Transcript Powerpoint Slides - Suraj @ LUMS

Wide Area Ethernet Services Using
GELS Architecture
Zartash Afzal Uzmi
Department of Computer Science
School of Science and Engineering
Lahore University of Management Sciences (LUMS)
Lahore, Pakistan
What we are going to talk about?
Given
– A network of nodes and
communication links
Problem
“Optimally” place traffic
on the given network
Options
(1) use 25+ years old STP
in the network
(2) use a newly proposed
GELS architecture
Question
– Is it feasible and/or better to use newly proposed GELS
architecture instead of traditional (STP) solution?
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What is GELS?



GMPLS control for Ethernet label switching
Ethernet uses IEEE 802.3 data plane
Control plane



Current (old): STP and its variants
Proposed: GMPLS (proposed by GELS!)
To evaluate GELS, we need to understand:


STP and its variants such as Rapid STP (RSTP)
GMPLS (generalized MPLS!)
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Tutorial Agenda

PART-I



PART-II



GMPLS and the GELS Architecture
Comparison of GELS with Rapid STP (Hands-on)
PART-IV


Introduction to STP for Bridges
PART-III


Introduction to MPLS and MPLS Terminology
Setting up a simulated MPLS network (Hands-on)
Restoration and Protection Routing with MPLS
PART-V

Comparison of GELS with RSTP (Hands-on)
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PART-I
Introduction to MPLS and MPLS Terminology
Setting up a simulated MPLS Network
Outline

Traditional IP Routing




Forwarding and routing
Problems with IP routing
Motivations behind MPLS
MPLS Terminology and Operation



MPLS Label, LSR and LSP, LFIB Vs FIB
Transport of an IP packet over MPLS
More MPLS terminology
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Outline

Traditional IP Routing




Forwarding and routing
Problems with IP routing
Motivations behind MPLS
MPLS Terminology and Operation



MPLS Label, LSR and LSP, LFIB Vs FIB
Transport of an IP packet over MPLS
More MPLS terminology
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Forwarding and routing

Forwarding:


Routing:


Computing the “best” path to the destination
IP routing – includes routing and forwarding



Passing a packet to the next hop router
Each router makes the forwarding decision
Each router makes the routing decision
MPLS routing


Only one router (source) makes the routing decision
Intermediate routers make the forwarding decision
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IP versus MPLS routing

IP routing


Each IP datagram is routed independently
Routing and forwarding is destination-based



Routers look at the destination addresses
May lead to congestion in parts of the network
MPLS routing


A path is computed “in advance” and a “virtual
circuit” is established from ingress to egress
An MPLS path from ingress to egress node is
called a label switched path (LSP)
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How IP routing works
Searching
Longest
Prefix Match
in FIB (Too
Slow)
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Problems with IP routing

Too slow



Too rigid – no flexibility


IP lookup (longest prefix matching) “was” a
major bottleneck in high performance routers
This was made worse by the fact that IP
forwarding requires complex lookup operation
at every hop along the path
Routing decisions are destination-based
Not scalable in some desirable applications

When mapping IP traffic onto ATM
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IP routing rigidity example
D
1
A
1
S
B




1
C
B
2
Packet 1: Destination A
Packet 2: Destination B
S computes shortest paths to A and B; finds D as next hop
Both packets will follow the same path


A
Leads to IP hotspots!
Solution?

Try to divert the traffic onto alternate paths
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IP routing rigidity example
D
1
A
4
S
B




A
1
C
B
2
Increase the cost of link DA from 1 to 4
Traffic is diverted away from node D
A new IP hotspot is created!
Solution(?): Network Engineering


Put more bandwidth where the traffic is!
Leads to underutilized links; not suitable for large networks
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Motivations behind MPLS

Avoid [slow] IP lookup



Provide some scalability for IP over ATM
Evolve routing functionality


Led to the development of IP switching in 1996
Control was too closely tied to forwarding
Evolution of routing functionality led to some
other benefits


Explicit path routing
Provision of service differentiation (QoS)
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IP routing versus MPLS routing
Traditional IP Label
Routing
Multiprotocol
Switching (MPLS)
1
2
S
D
3
4
5
MPLS allows overriding shortest paths!
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Outline

Traditional IP Routing




Forwarding and routing
Problems with IP routing
Motivations behind MPLS
MPLS Terminology and Operation



MPLS Label, LSR and LSP, LFIB Vs FIB
Transport of an IP packet over MPLS
More MPLS terminology
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MPLS label


To avoid IP lookup MPLS packets carry
extra information called “Label”
Packet forwarding decision is made using
label-based lookups
Label


IP Datagram
Labels have local significance only!
How routing along explicit path works?
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Routing along explicit paths


Idea: Let the source make the complete routing
decision
How is this accomplished?


