- Email: [email protected]
From GPRS to UMTS
Copyright ® IFAC Telematics Applications in Automation and Robotics, Weingarten, Gennany, 2001
FROM GPRS TO UMTS
Jiirgen Baumann Oscar Lopez-Torres (*presently at Motorola GmbH) T-Mobil- Deutsche Telekom MobilNet GmbH Oberkasseler Str. 2, 53227 Bonn, Germany Tel.: + 49 228 936 3336
Fax.: +49 228 936 883336
Tel.: + 49 228 936 3342
Fax.: +49 228 936 883342
Emails:[email protected] [email protected]
Abstract: The General Packet Radio Service GPRS is a new service in GSM, which is or will be introduced in the GSM networks world wide this year. It offers new functionalities like packet oriented data transmission and multi slot capabilities on the air interface. The multislot capabilities increases the data rates up to theoretically 170 kbitls. Due to limitations of the first generation of GPRS Mobile Stations and other technical reasons data rates up to 50 kbitls can be expected for the introduction of the service. UMTS is the next step to support data services with higher data rate than GPRS. UMTS comprises packet and circuit switched services. The packet domain is based on the new packed switching infrastructure introduced for GPRS. This paper describes briefly the new architecture of GPRS and gives an overview of the main new concepts and ideas, especially the QoS support is mentioned. In the second part the architecture of UMTS is discussed and especially the enhanced QoS mechanisms are explained Copyright «I200IIFAC
1
The general architecture is shown in figure 1.
INTRODUCTION
GPRS was designed to fulfil the requirements for high data rates but also for efficient use of the radio resource. The result is a system which bases the data transport on widely used protocols like Frame Relay and the Internet Protocol and an air interface which is capable of multiplexing MSs over the same channel.
2
GPRS Architecture
SYSTEM ARCHITECTURE OF GPRS
GPRS introduces two new switching nodes - the Serving GPRS Support Node (SGSN) and the Gateway GPRS Support Node (GGSN).
SGSN.5oM>g GPIlS ~ Node GGSN : Gltftlly GPRS Support Node
The Serving GPRS Support Node includes the interface to the Base Station Subsystem and is responsible for mobility management, authentication, ciphering, data compression and error correction.
Figure 1: Architecture of GPRS GPRS offers a robust tunnel mechanism, where packets arriving at the MS are transferred to the GGSN and vice versa. The GGSN relays the received packets from the MS on the external JP interface.
The Gateway GPRS Support Node is the Gateway to the external networks and supports functionalities like tunnelling, address translation and external authentication to JP networks. 73
2.1
In the following subchapter a brief explanation of the parameters are given.
Access Point Name Concept
For GPRS a new addressing mechanism has been defined. Since GPRS is a pure packet switched system, there is no possibility to "dial" a telephone number to get connected to a certain destination.
All parameters are negotiated with the network when setting up a so called GPRS context. This is equivalent with the existing circuit switched dial up process when dialling to the internet service provider using a modem via a telephone line.
Therefore, the Access Point Name concept was introduced. The APN should be interpreted as a more convenient substitute for the dialled number in telephony networks.
The requested QoS is compared to the subscribed QoS of the user and either excepted or negotiated down accordingly.
The APN is a logical name for the network the GPRS user wants to access. It is derived from the DNS (Domain Name System) used in the internet for translating World Wide Web and email addresses to physically routable addresses.
2.2.1
The service precedence indicates the relative priority of maintaining the service. For example under abnormal conditions (e.g. network congestion) packets which may be discarded can be identified. The following precedence levels are defined:
The format of the parameter may contain up to 62 characters separated by dots. The APN which is sent by the MS to the SGSN is resolved by a DNS query (Domain Name System). A DNS Server operated by the GPRS operator responds with a physical (routable) JP address. This is the corresponding address of the GGSN which is connected and responsible for the particular destination network.
High precedence: Service commitments will be maintained ahead of all other precedence levels. Normal precedence: Service commitments will be maintained ahead of low priority users. Low precedence: Service commitments will be maintained after the high and normal priority commitments have been fulfilled
The APNs have to be defined and configured by the GPRS operator for each destination network. The standard also allows the MS to signal no APN information to the network during the context activation procedure. In this case GPRS connects the MS to a default network defined by the GPRS operator.
