Abstract:
Systems and methods for switching communications across different data link layer protocols are provided. A switch which supports a first data link layer protocol can support differentiated services for a second data link layer protocol without performing routing in the second data link layer protocol. The differentiated services are provided by mapping a connection of the first data link layer protocol onto one of a plurality of connections of a second data link layer protocol. The mapping of frames is based on the connection carrying the frames of the first data link layer protocol and a type of service associated with the frames. The frames of the first data link layer protocol are forwarded to another switch using one of a plurality of connections based on the mapping.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     Wireless network operators typically rely upon backhaul transport networks from wireline carriers, such as Verizon, to provide a backhaul link for transmitting and receiving information between base sites and the network operator&#39;s core network. As used herein, a base site is a location where wireless base radios are located, and is also known in the art as a cell site.  FIG. 1  illustrates a conventional system for connecting a wireless network operator&#39;s base sites to the core network. A wireless network operator typically operates a number of base sites  110   a - 110   n  whose information is aggregated by an asynchronous transfer mode (ATM) switch  120  of the backhaul transport network  150 . ATM switch  120  transmits the aggregated information through the backhaul transport network  150  to another ATM switch  130 . ATM switch  130  transmits the aggregated information to a mobile switching office (MSO)  140  in the wireless network operator&#39;s core network. The MSO also transmits information destined for base sites  110   a - 110   n  using the backhaul transport network  150 . Aggregation by ATM is advantageous because it can utilize the multiplexing gain of multiple traffic flows. Accordingly, it can improve efficiency of the backhaul links and reduce the costs for wireless network operators.  
         [0002]     Currently most wireless network operators employ a time division multiplexing (TDM) communication protocol between base sites  110   a - 110   n  and the backhaul transport network  150 . TDM communication protocol can interoperate with ATM protocol. Some wireless network operators are considering implementation of an internet protocol-(IP) based core network and base sites. Accordingly, systems and methods which support both TDM and IP protocols on a backhaul between base sites and a wireless network operator&#39;s core network are necessary.  
       SUMMARY OF THE INVENTION  
       [0003]     Systems and methods for switching of frames are provided. A switch which operates according to a first data link layer protocol receives a frame formatted in a second data link layer protocol. Based on an identification of the connection on which the switch receives the frame and a value in a type of service field of the frame, the switch selects one of a plurality of connections for transmitting the received frame to another switch which operates according to the first data link layer protocol. The second switch, based on the connection carrying the frame received from the first switch, selects a connection to a router.  
         [0004]     In accordance with one embodiment of the present invention, a radio router, which operates according to a first data link layer protocol, employs a bridging module for forwarding frames to a switch, which operates according to a second data link layer protocol. A transceiver of the radio router receives packets of a first data link layer protocol and provides the packets to a processor. The processor generates frames in the first data link layer protocol and provides the frames to the bridging module over one of a plurality of connections.  
         [0005]     The bridging module converts the frames from the first data link layer protocol to frames in the second data link layer protocol, and forwards the frame to a switch over one of another plurality of connections. The selection of which one of the another plurality of connections to forward the frames is based upon a type of service field, such as a differentiated services code point field, in the frame of the first data link layer protocol.  
         [0006]     Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES  
       [0007]      FIG. 1  illustrates a conventional system for connecting a wireless network operator&#39;s base sites to the core network;  
         [0008]      FIG. 2   a  illustrates an exemplary system for connecting a wireless network operator&#39;s base site to the core network in accordance with one embodiment of the present invention;  
         [0009]      FIG. 2   b  illustrates an exemplary system for connecting a number of base sites to the core network in accordance with one embodiment of the present invention;  
         [0010]      FIG. 3  illustrates an exemplary system for connecting a wireless network operator&#39;s base sites to the core network in accordance with another embodiment of the present invention;  
         [0011]      FIG. 4  illustrates an exemplary method for forwarding information from base sites to a wireless network operator&#39;s backhaul transport network in accordance with the present invention; and  
         [0012]      FIG. 5  illustrates an exemplary method for forwarding information from a backhaul transport network to a wireless network operator&#39;s core network in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]     Because ATM and IP operate at different layers at the Open Systems Interconnection (OSI) protocol stack, any solution for supporting both TDM- and IP-based base sites must account for this difference. One technique for supporting TDM- and IP-based base sites is to provide a backhaul for the IP-based base sites which overlays the existing TDM-based backhaul. This technique provides separate switches and backhaul links for the TDM- and IP-based base sites. Because the backhaul links are typically leased by the wireless network operator, this technique can effectively double the backhaul cost.  