Let the ingress attach a label to the IP packet and let
intermediate routers make forwarding decisions only
On what basis should you choose different paths
for different flows?


Define some constraints and hope that the constraints
will take “some” traffic away from the hotspot!
Use CSPF instead of SPF (shortest path first)
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Label, LSP and LSR

Label
01234567890123456789012345678901
Label
| Exp|S|
TTL
Label = 20 bits
Exp = Experimental, 3 bits
S = Bottom of stack, 1bit
TTL = Time to live, 8 bits



Router that supports MPLS is known as label
switching router (LSR)
An “Edge” LSR is also known as LER (edge router)
Path which is followed using labels is called LSP
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LFIB versus FIB


Labels are searched in LFIB whereas normal IP
Routing uses FIB to search longest prefix match
for a destination IP address
Why switching based on labels is faster?




LFIB has fewer entries
Routing table FIB has larger number of entries???
In LFIB, label is an exact match
In FIB, IP is longest prefix match
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Mpls Flow Progress
D
R1
LSR4
R2
LSR1
D
LSR6
destination
LSR3
LSR2
R1 and R2 are
regular routers
LSR5
1 - R1 receives a packet for destination D connected to R2
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Mpls Flow Progress
R1
D
LSR4
R2
LSR1
D
LSR6
destination
LSR3
LSR2
LSR5
2 - R1 determines the next hop as LSR1 and forwards the packet
(Makes a routing as well as a forwarding decision)
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Mpls Flow Progress
R1
LSR4
LSR1
31
R2
D
D
LSR6
destination
LSR3
LSR2
LSR5
3 – LSR1 establishes a path to LSR6 and “PUSHES” a label
(Makes a routing as well as a forwarding decision)
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Mpls Flow Progress
R1
LSR4
R2
LSR1
D
LSR6
LSR3
17
destination
D
LSR2
LSR5
Labels have local
signifacance!
4 – LSR3 just looks at the incoming label
LSR3 “SWAPS” with another label before forwarding
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MPLS Flow Progress
R1
LSR4
R2
LSR1
D
LSR6
LSR3
17
destination
D
LSR2
LSR5
Path within MPLS cloud
is pre-established:
LSP (label-switched path)
5 – LSR6 looks at the incoming label
LSR6 “POPS” the label before forwarding to R2
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MPLS and explicit routing recap

Who establishes the LSPs in advance?


Ingress routers (usually!)
How do ingress routers decide not to always take
the shortest path?


Ingress routers use CSPF (constrained shortest path
first) instead of SPF
Examples of constraints:
 Do not use links left with less than 7Mb/s bandwidth
 Do not use blue-colored links for this request
 Use a path with delay less than 130ms
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CSPF

What is the mechanism? (in typical cases!)




First prune all links not fulfilling constrains
Now find shortest path on the rest of the topology
Requires some reservation mechanism
Changing state of the network must also be
recorded and propagated


For example, ingress needs to know how much
bandwidth is left on links
The information is propagated by means of routing
protocols and their extensions
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More MPLS terminology
Upstream
Downstream
172.68.10/24
LSR1
LSR2
Data
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Label advertisement

Always downstream to upstream label
advertisement and distribution
Upstream
Use label 5 for destination
171.68.32/24
Downstream
171.68.32/24
LSR1
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MPLS Data Packet
with label 5 travels
LSR2
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Label advertisement

Label advertisement can be downstream
unsolicited or downstream on-demand
Upstream
Sends label
Without any Request
Downstream
171.68.32/24
LSR2
LSR1
Upstream
Sends label ONLY after
receiving request
Downstream
171.68.32/24
LSR1
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Request For label
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LSR2
30
Setting up a simulated MPLS Network

Need a simulator


Need a network


Use famous European and NA networks
Need a traffic matrix


TOTEM with additional modules
Bandwidth for input-output pairs
Place traffic matrix on the network using
TOTEM simulator!
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PART-II
Introduction to STP for Bridges
Transparent Bridging
Ethernet LAN Segment
…
stations
Bridge
For stations, the two topologies are the same  transparent bridging
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Transparent Bridge Functions

Promiscuous Listening


Store and Forward


Every packet passed up to software
Based on a forwarding database
Filtering

Also based on forwarding database
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Example 1: Learning and Forwarding

