U.S. patent application number 10/571607 was filed with the patent office on 2007-08-23 for radio resource usage optimisation in a packet network.
Invention is credited to Janne Pesia, Mats Sagfors, Johan Torsner, Stefan Wager.
Application Number | 20070195697 10/571607 |
Document ID | / |
Family ID | 29226994 |
Filed Date | 2007-08-23 |
United States Patent
Application |
20070195697 |
Kind Code |
A1 |
Pesia; Janne ; et
al. |
August 23, 2007 |
Radio resource usage optimisation in a packet network
Abstract
A method of optimising the use of radio resources in a mobile
radio communication system during a combinational multimedia
session involving circuit switched and packet switched sessions
between user terminals, the method comprising: disabling an
in-sequence delivery option of packets between radio network
control nodes of the radio access network(s) serving the user
terminals for said packet switched session.
Inventors: |
Pesia; Janne; (Espoo,
FI) ; Sagfors; Mats; (Kyrkslatt, FI) ;
Torsner; Johan; (Masaby, FI) ; Wager; Stefan;
(Esbo, FI) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Family ID: |
29226994 |
Appl. No.: |
10/571607 |
Filed: |
August 5, 2004 |
PCT Filed: |
August 5, 2004 |
PCT NO: |
PCT/EP04/51725 |
371 Date: |
January 12, 2007 |
Current U.S.
Class: |
370/235 |
Current CPC
Class: |
H04W 28/10 20130101;
H04L 29/06 20130101; H04L 69/324 20130101; H04L 69/163 20130101;
H04W 80/10 20130101 |
Class at
Publication: |
370/235 |
International
Class: |
H04L 12/26 20060101
H04L012/26 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 12, 2003 |
GB |
0321425.1 |
Claims
1. A method of optimising the use of radio resources in a mobile
radio communication system during a combinational multimedia
session involving circuit switched and packet switched sessions
between user terminals associated with respective radio network
control nodes, where signals are transported over two cascaded
radio links, the method comprising: at a sending radio network
control node, disabling an in-sequence delivery option of packets
between the radio network control nodes of the radio access
network(s) serving the user terminals for said packet switched
session.
2. A method according to claim 1, wherein said packets are Service
Data Units, assembled at the RLC layer of the sending side radio
network controller, from Protocol Data Units.
3. A method according to claim 1, wherein said packets are Radio
Link Control Protocol Data Units which are tunneled from the
sending side radio network controller to the receiving side radio
network controller, the Protocol Data Units being assembled at the
receiving side terminal into Radio Link Control Service Data
Units.
4. A method of operating a radio network controller of a mobile
communications network, the method comprising disabling an
in-sequence delivery option for packets sent from the radio network
controller to another radio network controller and associated with
a packet switched session between two or more user terminals.
5. A method according to claim 4, the in-sequence delivery option
being an option of the Radio Link Control layer.
6. A method according to claim 5, wherein said packets are Radio
Link Control Service Data Units.
7. A method according to claim 5, wherein said packets are Radio
Link Control Protocol Data Units which are tunneled from the
sending side radio network controller to the receiving side radio
network controller.
8. A method of optimising the use of radio resources in a mobile
radio communication system during a combinational multimedia
session involving circuit switched and packet switched sessions
between user terminals, the method comprising: setting one or more
TCP sending parameters at least one user terminal for said packet
switched session so as to optimise radio resource usage, the TCP
parameter(s) being different from the parameter(s) used for
non-combinational multimedia session related packet traffic.
9. A method of operating a user terminal of a mobile radio
communication system, the method comprising: setting one or more
TCP sending parameters for a packet switched session associated
with a combinational multimedia session so as to optimise radio
resource usage, the TCP parameter(s) being different from the
parameter(s) used for non-combinational multimedia session related
packet traffic.
10. A method according to claim 8, wherein said TCP sending
parameters are segment size and/or initial window size.
11. A method according to claim 10 and comprising setting the TCP
sending parameters such that the TCP sending window is greater than
the size of the media to be sent.
