CN1754348A

CN1754348A - Method and system for avoiding tcp packet retransmission during mobile device handoff

Info

Publication number: CN1754348A
Application number: CN 200480005315
Authority: CN
Inventors: C·-T·周; Z·钟
Original assignee: Koninklijke Philips Electronics NV
Current assignee: Koninklijke Philips NV
Priority date: 2003-02-27
Filing date: 2004-02-23
Publication date: 2006-03-29

Abstract

Under the present invention, a wireless component such as an access point or a mobile device is configured to manage the buffering of newly transmitted TCP packets. Specifically, the wireless component can receive both forwarded TCP packets and newly transmitted TCP packets. If a set of newly transmitted TCP packets is received out of order (i.e., before a set of previously transmitted TCP packets that must be forwarded), one out of order (newly transmitted) TCP packet will be passed for each of a quantity of tokens present on the wireless component. Each out of order TCP packet that is not passed will be buffered. Once a previously requested forwarded TCP packet is received and passed, the quantity of tokens is restored to a predetermined quantity, and a commensurate number of buffered TCP packets can be passed.

Description

Be used to avoid TCP to wrap in the method and system that mobile device resend between transfer period

The present invention relates generally to and be used to avoid TCP to wrap in the method and system that mobile device resend between transfer period.Particularly, the invention provides buffering, with resending of the TCP bag of the forwarding that prevents to have postponed to the TCP of new transmission bag.

Because wireless network is more and more universal, the ability of mobile device is increasing.For example, current many mobile devices (for example, cell phone, personal digital assistant, portable computer etc.) can link to each other with network by wireless connections.Usually, in order to connect wireless network, mobile device must be associated for example " access point " with some parts there.Because their intrinsic portability, so mobile device often " switches (handoff) " to another access point from an access point.Particularly, because mobile device user moves away from the associated access point of his/her equipment, so being connected fail and failing even between access point and mobile device.In order to prevent the failure of end-to-end connection, this mobile device must find and related any available access point.

As everyone knows, wireless network can have a plurality of subnets.Except other parts, each subnet also comprises the access point that mobility agent (mobility agent) and one group of (for example one or more) mobile device can be related usually.For example, single subnet can be illustrated in whole " machines " in single geographical position, same building or the same Local Area Network etc.Network is divided into subnet, a plurality of advantages can be provided.For example, subnet allows this network to connect the internet with single shared network address.Though tissue can be taked to connect without the multiple internet of subnet, this can need the unnecessary use of the network address of the limited quantity that the internet distributed.

Usually, in the open system systems interconnection layer model, wireless sub network has a plurality of " layers ".Layer 1 is called physical layer, and layer 2 is called link layer (it comprises LLC and medium access control (MAC)), and layer 3 is called network layer, and layer 4 is called transport layer.When mobile device moves, switch and to be in these layers one or more layers.For example, as mentioned above, if mobile device moves in single wireless sub network, then layer 2 (link layer) switching between the access point may be essential.If mobile device moves between two subnets, be essential then in layer 3 (network layer) switching between the mobility agent and layer 2 (link layer) switching between the access point.Usually, switch according to I.E.E.E.802.11 (f) standard management layer 2, and switch according to mobile IP standard processing layer 3.

Owing in handoff procedure, have the difference of essence, consume more time so layer 3 switches to switch than layer 2 basically.Particularly, under mobile IP standard, " mobility " agency in the couple in router of specifying subnet, approximate each second sends " beacon ".These beacons are received by mobile device, as its method that links to each other with this particular subnet of verification.If mobile device moves out of the zone that is covered by first subnet, then will miss these beacons (for example, or they will not be received, or they will can not be received with enough " intensity ").Under any circumstance, if mobile device has missed three continuous beacons, then mobile IP standard indicates it must seek new subnet (that is, attempting the related new mobility agent of).