Transmission order




AD
 Ports 2, 3
DA
 Port 1
QA
 Filtered
ZC
 Ports 1, 3
Port 1
B
Port 2
A
Q
D
Z
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Port 3
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C
35
Example 2: Two Bridges
Port 1
A
Q
B1
Port 2
Port 1
D
B2
M
Port 2
K
T
What are the Station Caches after “complete” learning?
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Topologies with Loops

Problems



Frames proliferate
Learning process unstable
Multicast traffic loops forever
A
LAN 1
B1
B2
B3
LAN 2
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Spanning Tree Algorithm

A distributed Algorithm




Elects a single bridge to be the root bridge
Calculates the distance of the shortest path from each
bridge to the root bridge (cost)
For each LAN segment , elects a “designated” bridge
from among the bridges residing on that segment
 The designated bridge for a LAN segment is the one
closest to the root bridge
And…
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Spanning Tree Algorithm

For each bridge




Selects ports to be included in spanning tree
The ports selected are:
 The root port --- the port that gives the best path from
this bridge to the root
 The designated ports --- ports connected to a segment
on which this bridge is designated
Ports included in the spanning tree are placed in the
forwarding state
All other ports are placed in the blocked state
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Forwarding frames along the spanning tree
Forward and Blocked States of Ports


Data traffic (from various stations) is
forwarded to and from the ports selected
in the spanning tree
Incoming data traffic is always discarded
(this is different from filtering frames.
Why?) and is never forwarded on the
blocked ports
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Root Selection: Bridge ID


Each port on the Bridge has a unique LAN
address just like any other LAN interface card
Bridge ID is a single bridge-wide identifier that
could be:


A unique 48-bit address
Perhaps the LAN address of one of its ports
B

Port Address
Root Bridge is the one with lowest Bridge ID
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Path Length (Cost)



Path length is the number of hops from a bridge
to the root
While forming a spanning tree, we are interested
in the least cost path to the root
Cost can also be specified based on the speed of
the link


Not fair to treat a 10Mb/s link the same as a 1Gb/s link
A guideline for cost selection is in Table 8.5 of the
latest IEEE 802.1D standard
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Example Topology
1
4
8
5
6
7
10
11
2
0
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After algorithm execution
1
4
8
BP
RP
RP
DP
DP
RP
6
10
11
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RP
DP
RP
RP: Root Port
DP: Designated Port
BP: Blocked Port
DP
BP
DP
RP
RP
0
5
7
BP
RP
DP
RP
2
DP
DP
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The Spanning Tree
1
4
8
BP
RP
RP
DP
DP
RP
6
10
11
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RP
DP
RP
RP: Root Port
DP: Designated Port
BP: Blocked Port
DP
BP
DP
RP
RP
0
5
7
BP
RP
DP
RP
2
DP
DP
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Setting up a simulated STP Network

Need a simulator


Need a network


Use famous European networks
Need a traffic matrix


TOTEM with additional modules
Bandwidth for input-output pairs
Compromised CSPF algorithm

Paths over a shared medium network
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STP and wide area networks


Traditionally, STP is used in Bridged
Ethernet local area networks (LANs)
Ethernet means two things:



Physical and MAC layer standard (CSMA/CD)
A frame format
Use of Ethernet [from format] is becoming
popular in wide area networks

STP can be used in wide area networks to come
up with a loop free network topology
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Applying STP on a wide area network
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Applying STP on a wide area network
Things
March 30, 2008
will work okay but we would like to do better!
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Ethernet
Dominant LAN transport technology
 Speed and reach grew substantially in the
last 25 years
 Very flexible and cost-effective transport


Ethernet is seeing increasing deployment
in service provider networks
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Ethernet in the core - challenges

Existing control plane (STP)
 Network
link utilization – Low
 Resilience mechanism – Slow
 Rudimentary support for QoS and TE
Link
failure
March 30, 2008
Spanning
Spanningtree
tree
computed
recomputed
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Ethernet in the Core

Ethernet LANs use STP (or RSTP/MSTP)

Use of STP in Core Network leads to
challenges
Can we use an alternate control plane?

