Title: Method and system for dynamically assigning IP addresses in wireless networks
Abstract: A method is provided for IP-based wireless networks to support dynamic assignment of IP addresses to wireless mobile stations without broadcasting messages over the air and without modifications to standard IP for dynamic IP address assignment. When a mobile station enters a new cell, it sends a request to the base station for a new IP address. At the base station, DHCP proxy servers intercept and process broadcast DHCP messages so they are transmitted only to the address server and are blocked from being sent to the other base stations in the wired IP Network for broadcast to other mobile stations. When the address server creates a server-to-client message with the requested address and places it on the wired IP Network, DHCP proxy servers at the base stations convert the broadcast DHCP messages to unicast messages for transport over the air to only those mobile stations that are currently requesting new IP addresses or verifying their current IP addresses. The conversion is based on information contained in DHCP messages which passed through the base stations.
Patent Number: 7,016,353 Issued on 03/21/2006 to Proctor, et al.
| Inventors:
|
Proctor; Paul (Eatontown, NJ);
Zhang; Tao (Fort Lee, NJ)
|
| Assignee:
|
Telcordia Technologies, Inc. (Piscataway, NJ);
Toshiba America Research, Inc. (Piscataway, NJ)
|
| Appl. No.:
|
880530 |
| Filed:
|
June 13, 2001 |
| Current U.S. Class: |
370/392; 370/338; 370/401 |
| Current Intern'l Class: |
H04L 12/28 (20060101) |
| Field of Search: |
370/328,338,389,390,392,401
|
References Cited [Referenced By]
U.S. Patent Documents
Primary Examiner: Ngo; Ricky
Assistant Examiner: Ng; Christine
Attorney, Agent or Firm: Giordano; Joseph, Falk; James W.
Claims
What is claimed is:
1. A system for dynamically assigning IP addresses to mobile stations in wireless
networks including a plurality of base stations and operating according to a Dynamic
Host Configuration Protocol (DHCP) said system comprising:
a wired IP network connecting the base stations;
an address server connected to the wired IP network; and
a proxy server at each base station in the wired network, said proxy server intercepting
client-to-server requests for an IP address and modifying the request so that it
goes only to the address server, and not to other base stations, and intercepting
server-to-client IP address messages from the address server and making sure that
they are unicast only to the mobile stations requesting IP addresses and wherein
the proxy server changes a hops field in a received DHCP client-to-server message
so that the address server processes the message, but the proxy servers at other
base stations discard the message.
2. The system of claim 1 wherein the hops field is set to zero if the message
is from a mobile station and the proxy server changes it to a one when sending
it on the wired IP network.
3. A system for dynamically assigning IP addresses to mobile stations in wireless
networks including a plurality of base stations, said system comprising:
a wired IP network connecting to the base stations;
an address server connected to the wired IP network; and
a proxy server at each base station in the wired IP network, said proxy server
intercepting client-to-server requests for an IP address and modifying the request
so that it goes only to the address server, and not to the other base stations,
and intercepting server-to-client IP address messages from the address server and
making sure that they are unicast only to the mobile stations requesting IP address
and wherein the proxy server further includes a distribution table which stores
information about mobile stations requesting IP addresses and sends server-to-client
messages only to mobile stations listed in the table.
4. The system of claim 3 wherein the server-to-client message is unicast.
5. A method of dynamically assigning IP addresses to mobile stations in wireless
networks including a plurality of base stations, comprising the steps of:
receiving at a base station proxy server an address request message from a mobile
station requesting an address;
determining if the address request message is directly from the mobile station
or from another base station over a wired network segment;
if the address request is directly from a mobile station, altering the address
request message and sending it over the wired network segment to an address server;
if the address request message is from another base station, discarding the address
request message;
receiving at a base station proxy server an address designation message;
determining from a Distribution Table which mobile stations within the range
of the base station have requested address information; and
transmitting the address designation message containing an assigned IP address
only to those mobile stations identified.
