Abstract:
A method for exchanging control and customer data between network element in a communications network involves establishing a virtual connection between the routers, and exchanging the control and customer data over an http layer.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application claims the benefit under 35 USC 119(e) or prior U.S. provisional application Ser. No. 60/530,678 filed Dec. 19, 2003, the contents of which are incorporated herein by reference. 

   FIELD OF THE INVENTION 
   This invention relates to the field of data communication networks, and in particular to a method of passing application protocol streams between any device in a data communications network, such as a content based network having XML routers. 
   BACKGROUND OF THE INVENTION 
   Content-based networks are described in A. Carzaniga, M. J. Rutherford, A. L. Wolf. A routing scheme for content-based networking. Department of Computer Science, University of Colorado, June 2003, the contents of which are herein incorporated by reference. 
   In content routed networks, one of the factors that determine network scalability is the limited number of TCP connections supported by each router. Between any two adjacent content routers, both control and customer data needs to be exchanged. Within the control data flows, two distinct protocols are defined; the XML Link State Protocol (XLSP) and XML Subscription Management Protocol (XSMP), both of which are components of the Implicit Routing Protocol (IRP). Refer to co-filed application Ser. No. 60/530,615, which is herein incorporated by reference. In this example, there are three application protocol streams being exchanged between each pair of content routers: an XSMP control stream, an XLSP control stream, and a data stream. 
   A traditional method for passing these three data flows between devices would be to establish separate TCP connections for each data flow. Multiplexing and de-multiplexing of the data at each end would be accomplished via distinct TCP port numbers. However, this technique has two significant drawbacks:
         1. The number of TCP connections supported by any one networking device may be (relatively) small, and hence the wasteful usage of TCP connections would quickly limit the size and scalability of the network.   2. In a firewalled environment, the administrative overhead of configuring the firewalls to allow each type of connection significantly increases the administrative effort required to deploy the content routed network.       

   As an example, in  FIG. 1 , consider the relatively small network  1 . Here, the topology includes seven content routers  2 , interconnected with thirteen XML links  3 . Using TCP multiplexing, a total of thirty nine connections would be required. Each XML link  2  between a pair of content routers requires three TCP connections under this scheme since one TCP connection is needed to exchange customer data, which in a content-routed network is the events or documents that are being routed, a second TCP connection is needed for the XLSP protocol, and a third TCP connection is needed for the XSMP protocol. It is apparent that TCP connections would quickly limit network scalability, as the number of routers increases into the hundreds and number of XML links increases into the thousands or tens of thousands. Moreover, as new inter-router protocols are developed to enable new services or capabilities within the content routed network  1 , yet more TCP connections would be required between a pair of routers connected with an XML link, further compounding the problem. 
   SUMMARY OF THE INVENTION 
   The invention discloses a novel technique for multiplexing flows for customer data and one or more control protocols over a single HTTP/TCP connection, which allows the reduction by one half or more in the number of TCP connections required for a given network topology. The invention is applicable to any device where multiple protocols can share a single HTTP connection. 
   According to the present invention there is provided a method of passing application protocol streams between network elements in a data communications network, comprising establishing a virtual connection between said network elements, establishing an HTTP layer within said virtual connection; and multiplexing said application protocol streams over said HTTP layer. 
   The invention may be applied to XML routers in a content based network, although it is not limited to use with XML routers. 
   Embodiments of the invention can, for example, be used to identify control and data plane sub-systems within an XML router using HTTP Universal Resource Identifier (URI) arguments. HTTP and the HTTP URI is defined in RFC2616, “HyperText Transfer Protocol—HTTP/1.1”, June 1999; RFC1945, “Hypertext Transfer Protocol—HTTP/1.0”, May 1996, and also in RFC2396, “Uniform Resource Identifiers (URI): Generic Syntax.”, August 1998, all from The Internet Society. 
   Control and data traffic can be multiplexed over a single TCP connection, in which case HTTP is used as the de-multiplexing mechanism. 
   The invention also provides a method for ensuring that when control and data plane traffic is multiplexed over a single TCP connection, the prioritization of control plane messages is achieved via queue servicing. 
   The invention still further provides a router for use in a data communications network, wherein said router is configured to establish a virtual connection with other routers in the network, establish an HTTP layer within said virtual connection; and multiplex application protocol streams over said HTTP layer. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which: 
       FIG. 1  shows a Content Routing Network; 
       FIG. 2 : shows Multiplexing over HTTP/TCP; and 
       FIG. 3  shows Outbound Queue Scheduling. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In accordance with the principles of the invention all data exchanged between adjacent routers in the content based network of  FIG. 1  is carried via HTTP over TCP. A single TCP connection between routers can be achieved, if the HTTP layer is used to de-multiplex the control and data flows, as shown in  FIG. 2 . Two routers  10  and  11  are connected by an HTTP over TCP connection  12 , which is terminated by the HTTP function  16  in each router. Within the single HTTP over TCP connection  12 , there are three flows  13 ,  14  and  15 . Flow  13  connects the XLSP protocol  17  in each router  10  and  11 . Flow  14  connects the XSMP protocol  18  in each router  10  and  11 . Flow  15  connects the Data Plane Forwarding Engine (DP-FE)  19  in each router  10  and  11 . 
   HTTP identifies “paths” or locations for the exchanged data via field called the Uniform Resource Identifier (URI). The definition of the HTTP URI, specified in the reference above, allows the passing of arguments between the communicating devices. Arguments are identified by the leading character “?”. The general form of the HTTP Universal Resource Locator (URL), which is a form of a Universal Resource Identifier (URI) is:
     “http:” “//” host [“:” port] [abs_path [“?” query]]   

