Patent Grant
9432463
The present invention relates generally to a method and system for diverting an in-progress communication session. The communication protocol being used by a communication session is identified by inspection so as to allow diverting of communication sessions based upon the protocol.
In a data communications network it is sometimes desirable to divert data to a destination other than the destination addressed by an initiator. One common example is that of Internet web page caching, in which a request for web content may be directed to a geographically local server containing the same content rather than to the server addressed by the initiator. This reduces the communication fees.
Another example is that of peer-to-peer optimization, in which a request for a particular file is directed to a geographically local peer known to have the file. This optimization reduces the communication fees. An invention to redirect requests to reduce communication fees in a Peer to Peer network (P2P) is disclosed in U.S. application Ser. No. 10/138,336 and is herein incorporated by reference.
A first step in solving the problem of diverting data is by identifying communication sessions, which are using a protocol that can be diverted. In previous solutions, identification has been based simply on port number. The port number is found in every Transmission Communication Protocol (TCP) and User Datagram Protocol (UDP). Internet web caching has been done simply by forwarding all traffic destined for TCP port 80 to the caches. Since all packets including the very first are diverted, there is never any contact with the intended destination.
Current products, such as Alteon provided by Nortel Networks use a technique known as hierarchical search: a selection of traffic based on port number can be analyzed. Such searches require that a device accept connections as a full proxy. The protocol identification is inherently limited to examining content from the initiator of a communication session.
Optimizing peer-to-peer transfers is more difficult because the peer-to-peer protocols do not use fixed port numbers. These so-called dynamic-port protocols use randomly selected ports or share port numbers, such as 80, with other protocols. Thus, the content of the communication session must be analyzed for the tell tale signatures of peer-to-peer protocols.
Some current simple solutions for identifying protocols can classify communication sessions on the basis of examining single packets such as the Network Based Application Recognition (NBAR) product provided by Cisco Systems, Inc. If any packet matches a classification, all subsequent packets of the communication session can be marked to identify the protocol. NBAR does not provide the ability to redirect packets, nor is it able to mark all packets in a communication session, as some are lost before classification is made.
Other solutions use a full proxy technique. The network device accepts a connection from an initiator, examines the content and possibly opens a new session to the intended acceptor. Even if the protocol is not of interest, these two sessions must be managed by the device for the duration of the communication session. The content of the communication session must be analyzed to identify any protocol that doesn't use standardized port numbers.
Thus, there is need for a device, which can divert in-progress sessions based on the content of the initial, few packets of a communication session.
The present invention relates to a system and method for diverting an in progress communication session.
One aspect of the present invention is a method for examining a communication session, the session comprising a plurality of packets between a first node and a second node, the method comprising the steps of;
In another aspect of the present invention there is provided a system for diverting a communication session between an initiator and an acceptor the system comprising;
In another aspect of the present invention there is provided a system for examining a communication session, the session comprising a plurality of packets between a first node and a second node, the system comprising;
In yet another aspect of the present invention there is provided a computer readable medium comprising instructions for examining a communication session, the session comprising a plurality of packets between a first node and a second node, the medium comprising;
For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings which aid in understanding an embodiment of the present invention and in which:
In diverting a communication session already in progress, the following should be considered:
The present invention is placed within a data communications network. In the preferred embodiment, the present invention would reside in a point through which all communication sessions to be analyzed must pass.
Referring now to
Divert host 108 is designed to accept connections addressed to any host on the network as though it were that host. It decodes the encapsulation information provided by TSE 106 to determine which protocol to process. In the present invention encapsulation may be accomplished by using, but is not limited to the use of: Virtual Local Area Network tagging (VLAN, IEEE 802.1q), Multilabel Protocol Switching (MPLS), and Generic Routing Encapsulation (GRE, Network Working Group RFC 2784).
Core router 110 passes the packets in the communication session to a node acting as an acceptor in Network B (feature 112).
Referring now to
In another example of diversion of a communication session we now refer to
For the examples illustrated in
Referring now to
The main components of TSE 106 are: session state manager 152, protocol state machine 154, and pattern state machine 156. Session state manager 152 maintains a session state record (not shown) for each communication session, at least initially. The session state record is used by both protocol state machine 154 and pattern state machine 156 to track the progression of a communication session.
Packets arrive at session state manager 152. Packets may come from an initiator 122 an acceptor 124 or a divert host 108. When session state manager 152 receives a packet, it first determines if the packet is an attempt to start a new communication session. If this is the case state manager 152 creates a new session state record. By way of example, in a TCP session, a new state record will only be created if the packet has the SYN flag set. If the packet indicates a communication session already in progress, state manager 152 searches for a corresponding session state record in a session state table. If a state record cannot be found, an “allow” state is implied and the packet is allowed to proceed to its intended destination via forward module 158. This is the mechanism for allowing packets from protocols which are not of interest to pass without consuming state memory.
