Populating LFIB with LDP Assigned/Learned Labels

1
Lecture 8
2
Populating LFIB with LDP Assigned/Learned Labels

• Changes in the LFIB may be triggered routing or
  label advertisements events.
• Routing events corresponds e.g., IGP learns a new
  prefix or next hop for an existing prefix
  changes.
• Label advertisements corresponds to reception of
  Label Request and/or Label Mapping messages.

3
Summary - LDP Messages

• Address is used to advertise its interfaces
  addresses on establishment of new LDP session or
  when interface comes up.
• Label Request is used to request label-to-FEC
  mapping from a downstream LSR
• Label Mapping is used to advertise label-to-FEC
  binding in response either to Label Request (DoD)
  or unsolicited (DU).
• Label Release is used to inform the peer that
  the sender no longer needs a previously received
  or requested label.
• Label Withdraw is used to withdraw a previously
  advertised label.
• Note all LDP messages except Hello use TCP as a
  reliable transport.

4
Label Request Message
The encoding for the Label Request Message 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
-------------------------
------- 0 Label Request (0x0401)
Message Length
-------------------------
------- Message
ID
-------------------------
------- FEC TLV

-------------------------
------- Optional
Parameters
---------- --------------
------------------
5
Label Mapping Message
The encoding for the Label Mapping Message 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
-------------------------
------- 0 Label Mapping (0x0400)
Message Length
-------------------------
------- Message
ID
-------------------------
------- FEC TLV

-------------------------
------- Label
TLV
-------------------------
------- Optional
Parameters
-------------------------
-------
6
RSVP
Big Picture
7
Resource ReSerVation Protocol (RSVP)

• RSVP is a signaling protocol for requesting QoS
  for IP data flows.
• RSVP is NOT a routing protocol rather utilizes
  services of the unicast and multicast IP routing.
• RSVP messages are encapsulated in IP packets and
  hop-by-hop routed based on IP destination
  address.
• RSVP reservation requests are for simplex data
  flows.
• Two reservation requests are required for
  bi-directional data flows

8
RSVP Session

• RSVP session is described in terms three
  parameters (DestAddress, ProtocolId, DestPort)
• DestAddress
• IP destination address of the data packets
• ProtocolId
• IP protocol ID
• DestPort
• Destination TCP/UDP port

9
Data Microflow

• A single instance of an application-to-application
  flow of packets which is identified by
• Source IP address,
• Source Port,
• Destination IP address
• Destination Port

10
RSVP Reservation Model

• In RSVP, QoS reservation request is initiated by
  the receiver.
• Receiver-oriented reservation model is motivated
  by several factors e.g.
• Scalability (need to support larger number of
  users in multicast applications)
• Flexibility (e.g., to support receivers with
  different media formats)
• When an application in the receiver has some data
  to send,
• a request is passed from application to the RSVP
  process (protocol stack)
• RSVP protocol builds a message to make a QoS
  request
• RSVP reservation request is carried to all
  routers along the reverse direction of data flow
  to the source
• each router along allocated/reserves the
  requested QoS

11
RSVP Reservation Model
R2
RSVP Reservation Request
RSVP Reservation Request
Data flow
Sender
Receiver
R3
R2
R1
12
Differentiated QoS Mechanisms

• The requested QoS for a given data flow is
  enabled through set of mechanisms that are
  collectively referred to as traffic management
  functions.
• Connection Admission Control (CAC)
• CAC decides whether to accept or reject a
  reservation request.
• CAC is applies during signaling of the
  reservation request.
• Depending upon the router/switch architecture and
  the point of congestion, CAC function can be
  applied in ingress direction (e.g., ingress to
  switch fabric), egress (e.g., output link), or
  both ingress/egress points in the router/switch.
• Output link bandwidth CAC is the most widely used
  form.

13
Differentiated QoS Mechanisms

• Packet classification
• An entity that selects packets based on the
  contents of packet header according to defined
  rules.
• Metering (policing)
• The process of measuring the temporal (e.g.,
  arrival rate) of a traffic stream selected by a
  classifier. Commonly used metering (policing)
  method is known as leaky-bucket algorithm.
• The metered traffic may be marked, shaped, or
  dropped.

