1. Introduction
The deployment of 4G LTE has given birth to an all/end-to-end IP network, which extended the Internet and corporate access to mobile nodes. Eventually, the LTE Wireless all-packet-switched IP networks, lower latencies and larger bandwidths have converged the 3GPP and IETF worlds to create a universe where the Mobile Connectivity Services are flourishing. Furthermore, the user experience and behavior evolved from asking for just access to a quality and priority access, via wireless, to services traditionally accessed over wire-line. The consumer (general public) interest has shifted away from best effort services, for instance web browsing, to real-time and interactive services also known as delay sensitive services like VoLTE (Voice over LTE), ViLTE (Video over LTE) and online video Games. Moreover, the corporate customers are pushing to expediate their commercial traffic; as video conferencing, collaboration and many other applications, over both the Wireless (Radio) and Wireline (EPC core) portions of the network. In fact, most of the Wireless operators aren't indifferent about these Consumer and Enterprise traffic trends and could see the need for Quality of Service (QoS) offerings along with priority access differentiation. The Quality of Service (QoS) at Service and Bearer levels will be exposed in the following.
The standard defines the LTE QoS with the performance characteristics of IP packets making the IP flows of a category of services. 4 key parameters define the performance characteristics associated with the IP packets: (1) the precedence/priority value (1 to 9), (2) the packet delay in (ms), (3) the tolerated packet loss rate and (4) finally the bandwidth resource type (GBR and non-GBR). Different combinations of these 4 parameters define a Quality of Service Class; numerically represented by a Quality of Service (QoS) Class Identifier (QCI). The EPS nodes (PGW, SGW, eNB) utilize QCI (in addition to ARP) as a key parameter to classify the IP flows; and also request or allocate network resources accordingly.
3GPP TS 23.203 - Standardized QCI Characteristics
The deployment of 4G LTE has given birth to an all/end-to-end IP network, which extended the Internet and corporate access to mobile nodes. Eventually, the LTE Wireless all-packet-switched IP networks, lower latencies and larger bandwidths have converged the 3GPP and IETF worlds to create a universe where the Mobile Connectivity Services are flourishing. Furthermore, the user experience and behavior evolved from asking for just access to a quality and priority access, via wireless, to services traditionally accessed over wire-line. The consumer (general public) interest has shifted away from best effort services, for instance web browsing, to real-time and interactive services also known as delay sensitive services like VoLTE (Voice over LTE), ViLTE (Video over LTE) and online video Games. Moreover, the corporate customers are pushing to expediate their commercial traffic; as video conferencing, collaboration and many other applications, over both the Wireless (Radio) and Wireline (EPC core) portions of the network. In fact, most of the Wireless operators aren't indifferent about these Consumer and Enterprise traffic trends and could see the need for Quality of Service (QoS) offerings along with priority access differentiation. The Quality of Service (QoS) at Service and Bearer levels will be exposed in the following.
The standard defines the LTE QoS with the performance characteristics of IP packets making the IP flows of a category of services. 4 key parameters define the performance characteristics associated with the IP packets: (1) the precedence/priority value (1 to 9), (2) the packet delay in (ms), (3) the tolerated packet loss rate and (4) finally the bandwidth resource type (GBR and non-GBR). Different combinations of these 4 parameters define a Quality of Service Class; numerically represented by a Quality of Service (QoS) Class Identifier (QCI). The EPS nodes (PGW, SGW, eNB) utilize QCI (in addition to ARP) as a key parameter to classify the IP flows; and also request or allocate network resources accordingly.
3GPP TS 23.203 - Standardized QCI Characteristics
2. Service and Bearer Level QoS
2.1. Service level QoS
In both Uplink and Downlink directions, PDN-GWs classify IP flows (user traffic) into SDFs (Service Data Flows) using SDF templates (3/5 tuples Traffic Filters) explicitly received from PCRF over Gx interface, locally defined or implicitly assumed. PCRF defines a set of QoS parameters, for instance, a QCI (QoS Class Identifier), ARP (Allocation and Retention Priority), and a MBR (Maximum Bit Rate) parameters for explicitly Gx described SDFs based on the service definition in-use and subscriber entitlements in SPR/UDR. The HSS subscription profile specifies the APN QoS information parameters for all other SDFs at Initial IP-CAN session establishment requests. However, based on operators target PCC architecture, the PCRF has the upper hand to authorize different QoS parameter values or mirror the parameter values received via MME. The PCRF provisions the SDFs to PDN-GW over Gx as part of:
(1) the initial IP-CAN session establishment Gx association.