12. A method according to claim 10, wherein the setup of setting
the TCP window size comprises increasing the window size relative
to that used for non-combinational multimedia session related
packet traffic.
13. A method according to claim 9, wherein said TCP sending
parameters are segment size and/or initial window size.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to combinational multimedia
services and more particularly to a method of optimising the data
transmission associated with such service.
BACKGROUND TO THE INVENTION
[0002] IP Multimedia (IPMM) services provide a dynamic combination
of voice, video, messaging, data, etc. within the same session. By
growing the numbers of basic applications and the media which it is
possible to combine, the number of services offered to the end
users will grow, and the inter-personal communication experience
will be enriched. This will lead to a new generation of
personalised, rich multimedia communication services, including
so-called "combinational IP Multimedia" services which are
considered in more detail below.
[0003] IP Multimedia Subsystem (IMS) is the technology defined (in
TS 32.225, Release 5) by the Third Generation Partnership Project
(3GPP) to provide IP Multimedia services over 3G mobile
communication networks. IMS provides key features to enrich the
end-user person-to-person communication experience through the
integration and interaction of services. IMS allows new rich
person-to-person (client-to-client) as well as person-to-content
(client-to-server) communications over an IP-based network. The IMS
makes use of the Session Initiation Protocol (SIP) and Service
Delivery Protocol (SDP) to set up and control calls or sessions
between user terminals (or user terminals and web servers). IMS
sits on top of an access network which would typically be a General
Packet Radio Service (GPRS) network but which might use some
alternative technology, e.g. WiFi. FIG. 1 illustrates schematically
how the IMS fits into the mobile network architecture in the case
of a GPRS access network.
[0004] An example of a combinational IP Multimedia service is a
multimedia service that includes and combines both a Circuit
Switched media (such as voice) and a Packet Switched media over the
IP Multimedia domain (such as pictures, video, presence, instant
messages, etc.). A service referred to here as "WeShare" combines
the full IP Multimedia Subsystem (IMS) benefits of a multimedia
service with CS voice. The service enables a user, during a Circuit
Switched (CS) voice conversation with another user, to take a
picture, a video or audio clip, etc. and to share this content with
other users in (near) real time. Either party in the conversation
may initiate transmission of content to the other party.
SUMMARY OF THE INVENTION
[0005] FIG. 2 illustrates schematically the Radio Link
configuration for the Push-To-Watch service. The transport chain of
the Push-To-Watch service consists of two cascaded radio links as
shown in FIG. 2. In the state of the art solution, these links are
totally decoupled, meaning that retransmissions and window control
is done separately without coordination. Assuming both radio link
protocols perform selective repeat ARQ with in-sequence delivery
(as used in most cellular systems), this may lead to a situation
where the buffers of the Radio Link B drain because Radio Link A is
performing retransmissions.
[0006] Consider the following example. Radio Link A is performing a
retransmission of a Protocol Data Unit (PDU) number 3 from Terminal
A to UTRAN A (that is the RNC of UTRAN A). Because of the selective
repeat function, UTRAN A continues to receive PDU numbers 4 and 5,
but because of the in-sequence delivery function, it is unable to
forward any packets to UTRAN B (that is the RNC of UTRAN B) until
the missing PDU number 3 is received correctly. This behavior is
well known and will produce a certain jitter in the outgoing data
flow of Radio Link A. Because of the selective repeat function of
the radio link protocol, the radio link utilization in UTRAN A will
however remain good as long as the window is open. The problem
occurs in Radio Link B, where the jitter in the incoming data flow
from UTRAN A may cause the buffer at UTRAN B to drain, causing
radio link under utilization, which in turn prolongs the picture
transfer time.
[0007] It is an object of the present invention to optimise radio
resource usage in a packet network and in particular to optimise
the radio link layer performance for the so-called "Push-To-Watch"
service to be offered by mobile wireless network operators. The
Push-To-Watch service involves exchanging pictures on a packet
switched (PS) connection between users whilst a circuit switched
(CS) voice call is active.