6. The method of claim 5 wherein the step of transmitting is by unicasting.
7. The method of claim 5 wherein the wireless network is operating according
to a Dynamic Host Configuration Protocol (DHCP) and wherein the step of altering
the address request message comprises the step of changing a hops field in a received
DHCP client-to-server message so that the address server processes the message,
but the proxy servers at other base stations discard the message.
8. A system for dynamically assigning IP addresses to mobile stations in a wireless
network, said system comprising:
a plurality of base stations each of which serves a respective cell, each of
said base stations including
a dynamic host configuration proxy (DHCP) server which determines whether a DHCP
message can be unicast directly to a destination mobile station, and
a routing engine receiving a communication from said proxy server when said DHCP
message cannot be unicast directly to a destination mobile station, said routing
engine including a Distribution Table which maintains a list of IP addresses to
identify mobile stations requesting IP addresses, and said routing engine causing
the unicasting over a radio channel to an address of the destination mobile station
as identified by said Distribution Table.
9. The system in accordance with claim 8 wherein said base station further comprises
a second routing engine receiving communication from said proxy server when a DHCP
message can be unicast directly to a destination mobile station.
10. A system for dynamically assigning IP addresses to mobile stations in a wireless
network including a plurality of base stations defining cells into which the mobile
stations migrate, each said base station comprising
a proxy server intercepting mobile-to-base station requests for an IP address
and first and second routing engines for unicasting address messages only to mobile
stations requesting an address and
wherein said first routing engine receives communication from said proxy server
when the IP address can be directly unicast to a requesting mobile station and
said second routing engine receives communications from said proxy server when
an IP address can not be directly unicast to a requesting mobile station, said
second routing engine including a Distribution Table containing a list of IP addresses
identifying mobile stations to which an IP address can be unicast.
11. A system for dynamically assigning IP addresses to mobile stations in a wireless
network including a plurality of base stations defining cells,
a wired network connecting said base stations, and
a proxy server in each of said base stations, said proxy server identifying whether
a message is received ever the wired network from another base station and discarding
said message, or received from a mobile station in the cell of the base station
and causing an IP address to be unicast to that mobile station.
12. The system in accordance with claim 11 wherein said proxy server at a base
station changes the hops field in received messages to determine whether a message
is to be discarded or responded to.
13. The system in accordance with claim 12 wherein the proxy server further includes
a Distribution Table which stores a table associating mobile stations with IP addresses
and sends an IP address unicast message only to mobile stations listed in the table.
14. A method for dynamically assigning IP addresses to mobile stations in a wireless
network comprising the steps of:
receiving at a base station proxy server an address designation message;
determining from a Distribution Table which mobile stations within the range
of the base station have requested address information and to which a unicast message
can be sent; and
invoking a first routing engine when the address designation message cannot be
unicast to the intended mobile station in order to direct the message to that mobile
station; and
invoking a second routing engine when the address designation can be unicast
to the intended mobile station, which second routing engine unicasts the message
over a radio channel to an address of the designated mobile station.
15. The method of claim 14 wherein the network uses dynamic host configuration
proxy (DHCP) signaling.
16. The method of claim 15 wherein the messages have hop fields, and further
comprising the steps of
receiving at a base station DHCP proxy server an address request message from
a mobile station requesting an IP address;
determining if the address request message is directly from the mobile station
or from another base station over a wired network segment;
if the address request message is directly from a mobile station, altering the
hop field in the address request message and sending it over the wired network
segment to an address server;
if the address request message is from another base station, discarding the address
request message; and
transmitting the address designation message only to those mobile stations identified.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to the field of wireless Internet Protocol
("IP") networks, methods and protocols in personal communication systems (PCS)
and, more particularly, to a method and system for dynamically assigning IP addresses
in wireless networks without broadcasting over open air.
