GB2370453A

GB2370453A - Dividing communications protocol

Info

Publication number: GB2370453A
Application number: GB0031052A
Authority: GB
Inventors: Ian Lasseter Phillips
Original assignee: Roke Manor Research Ltd
Current assignee: Roke Manor Research Ltd
Priority date: 2000-12-20
Filing date: 2000-12-20
Publication date: 2002-06-26
Anticipated expiration: 2020-12-20
Also published as: GB0031052D0; GB2370453B

Abstract

A communications link between a first node and a second node, uses a protocol applied to subdivided data from a first communications protocol. In order to accommodate delays caused by the use of the IP protocol affecting the received quality of service, the data to be transmitted over the link is subdivided and may then be re-assembled after the link into a format applicable to the radio interface. A majority buffer may be used for data yet to be transmitted and a minority buffer for data that has just been transmitted. There may be a number of communications layers operating in accordance with different protocols coupled to an adaption layer for converting the different protocols into a format that can be handled by the node. The system may be applied in Asynchronous transfer Mode and internet protocol mobile networks, subject to non-deterministic delays and jitter.

Description

Communication Apparatus And Method This invention relates to communication apparatus and a communication method.

In communication systems such as GSM or 3GPP a Radio Access Network (RAN) is provided to pass user data to base-stations serving cells in the network. A typical RAN is shown in the prior art Figure 1.

It includes a Radio Network Controller (RNC) linked to a number of radio base-stations. The RNC includes the following functionality.

A Radio Resource Control (RRC) which has the function of controlling the allocation of radio resources within the RAN. In particular it allocates resources to individual user connections at the radio base-station in response to connection signalling either from mobiles within the RAN and/or from terrestrial users.

A Radio Link Control (RLC). This function matches user protocol data units to a size supported by the radio layer 1. As such it includes operations such as segmentation (breaking larger user data Packet Data Units (PDUs) into appropriate sized smaller units), padding (expanding

smaller user data PDUs to fixed length radio frames) and providing assured transmission (confirmed delivery and selective retransmission of lost data units).

A function called Medium Access Control (MAC). This function schedules individual PDUs for transmission across the air interface, and forwards the PDUs to the Radio Base-station at the appropriate time.

The base station includes the following functionality.

Radio Layer 1. This function represents the Layer 1 radio functions such as channelisation and multiplexing of multiple data streams A Radio Frequency Interface. This function represents the RF technology for actually transmitting a stream of bits across air to a mobile.

In order to achieve maximum scheduling efficiency on the air interface, the MAC function must attempt to pass data between the RNC and the Radio Basestation'just in time'prior to transmission. This behaviour

means that the data passed between the RNC is real time and synchronous (i. e. it must be delivered with hard time constraints and without variations in delay).

This real time, synchronous behaviour is in conflict with modem data networks such as Asynchronous Transfer Mode (ATM) and IP based networks. In such networks data from a single source is subject to delays due to packetisation delays (delays in mapping variable size data units to a fixed size underlying network) and sharing resources with other competing sources. Thus, in modem data networks individual data units may be subject to non-deterministic delays and jitter (variation in delay).

Mapping synchronous data flows to asynchronous networks requires additional mechanisms for measuring delay (e. g. additional in-band signalling) and correcting for jitter (e. g. playout buffers). This increases the cost and complexity of such interfaces.

According to the invention there is provided communication apparatus comprising a first communication node and a second communication

node ; a communication link between the nodes operating in accordance with a communication protocol ; the first node including a first link controller for accepting communication data in a first format for transmission to the second node over the communication link; a second link controller operably coupled to the communication link to receive data from the first link controller which first link controller subdividing the data having the first format and transmitting the subdivisions in a form compatible with the communication protocol.

The invention also provides a communication method for communicating data between a first node and a second node over a communications link comprising subdividing a first set of data in a first format and formatting the subdivisions into a second format compatible with a communications protocol operating on the communications link, and transmitting the data over the link to the second node.

Specific embodiments of the invention will now be described by way of example only with reference to the drawings in which: Figure 1 is a prior art figure;

Figure 2 shows a Radio Access Network Architecture in accordance with the invention ; Figure 3 is an alternative embodiment; and Figure 4 is a further embodiment of the invention.