[0008] According to a first aspect of the present invention there
is provided a method of optimising the use of radio resources in a
mobile radio communication system during a combinational multimedia
session involving circuit switched and packet switched sessions
between user terminals, the method comprising: [0009] disabling an
in-sequence delivery option of packets at one or both of the radio
network control nodes of the radio access network(s) serving the
user terminals for said packet switched session.
[0010] In a first embodiment of the invention, said packets are
Service Data Units, assembled at the sending side radio network
controller from Protocol Data Units.
[0011] In a second embodiment of the invention, said packets are
Protocol Data Units. These units are assembled at the receiving
side Terminal into Service Data Units.
[0012] According to a second aspect of the present invention there
is provided a method of operating a radio network controller of a
mobile communications network, the method comprising disabling an
in-sequence delivery option for packets associated with a packet
switched session between two or more user terminals.
[0013] A second problem associated with the transmission of packet
switched data in a combinational service has been identified. In
the state of the art processes, multimedia content such as pictures
is transmitted from a user Terminal A to a user Terminal B using an
end-to-end Transmission Control Protocol (TCP) connection as
already described with reference to FIG. 2. The round trip time
(RTT) is great due to the cascaded radio links (A and B). As is
well known, TCP defines a window which restricts the number of
unacknowledged IP packets which can be in transit at any given
time. The window size is increased as acknowledgements are received
and is decreased if no acknowledgements are received for some
specified period. The rate at which the window is opened depends on
the ACKs received at the sender from the receiver. If the ACKs are
delayed, the slow start period is prolonged. During slow start, TCP
is not able to fully utilize a given radio link, which means that
picture transfer times increase. The pictures transmitted with the
push-to-watch service will be relatively small in size, e.g. 3 to
50 kBytes, which means that TCP will mostly be operating in the
slow start phase for the period that it takes to send a
picture.
[0014] According to a third aspect of the present invention there
is provided a method of optimising the use of radio resources in a
mobile radio communication system during a combinational multimedia
session involving circuit switched and packet switched sessions
between user terminals, the method comprising: [0015] setting one
or more TCP sending parameters at least one user terminal for said
packet switched session so as to optimise radio resource usage, the
TCP parameter(s) being different from the parameter(s) used for
non-combinational multimedia session related packet traffic.
[0016] Said TCP sending parameter may be segment size or initial
window size.
[0017] According to a fourth aspect of the present invention there
is provided a method of operating a user terminal of a mobile radio
communication system, the method comprising: [0018] setting one or
more TCP sending parameters for a packet switched session
associated with a combinational multimedia session so as to
optimise radio resource usage, the TCP parameter(s) being different
from the parameter(s) used for non-combinational multimedia session
related packet traffic.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 illustrates schematically a mobile network
architecture incorporating IMS; and
[0020] FIG. 2 illustrates schematically a cascaded radio link
connecting two user terminals.
DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS
[0021] The Universal Mobile Telecommunications Service (UMTS)
provides for a radio access network known as the UMTS Terrestrial
Radio Access Network (UTRAN). The two main components of the UTRAN
are the Radio Network Controller (RNC) which controls the radio
resources, and the Node B which operates as a base station.
Different RNCs communicate with each other over the lur interface.
UMTS also provides for a core network which will comprise
components for facilitating the General Packet Radio Service (GPRS)
which is an example of a packet switched access service. In
particular, the core network will contain Serving GPRS Support
Nodes (SGSNs) and Gateway GPRS Support Nodes (GGSNs).
[0022] UMTS provides for a Radio Link Control (RLC) layer which is
responsible for controlling data transmission over the wireless
link. Whilst the RLC can operate in a number of modes, the mode of
interest here is the "acknowledged" mode which ensures error free
transmission for upper layers of the protocol stack. The RLC is
located both at the RNC and at the User Equipment (UE). In the case
of IP data transmission, the RLC layer receives IP packets from the
IP/TCP layers. These are referred to as RLC Service Data Units
(SDUs). The RLC segments the SDUs into Protocol Data Units (PDUs)
which are passed to the lower protocol layers (particularly the
Media Access Control (MAC) layer). RLC specifies an in-sequence
delivery option for SDUs according to which SDUs are delivered to
higher layers in sequence. When this option is turned off, an SDU
is delivered immediately all PDUs belonging to that SDU have been
received, regardless of whether or not earlier SDUs have been
successfully received. The in-sequence delivery option may be
inhibited by specifying this in the request sent by the core
network (e.g. the SGSN) to establish a PS bearer.
