Quality of Service

Overview

Alcatel-Lucent 1665 DMX supports the following Quality of Service (QoS) capabilities:

Private line service provides dedicated bandwidth between two points service (best QoS).
Fractional rate services provide basic rate control with SONET tributary granularity.
Committed information rate (CIR) policing provides rate limiting with 1 Mbps granularity.
Peak information rate (PIR) policing provides rate limiting with 1 Mbps granularity.
LNW170 enables advanced QoS capabilities including CIR rate metering.

For detailed information about Ethernet frame priority levels, see Priorities and 802.1Q VLAN mode.

QoS services (LNW74)

The LNW74 circuit packs provide 10 Mbps and 100 Mbps Private Line services. They do not contain an Ethernet Switch. Each LAN port is connected to its own VCG. 100 Mbps traffic can be rate-limited by provisioning less SONET bandwidth than required to carry the full line rate. Traffic is buffered and flow control is invoked when ingress traffic on a LAN port exceeds the VCG's SONET bandwidth. If flow control is disabled or ignored by the external equipment, Ethernet frames are dropped when the ingress buffer overflows. The LNW74 offers 1.5Mbps VT granularity.

QoS services (LNW170)

The capabilities of the LNW170 enable enhanced QoS features. The LNW170 can function in either Private Line or Switched mode.

The QoS capabilities of the LNW170 are different depending on the mode the card is in. Also, within the two modes below, there are a variety of traffic conditioners which can be applied, depending on the mode) which further govern the QoS capabilities of the pack.

Private Line: Alcatel-Lucent 1665 DMX can perform rate controlling at a sub-STS level and on a per-port basis in PL mode. In PL mode, if rate control is desired, the traffic management mode will be port mode (see Traffic Conditioners below).
Switched Mode: Alcatel-Lucent 1665 DMX can perform VLAN processing and enhanced QoS in switched mode. There are two settings within switched mode: Transparent and IEEE 802.1q mode. See Tagging Modes.

In order to provide enhanced QoS services, traffic must be classified, and conditioned. This is accomplished using traffic conditioners that are applied to packets at the boundary port (see Boundary vs. Interior Port below).

Traffic Management Mode

The QoS features available on any given port will vary depending on the particular traffic conditioners applied to that port. The 5 traffic conditioners supported by Alcatel-Lucent 1665 DMX are as follows:

PORT mode: One traffic conditioner for the port. All traffic that is permitted to be transported flows through a single traffic conditioner.
COSPORT mode: One traffic conditioner for each class of service at the port. All traffic for an individual CoS is provisioned with its own traffic conditioner.
TAGPORT mode: One traffic conditioner for each Packet Tag at the port. Traffic for all classes of service that have the same Packet Tag flow through a single traffic conditioner.
COSTAGPORT mode: One traffic conditioner for each class of service for each Packet Tag/VLAN at the port. All traffic for an individual CoS on each Packet Tag is provisioned with its own traffic conditioner.
NOTC mode: In this mode all traffic is bridged through the switch as usual but there is no traffic conditioning performed on the traffic. NOTC mode emulates the (basic) QoS behavior on the older Alcatel-Lucent 1665 DMX circuit packs (user_priority values 0,1,2 and 3 are mapped to CoS 0 and user_priority values 4,5,6 and 7 are mapped to CoS 3; no modification of user_priority bits in user packets).

Boundary versus interior ports

When speaking of QoS, a port is either a Boundary or Interior port. A boundary port is at the edge of a differentiated services (DiffServ) domain and an Interior port in a the core of a DiffServ domain. All traffic policing, conditioning, and marking is done at boundary ports. It is assumed that these functions have been performed by the time packets reach the interior ports. Boundary/Interior demarcation is controlled by an explicit parameter. By way of provisioning, a LAN port or VCG can be either boundary or interior. A LAN port is usually (and by default) a boundary port, and a VCG is usually (and by default) an interior port.

QoS functionality is built around the concept of boundary and interior ports. Though the terminology customer and network are often used in place of boundary and interior (where customer equals boundary and interior equals network), this is incorrect with reference to Alcatel-Lucent 1665 DMX. However, customer and network terminology is still applied to ports with respect to their overall VLAN tagging behavior, rather than QoS specific functions.