Yet in layer 3 handoff procedure, a plurality of problems can appear.Particularly, owing to attempt and must miss three agent beacon by the time before the agency is associated at mobile device, so will be at least through three seconds.Waiting time not only postpone to arrive at from the communicating by letter of mobile device, but also cause losing of TCP bag.For example, finished layer 3 up to mobile device and switched, any TCP bag that is intended to use for mobile device just will send to the associated previous subnet of this mobile device.Formerly access point cushions these TCP bags, then it is transmitted to new wireless sub network.Finish in case layer 3 switches, then will directly send the TCP bag of these new transmissions to new subnet.

Unfortunately, because the TCP of these new transmissions bag directly sends to new subnet, so there is very high possibility: they may arrive at prior to the TCP bag of some forwarding, even the TCP of later these new transmissions of transmission bag also is like this.Therefore, some TCP bag may be received disorderly, and this can trigger resending of TCP bag.For example, under standard " TCP " practice, when sending the TCP bag, start timer.If in the time cycle of distributing, do not receive " affirmation " returned from mobile device, then resend the TCP bag.If mobile device receives unordered TCP bag, then will beam back " affirmation " of the orderly bag that most recent is received to the TCP transmitter.This affirmation is substantially equal to " request " to the packet that misses.For example, suppose that TCP bag " 1-10 " sends from the TCP transmitter, is intended to use for mobile device.Further hypothesis TCP bag " 1-3 " must be transmitted to new wireless sub network from previous access point, and TCP bag " 4-10 " directly sends to this new wireless sub network from the TCP transmitter.If at first receive TCP bag " 4 ", then will beam back this TCP transmitter to the initial request of TCP bag " 1 ".If secondly receive TCP bag " 5 ", then send the request second time to TCP bag " 1 ".If receive TCP bag " 6 " for the third time, then will beam back this TCP transmitter to another request of TCP bag " 1 ".If after this receive TCP bag " 7 ", then will beam back this TCP transmitter to the request of TCP bag " 1 " the 4th time.Yet under standard " TCP " practice, this 4th time request resends TCP bag " 1 " with the trigger data source.Therefore, TCP bag " 1 " will resend, and be lost just as it, postpone even it just is forwarded process simply.

Attempting to handle in this problem, previous system has carried out buffering, and the TCP of taking this all newly to send wraps on the new agency and is cushioned, and arrives at up to the TCP of whole forwardings bag.Yet, because switching, layer 3 brings long latency time period, so should there be a large amount of buffering TCP bags, this can cause buffer to overflow and packet loss.

Consider foregoing, exist being used to avoid TCP to wrap in the needs of the method and system that mobile device resends between transfer period.Particularly, there are the needs of improved buffering, promptly can avoid the TCP bag to send to mobile device disorderly, do not resend and can not make buffer overflow and trigger TCP.

Usually, the invention provides and be used to avoid TCP to wrap in the method and system that mobile device resend between transfer period.Particularly, according to the present invention, one group (for example one or more) transmit the TCP bag and one group (for example one or more) new TCP bag that sends is received by radio parts (for example access point or mobile device).As everyone knows, each TCP bag in two groups has its sequence number at whole Bao Liuzhong order of sign.At each token in a plurality of tokens that are present on the radio parts, can transmit the TCP bag of the new transmission of " unordered ".Particularly, if the new TCP that sends receives before wrapping in the forwarding TCP bag with low sequence number, then it only can transmit when token exists.For this reason, if radio parts is an access point, then " transmission " new TCP bag that sends means the TCP bag that sends this new transmission to mobile device.If radio parts is a mobile device itself, then " transmission " new TCP bag that sends means that mobile device will handle the TCP of (or being allowed to handle) this new transmission and wrap.Under any circumstance, the TCP of each new transmission of being transmitted bag will cause that the quantity of token subtracts one.In case these tokens are used up, the then new TCP bag that sends must cushion on radio parts.Yet when receiving and transmitting the TCP bag of transmitting, the quantity of token will return to predetermined quantity (=3).The recovery of token will allow to transmit the buffering TCP bag of equivalent.