2. Description of the Related Art
Emerging IP (Internet Protocol) based wireless networks use IP protocols
for transport and control of data and/or voice over open air and over wired IP
networks. As a result, mobile stations utilizing the IP networks are required to
dynamically obtain IP addresses when the mobile stations move into new IP subnets.
Using conventional dynamic IP address allocation mechanisms (e.g., Dynamic Host
Configuration Protocol or DHCP), mobile stations and IP address servers (e.g.,
the DHCP servers) are often required to broadcast IP packets over a wide area.
For example, when a mobile station first enters a new IP subnet, typically it
does not possess the address of the IP address servers of the new IP subnet. Therefore,
the mobile station usually broadcasts packets to the DHCP server of the new IP
subnet to request assignment of new IP addresses. These packets contain IP broadcast
addresses as their IP destination addresses and are sent by standard IP network
devices to every IP host on the IP subnet, including all the wireless IP hosts.
For example, if N cells are supported by the same IP subnet, these DHCP messages
would be broadcast to all wireless IP hosts in all the N cells. This wide area
broadcast is a waste of scarce wireless resources.
FIG. 1 is a schematic block diagram which illustrates unnecessary broadcasting
of DHCP messages to mobile stations in a conventional wired IP Network or subnet.
Here, mobile station A is shown as having recently entered a new cell
50
which is served by base station
3 (BS
3). All mobile stations served
by all the base stations BS
1, BS
2, BS
3 (shown in FIG. 1) belong
to the same IP subnet
20.
By moving into a new cell
50, mobile station A may change subnet and hence
be required to request a new address. When mobile station A recognizes that it
has moved into a new cell, it uses standard DHCP procedures to validate its current
IP address and/or request a new IP address, if necessary. An exemplary simplified
standard procedure for a mobile station to use DHCP to obtain a new IP address
or to verify its current IP address is:
- (1) The mobile station broadcasts a DHCPDISCOVER message on a local
IP subnet in a broadcasted IP packet (i.e., a packet containing a broadcast destination
IP address). Here, the mobile station may include options where values for its
IP address are suggested, such as its current IP address; and
(2) a DHCP server responds with a DHCPOFFER message upon receiving the DHCPDISCOVER
message. The DHCPDISCOVER message will contain the IP address assigned to the mobile
station. The DHCP servers may also broadcast the DHCPOFFER messages back to the clients.
A mobile station may receive multiple DHCPOFFER messages from multiple servers.
Therefore, after receiving such DHCPOFFER messages, the mobile station broadcasts
a DHCPREQUEST message back to the servers. The DHCPREQUEST message may also be
used to acknowledge acceptance of an address assigned by a particular server to
a mobile station, and to decline offers from other servers.
Using the previously described conventional DHCP and standard IP network devices,
all the DHCP messages broadcast from a requesting mobile device and the DHCP servers
are routed to every mobile station on the same IP subnet serving the requesting
mobile station. Broadcasting IP packets in this manner to all mobile stations in
a "common" IP subnet wastes scarce, valuable resources in the wireless network
and consumes power within the mobile stations, since no other mobile station in
the IP subnet needs to receive the transmitted IP packets.
This waste becomes an acute problem when PPP (point-to-point protocol) is used
to support IP transport of packets over Code Division Multiple Access (CDMA) networks
(e.g., as suggested by the Third Generation Partnership Project II or 3GPP2). Specifically,
when PPP is used, base stations are required to send a separate copy of the broadcast
packet to each mobile station, which can lead to even more unnecessary signaling
traffic over the air.
In computer-related networking or telecommunications, the point-to-point protocol
is used for communicating information between a source and a destination over a
point-to-point link. PPP is widely used for transmitting Transmission Control Protocol/Internet
Protocol (TCP/IP) packets over dial-up telephone connections, such as between a
general purpose computer and an Internet Service Provider (ISP). TCP/IP is a set
of protocols developed by the United States Department of Defense for communications
over interconnected, sometimes dissimilar, networks and has become the de facto
standard for data communications over various networks, including the Internet.
