DLEP Credit-Based Flow Control Messages and Data ItemsLincoln LaboratoryMassachusetts Institute of Technology244 Wood StreetLexingtonMA02421-6426bcheng@ll.mit.eduLincoln LaboratoryMassachusetts Institute of Technology244 Wood StreetLexingtonMA02421-6426David.Wiggins@ll.mit.eduLabN Consulting, L.L.C.lberger@labn.net
This document defines new DLEP protocol Data Items that are used to
support credit-based flow control. The Data Items enable separate but
related functions: traffic classification and credit window control.
Traffic classification information is used to identify traffic flows
based on frame/packet content such as destination address. Credit
window control is used to regulate when data may be sent to an
associated virtual or physical queue. The Data Items are defined in
an extensible and reusable fashion. Their use will be mandated in
other documents defining specific DLEP extensions. This document also
introduces DLEP sub-data items.
The Dynamic Link Exchange Protocol (DLEP) is defined in . It provides the exchange of link related
control information between DLEP peers. DLEP peers are comprised
of a modem and a router. DLEP defines a base set of mechanisms as
well as support for possible extensions. DLEP defines Data Items
which are sets of information that can be reused in DLEP
messaging.
The base DLEP specification does not include any flow
identification beyond DLEP endpoints or flow control capability.
There are various flow control techniques theoretically possible
with DLEP. For example, a credit-window scheme for
destination-specific flow control which provides aggregate flow
control for both modem and routers has been proposed in , and a control plane pause
based mechanism is defined in .
This document defines DLEP Data Items and Messages which provide
flow identification, and a flow control mechanism for traffic sent
from a router to a modem. Flow control is provided using one or
more logical "Credit Windows", each of which will typically be
supported by an associated virtual or physical queue. Traffic
sent by a router will use traffic flow classification information
provided by the modem to identify which traffic is associated with
each credit window. In this case, a flow is identified based on
information found in a data plane header and one or more matches
are associated with a single flow. (For general background on
traffic classification see Section 2.3.)
Credit windows may be shared or dedicated on a per flow basis. The
Data Items are structured to allow for reuse of the defined
traffic classification information with non-credit window
applications as well as reuse of the credit window based flow
control with different traffic classification techniques.
This document defines traffic classification based on a DLEP
destination and flows identified by either DiffServ DSCPs (differentiated services codepoints) or IEEE
802.1Q Ethernet Priority Code Points
(PCP). The defined mechanism allows for credit windows to be shared
across traffic sent to multiple DLEP destinations and flows, or used
exclusively for traffic sent to a particular destination and/or flow.
The extension also supports the "wildcard" matching of any flow (DSCP
or PCP). Traffic classification information is provided such that it
can be readily extended to support other traffic classification
techniques, or be used by non-credit window related extensions, such
as or even
5-tuple IP flows.
Note that this document defines common Messages, Data Items and
mechanisms that are reusable. They are expected to be required by
DLEP extensions defined in other documents such as found in .
This document defines support for traffic classification using a
single new Data Item in for general
support and two new sub Data Items are defined to support
identification of flows based on DSCPs and PCPs. The document
supports credit window control by introducing two new DLEP
messages in , and five new DLEP Data
Items in .
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 when, and
only when, they appear in all capitals, as shown here.
The Traffic Classification Data Item is used to represent a list of
flows that may be used at the same time for traffic sent from a
router to a modem. The data plane information used to identify each
flow is represented in a separate sub Data Item. The Data Item and
Sub Data Item structure is intended to be independent of any
specific usage of the flow identification, e.g., flow control. The
Sub Data Item structure is also intended to allow for future traffic
classification types, e.g., 5-tuple flows. While the structure of
the Data Items is extensible, actual flow information is expected to
be used in an extension dependent manner. Support for DSCP and
PCP-based flows are defined via individual sub Data Items
below. Other types of flow identification, e.g., based on IP
protocol and ports, may be defined in the future via new sub Data
Items.
