TCP-aware agent sublayer (TAS) for robust TCP over wireless

• US 6,208,620 B1
• Filed: 08/02/1999
• Issued: 03/27/2001
• Est. Priority Date: 08/02/1999
• Status: Expired due to Fees

• Current Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Original Assignee: Nortel Networks Corporation
• Inventors: Joshi, Atul Suresh, Kumar, Apurva, Umesh, M. N., Sen, Sanjoy
• Primary Examiner(s): VINCENT, DAVID ROBERT
• Application Number:
  US09/365,443
• Time in Patent Office: 603 Days
• Field of Search: 370/231, 370/235, 370/236, 370/237, 370/252, 370/242, 370/394, 370/229, 370/428, 370/310, 370/328, 370/466, 370/469, 714/748, 714/749, 455/414, 455/422, 455/466, 455/556, 455/557, 455/504, 455/506
• US Class Current: 370/231
• CPC Class Codes: H04L 1/1809 Selective-repeat protocols
• CPC Class Codes: H04L 1/1854 Scheduling and prioritising arrangements
• CPC Class Codes: H04L 43/00 Arrangements for monitoring or testing data switching networks
• CPC Class Codes: H04L 43/0829 Packet loss
• CPC Class Codes: H04L 43/0864 Round trip delays
• CPC Class Codes: H04L 43/16 Threshold monitoring
• CPC Class Codes: H04L 69/161 Implementation details of TCP/IP or UDP/IP stack architecture; Specification of modified or new header fields
• CPC Class Codes: H04L 69/163 In-band adaptation of TCP data exchange; In-band control procedures
• CPC Class Codes: H04L 69/168 specially adapted for link layer protocols, e.g. asynchronous transfer mode [ATM], synchronous optical network [SONET] or point-to-point protocol [PPP]
• CPC Class Codes: H04L 69/321 Interlayer communication protocols or service data unit [SDU] definitions; Interfaces between layers
• CPC Class Codes: H04L 69/40 for recovering from a failure of a protocol instance or entity, e.g. service redundancy protocols, protocol state redundancy or protocol service redirection management of faults, events, alarms or notifications in data switching networks H04L41/06
• CPC Class Codes: H04L 9/40 Network security protocols
• CPC Class Codes: H04W 24/00 Supervisory, monitoring or testing arrangements
• CPC Class Codes: H04W 28/14 using intermediate storage
• CPC Class Codes: H04W 36/0011 for data sessions of end-to-end connection
• CPC Class Codes: H04W 80/06 Transport layer protocols, e.g. TCP [Transport Control Protocol] over wireless transmission control protocol/Internet protocol [TCP/IP] or user datagram protocol [UDP] H04L69/16

Abstract

Disclosed is a system for minimizing the effects of faults over an air link of a wireless transmission channel utilizing Transport Control Protocol (TCP). The system includes a TCP-Aware Agent Sublayer (TAS) in a protocol stack, which has a mechanism for caching both TCP packets during forward transmission and acknowledgment (ACK) return packets. The caching mechanism is located near a wireless link of the wireless transmission channel. The system also includes a link monitoring agent coupled to the TAS. The link monitoring agent monitors the condition of the wireless transmission channel for an occurrence of a predefined fault. Once a predefined fault is detected, a system response is implemented based on the type of fault encountered. When the fault is an air link packet loss, an associated packet is immediately retransmitted from the cache, and when the fault is a temporary disconnect, a congestion window of the TCP source is closed.

Claims

1. A system for minimizing the effects of faults over an air link of a wireless transmission channel utilizing Transport Control Protocol (TCP), said system comprising:

a TCP-Aware Agent Sublayer (TAS) in a protocol stack, said TAS including a caching mechanism coupled to a wireless link of said wireless transmission channel for caching TCP packets during forward transmission and acknowledgment (ACK) of return packets, wherein said caching mechanism includes means for routing a packet from an Internet Protocol (IP) sublayer to said TAS during forward transmission;

means, associated with said caching mechanism, for monitoring a condition of said wireless transmission channel for an occurrence of a predefined fault; and

means for responding to said occurrence wherein, when said fault is an air link packet loss, an associated packet is immediately retransmitted from said cache, and when said fault is a temporary disconnect, a congestion window of a TCP source is closed.