The point-to-point protocol provides a standard methodology for transporting multi-protocol
datagrams of information over point-to-point links. PPP comprises three main components:
(1) a methodology for encapsulating multi-protocol datagrams, (2) a link control
protocol (LCP) for establishing, configuring and testing the data link connection,
and (3) a family of network control protocols (NCPs) for establishing and configuring
different network-layer protocols.
An end-user sets up a PPP session between the source, e.g., a general purpose
computer or telecommunication device, and a destination (which can also be a general
purpose computer or telecommunication device) for transmitting data or information
thereto. In a PPP session, once the initial negotiation phases are successfully
completed, a session identifier is associated with the connection, thereby identifying
the PPP session. Typically, a single PPP connection exists between an end user's
computer and the destination, e.g., an Internet service provider (ISP) or another
computer connected to the Internet. The PPP session is closed when the end-user
of the network system completes the data or information transfer.
A PPP (point-to-point protocol) packet or frame consists of the user data and
any
headers of other protocols being encapsulated by the PPP. The frame is also provided
with a PPP header. The PPP header contains the information necessary to identify
and maintain an associated PPP session.
Encapsulation in PPP treats a collection of structured information
as a single entity without affecting or taking notice of its internal structure.
Thus, a message or packet constructed according to one protocol (such as a TCP/IP
packet) may be taken with its formatting data as an undifferentiated stream of
bits that is then broken up and packaged according to the higher level point-to-point
protocol to be sent over a particular network.
Code Division Multiple Access (CDMA) broadcast channels (e.g., the paging channel)
can also be used to transmit IP packets. However, conventional broadcast channels
used in CDMA networks are typically not designed for such time-sensitive traffic,
and no mechanism or standard is currently available for carrying IP packets over
such CDMA broadcast channels. Accordingly, there is a need for a method for supporting
dynamic IP address assignment without over the air broadcasting messages of the
protocol used for address assignments.
SUMMARY OF THE INVENTION
The invention is directed to a method and a system for IP-based wireless networks
to support dynamic assignment of IP addresses to wireless mobile stations without
broadcasting messages over the air and without modifications to standard IP for
dynamic IP address assignment. According to the invention, each base station converts
broadcast DHCP messages to unicast messages for transport over the air to only
those mobiles that are currently requesting new IP addresses or verifying their
current IP addresses. The conversion is based on information contained in the DHCP
messages which pass through the base stations and is implemented in DHCP proxy
servers located at each base station.
The DHCP proxy servers at the base stations intercept and process broadcast DHCP
messages to block client-to-server DHCP messages from being sent to mobile stations,
and to convert server-to-client DHCP messages broadcast from DHCP servers into
unicast IP packets for transport over the air to only those mobile stations which
are requesting new IP addresses or verifying their current IP addresses (a message
is unicast by sending it once through a single wireless channel to a single mobile station).
Client-to-server DHCP messages transmitted over a wired IP Network
or subnet are used to request and designate the address which is to be used to
identify the wireless connection of the transmitting mobile station (e.g., the
layer-2 or layer 1 address of the mobile station). These messages
are inserted into a Distribution Table which provides a list of identifiers used
to designate which mobile stations are requesting IP addresses or to verify existing
IP addresses. Upon entry of a mobile station into a new cell, the mobile station
sends a DHCPDISCOVER message in a broadcast IP packet. Instead of forwarding the
DHCP message to all mobile stations, however, other base stations discard the broadcast
IP packet prior to forwarding it to other mobile stations which may be accessing
local subnets by determining whether the source address of the broadcast IP packet
contains all zeros or whether a specific field in the DHCP message, known as the
"hops" field, is zero. The hops field identifies the number of additional hops
that a packet is allowed.
