Radio network emulator for a packet core network

Details Radio network emulator for a packet core network Radio network emulator for a packet core network

2001-02-02

2004-11-23

Chin, Wellington (Department: 2664)

Multiplex communications

Communication over free space

Having a plurality of contiguous regions served by...

C455S525000, C703S013000, C703S023000, C717S134000, C717S135000, C717S138000

Reexamination Certificate

active

06822947

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to emulation systems and, in particular, to an emulation system that simulates the effects of radio network operation on packet data transmissions within a packet core network including a wireless link.
2. Description of Related Art
A packet core network (PCN), such as the one used in a cdma2000 network, is configured in a manner much like other data communications networks. These networks include a succession of routers (or other communications nodes) that are interconnected and carry internet protocol (IP) traffic. In some cases, a radio link is provided between two routers of the network. This radio link introduces a phenomenon that is not often experienced in conventional data communications networks: that is, data transmission errors.
Transmission control protocol (TCP) is built such that when an error is detected in a packet transmission, the complete IP datagram is retransmitted. This error correction operation works fine when the data is transmitted over Ethernet or fiber (which have very low error rates on the order of 10E-07). In the case where the packet core network includes a radio network component, such as, for example, a radio communications link, the error rate may be much higher (on the order or 10E-03). Given the transmission of substantially large sized IP packets (for example, greater than one-thousand bits), there is a significant chance that each packet of a transmission carried over the radio link will experience an error. This would necessitate an extraordinarily large number of TCP retransmissions that may effectively block successful data transmission over the packet core network.
To address the foregoing concerns over packet size and TCP retransmissions, the radio network portion of the packet core network transmits data over the wireless radio link in airframes that are much smaller than typical IP datagrams. The IP datagram is segmented into a plurality of smaller packet data units (PDUs) or airframes that are communicated over the radio link. To combat the data transmission error problem over the radio link, cyclical redundancy check (CRC) and forward error correction (FEC) techniques are implemented with respect to each PDU transmission. At the receiver, errors in a radio link transmitted PDU are detected by the CRC and corrected by the FEC. If the detected error cannot be FEC corrected, the PDU (frame) is erased and a request is made for a retransmission of that frame (not the entire datagram as would be required by TCP). The net result is that transmission over the wireless radio link may be made essentially error free, but frame erasures and requests for retransmission will introduce to some degree a time delay in overall data transmission through the network. It is accordingly recognized that as the frame erasure rate (FER) increases for transmissions made in this manner, so does the associated network transmission delay.
Another concern with the use of a wireless radio link for packet data communications centers on bandwidth limitations. In spite of the improvements being made in wireless communications spectrum efficiency, existing wireless communications technologies (such as 2.5 G and 3 G cellular air interface technologies) have severely limited bandwidths in comparison to Ethernet or fiber communications networks. While the available bandwidth may be satisfactory when only one user (or limited small number of users) is accommodated for data communications, the per user available bit rate for data communications through the network over the wireless radio link rapidly decreases as the number of users increases. This problem is magnified when an essentially unlimited bandwidth Ethernet or fiber based packet core network is integrated with a restricted bandwidth radio network that acts as a bottleneck for data transmissions.
Communications engineers often need to test or demonstrate the operation of a packet core network. The implemented network available for testing may not physically include a radio network that includes a wireless radio link interconnection between routers. For purposes of such a demonstration, however, a need often exists to test how applications communicating over the packet core network would react if a radio network were included and if radio conditions on that network were less than ideal (i.e., when the data transmission frame erasure rate increases and/or the number of users increases with respect to use of the radio link). The present invention allows for this testing to be performed on a non-radio packet core network by simulating the adverse effects on data packet transmission experienced when communications are made over a radio link.
SUMMARY OF THE INVENTION
A plurality of routers are interconnected by communications links to form a packet core network (PCN). At one router, an emulator is provided to manipulate the transmission of internet protocol (IP) datagrams through the router in order to simulate the transmission effects of having one of the inter-router communications links fictionally comprise a radio link. This is accomplished by having the emulator determine a time delay that is applied against the transmission of each IP datagram. The effect of the applied delay is to simulate emulated radio link operation to erase received frames containing uncorrectable errors and request retransmission of those frames.
In another embodiment of the invention, a plurality of routers are interconnected by communications links to form a packet core network (PCN). At one router, an emulator is provided to manipulate the transmission of internet protocol (IP) datagrams through the router in order to simulate the transmission effects of having one of the inter-router communications links fictionally comprise a radio link. This is accomplished by having the emulator limit a data rate for router node handling of IP datagrams transmitted through the packet core network. The effect of the limited data rate operation is to simulate congestion on the emulated radio link due to the presence of other, competing users.
The emulator receives user input specifying radio link conditions (such as, for example, number of users, bit error rate, signal to noise ratio, frame erasure rate, mobile platform speed, and mobile to base distance). This input is used to determine a frame erasure rate (FER) value indicative of how frequently packet data units (PDUs) transmitted over the radio link are likely to be received with an uncorrectable error. From this value, a time delay is determined that is representative of the delay introduced in the through transmission of the IP datagrams due to the effect of frame erasures and retransmissions with respect to PDU transmissions over the emulated radio link. This input is further used to determine the data rate limitation imposed on router communication handling due to congestion from competing users of the emulated radio link.
In an embodiment of the invention, the packet core network comprises a non-radio packet core network and the radio link to be emulated comprises a wireless cellular radio link.


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