WO2000041418A1

WO2000041418A1 - Routing data in an ip-based communication system

Info

Publication number: WO2000041418A1
Application number: PCT/US1999/029308
Authority: WO
Inventors: Philip R. Roberts; Jay P. Jayapalan
Original assignee: Motorola Inc.
Priority date: 1999-01-08
Filing date: 1999-12-13
Publication date: 2000-07-13

Abstract

A home agent (103) establishes a first Internet Protocol (IP) tunnel (104) to a foreign agent (107). A first outer IP header is inserted before the datagram's existing IP header. A second IP tunnel (108) is established between the foreign agent (107) and a radio access network (RAN) (114). When the foreign agent (107) receives datagrams addressed to the remote unit (113), the foreign agent (107) tunnels the datagrams to the RAN (114). In particular, the foreign agent (107) strips the first outer IP header from the datagram and replaces the first outer IP header with a second outer IP header. The second outer IP header source and destination address identify the endpoints of the tunnel (foreign agent 107 and RAN 114, respectively). The RAN (114) unencapsulates packets forwarded from the foreign agent (107) in the tunnel and delivers them to the remote unit (113).

Description

ROUTING DATA IN AN IP-BASED COMMUNICATION SYSTEM

Field of the Invention

The present invention relates generally to communication systems and, in particular, to routing packets in an Internet-Protocol (IP) based communication system.

Background of the Invention

More and more next generation wireline and wireless communication systems are adopting the Internet Protocol (IP) based mode for transferring voice and data across the communication systems. Such a next generation wireless communications system is the IMT-2000 communication system as described in TR45.6-3G/98 Wireless IP Network Architecture based on IETF Protocols. Within such an IP-based communication system that permits mobility, remote units are typically assigned a "home" network where routers route data to the remote unit utilizing a known IP address. When the remote unit moves to another network, the remote unit contacts a serving switch (referred to as a foreign agent) that it has accessed the foreign agent's network, and the foreign agent provides the remote unit a care-of (c/o) IP address. The remote unit then notifies the home agent of the c/o address and the home agent routes all incoming packets to the c/o address to be distributed to the mobile via the foreign agent.

Although this solution for mobility works well, an underlying assumption in this solution is that the IP routing of packets destined to the mobile ends at the foreign agent and there can be no intervening routed IP network between the remote unit and the foreign agent since the intervening routed IP network cannot route packets using the destination address field of packets destined for that remote. In other words, simply providing the home agent with the c/o address of the foreign agent will not enable the system to route packets to remote units through intervening IP networks.

Such a system is also limited in its performance because the software in the mobile must detect its own movement and perform its own re-registration with the home agent after data link layers have been established. Because of the need for the radio link to already be established, and because of possibly large geographical separation between the mobile and the home agent, mobility management can be very slow and may result in unacceptably large amounts of lost information.

Therefore a need exists for a method and apparatus that allows for the routing of packets to remote units from foreign agents through intervening IP networks in a timely fashion.

Brief Description of the Drawings

FIG. 1 is a block diagram of a next-generation IP-based network in accordance with the preferred embodiment of the present invention. FIG. 2 illustrates the establishment of IP tunnels in accordance with the preferred embodiment of the present invention.

FIG. 3 is a flow chart showing operation of the communication system of FIG. 1 in accordance with the preferred embodiment of the present invention.

FIG. 4 is a flow chart showing operation of the foreign agent of FIG. 1 in accordance with the preferred embodiment of the present invention.

FIG. 5 is a flow chart showing operation of the foreign agent of FIG. 1 during a handoff in accordance with the preferred embodiment of the present invention.

