Method and system for secure cable modem registration

Abstract

A method and system for secure cable modem initialization in a data-over-cable system is provided. The method includes sending a unique identifier, such an Internet Protocol ("IP") address and a selected time-value, such as an approximate message send time-value, in a registration request message. A message integrity check value is calculated using the unique identifier, the selected time-value and one or more configuration parameters in a pre-determined order. The message integrity check value is added to the registration request message. A cable modem termination system receives the registration request message and uses the message integrity check value to authenticate the message and determine if the registration request message was sent within a pre-determined period of time (e.g., 1 second) from a recognized cable modem. If not, the registration request message is discarded and a log file entry is added to a log file with information from the registration request message (e.g., network level and data-link level network addresses). The network address and selected time-value uniquely identify the cable modem and help prevent a rouge user from intercepting a valid cable modem registration request message and using it at a later time to register a rouge cable modem. The log file helps track rouge users attacking the data-over-cable system. The method and system provide improved security for registering cable modems in a data-over-cable system.

Claims

I claim:

1. In a data-over-cable system including a plurality of network devices, a method of securely registering a network device, the method comprising the following steps:

receiving a first configuration file on a first network device from a first protocol server, the first configuration file including a plurality of configuration parameters;

creating a first message on the first network device including one or more configuration parameters from the first configuration file;

adding a unique identifier for the first network device to the first message;

adding a selected time-value to the first message, wherein the selected time-value indicates a sending time for the first message;

calculating a message integrity check value using the unique identifier, the selected time-value and one or more configuration parameters from the first configuration file in a pre-determined order to uniquely identify the configuration information for the network device;

adding the message integrity check value to the first message; and

sending the first message from the first network device to a second network device,

wherein the second network device uses the message integrity check value, the unique identifier of the first network device and the selected time-value to verify the integrity of the first message.

2. The method of claim 1 wherein the step of calculating a message integrity check value includes calculating the message integrity check value with a cryptographic hashing function.

3. The method of claim 2 wherein the cryptographic hashing function is MD5.

4. The method of claim 1 wherein the step of adding a unique identifier for the first network device to the first message includes adding any of Internet Protocol address or a Medium Access Protocol Address for the network device to the first message.

5. The method of claim 1 wherein the first network device is a cable modem the second network device is a cable modem termination system and the first protocol server is a Trivial File Transfer Protocol server.

6. The method of claim 1 wherein the first message is a cable modem registration request message used to register a cable modem in the data-over-cable system.

7. The message of claim 1 wherein the selected time-value is a number of seconds the first network device has been executing.

8. The method of claim 7 wherein the number of seconds the first network device has been executing includes the number of seconds the first network device has been executing since time 00:00 on Jan. 1, 1970.

9. The method of claim 1 wherein the step of calculating a message integrity check value includes:

calculating a first message integrity check value using the unique identifier, the selected time-value, one or more configuration parameters from the first configuration file, and one or more additional configuration parameters not from the first configuration file in a pre-determined order;

adding the first message integrity check value to the first message;

calculating a second message integrity check value using the unique identifier, the selected time-value, one or more configuration parameters from the first configuration file, one or more additional configuration parameters not from the first configuration file and the first message integrity check value in a pre-determined order; and

adding the second message integrity check value to the first message as the message integrity check value.

10. A computer readable medium having stored therein instructions for causing a central processing unit to execute the method of claim 1.

11. In a data-over-cable system including a plurality of network devices, a method of registering a network device, the method comprising the following steps:

receiving a first message on a second network device from a first network device; and

determining whether the first message is valid using a first message integrity check value included in the first message, and if so,

determining whether the first message was sent within a pre-determined time using a selected time-value from the first message, and if not,

discarding the first message;

creating a log entry in a log file on the second network device with a plurality of information from the first message, wherein the log entry is used to determine where the discarded first message was sent from in the data-over-cable system; and

sending a second message to the first network device as a response to the first message indicating rejection of the first message.

12. The method of claim 11 wherein the first network device is a cable modem, the first message is a cable modem registration request message, and the second network device is a cable modem termination system.

13. The method of claim 11 wherein the message integrity check value includes a first unique identifier for the first network device, a selected time-value indicating a sending time for the first message and a plurality of configuration parameters used to configure the first network device.

14. The method of claim 11 wherein the step of creating a log entry in a log file includes creating a log entry including a first network address, a second network address and the selected time-value.

15. The method of claim 14 wherein the first network address is a network level network address and the second network address is a data-link level network address.

16. The method of claim 15 wherein the network level address is an Internet Protocol address and the data-link level network address is a Medium Access Control address.

17. The method of claim 11 wherein the step of determining whether the first message is valid using a message integrity check value included in the first message includes calculating a second message integrity check value using a cryptographic hashing function and comparing it to the fist message integrity check value.

18. The method of claim 17 wherein the cryptographic hashing function is MD5.

19. The method of claim 11 further comprising:

determining whether the first message was sent within a pre-determined time using a selected time-value from the first message, wherein the first message integrity check value includes a unique identifier and a selected time-value from the first network device, and if so,

accepting the first message from the first network device; and

sending a second message to the first network device as a response to the first message indicating acceptance of the first message.

20. The method of claim 19 wherein the first message is a cable modem registration request message, the second message is a cable modem registration response message, the first network device is a cable modem, and the second network device is a cable modem termination system.

21. A computer readable medium having stored therein instructions for causing a central processing unit to execute the method of claim 11.