(2) an Application Function (AF) exchange over Rx.
(3) a TDF exchange over Sd for Application Detection and Control (ADC).
In practice, the SDF filter tuples are included either explicitly or referenced by a specific name in the Gx requests/responses.
Fig.1.Explicit SDF Filters
2.1. Service level QoS
In both Uplink and Downlink directions, PDN-GWs classify IP flows (user traffic) into SDFs (Service Data Flows) using SDF templates (3/5 tuples Traffic Filters) explicitly received from PCRF over Gx interface, locally defined or implicitly assumed. PCRF defines a set of QoS parameters, for instance, a QCI (QoS Class Identifier), ARP (Allocation and Retention Priority), and a MBR (Maximum Bit Rate) parameters for explicitly Gx described SDFs based on the service definition in-use and subscriber entitlements in SPR/UDR. The HSS subscription profile specifies the APN QoS information parameters for all other SDFs at Initial IP-CAN session establishment requests. However, based on operators target PCC architecture, the PCRF has the upper hand to authorize different QoS parameter values or mirror the parameter values received via MME. The PCRF provisions the SDFs to PDN-GW over Gx as part of:
(1) the initial IP-CAN session establishment Gx association.
(2) an Application Function (AF) exchange over Rx.
(3) a TDF exchange over Sd for Application Detection and Control (ADC).
In practice, the SDF filter tuples are included either explicitly or referenced by a specific name in the Gx requests/responses.
Fig.1.Explicit SDF Filters
If a name is provided, SDF filter tuples are statically defined at PGW as show in the following example. For instance, MMS, Visual Voicemail (VVM) and Internet browsing SDFs are returned in Gx CCA-I diameter message from PCRF.
Fig.2. PDN-GW locally Configured SDF Names
Fig.2. PDN-GW locally Configured SDF Names
the following are examples of static SDFs defined at PGW.
SDF MMS_PCC_Rule
allow http url contains "mmsc.network.com"
and tcp port =80
SDF VVM_PCC_Rule SDF
allow destination server = 189.60.60.60 255.255.255.255
and tcp port = 443
SDF Browsing_PCC_Rule SDF
allow ip destination server any
and tcp port =80
or tcp port =443
2.2. Bearer level QoS
The Traffic Flow templates associated with an EPS bearer are derivatives of SDF templates. In the Downlink direction, the PDN-GW maps the different SDFs having the same QCI and ARP values and matching a set of Traffic Flow Template (TFT) filters into a unique EPS bearer having comparable QCI and ARP values. In the Uplink direction, the UE (Mobile node) places the IP flows (user traffic) into the right EPS bearer using a TFT filter to EPS bearer mapping mechanism. Eventually, an EPS bearer fulfills the QoS requirements of the SDFs mapped into it. The Bearer level QoS parameters are derived either from the HSS Subscription profile (could be overwritten by PCRF) at IP-CAN session instantiation; or from the SDF associated QoS parameters received from PCRF via Gx. Unlike SDF QoS parameters confined within PDN-GW boundaries, the Bearer level QoS parameters are spread and enforced across different LTE and EPS network elements (UE, eNB, SGW and PGW).
PGW - SDF to EPS Bearer Mapping
SDF MMS_PCC_Rule
allow http url contains "mmsc.network.com"
and tcp port =80
SDF VVM_PCC_Rule SDF
allow destination server = 189.60.60.60 255.255.255.255
and tcp port = 443
SDF Browsing_PCC_Rule SDF
allow ip destination server any
and tcp port =80
or tcp port =443
2.2. Bearer level QoS
The Traffic Flow templates associated with an EPS bearer are derivatives of SDF templates. In the Downlink direction, the PDN-GW maps the different SDFs having the same QCI and ARP values and matching a set of Traffic Flow Template (TFT) filters into a unique EPS bearer having comparable QCI and ARP values. In the Uplink direction, the UE (Mobile node) places the IP flows (user traffic) into the right EPS bearer using a TFT filter to EPS bearer mapping mechanism. Eventually, an EPS bearer fulfills the QoS requirements of the SDFs mapped into it. The Bearer level QoS parameters are derived either from the HSS Subscription profile (could be overwritten by PCRF) at IP-CAN session instantiation; or from the SDF associated QoS parameters received from PCRF via Gx. Unlike SDF QoS parameters confined within PDN-GW boundaries, the Bearer level QoS parameters are spread and enforced across different LTE and EPS network elements (UE, eNB, SGW and PGW).
