12 Traffic Class - Figure 8 Cisco Media QoS Recommendations (RFC 4594-based)
RFC 4594 outlines twelve classes of media applications that have unique service level requirements:
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VoIP Telephony—This service class is intended for VoIP telephony (bearer-only) traffic (VoIP signaling traffic is assigned to the "Call Signaling" class). Traffic assigned to this class should be marked EF (DSCP 46). This class is provisioned with an Expedited Forwarding (EF) Per-Hop Behavior (PHB). The EF PHB—defined in RFC 3246—is a strict-priority queuing service, and as such, admission to this class should be controlled. Example traffic includes G,711 and G,729a.•
Broadcast Video—This service class is intended for broadcast TV, live events, video surveillance flows, and similar "inelastic" streaming media flows ("inelastic" flows refer to flows that are highly drop sensitive and have no retransmission and/or flow-control capabilities). Traffic in this class should be marked Class Selector 5 (CS5/DSCP 40) and may be provisioned with an EF PHB; as such, admission to this class should be controlled (either by an explicit admission control mechanisms or by explicit bandwidth provisioning). Examples traffic includes live Cisco Digital Media System (DMS) streams to desktops or to Cisco Digital Media Players (DMPs), live Cisco Enterprise TV (ETV) streams, and Cisco IP Video Surveillance (IPVS).•
Real-time Interactive—This service class is intended for (inelastic) room-based, high-definition interactive video applications and is intended primarily for audio and video components of these applications. Whenever technically possible and administratively feasible, data sub-components of this class can be separated out and assigned to the "Transactional Data" traffic class. Traffic in this class should be marked CS4 (DSCP 32) and may be provisioned with an EF PHB; as such, admission to this class should be controlled. An example application is Cisco TelePresence.•
Multimedia Conferencing—This service class is intended for desktop software multimedia collaboration applications and is intended primarily for audio and video components of these applications. Whenever technically possible and administratively feasible, data sub-components of this class can be separated out and assigned to the "Transactional Data" traffic class. Traffic in this class should be marked Assured Forwarding5 Class 4 (AF41/DSCP 34) and should be provisioned with a guaranteed bandwidth queue with DSCP-based Weighted-Random Early Detect (DSCP-WRED) enabled. Admission to this class should be controlled; additionally, traffic in this class may be subject to policing and re-marking6 . Example applications include Cisco Unified Personal Communicator, Cisco Unified Video Advantage, and the Cisco Unified IP Phone 7985G.•
Multimedia Streaming—This service class is intended for Video-on-Demand (VoD) streaming media flows which, in general, are more elastic than broadcast/live streaming flows. Traffic in this class should be marked Assured Forwarding Class 3 (AF31/DSCP 26) and should be provisioned with a guaranteed bandwidth queue with DSCP-based WRED enabled. Admission control is recommended on this traffic class (though not strictly required) and this class may be subject to policing and re-marking. Example applications include Cisco Digital Media System Video-on-Demand streams to desktops or to Digital Media Players.•
Network Control—This service class is intended for network control plane traffic, which is required for reliable operation of the enterprise network. Traffic in this class should be marked CS6 (DSCP 48) and provisioned with a (moderate, but dedicated) guaranteed bandwidth queue. WRED should not be enabled on this class, as network control traffic should not be dropped (if this class is experiencing drops, then the bandwidth allocated to it should be re-provisioned). Example traffic includes EIGRP, OSPF, BGP, HSRP, IKE, etc.•
Call-Signaling—This service class is intended for signaling traffic that supports IP voice and video telephony; essentially, this traffic is control plane traffic for the voice and video telephony infrastructure. Traffic in this class should be marked CS3 (DSCP 24) and provisioned with a (moderate, but dedicated) guaranteed bandwidth queue. WRED should not be enabled on this class, as call-signaling traffic should not be dropped (if this class is experiencing drops, then the bandwidth allocated to it should be re-provisioned). Example traffic includes SCCP, SIP, H.323, etc.•
Operations/Administration/Management (OAM)—This service class is intended for—as the name implies—network operations, administration, and management traffic. This class is important to the ongoing maintenance and support of the network. Traffic in this class should be marked CS2 (DSCP 16) and provisioned with a (moderate, but dedicated) guaranteed bandwidth queue. WRED should not be enabled on this class, as OAM traffic should not be dropped (if this class is experiencing drops, then the bandwidth allocated to it should be re-provisioned). Example traffic includes SSH, SNMP, Syslog, etc.•
Transactional Data (or Low-Latency Data)—This service class is intended for interactive, "foreground" data applications ("foreground" applications refer to applications that users are expecting a response—via the network—in order to continue with their tasks; excessive latency in response times of foreground applications directly impacts user productivity). Traffic in this class should be marked Assured Forwarding Class 2 (AF21 / DSCP 18) and should be provisioned with a dedicated bandwidth queue with DSCP-WRED enabled. This traffic class may be subject to policing and re-marking. Example applications include data components of multimedia collaboration applications, Enterprise Resource Planning (ERP) applications, Customer Relationship Management (CRM) applications, database applications, etc.•
Bulk Data (or high-throughput data)—This service class is intended for non-interactive "background" data applications ("background" applications refer to applications that the users are not awaiting a response—via the network—in order to continue with their tasks; excessive latency in response times of background applications does not directly impact user productivity. Furthermore, as most background applications are TCP-based file-transfers, these applications—if left unchecked—could consume excessive network resources away from more interactive, foreground applications). Traffic in this class should be marked Assured Forwarding Class 1 (AF11/DSCP 10) and should be provisioned with a dedicated bandwidth queue with DSCP-WRED enabled. This traffic class may be subject to policing and re-marking. Example applications include E-mail, backup operations, FTP/SFTP transfers, video and content distribution, etc.•
Best Effort (or default class)—This service class is the default class. As only a relative minority of applications will be assigned to priority, preferential, or even to deferential service classes, the vast majority of applications will continue to default to this best effort service class; as such, this default class should be adequately provisioned7 . Traffic in this class is marked Default Forwarding8 (DF or DSCP 0) and should be provisioned with a dedicated queue. WRED is recommended to be enabled on this class. Although, since all the traffic in this class is marked to the same "weight" (of DSCP 0), the congestion avoidance mechanism is essentially Random Early Detect (RED).•
Scavenger (or Low-Priority Data)—This service class is intended for non-business related traffic flows, such as data or media applications that are entertainment-oriented. The approach of a less-than best effort service class for non-business applications (as opposed to shutting these down entirely) has proven to be a popular, political compromise: these applications are permitted on enterprise networks, as long as resources are always available for business-critical voice, video, and data applications. However, as soon the network experiences congestion, this class is the first to be penalized and aggressively dropped. Furthermore, the scavenger class can be utilized as part of an effective strategy for DoS and worm attack mitigation9 . Traffic in this class should be marked CS110 (DSCP 8) and should be provisioned with a minimal bandwidth queue that is the first to starve should network congestion occur. Example traffic includes YouTube, Xbox Live/360 Movies, iTunes, BitTorrent, etc.
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