2.2.2
Delay
GPRS is not a "store and forward" service - although data is temporarily stored at network nodes during transmission - thus, any delay incurred is due to technical transmission characteristics (or limitations) of the system and is to be minimised for a particular delay class. The delay parameter thus defmes the maximum values for the mean delay and 95-percentile delay to be incurred by the transfer of data through the GPRS network(s). The delay parameter defines the end-to-end transfer delay incurred in the transmission of a packet through the GPRS network(s).
This minimises the configuration work of the client software which is an important factor for the acceptance of a new service. Two additional capabilities of the APN concept shall be briefly described. A single GGSN can handle overlapping address spaces of the connected networks. For example two connected intranets might use and assign the same private addresses for the Mobile Stations. The GGSN can handle this situation, if a tunnel protocol is used for the APNs between the GGSN and the intranets.
This includes the radio channel access delay (on uplink) or radio channel scheduling delay (on downlink), the radio channel transit delay (uplink and/or downlink paths) and the GPRS-network transit delay (mUltiple hops). It does not include transfer delays in external networks.
Another capability of GPRS is the verification of the APN demanded by the MS and the APN the user has subscribed. Therefore, it can be guaranteed that only allowed MS can have access to a certain network and closed user groups can be built up.
2.2
Precedence
Quality o/Service - QoS
In GPRS each single connection can be set up with different Quality of Service attributes. The four different parameters are
•
Precedence
•
Delay
•
Reliability
•
Throughput
Delay Class
Delay (maximum values) Packet size: 128 octets Mean 95 Transfer percentile Delay (sec) Delay
!(sec) 1. (Predictive) 2. (Predictive) 3. (Predictive) 4. (Best Effort)
< 1.5 <0.5 <25 <5 <250 <50 Unspecified
Table 1: Delay Classes in GPRS
74
2.2.3
individual user, the PPP protocol was chosen for compatibility reasons. Compatibility to the PPP stack is a very important functionality, since no new software is needed to use a GPRS MS together with a Laptop or other portable devices.
Reliability
The reliability parameter indicates the transmission characteristics that are required by an application. The reliability class defines the probability of loss of, duplication of, mis-sequencing of or corruption of a Packets.
Instead of a telephone number the string *99# has to be configured in the dialer software. This special telephone number indicates to the Mobile Station to activate a GPRS service and not to set up a circuit switched modem or ISDN connection.
Five classes are defined. The individual classes define which protocol on the according interfaces is using an acknowledge or unacknowledged mode.
If a special APN shall be activated, it can be done using AT commands, which were originally defined to configure a modem with certain parameters oe to initiate the dialling process.
The appropriate class depends strongly on the error sensitivity of the application.
2.2.4
But there are also restrictions. With this interface the multi session functionality of GPRS can not be used.
Throughput
The throughput parameter indicates the user data throughput requested by the user.
The multi session concept in GPRS offers the support of different contexts for the same MS simultaneously. Each context can have its own Quality of Service profile (e.g. priority or reliability class) and its own destination networks.
Throughput is defined by two negotiable parameters: •
Maximum bit rate.
•
Mean bit rate (includes, for example for "bursty" transmissions, the periods in which no data is transmitted. )
The number is limited to 14 contexts This is possible, because within GPRS different logical tunnels can be established between the MS and the GGSN.
The GPRS standard does not define how these parameters are really implemented. A lot of combination of the parameters are possible, which makes an similar implementation of all GPRS infrastructure vendors very unlikely.
Each context is uniquely identified by an individual IP address. This was the only solution since PPP on the MS side and IP version 4 on the GGSN side had when GPRS was standardised no standard mechanism to differentiate between several information flows or Quality of Service for a single IP address.
This problem and also the complexity of implementing Quality of Service in packet data networks in general, lead to the consequence that none of the GPRS infrastructure vendor has implemented QoS in the first releases. Therefore today no differentiated services can be offered by operators.
2.2.5
For example if the same IP address would have been used for different contexts of one MS, the GGSN could not find the co'rresponding MS tunnel for a received packet, since several logical tunnels exist for the MS or the IP address respectively.