GELS Architecture


For Core Networks, use GMPLS as the
Ethernet control plane
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PART-III
GMPLS and the GELS Architecture
Comparison of GELS with Rapid STP (Hands-on)
MPLS challenges


Newer devices are capable of switching on the basis of:
 Interface (FSC)
 Wavelength (LSC)
 TDM timeslot
MPLS works with packet switch devices only
 Looks at the label and forwards an incoming packet
Incompatibility of MPLS with newer
devices

Solution:
 Generalize MPLS to GMPLS (RFC 3945)
GMPLS offers a control plane for
devices with ANY data plane
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GMPLS: Introduction


Extends MPLS to support non-packet
based interfaces (like TDM, OTN,
Ethernet etc.)
Concept of LSP and label is generalized


Such as timeslots as labels or layer 2 LSP
Provides a unified control plane for various
data planes
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GMPLS: Supported Interfaces

Packet Switch Capable Interfaces (PSC)



Interfaces that recognize packet boundaries
and forward data based on packet headers
Example: IP
GMPLS labels are based on packet header
values
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GMPLS: Supported Interfaces

Layer-2 Switch Capable (L2SC) Interfaces



Interfaces that recognize frame/cell
boundaries and forward data based on
frame/cell headers
Examples: Ethernet, ATM
GMPLS labels are based on frame/cell header
values
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GMPLS: Supported Interfaces

Time Division Multiplex Capable (TDM)
Interfaces



Interfaces that switch data based on the
data’s time slot
Examples: SONET/SDH
GMPLS labels are actual time slots
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GMPLS: Supported Interfaces

Lambda Switch Capable (LSC) Interfaces



Interfaces that switch data based on the wavelength or
waveband on which data is received
Examples: Photonic Cross-Connect (PXC), Optical CrossConnect (OXC)
GMPLS labels are either
 wavelength (value of lambda), or
 (waveband id + lambda range)
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GMPLS: Supported Interfaces

Fiber Switch Capable (FSC) Interfaces



Interfaces that switch data based on the
physical media
Examples: PXC and OXC that can operate at
the level of single or multiple fibers
GMPLS labels are actual fibers
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GMPLS: Enhancements to MPLS

GMPLS incorporates enhancements to
MPLS including:




Constraining Label Choices
Out of Band Signaling
Reducing Signaling Latency
Link Management Protocol
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Constraining Label Choices


What is meant by constraining label choices?
 In MPLS, the upstream node requests a label and the
downstream node assigns one from the available set of labels
 In GMPLS, the downstream node can be constrained to select
a specific label or a label from a given label set
Why constrain label choices?
 Some optical switches may not have the capability to switch
wavelengths or may not prefer too much switching
(wavelength conversion introduces distortion)
 Nodes may need to assign a specific label which is chosen by
a centralized server
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Constraining Label Choices

Two ways of constraining label choices


Label Set: Upstream node specifies a label set to the
downstream node which selects a label from this set
Explicit Label Set: A central node, having complete
information about label assignments in network, can
select labels on each link for each LSP; all nodes along
the LSP have to assign the pre-selected labels
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Out of Band Signaling


Protocol Layers for data and control plane:
 In MPLS, IP is used for communicating data as well as control
messages. Thus, data and control channels are at the same
protocol layer
 In GMPLS, control messages are still communicated at IP
layer, while the GMPLS supported forwarding (data) planes
can be at lower layers
Granularity of Layers
 Lower layers have coarse granularity e.g., thousands of MPLS
LSPs traverse a single wavelength
 Assigning a separate wavelength or fiber for a single control
channel may not be efficient
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Out of Band Signaling



In GMPLS out of band signaling is preferred due to:
 difference in control and data protocol layers
 possible wastage of resources if control channel uses the
data plane at relatively lower layers
Control channels use IP which may run over any transport
such as ethernet etc.
Process of identifying data and control paths for an LSP:
 First, we calculate the data path for an LSP request
 Then, we calculate the control path that traverses all nodes
in the data path
 Since control channel topology may be different from the
data topology, the data and control paths MAY be different
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Out of Band Signaling
Data
path
Reserve
Reserve
Control
March 30, 2008
path
Forward
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Out of Band Signaling: Issues



In in-band signaling, all nodes that receive the control
message for resource reservation have to reserve resources
on the same interface on which the control message is
received
However, in out of band signaling:
 If the node that receives the control message is not in the
data path it should simply forward the message to the next
control node.
 If the node is in the data path, it has to identify the data
interface on which the reservation is required
GMPLS handles the above issues through extensions in
resource reservation protocols
March 30, 2008
AICCSA 2008: Wide Area Ethernet Services Using GELS
67
Signaling Latency: Problem



In MPLS/GMPLS, actual switching/label
assignment decision is made during the return
path of signaling request
Configuring a IP/MPLS router for switching is not
too time consuming
However, configuring an OXC for switching
requires extra time


micro mirrors have to be adjusted
subsequent wait time for the resulting movement
vibrations to damp away
March 30, 2008
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68
Reducing Signaling Latency