PGW - SDF to EPS Bearer Mapping
3. GBR vs Non-GBR SDFs/Bearers
The 3GPP TS-23.203 standards define two groups of QoS Class Identifiers (QCI) that could be allocated, based on the underlying transport requirements, to Service Data Flows (SDFs) and thus EPS bearers. The resource type characteristic of the QCI defines the underlying transport requirements in matter of bandwidth reservation: GBR (Guaranteed Bit Rate) and non-GBR (non Guaranteed Bit Rate).
3.1. GBR vs Non-GBR SDFs
PDN-GWs allocate, in reserve mode, network resources (bandwidth) to IP flows belonging to an SDF tagged as GBR. In other words, a portion of the PGW network resources are exclusively dedicated to the transport/processing of the GBR SDF no matter the congestion status of the network (at PDN-GW). Ultimately, a GBR SDF is assigned the following parameters: a QCI (QoS Class Identifier), a GBR (Uplink/Downlink), a MBR (Maximum Bit Rate Uplink/Downlink) and an ARP (Allocation and Retention Priority). The MBR (Uplink/Downlink) values are always greater than or equal to GBR (Uplink/Downlink) values. Unlike GBR, the MBR represent the available bandwidth to SDF IP flows under non-congested network conditions and usually comes with some extra-room on top of the GBR.
Unlike GBR SDFs, the Non-GBR SDFs are subject to Best Effort network resources allocation within APN-AMBR available bandwidth boundaries. The network resources are allocated if available meaning the Non-GBR SDF IP flows are open to delays waiting for resources in use to be free again. Like GBR SDFs, the same QoS parameters are assigned to Non-GBR SDFs with the exception of the GBR parameter that doesn't apply. Furthermore, the MBR is replaced with the APN-AMBR; representing the available bandwidth that could be shared with all Non-GBR SDFs belonging to the same APN.
3.2. GBR vs Non-GBR Bearers
Bearers are virtual channels dynamically created and uniquely identified with a set of identifiers across the EPC and LTE access network. Bearers are meant to transport user traffic (IP flows) between a UE and PDN-GWs and vice-versa. PDN-GWs map the SDFs to EPS bearers satisfying the requested service type Quality of Service. IP flows (SDFs) belonging to a specific service will inherit the EPS bearer (mapped to) QoS (Performance characteristics) in both uplink and downlink directions. An EPS bearer is fragmented into hop by hop bearers:
(1) The Radio Bearer runs over the LTE-Uu wireless interface and uses the C-RNTI (Cell Radio Network Temporary
Identity) value as identifier.
(2) The S1-U bearer running a GTPv1 protocol and utilizing unique Tunnel IDs (TEID), at both eNB and SGW end
points, per EPS Bearer.
(3) The S5/S8 bearer running a GTPv1 protocol associated with unique TEIDs per EPS bearer at SGW and PDN-GW
end points.
Therefore, the EPS Bearer QoS parameters will map into hop by hop bearers at the LTE and EPC Network elements level. eNB, SGW, and PDN-GW will reserve Network resources (Bandwidth) for GBR bearers to honor the QoS characteristics (QCI, GBR, MBR and ARP) of the end to end bearer. On the LTE-Uu, the eNB scheduler will reserve over the air resources and comparable bandwidth on the Wired S1-U interface. SGW and PDN-GW will also honor the same QoS characteristics bidirectional (uplink/downlink) on the ingress and egress interfaces corresponding to S1-U, S5/8 references points. The following QoS parameters are applied for GBR bearers:
PDN-GW/SGW : QCI, ARP, GBR, MBR.
eNB : QCI, ARP, GBR, MBR
UE: MBR
Non-GBR bearers are subject to available network resources where IP flows might be delayed waiting for shared resources in use to be free again. In fact, he best effort concept applies to non-GBR bearers and the following QoS parameters are applied per node:
PDN-GW/SGW : QCI, ARP(*), APN-AMBR(**)
eNB : QCI, ARP, APN-AMBR, UE-AMBR
UE: APN-AMBR
The APN-AMBR is the maximum bit rate (bandwidth) allowed per APN assuming the network resources are available. If the aggregate IP flows' (falling under the same APN) consumed bandwidth exceed the APN-AMBR, the related network element, where the overage first occurs, will start dropping packets to keep bandwidth consumption within APN-AMBR boundaries.
