Sub-segment based transport layer protocol for wireless medium

• US 20050265353A1
• Filed: 05/03/2005
• Published: 12/01/2005
• Est. Priority Date: 05/05/2004
• Status: Active Grant

• Current Assignee: New Jersey Institute of Technology
• Original Assignee: New Jersey Institute of Technology
• Inventors: Ansari, Nirwan, Sengupta, Somenath
• Granted Patent: US 7,965,674 B2
• Time in Patent Office: Days
• US Class Current: 370/395.520
• CPC Class Codes: H04L 47/10 Flow control; Congestion control
• CPC Class Codes: H04L 47/193 at the transport layer, e.g. TCP related
• CPC Class Codes: H04L 47/27 Evaluation or update of window size, e.g. using information derived from acknowledged [ACK] packets
• CPC Class Codes: H04L 69/16 Implementation or adaptation of Internet protocol [IP], of transmission control protocol [TCP] or of user datagram protocol [UDP]
• CPC Class Codes: H04L 69/163 In-band adaptation of TCP data exchange; In-band control procedures
• CPC Class Codes: H04L 69/165 Combined use of TCP and UDP protocols; selection criteria therefor
• CPC Class Codes: H04W 28/02 Traffic management, e.g. flow control or congestion control
• CPC Class Codes: H04W 8/04 Registration at HLR or HSS [Home Subscriber Server]
• CPC Class Codes: H04W 80/00 Wireless network protocols or protocol adaptations to wireless operation
• 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
• CPC Class Codes: Y02D 30/00 Reducing energy consumption in communication networks
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

The invention enables the use of TCP protocol for reliable transport of data over a wireless network, resolving the problems associated with frequent packet loss. Additional benefits include delivery of significant performance improvement, bandwidth saving and backward compatibility compared to the wire-line TCP protocol, and contribution to power savings in wireless handsets and devices. To make the retransmission process more granular, transport layer segments are subdivided into sub-segments. The invention utilizes a split TCP based approach and produces a series of smaller-sized segments that share the same transport layer header. A NACK-based message exchange, a new header format and a special windowing protocol are used to achieve reliability, flow-control, and efficient buffer handling.

Claims

1. A method for improving the transmission control protocol (TCP) for wireless media, comprising:

dividing the transport layer segment into a header and a series of sub-segments, each sub-segment sharing the same transport layer heading;

each sub-segment carrying (1) checksum of the TCP header as the correlation ID to associate the transport layer header with a sub-segment;

(2) checksum for itself to detect the corruption of the sub-segment; and

(3) the corresponding sub-segment number, which is unique in the context of a segment.

2. A method in accordance with claim 1, wherein the overhead size of each sub-segment is less than 10%.

3. A method in accordance with claim 1, wherein each sub-segment can be as small as one RLC PDU payload.

4. A method in accordance with claim 1, wherein the protocol stack comprises the following overlying layers:

(1) a physical wireless medium layer for carrying the headers and data from upper layers in the form of an electromagnetic wave;

(2) an RLC layer for encapsulating the headers and data from the upper layer into a link layer frame structure, and for use in forward error correction;

(3) an IP Layer for routing the PDUs attached with IP headers, and interacting with an adapter layer before moving packets in the IP layer up to the transport layer.

(4) an adapter layer for identifying the appropriate IP header associated with a transport layer sub-segment and caching the IP and the transport layer related header of a segment until its successful arrival is complete; and

(5) wireless TCP layer for providing reliability, duplicating handling, message ordering, and flow control, based on the use of sub-segments.

5. A method in accordance with claim 4, wherein the said adaptor layer uses a correlation ID associated with each sub-segment to determine the corresponding IP header and the transport layer protocol header.

6. A method in accordance with claim 5, wherein the checksum of the said TCP header is used as the correlation ID.

7. A method in accordance with claim 5, wherein the said IP layer communicates with the adapter layer via callback and the adapter layer is pre-registered with the IP layer to make the proposed protocol work.

8. A method in accordance with claim 1, wherein the action sequence involved with the process of sending transport layer PDU comprises the steps of:

(a) connection establishment;

(b) transport layer dividing of the total payload in series of sub-segments;

(c) transport layer creating for each segment a transport header of 20 bytes and passing it to the said adapter layer; and

(d) the said adapter layer passing the transport header to the IP layer to attach an IP header with it, the two headers together forming a payload for the said RLC layer.

9. A method in accordance with claim 8 wherein twelve sub-segments together form a virtual transport layer segment, each sub-segment being equivalent to an RLC PDU (40 bytes), whereby twelve of them will create a virtual transport layer segment (approximately 540 bytes), whereby the said virtual segment is the same in size as a standard TCP segment to facilitate in mapping the proposed protocol to the standard TCP.

10. A method in accordance with claim 8, wherein for other sub-segments, the adapter layer tunnels through the IP layer and directly passes the sub-segment to the link layer.

11. A method in accordance with claim 1, wherein the action sequence involved with the process of receiving transport layer PDUs comprises as its steps:

(a) upon a packet reaching the IP layer, IP validation being effected if the checksum of the IP header is correct;

(b) upon the validation succeeding, the said IP layer passing the packet to the adapter layer;

(c) if the protocol field of the IP header does not indicate other protocols, the adapter layer returning the control to the IP layer for further processing;

(d) if (c) is inapplicable, the said adapter layer confirming the checksum of the sub-segment, caching the IP header and the transport header and not returning control to the IP layer;

(e) if validation in the IP layer fails, instead of dropping the packet it calls back the adapter layer;

(f) if (e) is applicable the adapter layer passing the said recalled packet to the transport layer.

(g) if the checksum is confirmed, the transport layer verifying the correctness of the packet assuming that it is a non-header sub-segment;

(h) if verification fails, the packet dropped and the control not being returned to the IP layer; and

(i) if verification is successful, the adapter layer associating the cached headers to the sub-segment and the control not being returned to the IP layer.

12. A method in accordance with claim 1, wherein a three-way handshaking, like TCP, is used for the connection establishment, the flow being as follows.

(1) Sender sends a transport layer PDU once the receiver window allows;

(2) Sender stores the sent PDU in a buffer;

(3) Receiver receives said sent PDU;

(4) Receiver periodically finds the out-of-sequence PDUs in the queue and sends a NACK to inform the sender about the lost PDU;

(5) Sender retransmits the lost PDU.

(6) Receiver periodically sends a notification carrying a list of sequence numbers indicating the set of PDUs received;

(7) Upon the notification reaching the sender, the sender updates its storage buffer by deleting the PDUs identified in the notification;

(8) The sender periodically checks its storage buffer, and if a particular PDU remains in the buffer for a period of time that is longer than the time required to receive two successive notifications, a retransmission takes place; and

(9) A positive ACK is sent to the receiver in response to the notification, and in the absence of this positive ACK, the receiver retransmits the notification.