2. The system of claim 1, wherein said monitoring means is implemented by a link monitoring agent coupled to said TAS, which predicts when a disconnection occurs, said monitoring means further includes means for checking a frame error rate (FER) and a radio link protocol (RLP) negative acknowledgment (NAK).

3. The system of claim 2, further comprising:

means for determining when a number of errored air link frames in a set of consecutive frames reaches a pre-defined threshold;

means for predicting a disconnect in a forward channel; and

means for signaling said TAS to begin delaying ACK packets.

4. The system of claim 2, further comprising:

means for predicting an onset of a disconnection or a lack of radio bandwidth utilizing said link monitoring agent; and

means for increasing a round trip delay of current ACK packets by delaying said ACK packets by a predetermined amount at said TAS.

5. The system of claim 1, wherein said responding means further includes:

means for resetting a window field in an ACK packet to a value which signals congestion at a destination; and

means for sending said ACK packet to said TCP source to induce said TCP source to stop transmitting.

6. The system of claim 5, wherein said resetting means further includes:

means for storing an original value of said window field, contemporaneously with said setting means;

means for restoring said original value when said disconnection is over; and

means for sending said ACK packet having said original value in said window field to said TCP source, said means prompting said TCP source to resume transmitting packets from a point at which it stopped transmitting packets.

7. The system of claim 5, wherein said resetting means includes:

means for modifying a previous ACK packet to resemble said new ACK packet when no new ACK packet is received from the transmission channel;

means for resetting said window field in said modified previous ACK packet.

8. The system of claim 1, said responding means including means for retransmitting a TCP packet when a retransmission timer expires.

9. A method for minimizing the effects of faults over an air link of a wireless transmission channel utilizing Transport Control Protocol (TCP), said method comprising the steps of:

caching TCP packets during forward transmission and acknowledgment (ACK) of return packets utilizing a TCP-Aware Agent Sublayer (TAS) in a protocol stack coupled to a wireless link of said wireless transmission channel, wherein a packet is routed from an Internet Protocol (IP) sublayer to said TAS during forward transmission;

monitoring a condition of said wireless transmission channel for an occurrence of a predefined fault; and

responding to said occurrence by, when said fault is an air link packet loss, immediately retransmitting an associated packet from said cache and, when said fault is a temporary disconnect, shutting off a congestion window of a TCP source.

10. The method of claim 9, wherein said monitoring step is implemented by a link monitoring agent coupled to said TAS, which predicts when a disconnection occurs, said monitoring step further includes the steps of:

determining a frame error rate (FER); and

identifying a radio link protocol (RLP) negative acknowledgment (NAK).

11. The method of claim 10, further comprising the steps of:

determining when a number of errored air link frames in a set of consecutive frames reaches a pre-defined threshold;

predicting a disconnect in a forward channel; and

signaling TAS to begin delaying ACK packets in response to said predicting step.

12. The method of claim 10, further comprising the steps of:

predicting an onset of a disconnection or a lack of radio bandwidth utilizing said link monitoring agent; and

increasing a round trip delay of current ACK packets by delaying said ACK packets by a predetermined amount at said TAS.

13. The method of claim 9, said responding step further includes the steps of:

resetting a window field in an ACK packet to a value corresponding to a congestion at a destination; and

sending said ACK packet to said TCP source to induce said TCP source to stop transmitting.

14. The method of claim 13, wherein said resetting step further includes the steps of:

storing an original value of said window field, contemporaneously with said setting step;

restoring said original value when said disconnection is over; and

sending said ACK packet having said original value in said window field to said TCP source to prompt said TCP source to resume transmitting packets from the point at which it stopped transmitting packets.

15. The method of claim 13, wherein when no new ACK packet is received from the transmission channel, said resetting step includes the step of:

modifying a previous ACK packet to include characteristics of said new ACK packet; and

resetting said window field in said modified previous ACK packet.

16. The method of claim 9, said responsive step including the step of retransmitting a TCP packet when a retransmission timer expires.