Public Safety Communications Research (PSCR)
Priority, Pre‐emption, QoS
Department of Commerce–Boulder Labs

LTE Functionality
• Priority services, the ability to pre‐empt users, and Quality of Service are all crucial to a public safety broadband network.
– LTE as a standard has more control over this, than any other previous wireless broadband technology
• Since most of the these features within 3GPP have never been commercially deployed and the way in which public safety will se them is unique – it is crucial to understand what LTE can provide.
• NCS, 3GPP, IETF all have documented QoS at various levels

LTE Access Control & QoS Mechanisms
• Cell Status
• Cell Barring
• Access Classes
• Bearers
– GBR: Guaranteed Bit Rate
– MBRL: Maximum Bit Rate
– Non GBR
– Default
– Dedicated
• TFT: Traffic Flow Template
– Uplink
– Downlink
– Bearer Level
– SDFL: Service Data Flow Level
• QCI: QoS Class Identifier
• ARP: Allocation Retention Priority
• APN-AMBR: Aggregate Maximum Bit Rate
• UE‐AMBR

Access Barring
• Cell Status (Access Barring) and Special Reservations (Access Reserved) control cell selection and reselection procedures.
– Cell Barring: UE isn’t permitted to select/re‐select cell, even for emergency calls
• UE reselects another cell according to specific rules
– Cell Reserved: Reserve cells for operator activities–maintenance, special events etc.
• Only specific access classes 11 or 15 allowed for cell selection/re‐selection

Access Control
• Access control using access classes:
– Can be used to prevent devices of commercial users from initiating an RRC connection
– Can be manually invoked by the LTE network operator on some or all cells to suspend commercial traffic during an overload situation (% basis)
– Recommendation is to follow commercial practice:
• Access classes 0 through 9 should be randomly allocated to commercial subscribers on public/private combined networks
• Access classes 12, 13 and 14 can be used for Public Safety User. 3GPP specifications are :
– Class 12: Security Services
– Class 13: Public Utilities
– Class 14: Emergency Services
• Access class 11 and 15 are reserved for LTE network administrative use
– Example is testing a new cell before it is placed into service

Allocation Retention Priority
• ARP is stored in the Subscriber profile (HSS) typically on a per APN basis ‐ not included within the EPS QoS Profile sent to the UE
– Priority level: 1 – 15
– Pre‐emption capability: determines whether a bearer with a lower ARP priority level should be dropped to free up the required resources
– Pre‐emption vulnerability: determines whether a bearer is applicable for dropping by a pre‐emption capable bearer with a higher ARP priority value
• At every Radio Bearer (RB) setup request (including HO and RRC connection re‐establishment), the eNB Radio Admission Control (RAC) entity will check the current eNB hard limit capacities, which icludes factors such as:
– maximum number of UEs and RBs, number of RBs on GBR
• ARP controls how the eNodeB reacts when when there are insufficient resources to establish the new RB
– Deny the RB request
– Preempt an existing RB and accept the new RB request

QCI
• QCI 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).

Traffic Flow Template
• TFT is set of all packet filters associated with an EPS bearer.
– A default bearer may or may not be associated with a TFT (based on HSS data) but a dedicated bearer is always associated with a TFT
• Bearer level QoS is associated with a bearer and all traffic mapped to that will receive same bearer level packet forwarding treatment.
– A packet filter may be associated with a protocol.
– A packet filter Identifier shall be used to identify a packet filter.
– Uplink TFT used by the UE
– Downlink TFT used by the PDN
• Each EPS bearer is associated with the following bearer level QoS parameters:
– QoS Class Identifier (QCI);
– Allocation and Retention Priority (ARP).
• Each GBR bearer is additionally associated with the following bearer level QoS parameters:
– Guaranteed Bit Rate (GBR);
– Maximum Bit Rate (MBR).
• Each APN is associated with an Aggregate Maximum Bit Rate (APN AMBR).
• Each UE is associated with UE Aggregate Maximum Bit Rate (UE AMBR).