The table below details what traffic management modes are allowed to be provisioned on ports depending on wether they are boundary or interior ports. Attempts to provision a VLAN tagging mode/traffic management mode combination that is not listed in the table below will be denied.

Table A-5: Allowed traffic management modes per port type

VLAN Tagging Mode	Port Type	Traffic Management Mode
VLAN Tagging Mode	Port Type	LNW170
Private Line	Boundary Port¹	NOTC
	Boundary Port¹	PORT
	Interior Port¹	N/A
Transparent	Boundary Port	COSPORT
		NOTC
		PORT
	Interior Port	N/A
802.1TAG	Boundary Port	NOTC
		PORT
		TAGPORT
		COSPORT
		COSTAGPORT
	Interior Port	N/A

Notes:

In Private Line mode, it is not possible to change the Boundary/Interior demarcation of LAN and VCG ports. A VCG can be a boundary port, but this limits the traffic management mode provisionable for that port to NOTC only.

Untagged or unprovisioned packets

The table below explains what happens at the ingress when untagged or unconditioned packets are received. If a packet arrives at a port and it is marked with a CoS and Packet Tag for which a traffic conditioner has not been provisioned at that particular port, the traffic is handled as described in the table below.

Table A-6: Handling of untagged or unprovisioned service at boundary ports

VLAN tagging mode	Traffic Management mode	Untagged traffic	CoS-Packet Tag Traffic Conditioner not provisioned
Private Line	NOTC	Pass all traffic unmodified	Pass all traffic unmodified
Private Line	PORT	Pass all traffic unmodified	Pass all traffic unmodified
Transparent	NOTC	Tag with default port tag and default CoS and pass traffic	Not Applicable
Transparent	PORT	Tag with default port tag and default CoS and pass traffic	Tag with default port tag and default CoS and pass traffic unmetered (marked Yellow)
802.1TAG	NOTC	Tag with default VLANid and default CoS and pass traffic	Not Applicable

QoS in Private Line mode

Private Line mode should be employed when deploying point-to-point service connections using dedicated resources. Private Line can either be a full-rate service or a sub-rate service. Full-rate services dedicate enough network resources to transport the data from the ingress Boundary Port through the network to the egress Boundary Port at the full data rate of the Boundary Ports. Sub-rate services transport data at a fraction of the full data rate of the Boundary Ports.

In Private Line Mode, the Boundary Ports (see Boundary vs. Interior Ports above) can have either NOTC or PORT traffic management mode; the Interior Ports are always NOTC. All packets received are handled uniformly using a single queue. Packets are not modified or remarked in this mode. Therefore, it is not possible to encode color. Consequently, packets are either dropped or passed-through transparently. This is achieved by setting CIR values equal to PIR values and by forcing CBS to equal PBS.

QoS in transparent and 802.1q mode

Transparent mode provides a trunked Private Line or "Virtual Private LAN" service. The Boundary Ports use either a NOTC or PORT traffic management mode. In transparent mode, customers packets are not changed.

In NOTC mode, just as with Private Line, there is no traffic conditioning performed on any of the boundary Ports. Traffic conditioning is never performed on the Interior ports.

In the PORT mode all traffic that enters the port is tagged (stacked VLAN) with the provisioned TPID and the default port tag. The CoS is set to the default priority for that port and the user_priority is set based on this CoS and the conformance level determined in the traffic conditioner.

Packets that are within the committed contract parameters are marked with a Drop Precedence of DP1 (green). Packets that arrive out of the guaranteed contract, but within some allowable excess, are marked with a Drop Precedence of DP0 (yellow). Packets that arrive outside of the allowed excess are discarded.

The user_priority is determined from the CoS level and Drop Precedence. The packet is remarked with this user_priority before leaving the egress port.

In both NOTC and PORT mode, if no default priority is specified for the port, the CoS value is set to 0. There is no traffic conditioning on Interior Ports (see Boundary vs. Interior Ports above).

With Transparent tagging, both PIR, CIR, PBS and CBS are used to allocate the appropriate network resources to each service. Transparent mode supports user network configurations with more than two nodes in case a multipoint "Virtual Private LAN" service is needed. For this service each Boundary Port is provisioned with the same default port tag and default priority. This results in the required traffic separation to provide a virtual private network.

802.1q mode

The 802.1TAG tagging mode assumes that packets arrive at the boundary to the network already tagged with a standards-compliant VLAN tag. It is possible then to offer a number of services at a single port simultaneously.