Server-to-client DHCP messages transmitted over a wired IP Network
or subnet are only forwarded to mobile stations which are actively requesting new
IP addresses. When none of the mobile stations currently served by a base station
is requesting a new IP address (or verifying its current IP address), the base
station will discard all server-to-client DHCP messages forwarded to it from other
base stations.
By dynamically assigning addresses to mobile stations in a wireless network,
valuable
system resources are conserved, independent development of radio and IP components
of a wireless network is facilitated, and client-to-server broadcast DHCP messages
are prevented from being sent to mobile devices. In addition, IP-based wireless
base stations convert server-to-client broadcast DHCP messages to unicast messages
for transport over the air to only mobiles which are either requesting new IP addresses
or verifying their current IP addresses. Further, standard operations of DHCP are
supported without having to broadcast DHCP messages over the air.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other advantages and features of the invention will become
more apparent from the detailed description of the preferred embodiments of the
invention given below with reference to the accompanying drawings in which:
FIG. 1 is a schematic block diagram which illustrates unnecessary broadcasting
of DHCP messages to mobile stations in a conventional wired IP Network or subnet;
FIG. 2 is a schematic block diagram of an exemplary wired IP Network or subnet
in which the method of the invention is implemented;
FIG. 3 is an exemplary diagram of a protocol stack of a base station configured
in accordance with the present invention;
FIG. 4 is a diagram which illustrates the processing of client-to-server DHCP
messages by base stations configured in accordance with the protocol stack shown
in FIG. 3;
FIG. 5 is a diagram which illustrates the processing of server-to-client DHCP
messages by base stations configured in accordance with the protocol stack shown
in FIG. 3;
FIG. 6 is a flow chart illustrating an embodiment of the method of the invention
which is implemented by base stations to process received client-to-server DHCP
messages in accordance with the invention; and
FIG. 7 is a flow chart illustrating an embodiment of the method of the invention
which is implemented by the base stations to process received server-to-client
DHCP messages in accordance with the invention.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
FIG. 2 is a schematic block diagram of a wired IP Network
200 or subnet
in which the method of the invention is implemented. The exemplary network shown
in FIG. 2 includes a DHCP server
210 which is directly connected to the
wired IP network
200. Alternatively, the DHCP servers may be indirectly
connected to the local subnet. A router
220 is provided for connecting additional
networks, such as the Internet, to the IP Network
200 or subnet. The IP
network
200 further includes cells
240,
250,
260 which
are each served by a respective base station BS
1, BS
2, BS
3
which are resident in wireless network
230. Naturally, it will be appreciated
that the wireless network
230 can include more or less than the specific
number of cells and base stations illustrated.
The base station architecture in accordance with this illustrative embodiment
of the invention utilizes a protocol stack
300 as shown in FIG.
3.
Specifically, a DHCP proxy server
310, which preforms an application process,
resides in the protocol stack
300 above a first IP layer and provides communications
with mobile stations and a second IP layer
330 that provides communications
with wireline stations. A dynamic host configuration protocol (DHCP) that can be
unicast to a mobile station is communicated over path
312 to a standard
IP routing engine or server
321 in IP layer
320. DHCP messages to
and from the DHCP server
310 for local wireline stations are communicated
from DHCP proxy server
310 over path
314 to the IP layer
330.
In accordance with one aspect of the invention, DHCP messages that cannot be
unicast
directly to a mobile station are communicated over path
313 to a special
IP routing engine or server
322 that manages a Distribution Table
333.
As noted above, the Distribution Table
333 is a mapping table which maintains
a list of addresses which identify wireless channels to identify the mobile stations
which are requesting IP addresses or verifying existing IP addresses. Packets carrying
DHCP messages are thus sent from the special routing engine
322 over paths
326 to radio channels
341 in a wireless layer
340, i.e., Layer
1 or Layer
2. These messages are in turn transmitted to the mobile
stations that are verifying or requesting IP addresses. The addresses maintained
in the Distribution Table
333 thus can be, for example, Layer
1 and
Layer
2 addresses of the mobile stations.