         [0014]     Another technique for supporting TDM- and IP-based base sites is to provide IP routing capability for current ATM switches. Specifically, this technique performs IP routing on the ATM switches which interface with the IP-based base sites. IP routing would require costly upgrades to current ATM switches, and therefore, is undesirable. Additionally, IP routing can cause scalability issues because IP routing protocol can typically support several hundred nodes, while the backhaul network may require thousands of switches.  
         [0015]      FIG. 2   a  illustrates an exemplary system for connecting a wireless network operator&#39;s base sites to the core network in accordance with one embodiment of the present invention. The system includes routers  210  and  220 , and ATM switches  230  and  260 . Routers  210  and  220  are respectively coupled to switches  230  and  260  via point-to-point/multi-link point-to-point (PPP/MLPPP) communication sessions over TDM communication links.  
         [0016]     In accordance with exemplary embodiments of the present invention, router  210  is an IP-based radio router, which acts as a base transceiver station (BTS) and is coupled to a base site. The router  210  can communicate with wireless stations using any type of air-interface protocol. Information received by router  210  from the wireless stations is included in IP packets, which are sent over a communication link (e.g., a T 1 , T 3 , E 1 , or the like) to the wireless network operator&#39;s core network. As used herein, wireless stations include cellular telephones, personal digital assistants (PDAs), computers with wireless modems, or the like. These wireless stations can be stationary or mobile. Router  220  can be an aggregation router located, for example, in an MSO. Similar to router  210 , router  220  is an IP-based router.  
         [0017]     ATM switch  230  includes processor  235   a  and memory  240 . Processor  235   a  can be a microprocessor, application specific integrated circuit (ASIC), field programmable gate array (FGPA), or the like. Memory  240  includes tables  245  and  250 . ATM switch  260  is similar to ATM switch  230 , except for the contents of the memory. Specifically, instead of including tables  245  and  250 , the memory  265  of ATM switch  260  includes tables  270  and  275 . Memories  240  and  265  can be solid state memory, flash memory, hard-disk drives, or the like.  
         [0018]     Both ATM and IP provide for different handling of different types of traffic. IP provides differentiated services for different types of IP packets using a type of service (TOS) field in the IP packet header. The value in the type of service field is known in the art as the differentiated services code point (DSCP) value. IP differentiated services provides expedited forwarding (EF), assured forwarding (AF), best effort forwarding (BE) and the like types of service. ATM provides for different handling of different types of traffic using different virtual connections. ATM connections can be constant bit rate (CBR), real-time variable bit rate (rt-VBR), non-real time variable bit rate (nrt-VBR), available bit rate (ABR), and unspecified bit rate (UBR). Accordingly, the present invention maps frames encapsulating IP packets received from IP-based radio routers to ATM connections based on the value in the type of service field of the IP header. Additionally, because the ATM switches may support more than one IP-based radio router, the present invention also performs the mapping based upon the layer- 2  connection carrying the IP packets.  
         [0019]     Tables  245  and  250  illustrate an exemplary mapping of IP differentiated services to ATM connection types. Specifically, EF frames associated with PPP session A are mapped into rt-VBR virtual connection  100 , AF frames associated with PPP session A are mapped into nrt-VBR virtual connection  101 , and BE frames associated with PPP/MLPPP connection A are mapped into UBR connection  102 .  
         [0020]     Switch  230  performs a similar mapping for frames received from switch  260  over the plurality of virtual connections. Specifically, based upon the virtual connection on which the frame is received from switch  260 , switch  230  will set the type of service value of the IP packet and place the corresponding frame on a PPP/MLPPP session based on the mapping tables. Alternatively, instead of the switch  230  setting the type of service value, this value can be set by router  220  before the packet is sent to switch  260 .  
         [0021]     Switch  260  performs similar mapping to that described above in connection with switch  230 . Specifically, switch  260  maps frames received over one of the plurality of virtual connections onto a particular PPP/MLPPP session. Similarly, switch  260  maps frames received from aggregation router  220  onto one of the plurality of virtual connections based upon which PPP session carried the frame and the value in the type of service field in the IP header of the frame.  