22. In a data-over-cable system including a plurality of cable modems, a method of securely registering a cable modem, the method comprising the following steps:

receiving a first configuration file on a cable modem from a Trivial File Transfer Protocol server, the first configuration file including a plurality of configuration parameters to configure the cable modem;

creating a registration request message on the cable modem including configuration parameters from the first configuration file;

adding an Internet Protocol address for the cable modem to the registration request message;

adding a selected time-value to the registration request message, wherein the selected time-value indicates a sending time of the registration request message;

calculating a message integrity check value using a cryptographic hashing function with the Internet Protocol address, the selected time-value and one or more configuration parameters from the first configuration file in a pre-determined order to uniquely identify the configuration parameters for the cable modem;

adding the message integrity check value to the registration request message; and

sending the registration request message from the cable modem to a cable modem termination system,

wherein the cable modem termination system uses the registration request message integrity check value, the Internet Protocol address for the cable modem and a selected time-value indicating when the registration request message was sent from the cable modem to verify the integrity of the registration request message.

23. A computer readable medium having stored therein instructions for causing a central processing unit to execute the method of claim 22.

Description

FIELD OF INVENTION

The present invention relates to communications in computer networks. More specifically, it relates to a method and system for secure cable modem initialization in a data-over-cable system.

BACKGROUND OF THE INVENTION

Cable television networks such as those provided by Comcast Cable Communications, Inc., of Philadelphia, Pa., Cox Communications of Atlanta Ga., Tele-Communications, Inc., of Englewood Colo., Time-Warner Cable, of Marietta Ga., Continental Cablevision, Inc., of Boston Mass., and others provide cable television services to a large number of subscribers over a large geographical area. The cable television networks typically are interconnected by cables such as coaxial cables or a Hybrid Fiber/Coaxial ("HFC") cable system which have data rates of about 10 Mega-bits-per-second ("Mbps") to 30+ Mbps.

The Internet, a world-wide-network of interconnected computers, provides multi-media content including audio, video, graphics and text that requires a large bandwidth for downloading and viewing. Most Internet Service Providers ("ISPs") allow customers to connect to the Internet via a serial telephone line from a Public Switched Telephone Network ("PSTN") at data rates including 14,400 bps, 28,800 bps, 33,600 bps, 56,000 bps and others that are much slower than the about 10 Mbps to 30+ Mbps available on a coaxial cable or HFC cable system on a cable television network.

With the explosive growth of the Internet, many customers have desired to use the larger bandwidth of a cable television network to connect to the Internet and other computer networks. Cable modems, such as those provided by 3Com Corporation of Santa Clara, Calif., U.S. Robotics Corporation of Skokie, Ill., and others offer customers higher-speed connectivity to the Internet, an intranet, Local Area Networks ("LANs") and other computer networks via cable television networks. These cable modems currently support a data connection to the Internet and other computer networks via a cable television network with a data rate of up to 30+ Mbps which is a much larger data rate than can be supported by a modem used over a serial telephone line.

However, most cable television networks provide only unidirectional cable systems, supporting only a "downstream" data path. A downstream data path is the flow of data from a cable system "headend" to a customer. A cable system headend is a central location in the cable television network that is responsible for sending cable signals in the downstream direction. A return data path via a telephone network, such as a public switched telephone network provided by AT&T and others, (i.e., a "telephony return") is typically used for an "upstream" data path. An upstream data path is the flow of data from the customer back to the cable system headend. A cable television system with an upstream connection to a telephony network is called a "data-over-cable system with telephony return."

An exemplary data-over-cable system with telephony return includes customer premise equipment (e.g., a customer computer), a cable modem, a cable modem termination system, a cable television network, a public switched telephone network, a telephony remote access concentrator and a data network (e.g., the Internet). The cable modem termination system and the telephony remote access concentrator together are called a "telephony return termination system."

The cable modem termination system receives data packets from the data network and transmits them downstream via the cable television network to a cable modem attached to the customer premise equipment. The customer premise equipment sends response data packets to the cable modem, which sends response data packets upstream via public switched telephone network to the telephony remote access concentrator, which sends the response data packets back to the appropriate host on the data network.

When a cable modem used in the data-over-cable system with telephony return is initialized, a connection is made to both the cable modem termination system via the cable network and to the telephony remote access concentrator via the public switched telephone network. When a cable modem is initialized, it will initialize one or more downstream channels (i.e., downstream connections) to the cable modem termination system via the cable network or the telephony remote access concentrator via the public switched telephone network.

Once a cable modem has been initialized in a data-over-cable system, it registers with a cable modem termination system to allow the cable modem to receive data over a cable television connection and/or from a data network (e.g., the Internet or an Intranet). The cable modem forwards configuration information it receives in a configuration file during initialization to the cable modem termination system as part of a registration request message. The cable modem termination system performs a number of tests on the configuration in the registration request message to confirm the integrity of the configuration information. For example, the configuration information typically includes one or more Message Integrity Check ("MIC") fields. The MIC fields are created on the cable modem by performing a cryptographic hashing function on the configuration information (e.g., with Message Digest 5 ("MD5")), and sending the MIC fields with the configuration information in the registration request message. The cable modem termination system verifies the integrity of the configuration information in the registration request message using the same cryptographic hashing function on the configuration information and comparing the cryptographic hashing values to cryptographic hashing function values in the MIC fields.

There are several problems associated with sending configuration information from a cable modem to a cable modem termination system in the registration request message. Configuration information sent from a cable modem to a cable modem termination system with MIC fields is still vulnerable to malicious attacks. The configuration information in the registration request message can be intercepted and used in rouge cable modems that may attack the data-over-cable system or obtain free services on the data-over-cable system. The MIC fields allow the integrity of the configuration information to be verified at the cable modem termination system. However, the MIC fields do not include an identifier for a cable modem sending the configuration information, nor do the MIC fields identify a time period during which the configuration information can be used. Thus, the MIC fields, as they are presently used in the configuration information, do not prevent a malicious user from intercepting and re-using the configuration file for another cable modem at another time.