The list of flows contained in the Data Item can be used per sender
or shared across multiple senders. Each list of flows is identified
using a "Traffic Classification Identifier" or "TID" and is expected
to represent a valid combination of data plane identifiers that may
be used at the same time. Each flow is identified via a "Flow
Identifier" or "FID". Each FID is defined in a sub Data Item which
carries the data plane identifier or identifiers used to associate
traffic with the flow. A DLEP destination address is also needed to
complete traffic classification information used in extensions such
as flow control. This information is expected to be provided in an
extension specific manner. For example, this address can be provided
by a modem when it identifies the traffic classification set in a
Destination Up Message using the Credit Window Associate Data Item
defined in .
This sections defines the Traffic Classification Data Item. This
Data Item is used by a modem to provide a router with traffic
classification information. When an extension requires use of
this Data Item the Traffic Classification Data Item SHOULD be
included by a modem in any Session Initialization Response Message
that also indicates support for an extension that requires support
for the credit window control mechanisms defined in this document,
e.g., see . Updates to
previously provided traffic classifications or new traffic
classifications MAY be sent by a modem by including the Data Item
in Session Update Messages. More than one Data Item MAY be
included in a message to provide information on multiple traffic
classifiers.
The set of traffic classification information provided in the data
item is identified using a Traffic Classification Identifier, or
TID. The actual data plane related information used in traffic
classification is provided in a variable list of Traffic
Classification Sub Data Items.
The format of the Traffic Classification Data Item is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data Item Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Traffic Class. Identifier (TID)| Num SDIs | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Traffic Classification Sub Data Item 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: ... :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Traffic Classification Sub Data Item n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
TBA1Variable
Per Length
is the number of octets in the Data Item, excluding the Type and
Length fields.
A 16-bit unsigned integer identifying a traffic classification
set. There is no restriction on values used by a modem, and there
is no requirement for sequential or ordered values.
An 8-bit unsigned integer indicating the number of Traffic
Classification Sub Data Items included in the Data Item. A value
of zero (0) is allowed and indicates that no traffic should be
matched against this TID.
MUST be set to zero by the sender (a modem) and ignored by the
receiver (a router).
Zero or more Traffic Classification Sub Data Items of the format
defined below MAY be included. The number MUST match the value
carried in the Num SDIs field.
A router receiving the Traffic Classification Data Item MUST
locate the traffic classification information that is associated
with the TID indicated in each received Data Item. If no
associated traffic classification information is found, the router
MUST initialize a new information set using the values carried in
the Data Item. When associated traffic classification information
is found, the router MUST update the information using the values
carried in the Data Item. In both cases, a router MUST also
ensure that any data plane state, e.g., see , that is associated with the TID is updated
as needed.
All Traffic Classification Sub Data Items share a common format
that is patterned after the standard DLEP Data Item format, see
Section 11.3. There is no requirement
on, or meaning to sub Data Item ordering. Any errors or
inconsistencies encountered in parsing sub Data Items are
handled in the same fashion as any other Data Item parsing error
encountered in DLEP.
The format of the Traffic Classification Sub Data Item is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub Data Item Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value... :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A 16-bit unsigned integer that indicates the type and
corresponding format of the Data Item's Value field. Sub Data
Item Types are managed according to the IANA registry described
in .
Variable
Copying , Length is a 16-bit unsigned
integer that is the number of octets in the sub Data Item,
excluding the Type and Length fields.
The DiffServ Traffic Classification Sub Data Item is used to
identify the set of DSCPs that should be treated as a
single flow, i.e., receive the same traffic treatment. DSCPs are
identified in a list of DiffServ fields. An implementation that
does not support DSCPs and wants the same traffic treatment for
all traffic to a destination or destinations would indicate
0 DSCPs.
The format of the DiffServ Traffic Classification Sub Data Item
is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Must be two (2) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flow Identifier (FID) | Num DSCPs | DS Field 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DS Field 2 | ... | DS Field n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Variable
Length is defined above. For this Sub Data Item, it is
equal to three (3) plus the value of the Num DSCPs field.
A 16-bit unsigned integer representing the data plane
information carried in the sub Data Item that is to be used in
identifying a flow. The value of 0xFFFF is reserved and MUST
NOT be used in this field.
An 8-bit unsigned integer indicating the number of DSCPs
carried in the sub Data Item. A zero (0) indicates a (wildcard)
match against any DSCP value.
Each DS Field is an 8-bit whose definition is the same as .