         [0022]     Because switches  230  and  260  are ATM switches, these switches can switch TDM frames between the MSO and the conventional base sites using conventional switching techniques. Although  FIG. 2  illustrates the mapping being performed by the main processor and memory of the ATM switch, the mapping can be performed by a separate processor and memory, an ASIC, FPGA, or the like.  
         [0023]     As discussed above, ATM switch  230  may support a number of IP-based radio routers.  FIG. 2   b  illustrates an exemplary system for connecting a number of base sites to the core network in accordance with the present invention. The mapping performed for information received from radio router  210  will be similarly performed for other radio routers coupled to ATM switch  230 . For example, another radio router  215  may have a PPP/MLPPP session C with ATM switch  230 . Like PPP/MLPPP session A, PPP session C can include DSCP values EF, AF and BE. Accordingly, memory  240  includes table  255  for mapping frames carried on PPP session C onto rt-VBR  103 , nrt-VBR  104  and UBR  105  connections between ATM switches  230  and  260 . Similarly, memory  265 , includes table  280  for mapping frames carried on connections rt-VBR  103 , nrt-VBR  104  and UBR  105  onto PPP/MLPPP D.  
         [0024]      FIG. 3  illustrates an exemplary system for connecting a wireless network operator&#39;s base sites to the core network in accordance with another embodiment of the present invention. In accordance with this embodiment, the mapping is performed by a bridging module in the radio router. The radio router  310  includes a transceiver  320 , processor  325 , memory  330  and bridging module  345 .  
         [0025]     The transceiver  320  is coupled for bidirectional communication with one or more wireless stations (not illustrated) over communication link  305 . Although  FIG. 3  illustrates only a single communication link  305 , more than one communication link can be used to couple the transceiver  320  with the one or more wireless stations. The one or more communication links can be 802.11, CDMA, TDMA, iDEN, GSM, Bluetooth, WiMax, or the like.  
         [0026]     The processor  325  receives IP packets from one or more wireless stations and establishes a PPP/MLPPP connection with bridging module  345 . The processor  325 , using the memory  330 , generates frames for transmission to the bridging module  345 . The bridging module  345  receives frames carried on a PPP/MLPPP connection and maps the frames into one of a plurality of ATM virtual connections. Because there is a single PPP session, the mapping is based only on a value in the type of service field of the IP frame. The bridging module  345  can be implemented as a processor with associated memory, ASIC, FPGA, or the like. Moreover, the bridging module need not be a component of the radio router  310 , but instead can be located anywhere between the radio router  310  and an ATM switch.  
         [0027]      FIG. 4  illustrates an exemplary method for forwarding information from base sites to a backhaul transport network in accordance with the present invention. A switch, such as an ATM switch, receives a frame encapsulating an IP packet (step  410 ) and identifies a connection which carried the frame (step  420 ). The switch then removes the PPP header of the frame in order to examine the IP packet (step  430 ). The switch identifies a type of service associated with the IP packet by examining the type of service field of the IP packet (step  440 ). The switch then encapsulates the IP packet in an ATM header, breaks the resulting frame into ATM cells, and transmits the ATM cells over an ATM connection based on the identified connection carrying the IP packet and a type of service associated with the IP packet (step  450 ).  
         [0028]      FIG. 5  illustrates an exemplary method for forwarding information from a backhaul transport network to a wireless network operator&#39;s core network in accordance with the present invention. An ATM switch receives an ATM frame from another ATM switch (step  510 ) and identifies the ATM connection carrying the ATM frame (step  520 ). The switch removes the ATM overhead from the ATM frame (step  530 ). The switch then sets the type of service field based on the identified ATM connection (step  540 ). Alternatively, the type of service field can be set. The switch encapsulates the packet into a PPP frame and transmits the IP frame over a particular connection based on the identified ATM connection (step  550 ).  
         [0029]     Although exemplary embodiments have been described above in connection with a mapping between PPP/MLPPP and ATM connections, the present invention is applicable to any type of system where it is desired to bridge different types of layer  2  technologies while providing differentiated services. For example, instead of a PPP/MLPPP connection between an ATM switch and an aggregation router, an Ethernet connection can be employed. Additionally, other types of protocols and switches other than ATM can be employed so long as the protocol supports some type of technique for providing different handling for different types of data.  
         [0030]     Although exemplary embodiments have been described in connection with particular class of service types, the present invention is equally applicable to other class of service types. For example, instead of using the DSCP value, the entire TOS byte can be used. Alternatively, the IP precedence bits, i.e., the first three bits in the TOS byte can be used.  
         [0031]     The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.