For example, a rouge user could intercept configuration information in a registration request message sent from a legitimate cable modem to the cable modem termination system. At a later time, the rouge user transmits all of the configuration information exactly as it was intercepted back to cable modem termination system in another cable modem registration request message. Since the configuration information was re-transmitted exactly as it was intercepted, when the cable modem termination system checks the MIC fields, the configuration information is verified as valid and the rouge user could masquerade as a "legitimate" cable modem user thereby receiving free services or attacking the data-over-cable system.

It is therefore desirable to improve the security for transferring configuration information from cable modems to the cable modem termination system in a data-over-cable system so the configuration information in a configuration file cannot be re-used by other cable modems at another time.

SUMMARY OF THE INVENTION

In accordance with an illustrative embodiment of the present invention, the problems associated with sending secure cable modem configuration information are overcome. A method and system for secure network device registration in a data-over-cable system is provided. The method includes receiving a first configuration file on a first network device from a first protocol server, the first configuration file including multiple configuration parameters. A first message is created on the first network device including one or more configuration parameters from the first configuration file. A unique identifier (e.g., a network address) for the first network device is added to the first message. A selected time-value is added to the first message, wherein the selected time-value indicates an approximate sending time of the first message. A message integrity check value is calculated using the unique identifier, the selected time-value and one or more configuration parameters from the configuration file in a pre-determined order to uniquely identify the configuration information for the first network device. The message integrity check value is calculated using a pre-determined cryptographic technique. The message integrity check value is added to the first message. The first message is sent from the first network device to a second network device, wherein the second network device uses the message integrity check value including the unique identifier and selected time-value to uniquely identify the first network device and prevent another network device from using the configuration information in the first message at a later time.

In an illustrative embodiment of the present invention, a cable modem creates a registration request message that includes configuration information from a file obtained by a cable modem from a Trivial File Transfer Protocol server. The cable modem receives the name of the configuration file from a Dynamic Host Configuration Protocol ("DHCP") server during an initialization sequence. The cable modem adds an IP address, Medium Access Protocol Address ("MAC") or other unique identifier to the registration request message. The IP address is also obtained by the cable modem from a DHCP server during an initialization sequence. The cable modem selects a time-value and adds it to the registration request message, wherein the selected time-value indicates an approximate sending time of the registration request message. A message integrity check value is calculated using the IP address, the selected time-value and one or more configuration parameters in a pre-determined order to uniquely identify the configuration information for the cable modem. The message integrity check value is calculated using a predetermined cryptographic technique (e.g., MD 5). The message integrity check value with the IP address and selected time value is added to the registration request message. The registration request message is sent from the cable modem to the cable modem termination system.

The cable modem termination system uses the message integrity check value to verify the integrity of the configuration information, as well as uniquely identify the cable modem, and determine a time period for which the registration request message is valid. For example, if the cable modem termination system validates the configuration information but detects the selected time-value is different by a predetermined amount (e.g., 1 second) from an internal time value on the cable modem termination system, the cable modem termination system discards the registration request message. However, the present invention is not limited to cable modems, cable modem termination systems, or registration request messages and other network devices and messages could also be used.

The method and system of the present invention provide improved security for cable modem registration. For a rouge user to attack a data-over-cable system, the rouge user must intercept the registration request message, modify the IP address for the cable modem and/or the selected time-value, re-calculate a message integrity check value with a rouge IP address and/or selected time value, and re-transmit the registration request message all within a pre-determined time period that is used by the cable modem termination system (e.g., 1 second) for checking registration request messages.

The rouge user may also have to determine the cryptographic technique being used to create the message integrity check value and guess the predetermined time period that is used by the cable modem termination system for checking registration request messages. Since the pre-determined time period that is used by the cable modem termination system for checking registration request messages is small, the probability a rouge user can successfully attack the data-over-cable system is reduced.

In addition, if the cable modem termination system detects that the selected time-value is different than a pre-determined time period, the cable modem termination system discards the registration request message and creates a log entry in a log file including information from the registration request message such as a network address for the rouge user, the IP address, and/or the selected time-value. The log file is an added security measure that aids the cable modem termination system in determining when and where a potential attack from a rouge user came from. Repeated attempts by a rouge user from a network address on the data-over-cable system can be determined by checking the log file. The cable modem termination system can deny access to cable modem at a connection or network address that continually sends invalid registration request messages.

The foregoing and other features and advantages of an illustrative embodiment of the present invention will be more readily apparent from the following detailed description, which proceeds with references to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a cable modem system with telephony return;

FIG. 2 is a block diagram illustrating a protocol stack for a cable modem;

FIG. 3 is a block diagram illustrating a Telephony Channel Descriptor message structure;

FIG. 4 is a block diagram illustrating a Termination System Information message structure;

FIG. 5 is a flow diagram illustrating a method for addressing hosts in a cable modem system;

FIG. 6 is a block diagram illustrating a Dynamic Host Configuration Protocol message structure;

FIGS. 7A and 7B are a flow diagram illustrating a method for discovering hosts in a cable modem system;

FIG. 8 is a block diagram illustrating a data-over-cable system for the method illustrated in FIGS. 7A and 7B;

FIG. 9 is a block diagram illustrating the message flow of the method illustrated in FIGS. 7A and 7B;

FIGS. 10A and 10B are a flow diagram illustrating a method for resolving host addresses in a data-over-cable system;

FIGS. 11A and 11B are a flow diagram illustrating a method for resolving discovered host addresses; and

FIG. 12 is a block diagram illustrating the message flow of the method illustrated in FIGS. 10A and 10B;

FIGS. 13A and 13B are a flow diagram illustrating a method for obtaining addresses for customer premise equipment;

FIGS. 14A and 14B are a flow diagram illustrating a method for resolving addresses for customer premise equipment;

FIGS. 15A and 15B are a flow diagram illustrating a method for addressing network host interfaces from customer premise equipment;

FIGS. 16A and 16B are a flow diagram illustrating a method for resolving network host interfaces from customer premise equipment;

FIG. 17 is a block diagram illustrating a message flow for the methods in FIGS. 15A, 15B, and 16A and 16B;

FIG. 18 is a block diagram illustrating a data-over-cable system for secure registration;

FIG. 19 is a flow diagram illustrating a method for secure registration for a network device;

FIG. 20 is a flow diagram illustrating a method for secure registration for a cable modem;

FIG. 21 is a flow diagram illustrating a method for calculating a message integrity check value;

FIG. 22 is a block diagram illustrating a cable modem registration request message; and

FIG. 23 is a flow diagram illustrating a method for checking validity of a cable modem registration request message.

DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT

Cable Modem System With Telephony Return

FIG. 1 is a block diagram illustrating a data-over-cable system with telephony return 10, hereinafter data-over-cable system 10. Most cable providers known in the art predominately provide uni-directional cable systems, supporting only a "downstream" data path. A downstream data path is the flow of data from a cable television network "headend" to customer premise equipment (e.g., a customer's personal computer). A cable television network headend is a central location that is responsible for sending cable signals in a downstream direction. A return path via a telephony network ("telephony return") is typically used for an "upstream" data path in uni-directional cable systems. An upstream data path is the flow of data from customer premise equipment back to the cable television network headend.

However, data-over-cable system 10 of the present invention may also provide a bi-directional data path (i.e., both downstream and upstream) without telephony return as is also illustrated in FIG. 1 and the present invention is not limited to a data-over-cable system with telephony return. In a data-over cable system without telephony return, customer premise equipment or cable modem has an upstream connection to the cable modem termination system via a cable television connection, a wireless connection, a satellite connection, or a connection via other technologies to send data upstream to the cable modem termination system.

Data-over-cable system 10 includes a Cable Modem Termination System ("CMTS") 12 connected to a cable television network 14, hereinafter cable network 14. Cable network 14 includes cable television networks such as those provided by Comcast Cable Communications, Inc., of Philadelphia, Pa., Cox Communications, or Atlanta, Ga., Tele-Communications, Inc., of Englewood Colo., Time-Warner Cable, of Marietta, Ga., Continental Cablevision, Inc., of Boston, Mass., and others. Cable network 14 is connected to a Cable Modem ("CM") 16 with a downstream cable connection.

CM 16 is connected to Customer Premise Equipment ("CPE") 18 such as a personal computer system via a Cable Modem-to-CPE Interface ("CMCI") 20. CM 16 is connected to a Public Switched Telephone Network ("PSTN") 22 with an upstream telephony connection. PSTN 22 includes those public switched telephone networks provided by AT&T, Regional Bell Operating Companies (e.g., Ameritch, U.S. West, Bell Atlantic, Southern Bell Communications, Bell South, NYNEX, and Pacific Telesis Group), GTE, and others. The upstream telephony connection is any of a standard telephone line connection, Integrated Services Digital Network ("ISDN") connection, Asymmetric Digital Subscriber Line ("ADSL") connection, or other telephony connection. PSTN 22 is connected to a Telephony Remote Access Concentrator ("TRAC") 24. In a data-over cable system without telephony return, CM 16 has an upstream connection to CMTS 12 via a cable television connection, a wireless connection, a satellite connection, or a connection via other technologies to send data upstream outside of the telephony return path. An upstream cable television connection via cable network 14 is illustrated in FIG. 1.

FIG. 1 illustrates a telephony modem integral to CM 16. In another embodiment of the present invention, the telephony modem is a separate modem unit external to CM 16 used specifically for connecting with PSTN 22. A separate telephony modem includes a connection to CM 16 for exchanging data. CM 16 includes cable modems provided by the 3Com Corporation of Santa Clara, Calif., U.S. Robotics Corporation of Skokie, Ill., and others. In yet another embodiment of the present invention, CM 16 includes functionality to connect only to cable network 14 and receives downstream signals from cable network 14 and sends upstream signals to cable network 14 without telephony return. The present invention is not limited to cable modems used with telephony return.

CMTS 12 and TRAC 24 may be at a "headend" of cable system 10, or TRAC 24 may be located elsewhere and have routing associations to CMTS 12. CMTS 12 and TRAC 24 together are called a "Telephony Return Termination System" ("TRTS") 26. TRTS 26 is illustrated by a dashed box in FIG. 1. CMTS 12 and TRAC 24 make up TRTS 26 whether or not they are located at the headend of cable network 14, and TRAC 24 may in located in a different geographic location from CMTS 12. Content severs, operations servers, administrative servers and maintenance servers used in data-over-cable system 10 (not shown in FIG. 1) may also be in different locations. Access points to data-over-cable system 10 are connected to one or more CMTS's 12 or cable headend access points. Such configurations may be "one-to-one", "one-to-many," or "many-to-many," and may be interconnected to other Local Area Networks ("LANs") or Wide Area Networks ("WANs").

TRAC 24 is connected to a data network 28 (e.g., the Internet or an intranet) by a TRAC-Network System Interface 30 ("TRAC-NSI"). CMTS 12 is connected to data network 28 by a CMTS-Network System Interface ("CMTS-NSI") 32. The present invention is not limited to data-over-cable system 10 illustrated in FIG. 1, and more or fewer components, connections and interfaces could also be used.

Cable Modem Protocol Stack

FIG. 2 is a block diagram illustrating a protocol stack 36 for CM 16. FIG. 2 illustrates the downstream and upstream protocols used in CM 16. As is known in the art, the Open System Interconnection ("OSI") model is used to describe computer networks. The OSI model consists of seven layers including from lowest-to-highest, a physical, data-link, network, transport, session, application and presentation layer. The physical layer transmits bits over a communication link. The data link layer transmits error free frames of data. The network layer transmits and routes data packets.