A first aspect of the present invention is, provides a kind of and is used to avoid TCP to wrap in the method that mobile device resend between transfer period, comprising: receive one group of new TCP bag that sends on radio parts; Check the sequence number of each TCP bag in the new TCP bag that sends of this group, so that identify one group of unordered TCP bag; At each token in a plurality of tokens that are present on the radio parts, transmit in the unordered TCP bag of this group; And at each the unordered TCP bag that is transmitted, the quantity of token subtracts one.

A second aspect of the present invention is, provides a kind of and is used to avoid TCP to wrap in the method that mobile device resend between transfer period, comprising: receive one group of TCP bag that is used for the new transmission of mobile device at access point; Check the sequence number of each TCP bag in the new TCP bag that sends of this group, so that identify one group of unordered TCP bag; At each token in a plurality of tokens that are present on the access point, send in the unordered TCP of this group bag one to mobile device, and at each the unordered TCP bag that sends to mobile device, the quantity of token subtracts one; Receive the TCP bag of transmitting from the associated previous access point of mobile device; And, the TCP bag of transmit transmitting to mobile device, and if the TCP that transmits bag by the previous request of mobile device, then the quantity with token returns to predetermined quantity.

A third aspect of the present invention is, provides a kind of and is used to avoid TCP to wrap in the system that mobile device resend between transfer period, comprises radio parts, and this radio parts is configured to: receive one group of new TCP bag that sends at radio parts; Check that the sequence number of each TCP bag in the new TCP bag that sends of this group is so that identify one group of unordered TCP bag; At each token in a plurality of tokens that are present on the radio parts, transmit in the unordered TCP bag of this group; And at each the unordered TCP bag that is transmitted, the quantity of token subtracts one.

Therefore, the invention provides and be used to avoid TCP to wrap in the method and system that mobile device resend between transfer period.

In conjunction with the accompanying drawings, from the detailed description of following various aspects of the present invention, understand these and other feature of the present invention with easier, wherein:

Fig. 1 shows the wireless network figure with two subnets.

Fig. 2 shows the flow chart that TCP bag according to the present invention transmits and cushions.

Fig. 3 shows the block diagram according to mobile device of the present invention and access point.

These figure only schematically show, and are not intended to portray concrete parameter of the present invention.These figure are intended to only describe general embodiment of the present invention, thereby should not be counted as the restriction to scope of the present invention.In these figure, identical numeral components identical.

Referring now to Fig. 1, the wireless network 10 with two wireless sub network 12A-B is shown.As directed, two wireless sub network 12A-B comprise similar parts.These parts comprise router one 4A-B, outside/mobility agent 16A-B, medium access control (MAC) bridger 18A-B and access point 20A-D.Gateway 22 places between the wireless sub network 12A-B, will be routed to mobile device 26 from the TCP bag that correspondent node/device 24 receives.Usually, router one 4A-B and mobility agent 16A-B can be used as the parts of layer 3 (network layers), and MAC bridger 18A-B and access point 20A-D can be used as the parts of layer 2 (link layers).Under any circumstance, in order to connect specific subnet, mobile device 26 will be associated with the mobility agent and the access point of there.After being associated, any from TCP bag corresponding device 24, that be equipment 26 appointments, will send to mobile device 26 by router, MAC bridger and mobile device 26 associated wireless sub network access points.Be to be understood that it is illustrative that 10 of wireless networks are intended to, and should understand the parts that can comprise other with and/or can have other equipment.For this reason, the quantity of the parts shown in it is also understood that (for example access point) also is illustrative, rather than is intended to restriction.In addition, it is also understood that mobility agent 16A-B, is the general part of router one 4A-B, or links to each other with router one 4A-B.They so do not illustrate in Fig. 1, just for notional purpose.

