Quality of Service

Overview

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

Peak information rate (PIR) control on LNW66 circuit packs

The LNW66 circuit packs support a provisionable PIR rate limiting mechanism for traffic entering the SONET network. A PIR value, in multiples of 1 Mbps, can be provisioned per VLAN for traffic leaving a VCG toward the SONET network. Traffic in excess of the provisioned value for each VLAN is dropped. The PIR capability applies to all tagging modes supported by the listed circuit packs.

The PIR policer uses a leaky bucket mechanism with a provisionable burst size and credit interval. The burst size determines how many tokens get put into the bucket each time it is replenished. This determines the length of a traffic burst that can be tolerated before packets are discarded. The credit interval determines the frequency with which the bucket is replenished. The burst size and credit interval parameters affect policing for all ports (in Private Line mode), all VLANs (in 802.1Q mode) or all port tags (in transparent mode) on a particular Ethernet circuit pack.

When sending data from a Gigabit Ethernet circuit pack, through the SONET network to a Fast Ethernet circuit card, the function described above is slightly different. With this configuration, the worst case is that a number of bytes equal to the full size of the token bucket in the GbE circuit pack will be sent using whatever SONET bandwidth has been provisioned (approximately 1 Gb/s in the worst case) to the Fast Ethernet card. The egress FE LAN port is limited to sending the data out at 100 Mb/s. If the rapid arrival of a token bucket's worth of bytes exceeds the limited egress buffering capacity of the FE LAN port, packets are dropped. This loss of packets can be minimized by minimizing the number of bytes in the token bucket at the GbE sending end by setting the smallest practical credit interval and burst size.

For more information, see Metering (CIR and PIR).

Adding tokens

Every credit interval, tokens are added to the token bucket for each VLAN/Port TAG/LAN port for which a PIR is provisioned. Each token represents 1 byte. (One credit interval is provisioned per circuit pack, and the provisioned credit interval applies to all VLANs/Port TAGs/LAN ports on that circuit pack. The credit interval is a multiple of 524.288s; the multiple is determined by the provisionable credit interval parameter.)

The number of available tokens (A) in the token bucket for each VLAN/Port TAG/LAN port is increased by, at most (PIR*credit interval)/8 each credit interval. PIR is the provisioned PIR in Mbps, and credit interval is the provisioned credit interval for the circuit pack. The divisor, 8, is required to convert from bits to bytes.

The number of available tokens (A) in each token bucket is subject to a maximum, which is determined by the provisioned PIR, the provisioned credit interval, and the provisioned maximum burst parameter. So each credit interval (A) = min (A + (PIR*credit interval)/8, BRST*(PIR*credit interval)/8).

The maximum burst represents the maximum size (in bytes) of the burst (above the PIR) that is passed by the policer. That is, a burst of this size (or smaller) is allowed through the policer if the token bucket for the VLAN/Port TAG/LAN port is full (for example, because no packets have been processed for BRST credit intervals). If a burst of this size is passed, then the token bucket is emptied and another burst will not be allowed through the policer until enough tokens have been accumulated in the token bucket. Another way to look at this is that the policer will pass a burst of packets above the PIR, as long as the long term average is no more than the provisioned PIR, where long term is defined as BRST*credit_interval.

Removing tokens

When a packet arrives, the token bucket for the associated VLAN/Port TAG/LAN port is checked. If no tokens are available for the VLAN/Port TAG/LAN port, then the packet is discarded. If tokens are available, the packet is forwarded and the number of available tokens for that VLAN/Port TAG/LAN port is decreased by the packet size.

If A >= 1 A = A - packet size, forward the packet, else discard the packet.

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.

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:

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-4: Allowed traffic management modes per port type

VLAN Tagging Mode

Port Type

Traffic Management Mode

LNW170

Private Line

Boundary Port 1

NOTC

PORT

Interior Port 1

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:

  1. 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-5: 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:

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

Table A-6: 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-7: 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-8: 802.1 VLAN tagging and traffic management modes

802.1TAG

NOTC

PORT

TAGPORT

COSPORT

COSTAG- PORT

No. Services at 1 port 1

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 Network 2

1

1 to 4093

1 to 4093

1 to 16,372

1 to 16,372

Max. CoS Support 3

No

4 CoS/Port

4 CoS/VLAN

4 CoS/Port

4 CoS/VLAN

Traffic Conditio-ning 4

None

PIR

PBS

CIR

CBS

PIR

PBS

CIR

CBS

PIR

PBS

CIR

CBS

PIR

PBS

CIR

CBS

Packets Altered 5

Maybe untag'd

Maybe

VLANid

user_priority

Maybe

VLANid

user_priority

Maybe

VLANid

user_priority

Maybe

VLANid

user_priority

Notes:

  1. 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.

  2. 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.

  3. 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.

  4. The traffic conditioning parameters shown are those available via TL1. In a practical sense fewer parameters are needed to provision the service.

  5. 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-9: Private Line and transparent VLAN tagging and traffic management modes

Private Line

Transparent

NOTC

PORT

NOTC

PORT

COSPORT

No. Services at 1 port 1

1

1

1

1

No. Services on Network 2

1

1

1

1 to 4093

Max. CoS Support 3

No

No

No

1 CoS/Port

Traffic Conditio-ning 4

None

PIR

PBS

CIR

CBS

None

PIR

PBS

CIR

CBS

Packets Altered 5

No

No

No

No

Notes:

  1. 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.

  2. 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.

  3. 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.

  4. The traffic conditioning parameters shown are those available via TL1. In a practical sense fewer parameters are needed to provision the service.

  5. 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.

View the figure

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-33: Flow and classifications of traffic through QoS packet switch
Flow and classifications of traffic through QoS packet switch+

The Ingress Port functions are as follows:

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:

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