Suggested Label





Upstream node suggests a label to the downstream node
It configures its switching based on this label
Downstream node is not constrained to select this label
but should prefer this assignment
If another label is assigned by the downstream node,
the configuration is done for the actual label
Reduces signaling latency in general
March 30, 2008
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69
Suggested label: Example
Use
label 11
Use
label 12
Used
labels
10
15
20
12
March 30, 2008
AICCSA 2008: Wide Area Ethernet Services Using GELS
Used
labels
11
16
21
12
70
GMPLS/MPLS with Ethernet

GMPLS support for Ethernet


Ethernet over MPLS


Ethernet control plane is replaced by GMPLS control
plane
Ethernet frames are carried over an MPLS cloud, giving
a virtual LAN type environment
MPLS over Ethernet

MPLS packets are carried over an Ethernet transport
March 30, 2008
AICCSA 2008: Wide Area Ethernet Services Using GELS
71
GELS

Proposes to use GMPLS control plane for
Ethernet Bridge
the Ethernet data plane!
GELS is in draft stages in IETF
 No quantitative performance
comparison available so far

March 30, 2008
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72
GMPLS Support for Ethernet




GMPLS control plane dictates the
forwarding of ethernet frames
Provides a connection oriented ethernet
service
Spanning tree protocols are replaced by
GMPLS constraint based routing
Allows traffic engineering and rerouting of
ethernet connections.
March 30, 2008
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73
GMPLS controlled Ethernet Label Switching (GELS)

Architecture


GMPLS enabled bridges in the core that switch the
Ethernet frame based on a ‘label’
Bridges could be part of a multi-layer network --- nodes
are called Ethernet Label Edge Routers (E-LER) and
Ethernet Label Switched Routers (E-LSR) regardless of
the type/number of layers
 Typical GELS layers: IP, Ethernet, and Lambda i.e. IP
over Ethernet over Lambda
 E-LERs and E-LSRs need not have IP layer i.e. only have
functionality of layer 2 and below
March 30, 2008
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74
GELS- Architecture

Ethernet Label Edge Router (E-LER)




ingress or egress points of a GMPLS Ethernet network
at the ingress: takes an incoming native frame, adds an
Ethernet label, and forwards it to the appropriate label
controlled interface
at the egress: removes the label and forwards it to a
non-label controlled interface
Ethernet Label Switched Router (E-LSR)

takes an incoming labeled ethernet frame and forwards
the frame to the appropriate label controlled interface
March 30, 2008
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75
E-LER and E-LSR functionality
Ethernet
Ethernet
E-LER
March 30, 2008
Ethernet
E-LSR
AICCSA 2008: Wide Area Ethernet Services Using GELS
Ethernet
E-LER
76
Services offered by GELS


Metro Ethernet Forum has defined two service types:
Ethernet Line Service (ELS) and Ethernet LAN Service
(E-LAN)
ELS



Point to Point Ethernet Service
Similar to Frame Relay or ATM Virtual Circuit
E-LAN


Multipoint to Multipoint Ethernet Service (like a normal
Ethernet LAN)
A new site automatically gains access to all previously
existing sites
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77
ELS and E-LAN
Initial scope of GELS is limited to Point to Point Ethernet LSPs
March 30, 2008
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78
GELS --- Choice of Label


The selection of label has been the most controversial issue
in GELS --- still no consensus
What are the considerations?
 Label should not require changes in data plane

IETF’s role is restricted to GMPLS which mandates changes in
control plane ONLY
Any change in data plane is unlikely to be supported by IEEE.

i.e., label space should be sufficient




The label should allow large number of nodes to be addressed
It should allow co-working of 802.1 bridges having VLAN
capability with GMPLS enabled Ethernet Routers
Should be scalable --- the forwarding table entries and
changes to OSPF-TE and RSVP-TE should be manageable
March 30, 2008
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79
Label Options: VLAN ID

VLAN ID can be used as a label with MAC
learning switched off


Pros


This ensures that switching is done on the basis of
VLAN id
Doesn’t require changes in Data Plane
Cons


VLAN id cannot be used within LANs --- their
functionality would be lost
Limited label space --- 12 bits
March 30, 2008
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80
Label Options: VLAN ID (Q in Q)




Stack VLAN ids: use separate VLAN ids for
metro/core while preserving the ids used in
individual LANs
Example: Cisco’s Q in Q (used for metro Ethernet
but doesn’t use GMPLS control plane)
Pros