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| DSCP | CU |
+---+---+---+---+---+---+---+---+
DSCP: differentiated services codepoint
CU: currently unused, MUST be zero
A router receiving the Traffic Classification Sub Data
Item MUST validate the information on receipt, prior to using
the carried information, including potentially updating the data
behavior as determined by the extension requiring the use of the
Sub Data Item. Validation failures MUST be treated as an error as
described above.
Once validated, the receiver MUST ensure that each DS Field
value is listed only once across the whole Traffic
Classification Data Item. Note, this check is across the Data
Item and not the individual sub Data Item. If the same DS Field
value is listed more than once within the same Traffic
Classification Data Item, the Data Item MUST be treated as an
error as described above.
The Ethernet Traffic Classification Sub Data Item is used to
identify the VLAN and PCPs that should be treated as a single
flow, i.e., receive the same traffic treatment. Ethernet Priority
Code Point support is defined as part of the IEEE 802.1Q tag format and includes a 3 bit "PCP"
field. The tag format also includes a 12 bit VLAN identifier
(VID) field. PCPs are identified in a list of priority fields. An
implementation that does not support PCPs and wants the same
traffic treatment for all traffic to a destination or destinations
would indicate 0 PCPs. Such an implementation could identify a
VLAN to use per destination.
The format of the Ethernet Traffic Classification
Sub Data Item is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Must be two (3) | Length (8) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flow Identifier (FID) |NumPCPs| VLAN Identifier (VID) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Pri. 1| Pri. 2| Pri. 3| Pri. 4| Pri. 5| Pri. 6| Pri. 7| Pri. 8|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Variable
Length is defined above. For this Sub Data Item, it is
equal to eight (8).
A 16-bit unsigned integer representing the data plane
information carried in the sub Data Item that is to be used in
identifying a flow. The value of 0xFFFF is reserved and MUST
NOT be used in this field.
A 16-bit unsigned integer representing the data plane
information carried in the sub Data Item that is to be used in
identifying a flow.
A 12-bit unsigned integer field indicating the VLAN to be
used in traffic classification. A value of zero (0) indicates
that the VID is to be ignored and any VID is to be accepted during
traffic classification.
Each Priority Field is an 4-bit whose definition includes the
PCP field defined in
0 1 2 3
+---+---+---+---+
| PCP |DEI|
+---+---+---+---+
PCP: Priority code point
DEI: currently unused, MUST be zero
A router receiving the Traffic Classification Sub Data
Item MUST validate the information on receipt, prior to the using
the carried information, including potentially updating the data
behavior as determined by the extension requiring the use of the
Sub Data Item. Validation failures MUST be treated as an error as
described above.
Once validated, the receiver MUST ensure that each Priority
Field value is listed only once across the whole Traffic
Classification Data Item. Note, this check is across the Data
Item and not the individual sub Data Item. If the same Priority
Field value is listed more than once within the same Traffic
Classification Data Item, the Data Item MUST be treated as an
error as described above.
This section defines additions to DLEP used in credit based flow
control. In addition to the Traffic Classification Data Item, two
new messages and five Data Items are defined to support credit
window control. The use of credit window control impacts the data
plane.
The credit window control mechanisms defined in this document
support credit based flow control of traffic sent from a router to a
modem. The mapping of specific flows of traffic to a particular
credit window is based on the Traffic Classification Data Item
defined in . Both types of DLEP endpoints,
i.e., a router and a modem, negotiate the use of extension during
session initialization, e.g., see . When using
credit windows, data traffic is only allowed to be sent by the
router to the modem when there are credits available.
Credits are managed on a per logical "Credit Windows" basis. Each
credit window can be thought of as corresponding to a queue within a
modem. Credit windows may be shared across, or dedicated to,
destinations and data plane identifiers, e.g., DSCPs, at a
granularity that is appropriate for a modem's implementation and its
attached transmission technology. As defined below, there is a
direct one-for-one mapping of credit windows to flows as identified
by FIDs carried within the Traffic Classification Data Item. Modems
pass to the router information on their credit windows and FIDs
prior to a router being able to send data when an extension
requiring the use of credit window control is used. In addition to
the traffic classification information associated with an FID,
routers provide an initial credit window size, as well as the
maximum size of the logical queue associated with each credit
window. The maximum size is included for informative and potential
future uses.