Detailed Description of the Drawings

To address the need for routing in an IP-based communication system, a method and apparatus is provided wherein home agent establishes a first Internet Protocol (IP) tunnel (104) to a foreign agent. A first outer IP header is inserted before the datagram's existing IP header. A second IP tunnel is established between the foreign agent and a radio access network (RAN). When the foreign agent receives datagrams addressed to the remote unit, the foreign agent tunnels the datagrams to the RAN. In particular, the foreign agent strips the first outer IP header from the datagram and replaces the first outer IP header with a second outer IP header. The second outer IP header source and destination address identify the endpoints of the tunnel (foreign agent and RAN, respectively). The RAN unencapsulates packets forwarded from the foreign agent in the tunnel and delivers them to the remote unit. Because datagrams are re-tunneled to appropriate RANs through intervening network, the above system allows for the routing of packets to remote units through intervening networks. Therefore remote units that maintain an IP address for lengthy periods of time can effectively be contacted by their home agent through networks existing between a foreign agent and a RAN. The present invention encompasses a method for routing data within a packet-based communication system. Within the communication system an intervening packet-based network exists between a radio-access network (RAN) and a foreign agent. The method comprises the steps of receiving a second datagram from a home agent, where the second datagram comprises an encapsulated first datagram that is addressed to a remote unit. A RAN currently serving the remote unit is determined from the encapsulated first datagram and then the first datagram is re-encapsulated to form a third datagram. Finally the third datagram is routed to the RAN.

Additionally, the present invention encompasses a method for routing in an Internet-Protocol (IP) based communication system where an intervening IP- based network exists between a radio-access network (RAN) and a foreign agent. The method comprises the steps of receiving a second IP datagram at the foreign agent transmitted from a home agent via a first IP tunnel established between the home agent and the foreign agent, where the second IP datagram comprises an encapsulated first IP datagram that is addressed to a remote unit. A RAN currently serving the remote unit is determined from the first datagram and the first datagram is re-encapsulated to form a third IP datagram. A second IP tunnel is then established between the foreign agent and the RAN, and the third datagram is routed from the foreign agent to the RAN via the second tunnels established between the foreign agent and the RAN.

The present invention additionally encompasses a foreign agent having a radio-access network (RAN) coupled to the foreign agent through an intervening network. The foreign agent comprises an input for receiving a second datagram, via a first tunnel, from a home agent, where the second datagram comprises an encapsulated first datagram that contains an address to a remote unit. The foreign agent additionally comprises a database comprising the address to the remote unit and an associated tunnel to the RAN and an output for transmitting the first datagram to the RAN, via a second tunnel, within an encapsulated third datagram. Turning now to the drawings, wherein like numerals designate like components, FIG. 1 is a block diagram of communication system 100 in accordance with the preferred embodiment of the present invention. In the preferred embodiment of the present invention, communication system 100 utilizes a modified IP-based transport as described in the Network Working Group Request for Comments: 2002, (RFC 2002) by C. Perkins, which is incorporated by reference herein. Communication system 100 comprises home network 101, home agent 103, first foreign network 105, foreign agent 107, second foreign network 109 (which in the preferred embodiment is an intervening network between foreign agent 107 and radio access networks (RANs) 114-116). Additionally, RANs 114-116 comprise generic network elements of typical cellular infrastructure equipment configured in well known manners with processors, memories, instruction sets, and the like, which function in any suitable manner to perform over-the-air voice and data communication to and from remote unit 113. Additionally, within a RAN, specific network elements that communicate with the foreign agent may need to change as the mobile moves (e.g., base stations may need to change as the remote unit moves).

In the preferred embodiment of the present invention RANs 114-116 are generic network elements that utilize a Code Division Multiple Access (CDMA) system protocol as described in Cellular System Remote unit-Base Station Compatibility Standard of the Electronic Industry Association/Telecommunications Industry Association Interim Standard 95B (TIA/EIA/IS-95B), which is incorporated by reference herein. (EIA/TIA can be contacted at 2001 Pennsylvania Ave. NW Washington DC 20006). However, in alternate embodiments communication RANs 1 14-1 16 may utilize other digital cellular communication system protocols. As shown, each RAN 114-116 has respective coverage area 117-119.