VLAN functionality is not lost

Requires modification in data plane since stacking of
VLAN ids is not supported
Cons
March 30, 2008
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81
Label Options: MPLS shim label


Already defined in MPLS to be used with
Ethernet as layer 2 technology
Pros


Doesn’t require changes in data plane
Cons

Doesn’t work at the Ethernet level (layer 2) --- works at
MPLS layer which means that MPLS/IP layer
functionality has to be added to ethernet switches.
Then why not use ethernet over MPLS?
March 30, 2008
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82
Label Options: Use of proprietary
MAC addresses





Use different/proprietary MAC addresses for forwarding in
the GMPLS core
First three bytes of MAC address are the Organizational
Unit Identifier (OUI)
Reserve OUI for use in GELS
Pros
 Large label space
 No changes required in E-LSR
Cons
 MAC address has to be overwritten at the E-LER, thereby
requiring change in the data plane
March 30, 2008
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83
Label Options: Use of new tag
protocol identifier (tpid)

First two bytes of Q-tag are tpid

e.g, value of 0x8100 in the first two bytes indicate a
(C-)VLAN in the next two bytes
idea is to use a different tpid for the GMPLS label

Large label space (2 bytes)

Require changes in data plane




Acreo have built a tpid based solution for GELS
Pros
Cons
March 30, 2008
AICCSA 2008: Wide Area Ethernet Services Using GELS
84
Label Options: Use of MAC address
+ VLAN id


Use a combination of Destination MAC
address + VLAN id as the label
Pros


Large label space
Cons


Require changes in data plane
Labels cannot be link local
March 30, 2008
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85
GELS: Future Work

Need a consensus on the choice of label



Evaluate the several proposals that have been made
already and possibly some new ones as well
Based on the choice of label and other GELS
requirement, design appropriate extensions to
OSPF-TE and RSVP-TE
Design a mechanism to interoperate traditional
MAC learning/flooding with GMPLS based control
plane
March 30, 2008
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86
GELS Evaluation
Simulation based evaluation of GELS
 Rapid STP (RSTP) versus GMPLS

 How
does old control plane compare with new
control plane?

Considered:
Normal network operation
2. Single element failures
1.
March 30, 2008
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87
Approach for Evaluation of GELS
Consider a well known network (e.g., European COST266)
Compare old and new solutions (STP vs. GELS)
Approach
for Evaluation of GELS
Network behaves normally
Portion of Network fails
Which solution places more
traffic on the network?
Which solution recovers
faster from the failure?
Methodology
Develop software tools for:
(1) simulating GELS architecture
(2) simulating traditional solution
March 30, 2008
AICCSA 2008: Wide Area Ethernet Services Using GELS
Compare results
STP vs. GELS
88
PART-IV
Restoration and Protection with MPLS
IP versus MPLS (recall)


In IP Routing, each router makes its own routing
and forwarding decisions
In MPLS:




source router makes the routing decision
Intermediate routers make forwarding decisions
A path is computed and a “virtual circuit” is established
from ingress router to egress router
An MPLS path or virtual circuit from source to
destination is called an LSP (label switched path)
March 30, 2008
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90
Protection and Restoration

Restoration



Protection



Pre-determined recovery – backup paths “in advance”
Primary and backup are provisioned at the same time
IP supports restoration


On-demand recovery – no preset backup paths
Example: existing recovery in IP networks
Because it is datagram service
MPLS supports restoration as well as protection

Because it is virtual-circuit service
March 30, 2008
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91
Restoration in IP network

In traditional IP, what happens when a link
or node fails?




Failure information needs to be disseminated in
the network
During this time, packets may go in loops
Restoration latency is in the order of seconds
We look for protection possibilities in an
MPLS network, but…

First we need to look at the QoS requirements
March 30, 2008
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92
QoS Requirements

Bandwidth Guaranteed Primary Paths

Bandwidth Guaranteed Backup Paths


BW remains provisioned in case of network failure
Minimal “Protection or Restoration Latency”

Protection/Restoration latency is the time that elapses
between:
 “the occurrence of a failure”, and
 “the diversion of network traffic on a new path”
Restoration is generally SLOWER than protection
March 30, 2008
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93
Protection in MPLS