The Distribution Table
333 is used by the base station to distribute DHCP
messages to a destination mobile station. The DHCP proxy server
310 determines
whether a DHCP message can be unicast to the destination mobile station (a message
is unicast by sending it once through a single wireless channel to a single mobile
station). If the DHCP message can be unicast to the destination mobile station,
the DHCP proxy places the DHCP message into an IP packet and the destination IP
address is set to a unicast address for the destination mobile station. The IP
packet containing the DHCP message is sent to the Standard IP routing engine
321.
The unicast standard IP routing engine
321 performs a process which is used
to determine where to forward the broadcast IP packets. The standard IP routing
engine
321 also delivers the IP packet over a specific wireless channel
341 to the destination mobile station.
If, on the other hand, a DHCP message cannot be unicast to a mobile station,
i.e., the DHCP proxy cannot determine a specific destination mobile station to
receive a unicast DHCP message, then the DHCP proxy
310 places the DHCP
message into an IP packet which contains a broadcast IP destination address and
sends the packet to the special IP routing engine
322, in which the Distribution
Table
333 is maintained. The special IP layer routing engine
322
performs a process which accesses the Distribution Table
333 to determine
the address to send the IP packet, as discussed above. In particular, to the mobile
stations identified by the Distribution Table
360 which are requesting IP
addresses or verifying existing IP addresses.
In the case of communications with a wireline IP subnet, use is made of IP layer
330, which is a standard layer implementation protocol. Messages from IP
layer
330 pass to wire line layers
350, i.e., wire line Layer
1
and wire line Layer
2, and from there to the local wireline IP subnet.
FIG. 4 is a diagram which illustrates the processing of client-to-server DHCP
messages by base stations configured in accordance with the protocol stack shown
in FIG.
3. Here, received client-to-server DHCP messages transmitted over
the air from the mobile stations designate whether the address used to identify
the wireless connection of the transmitting mobile station (e.g., the layer-
2
or layer
1 address of the mobile station) is to be inserted into the Distribution
Table
333 shown in FIG.
3.
To intercept the DHCP messages, which are passed through a base station for processing,
a DHCP proxy server
310 is operated on conventional User Datagram Protocol
(UDP) ports allocated for DHCP clients and servers. Every client-to-server DHCP
message is automatically intercepted by a local DHCP proxy server
310 (i.e.,
the proxy on the local base station) because these IP packets contain a broadcast
IP destination address and use conventional DHCP server UDPs. (Similarly, every
server-to-client DHCP message is automatically intercepted by the local client
proxy.) On the other hand, unicast DHCP messages are passed through the base station
without being processed by a DHCP proxy.
Using the "hops" field in the DHCP message, the DHCP proxy server
310
determines whether a client-to-server DHCP message originated directly from a mobile
or from another DHCP proxy server. DHCP protocol requires the DHCP clients to set
the "hops" field to zero when sending client-to-server DHCP messages. Each DHCP
proxy server checks the "hops" field in each client-to-server DHCP message received.
If the value in the "hops" field is zero, the message is directly from a mobile
station. In such a case, the DHCP proxy server
310 sets the value of the
"hops" field to 1, and broadcasts the messages on the local wired IP network
200
which connects the base stations to the network.
The other DHCP proxy servers
310′,
310" discard any client-to-server
DHCP messages received from DHCP proxy server
310. These other servers
310′,
310" receive client-to-server DHCP messages from DHCP proxy servers
310
only when such messages are broadcast by the originating DHCP proxy server
310
to the local IP subnet
200 that connects the proxies (i.e., the base stations).
These DHCP messages (packets) are not intended for the mobile stations, but instead
are intended for the DHCP servers
210. In other words, if a base station
receives a DHCP message and determines on the bases of the "Hops" field that this
message is from another base station, rather than directly from another mobile
station, then the base station will discard the received DHCP message. If a DHCP
message (broadcast IP packet) contains all zeros or has a "Hops" field which is
zero, then it is a message which has originated from a mobile station. If the "Hops"
field is set to "1", it is from another base station and should be discarded.