   Within the “query” portion, the “?name” argument is used to identify and de-multiplex data flows to the appropriate sub-systems within the content router, for example, the three subsystems  17 ,  18  and  19  shown in  FIG. 2 . For example,
         http://&lt;router_ip&gt;/?name=&lt;subsystem_name&gt;       

   There are three currently recognized values for &lt;subsystem_name&gt;, which are identified in  FIG. 2 . As an example, when sending an XLSP message to the adjacent content router with IP address 192.168.10.1, the URI would be:
         http://192.168.10.1/?name=XLSP       

   The default subsystem is the DP-FE, and if an HTTP message is received without the name=&lt;subsystem_name&gt; parameter specified, then the DP-FE subsystem  19  is selected by default. 
   Another method to use a single HTTP session to multiplex/demultiplex multiple protocol flows is to use the “absolute path” portion of the URI to specify the subsystem. For example:
         http://192.168.10.1/&lt;subsystem_name&gt;
 
where subsystem name is one of those specified in  FIG. 2 . For example, for the XLSP subsystem  17 , the URI would be:
   http://192.168.10.1/XLSP       

   Additionally, other HTTP header fields could be utilized instead of the HTTP URI in order to specify the subsystem name for the purposes of multiplexing/demultiplexing multiple protocol flows over a single HTTP connection. HTTP consists of numerous header fields to carry various control information, such as the HTTP content length. One of these existing fields could be used to define the subsystem, or a new header field could be defined. For example, the defined HTTP “pragma” general-header field could be used to specify the subsystem. For example, in order to specify the XLSP subsystem:
     Pragma: XLSP   

   Alternatively, if a new field “subsystem” was defined and used as part of the HTTP header, the subsystem could be specified as:
         subsystem=XLSP       

   The technique of multiplexing control and data flows over a single TCP connection presents a potential problem in the prioritization of control traffic over data traffic (or more generally higher priority application traffic over lower priority application traffic). In the presence of heavy volumes of customer dataplane traffic (handled by the DP-FE subsystem  19  of  FIG. 2 ), links can become congested, which can lead to significant delays or lost messages. It is critical that the Implicit Routing Protocol (IRP) protocol messages are isolated from these effects, as they can lead to routing instabilities, routing cycles and lost subscriptions; all of which lead to a disruption in customer data. Note that the IRP function is composed of the XLSP subsystem and the XSMP subsystem. The IRP is described in co-filed application Ser. No. 60/530,615. 
   Design techniques are applied to the outbound traffic direction to mitigate the effect of congestion on IRP protocol traffic. 
   Congestion on a TCP connection is reflected by a backup of outgoing messages ready to be sent on that connection. These messages are stored internally in the content router in a software queuing data structure (which can also be implemented as a hardware queue if the HTTP over TCP function is implemented using hardware acceleration). By separating the control and dataplane traffic into separate queues, and imposing a queue servicing and scheduling discipline across the queues, it is possible to minimize the delays experienced by the control traffic. 
   The scheduling discipline chosen is a Work Conserving-Weighted Round Robin, as depicted in  FIG. 3 . Work conserving involves scheduling disciplines which always make use of available link bandwidth. Weighted Round Robin is a scheduling discipline which cycles through a set of queues, and grants access to the physical medium based on weights assigned to the queues. In this scheme, the two queues can be assigned weights M:N, such that under congestion scenarios, the bandwidth received by the control queue is M/(N+M) of the total available bandwidth. Typical values for M:N are 5:1. 
   Since the ratio of data plane traffic to control messaging is typically largely biased in favor of the data plane (i.e. in typical network operations there are many more data plane messages than control plane messages), it is rare that control messaging will ever consume the full bandwidth available to it. In these cases the work conserving aspect of the scheduler kicks in: if one of the queues has no data to send in its timeslot, the other queue is serviced. 
   The queuing is shown in  FIG. 3 . A single TCP socket (TCP connection)  20  carries the three application flows of XLSP  23 , XSMP  24  and DP-FE  25  as described above, using HTTP  22 . The XLSP subsystem  23  produces a message flow  26 . The XSMP subsystem  24  produces a message flow  27 . The DP-FE subsystem  25  produces a message flow  28 . These messages are formatted as HTTP by the HTTP block  22 . The XLSP  23  and XSMP  24  messages are placed into queue  30 , and the DP-FE  25  messages are placed into queue  29 . The Work Conserving-Weighted Round Robin (WC-WRR) block  31  is responsible for managing the removal of messages from queues  30  and  29  for sending to the TCP connection manager block  21 , which manages the TCP connection  20 . Queue  30  carries the control plane traffic, and queue  29  carries the dataplane traffic. 
   In  FIG. 3 , a single queue  30  is used for both XLSP  23  and XSMP  24 , which together comprise the IRP. However, each of these two subsystems could be given their own queue if the traffic between XLSP and XSMP needed different priority treatment. In addition, additional subsystems could be added to the system in addition to the three shown, and this could result in the addition of additional queues, or the new subsystems could share existing queues  29  and  30 . 
   It will be appreciated by persons skilled in the art that many variants of the invention are possible. 
   All references mentioned above are herein incorporated by reference.