As implied above, various results can appear in the switching of mobile device 26.No matter mobile device 26 switches to access point (for example, from access point 20A to access point 20B) from access point in the specific wireless subnet, still switches between wireless sub network (for example from wireless sub network 12A to wireless sub network 12B), and these results can take place.Particularly, no matter when mobile device 26 switches, and some TCP bag all must be forwarded, and other TCP bag can directly send after switching.For example, if mobile device switches to access point 20B from access point 20A, then some TCP bags will be access in a 20A and receive in handoff procedure, and must be transmitted to access point 20B.In addition, after switching, newly-generated TCP bag will directly send to access point 20B.Though I.E.E.E.802.11 (f) standard provides some communications between access point 20A-D, the bag buffering is not effectively managed, and can overflow and cause the TCP packet loss.

This influence can be exaggerated when wireless sub network 12B switches from wireless sub network 12A at mobile device 26.Particularly, as implied above, for the generation of this switching, mobile device 26 must all switch at layer 2 and layer 3.That is, mobile device 26 must be all related with mobility agent (for example acting on behalf of 16B) and the access point (for example access point 20C) of wireless sub network 12B.Because it is long (for example to relate to the latency time period of layer 3 switching, at least three seconds), then there is higher possibility: the new TCP bag that sends (the TCP bag that for example after switching, sends, can be routed directly to subnet 12B), will before the TCP bag of the previous transmission that must transmit from access point 20B, arrive.Therefore, the new TCP bag that sends can arrive access point 20C disorderly.Still as implied above, the TCP bag of each unordered reception will cause the duplicate acknowledgment to the suitable TCP bag of being beamed back corresponding equipment 24.Yet in " TCP " practice, the 4th time duplicate acknowledgment resends triggering the TCP bag that may just postpone (not losing).Although can act on behalf of the 16B place or provide buffering at access point 20C place under the I.E.E.E.802.11 standard under mobile IP standard, previous system manage buffer by this way, promptly avoids buffer to overflow or TCP bag resends.

According to the present invention, or access point (for example access point 20B or 20C), or mobile device 26, can dispose to avoid TCP to wrap this mode that resends with the TCP packet loss.Particularly, with reference to Fig. 2, show according to buffer management scheme 40 of the present invention.Should understand in advance, although buffer management scheme 40 is generally implemented at access point (for example access point 20A-D), it can or be implemented at access point, or implements at mobile device 26.For this reason, access point 20A-D and mobile device 26 are called radio parts 50 at this jointly.What under any circumstance, received by buffer management system 40 is 42 and one groups of (for example one or more) new TCP bags 44 that send of TCP bag that a group (for example one or more) transmit.The TCP bag that TCP bag 42 expressions of transmitting are transmitted from another access point (for example from access point 20B to access point 20C), and the TCP bag that 44 expressions of TCP bag directly send from corresponding device 24 (Fig. 1).Should be appreciated that buffer management scheme 40 can be used for switching in the subnet of mobile device 26 or between subnet.For example, no matter mobile device 26 switches (switching in the subnet) from access point 20A to access point 20B, still switches to access point 24C (between subnet) from access point 20B, and buffer mechanism 40 all is available.