Modems provide an initial credit window size at the time of "Credit
Window Initialization". Such initialization can take place during
session initiation or any point thereafter. It can also take place
when rate information changes. Additional "Credit Grants", i.e.,
increments to Credit Window size, are provided using a Destination
Up or the new "Credit Control" Message. A router provides its view
of the Credit Window, which is known as "Status", in Destination Up
Response and the new "Credit Control Response" Messages. Routers
can also request credits using the new "Credit Control" Message.
When modems provide credits to a router, they will need to take into
account any overhead of their attached transmission technology and
map it into the credit semantics defined in this document. In
particular, the credit window is defined below to include per frame
(packet) MAC headers, and this may not match the actual overhead of
the modem attached transmission technology. In that case a direct
mapping, or an approximation will need to be made by the modem to
provide appropriate credit values.
Actual flows of traffic are mapped to credit windows based on flow
identification information provided by modems in the Traffic
Classification Data item defined in . This
data item supports traffic classification on a per destination or
more fine grain level. Routers use the combination of the DLEP
identified destination and flow information associated with a credit
window in order to match traffic they send to specific credit
windows.
When a destination becomes reachable, a modem "Associates"
(identifies) the appropriate traffic classification information via
the TID to be used for traffic sent by the router to that
destination. As defined, each credit window has a corresponding
FID. This means that the use of FIDs, TIDs and the association of a
TID to a DLEP destination enables a modem to share or dedicate
resources as needed to match the specifics of its implementation and
its attached transmission technology.
The defined credit window control has similar objectives as the
control found in .
One notable difference from that credit control is that in this
document, credits are never provided by the router to the modem.
When credit windowing is used, a router MUST NOT send data traffic
to a modem for forwarding when there are no credits available in the
associated Credit Window. This document defines credit windows in
octets. A credit window value MUST be larger than the number of
octets contained in a packet, including any MAC headers used between
the router and the modem, in order for the router to send the packet
to a modem for forwarding. The credit window is decremented by the
number of sent octets.
A router MUST identify the credit window associated with traffic
sent to a modem based on the traffic classification information
provided in the Data Items defined in this document. Note that
routers will typically view a DLEP destination as the next hop MAC
address.
Two new messages are defined in support for credit window control:
the Credit Control and the Credit Control Response Message. Sending
and receiving both message types is REQUIRED to support the credit
window control defined in this document.
Credit Control Messages are sent by modems and routers. Each
sender is only permitted to have one message outstanding at one
time. That is, a sender (i.e., modem or router) MUST NOT send a
second or any subsequent Credit Control Message until a Credit
Control Response Message is received from its peer (i.e., router
or modem).
Credit Control Messages are sent by modems to provide credit
window increases. Modems send credit increases when there is
transmission or local queue availability that exceeds the credit
window value previous provided to the router. Modems will need to
balance the load generated by sending and processing frequent credit
window increases against a router having data traffic available to send,
but no credits available.
Credit Control Messages MAY be sent by routers to request
credits and provide window status. Routers will need to
balance the load generated by sending and processing frequent credit
window requests against a having data traffic available to send,
but no credits available.
The Message Type value in the DLEP Message Header is set to TBA2.
A message sent by a modem, MUST contain one or more
Credit Window Grant Data Items as defined below in . A router receiving this message MUST
respond with a Credit Control Response Message.
A message sent by a router, MUST contain one or more Credit Window
Request Data Items defined below in and SHOULD contain a Credit Window
Status Data Item, defined in ,
corresponding to each credit window request. A modem receiving
this message MUST respond with a Credit Control Response
Message based on the received message and Data Item and the
processing defined below, which will typically result in credit
window increments being provided.
Specific processing associated with each Credit Data Item is
provided below.
Credit Control Response Messages are sent by routers to report
the current Credit Window for a destination. A message sent by
a router, MUST contain one or more Credit Window Status Data
Items as defined below in .
Specific receive processing associated with the Credit Window
Status Data Item is provided below.
Credit Control Response Messages sent by modems MUST contain one
or more Credit Window Grant Data Items. A Data Item for every
Credit Window Request Data Item contained in the corresponding
Credit Control Response Message received by the modem MUST be
included. Each Credit Grant Data Item MAY provide zero or more
additional credits based on the modem's transmission or local
queue availability. Specific receive processing associated with
each Grant Data Item is provided below.