Prior to describing operation of communication system 100 in accordance with the preferred embodiment of the present invention the following definitions give necessary background information. Interveniπg Network:

A network between a foreign agent and a RAN that routes packets through the network based on a destination address protocol field within the IP packet to be delivered. Remote units have a destination address with a different

(foreign) network.

Remote Unit:

A host or router that changes its point of attachment from one network or subnetwork to another. A mobile node may change its location without changing its IP address; it may continue to communicate with other Internet nodes at any location using its (constant) IP address, assuming link-layer connectivity to a point of attachment is available. In the preferred embodiment of the present invention remote unit 113 is preferably a Code Division Multiple Access (CDMA) remote unit manufactured by Motorola, Inc. of Schaumburg, IL. Home Agent

A router on a mobile node's home network which tunnels datagrams for delivery to the mobile node when it is away from home, and maintains current location information for the mobile node. In the preferred embodiment of the present invention home agent 103 is preferably a modified 7500 series router manufactured by Cisco, Inc.

Foreign Agent A router on a mobile node's visited network which provides routing services to the mobile node while registered. The foreign agent detunnels and delivers datagrams to the mobile node that were tunneled by the mobile node's home agent. For datagrams sent by a mobile node, the foreign agent may serve as a default router for registered mobile nodes. In the preferred embodiment of the present invention foreign agent 107 is preferably a modified 7500 series router manufactured by Cisco, Inc.

Care-of Address The termination point of a tunnel toward a mobile node, for datagrams forwarded to the mobile node while it is away from home. The protocol can use two different types of care-of address: a "foreign agent care-of address" is an address of a foreign agent with which the mobile node is registered, and a "co-located care-of address" is an externally obtained local address which the mobile node has associated with one of its own network interfaces. Foreign Network

Any network other than the mobile node's home network. In the preferred embodiment of the present invention foreign networks 109 and 105 are preferably IP-based networks.

Home Address

An IP address that is assigned for an extended period of time to a mobile node. It remains unchanged regardless of where the node is attached to the Internet.

Home Network

A network, possibly virtual, having a network prefix matching that of a mobile node's home address. Note that standard IP routing mechanisms will deliver datagrams destined to a mobile node's home address to the mobile node's home network.

Tunnel

The path followed by a datagram while it is encapsulated. The model is that, while it is encapsulated, a datagram is routed to a knowledgeable decapsulating agent, which unencapsulates the datagram and then correctly delivers it to its ultimate destination.

Operation of communication system 100 in accordance with the preferred embodiment of the present invention occurs as follows: In the preferred embodiment of the present invention remote unit 113 has a long-term IP address (home address) existing on home network 101, however in an alternate embodiment of the present invention remote unit has an IP address assigned in the visited network for the duration of the session. As shown in FIG. 1, RANs 114- 116 have established at system initialization time tunnels (only tunnel 108 shown) between the foreign agent and the RANs. Also shown in FIG 1, remote unit 113 is in communication with RAN 114, through foreign network 109. During data call initiation with RAN 114, RAN 114 contacts foreign agent 107 and notifies foreign agent 107 that remote unitl l3 has accessed the foreign agent's network. In turn, foreign agent 107 assigns remote unit 113 a c/o IP address, which is the IP address for foreign agent 107. The remote unit then notifies home agent 103 of its c/o address and the home agent 103 then routes all incoming datagrams that are addressed to remote unit 113 to the c/o address. In the preferred embodiment of the present invention home agent 103 establishes a first IP tunnel 104 to foreign agent 107 as described in RFC 2002 and Network Working Group Request for Comment: 2003 (RFC 2003) by C. Perkins, and incorporated by reference herein. In particular, every incoming IP datagram that is addressed to remote unit 113 is encapsulated (carried as a payload) within a second IP datagram. A first outer IP header is inserted before the datagram's existing IP header. As described in RFC2003, the first outer IP header source address and destination address identify the "endpoints" of the tunnel. The inner IP header source address and destination address identify the original sender and recipient (remote unit 113) of the datagram, respectively. The inner IP header is basically unchanged by the encapsulator. Thus operation of communication system 100 serves to reroute all datagrams delivered to home network 101 that are destined to remote unit 113. These datagrams are rerouted to foreign agent 107, and received by foreign agent 107 at input 102.

