Eric's Tech Notes

HOWTO guides to sometimes complicated tasks

3GPP EPC QOS Design

This HOWTO assumes you know Cisco IOS QOS and can implement your preferred enforcement on IP networks between EPS elements. Material in this HOWTO was gathered from 3GPP TS 23.401 section 4.7 and Cisco LTE CLI guide. For a general understanding let's take a look at DCSP marking values in the diagram below. Keep in mind that StarOS supports AF, BE, and EF markings.

DSCP Mapping
QCI to DSCP Mapping
QCIPriorityPacket DelayPacket LossDSCP/Dec/HEXService ExamplesUMTS Class
12100ms10^-2EF/46/2EConversational Voice (GBR)Conversational
24150ms10^-3EF/46/2EConversational Video (GBR)Conversational
3350ms10^-3EF/46/2EReal Time Gaming (GBR)Conversational
45300ms10^-6AF41/34/22MM Streaming (GBR)Streaming
51100ms10^-6AF31/26/1AIMS SignalingStreaming
Interactive/1
66300ms10^-6AF31/26/1ATCP, ftp, apps High priorityInteractive/1
77100ms10^-3AF21/18/12VoIP, video, apps non-GBRInteractive/2
88300ms10^-6AF11/10/0ATCP, ftp, apps Reg. PriorityInteractive/3
99300ms10^-6BE/0/00TCP, ftp, apps Low PriorityBackground

Control Plane QOS

Control plane QOS if very simple compared to the user plane marking and enforcement. Below we have a diagram showing the control plane in purple with both SCTP and GTP encapsulations. In all our control plane examples we use ef marking but this is just for example and your customer may choose differently. There is only marking on the control plane and if you need policing or shaping you will have to use an external node. It's assumed the control plane traffic would never be enforced via policing or shaping as this would degrade the users experience.

Basic EPC

The configuration needed to do control plane marking is provided below for MME, SGW, and PGW. Please not the eNodeB will also need to support prioritization over RAN based on DSCP for control plane and QCI for user plane plus its traffic towards MME and SGW. We also have marking enabled for diameter towards HSS so you might want to check if your HSS vendor supports marking in the return path.

MME-S1-MME: mme-service MME-SVC s1-mme ip qos-dscp ef MME-S11: egtp-service MME-EGTP-SVC gtpc ip qos-dscp ef interface-type interface-mme MME-S6a: diameter endpoint HSS dscp ef SGW-S11: egtp-service SGW-EGTP-S11-SVC gtpc ip qos-dscp ef interface-type interface-sgw-ingress SGW-S5: egtp-service SGW-EGTP-S5-SVC gtpc ip qos-dscp ef interface-type interface-sgw-egress PGW-S5: egtp-service PGW-EGTP-S5-SVC gtpc ip qos-dscp ef interface-type interface-pgw-ingress

User Plane QOS

For user place we have marking and enforcement. First we have to understand all the variable in play and how they apply to each APN/UE. The items listed below will be cover high-level details with respect to each QOS attribute and how they interact with each other:

  1. DSCP Marking
    DSCP marking is show in first section via table.

  2. UE-AMBR (per subscriber)
    UE-AMBR is initially/optionally provided by HSS and is included in ULA in subscriber data. This value is the maximum bit-rate (in bits per second) that all bearer used by a subscriber can utilize. It's used by UE and PGW to set maximum possible UL and DL date speeds and policing per subscriber. UE-AMBR will be lowest of either pre-configured UE-AMBR via HSS or Sum of all ANP-AMBRs for that subscriber.

  3. APN-AMBR (per subscriber)
    APN-AMBR is initially/optionally provided by HSS and is included in ULA in apn context data(potentially different for each context/apn). This value is the maximum bit-rate (in bits per second) that all PDNs combined per APN per subscriber. It's used by UE and PGW to set UL and DL date speeds and policing for all APNs combined per UE. You can only have UE-AMBR on Non-GBR bearer. Note that APN-AMBRs when added up between all active APNs cannot exceed UE-AMBR.