Implementation ofQoS in the networks
As a consequence clients have to support several IP addresses to be able to use the multi session functionality.
The GPRS standard does not define how the QoS parameters shall be used to control the resource allocation. This will lead to different interpretations. A lot of combination of the parameters are possible, which makes an similar implementation of all GPRS infrastructure vendors very unlikely.
There are no such requirement in existing systems. Therefore, no such clients exists today. Nevertheless manufacturers of mobile stations will be able to use this functionality, since they don't need an external interface like PPP to connect their applications to the GPRS service.
This problem and additional the complexity of implementing Quality of Service in packet data networks in general, lead to the consequence that none of the GPRS infrastructure vendor has implemented QoS in their first releases. Therefore today no differentiated services can be offered by operators.
2.3
One example for supporting the multi session principle will be possible by the new generation of Mobile Stations comprising a WAP Browser (Wireless Application Protocol). With such a Browser it will be possible to browse in the internet on special pages activating a certain APN. Simultaneously it will be possible to be connected to an intranet via an external device to read the email. Both sessions might have activated a different Quality of Service and different APNs.
Multi Session Capability
The standard interface to the GPRS service is based on the PPP Protocol (point to Point) which was originally introduced as a protocol to dial in with a computer over a telephone network using modems. This protocol is today included in all standard operating systems (e.g. so called dialer in microsoft operating systems). Although in GPRS no telephone line is switched exclusively for each
For UMTS this restriction will not exist anymore. In the mean time QoS support is also defined for the intemet protocol. Therefore UMTS is able to use the 75
Some of these parameters need also to be transferred to the remote access in the JP network.
functionality and integrate it into there concepts, which will be further explained in the next chapters.
3
QUALITY OF SERVICE FROM GPRS TO UMTS
This section treats in a general manner the QoS in the packet and multimedia domains in the UMTS architecture, as a progression of the mobile switched packet domain, namely GPRS covered in previous Sections. Specific node and naming functionality explanations in the mobile network are avoided when possible, when trying to explain the general principle in which current UMTS work has been done. The QoS topic has come up to high scrutiny in third generation mobile networks because the necessity to replace existing second generation (GSM) speech services with multimedia and packet voice services; e.g., VolP. One main goal into this direction is to diminish transmission costs requirements imposed by most second generation mobile systems when it comes to speech services, circuit switched in nature, both in core and radio access networks, while offering an acceptable and comparable QoS, also for new services to be offered. The challenge is not yet achieved as of the writing of this paper, however, the paper aims to provide an overview of the tools used to tackle the main issues.
Figure 3: End-to-End UMTS QoS Architecture In more detail, and making reference to Figure 4 in a specific scenario in a mobile originating session, the mapping of APls QoS Parameters; e.g., generic QoS (GQOS) requesting characteristics to be conveyed by the IP network, could take place in such a manner that: token rate, token bucket size, peak bandwidth, and latency, are translated to the UMTS architectural parameters: guaranteed bit rate, maximum SDU size, maximum bit rate, and transfer delay, respectively. The API QoS mapping relieves the application to be UMTSaware.
Figure 2 shows the general model for an architecture based on a bi-dimensional QoS parameter mapping principle.
AfT·. .
QoIIPw_• . . - . , ....
Pr.........,. Hr
~1F.oJ=;t APl s
IGP
~
Paramete
SlU MTS DoS P nmeler f\:la
_
~ofQollAl'l_
-
!j,
in~
.
n
UMrS_
RNC
SGSN
a.- ..
GGSN
---- .-
UMTS Bearer Senke
I
- - ---
----- - - - -
MoP.... orQoS TraIIk: c ....
Radio Accal Bearer
Figure 2: Two Dimension Parameter Mapping Model for the Architecture
",lETr DIII'... CIas
'
lu ..... Core Network Bearer
Figure 4: Mapping of API QoS Parameters to UMTS Architectural Parameters to Diffserv QoS Classes
Following this model, the parameter mapping concept is necessary for both, the protocol layers and also interface-wise - as shown in the diagram axes, in order to obtain and interpret QoS requirements from/to the PLMN to/from external networks. Interworking from the GRPRlUMTS PLMN to external networks, including lP-based networks (; e.g., internet or intranet) require parameter mapping to properly set up required bearers end-to-end at different strata-levels, as shown in the UMTS QoS architecture in Figure 3 (ref.1). Thus, referring to Figures 2 and 3, application programming interfaces (APIs), GPRSIUMTS QoS -local to the PLMN, UMTS radio access bearer (RAB), and bearer service parameters, need to be mapped to external parameters at different interfaces and protocol levels.