The UE-AMBR is the maximum bit rate (bandwidth) allowed per UE assuming the network resources are available. if the aggregate IP flows' (belonging to different APNs) consumed bandwidth exceed the UE-AMBR, the eNB will start dropping packets to keep the allowed bandwidth under control.
Note*: The ARP is mainly used by the eNB to control bearer resources take over or give away in regards to other bearers in case of radio network resources congestion.
Note** that APN-AMBR and UE-AMBR are applied to non-GBR bearers only. The GBR bearers are controlled be individual MBR values provisioned from PCRF at bearer creation.
The 3GPP TS-23.203 standards define two groups of QoS Class Identifiers (QCI) that could be allocated, based on the underlying transport requirements, to Service Data Flows (SDFs) and thus EPS bearers. The resource type characteristic of the QCI defines the underlying transport requirements in matter of bandwidth reservation: GBR (Guaranteed Bit Rate) and non-GBR (non Guaranteed Bit Rate).
3.1. GBR vs Non-GBR SDFs
PDN-GWs allocate, in reserve mode, network resources (bandwidth) to IP flows belonging to an SDF tagged as GBR. In other words, a portion of the PGW network resources are exclusively dedicated to the transport/processing of the GBR SDF no matter the congestion status of the network (at PDN-GW). Ultimately, a GBR SDF is assigned the following parameters: a QCI (QoS Class Identifier), a GBR (Uplink/Downlink), a MBR (Maximum Bit Rate Uplink/Downlink) and an ARP (Allocation and Retention Priority). The MBR (Uplink/Downlink) values are always greater than or equal to GBR (Uplink/Downlink) values. Unlike GBR, the MBR represent the available bandwidth to SDF IP flows under non-congested network conditions and usually comes with some extra-room on top of the GBR.
Unlike GBR SDFs, the Non-GBR SDFs are subject to Best Effort network resources allocation within APN-AMBR available bandwidth boundaries. The network resources are allocated if available meaning the Non-GBR SDF IP flows are open to delays waiting for resources in use to be free again. Like GBR SDFs, the same QoS parameters are assigned to Non-GBR SDFs with the exception of the GBR parameter that doesn't apply. Furthermore, the MBR is replaced with the APN-AMBR; representing the available bandwidth that could be shared with all Non-GBR SDFs belonging to the same APN.
3.2. GBR vs Non-GBR Bearers
Bearers are virtual channels dynamically created and uniquely identified with a set of identifiers across the EPC and LTE access network. Bearers are meant to transport user traffic (IP flows) between a UE and PDN-GWs and vice-versa. PDN-GWs map the SDFs to EPS bearers satisfying the requested service type Quality of Service. IP flows (SDFs) belonging to a specific service will inherit the EPS bearer (mapped to) QoS (Performance characteristics) in both uplink and downlink directions. An EPS bearer is fragmented into hop by hop bearers:
(1) The Radio Bearer runs over the LTE-Uu wireless interface and uses the C-RNTI (Cell Radio Network Temporary
Identity) value as identifier.
(2) The S1-U bearer running a GTPv1 protocol and utilizing unique Tunnel IDs (TEID), at both eNB and SGW end
points, per EPS Bearer.
(3) The S5/S8 bearer running a GTPv1 protocol associated with unique TEIDs per EPS bearer at SGW and PDN-GW
end points.
Therefore, the EPS Bearer QoS parameters will map into hop by hop bearers at the LTE and EPC Network elements level. eNB, SGW, and PDN-GW will reserve Network resources (Bandwidth) for GBR bearers to honor the QoS characteristics (QCI, GBR, MBR and ARP) of the end to end bearer. On the LTE-Uu, the eNB scheduler will reserve over the air resources and comparable bandwidth on the Wired S1-U interface. SGW and PDN-GW will also honor the same QoS characteristics bidirectional (uplink/downlink) on the ingress and egress interfaces corresponding to S1-U, S5/8 references points. The following QoS parameters are applied for GBR bearers:
PDN-GW/SGW : QCI, ARP, GBR, MBR.
eNB : QCI, ARP, GBR, MBR
UE: MBR
Non-GBR bearers are subject to available network resources where IP flows might be delayed waiting for shared resources in use to be free again. In fact, he best effort concept applies to non-GBR bearers and the following QoS parameters are applied per node:
PDN-GW/SGW : QCI, ARP(*), APN-AMBR(**)
eNB : QCI, ARP, APN-AMBR, UE-AMBR
UE: APN-AMBR
The APN-AMBR is the maximum bit rate (bandwidth) allowed per APN assuming the network resources are available. If the aggregate IP flows' (falling under the same APN) consumed bandwidth exceed the APN-AMBR, the related network element, where the overage first occurs, will start dropping packets to keep bandwidth consumption within APN-AMBR boundaries.