[0023] As has been discussed above, in the case of user to user
data transmission, the RLC buffers at the receiving RNC may become
empty due to retransmission requirements at the sending RNC. This
results in inefficient use of the wireless interface at the
receiving side. The solution proposed here is to disable the
in-sequence delivery option at the RNC of the first radio link,
(i.e. from Terminal A to the RNC of UTRAN A) for the Push-To-Watch
service, upon detection that the Push-To-Watch service has been
activated. The IMS may notify the SGSN of the nature of the bearer,
allowing the SGSN to inhibit the in-sequence delivery option in the
PS bearer setup request sent to the RNC. In a first version this
can be done at the Service Data Unit (SDU) level, so that Radio
Link A is able to forward an SDU as soon as all of the PDU
components have been received. As the RLC layer at the RNC already
includes the option to disable of in-sequence delivery, no changes
to the relevant RLC protocol are required to implement this
solution.
[0024] In an alternative embodiment, the reassembly function at the
RLC layer of the RNC of Radio Link A is disabled so that the RLC
forwards PDUs (i.e. the sub-components of the SDUs) to Radio Link B
as soon as they have been correctly received. Radio Link B will
then use the same PDUs and sequence numbers as in Radio Link A,
reassembling the PDUs into SDUs as they are correctly received in
Terminal B. This requires a tunneling of the Radio Link PDUs from
Radio Link A to Radio Link B. This approach offers increased
granularity in the transmission path, offering the possibility of
better use of the radio links. However the price is that the RLC
protocol must be changed.
[0025] Embodiments of the invention Improve radio link utilization,
and therefore picture transfer times are reduced for the
Push-To-Watch service.
[0026] A different problem to that addressed by the first and
second embodiments arises when the TCP transport protocol is used
to control the transport of IP packets between user terminals. As
has already been discussed, this problem results from the
relatively long Round Trip Time (RTT) of the cascaded radio links
(FIG. 2), and the effect that this has on the opening of the TCP
transmission window. In the case of Push-to-Watch, the relatively
small size of the associated media (e.g. less than 50 kbytes) means
that the entire media will be transmitted under the slow start
conditions. Push-to-Watch is designed as an "immediate" service and
the slow start conditions will seriously detract from this.
[0027] One solution to this problem would be to use a proprietary
protocol for the media (picture etc) transmissions. However, this
would inevitably lead to interoperability problems between
terminals from different vendors. A preferred solution is to use
modified TCP parameters at the TCP sender in dependence upon the
service to which the data to be sent relates. For example, when the
sender wishes to send picture data associated with Push-To-Watch,
the TCP parameters are altered from their "normal" values. TCP
parameters to modify are the segment size and initial window. These
will affect the slow start performance and are usually used to
ensure a fair share of resources between users in the Internet.
Because of the closed nature of the transmission chain, a diversion
from the normal recommendations is acceptable. The transmission
rate of Radio Link A will limit the rate of traffic entering the
core network.
[0028] The maximum segment size (MSS) shall be set to 1460 bytes
(smaller segment sizes will lead to increased IP overheads). The
second radio link will be idle until the first segment has
traversed Radio Link A, and a larger size will only prolong this
time, and therefore also the total picture transfer time. The
initial window shall be set as large as possible, still ensuring
that the RLC buffers do not overflow or drop packets in Terminal A.
Ideally, the initial window is set larger than or equal to the
picture size being transmitted. This means that Radio Link A has
full utilization immediately and the picture transfer time is then
not limited by the transport layer.
[0029] This embodiment of the invention helps reduce picture
transmission times for the Push-To-Watch service.
* * * * *