The Message Type value in the DLEP Message Header is set to TBA3.
Five new Data Items are defined to support credit window control.
The Credit Window Initialization
Data Item is used by a modem to identify a credit window and set its
size.
The Credit Window Association
Data Item is used by a modem to identify which traffic classification
identifiers (flows) should be used when sending traffic to a particular DLEP
identified destination.
The Credit Window Grant is used by a modem to provide additional
credits to a router.
The Credit Request is used by a router to request additional
credits.
The Credit Window Status is used to advertise the sender's view of
number of available credits for state synchronization purposes.
Any errors or inconsistencies encountered in parsing Data Items
are handled in the same fashion as any other data item parsing error
encountered in DLEP, see . In particular, the
node parsing the Data Item MUST terminate the session with a
Status Data Item indicating Invalid Data.
The Credit Window Initialization Data Item is used by a modem to
identify a credit window and set its size. This Data Item
SHOULD be included in any Session Initialization Response
Message that also indicates support for an extension that
requires support for the credit window control mechanisms
defined in this document, e.g., see . Updates to
previously identified credit windows or new credit windows MAY
be sent by a modem by including the Data Item in Session Update
Messages. More than one data item MAY be included in a message
to provide information on multiple credit windows.
The Credit Window Initialization Data Item identifies a credit
window using a Flow Identifier, or FID. It also provides the
size of the identified credit window. Finally, a queue size (in
bytes) is provided for informational purposes. Note that to be
used, a FID must be defined within a Traffic Classification Data
Item and the associated TID must be provided via a Credit Window
Association Data Item.
The format of the Credit Window Initialization Data Item is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data Item Type | Length (16) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flow Identifier (FID) | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Credit Value :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Credit Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Scale | Credit Window Size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
TBA4 16
Per Length
is the number of octets in the Data Item. It MUST be equal to
sixteen (16).
A flow identifier as defined by the Traffic Classification
Data Item. The FID also uniquely identifies a credit
window.
MUST be set to zero by the sender (a modem) and ignored by the
receiver (a router).
A 64-bit unsigned integer representing the credits, in octets, to
be applied to the Credit Window. This value includes MAC
headers as seen on the link between the modem and router.
An 8-bit unsigned integer indicating the scale used in the Credit Window
Size fields. The valid values are:
Value Scale
------------
0 B - Bytes (Octets)
1 KB - Kilobytes (B/1024)
2 MB - Megabytes (KB/1024)
3 GB - Gigabytes (MB/1024)
A 24-bit unsigned integer representing the maximum size, in the
octet scale indicated by the Scale field, of the associated credit
window.
A router that receives a Credit Window Initialization Data Item
MUST ensure that the FID field value has been provided by the
modem in a Traffic Classification Data Item carried in either
the current or previous message. If the FID cannot be found the
router SHOULD report or log this information. Note that
no traffic will be associated with the credit window in this
case. After FID validation, the router MUST locate the credit
window that is associated with the FID indicated in each
received Data Item. If no associated credit window is found,
the router MUST initialize a new credit window using the values
carried in the Data Item. When an associated credit window is
found, the router MUST update the credit window and associated
data plane state using the values carried in the Data Item. It
is worth noting, that such updates can result in a credit window
size being reduced, for example, due to a transmission rate
change on the modem.
The Credit Window Associate Data Item is used by a modem to
associate traffic classification information with a destination.
The traffic classification information is identified using a TID
value that has previously been sent by the modem or is listed
in a Traffic Classification Data Item carried in the
same message as the Data Item.
A single Credit Window Associate Data Item MUST be included in all
Destination Up and Destination Update Messages sent by a modem when
the credit window control defined in this document is used. Note
that a TID will not be used unless it is listed in a Credit Window
Associate Data Item.
The format of the Credit Window Associate Data Item is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data Item Type | Length (2) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Traffic Class. Identifier (TID)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
TBA5 2
Per Length
is the number of octets in the Data Item. It MUST be equal to
two (2).
A 16-bit unsigned integer identifying a traffic
classification set that has been identified in a Traffic
Classification Data Item, see .
