Help us improve your experience.

Let us know what you think.

Do you have time for a two-minute survey?

Navigation
Guide That Contains This Content
[+] Expand All
[-] Collapse All

    Quality of Service Overview

    Quality of service (QoS) allows both subscribers and services to be differentiated. Premium subscribers can be prioritized over basic subscribers, while real-time services can be prioritized over non-real-time services. The importance of QoS increases during periods of congestion. An unloaded network can meet the needs of all subscribers and services. However, as the network load increases, the prioritization of traffic determines whether performance for subscribers and services can be maintained or will be degraded.

    In a mobile network, network resources are shared among multiple services (including Internet, voice, video, e-mail, and file sharing), each of which has different QoS requirements in terms of required bit rates, acceptable packet loss rates, and packet delay. On the MobileNext Broadband Gateway, you configure QoS profiles and policies to define the QoS treatment for mobile subscribers in 3G and 4G networks.

    This topic covers:

    Initial QoS

    When a bearer is first established on the broadband gateway, an initial level of QoS is assigned to the bearer based on QoS attributes in the QoS information element (IE) that specify the traffic characteristics for a bearer. Traffic characteristics include delay class, reliability class, precedence class, and traffic class or traffic handling priority (3G subscribers) or QoS Class Identifier (4G subscribers).

    Differentiated Services

    The broadband gateway supports QoS using the Differentiated Services (DiffServ) model. The DiffServ model is a multiple-service model that addresses different QoS requirements. With DiffServ, the network tries to deliver a particular kind of service based on the QoS specified by each packet, for example, using the 6-bit DiffServ code point (DSCP) setting in IP packets.

    Standards for Differentiated Services are described in the following documents:

    • RFC 2474, Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers
    • RFC 2475, An Architecture for Differentiated Services

    QoS Parameters in 3G Networks

    In a 3G network, subscriber traffic is classified based on traffic classes. Each traffic class is associated with a maximum bit rate and a guaranteed bit rate, which can be configured independently for uplink and downlink subscriber traffic. To define the packet-forwarding treatment for bearer requests received on the broadband gateway, each traffic class (and for the Interactive class, traffic class/traffic handling priority) is mapped to a forwarding class and packet loss priority (PLP) in a QoS classifier profile.

    Note: If traffic is not mapped to a forwarding class and packet loss priority, the classification specified in the bearer request, coming from either the Gn or Gi interface, is carried over.

    Table 1 shows the supported traffic classes, as defined in the 3GPP standards.

    Table 1: Traffic Classes for a 3G Network

    Traffic ClassDescriptionExample Services

    Conversational

    Conversational pattern with very low delay and jitter. This is the most delay-sensitive traffic class.

    Voice and real-time multimedia messaging such as VoIP and video conferencing.

    Streaming

    Delay and jitter requirements are not as strict as with conversational traffic class.

    Streaming type applications such as video on demand.

    Interactive

    Interactive class enables prioritization between Packet Data Protocol (PDP) contexts, which allows end-user or service prioritization. Interactive class is associated with a traffic handling priority (THP). THP values can be 1 through 3.

    Streaming type applications such as video on demand, Web browsing, and Telnet.

    Background

    Best effort is acceptable for data delivery. This is the least delay-sensitive traffic class.

    Background type applications such as e-mail and FTP.

    A policy profile defines the QoS treatment to apply for each traffic class or traffic handling priority. Figure 1 shows the QoS parameters that the broadband gateway evaluates to determine whether to limit, upgrade, or reject an incoming PDP context request.

    Figure 1: Key QoS Parameters for PDP Context Requests

    Key QoS Parameters for PDP
Context Requests

    The guaranteed bit rate (GBR), shown in Figure 1, defines the minimum bit rate that is expected to be available to the PDP context when required. The GBR signifies that a certain amount of bandwidth is reserved for the PDP context, regardless of whether or not the GBR is used. Consequently, a PDP context with a GBR always takes up resources even when no traffic is forwarded. Under normal operating conditions, the PDP context should not experience any packet loss due to congestion on the network. This is ensured because the PDP context is subject to admission control during initial setup, and a network allows the PDP context with a GBR only if sufficient resources are available. You can specify the GBR independently for uplink and downlink traffic.

    The maximum bit rate (MBR), shown in Figure 1, defines the maximum bit rate that is expected to be available to the PDP context when required. An MBR limits the bit rate that will be provided to a PDP context. Any traffic that exceeds the MBR can be dropped. You can specify the MBR independently for uplink and downlink traffic.