First we define Protection level
Path protection
 Also called end-to-end protection
 For each primary LSP, a node-disjoint backup LSP is set up
 Upon failure, ingress node diverts traffic on the backup path
Local Protection
 Upon failure, node immediately upstream the failed element
diverts the traffic on a “local” backup path
Path Protection  More Latency
Local Protection  Less Latency
March 30, 2008
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94
Protection in MPLS
Path Protection
S
1
2
3
D
This type of “path Protection”
still takes 100s of ms.
Primary Path
Backup Path
March 30, 2008
We may explore “Local Protection” to
quickly switch onto backup paths!
AICCSA 2008: Wide Area Ethernet Services Using GELS
95
Local Protection: Fault Models
Link
Protection
Node
Protection
Element
Protection
March 30, 2008
A
B
C
D
A
B
C
D
A
B
C
AICCSA 2008: Wide Area Ethernet Services Using GELS
D
96
Reliability in Core Networks

In Core Networks, we can use GELS with:



Protection, or
Restoration
With this background on network recovery,
we are now ready to compare STP with the
GMPLS control plane
March 30, 2008
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97
PART-V
Comparison of GELS with RSTP
(Hands-on)
GELS Evaluation
Simulation based evaluation of GELS
 Rapid STP (RSTP) versus GMPLS

 How
does old control plane compare with new
control plane?

Considered:
Normal network operation
2. Single element failures
1.
March 30, 2008
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99
How efficiently Criteria
Evaluation
can we use the
network?
Average
link
utilization
Normal
network
condition
Number of
LSPs
placed
Total
bandwidth
placed
Evaluation
criteria
Single link
failure
RSTP
convergence
time
Failed
network
condition
Restoratio
n
Protection
How quickly can
we recover from
failure?
March 30, 2008
Single node
failure
AICCSA 2008: Wide Area Ethernet Services Using GELS
GELS
recovery
GELS
recovery
schemes
100
Evaluation challenges

How to compare contention-based
Ethernet with reservation based GMPLS?
 Allow
partial placement of LSPs in GMPLS
instead of YES/NO placement
Available:
Available
15
:0
GMPLSGMPLS
with Compromised
with CSPF CSPF
Capacit
y: 100
Request: 25
Placed: 15
0
March 30, 2008
LSP not
placed
placed
Bandwidth placed: 0%
60%
AICCSA 2008: Wide Area Ethernet Services Using GELS
101
GELS: Convergence time
Restoration: trest = tsig + tproc + tres +
tsw
Reserve new LSP
Switch traffic onto new
tres
: Reservation
LSP
Protection:
tprot = tsig +
delay
tsw: Switching
delay
Computetnew
LSP
sw
tproc: Processing
delay
Ingres
s
Failure
notification sent
to ingress
tsig: Signaling
delay
March 30, 2008
Potential new
path
Link
failure
LSP
Egres
s
Nearest
upstream node
to the failure
AICCSA 2008: Wide Area Ethernet Services Using GELS
102
Timing parameter values
 tsig(Signaling

delay):
Based on 1ms/200 km link propagation delay
 tproc(Processing

5ms
 tres(Reservation

delay):
Based on 1ms/200 km link propagation delay
 tsw(Switching

delay):
delay):
1ms
March 30, 2008
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103
GELS restoration recovery time
LSP 1
LSP 2
Ingress has lost
multiple LSPs
1. Compute
2. Reserve
3. Switch
Nearest
Sequentially
upstream node
for LSP 1
Convergence
time is tmax
Sequentially
Or
In parallel
Link failure
Convergence
time is tmin
Nearest
Sequentially
upstream node
for LSP 2
Failure
signaled to
ingress
March 30, 2008
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104
GELS Centralized restoration
Some deployments may use centralized
instead of distributed failure recovery
 A central server handles restoration of
LSPs affected by a failure
 Two options:

 Path
Computation Element (PCE)
 Network Management System (NMS)
March 30, 2008
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105
Path Computation Element (PCE)
PCE is an entity responsible for path
computation on request from a Path
Computation Client (PCC)
 It could be a node or a process
 PCE may or may not reside on the same
node as the PCC

Node A
PCE
PCC
March 30, 2008
Node B
PCC
AICCSA 2008: Wide Area Ethernet Services Using GELS
Node C
PCE
106
Path Computation Element (PCE)
PCC sends a targeted request to a PCE
 PCC may not broadcast a request
 The PCE may compute the end-to-end path
itself
 A PCE may cooperate with other PCEs to
determine intermediate loose hops

PCC
March 30, 2008
PCE
PCE
AICCSA 2008: Wide Area Ethernet Services Using GELS
PCE
107
Our PCE scenario
A single central PCE server for the routing
domain
 Nearest upstream node to the point of
failure sends restoration request to PCE
upon a failure event
 PCE computes the new path and sends this
path to the ingress
 Ingress reserves the new LSP
 Ingress switches traffic onto new LSP