A router that receives the Credit Window Associate Data Item MUST
locate the traffic classification information indicated by the
received TID. If no corresponding information can be located, the
Data Item MUST be treated as an error as described above. Once the
traffic classification information is located, it MUST be associated
with the destination and the router MUST ensure that any data plane
state, see , that is associated with the
TID and its corresponding FIDs is updated as needed.
The Credit Window Grant Data Item is used by a modem to
provide credits to a router. One or more Credit Window Grant Data
Items MAY be carried in the DLEP Destination Up, Destination Announce
Response, Destination Update, Credit Control Messages, and Credit
Control Response Messages. Multiple
Credit Window Grant Data Items in a single message are used to
indicate different credit values for different credit windows. In all
message types, this Data Item provides an additional number of octets
to be added to the indicated credit window. Credit windows are
identified using FID values that have been previously been
sent by the modem or are listed in a Credit Window Initialization
Data Item carried in the same messages as the Data Item.
The format of the Credit Window Grant Data Item is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data Item Type | Length (12) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flow Identifier (FID) | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Additional Credits :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Additional Credits |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
TBA612
Per , Length
is the number of octets in the Data Item. It MUST be equal to
twelve (12).
A flow identifier as defined by the Traffic Classification
Data Item. The FID also uniquely identifies a credit
window.
A 64-bit unsigned integer representing the credits, in octets, to
be added to the Credit Window. This value includes MAC
headers as seen on the link between the modem and router. A value
of zero indicates that no additional credits are being provided.
When receiving this Data Item, a router MUST identify the credit
window indicated by the FID. If the FID is not known to the router,
it SHOULD report or log this information and discard the Data Item.
It is important to note that while this Data Item can be received in a
destination specific message, credit windows are managed independently
from the destination identified in the message carrying this Data
Item, and the indicated FID MAY even be disjoint from the identified
destination.
Once the credit window is identified, the credit window size MUST be
increased by the value contained in the Additional Credits field. If
the increase results in a window overflow, i.e., the size of the
credit window after the increase is smaller than the original credit
window size, the Credit Window must be set to its maximum
(0xFFFFFFFFFFFFFFFF).
No response is sent by the router to a modem after processing a Credit
Window Grant Data Item received in a Credit Control Response Message.
In other cases, the receiving router MUST send a
Credit Window Status Data Item or items reflecting the
resulting Credit Window value of the updated credit window. When the
Credit Grant Data Item is received in a Destination Up Message, the
Credit Window Status Data Item(s) MUST be sent in the
corresponding Destination Up Response Message. Otherwise, a
Credit Control Message MUST be sent.
The Credit Window Status Data Item is used by
a router to report the current credit window size to its peer modem. One
or more Credit Window Status Data Items MAY be carried in a
Destination Up Response Message or a Credit Control Response Message.
As discussed above, the Destination Up Response Message is used when
the Data Item is sent in response to a Destination Up Message, and
the Credit Control Response Message is sent in response to a Credit
Control Message. Multiple Credit Window Status Data Items in a
single message are used to indicate different sizes of different
credit windows. Similar to the Credit Window Grant, credit windows
are identified using FID values that have been previously been sent
by the modem.
The format of the Credit Window Status Data Item is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data Item Type | Length (12) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flow Identifier (FID) | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Credit Window Size :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Credit Window Size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
TBA712
Per Length
is the number of octets in the Data Item. It MUST be equal to
twelve (12).
A flow identifier as defined by the Traffic Classification
Data Item. The FID also uniquely identifies a credit
window.
A 64-bit unsigned integer, indicating
the current number of credits, in octets, available for the
router to send to the modem. This is referred to as the
Modem Receive Window in .
When receiving this Data Item, a modem MUST identify the credit
window indicated by the FID. If the FID is not known to the modem,
it SHOULD report or log this information and discard the Data Item. As
with the Credit Window Grant Data Item, the FID MAY be unrelated to
the Destination indicated in the message carrying the Data Item.
Once the credit window is identified, the modem SHOULD check the
received Credit Window Size field value against the outstanding credit
window's available credits at the time the most Credit Window
Initialization or Grant Data Item associated with the indicated FID
was sent. If the values significantly differ, i.e., greater than can
be accounted for based on observed data frames, then the modem SHOULD
send a Credit Window Initialization Data Item to reset the associated
credit window size to the modem's current view of the available
credits. As defined above, Credit Window Initialization Data Items are
sent in Session Update Messages. When multiple Data Items need to be
sent, they SHOULD be combined into a single message when possible.