The UE-AMBR is the maximum bit rate (bandwidth) allowed per UE assuming the network resources are available. if the aggregate IP flows' (belonging to different APNs) consumed bandwidth exceed the UE-AMBR, the eNB will start dropping packets to keep the allowed bandwidth under control.
Note*: The ARP is mainly used by the eNB to control bearer resources take over or give away in regards to other bearers in case of radio network resources congestion.
Note** that APN-AMBR and UE-AMBR are applied to non-GBR bearers only. The GBR bearers are controlled be individual MBR values provisioned from PCRF at bearer creation.
4. Default vs Dedicated bearers
In LTE, Default bearers are Network initiated following an initial UE combined "Attach/PDN request" respectively mapping to Mobility Management (MM) and Session Management (SM) entities in the UE and Core Network. Dedicated bearers are also network initiated as a result of (1) an Rx request triggering a PCRF policy definition followed with a charging rule install into PDN-GW/PCEF; (2) a PCRF charging rule Install following a PDN-GW/PCEF ADC rule traffic detection (TD) previously coordinated and installed through PCRF via Sd and Gx interfaces.
As per 3GPP standards, default bearers are non-GBR bearers and operate in always-on mode to transport the non-GBR SDFs (IP flows) matching the default bearer QoS. APN-AMBR and UE-AMBR control the bandwidth/network resources ought to be consumed by IP flows traversing the default bearers.
Dedicated bearers are always linked to a default bearer and temporarily created to service SDFs with higher QoS requirements than the default bearer QoS; and torn down whenever unsolicited. Dedicated bearers could be either GBR or non-GBR. The non-GBR bearers inherit the default bearer Bit rate characteristics, however, the GBR bearers are allocated specific GBR and MBR values independently from the default bearer.
In LTE, Default bearers are Network initiated following an initial UE combined "Attach/PDN request" respectively mapping to Mobility Management (MM) and Session Management (SM) entities in the UE and Core Network. Dedicated bearers are also network initiated as a result of (1) an Rx request triggering a PCRF policy definition followed with a charging rule install into PDN-GW/PCEF; (2) a PCRF charging rule Install following a PDN-GW/PCEF ADC rule traffic detection (TD) previously coordinated and installed through PCRF via Sd and Gx interfaces.
As per 3GPP standards, default bearers are non-GBR bearers and operate in always-on mode to transport the non-GBR SDFs (IP flows) matching the default bearer QoS. APN-AMBR and UE-AMBR control the bandwidth/network resources ought to be consumed by IP flows traversing the default bearers.
Dedicated bearers are always linked to a default bearer and temporarily created to service SDFs with higher QoS requirements than the default bearer QoS; and torn down whenever unsolicited. Dedicated bearers could be either GBR or non-GBR. The non-GBR bearers inherit the default bearer Bit rate characteristics, however, the GBR bearers are allocated specific GBR and MBR values independently from the default bearer.
QoS Provisioning
QoS Enforcement
7. Wireless to Wire-line QoS mapping
The wireless mobile provider network is a mix of Wireless and wired infrastructure. The wireless portion of the network covers the Over-The-Air (OTA) LTE-Uu interface between the mobile device (UE) and eNB. The wired portion spans all the interfaces beyond the eNB including the EPC core, SGi service chains, the Public Internet and/or dedicated connections.
Bearer Preemption (ARP-PL, PCI and PVI).
QoS Enforcement
7. Wireless to Wire-line QoS mapping
The wireless mobile provider network is a mix of Wireless and wired infrastructure. The wireless portion of the network covers the Over-The-Air (OTA) LTE-Uu interface between the mobile device (UE) and eNB. The wired portion spans all the interfaces beyond the eNB including the EPC core, SGi service chains, the Public Internet and/or dedicated connections.
Bearer Preemption (ARP-PL, PCI and PVI).