As discussed above, mobility may be restricted when intervening network 109 exists between remote unit 113 and the foreign agent 107. In the preferred embodiment of the present invention a second IP tunnel 108 is established between foreign agent 107 and RAN 114 to address this issue. Upon origination of remote unit 113 with RAN 114, RAN 114 sets up a call within the IP tunnel between foreign agent 107 and RAN 114. When foreign agent 107 receives datagrams addressed to remote unit 113, foreign agent 107 routes the data via tunneling the datagrams to RAN 114. In particular, foreign agent 107 strips the first outer IP header from the datagram (unencapsulates the datagram) and replaces the first outer IP header with a second outer IP header to form a third datagram. This datagram is output from foreign agent 107 via output 110. In the preferred embodiment of the present invention, the second outer IP header source and destination address identify the endpoints of the tunnel (foreign agent 107 and RAN 114, respectively). This process is illustrated in FIG. 2.

With reference to FIG. 2, when IP datagram 201 is received by home network 101, IP datagram 201 contains a source and destination IP address. In this case, the destination IP address is the IP address for remote unit 113. Home agent 103 intercepts the datagram and tunnels it to foreign agent 107. In particular, home agent 103 encapsulates the original IP datagram 201 within second datagram 202, with the outer header identifying the endpoints of the tunnel (home agent 103 and foreign agent 107). As discussed above, the inner IP header remains unchanged. Once second datagram 202 is received by foreign agent 107 it then routes the datagram to RAN 114 by stripping the outer addresses (home agent 103 and foreign agent 107) and re-encapsulates datagram 201 forming third datagram 203. Third datagram 203 contains the original IP datagram with a second outer header identifying the endpoints of the second IP tunnel (foreign agent 107 and RAN 114). When third datagram 203 is received by RAN 113 it is distributed to remote unit 113.

Because IP datagrams are re-tunneled to appropriate RANs 114-116 through intervening network 109, the above system 100 allows for the routing of packets to remote units through intervening IP networks. Therefore remote units that maintain an IP address for lengthy periods of time can effectively be contacted by their home agent through networks existing between a foreign agent and a RAN.

FIG. 3 is a flow chart showing operation of the communication system of FIG. 1 in accordance with the preferred embodiment of the present invention. The logic flow begins at step 301 where remote unit 113 registers with RAN 114. At step 305 RAN 114 provides remote unit 113 a c/o address for foreign agent 107 and remote unit 113 provides the c/o address to home agent 103 (step 310). Next, at step 315 an IP datagram is received by home network 101 and home agent 103 tunnels the datagram to foreign agent 107 through tunnel 104 existing in foreign network 105. As discussed above, home agent 103 encapsulates the original (first) IP datagram 201 within second datagram 202, having first outer header 210 identifying the endpoints of first tunnel 104 (home agent 103 and foreign agent 107). At step 320 foreign agent 107 receives second datagram 202 from home agent 103, strips first outer header 210, and encapsulates the original IP datagram 201 with second outer header 215 identifying the endpoints of second tunnel 108 to form third datagram 203. Finally, at step 325 a third datagram 203 is received and unencapsulated by RAN 114 and the original datagram 201 is delivered to remote unit 113.