Mapping is also necessary at the mobile network border, by for instance the GGSN, because on one hand JP networks tend to have different mechanisms, not fully accepted or sufficiently spread out in the IETF packet community, specially for real time services; on the other hand Iu and Core Network Bearers local to the PLMN also need to be setup.
76
4
MERGING THE CONCEPTS: INTERWORKING WITH IP FIXED NETWORKS AND USING UMTS SPECIFIC QOS SCENARIOS
Figure 6, shows the scenario where the UE provides IP bearer QoS information. The IP bearer QoS information is used by the GGSN to support packet classification and admission control functions. The GGSN supports DS and RSVP, and performs admission control for the connection to the IP core network based on dynamically controlled resources. The use of RSVP signalling allows the routers in the IP core network to perform admission control on a per-flow basis.
A logical step in third generation mobile networks is to re-use some of the GPRS mechanisms, to offer non-real time and real time services; with a proper Diffserv categorization for the uni-media and multimedia environments supported with end-to-end RSVP concepts. The UMTS QoS characteristics are used to set up and release the previous GPRS PDP contexts, as mentioned in Section 2.2. The concept ofPDP context has been extended in UMTS to also include sub-flows that can be mapped to the components of a multimedia session. Still under consideration is the fact that RSVP support might require flow establishment, and possibly aggregation of flows, within the UMTS packet core network. Differentiated services would require that either one QoS profile for each traffic type or alternatively the priority and traffic type information is included in the data packets.
n.U&..,-..t : Q.s .. UMn-.lW", :
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: QeS _ _
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-=
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: ...... DS_UVP.
-1J~~~}~-:==!: OOSN
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Still currently under specification development there are six defined scenarios (ref. 2) intended to provide end-toend quality of service for the multimedia and packet services in UMTS. As mentioned before, a main target is to support real time services, where evolved GPRS signalling is used to control the QoS in the radio interface core network, while Diffserv (DS) is used to provide the IP bearer QoS over the core network. The six scenarios are different mainly in the way in which the IP bearer QoS is supported.
Figure 6: UE Supports IP Parameters in PDP Context Activation Signalling and the GGSN Provides Interworking With RSVP Signalling These scenarios use per-flow RSVP as the admission control protocol for the DS network. This is a more scalable approach as compared to traditional RSVP because the classification and scheduling; i.e., all operations in the forwarding plane, are performed on DS behavior aggregates, rather than microflows - one advantage of combining both, DS and RSVP.
The reader is referred to [ref. 2] for a detailed discussion of all scenarios. In this Section, only the end-to-end scenarios with RSVP are considered, since initial work to extend the SIP call control protocol has shown that these scenarios might be considered as supersets of the other four.
The radio resources on the other side are one of the more important issues to be managed by QoS in UMTS. This paper is not intended to cover that area. It is enough to say now that a prime issue on the radio part ofUMTS is the correct admission control functionality to allow sessions in the mix of the cells without disturbing previous on-going session. Specially, when hungrybandwidth users request to setup a call or session.
Figure 5 shows an scenario where the user equipment (UE) supports RSVP enabled applications and the GGSN relays RSVP signalling. Here RSVP signalling is generated by TEIMT equipment. Thus, for end-to-end QoS support, the GGSN does not generate RSVP messages because the UE is controlling the RSVP exchange.
Finally, on-going work is on the area of call control SIP protocols to convey end-to-end parameters in combination with RSVP for mobile-to-mobile and mobile-to-fixed terminal calls. From the scenarios and requirements above, it is easy to recognize that the challenge at hand is large to support prime services and multimedia services with UMTS packet mobile networks, specially for a real time service like VoIP. An optimal solution relies beavily on a variety of scenarios to be covered.