With reference to Figure 2, a Radio Access Network RAN 1 in accordance with the invention includes a Radio Network Controller RNC 2 and a number of base-stations 3. The base-stations 3 and the RAN 2 are connected via a communications link 4 operating in accordance with a communications protocol called Internet Protocol (IP).

The RNC 2 includes and input and output port for control signalling and a further input and output port for user data. These connect to other networks in a manner well known to the man skilled in the art. A Radio Resource Control (RRC) 5 is also provided within the RNC 2 and this function controls the allocation of radio resources within the RAN 1.

The RNC 2 also includes a so called"Thick"Radio Link Control RLC 6. This differs in relation to the RLC of the prior art in that interoperates with a further Radio Link Control present in the base-station 3

in a manner to be later described. The inter-operation takes place via the IP communications link 4.

The base-stations 3 are provided with nominally identical functional blocks. The IP communication link 4 is coupled to a so-called"THIN" Radio Link Control 7 and hence to a Medium Access Control (MAC) 8.

This in turn is coupled to a Radio Layer 1 function 9 and hence via a radio frequency interface 10 to units served by the base-station 3.

Thus in the architecture in accordance with the invention, In the revised architecture, as shown in Figure 2, the MAC function together with a so-called'THIN'RLC Layer are placed at the Radio Base-station, in addition to the Radio Layer 1 and Radio Frequency Interface.

By locating MAC and RLC functions at the Radio Base-station then any non-real time user data may be transferred in a non-real time manner between the RNC 2 and the Radio Base-station 3. This provides an advantage since in emerging mobile communications markets, such as 3GPP, it is thought that the vast majority of data transferred will be non-real time network data such as internet traffic.

Further the MAC scheduling, which is by definition a real-time activity is simplified in that this function is now co-located with the RF functions and the air interface.

However, in the RAN, it is necessary that a mobile as it moves from radio cell to radio cell must handover from one Radio Base-station to another. If the entire RLC function were to be located at the Radio Base-station a substantial amount of data would require to be transferred from one base-station to another on handover. As basestations are frequently linked by low data rate interfaces such handover traffic would be a strong disadvantage.

In order to overcome this handover problem, a THIN-THICK split RLC function as shown in Figure 3 may be used.

The operation of the proposed THIN-THICK RLC is as follows: The user data is buffered at the RNC within the THICK RLC function

The user data is partitioned into : * A majority buffer which holds user data exclusively at the RNC * A minority buffer which holds a copy of user data held at the RNC and at the Radio Base-station * Data is transferred through the Majority and then the Minority Buffer in a First IN First Out (FIFO) manner * Data is copied to the Radio Base-station as it enters the minority buffer at the RNC, thereby maintaining a copy at the RNC and at the Radio Base-station.

* Data is deleted from the minority buffer at the Base-station when it is successfully sent over air. The deletion is confirmed back to the RNC where the corresponding deletion occurs in the RNC minority buffer.

* On handover between Radio Base-stations, the RNC can : 'Request that the THIN RLC stop sending data * Immediately send a complete copy of the minority buffer RLC data to the new base-station.

The above operation permits data to be transferred non real time between RNC and Radio Base-stations. It also permits a one-way transfer of RLC buffer information on handover thereby reducing the total load on the RNC-Base-station data links.

The necessary RLC control functions are essentially small but requiring fast processing and the ability to handle data transfers. As such this is well within the capability of current FPGA and memory technology.

In a further embodiment of the invention the two part"Thick"and "Thin"RLC is used to permit the integration of various communication standards into one communications network utilising the IP protocol.

Examples of the standards are

* GSM . 3GPP FDD and TDD * Hyperlan2.

Each layer 1 entity would take responsibility for maintaining the air interface according to the existing standards. In addition a custom MAC

layer is defined for each Layer 1. This layer takes responsibility for functions like : 'air interface management * scheduling 'power management etc.

A common'thin'RLC layer is proposed which matches received user data to the requirements of the underlying radio architecture. The RLC layer will provide service such as in-sequence and assured transmission as required by higher layer services. Such an RLC would need to support variable sized segmentation and re-assembly in order to match to a variety of radio capabilities.