FIG. 4 is a flow chart showing the operation of foreign agent 107 of FIG. 1 in accordance with the preferred embodiment of the present invention. Although FIG. 1 shows a single remote unit 113 in communication with RAN 114 utilizing a single tunnel 109, one of ordinary skill in the art will recognize that multiple remote units may be simultaneously in communication with RAN 1 14, each having their own unique IP address and tunnel. Additionally, a single remote unit 113 may be involved in multiple simultaneous calls, each having a unique IP address and sharing the same tunnel, or each having the same IP address and same tunnel, but identified by an appropriate protocol element, such as a call id. In order to keep track of all tunnels existing between foreign agent 107 and RAN 114, foreign agent stores this information within table (memory) 106 and updates table 106 as necessary. Table 106 consists of a row of data for each call that RANs 114-116 are involved in. Each row contains an IP address and a corresponding tunnel ID. In alternate embodiments of the present invention, table 106 may contain other entries in order to associate other parameters with the mobile IP address. For example, a certain quality of service may be associated with a particular IP address and stored within table 106. The logic flow begins at step 401 where foreign agent receives second datagram 202 with first IP datagram 201 embedded therein. As discussed above, the second datagram is received through a tunnel existing between home agent 103 and foreign agent 106. At step 405 foreign agent 107 analyzes the datagram, determines a mobile IP address from the datagram, and accesses table 106 to determine the RAN currently serving remote unit 113 via the particular tunnel ID. From this information foreign agent 107 then determines a particular tunnel to rout the first IP datagram (step 410) and re-encapsulates the first IP datagram within a third IP datagram (step 415). In particular, foreign agent 107 strips the first outer header from the second datagram, determines a second outer header for the datagram, and encapsulates the first datagram within a third datagram comprising the second outer header. Finally, at step 420, the first IP datagram is routed through the particular tunnel to RAN 114.

As one of ordinary skill in the art will recognize, as remote unit 113 moves to the periphery of a particular coverage area 117-119, it will be handed off to a RAN 114-116 that can better serve remote unit 113. During this process, communication with a serving RAN is terminated and communication begins with a new RAN. In order to expedite this process, the preferred embodiment of the present invention utilizes an approach that does not require home agent 103 to be notified when a handoff occurs. When a call is initiated or handed off at a particular RAN, the RAN sends a notice to the foreign agent which creates an entry in its mapping table. When datagrams are received by the RAN, the RAN unencapsulates packets forwarded from the foreign agent in that tunnel and delivers them to the mobile.

FIG. 5 is a flow chart showing operation of foreign agent 107 of FIG. 1 during such a handoff. The logic flow begins at step 501 where remote unit 113 is actively communicating with RAN 114, utilizing tunnel 108. In other words, home agent 103 supplies foreign agent 107 with IP datagrams that arrive at home network 101 addressed to remote unit 113. In turn, foreign agent 107 routes the IP datagrams to RAN 114 via tunnel 108. Next, at step 505 remote unit 113 is handed off to RAN 115 using normal handover procedures. More particularly, radio network signaling such as that described in IS-95B sections 6.6.6 and 7.6.6 is utilized to transfer communication from RAN 114 to RAN 115. At step 510 RAN 115 determines (via IS-95B signaling) that communication with remote unit 113 is now taking place. At step 515 RAN 115 notifies foreign agent of the handoff and establishes a new call within a tunnel between existing between RAN 115 and foreign agent 107. In particular when radio network signaling notifies RAN 115 that remote unit 113 has been transferred to it, RAN 115 notifies foreign agent 107 that a new call is being established in the already existing tunnel between foreign agent 107 and RAN 115. The notification associates the call and the remote unit 113 with the tunnel. In response, foreign agent receives notification that a handover has occurred, and immediately updates table 106 to associate a tunnel ID with the IP address of remote unit 113 (step 520). Finally at step 525 foreign agent 107 routes all datagrams associated with remote unit 113 (i.e., having the remote unit's IP address) to RAN 115 via the tunnel. Because foreign agent 107 updates table 106 when remote unit 113 is handed off to a different RAN, home agent 103 does not need to update its c/o address when remote unit 113 is handed off. More particularly, remote unit's in communication with RANs 1 14-116 share the same c/o address (IP address of foreign agent 107), with foreign agent 107 determining where to route a particular datagram. Because of this, home agent 103 utilizes the same c/o address both before and after handoff, resulting in faster handovers for remote unit 113.