For downstream data transmission, CM 16 is connected to cable network 14 in a physical layer 38 via a Radio Frequency ("RF") Interface 40. In an illustrative embodiment of the present invention, RF Interface 40 has an operation frequency range of 50 Mega-Hertz ("MHz") to 1 Giga-Hertz ("GHz") and a channel bandwidth of 6 MHz. However, other operation frequencies may also be used and the invention is not limited to these frequencies. RF interface 40 uses a signal modulation method of Quadrature Amplitude Modulation ("QAM"). As is known in the art, QAM is used as a means of encoding digital information over radio, wire, or fiber optic transmission links. QAM is a combination of amplitude and phase modulation and is an extension of multiphase phase-shift-keying. QAM can have any number of discrete digital levels typically including 4, 16, 64 or 256 levels. In one embodiment of the present invention, QAM-64 is used in RF interface 40. However, other operating frequencies modulation methods could also be used. For more information on RF interface 40 see the Institute of Electrical and Electronic Engineers ("IEEE") standard 802.14 for cable modems incorporated herein by reference. IEEE standards can be found on the World Wide Web at the Universal Resource Locator ("URL") "www.ieee.org." However, other RF interfaces 40 could also be used and the present invention is not limited to IEEE 802.14 (e.g., RF interfaces from Multimedia Cable Network Systems ("MCNS") and others could also be used).

Above RF interface 40 in a data-link layer 42 is a Medium Access Control ("MAC") layer 44. As is known in the art, MAC layer 44 controls access to a transmission medium via physical layer 38. For more information on MAC layer protocol 44 see IEEE 802.14 for cable modems. However, other MAC layer protocols 44 could also be used and the present invention is not limited to IEEE 802.14 MAC layer protocols (e.g., MCNS MAC layer protocols and others could also be used).

Above MAC layer 44 is an optional link security protocol stack 46. Link security protocol stack 46 prevents authorized users from making a data connection from cable network 14. RF interface 40 and MAC layer 44 can also be used for an upstream connection if data-over-cable system 10 is used without telephony return.

For upstream data transmission with telephony return, CM 16 is connected to PSTN 22 in physical layer 38 via modem interface 48. The International Telecommunications Union-Telecommunication Standardization Sector ("ITU-T", formerly known as the CCITT) defines standards for communication devices identified by "V.xx" series where "xx" is an identifying number. ITU-T standards can be found on the World Wide Web at the URL "www.itu.ch."

In one embodiment of the present invention, ITU-T V.34 is used as modem interface 48. As is known in the art, ITU-T V.34 is commonly used in the data link layer for modem communications and currently allows data rates as high as 33,600 bits-per-second ("bps"). For more information see the ITU-T V.34 standard. However, other modem interfaces or other telephony interfaces could also be used.

Above modem interface 48 in data link layer 42 is Point-to-Point Protocol ("PPP") layer 50, hereinafter PPP 50. As is known in the art, PPP is used to encapsulate network layer datagrams over a serial communications link. For more information on PPP see Internet Engineering Task Force ("IETF") Request for Comments ("RFC"), RFC-1661, RFC-1662 and RFC-1663 incorporated herein by reference. Information for IETF RFCs can be found on the World Wide Web at URLs "ds.internic.net" or "www.ietf.org."

Above both the downstream and upstream protocol layers in a network layer 52 is an Internet Protocol ("IP") layer 54. IP layer 54, hereinafter IP 54, roughly corresponds to OSI layer 3, the network layer, but is typically not defined as part of the OSI model. As is known in the art, IP 54 is a routing protocol designed to route traffic within a network or between networks. For more information on IP 54 see RFC-791 incorporated herein by reference.

Internet Control Message Protocol ("ICMP") layer 56 is used for network management. The main functions of ICMP layer 56, hereinafter ICMP 56, include error reporting, reachability testing (e.g., "pinging") congestion control, route-change notification, performance, subnet addressing and others. Since IP 54 is an unacknowledged protocol, datagrams may be discarded and ICMP 56 is used for error reporting. For more information on ICMP 56 see RFC-971 incorporated herein by reference.

Above IP 54 and ICMP 56 is a transport layer 58 with User Datagram Protocol layer 60 ("UDP"). UDP layer 60, hereinafter UDP 60, roughly corresponds to OSI layer 4, the transport layer, but is typically not defined as part of the OSI model. As is known in the art, UDP 60 provides a connectionless mode of communications with datagrams. For more information on UDP 60 see RFC-768 incorporated herein by reference.

Above the network layer are a Simple Network Management Protocol ("SNMP") layer 62, Trivial File Protocol ("TFTP") layer 64, Dynamic Host Configuration Protocol ("DHCP") layer 66 and a UDP manager 68. SNMP layer 62 is used to support network management functions. For more information on SNMP layer 62 see RFC-1157 incorporated herein by reference. TFTP layer 64 is a file transfer protocol used to download files and configuration information. For more information on TFTP layer 64 see RFC-1350 incorporated herein by reference. DHCP layer 66 is a protocol for passing configuration information to hosts on an IP 54 network. For more information on DHCP layer 66 see RFC-1541 incorporated herein by reference. UDP manager 68 distinguishes and routes packets to an appropriate service (e.g., a virtual tunnel). More or few protocol layers could also be used with data-over-cable system 10.

CM 16 supports transmission and reception of IP 54 datagrams as specified by RFC-791. CMTS 12 and TRAC 24 may perform filtering of IP 54 datagrams. CM 16 is configurable for IP 54 datagram filtering to restrict CM 16 and CPE 18 to the use of only their assigned IP 54 addresses. CM 16 is configurable for IP 54 datagram UDP 60 port filtering (i.e., deep filtering).