In 802.1q mode, the packets should be tagged by the subscriber, however, some packets may arrive untagged. The CoS level for tagged packets is determined either by the default port CoS level (PORT mode) or the default VLAN CoS level (TAGPORT mode), or by examining the user_priority and setting the CoS according to a fixed mapping (NOTC and PORT mode), or according to a provisionable mapping table. The mapping table is associated either with a port (COSPORT mode) or a VLAN (COSTAGPORT mode). Untagged traffic is tagged with the default VLAN. The CoS is then set to either the default port CoS level (NOTC, PORT, COSPORT mode) or the default VLAN CoS level (TAGPORT, COSTAGPORT mode). The packets are then conditioned (except for NOTC) in the same fashion as tagged traffic.

Priority-tagged traffic is tagged with the default VLAN, and the CoS level is determined as it would be for a tagged packet.

In all cases, the Drop Precedence (DP) is set according to the level of conformance specified in the customer's SLA contract.

The functionality of each traffic management with regard to 802.1q mode is detailed below:

PORT: The PORT mode of operation, is very similar to the services offered in the Transparent tagging mode, except that in this case the standard TPID (Ethertype) of 8100 is used so that this mode is interoperable with other 802.3 networks. Also more than one VLANid can be supported at a single port and treated as a single traffic flow. In this mode the traffic conditioning for all traffic that is admitted to the port is performed as an aggregate data flow by a single traffic conditioner. Only traffic that is either untagged or tagged with a VLANid that has been provisioned at the port is admitted. In this mode the user_priority bits are remarked according to the user_priority (0,1,2,3 map to CoS 0 and 4,5,6,7 map to CoS 3) of the packets unless overruled by the default priority. Drop Precedence is determined as a result of the packets conformance to the SLA. Any remarking that occurs is irreversible and is present on the packet at the network egress.
TAGPORT: In the TAGPORT mode of operation, a single CoS is associated with each VLAN. The traffic flows through a traffic conditioner per VLAN where it is metered and policed as per the terms of the SLA. In this mode each VLAN has its own PIR, CIR, PBS and CBS. Packets that arrive untagged are tagged with the port default VLANid and CoS for that VLAN. As with the other modes, the Drop Precedence is determined based on the conformance to the SLA. Any remarking that occurs is irreversible and is present on the packet at the network egress.
COSTAGPORT: In the COSTAGPORT mode of operation, traffic for each CoS on each VLAN flows through its own traffic conditioner. Traffic that is tagged with one of the port's provisioned VLANids is admitted to the network. Packets that arrive untagged or priority-tagged are tagged with the port default VLANid. Packets tagged with an unprovisioned VLANid are discarded. The user_priority bits in a priority-tagged frame are used to determine the CoS when selecting the traffic conditioner. In this mode each CoS on each VLAN has its own PIR, CIR, PBS and CBS. On each VLAN each CoS can be individually enabled or disabled. The Drop Precedence is determined by the SLA conformance level and the packet is remarked accordingly. This marking is not reversible and is present when the packet egresses the network.
COSPORT: In the COSPORT mode of operation, traffic for each class of service flows through its own traffic conditioner. Traffic that is tagged with one of the port's provisioned VLANids is admitted to the network. Packets that arrive untagged or priority-tagged are tagged with the port default VLANid. Packets tagged with an unprovisioned VLANid are discarded. The user_priority bits in a priority-tagged frame are used to determine the CoS when selecting the traffic conditioner. In this mode each CoS has its own PIR, CIR, PBS and CBS. Each CoS can be individually enabled or disabled. The Drop Precedence is remarked according to the conformance to the SLA. This marking is not reversible and is present when the packet egresses the network.

The table below shows the default mapping of user priority bits to CoS.

Table A-7: Default mapping of user priority to CoS

user_priority	CoS
000	1
001	0
010	0
011	1
100	2
101	2
110	3
111	3

The table below shows the default mapping of DSCP to CoS. Alcatel-Lucent 1665 DMX supports DSCP for traffic classification on the LNW170. DSCP to CoS is available in PORT mode only. DSCP can be used as an alternative to priority bits. The criteria for traffic classification can be user priority bits, DSCP, VLANid, or default value. DSCP allows for three differentiated services code point values: IP precedence value (also called Class Selector-- CS in the table below), Assured Forwarding (AF), and Expedited Forwarding (EF).