Further a thin-thick split RLC layer is proposed between the basestation and the U-plane server. This idea attempts to overcome the limitations/inefficiencies in RLC which can occur during frequent handover between base-stations. The essential idea is that the bulk of any data is held in the U plane server with a limited amount held at the Base-station. An advanced RLC protocol would be defined between the U-plane server and the Base-station which would allow recovery on

demand of any unsent data from the base-station in the event of handover.

All user data is then routed to/from a common U-plane server via the associated IP network. The U-plane server then provides access to the terrestrial IP network and hence to the required recipient.

Additionally separate C plane servers are defined which handle the Radio Resource Management and Signalling for each type of Radio Layer 1 interface.

This invention thus enables a close-coupled integration of competing radio interface standards in a common architecture. This close coupling permits efficient implementation of a distributed architecture. However it does so by changing higher layer functions/architectural split of individual mobile standards whilst aiming to retain the radio layer 1 unchanged. Thus it converges higher layers into a generic standard suitable for handling all types of data transport.

A corresponding multi-mode terminal e. g. implemented using software radio techniques is also assumed.

Figure 4 shows an illustrative embodiment of a communications system utilising this approach.

Each of the existing and emerging standards in effect defines an entire communication system rather than just a means to access the RF resources. The danger in such an approach for developers is that it is difficult to determine which of the competing standards will achieve an adequate market share. Developing every technology is expensive and backing the wrong technology only could be commercially disastrous.

The idea proposed here would allow development and exploitation of each radio technology by developing RF/layer 1 interfaces as each new technology emerges whilst retaining the investment in the remaining system. In the mobile communications market there appear to be two

main commercial drivers : * voice 'data-mainly web and corporate data networks.

In addition mobile operators are adding further concerns : * IP Internet Protocol is perceived as a low cost network option

. Operators wish to retain and exploit existing standards * Licences now form a substantial part of the operating cost, thus the ability to simultaneously exploit a variety of technologies is of high value to an operator.

Third party resellers of telecom services are becoming well accepted where one operator sells service and phones to direct to the users, whilst other operators provide infra structure and sell service wholesale to the user providers.

In the illustrated system one operator might provide a GSM backbone and another operator provide 3GPP and Hyperlan2. A third operator would then have wholesale contracts with the first two operators and sell phones and contracts to the user.

Advantages of the system are: * A convergent architecture for mobile communications Additions to existing standards By retaining existing radio layer interfaces changes might not necessarily interfere with existing mobiles.

Claims

CLAIMS 1. Communication apparatus comprising a first communication node and a second communication node; a communication link between the nodes operating in accordance with a communication protocol; the first node including a first link controller for accepting communication data in a first format for transmission to the second node over the communication link; a second link controller operably coupled to the communication link to receive data from the first link controller which first link controller subdividing the data having the first format and transmitting the subdivisions in a form compatible with the communication protocol.
2. Apparatus as claimed in claim 1 wherein the first link controller further comprises a majority and a minority buffer wherein the majority buffer contains data to be transmitted over the communications link and the second buffer includes a copy of data already sent over the link.
3. Apparatus as claimed in claim 2 wherein the minority buffer includes a copy of data most recently transmitted.
4. Apparatus as claimed in any one of claims 1,2, or 3 wherein the communications protocol is Internet Protocol.
5. Apparatus for communication substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.
6. A communications network comprising apparatus as described in any one of claims 1 to 5 and further comprising communication layers operating in accordance with different communication protocols coupled to an adaptation layer coupled to the node for converting data from the communication layers into a form that can be handled by the node.
7. A communication method for communicating data between a first node and a second node over a communications link comprising subdividing a first set of data in a first format and formatting the subdivisions into a second format compatible with a communications protocol operating on the communications link, and transmitting the data over the link to the second node.
8. A method as claimed in claim 7 wherein at the second node the subdivisions are reformatted into the first format.
9. A method as claimed in claim 7 or 8 wherein data received form one or more of a plurality of communication layers operating in accordance with different communication protocols is adapted to the first format.
10. A communication method substantially as hereinbefore described with reference to and as illustrated by the drawings.