CM 16 forwards IP 54 datagrams destined to an IP 54 unicast address across cable network 14 or PSTN 22. Some routers have security features intended to filter out invalid users who alter or masquerade packets as if sent from a valid user. Since routing policy is under the control of network operators, such filtering is a vendor specific implementation. For example, dedicated interfaces (i.e., Frame Relay) may exist between TRAC 24 and CMTS 12 which preclude filtering, or various forms of virtual tunneling and reverse virtual tunneling could be used to virtually source upstream packets from CM 16. For more information on virtual tunneling see Level 2 Tunneling Protocol ("L2TP") or Point-to-Point Tunneling Protocol ("PPTP") in IETF draft documents incorporated herein by reference by Kory Hamzeh, et. al (IETF draft documents are precursors to IETF RFCs and are works in progress).

CM 16 also forwards IP 54 datagrams destined to an IP 54 multicast address across cable network 14 or PSTN 22. CM 16 is configurable to keep IP 54 multicast routing tables and to use group membership protocols. CM 16 is also capable of IP 54 tunneling upstream through the telephony path. A CM 16 that wants to send a multicast packet across a virtual tunnel will prepend another IP 54 header, set the destination address in the new header to be the unicast address of CMTS 12 at the other end of the tunnel, and set the IP 54 protocol field to be four, which means the next protocol is IP 54.

CMTS 12 at the other end of the virtual tunnel receives the packet, strips off the encapsulating IP 54 header, and forwards the packet as appropriate. A broadcast IP 54 capability is dependent upon the configuration of the direct linkage, if any, between TRAC 24 and CMTS 12. CMTS 12, CM 16, and TRAC 24 are capable of routing IP 54 datagrams destined to an IP 54 broadcast address which is across cable network 14 or PSTN 22 if so configured. CM 16 is configurable for IP 54 broadcast datagram filtering.

An operating environment for CM 16 of the present invention includes a processing system with at least one high speed Central Processing Unit ("CPU") and a memory system. In accordance with the practices of persons skilled in the art of computer programming, the present invention is described below with reference to acts and symbolic representations of operations that are performed by the processing system, unless indicated otherwise. Such acts and operations are sometimes referred to as being "computer-executed", or "CPU executed."

It will be appreciated that the acts and symbolically represented operations include the manipulation of electrical signals by the CPU. The electrical system represent data bits which cause a resulting transformation or reduction of the electrical signal representation, and the maintenance of data bits at memory locations in the memory system to thereby reconfigure or otherwise alter the CPU's operation, as well as other processing of signals. The memory locations where data bits are maintained are physical locations that have particular electrical, magnetic, optical, or organic properties corresponding to the data bits.

The data bits may also be maintained on a computer readable medium including magnetic disks, optical disks, organic disks, and any other volatile or non-volatile mass storage system readable by the CPU. The computer readable medium includes cooperating or interconnected computer readable media, which exist exclusively on the processing system or is distributed among multiple interconnected processing systems that may be local or remote to the processing system.

Initialization Of A Cable Modem With Telephony Return

When CM 16 is initially powered on, if telephony return is being used, CM 16 will receive a Telephony Channel Descriptor ("TCD") from CMTS 12 that is used to provide dialing and access instructions on downstream channels via cable network 14. Information in the TCD is used by CM 16 to connect to TRAC 24. The TCD is transmitted as a MAC management message with a management type value of TRI_TCD at a periodic interval (e.g., every 2 seconds). To provide for flexibility, the TCD message parameters are encoded in a Type/Length/Value ("TLV") form. However, other encoding techniques could also be used. FIG. 3 is a block diagram illustrating a TCD message structure 70 with MAC 44 management header 72 and Service Provider Descriptor(s) ("SPD") 74 encoded in TLV format. SPDs 74 are compound TLV encodings that define telephony physical-layer characteristics that are used by CM 16 to initiate a telephone call. SPD 74 is a TLV-encoded data structure that contains sets of dialing and access parameters for CM 16 with telephony return. SPD 74 is contained within TCD message 70. There may be multiple SPD 74 encodings within a single TCD message 70. There is at least one SPD 74 in TCD message 70. SPD 74 parameters are encoded as SPD-TLV tuples. SPD 74 contains the parameters shown in Table 1 and may contain optional vendor specific parameters. However, more or fewer parameters could also be used in SPD 74.

    TABLE 1
    SPD 74 Parameter      Description
    Factory Default Flag  Boolean value, if TRUE(1), indicates a
                          SPD which should be used by CM 16.
    Service Provider Name This parameter includes the name of a
                          service provider. Format is standard
                          ASCII string composed of numbers and
                          letters.
    Telephone Numbers     These parameters contain telephone
                          numbers that CM 16 uses to initiate a
                          telephony modem link during a login
                          process. Connections are attempted in
                          ascending numeric order (i.e., Phone
                          Number 1, Phone Number 2 . . .). The SPD
                          contains a valid telephony dial string as
                          the primary dial string (Phone Number 1),
                          secondary dial-strings are optional.
                          Format is ASCII string(s) composed of:
                          any sequence of numbers, pound "#" and
                          star "*" keys and comma character ","
                          used to indicate a two second pause in
                          dialing.
    Connection Threshold  The number of sequential connection
                          failures before indicating connection
                          failure. A dial attempt that does not result
                          in an answer and connection after no
                          more than ten rings is considered a
                          failure. The default value is one.
    Login User Name       This contains a user name CM 16 will use
                          an authentication protocol over the
                          telephone link during the initialization
                          procedure. Format is a monolithic
                          sequence of alphanumeric characters in
                          an ASCII string composed of numbers
                          and letters.
    Login Password        This contains a password that CM 16 will
                          use during authentication over a
                          telephone link during the initialization
                          procedure. Format is a monolithic
                          sequence of alphanumeric characters in
                          an ASCII string composed of numbers
                          and letters.
    DHCP Authenticate     Boolean value, reserved to indicate that
                          CM 16 uses a specific indicated DHCP 66
                          Server (see next parameter) for a DHCP
                          66 Client and BOOTP Relay Process
                          when TRUE (one). The default is FALSE
                          (zero) which allows any DHCP 66 Server.
    DHCP Server           IP 54 address value of a DHCP 66 Server
                          CM 16 uses for DHCP 66 Client and
                          BOOTP Relay Process. If this attribute is
                          present and DHCP 66 Authenticate
                          attribute is TRUE(1). The default value is
                          integer zero.
    RADIUS Realm          The realm name is a string that defines a
                          RADIUS server domain. Format is a
                          monolithic sequence of alphanumeric
                          characters in an ACSII string composed
                          of numbers and letters.
    PPP Authentication    This parameter instructs the telephone
                          modem which authentication procedure to
                          perform over the telephone link.
    Demand Dial Timer     This parameter indicates time (in
                          seconds) of inactive networking time that
                          will be allowed to elapse before hanging
                          up a telephone connection at CM 16. If
                          this optional parameter is not present, or
                          set to zero, then the demand dial feature
                          is not activated. The default value is zero.
    Vendor Specific Extensions Optional vendor specific extensions.