Table A-8: Default mapping of DSCP to CoS

CoS	DSCP	Binary	Decimal
0	Default	000000	0
0	CS1	001000	8
2	AF11	010010	10
2	AF12	001100	12
2	AF13	001110	14
1	CS2	010000	16
1	AF21	010010	18
1	AF22	010100	20
1	AF23	010110	22
1	CS3	011000	24
0	AF31	011010	26
0	AF32	011100	28
0	AF33	011110	30
2	CS4	100000	32
0	AF41	100010	34
0	AF42	100100	36
0	AF43	100110	38
2	CS5	101000	40
3	EF	101110	46
3	CS6	110000	48
3	CS7	111000	56

The tables below show the characteristics of services offered with the different VLAN tagging modes and traffic management modes. These characteristics include the number of services allowed at a port as well as the number allowed on the network.

Table A-9: 802.1 VLAN tagging and traffic management modes

	802.1TAG
	NOTC	PORT	TAGPORT	COSPORT	COSTAG- PORT
No. Services at 1 port¹	1	1	1 per VLANid 4093 max.	1 per CoS Level 4 max.	1 per CoS Level per VLANid 16,372 max.
No. Services on Network²	1	1 to 4093	1 to 4093	1 to 16,372	1 to 16,372
Max. CoS Support³	No	4 CoS/Port	4 CoS/VLAN	4 CoS/Port	4 CoS/VLAN
Traffic Conditio-ning⁴	None	PIR PBS CIR CBS	PIR PBS CIR CBS	PIR PBS CIR CBS	PIR PBS CIR CBS
Packets Altered⁵	Maybe untag'd	Maybe VLANid user_priority	Maybe VLANid user_priority	Maybe VLANid user_priority	Maybe VLANid user_priority

Notes:

The number of services at a port is the number of traffic conditioners used, except for the NOTC mode where there is 1 service with no traffic conditioner.
The number of services on a network is the total number of separate VLANids/default port tags allowed on the network in separate services times the number of traffic conditioners that are allowed for each VLANid/default port tag.
The maximum number of Classes of Service supported is the number that will be passed through any traffic conditioner on that port. For example, in 802.1TAG mode the PORT mode will allow all 4 CoS Levels to pass through a common traffic conditioner, whereas, in Transparent mode the PORT mode tags all traffic with the default CoS and therefore only a single CoS is supported.
The traffic conditioning parameters shown are those available via TL1. In a practical sense fewer parameters are needed to provision the service.
Packets are considered altered if the user packet that leaves the network at an egress Customer Port is not identical to the packet that entered the network at an ingress Customer Port. Packets are generally altered in 802.1TAG mode due to the addition of a VLAN tag or the alteration of the user_priority.

Table A-10: Private Line and transparent VLAN tagging and traffic management modes

	Private Line		Transparent
	NOTC	PORT	NOTC	PORT	COSPORT
No. Services at 1 port¹	1	1	1	1
No. Services on Network²	1	1	1	1 to 4093
Max. CoS Support³	No	No	No	1 CoS/Port
Traffic Conditio-ning⁴	None	PIR PBS CIR CBS	None	PIR PBS CIR CBS
Packets Altered⁵	No	No	No	No

Notes:

The number of services at a port is the number of traffic conditioners used, except for the NOTC mode where there is 1 service with no traffic conditioner.
The number of services on a network is the total number of separate VLANids/default port tags allowed on the network in separate services times the number of traffic conditioners that are allowed for each VLANid/default port tag.
The maximum number of Classes of Service supported is the number that will be passed through any traffic conditioner on that port. For example, in 802.1TAG mode the PORT mode will allow all 4 CoS Levels to pass through a common traffic conditioner, whereas, in Transparent mode the PORT mode tags all traffic with the default CoS and therefore only a single CoS is supported.
The traffic conditioning parameters shown are those available via TL1. In a practical sense fewer parameters are needed to provision the service.
Packets are considered altered if the user packet that leaves the network at an egress Customer Port is not identical to the packet that entered the network at an ingress Customer Port. Packets are generally altered in 802.1TAG mode due to the addition of a VLAN tag or the alteration of the user_priority.