The descriptions of the invention, the specific details, and the drawings mentioned above, are not meant to limit the scope of the present invention. For example, although the preferred embodiment of the present invention was described above having second tunnel between RAN 114 and foreign agent 107, one of ordinary skill in the art will recognize that second tunnel 108 may terminate at specific network elements within RAN 114. Specifically, it is envisioned that all tunnels between foreign agent 107 and RANs 114-1 16 terminate at a selection and distribution unit (SDU) existing within a RAN, and that the termination address for the second tunnel is an actual address of an SDU. (SDUs are described in detail in IS-634 sections IS634A000). It is the intent of the inventors that various modifications can be made to the present invention without varying from the spirit and scope of the invention, and it is intended that all such modifications come within the scope of the following claims and their equivalents.

Claims

1. A method for routing in an Internet-Protocol (IP) based communication system, wherein an intervening IP-based network exists between a radio-access network (RAN) and a foreign agent, the method comprising the steps of: determining that communication with a remote unit is taking place; notifying a foreign agent that communication with the remote unit is taking place; and based on the notification, receiving a datagram from the foreign agent via a tunnel established between the foreign agent, wherein the datagram comprises an encapsulated first datagram that is addressed to a remote unit.

2. A method for routing data within a packet-based communication system, wherein an intervening packet-based network exists between a radio-access network (RAN) and a foreign agent, the method comprising the steps of: receiving a second datagram from a home agent, wherein the second datagram comprises an encapsulated first datagram that is addressed to a remote unit; determining a RAN currently serving the remote unit from the encapsulated first datagram; re-encapsulating the first datagram to form a third datagram; and routing the third datagram to the RAN.

3. The method of claim 2 wherein the step of receiving the second datagram from the home agent comprises the step of receiving the second datagram from the home agent via a tunnel established between the home agent and the foreign agent.

4. The method of claim 2 wherein the step of receiving the second datagram from the home agent comprises the step of receiving an Internet-Protocol (IP) datagram from the home agent.

5. The method of claim 2 wherein the step of determining the RAN currently serving the remote unit comprises the steps of: analyzing the first datagram to determine an address for the remote unit; and accessing memory to determine an associated RAN for the address.

6. The method of claim 2 wherein the step of determining the RAN currently serving the remote unit comprises the steps of: analyzing the first datagram to determine an Internet-Protocol (IP) address for the remote unit; and accessing memory to determine an associated RAN for the IP address.

7. The method of claim 2 wherein the step of re-encapsulating the first datagram that is addressed to the remote unit comprises the steps of: stripping a first outer header from the second datagram; determining a second outer header for the first datagram; and encapsulating the first datagram within a third datagram comprising the second outer header.

8. The method of claim 2 wherein the step of routing the third datagram to the RAN comprises the step of routing the third datagram to the RAN via a tunnel established between a foreign agent and the RAN.

9. A method for routing in an Internet-Protocol (IP) based communication system, wherein an intervening IP-based network exists between a radio-access network (RAN) and a foreign agent, the method comprising the steps of: receiving a second IP datagram at the foreign agent transmitted from a home agent via a first IP tunnel established between the home agent and the foreign agent, wherein the second IP datagram comprises an encapsulated first IP datagram that is addressed to a remote unit; determining a RAN currently serving the remote unit from the first datagram; re-encapsulating the first datagram to form a third IP datagram; establishing a second IP tunnel between the foreign agent and the RAN; and routing the third datagram from the foreign agent to the RAN via the second tunnel established between the foreign agent and the RAN.

10. A foreign agent having a radio-access network (RAN) coupled to the foreign agent through an intervening network, the foreign agent comprising: an input for receiving a second datagram, via a first tunnel, from a home agent, wherein the second datagram comprises an encapsulated first datagram that contains an address to a remote unit; a database comprising the address to the remote unit and an associated tunnel to the RAN; an output for transmitting the first datagram to the RAN, via a second tunnel, within an encapsulated third datagram.