QCI Table – TS 23.203

ARP Mapping

Layer 3 IP Precedence and DSCP
• IPV4: The three most significant bits of ToS byte are called IP Precedence.
• Diffserv: Six most significant bits of ToS byte are called Diffserv Code Point (DSCP) – remaining two bits are used for flow control
• EF: Expedited Forwarding defined in RFC3246. DSCP 46
• AFxy: Assured Forwarding defined in RFC 2597 ‐ where x corresponds to IP precedence value (only 1‐4 are used for AF classes) and y corresponds to the drop precedence value (either 1, 2, 3) with the higher value denoting higher likelihood of dropping. DSCP 10/12/14, 18/20/22, 26/28/30, 34/36/38
• CSx: Class Selector defined in RFC2474 ‐ where x corresponds to the IP precedence value (1‐7). DSCP 8,16,32,40,48,56
• BE: Best Effort of Default Marking value (RFC2474). DSCP 0

DSCP Mapping to QCI, ARP and PS Apps

QoS Mapping

Demo Network Implementations
• Design network to support full End‐to‐End QoS
• Start with Best effort data (start simple …):
– Map default bearer to QCI 8 or 9 [in HSS subscriber profile]
– Investigate use Aggregate Maximum Bit Rate (AMBR) [in HSS subscriber profile] to create different levels of Best Effort Service
• Support use of QoS bearers
– Determine overall QoS mapping possible in Release 8
• Develop test cases
– Requires PCRF and Rx interface to Application Servers

Discussion
• How can we accomplish meeting public safety’s QoS goals? Does our template meet those needs?
• What parts are available?
– Access Control
– Access Barring
– Allocation Retention Priority
– Traffic Flow Template
• When will they be available?

Working Group
• We will send around a sign up sheet

Questions?

User groups Non-GBR bearer GBR bearer
Can preempt
Vulnera
ble
Can preempt
Vulnera
ble
1 Yes No Yes No Reserved for Serving Network
2 1st responder at
home (A)
Yes No Yes No Priority 1 user non video traffic
3 1st responder at
home (B)
Yes No Yes No Priority 1 user video traffic
Priority 2 user non-video traffic
4 1st responder at
home (C)
Yes No Yes No Priority 2 user video traffic
Priority 3 user non-video traffic
5 1st responder at
home (D)
1st responder
visiting (A)
Yes No Yes No Priority 3 user video traffic
Priority 4 user non-video traffic
6 PS support at
home (A)
1st responder
visiting (B)
No Yes Yes No Priority 4 user video traffic
Priority 5 user for non video traffic
7 No Yes Yes No E911
8 PS support at
home (B)
No Yes Yes No GBR Voice Calls (non-PTT)
9 PS support at
home (C)
No Yes Yes No GBR non-voice and IMS signaling
10 PS other (A) PS support visiting
(A)
No Yes No Yes Regular subscriber general data
IMS signaling
11 PS other (B) PS support visiting
(B)
No Yes No Yes Voice calls
12 No Yes No Yes Reserved for Serving Network
13 No Yes No Yes Reserved for Serving Network
14 Commercial
user
No Yes No Yes Priority 1 Commercial Users non-video
traffic
15 Commercial
user
No Yes No Yes Priority 1 Commercial Users video
traffic
Priority 2 Commercial Users non-video
traffic
Expedited
Forwarding
DSCP
Name
DSCP
Value
RFC
Standard
EF
46
RFC3246
Assured
Forwarding
Drop
Class
1
Class
2
Class
3
Class
4
RFC
Standard
Low
AF11
/
DSCP
10
AF21/
DSCP
18
AF31/
DSCP
26
AF41/
DSCP
34
RFC 2597
Medium
AF12
/
DSCP
12
AF22/
DSCP
20
AF32/
DSCP
28
AF42/
DSCP
36
RFC 2597
High
AF13
/
DSCP
14
AF23/
DSCP
22
AF33/
DSCP
30
AF43/
DSCP
38
RFC 2597
Class
Selector
DSCP
Name
DSCP
Value
RFC
Standard
CS
7
56
RFC
2474
CS
6
48
RFC 2474
CS
5
40
RFC 2474
CS
4
32
RFC 2474
CS
3
24
RFC 2474
CS
2
16
RFC 2474
CS
1
8
RFC 2474
CS
0
0
(Best
Effort)
RFC 2474
QCI,
ARP
to
DSCP
Mapping
QCI
*ARP
QoS
Level
Traffic
Class
Public
Safety
Apps
QCI
1
1-­‐15
PlaQnum
ConversaQonal
Voice
–
PTT,
telephony
QCI
2
1-­‐15
Gold
Streaming
Video
–
Surveillance
video,
In-­‐car
Streaming
QCI
6
1-­‐15
Silver
InteracQve
Interac,ve
-­‐
Web,
CAD,
GIS,
Database
and
Records
QCI
8
QCI
9
1-­‐15
Bronze
Background
Best
Effort
-­‐
Email,
SMS,
MMS,
Alert
NoQficaQons
* ARP value still needs to be defined.