According to the present invention, the TCP bag 42 that allows to transmit is directly passed to mobile device 26, and the new TCP bag 44 that sends suffers possible buffering in buffer 46.Particularly, as known in the art, give each TCP in the stream sequence number that is responsible for assigning, it indicates this TCP to wrap in order in the stream.Generally speaking, TCP bag will have than wrapping lower sequence number with the 2nd TCP in first-class.As implied above, the forwarding of TCP bag can cause that the rheology of TCP bag gets unordered.For example, suppose that stream wraps " 1-10 " by TCP and forms.Suppose that also TCP bag " 1-3 " is received by mobile device 26 associated previous access points.Therefore, TCP bag " 1-3 " must be transmitted to new access point.The TCP bag " 4-10 " of supposing this stream in addition is new the transmission.That is, TCP bag " 4-10 " sends from corresponding device 24, and is routed directly to new access point.When reception TCP wrapped 4, standard TCP practice indication generates confirmed also to beam back corresponding device 24, and it indicates TCP bag 4 to be received.As mentioned above, this affirmation will indicate TCP bag " 1 " not to be received.If next TCP bag " 5-7 " is received, then will generate the second time, for the third time with the 4th this affirmation.Under " TCP " practice, duplicate acknowledgment will cause that corresponding device 24 resends TCP bag " 1 " for the third time.Therefore, even bag " 1 " is not lost, it will be resend.In order to handle this problem, buffer management system 40 provides a plurality of tokens 48.TCP bag 44 at 48, one unordered new transmissions of token of each existence will be by " transmission ".For this reason, if radio parts 50 is access points, then the TCP of unordered new transmission bag 44 will send to mobile device 26 at each token that exists on this access point.If radio parts 50 is mobile devices 26, then the TCP of unordered new transmission bag 44 will be handled (or allowing mobile device to handle) by mobile device at the token of each existence.In any situation, at the TCP bag 44 of each unordered new transmission of being transmitted, the quantity of the token on the radio parts 50 will subtract one.In this exemplary embodiments, token 48 provides according to predetermined quantity, and this predetermined quantity is less than the quantity that triggering is resend the request of TCP bag.For example, if three duplicate acknowledgments that the TCP that misses is wrapped will cause that corresponding device 24 resends TCP bag (for example TCP bag " 1 "), then buffer management system 40 will comprise three tokens.

Use above-mentioned example, suppose to exist three tokens 48.If TCP bag " 4 " at first is received, then it will be transmitted, and can remain two tokens (and the affirmation/request of TCP being wrapped " 1 " will be sent out).If TCP bag " 5 " then is received, then it will be transmitted, and an only surplus token (and the affirmation/request second time of TCP being wrapped " 1 " will be sent out).If TCP bag " 6 " next is received, then it also will be transmitted, and does not have token remaining (and the affirmation/request for the third time of TCP being wrapped " 1 " will be sent out).If TCP bag " 7 " next is received, then it will be stored in the buffer 46, and this is because there is not token remaining.This will prevent that TCP bag " 7 " from transmitting to mobile device 26, and prevent to generate the 4th request to " missing " TCP bag 1.Therefore, avoided resending of TCP bag " 1 ".Equally, if TCP bag " 8 " next is received, then it also will be stored in the buffer 46, to avoid resending of TCP bag " 1 ".Yet if TCP bag " 1 " is received afterwards at TCP bag " 8 ", it will be transmitted, and token 48 will be added full again.That is, token 48 returns to predetermined quantity (for example 3) when receiving and transmitting the TCP bag of request (i.e. the forwarding TCP of request bag).

In case token 48 has been added full again, then TCP bag " 7 " and " 8 " will be transmitted, and each TCP bag consumes a token simultaneously.Therefore, only surplus next token 48, and will send the first time and the affirmation/request for the second time of the TCP that misses being wrapped " 2 " to corresponding device 24.If TCP bag " 9 " and " 10 " next arrives, then TCP bag " 9 " will transmit, and not have token to be left (and, will send the affirmation for the third time of TCP being wrapped " 2 ").Because do not have remaining token 48 afterwards,, return to predetermined quantity again up to TCP bag " 2 " transmission and token 48 so TCP bag " 10 " will be stored in the buffer 46 at transmission TCP bag " 9 ".Till this process will last till that whole TCP bags has been transmitted.

Should be appreciated that the present invention can realize with the combination of hardware, software or hardware and software.For this reason, instruction of the present invention can be by implementing based on software or hardware based device in the radio parts (access point and/or mobile device).The parts that are suitable for implementation in this described method of any kind of all are suitable.The general combination of hardware and software can be the parts with computer program, and this computer program is realized correlation method described herein when being loaded and carry out.Replacedly, can use the parts of special-purpose, these parts comprise the specialized hardware that is used to realize one or more functional tasks of the present invention.The all right embeddeding computer program product of the present invention, it comprises the whole individual features that can implement said method, and can realize these methods when it is loaded into computer system.Computer program, software program, program or software, refer to the expression of one group of instruction of any language, code and symbol in this article, the instruction of this group is intended to cause having the system of information processing capability or directly carry out specific function, or one of two kinds of situations are back or carry out specific function behind both of these case below: (a) convert another language, code and symbol to; And/or (b) duplicate with different material forms.