    TABLE 2
    TSI 76 Parameter          Description
    Downstream Channel        This field contains an IP 54 address of
    IP Address 80             CMTS 12 available on the downstream
                              channel this message arrived on
    Registration IP Address 82 This field contains an IP 54 address
                              CM 16 sends its registration request
                              messages to. This address MAY be
                              the same as the Downstream Channel
                              IP 54 address.
    CMTS Boot Time 84         Specifies an absolute-time of a CMTS
                              12 recorded epoch. The clock setting
                              for this epoch uses the current clock
                              time with an unspecified accuracy.
                              Time is represented as a 32 bit binary
                              number.
    Downstream Channel ID 86  A downstream channel on which this
                              message has been transmitted. This
                              identifier is arbitrarily chosen by CMTS
                              12 and is unique within the MAC 44
                              layer.
    Epoch 88                  An integer value that is incremented
                              each time CMTS 12 is either re-
                              initialized or performs address or
                              routing table flush.
    Vendor Specific Extensions 90 Optional vendor extensions may be
                              added as TLV encoded data.

    TABLE 3
    1.   An IP 54 datagram from data network 28 destined for CM 16 arrives on
     CMTS-NSI 32 and
         enters CMTS 12.
    2.   CMTS 12 encodes the IP 54 datagram in a cable data frame, passes it to
     MAC 44 and
         transmits it "downstream" to RF interface 40 on CM 16 via cable
     network 14
    3.   CM 16 recognizes the encoded IP 54 datagram in MAC layer 44 received
     via. RF interface 40.
    4.   CM 16 responds to the cable data frame and encapsulates a response IP
     54 datagram in a
         PPP 50 frame and transmits it "upstream" with modem interface 48 via
     PSTN 22 to TRAC 24.
    5.   TRAC 24 decodes the IP 54 datagram and forwards it via TRAC-NSI 30 to
     a destination on
         data network 28.

         TABLE 4
         DCHP 66
         Parameter        Description
         OP 110           Message op code/message type.
                          1 BOOTREQUEST, 2 = BOOTREPLY.
         HTYPE 112        Hardware address type (e.g., `1` = 10
                          Mps Ethernet).
         HLEN 114         Hardware address length (e.g. `6` for 10
                          Mbps Ethernet).
         HOPS 116         Client sets to zero, optionally used by
                          relay-agents when booting via a relay-
                          agent.
         XID 118          Transaction ID, a random number
                          chosen by the client, used by the client
                          and server to associate messages and
                          responses between a client and a
                          server.
         SECS 120         Filled in by client, seconds elapsed
                          since client started trying to boot.
         FLAGS 122        Flags including a BROADCAST bit.
         CIADDR 124       Client IP address; filled in by client in
                          DHCPREQUEST if verifying previously
                          allocated configu ration parameters.
         YIADDR 126       `Your` (client) IP address.
         SIADDR 128       IP 54 address of next server to use in
                          bootstrap; returned in DHCPOFFER,
                          DHCPACK and DHCPNAK by server.
         GIADDR 130       Gateway relay agent IP 54 address,
                          used in booting via a relay-agent.
         CHADDR           Client hardware address (e.g., MAC
         132              layer 44 address).
         SNAME 134        Optional server host name, null
                          terminated string.
         FILE 136         Boot file name, terminated by a null
                          string.
         OPTIONS          Optional parameters.
         138

    TABLE 5
    1.   A network host client broadcasts a DHCP 66 discover message on its
     local physical subnet.
         The DHCP 66 discover message may include options that suggest values
     for a network host
         interface address. BOOTP relay agents may pass the message on to DHCP
     66 servers not
         on the same physical subnet.
    2.   DHCP servers may respond with a DHCPOFFER message that includes an
     available
         network address in the `yiaddr` field (and other configuration
     parameters in DHCP 66 options)
         from a network host interface. DHCP 66 servers unicasts the DHCPOFFER
     message to the
         network host client (using the DHCPIBOOTP relay agent if necessary) if
     possible, or may
         broadcast the message to a broadcast address (preferably
     255.255.255.255) on the client's
         subnet.
    3.   The network host client receives one or more DHCPOFFER messages from
     one or more
         DHCP 66 servers. The network host client may choose to wait for
     multiple responses.
    4.   The network host client chooses one DHCP 66 server with an associated
     network host
         interface from which to request configuration parameters, based on the
     configuration
         parameters offered in the DHCPOFFER messages.

         TABLE 6
         DCHP 66
         Parameter        Description
         OP 110           Set to BOOTREQUEST.
         HTYPE 112        Set to network type (e.g., one for 10 Mbps
                          Ethernet).
         HLEN 114         Set to network length (e.g., six for 10 Mbps
                          Ethernet)
         HOPS 116         Set to zero.
         FLAGS 118        Set BROADCAST bit to zero.
         CIADDR 124       If CM 16 has previously been assigned an IP
                          54 address, the IP 54 address is placed in this
                          field. If CM 16 has previously been assigned
                          an IP 54 address by DHCP 66, and also has
                          been assigned an address via IPCP, CM 16
                          places the DHCP 66 IP 54 address in this
                          field.
         GIADDR 130       CM 16 places the Downstream Channel IP 54
                          address 80 of CMTS 12 obtained in TSI
                          message 76 on a cable downstream channel
                          in this field.
         CHADDR 132       CM 16 places its 48-bit MAC 44 LAN address
                          in this field.