Metering (CIR and PIR)

Rate-shaped services offer a statistical multiplexing model that makes efficient use of shared bandwidth. Alcatel-Lucent 1665 DMX supports two of the primary forms of rate control. The two primary forms of rate control are rate limiting, and guaranteed rate services (plus various combinations of both).

Rate limiting is achieved using Peak Information Rate (PIR) provisioning. Guaranteed rate service is achieved using Committed Information Rate (CIR) provisioning. PIR institutes a limit, or "ceiling", of maximum bandwidth to be allocated to a particular customer at any time. CIR, on the other hand, provides a guaranteed minimum, or "floor" throughput even during periods of high congestion.

When SLAs are written using CIR, Excess Burst Size (PBS), and Committed Burst Size (CBS), they guarantee a CIR and CBS at a particular data rate. Traffic can be allowed to burst up to an excess burst size (PBS) beyond the CBS. This traffic will only be transmitted on a Best Effort basis. Any traffic above the PBS is discarded. In this type of SLA, PIR is equal to CIR. The CIR must always be less than the maximum bandwidth that the port can support. If either CIR or PBS is set to zero, service is effectively terminated.

The second method used to specify SLAs employs CBS, PIR, CIR, and PBS. Burst Time can also be used in place of PBS. With SLAs of this sort, PIR, CIR, PBS, and CBS must be provisioned.

The figure below details the flow of traffic through the QoS packet with on the LNW170 circuit packs. The ingress and egress functions of the switch are explained further below the figure. The DSCP Field on the ingress port. DSCP functions only on the LNW170, though DSCP.

Figure A-27: Flow and classifications of traffic through QoS packet switch

The Ingress Port functions are as follows:

Traffic Classification: Determines class of service (CoS), the criteria can be 802.1p user priority, DSCP, VLANid, or default value. Each class is mapped to an output queue. Internal management is classified into its own class.
Flow Classification: A flow is a grouping of traffic based on certain criteria. The flow classification determines which Traffic Conditioner is used and multiple flows can be aggregated at a single traffic conditioner. Criteria is based on packet header, input port, flow, physical port, VLANid, DSCP, and/or 802.1p user priority.
Traffic Conditioner: Traffic Conditioners perform the metering, policing, marking, and counting of ingress packets. The parameters are PIR, CIR, PBS, and CBS. Metering measures the data rate which determines wether the packets conform to the settings for the user/port. Packets are marked according to conformance level (this is an internal marking). Policing discards packets that exceed the PIR, PBS, or PBS (see Metering above). The conformance level determines the drop precedence (DP) for non-conforming packets.

Note: Flow Classification and Traffic Conditioning only apply to boundary ports. Once CoS and DP are determined at the boundary port, they are used consistently throughout the network. At internal ports, CoS and DP are then used to determine egress functions (i.e. dropping and queuing). For information on boundary and internal port demarcation, see the section below entitled Boundary versus Interior Ports.

The Egress Port functions are as follows:

Dropping: Also known as Egress Queueing, Dropping is based on conformance level and the fullness of the queue. The drop function takes into account the total allocation queue for a particular port only. There are two drop methods employed by Alcatel-Lucent 1665 DMX: Tail Drop and Weighted Random Early Detection (WRED). The tail drop method discards all packets exceeding the maximum queue size. It uses only one parameter: Maximum Queue Size. WRED dropping starts at the minimum threshold and increases up to the maximum. Two drop parameters govern WRED: Minimum Threshold and Maximum Threshold. The CoS parameter, Maximum Drop Probability, is also provisionable in the WRED method. packets labeled with a higher drop precedence (DP) are discarded prior to those with a lower drop precedence.
Scheduling: Scheduling allocates service for each queue. There are queues for each port: Expedited Forwarding (EF), Assured Forwarding (AF). A combination of two algorithms controls scheduling. Packets in the Strict Priority queue are transmitted first. Strict Priority is used for EF queue. Weighted Round Robin (WRR) ensures that the remaining bandwidth is allocated to each queue based on a provisioned weighting factor. WRR is used for the AF queues.

Egress functions support four classes of service (CoS). EF guaranteed low latency. There are three levels of AF offering various degrees of guaranteed delivery including best-effort. Packets are handled differently depending on wether they originated from Boundary or Interior ports.
Three Colors: RED: for packets that exceed peak rate limits.

Yellow: for packets that exceed committed rate limits.

Green: for packets within committed rate limits.