    QoS Parameters in 4G Networks

    In a 4G network, subscriber traffic is classified based on the QoS Class Identifier (QCI), which is associated with priority, specify delay, and packet loss values, and determines the user plane treatment for IP packets transported on a bearer. The QCI determines which bearers are categorized as GBR (dedicated) and which are categorized as non-GBR (default). The broadband gateway supports only default bearers, which correspond to QCI values 5 through 9. QCI values 1 through 4 correspond to dedicated bearers, which the broadband gateway does not support. Table 2 shows the supported QoS Class Identifiers and the associated set of QoS characteristics, as defined in the 3GPP standards.

    Table 2: QoS Class Identifier for a 4G Network

    Qos Class IdentifierPriorityPacket Delay BudgetPacket Error Loss RateExample Services

    5

    1

    100 milliseconds (ms)

    10-6

    IP Multimedia Subsystem(IMS) signaling

    6

    7

    10 ms

    10-3

    Voice, video (live streaming), iInteractive gaming

    7

    6


    300 ms


    10-6

    Video (buffered streaming), TCP-based (e-mail, chat, FTP, P2P file sharing)

    8

    8

    9

    9

    The priority associated with each QCI is applied when packets are forwarded across the network. Higher-priority packets are transferred before lower-priority packets.

    The packet delay budget associated with each QCI defines an upper boundary for the packet delay between the user equipment and the policy and charging enforcement function (PCEF) within the broadband gateway.

    The packet error loss rate defines the percentage of higher layer packets—for example, IP packets—that are lost during periods when the network is not congested.

    Note: To define the packet-forwarding treatment for bearer requests received on the broadband gateway, each QCI must be mapped to a forwarding class and packet loss priority (PLP) in the QoS classifier profile. If a QCI is not mapped to a forwarding class and PLP, the classification specified in the bearer request, coming from either the S5 or SGi interface, is carried over.

    A policy profile defines the QoS treatment to be applied to default bearer requests based on the configured QoS parameters. Figure 2 shows the QoS parameters that the broadband gateway processes to determine whether to limit, upgrade, or reject bearer requests.

    Figure 2: Key QoS Parameters for 4G Default Bearer Requests

    Key QoS Parameters for 4G Default
Bearer Requests

    Each default bearer is associated with a QCI value, aggregate maximum bit rate (AMBR), and allocation and retention priority (ARP) value.

    Aggregate Maximum Bit Rate

    The AMBR defines the maximum allowed throughput for a user equipment based on the sum of all total bit rates that all non-GBR bearers associated with an access point name (APN) are allowed to use. Thus the AMBR limits the total non-GBR traffic for an APN. You can configure the AMBR independently for uplink and downlink traffic.

    Allocation and Retention Priority

    The allocation and retention priority (ARP) indicates a priority level for the allocation and retention of bearers. The mobile network uses ARP to decide whether to accept a request to establish a bearer, or reject the request when resources are limited. When performing admission control and network resources are limited, the network uses the ARP to prioritize establishing or modifying bearers with a higher ARP over bearers with a lower ARP.

    In a 4G network, ARP priority level (PL) values range from 1 through 15, where 1 corresponds to the highest priority and 15 corresponds to the lowest priority. In a 3G network, ARP values range from 1 through 3, where 1 corresponds to the highest priority and 3 corresponds to the lowest priority. The more sensitive the QoS application, the lower the corresponding PL or ARP value.

    Preemption

    The broadband gateway uses ARP values to manage the allocation and retention of resources for bearers. When preemption is enabled in a 4G network, the broadband gateway evaluates the PL and the preemption vulnerability (PVI) and preemption capability (PCI) flags in the GTPv2 packet header to determine whether a bearer is a candidate for deletion:

    • PCI—Preemption capability information determines whether a bearer with a lower PL priority level should be dropped to free up the required resources.
    • PVI—Preemption vulnerability information determines whether a bearer is a candidate for dropping by another preemption capable bearer with a higher PL value.
    • PL—Priority level information defines the allocation and retention priority of the bearer.

    Note: In a 3G network, PDP context requests do not support the PVI and PCI flags, so when preemption is enabled, the broadband gateway uses ARP values to determine the preemption capability and preemption vulnerability of PDP contexts. You can use the command-line interface (CLI) to independently enable or disable preemption capability and preemption vulnerability.

    Published: 2011-11-17