  4. QCI
    QCI or QoS Class Identifier is a scalar that is used as a reference to access node-specific parameters that control bearer level packet forwarding treatment (e.g. scheduling weights, admission thresholds, queue management thresholds, link layer protocol configuration, etc.), and that have been pre-configured by the operator owning the access node (e.g. eNodeB). A one-tone(single bucket) mapping of standardized QCI values to standardized characteristics is captured in TS 23.203

  5. GBR
    The GBR denotes the bit rate that can be expected to be provided by a GBR bearer. The MBR limits the bit rate that can be expected to be provided by a GBR bearer (e.g. excess traffic may get discarded by a rate policing function).

  6. MBR
    The MBR for a GBR bearer is equal to the GBR in current 3GPP release. Support for "MBR > GBR" bearers may be introduced in a future Release.

  7. Non-GBR
    Non GBR bearers will use a combination of APN-AMBR and UE-AMBR.

  8. ARP
    Priority will determine which bearers will be provisioned during contention for resources primarily on EUTRAN. Lower numerical value will have better priority. (At eNodeB and PGW) Once successfully established, a bearer's ARP shall not have any impact on the bearer level packet forwarding treatment (e.g. scheduling and rate control). Such packet forwarding treatment should be solely determined by the other EPS bearer QoS parameters: QCI, GBR and MBR, and by the AMBR parameters. The ARP is not included within the EPS QoS Profile sent to the UE.

  9. ARP Pre-Emption Capability
    This flag determines whether a bearer will be allowed to prioritize itself over another bearer with lower priority along with vulnerability flag set. (At eNodeB)

  10. ARP Pre-Emption Vulnerability
    This flag specifies if bearer can be candidate to remove for higher priority bearers which have Pre-Emption Capabilities set. (At eNodeB)

Notes:

User Plane QOS

The section covers SGi QCI Mapping Plus SGi/S5 APN-AMBR Rate Limiting. The APN will first need to map QCI to DSCP values so the raw user packets are marks as they leave SGi. Once the mapping is done we can add policing APN-AMBR which implies non-BGR bearers.

apn ipv4v6.com ip qos-dscp qci 1 ef qci 2 ef qci 3 ef qci 4 af41 qci 5 af31 qci 6 af31 qci 7 af21 qci 8 af11 qci 9 be apn-ambr rate-limit direction downlink burst-size auto-readjust violate-action lower-ip-precedence apn-ambr rate-limit direction uplink burst-size auto-readjust violate-action lower-ip-precedence Options: violate-action drop - drop the packet lower-ip-precedence - transmit the packet after lowering the ip-precedence (increaseing the DSCP drop-precedence) <- sets DSCP to 0x00 or BE transmit - transmit the packet

SGW Policing

In this section we cover S1-U & S5 Rate Limiting for Both GBR & Non-GBR. SGW based rate limiting for non-GBR & GBR bearers is configurable in SGW as shown below. This is a two bucket three color design of policing.

sgw-service SGW-SVC associate subscriber-map SM1 lte-policy subscriber-map SM1 precedence 1024 match-criteria all operator-policy-name OP1 operator-policy name OP1 apn default-apn-profile AP1 apn-profile AP1 qos rate-limit direction downlink - apply the QoS treatment in the downlink direction burst-size - Burst size in bytes exceed-action - Action to be taken on packets that exceed the committed-rate but not violate. gbr-qci - configure traffic policing for gbr bearers non-gbr-qci - configure traffic policing for non gbr bearers violate-action - Action to be taken on packets that exceed the committed-rate and peak-rate. uplink - apply the QoS treatment in the uplink direction burst-size - Burst size in bytes exceed-action - Action to be taken on packets that exceed the committed-rate but not violate. gbr-qci - configure traffic policing for gbr bearers non-gbr-qci - configure traffic policing for non gbr bearers violate-action - Action to be taken on packets that exceed the committed-rate and peak-rate.

SGW & PGW Marking

This section covers S1-U & S5 QCI Mapping. The GTP user plane tunnel between eNodeB and PGW now needs to have QCI to DSCP, Delay, Drop Threshold and policing interval set. This profile needs to be applied to both SGW and PGW.