With reference to Fig. 3, show block diagram according to radio parts 50 of the present invention.This block diagram illustrations instruction of the present invention (for example buffer management system 40) can be implemented as hardware, software or the combination of the two.And this block diagram display buffer management system 40 can realize on mobile device 26 or access point 20A-D.Also should understand in advance, it is illustrative that block diagram shown in Figure 3 only is intended to, and mobile device or access point will comprise unshowned add ons probably.Under any circumstance, as shown, wireless device 50 generally includes processor 52, memory 54, transmitter receiver 56 and effective packing device (active packetizer) 58.

The memory 54 of radio parts 50 can comprise data 60 and/or be used to realize the code 62 of function of the present invention described herein.For example, the buffer management system 40 of supposing Fig. 2 is implemented as the program code 62 (although it may be implemented as such as the hardware in the processor 52) in the radio parts 50.Because the TCP bag receives by transmitter receiver 56, so radio parts 50 is configured to check the sequence number of TCP bag, to determine that whether the TCP bag is by unordered reception.If the new TCP bag that sends is by unordered reception (for example, if the new TCP that sends is received before wrapping in the forwarding TCP bag with low sequence number), then radio parts 50 will only transmit it when token exists.For this reason, if radio parts 50 is access points, then new TCP bag that sends will send to mobile device 26 at the token of each existence.On the contrary, if radio parts 50 is mobile devices, then new TCP bag that sends will be at the token of each existence and processed.Under any circumstance, at the TCP bag of each new transmission of being transmitted, the quantity of token will subtract one, and will send the affirmation/request to correct TCP bag.In case whole tokens is used up, then the TCP bag of the new transmission that will receive before " request " transmits the TCP bag is buffered in the memory 54, arrives up to the TCP bag of transmitting.After the TCP bag of transmitting arrives, token quantity will return to predetermined quantity (for example 3), and the buffering TCP of equivalent bag will be transmitted.

Therefore, according to the present invention, radio parts 50 is configured to: receive and transmit and the new TCP bag that sends; Check the sequence number of each TCP bag, so that identify the TCP bag of one group (for example one or more) unordered (the new transmission); Token at each existence transmits a unordered TCP bag; At each unordered TCP bag that transmits, the quantity of token subtracts one; Cushion any unordered TCP bag that is not transmitted; Transmit the TCP bag of any forwarding; And, when having transmitted " request " forwarding TCP bag, token quantity is returned to predetermined quantity.

For the purpose of illustration and description, represented foregoing description to the preferred embodiment of the present invention.It is not exhaustive, or is intended to the present invention is limited to disclosed precise forms, and obviously, any change and variation are possible.Conspicuous to those skilled in the art these modifications and variations are included in the scope of the present invention that claims limit.

Claims

1. one kind is used to avoid TCP to wrap in the method that mobile device (26) resend between transfer period, comprising:

Go up the TCP bag (44) that receives one group of new transmission at radio parts (50);

Check the sequence number of each TCP bag in the new TCP bag (44) that sends of this group, so that identify one group of unordered TCP bag;

At each token in a plurality of tokens (48) that are present on the radio parts (50), transmit in the unordered TCP bag of this group; And

At each the unordered TCP bag that is transmitted, the quantity of token (48) subtracts one.

2. the method for claim 1 comprises that also this each TCP that organizes unordered TCP bag that buffering is not transmitted wraps.