References: Ref. 1. - 3GPP TS 23.107, QoS Concept and Architecture. Ref. 2. - 3GPP TS 23.207, End-to-End QoS Concept and Architecture. Figure 5: UE Supports RSVP Signalling, IntServ, and DiffServ
77
FROM GPRS TO UMTS
Jiirgen Baumann Oscar Lopez-Torres (*presently at Motorola GmbH) T-Mobil- Deutsche Telekom MobilNet GmbH Oberkasseler Str. 2, 53227 Bonn, Germany Tel.: + 49 228 936 3336
Fax.: +49 228 936 883336
Tel.: + 49 228 936 3342
Fax.: +49 228 936 883342
Emails:[email protected] [email protected]
Abstract: The General Packet Radio Service GPRS is a new service in GSM, which is or will be introduced in the GSM networks world wide this year. It offers new functionalities like packet oriented data transmission and multi slot capabilities on the air interface. The multislot capabilities increases the data rates up to theoretically 170 kbitls. Due to limitations of the first generation of GPRS Mobile Stations and other technical reasons data rates up to 50 kbitls can be expected for the introduction of the service. UMTS is the next step to support data services with higher data rate than GPRS. UMTS comprises packet and circuit switched services. The packet domain is based on the new packed switching infrastructure introduced for GPRS. This paper describes briefly the new architecture of GPRS and gives an overview of the main new concepts and ideas, especially the QoS support is mentioned. In the second part the architecture of UMTS is discussed and especially the enhanced QoS mechanisms are explained Copyright «I200IIFAC
1
The general architecture is shown in figure 1.
INTRODUCTION
GPRS was designed to fulfil the requirements for high data rates but also for efficient use of the radio resource. The result is a system which bases the data transport on widely used protocols like Frame Relay and the Internet Protocol and an air interface which is capable of multiplexing MSs over the same channel.
2
GPRS Architecture
SYSTEM ARCHITECTURE OF GPRS
GPRS introduces two new switching nodes - the Serving GPRS Support Node (SGSN) and the Gateway GPRS Support Node (GGSN).
SGSN.5oM>g GPIlS ~ Node GGSN : Gltftlly GPRS Support Node
The Serving GPRS Support Node includes the interface to the Base Station Subsystem and is responsible for mobility management, authentication, ciphering, data compression and error correction.
Figure 1: Architecture of GPRS GPRS offers a robust tunnel mechanism, where packets arriving at the MS are transferred to the GGSN and vice versa. The GGSN relays the received packets from the MS on the external JP interface.
The Gateway GPRS Support Node is the Gateway to the external networks and supports functionalities like tunnelling, address translation and external authentication to JP networks. 73
2.1
In the following subchapter a brief explanation of the parameters are given.
Access Point Name Concept
For GPRS a new addressing mechanism has been defined. Since GPRS is a pure packet switched system, there is no possibility to "dial" a telephone number to get connected to a certain destination.
All parameters are negotiated with the network when setting up a so called GPRS context. This is equivalent with the existing circuit switched dial up process when dialling to the internet service provider using a modem via a telephone line.
Therefore, the Access Point Name concept was introduced. The APN should be interpreted as a more convenient substitute for the dialled number in telephony networks.
The requested QoS is compared to the subscribed QoS of the user and either excepted or negotiated down accordingly.
The APN is a logical name for the network the GPRS user wants to access. It is derived from the DNS (Domain Name System) used in the internet for translating World Wide Web and email addresses to physically routable addresses.
2.2.1
The service precedence indicates the relative priority of maintaining the service. For example under abnormal conditions (e.g. network congestion) packets which may be discarded can be identified. The following precedence levels are defined:
The format of the parameter may contain up to 62 characters separated by dots. The APN which is sent by the MS to the SGSN is resolved by a DNS query (Domain Name System). A DNS Server operated by the GPRS operator responds with a physical (routable) JP address. This is the corresponding address of the GGSN which is connected and responsible for the particular destination network.
High precedence: Service commitments will be maintained ahead of all other precedence levels. Normal precedence: Service commitments will be maintained ahead of low priority users. Low precedence: Service commitments will be maintained after the high and normal priority commitments have been fulfilled
The APNs have to be defined and configured by the GPRS operator for each destination network. The standard also allows the MS to signal no APN information to the network during the context activation procedure. In this case GPRS connects the MS to a default network defined by the GPRS operator.