Upon entry of a mobile station into a new cell, i.e., the cell of base station
BS
1, the mobile station sends a DHCPDISCOVER message in a broadcast IP packet.
Since this message will have a "Hops" field of zero, the DHCP Proxy
310
changes the "Hops" field to 1 and sends the request out over the wired IP Network
or subnet
200. The DHCP Server
210 receives and interprets the request.
Also, the other base stations, i.e., BS
2 and BS
3, receive it. However,
the DHCP Proxies
310′ and
310" see that the "Hops" field is
1, and instead of sending it on to the mobile stations, they discard it. In this
manner, DHCP messages broadcast from the mobile stations will never be sent to
other mobile stations.
FIG. 5 is a diagram which illustrates the processing of server-to-client DHCP
messages by base stations configured in accordance with the protocol stack shown
in FIG.
3. In particular, FIG. 5 shows the path by which DHCP Server
210
sends address information to the requesting mobile stations. Here, server-to-client
DHCP messages transmitted over the wired IP Network or subnet
200 are only
forwarded to mobile stations which are actively requesting new IP addresses. Upon
entry of a mobile station (e.g., A and/or B) into a new cell (e.g.,
520
and/or
530, respectively), the mobile station sends a DHCPDISCOVER message
in a broadcast IP packet as described above with respect to FIG.
4. In response,
the DHCP Server generates an IP address message which it applies to wired IP Network
or subnet
200. Instead of all base stations accepting any forwarded server-to-client
DHCP messages and broadcasting them to the mobile stations, only the base stations
BS
1 and BS
2, which are receiving DHCPDISCOVER messages in broadcast
IP packets, operate to relay the server-to-client message. If a base station such
as BS
1 is not receiving such a message, it discards the forwarded server-to-client
DHCP messages. This determination is made by the DHCP Proxy servers
310,
310′ and
310" at each of the base stations.
Specifically, DHCP servers are often required to broadcast responses
to IP hosts. These include messages, such as a DHCPOFFER message, a DHCPACK message
and a DHCPNAK message. The server-to-client messages broadcast from DHCP servers
210 are intercepted by the DHCP client proxy
310 at each base station
on the IP subnet
200 because packets carrying the server-to-client messages
contain an IP broadcast destination address and are addressed to a Universal Data
Port (UDP) which is assigned to DHCP clients.
Generally, it is impossible for a client proxy to determine the valid
IP address for a mobile station by only reading the server-to-client DHCP messages.
For example, the assigned IP address contained in the DHCPOFFER message may be
simultaneously assigned to multiple hosts by the DHCP server. This means that packets
sent to the assigned IP address contained in the DHCPOFFER message may be routed
to any one of the mobile stations which are assigned to the same IP address. Accordingly,
to permit a client proxy to convert each server-to-client DHCP broadcast message
into unicast messages destined to only mobile stations which are in the process
of obtaining new IP addresses or verifying their current IP addresses, each base
station uses the special IP routing engine
322 and the Distribution Table
333 shown in FIG. 3 to determine which mobile stations should be sent the
packet. This Distribution Table maintains a set R of mobile stations in a local
cell which are currently requesting or verifying IP addresses. The special IP routing
engine maps the IP broadcast to all hardware addresses of the mobile stations in
set R. The DHCP proxy
310 in FIG. 5 sends each server-to-client DHCP broadcast
message only to the mobile stations in set R. Relative to the total number of mobile
stations served by each base station, the number of mobile stations in set R is
typically very small. As a result, packets sent to mobile stations contained in
set R may be delivered over point-to-point radio channels without incurring unreasonable
over-the-air system "overhead" expenditures.
