP Performance

In this experiment, we study the impact of the number of table

entries on Mobile IP forwarding scalability. we also increase the

routing and label table size from 5 entries to 8000 entries. We

measure TCP throughput using ttcp by downloading data from

CN to MN. Each data point is an average of 5 independent mea-

surements. From Figure 13, we can find that the TCP through-

put in Mobile IP scheme drops with the increasing routing table

size. In MPLS-Mobile IP integration scheme, the throughput is

constant. The reason for this phenomenon is as explained in the

last experiment.

D. Roundtrip Delay

In this experiment, we measure the roundtrip delay. We also

increase the routing and label table size from 5 entries to 8000

entries. We measure the roundtrip delay using ping from CN to

MN. We set the packet size as 1000 bytes. Each data point is

an average of 20 consecutive measurements. From Figure 14,

we can find that the roundtrip delay in Mobile IP scheme in-creases with the increasing routing table size. In MPLS-Mobile

IP integration scheme, the delay is constant. The reason for this

phenomenon is as explained in the first experiment. In addition

to the HA performance improvement, it also benefits from fast

switching because packet is label switched along the whole path

from CN to FA and back to CN.

VII. CONCLUSIONS

In this paper, We provided the signaling and control mecha-

nisms to integrate Mobile IP and MPLS. This integration makes

IP-in-IP tunneling in the data forwarding process unnecessary.

Instead we use MPLS to switch the packet. Switching is much

faster than conventional IP forwarding, the transmission delay

and packet processing overhead is reduced. The whole forward-ing process is done at the MPLS layer and HA doesn’t need to

go up to the IP layer to do the IP tunneling. So the scalability

of Mobile IP is much improved. In addition, since label header

is much smaller than IP header, the traffic overhead from HA to

FA is also reduced.

This work is an initial step towards integrating the MPLS and

Mobile IP protocols. Other future work includes provisioning of

QoS guarantees and route optimization support for our scheme.

REFERENCES

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[13] Charles E. Perkins, “Mobile-IP Local Registration with Hierarchical For-eign Agents”, 22 February 1996.

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