2.2.2
Delay
GPRS is not a "store and forward" service - although data is temporarily stored at network nodes during transmission - thus, any delay incurred is due to technical transmission characteristics (or limitations) of the system and is to be minimised for a particular delay class. The delay parameter thus defmes the maximum values for the mean delay and 95-percentile delay to be incurred by the transfer of data through the GPRS network(s). The delay parameter defines the end-to-end transfer delay incurred in the transmission of a packet through the GPRS network(s).
This minimises the configuration work of the client software which is an important factor for the acceptance of a new service. Two additional capabilities of the APN concept shall be briefly described. A single GGSN can handle overlapping address spaces of the connected networks. For example two connected intranets might use and assign the same private addresses for the Mobile Stations. The GGSN can handle this situation, if a tunnel protocol is used for the APNs between the GGSN and the intranets.
This includes the radio channel access delay (on uplink) or radio channel scheduling delay (on downlink), the radio channel transit delay (uplink and/or downlink paths) and the GPRS-network transit delay (mUltiple hops). It does not include transfer delays in external networks.
Another capability of GPRS is the verification of the APN demanded by the MS and the APN the user has subscribed. Therefore, it can be guaranteed that only allowed MS can have access to a certain network and closed user groups can be built up.
2.2
Precedence
Quality o/Service - QoS
In GPRS each single connection can be set up with different Quality of Service attributes. The four different parameters are
•
Precedence
•
Delay
•
Reliability
•
Throughput
Delay Class
Delay (maximum values) Packet size: 128 octets Mean 95 Transfer percentile Delay (sec) Delay
!(sec) 1. (Predictive) 2. (Predictive) 3. (Predictive) 4. (Best Effort)
< 1.5 <0.5 <25 <5 <250 <50 Unspecified
Table 1: Delay Classes in GPRS
74
2.2.3
individual user, the PPP protocol was chosen for compatibility reasons. Compatibility to the PPP stack is a very important functionality, since no new software is needed to use a GPRS MS together with a Laptop or other portable devices.
Reliability
The reliability parameter indicates the transmission characteristics that are required by an application. The reliability class defines the probability of loss of, duplication of, mis-sequencing of or corruption of a Packets.
Instead of a telephone number the string *99# has to be configured in the dialer software. This special telephone number indicates to the Mobile Station to activate a GPRS service and not to set up a circuit switched modem or ISDN connection.
Five classes are defined. The individual classes define which protocol on the according interfaces is using an acknowledge or unacknowledged mode.
If a special APN shall be activated, it can be done using AT commands, which were originally defined to configure a modem with certain parameters oe to initiate the dialling process.
The appropriate class depends strongly on the error sensitivity of the application.
2.2.4
But there are also restrictions. With this interface the multi session functionality of GPRS can not be used.
Throughput
The throughput parameter indicates the user data throughput requested by the user.
The multi session concept in GPRS offers the support of different contexts for the same MS simultaneously. Each context can have its own Quality of Service profile (e.g. priority or reliability class) and its own destination networks.
Throughput is defined by two negotiable parameters: •
Maximum bit rate.
•
Mean bit rate (includes, for example for "bursty" transmissions, the periods in which no data is transmitted. )
The number is limited to 14 contexts This is possible, because within GPRS different logical tunnels can be established between the MS and the GGSN.
The GPRS standard does not define how these parameters are really implemented. A lot of combination of the parameters are possible, which makes an similar implementation of all GPRS infrastructure vendors very unlikely.
Each context is uniquely identified by an individual IP address. This was the only solution since PPP on the MS side and IP version 4 on the GGSN side had when GPRS was standardised no standard mechanism to differentiate between several information flows or Quality of Service for a single IP address.
This problem and also the complexity of implementing Quality of Service in packet data networks in general, lead to the consequence that none of the GPRS infrastructure vendor has implemented QoS in the first releases. Therefore today no differentiated services can be offered by operators.
2.2.5
For example if the same IP address would have been used for different contexts of one MS, the GGSN could not find the co'rresponding MS tunnel for a received packet, since several logical tunnels exist for the MS or the IP address respectively.
