1
IMIC, 8/30/99
Constraint
-
Based Unicast and Multicast:
Practical Issues
Bala Rajagopalan
NEC C&C Research Labs
Princeton, NJ
braja@ccrl.nj.nec.com
2
IMIC, 8/30/99
What is Constraint
-
Based Routing?
•
Includes QoS
-
based routing and policy routing
•
New jargon to establish technical territory
•
Devised in the context of MPLS LSPs, but applies to microflows also
(generically, “flows”)
Flow with BW,
Delay, Loss &
Policy
Requirements
Link with bw, delay, loss
properties
Network with
bw, delay, loss
properties
Inter
-
domain
routing policies
Source
Dest
3
IMIC, 8/30/99
A Methodology for IP Network Design
Flow
Routing
Node
-
Pair Traffic
Demands & Initial
Topology
Link Capacity
Determination
Traffic Flow
on Links
Scheduling &
Buffering Scheme
Topology Optimization
Network Topology
& Routing
•
Constraint
-
based routing capability results in efficient design and resource utilization
4
IMIC, 8/30/99
Traffic Engineering and Constraint Based Routing
•
Current
TE
goal
is
to
map
traffic
onto
the
network
such
that
available
resources
are
utilized
efficiently
and
QoS
requirements
of
traffic
is
satisfied
•
MPLS
LSPs
are
envisioned
for
creating
virtual
trunks
that
carry
traffic
between
node
pairs
(equivalent
of
frame
-
relay
or
ATM
PVCs)
.
LSPs
isolate
resources
for
different
flow
aggregates
LSP 1
LSP 2
LSP 3
Microflows within an LSP
Routing constraints:
•
Resource requirement
•
Priority & Preemption
•
Policy
•
Resiliency requirement
Re
-
optimization of routing
5
IMIC, 8/30/99
Service Models (1) : VPN
•
Customer provides point
-
to
-
point demands and QoS requirements
•
Service provider capacity engineers and establishes virtual trunks (LSPs)
SP Network
Internet
Virtual Trunk
6
IMIC, 8/30/99
Service Model (2) : Diffserv
•
Service provider establishes SLAs with customers
–
SLAs indicate service quality based on traffic parameters
–
SLAs need not require customer specification of traffic matrix
Network design is difficult
SLA1
SLA2
SLA3
SLA4
SP1
SP2
source
dest
Traffic from source to dest must
receive treatment as per SLA1,
even though it goes through a
foreign SP. Also, dest may not be
known apriori.
7
IMIC, 8/30/99
Traffic Engineering for Diffserv
•
In principle:
–
Derive
point
-
to
-
point
demands
from
SLAs
and
traffic
measurements
–
Determine
virtual
trunking
requirements
between
node
pairs
–
Establish
trunks
using
CBR
dest
SLA1
SLA2
SLA3
SLA4
SP1
SP2
source
Virtual Trunks
8
IMIC, 8/30/99
Constraint
-
Based Routing Model in Summary
•
Given
:
Network
topology,
resource
availability,
policy
and
other
attributes
of
nodes
and
links
•
Flows
:
Aggregated
microflows
or
virtual
trunks
•
Dynamism
:
Keep
track
of
network
state
changes
;
dynamic
rerouting
of
flows
after
topological
changes
;
redundant
paths
and
load
-
balancing?
•
Routing
architecture
:
Distributed
•
Route
computation
:
Based
on
apriori
notions
of
optimization
of
resource
usage,
traffic
parameters,
routing
metrics,
etc
.
•
Route
computation
trigger
:
By
operator
using
offline
mechanisms
•
Route
maintenance
:
Based
on
specified
policies
•
Multicast
:
??
9
IMIC, 8/30/99
Practical Issues
•
Scalability
:
No
experience
with
large
-
scale
state
-
dependent
routing
in
the
Internet
;
current
proposals
limited
to
intradomain
flat
networks
•
Interdomain
Routing
:
State
transfer
between
domains
for
CBR?
•
Flexibility
in
Routing
:
CBR,
being
a
tool
for
optimization,
invites
proprietary
solutions
.
How
to
accommodate
a
plurality
of
solutions?
•
Multicast
:
What
is
the
model?
–
Static
trees,
computed
centrally
–
Dynamic
trees
on
a
per
-
group
basis?
•
Integration
within
a
service
management
framework
:
Defining
the
interfaces
to
capacity
management,
provisioning,
and
offline
network
analysis
.
10
IMIC, 8/30/99
CBR Approach 1: IGP Extensions (e.g., OSPF)
•
Add
CBR
features
to
existing
IGP
s
.
t
.
changes
are
minimal
•
Some
IGPs
provide
mechanisms
for
adding
new
messages,
e
.
g
.
,
OSPF
transparent
LSAs
Flood Resource LSAs
New route computation proc.
New update procedures
New resource tracking proc.
(only bw defined so far)
Existing DB representation
Only single area considered
Area 1
Area 2
11
IMIC, 8/30/99
CBR Approach 2: Proprietary Protocols
•
Proprietary message formats, update protocols, hierarchy arrangements, database
representation, etc.
•
Proprietary CBR features: Flow definition, priority, preemption, rerouting features, etc.
•
Requires homogeneous equipment
Proprietary Flooding
Area 1
Area 2
12
IMIC, 8/30/99
CBR Approach 3: Distributed Overlay
•
Utilize underlying IGP (DV or link state) for reachability computations
•
Efficient update propagation techniques for scalability (facilitates dynamic routing)
•
IGP
-
independent state representation
–
State aggregation for hierarchical routing possible
–
Metric values not constrained by IGP limitations
•
Requires only the definition of a standard interface between IGPs and CBR protocols, to be
implemented locally
CBR Protocol
CBR Database
Topology Mapping &
Interface Functions
Intra
-
domain LS Protocol
LS Database
To Peers
To Peers
13
IMIC, 8/30/99
CBR Overlay: Essential Ideas
•
CBR protocol utilizes underlying IGP for building an MST of the topology (MST based
on administrative link cost)
•
State information broadcast on the MST
•
State information synchronized and maintained as MST changes
–
Requires interface function to indicate topology change
Pt
-
to
-
Pt or broadcast link
Router
To nodes E
-
I
A
B
C
D
To nodes J
-
M
To nodes N
-
Q
To nodes R
-
W
A: Mcast updates from E
-
I, request sync.
B: Unicast updates from J
-
M
C: Unicast updates from N
-
Q
Network and MST
CBR sync. on a LAN
14
IMIC, 8/30/99
CBR Overlay on OSPF
•
Hierarchical
MST
construction
;
one
for
each
area
and
one
for
the
backbone
•
CBR
topology
database
generated
from
OSPF
database
using
interface
functions
•
Independent
representation
of
network
state,
including
summary
state
for
external
areas
•
Updates
sent
on
backbone
MST
are
propagated
on
area
MSTs
Area 1
Area 2
Backbone Area
Area 1
Area 2
Backbone Area
15
IMIC, 8/30/99
Route Computation
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