3. the method for claim 1 also comprises:

Go up the TCP bag (42) that receives forwarding at radio parts (50);

Transmit the TCP bag of transmitting (42); And

If the TCP that transmits bag (42) is previous request, then token (48) quantity is returned to predetermined quantity.

4. the method for claim 3, the new TCP bag (44) that sends of the TCP that wherein transmits bag (42) and this group comprise that TCP wraps and flow.

5. the method for claim 1, wherein radio parts (50) is access point (20C), and wherein transmission step comprises: at each token in a plurality of tokens (48) that are present on the access point (20C), send the unordered TCP of this group bag one from access point (20C) to mobile device (26).

6. the method for claim 5 wherein, goes up the TCP bag (42) that receives forwarding from the associated previous access point (20B) of mobile device (26) at access point (20C).

7. the method for claim 1, wherein radio parts (50) is mobile device (26), and wherein transmission step comprises: at each token in a plurality of tokens (48) that are present on the mobile device (26), permission mobile device (26) is handled in the unordered TCP bag of this group.

8. the process of claim 1 wherein that the quantity of this token (48) comprises three tokens.

9. one kind is used to avoid TCP to wrap in the method that mobile device (26) resend between transfer period, comprising:

Receive one group of TCP bag (44) that is used for the new transmission of mobile device (26) at access point (20C);

At each token in a plurality of tokens (48) that are present on the access point (20C), send in the unordered TCP of this group bag one to mobile device (26), and at each the unordered TCP bag that sends to mobile device (26), the quantity of token (48) subtracts one;

Receive the TCP bag of transmitting (42) from the associated previous access point (20B) of mobile device (26); And

The TCP bag of transmit transmitting to mobile device (26) (42), and if the TCP that transmits bag (42) by the previous request of mobile device (26), then the quantity with token (48) returns to predetermined quantity.

10. the method for claim 9 also comprises not each TCP bag in the unordered TCP bag of this group that mobile device (26) sends of buffering.

11. the method for claim 10, comprise also that at each token in the token (48) that recovers quantity the TCP that transmits one of them buffering to mobile device (26) wraps, wherein, at the TCP bag of each buffering that sends to mobile device (26), the quantity of token (48) subtracts one.

12. the method for claim 9, wherein the quantity of this token (48) comprises three tokens.

13. one kind is used to avoid TCP to wrap in the system that mobile device (26) resend between transfer period, comprises radio parts (50), radio parts (50) is configured to: go up at radio parts (50) and receive one group of new TCP bag (44) that sends; Check the sequence number of each TCP bag in the new TCP bag that sends of this group, so that identify one group of unordered TCP bag; At each token in a plurality of tokens (48) that are present on the radio parts (50), transmit in the unordered TCP bag of this group; And at each the unordered TCP bag that is transmitted, the quantity of token (48) subtracts one.

14. the system of claim 13, wherein, radio parts (50) also is configured to cushion this each TCP that organizes unordered TCP bag that does not transmit and wraps.

15. the system of claim 13, wherein, radio parts (50) also is configured to: receive the TCP bag of transmitting (42); Transmit the TCP bag of transmitting (42); And if the TCP that transmits bag (42) is previous request, then the quantity with token (48) returns to predetermined quantity.

16. the system of claim 13, wherein radio parts (50) is access point (20C), and wherein access point (20C) is configured to: by sending in the unordered TCP of this group bag one at each token in a plurality of tokens (48) that are present on the access point (20C) to mobile device (26), transmit the unordered TCP of this group and wrap.

17. the system of claim 16 wherein, goes up the TCP bag that receives forwarding from the associated previous access point (20B) of mobile device (26) at access point (20C).

18. the system of claim 13, wherein radio parts (50) is mobile device (26), and wherein mobile device (26) is configured to: by handle in the unordered TCP bag of this group at each token permission mobile device (26) in a plurality of tokens (48) that are present on the mobile device (26), transmit the unordered TCP bag of this group.

19. the system of claim 13, wherein the quantity of this token (48) comprises three tokens.