If session state manager 152 determines that a state record exists, the current packet is examined by protocol state machine 154. If the session state record indicates DIVERT, then the packet is sent to a divert host 108 via divert module 159. If the session state record is in MARK state, the packet is marked and sent to its intended destination via forward module 158. If the session state record is in INSPECT state the packet is sent to pattern state machine 156 to be examined. If pattern state machine identifies the packet to be part of a protocol of interest, then it sets the session state record to DIVERT and protocol state machine 154 then sends the packet to a divert host 108 via divert module 159. If pattern state machine 156 concludes that no protocol of interest exists, then the session state record is deleted, thus allowing all packets to pass directly through TSE 106 without maintaining state. If pattern state machine 156 determines that the packets of the communication session should be marked, the session state record is changed to MARK so that all packets are marked before being sent by forward module 158.
Session state records will be deleted in the cases of a pattern match resulting in “allow”, timeout due to inactivity, or indications that the session cannot be diverted for other reasons. Other reasons may include the inability to connect to a host or the presence of unsupported communication options.
In the preferred embodiment of the present invention, a different protocol state machine 154 is required for each communications transport protocol of interest. (e.g.TCP, UDP).
As indicated previously, TSE 106 may redirect initiator/acceptor communications to initiator/divert host and it may also redirect initiator/ acceptor communications to a divert host/acceptor.
Referring now to
As shown in Table 1, INSPECT state 168 may remain in an undecided mode until it determines to allow or divert.
Not shown in
Referring now to
As the UDP protocol does not have a start indication (as SYN does with TCP), an implicit “allow” is not possible; any packet will create a session if it doesn't exist. Sessions are closed by timeout.
Referring back to
When protocol state machine 154 is in the INSPECT state (168, 194), the pattern state of the current communication session is used in conjunction with the contents of the current packet to determine the next pattern state or to move protocol state machine 154 into another state.
Table 3 illustrates a simple example of a pattern state machine 156 that distinguishes between three protocols, namely:
Once a pattern is definitively matched, divert host 108 is chosen and a scheme is selected for tagging packets deliver to divert host 108. For example, the scheme could be VLAN tagging of Ethernet packets, MPLS tagging or some other form of tagging. The choice of scheme allows a divert host 108 to know which protocol is to be used, since divert host 108 may not otherwise have enough information to know the protocol.
The present invention resides in Traffic Switching Element (TSE) 106. TSE 106 is capable of marking or diverting in-progress communication sessions, including sessions using the TCP protocol, on the basis of pattern-matching the content of the communication. Marking packets in a communication stream allows devices such as distribution router 104 and core router 110 (see
The TCP standard (RFC: 793, Transmission Control Protocol, DARPA Internet Program, Protocol Specification, September 1981), specifies “sequence numbers” to be carried within each packet to indicate the relative position of the packet with respect to the start of the communication session. Also “acknowledgement numbers”are carried within packets traveling in the opposite direction to indicate which data has been received. Since the initial sequence number for each session is chosen arbitrarily by the acceptor, the chance is very low that a divert host 108 would choose the same initial sequence number as the original acceptor 124.
One solution to the problem is to indicate to divert host 108 which initial sequence number was used by acceptor 124. However, since there is currently no standard for communicating this, custom modification of divert host 108 is required.
In the present invention sequence numbers sent from divert host 108 to initiator 122 are re-mapped. In the present invention, splicing includes re-mapping of sequence numbers set from divert host 108 to initiator 122. When a packet is received by TSE 106 from a divert host 108 the sequence number is increased by the difference between the initial sequence number of the acceptor 124 and the initial sequence number of the divert host 108. Similarly, acknowledgement numbers in packets traveling from initiator 122 to divert host 108 are decreased by the same difference. For those packets containing TCP selective-acknowledgement fields, the selective-acknowledgements are treated the same as the acknowledgement numbers.
TCP RFC 1323, TCP Extensions for High Performance, May 1992, requires each TCP packet to contain a “window” value, which represents how many bytes may be sent without acknowledgement. The standard also provides for an optional “window scaling” parameter to be provided by each node to packets containing the SYN flag. This scaling indicates how the window field is to be interpreted and is to be used for the duration of the session. A difficulty is that a divert host 108 may choose a different window scaling than that of acceptor 124. As with sequence numbers, divert host 108 could theoretically be informed of which value to use. However, without a standard way of communicating this, custom modification of divert host 108 would be required.
The inventors have chosen to re-scale window values into the correct range. In the preferred embodiment, when splicing, the inventors have chosen to re-scale window values into the correct range. For a packet from divert host 108 being sent to an initiator 122, the window value is scaled down by the difference between the window scale of acceptor 124 and the window scale of divert host. If the difference is negative the window is scaled up.
Although the examples presented herein are for TCP/IP and UDP, making a decision to alter a communication session transparently based on the contents of it can be applied to other communication protocols.
Although the present invention has been described as being a software based invention, it is the intent of the inventors to include computer readable forms of the invention. Computer readable forms meaning any stored format that may be read by a computing device.
Although the present invention has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art without departing from the spirit and scope of the invention as outlined in the claims appended hereto.
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| Number | Date | Country | |
|---|---|---|---|
| 20040193714 A1 | Sep 2004 | US |