Alternatively, and also in cases where there are small differences,
the modem MAY adjust the values sent in Credit Window Grant Data Items
to account for the reported Credit Window.
The Credit Window Request Data Item is used by a router to
request additional credits for particular credit windows. Credit
Window Request Data Items are carried in Credit Control Messages, and
one or more Credit Window Request Data Items MAY be present in a
message.
Credit windows identified using a FID as defined above in . Multiple FIDs MAY be present to allow for the
case where the router identifies that credits are needed in multiple
credit windows. A special FID value, as defined below, is used to
indicate that a credit request is being made across all queues.
The format of the Credit Window Request Data Item is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data Item Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flow Identifier (FID) | ... :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: ... | Flow Identifier (FID) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
TBA8Variable
Per Length
is the number of octets in the Data Item, excluding the Type and
Length fields. It will equal the number of FID
fields carried in the Data Item times 2 and MUST be at least 2.
A flow identifier as defined by the Traffic Classification
Data Item. The FID also uniquely identifies a credit
window.
The special value of 0xFFFF indicates that the
request applies to all FIDs.
A modem receiving this Data Item MUST provide a Credit Increment for
the indicated credit windows via Credit Window Grant Data Items
carried in a new Credit Control Message. Multiple values and queue
indexes SHOULD be combined into a single Credit Control Message when
possible. Unknown FID values SHOULD be reported or logged and then
ignored by the modem.
This section provides several network management guidelines
to implementations supporting the credit window mechanisms defined
in this document.
Modems MAY support the configuration of the number of credit
windows (queues) to advertise to a router.
Routers may have limits on the number of queues that they can
support and, perhaps, even limits in supported credit window
combinations, e.g., if per destination queues can even be
supported at all. When modem-provided credit window information
exceeds the capabilities of a router, the router MAY use a subset of
the provided credit windows. Alternatively, a router MAY reset the
session and indicate that the extension is not supported. In either
case, the mismatch of capabilities SHOULD be reported to the user via
normal network management mechanisms, e.g., user interface or error
logging.
The data items defined in this document will only be used when
extensions require their use.
This document introduces credit window control and flow mechanisms
to DLEP. These mechanisms do not inherently introduce any
additional threats above those documented in . The approach taken to Security in that document
applies equally to the mechanism defined in this document.
This document requests the assignment of several values by IANA. All
assignments are to registries defined by .
This document requests 2 new assignments to the DLEP Message Registry
named "Message Values" in the range with the "Specification Required"
policy. The requested values are as follows:
Type CodeDescriptionTBA2Credit ControlTBA3Credit Control Response
This document requests the following new assignments to the DLEP Data Item
Registry named "Data Item Type Values" in the range with the "Specification
Required" policy. The requested values are as follows:
Type CodeDescriptionTBA1Traffic ClassificationTBA4Credit Window InitializationTBA5Credit Window AssociationTBA6Credit Window GrantTBA7Credit Window StatusTBA8Credit Window Request
Upon approval of this document, IANA is requested to create a new
DLEP registry, named "Sub Data Item Type Values". The registry
shall identify the type code value, the Data Item which may use the
value, and a description of the value. While the same value may be
reused in different Data Items, this is not recommended at this time.
The following table provides initial registry values and the
defined policies that should apply to the registry:
Type CodeValid Data ItemsDescription0N/AReserved1N/AReserved (for pause sub-DI)2DiffServ Traffic ClassificationDiffServ Traffic Classification3Ethernet Traffic ClassificationEthernet Traffic Classification4-65407Specification Required65408-65534Private Use65535Reserved
IEEE Standard for Local and metropolitan area networks--Bridges and Bridged Networks
IEEE
This standard specifies how the Media Access Control (MAC) Service is supported by Bridged Networks, the principles of operation of those networks, and the operation of MAC Bridges and VLAN Bridges, including management, protocols, and algorithms
The sub Data Item format was inspired by Rick Taylor's "Data Item
Containers". He also proposed the separation of credit windows
from traffic classification at IETF98. Many useful comments were
received from contributors to the MANET working group. This
document was derived from as a result of
discussions at IETF101.