In accordance with the invention, a Distribution Table
333 is built and
maintained by using the DHCP proxy server shown in FIG. 3 to insert a hardware
address of a mobile station into the Distribution Table
333 when a client-to-server
DHCP message from a mobile station is received by the DHCP proxy server. In preferred
embodiments of the invention, every client-to-server DHCP message contains the
hardware address of the client.
The DHCP proxy is used to remove the hardware address of the mobile station from
the Distribution Table
333 when the base station receives a DHCPOFFER message,
a DHCPACK message, a DHCPNAK message for the mobile station, or after the expiration
of a predetermined time interval. The DHCP proxy server does not have to wait for
the mobile station to confirm acceptance of an offered IP address before removing
the hardware address of the mobile station from the Distribution Table
333.
This is because if the mobile station rejects all the offered IP addresses, the
mobile station either re-requests a new IP address, or ceases to request new IP
addresses. In each case, it is safe for the proxy to remove the mobile's hardware
address from the mapping table. In the first case, the mobile's hardware address
will be inserted into the mapping table again when the mobile sends a new client-to-server
DHCP message. In the second case, the mobile station's hardware address no longer
needs to be in the Distribution Table.
FIG. 6 is a flow chart illustrating and embodiment of the method of the invention.
Upon receipt of a client-to-server DHCP message (step
600), a test is performed
to determine whether the received message is directly from a mobile station or
via other base stations (step
610). If the received message is not directly
from a mobile station, then the DHCP message is discarded (step
620), and
a return to step
600 occurs to await receipt of additional DHCP messages.
On the other hand, if the received message is directly from a mobile station,
then an address used to identify the wireless connection of the transmitting mobile
station (e.g., the Layer-
2 or Layer
1 address of the mobile station)
is inserted into a Distribution Table
333 which is resident in the base
station associated with the respective mobile station (step
630). The DHCP
message is then forwarded to the local wireline IP subnet (step
640), and
a return to step
600 occurs to await the receipt of additional DHCP messages.
FIG. 7 is flow chart illustrating the method of the invention which is implemented
by base stations to process received server-to-client DHCP messages in accordance
with one illustrative embodiment of the invention. Upon receipt of a server-to-client
DHCP message destined for a local mobile (step
700), a determination is
then made (step
702) as to whether the DHCP message can be unicast to its
intended destination mobile station. If the DHCP message can be unicast, then the
packet is delivered (step
704) to the standard routing engine
321.
After sending the message to the mobile station, the DHCP proxy removes the corresponding
mobile's hardwave address from the Distribution Table (step
706), and a
return is made to step
700 to await receipt of further DHCP messages. However,
if the DHCP message can not be unicast to its intended destination mobile station,
then the packet is delivered (step
708) to the special IP routing engine
322 which will deliver the packet to, and only to, mobile stations identified
in its Distribution Table
333. Again the hardwave address corresponding
to the destined mobile is removed from the Distribution Terminal (step
710),
a return is then made back to step
700 for further DHCP messages.
The method of the invention provides dynamic assignment of addresses to mobile
stations in a wireless network. As a result, valuable system resources are conserved,
independent development of radio and IP components of a wireless network is facilitated,
and client-to-server broadcast DHCP messages are prevented from being sent to mobile
devices. In addition, IP-based wireless base stations convert server-to-client
broadcast DHCP messages to unicast messages for transport over the air to only
those mobiles which are either requesting new IP addresses or verifying their current
IP addresses. Further, standard operations of DHCP are supported without having
to broadcast DHCP messages over the air.
Although the invention has been described and illustrated in detail, it
is to be understood that the same is by way of illustration and example, and is
not to be taken by way of limitation. In addition, it should be understood that
DHCPs are an exemplary protocol for dynamic IP address assignment and that the
invention is applicable to other protocols for dynamic address assignment. Moreover,
the spirit and scope of the present invention are to be limited only by the terms
of the appended claims.
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