         TABLE 7
         DHCP 66 Parameter     Description
         FLAGS 122             BROADCAST bit set to zero.
         YIADDR 126            IP 54 address from a network
                               host interface to allow CM 16 to
                               receive data from data network
                               28 via a network host interface
                               available on CMTS 12.
         SIADDR 128            An IP 54 address for a TFTP 64
                               server to download configuration
                               information for an interface host.
         CHADDR 132            MAC 44 address of CM 16.
         SNAME 134             Optional DHCP 66 server
                               identifier with an interface host.
         FILE 136              A TFTP 64 configuration file
                               name for CM 16.

         TABLE 8
         DHCP 66
         Parameter      Description
         OP 110         Set to BOOTREQUEST.
         HTYPE 112      Set to network type (e.g., one for 10 Mbps
                        Ethernet).
         HLEN 114       Set to network Iength (e.g., six for 10 Mbps
                        Ethernet)
         HOPS 116       Set to zero.
         FLAGS 118      Set BROADCAST bit to zero.
         CIADDR 124     If CM 16 has previously been assigned an IP
                        address, the IP address is placed in this field.
                        If CM 16 has previously been assigned an IP
                        address by DHCP 66, and also has been
                        assigned an address via IPCP, CM 16 places
                        the DHCP 66 IP 54 address in this field.
         YIADDR 126     IP 54 address sent from the selected network
                        interface host in DCHPOFFER message
         GIADDR 130     CM 16 places the Downstream Channel IP 54
                        address 80 CMTS 12 obtained in TSI
                        message 76 on a cable downstream channel
                        in this field.
         CHADDR 132     CM 16 places its 48-bit MAC 44 LAN address
                        in this field.
         SNAME 134      DHCP 66 server identifier for the selected
                        network interface host

         TABLE 9
         DHCP 66 Parameter     Description
         FLAGS 122             Set a BROADCAST bit to zero.
         YIADDR 126            IP 54 address for the selected
                               network host interface to allow
                               CM 16 to receive data from data
                               network 28.
         SIADDR 128            An IP 54 address for a TFTP 64
                               server to download configuration
                               information for an interface host.
         CHADDR 132            MAC 44 address of CM 16.
         SNAME 134             DHCP 66 server identifier
                               associated with the selected
                               network host interface.
         FILE 136              A configuration file name for an
                               network interface host.

         TABLE 10
         Type        Length      Description of Value
         1           4           Receive frequency
         2           1           Upstream channel identifier
         4x          N           Class of service header
         41          1           Class identifier
         42          4           Maximum downstream data
                                 rate in bits/sec
         43          4           Maximum upstream data rate
                                 in bits/sec
         44          1           Upstream channel priority
         45          4           Upstream guaranteed
                                 minimum data rate in bits/sec
         46          2           Maximum upstream
                                 configuration setting in
                                 minislots
         47          1           Privacy enable
         8           3           Vendor Identifier configuration
                                 setting
         17x         N           Baseline privacy settings
                                 header
         171         4           Authorize timeout seconds
         172         4           Reauthorize wait timeout
                                 seconds
         173         4           Authorization wait timeout
                                 seconds
         174         4           Operational wait timeout
                                 seconds
         175         4           Re-key wait timeout seconds
         176         4           TEK grace time seconds
         9           N           Software upgrade filename
         10          1           SNMP access control
         11          N           Arbitrary SNMP object setting
         0           N           Padding for 4-byte boundary
         3           1           Network access
         6           16          CM-MIC
         7           16          CMTS-MIC
         255         N/A         End-of-file

           TABLE 11
           Type        Length        Descrition of Value
           Y           4             Unique identifer, e.g., P54
                                     address of CM 16

           TABLE 12
           Type      Length        Description of Value
           Z         4             Number of seconds since
                                   00:00 on January 1, 1970.
                                   (UNIX Epoch Time, RFC-868)

         TABLE 13
         Type        Length        Description of Value
         T           1             Registration request message
                     version

    TABLE 14
    Registration request
    message values     Definition of value
    0                  Default, no additional configuration parameters
                       added.
    1                  Additional configuration parameters added.

    TABLE 15
    CMTS-MIC field for a cable modem registration request message is
    calculated by performing an MD5 digest over the following configuration
    parameters fields, when present in the configuration
    file, in the order shown:
    .cndot.Downstream Frequency Configuration parameter
    .cndot.Upstream Channel ID Configuration parameter
    .cndot.Network Access Configuration parameter
    .cndot.Class of Service Configuration parameter
    .cndot.Vendor ID Configuration parameter
    .cndot.Baseline Privacy Configuration parameters
    .cndot.Vendor specific Configuration parameters
    .cndot.CM-MIC value
    .cndot.Authentication string.
    The configuration parameters fields are treated as if they were contiguous
    data when calculating the MD5 digest.

    TABLE 16
    1.   Use the configuration parameters from the configuration file sent to
         CM 16 as shown in Table 15 when present in the order listed.
    2.   Use the unique identifier, selected time-value and one or more of the
         following additional configuration parameters and calculate a
         CMTS-MIC value by performing an MD5 digest
         Over the following configuration parameters, when present in the
         registration request message, in the order shown:
    .cndot. One or more configuration parameters (Table 10, Table 15).
    .cndot. Selected time-value (Table 12)
    .cndot. Unique identifier (Table 11)
    .cndot. One or more configuration parameters (Table 10, Table 15).