Implementation ofQoS in the networks
As a consequence clients have to support several IP addresses to be able to use the multi session functionality.
The GPRS standard does not define how the QoS parameters shall be used to control the resource allocation. This will lead to different interpretations. A lot of combination of the parameters are possible, which makes an similar implementation of all GPRS infrastructure vendors very unlikely.
There are no such requirement in existing systems. Therefore, no such clients exists today. Nevertheless manufacturers of mobile stations will be able to use this functionality, since they don't need an external interface like PPP to connect their applications to the GPRS service.
This problem and additional the complexity of implementing Quality of Service in packet data networks in general, lead to the consequence that none of the GPRS infrastructure vendor has implemented QoS in their first releases. Therefore today no differentiated services can be offered by operators.
2.3
One example for supporting the multi session principle will be possible by the new generation of Mobile Stations comprising a WAP Browser (Wireless Application Protocol). With such a Browser it will be possible to browse in the internet on special pages activating a certain APN. Simultaneously it will be possible to be connected to an intranet via an external device to read the email. Both sessions might have activated a different Quality of Service and different APNs.
Multi Session Capability
The standard interface to the GPRS service is based on the PPP Protocol (point to Point) which was originally introduced as a protocol to dial in with a computer over a telephone network using modems. This protocol is today included in all standard operating systems (e.g. so called dialer in microsoft operating systems). Although in GPRS no telephone line is switched exclusively for each
For UMTS this restriction will not exist anymore. In the mean time QoS support is also defined for the intemet protocol. Therefore UMTS is able to use the 75
Some of these parameters need also to be transferred to the remote access in the JP network.
functionality and integrate it into there concepts, which will be further explained in the next chapters.
3
QUALITY OF SERVICE FROM GPRS TO UMTS
This section treats in a general manner the QoS in the packet and multimedia domains in the UMTS architecture, as a progression of the mobile switched packet domain, namely GPRS covered in previous Sections. Specific node and naming functionality explanations in the mobile network are avoided when possible, when trying to explain the general principle in which current UMTS work has been done. The QoS topic has come up to high scrutiny in third generation mobile networks because the necessity to replace existing second generation (GSM) speech services with multimedia and packet voice services; e.g., VolP. One main goal into this direction is to diminish transmission costs requirements imposed by most second generation mobile systems when it comes to speech services, circuit switched in nature, both in core and radio access networks, while offering an acceptable and comparable QoS, also for new services to be offered. The challenge is not yet achieved as of the writing of this paper, however, the paper aims to provide an overview of the tools used to tackle the main issues.
Figure 3: End-to-End UMTS QoS Architecture In more detail, and making reference to Figure 4 in a specific scenario in a mobile originating session, the mapping of APls QoS Parameters; e.g., generic QoS (GQOS) requesting characteristics to be conveyed by the IP network, could take place in such a manner that: token rate, token bucket size, peak bandwidth, and latency, are translated to the UMTS architectural parameters: guaranteed bit rate, maximum SDU size, maximum bit rate, and transfer delay, respectively. The API QoS mapping relieves the application to be UMTSaware.
Figure 2 shows the general model for an architecture based on a bi-dimensional QoS parameter mapping principle.
AfT·. .
QoIIPw_• . . - . , ....
Pr.........,. Hr
~1F.oJ=;t APl s
IGP
~
Paramete
SlU MTS DoS P nmeler f\:la
_
~ofQollAl'l_
-
!j,
in~
.
n
UMrS_
RNC
SGSN
a.- ..
GGSN
---- .-
UMTS Bearer Senke
I
- - ---
----- - - - -
MoP.... orQoS TraIIk: c ....
Radio Accal Bearer
Figure 2: Two Dimension Parameter Mapping Model for the Architecture
",lETr DIII'... CIas
'
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Figure 4: Mapping of API QoS Parameters to UMTS Architectural Parameters to Diffserv QoS Classes
Following this model, the parameter mapping concept is necessary for both, the protocol layers and also interface-wise - as shown in the diagram axes, in order to obtain and interpret QoS requirements from/to the PLMN to/from external networks. Interworking from the GRPRlUMTS PLMN to external networks, including lP-based networks (; e.g., internet or intranet) require parameter mapping to properly set up required bearers end-to-end at different strata-levels, as shown in the UMTS QoS architecture in Figure 3 (ref.1). Thus, referring to Figures 2 and 3, application programming interfaces (APIs), GPRSIUMTS QoS -local to the PLMN, UMTS radio access bearer (RAB), and bearer service parameters, need to be mapped to external parameters at different interfaces and protocol levels.