14
Differentiated QoS Mechanisms

• Marking
• The process of setting the differentiated service
  (DS) code point (i.e., TOS field) in a packet
  based on defined rules.
• For example, if the traffic exceeds the
  negotiated SLA, it may be remarked with lower
  priority.
• Shaping
• The process of delaying packets within a traffic
  stream to cause them to conform to some
  predefined profile (or contract).
• For example, the egress traffic from a node may
  be shaped to leaky-bucket algorithm.

15
Differentiated QoS Mechanisms

• Packet Scheduling
• The process of delaying packets within a traffic
  stream to cause them to conform to some
  predefined profile (or contract).
• The process of packets transmission where the
  packet departure are scheduled based on priority
  and/or to enable share/guarantee bandwidth
• Examples of commonly used schedulers include
• Strict priority
• Round-Robin (RR)
• Weighted Round-Robin (WRR)
• Weighted Fair Queuing (WFQ)
• Shaper is a special type of scheduler.

16
Guaranteed Service

• Guaranteed service requires end-to-end bandwidth
  and delay guarantees.
• For example, real-time applications such as voice
  need guaranteed service.
• Controlled-load service can tolerate certain
  level of packet loss and delay. Controlled-load
  service is expected to receiver better service
  than the traditional best effort services as the
  network load increases.
• For example, adaptive real-time applications
  fall under this category.
• Best-effort service does not require end-to-end
  bandwidth and delay guarantees.
• For example, data applications.

17
FLOWSPEC Object

• RSVP reservation request is described in terms of
  a pair of objects namely FLOWSPEC and
  FILTERSPEC. Collectively, this pair of objects
  are referred to as the flow descriptor.
• The FLOWSPEC object carries information that is
  required for making a reservation (from
  receivers perspective).
• When making a reservation for a guaranteed
  service, FLOWSPEC object contains traffic and QoS
  such as data rate and delay parameters.

18
FLOWSPEC Object

• TSpec specifies the traffic parameters such as
  peak data rate (p), token bucket rate (r) (i.e.,
  average data rate), token bucket size (b)
• RSpec specifies the required level of QOS and
  consists of parameters such as rate R (bytes/sec)
  and a slack term (S) in microseconds
• TSpec is used to program metering or policing
  entity.
• RSpec is used to perform CAC and program the
  packet scheduler.

19
FLOWSPEC Object (guaranteed service)
31 24 23 16 15
8 7 0 ----------
---------------------- 1
0 (a) Unused 10
(b) ------------
-------------------- 2
2 (c) 0 reserved 9 (d)
--------------
------------------ 3
127 (e) 0 (f) 5 (g)
---------------
----------------- 4
Token Bucket Rate r (32-bit IEEE floating point
number) ---------------
----------------- 5
Token Bucket Size b (32-bit IEEE floating point
number) ---------------
----------------- 6
Peak Data Rate p (32-bit IEEE floating point
number) -------------
------------------- 7
Minimum Policed Unit m (32-bit integer)
---------------
----------------- 8
Maximum Packet Size M (32-bit integer)
---------------
----------------- 9
130 (h) 0 (i) 2 (j)
----------------
---------------- 10 Rate
R (32-bit IEEE floating point number)
-----------------
--------------- 11 Slack
Term S (32-bit integer)
------------------
--------------
TSpec
RSpec
20
FLOWSPEC Object (controlled-load service)
31 24 23 16 15
8 7 0 ----------
---------------------- 1
0 (a) reserved 7
(b) ------------
-------------------- 2
5 (c) 0 reserved 6 (d)
--------------
------------------ 3
127 (e) 0 (f) 5 (g)
---------------
----------------- 4
Token Bucket Rate r (32-bit IEEE floating point
number) ---------------
----------------- 5
Token Bucket Size b (32-bit IEEE floating point
number) ---------------
----------------- 6
Peak Data Rate p (32-bit IEEE floating point
number) -------------
------------------- 7
Minimum Policed Unit m (32-bit integer)
---------------
----------------- 8
Maximum Packet Size M (32-bit integer)
---------------
-----------------
TSpec