pgw-service PGW-SVC associate qci-qos-mapping QCI-QOS-MAP sgw-service SGW-SVC associate qci-qos-mapping QCI-QOS-MAP qci-qos-mapping QCI-QOS-MAP qci 1 gbr traffic-policing interval 100 max-packet-delay 100 max-error-rate 2 uplink user-datagram dscp-marking 0x2e encaps-header copy-inner downlink user-datagram dscp-marking 0x2e encaps-header copy-inner qci 2 gbr traffic-policing interval 100 max-packet-delay 150 max-error-rate 3 uplink user-datagram dscp-marking 0x2e encaps-header copy-inner downlink user-datagram dscp-marking 0x2e encaps-header copy-inner qci 3 gbr traffic-policing interval 100 max-packet-delay 50 max-error-rate 3 uplink user-datagram dscp-marking 0x2e encaps-header copy-inner downlink user-datagram dscp-marking 0x2e encaps-header copy-inner qci 4 gbr traffic-policing interval 100 max-packet-delay 300 max-error-rate 6 uplink user-datagram dscp-marking 0x22 encaps-header copy-inner downlink user-datagram dscp-marking 0x22 encaps-header copy-inner qci 5 non-gbr traffic-policing interval 100 max-packet-delay 100 max-error-rate 6 uplink user-datagram dscp-marking 0x1a encaps-header copy-inner downlink user-datagram dscp-marking 0x1a encaps-header copy-inner qci 6 non-gbr traffic-policing interval 100 max-packet-delay 300 max-error-rate 6 uplink user-datagram dscp-marking 0x1a encaps-header copy-inner downlink user-datagram dscp-marking 0x1a encaps-header copy-inner qci 7 non-gbr traffic-policing interval 100 max-packet-delay 100 max-error-rate 3 uplink user-datagram dscp-marking 0x12 encaps-header copy-inner downlink user-datagram dscp-marking 0x12 encaps-header copy-inner qci 8 non-gbr traffic-policing interval 100 max-packet-delay 300 max-error-rate 6 uplink user-datagram dscp-marking 0x0a encaps-header copy-inner downlink user-datagram dscp-marking 0x0a encaps-header copy-inner qci 9 non-gbr traffic-policing interval 100 max-packet-delay 300 max-error-rate 6 uplink user-datagram dscp-marking 0x00 encaps-header copy-inner downlink user-datagram dscp-marking 0x00 encaps-header copy-inner

MME AMBR and MBR

On MME you will also want to setup QCI, ARP, and APN-AMBR via CLI below in blue. Note we set QCI to 9 (DSCP=BE), UL/DL rate to 8Mb/s and ARP to 1 which translates into little resource reservation and almost no chance of being pre-empted. For UE-AMBR, we set this value via call-control-profile as shown in green below. Note both AMBRs have their cap set to minimum or HSS or local CLI, whichever is lower. This type of limit might be good for MVNO or Roaming types of subscriber scenarios.

mme-service MME1-SVC associate subscriber-map SM1 lte-policy subscriber-map SM1 precedence 1024 match-criteria all operator-policy-name OP1 operator-policy name OP1 associate call-control-profile CCP1 apn default-apn-profile AP1 apn-profile AP1 qos prefer-as-cap both-hss-and-local minimum qos dedicated-bearer mbr max-ul 4000000 max-dl 4000000 qos default-bearer qci 9 qos default-bearer arp 1 preemption-capability may vulnerability not-preemptable qos apn-ambr max-ul 8000000 max-dl 8000000 Options: preemption-capability may - Bearer may be preempted shall-not - Bearer shall not be preempted vulnerability not-preemptable - Bearer is not preemptable preemptable - Bearer is preemptable qos prefer-as-cap both-hss-and-local - Configure policy for HSS and/or Local values local-when-subscription-not-available - reject if subscription values exceed local minimum - use minimum of hss and local, and use local only if hss does not send it subscription-exceed-reject - reject if subscription values exceed local local - Prefer local configuration for qos capping call-control-profile CCP1 qos ue-ambr max-ul 8000000 max-dl 8000000 qos ue-ambr prefer-as-cap both-hss-and-local minimum Options: both-hss-and-local local-when-subscription-not-available - Use local values only when subscription is not available minimum - Prefer minimum of HSS and local value subscription-exceed-reject - when subscription values exceed local values, send reject

Conclusion and Thoughts

The QOS in EPC is still evolving and there is still work to be done on UE initiated bearers as well as handover support for QOS with MS-Only and MS/NW based Bearer Resource Control. We highly recommend you spend some time reading 23.401 section 4.7 along with the whitepapers links at the top from Amit Ghadge.

RAN Design for LTE Advanced:

LTE Advanced