Mapping is also necessary at the mobile network border, by for instance the GGSN, because on one hand JP networks tend to have different mechanisms, not fully accepted or sufficiently spread out in the IETF packet community, specially for real time services; on the other hand Iu and Core Network Bearers local to the PLMN also need to be setup.
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4
MERGING THE CONCEPTS: INTERWORKING WITH IP FIXED NETWORKS AND USING UMTS SPECIFIC QOS SCENARIOS
Figure 6, shows the scenario where the UE provides IP bearer QoS information. The IP bearer QoS information is used by the GGSN to support packet classification and admission control functions. The GGSN supports DS and RSVP, and performs admission control for the connection to the IP core network based on dynamically controlled resources. The use of RSVP signalling allows the routers in the IP core network to perform admission control on a per-flow basis.
A logical step in third generation mobile networks is to re-use some of the GPRS mechanisms, to offer non-real time and real time services; with a proper Diffserv categorization for the uni-media and multimedia environments supported with end-to-end RSVP concepts. The UMTS QoS characteristics are used to set up and release the previous GPRS PDP contexts, as mentioned in Section 2.2. The concept ofPDP context has been extended in UMTS to also include sub-flows that can be mapped to the components of a multimedia session. Still under consideration is the fact that RSVP support might require flow establishment, and possibly aggregation of flows, within the UMTS packet core network. Differentiated services would require that either one QoS profile for each traffic type or alternatively the priority and traffic type information is included in the data packets.
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Still currently under specification development there are six defined scenarios (ref. 2) intended to provide end-toend quality of service for the multimedia and packet services in UMTS. As mentioned before, a main target is to support real time services, where evolved GPRS signalling is used to control the QoS in the radio interface core network, while Diffserv (DS) is used to provide the IP bearer QoS over the core network. The six scenarios are different mainly in the way in which the IP bearer QoS is supported.
Figure 6: UE Supports IP Parameters in PDP Context Activation Signalling and the GGSN Provides Interworking With RSVP Signalling These scenarios use per-flow RSVP as the admission control protocol for the DS network. This is a more scalable approach as compared to traditional RSVP because the classification and scheduling; i.e., all operations in the forwarding plane, are performed on DS behavior aggregates, rather than microflows - one advantage of combining both, DS and RSVP.
The reader is referred to [ref. 2] for a detailed discussion of all scenarios. In this Section, only the end-to-end scenarios with RSVP are considered, since initial work to extend the SIP call control protocol has shown that these scenarios might be considered as supersets of the other four.
The radio resources on the other side are one of the more important issues to be managed by QoS in UMTS. This paper is not intended to cover that area. It is enough to say now that a prime issue on the radio part ofUMTS is the correct admission control functionality to allow sessions in the mix of the cells without disturbing previous on-going session. Specially, when hungrybandwidth users request to setup a call or session.
Figure 5 shows an scenario where the user equipment (UE) supports RSVP enabled applications and the GGSN relays RSVP signalling. Here RSVP signalling is generated by TEIMT equipment. Thus, for end-to-end QoS support, the GGSN does not generate RSVP messages because the UE is controlling the RSVP exchange.
Finally, on-going work is on the area of call control SIP protocols to convey end-to-end parameters in combination with RSVP for mobile-to-mobile and mobile-to-fixed terminal calls. From the scenarios and requirements above, it is easy to recognize that the challenge at hand is large to support prime services and multimedia services with UMTS packet mobile networks, specially for a real time service like VoIP. An optimal solution relies beavily on a variety of scenarios to be covered.
References: Ref. 1. - 3GPP TS 23.107, QoS Concept and Architecture. Ref. 2. - 3GPP TS 23.207, End-to-End QoS Concept and Architecture. Figure 5: UE Supports RSVP Signalling, IntServ, and DiffServ
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