March 30, 2008
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108
GELS centralized restoration: PCE
Notify the ingress of
the new path
tsig2: signaling delay
Restoration: trest = tsig1 + tproc + tsig2 + tres
+ tsw Switch traffic
Reserveonto
newnew
LSP
tres
: Reservation
LSP
delay
tsw: Switching
delay
Ingres
s
Failure
notification sent
to PCE
tsig1: Signaling
delay
March 30, 2008
PCE
Compute new LSP
tproc: Processing
Potential delay
new
path
Link
failure
LSP
Egres
s
Nearest
upstream node
to the failure
AICCSA 2008: Wide Area Ethernet Services Using GELS
109
GELS restoration: PCE
Central PCEs are typically high end
multiprocessor platforms
 Router platforms are not as fast as
central PCEs
 Centralized PCEs should be able to
compute paths more quickly than routers
 Centralized PCEs should also be able to
perform multiple path computations
simultaneously

March 30, 2008
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110
GELS restoration: NMS
NMS is also a centralized restoration
scenario
 Here, the central server performs path
computation as well as reservation
 It may use SNMP for path reservation
 Once path has been reserved, the ingress
is notified
 Ingress switches traffic onto new LSP

March 30, 2008
AICCSA 2008: Wide Area Ethernet Services Using GELS
111
GELS centralized restoration: NMS
Reserve resources
along the new path
Notifytthe
ingress
sig2: signaling delay
Restoration: trest =oftthe
tproc
sig1 +
new
LSP+ tsig2 + tres
+ tsw
Switch traffic onto new
LSP
tsw: Switching delay
Ingres
s
Failure
notification sent
to NMS
tsig1: Signaling
delay
March 30, 2008
NMS
Compute new LSP
tproc: Processing
Potential delay
new
path
Link
failure
LSP
Egres
s
Nearest
upstream node
to the failure
AICCSA 2008: Wide Area Ethernet Services Using GELS
112
Timing parameter values
 tsig(Signaling

delay):
Based on 1ms/200 km link propagation delay
 tproc(Processing

1ms
 tres(Reservation

delay):
Based on 1ms/200 km link propagation delay
 tsw(Switching

delay):
delay):
1ms
March 30, 2008
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113
Simulation setup - networks
(1)
CopenhagenHelsinki
(1)
Oslo (2)
COST
COST 266:
239: 11
50nodes
nodes
Stockholm (3)
Glasgow (4)
Belfast (5)
Dublin (7)
Copenhagen (6)
Liverpool (8)
Birmingham (9)
Amsterdam (3)
Amsterdam (11)Hamburg (12) Berlin (13)
London (10)
Brussels (15) Dusseldorf (16)
Leipzig (18)
London (2)
Berlin (4)
Warsaw (14)
Krakow (23)
Brussels (5)
Frankfurt (17)
Prague (22)
Strasbourg (20) Munich (21)
Luxembourg (6)
Paris (19)
Bordeaux (30)
Basel (25) Zurich (26)
Vienna (24)
Salzburg (27) Graz (29)
Lyon (31)
Milan (32)
Zagreb (33)
Toulouse (34)
Paris (8)
Porto (39)
Prague (7)
Budapest (28)
Marseille (42)
Zaragoza (40)
Turin (35)
Zurich (9)
Belgrade (37)
Bukarest
Vienna
(10) (38)
Bologna (36)
Sofia (46)
Lisbon (43)
Madrid (44)
Barcelona (41)
Rome (45)
Neapel (48)
Milan (11)
Seville (47)
Palermo (49)
March 30, 2008
AICCSA 2008: Wide Area Ethernet Services Using GELS
Athens (50)
114
Traffic matrices
LSP requests arrive one-by-one
 Randomly chosen ingress and egress nodes
 Bandwidth request 1, 2 or 3 Gb/s chosen
with equal probability

March 30, 2008
AICCSA 2008: Wide Area Ethernet Services Using GELS
115
Simulation environment

Based on:
 Bridgesim1
for native Ethernet
 TOTEM2 for GMPLS-controlled Ethernet

Enhancements to simulators:
 Implementation
of C-CSPF
 Computation of recovery time
1: http://www.cs.cmu.edu/~acm/bridgesim/index.html
2: http://totem.info.ucl.ac.be/
March 30, 2008
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116
How much traffic can be placed?
A famous European network (COST266)
March 30, 2008
AICCSA 2008: Wide Area Ethernet Services Using GELS
117
Results: Using old solution (STP)
Black links indicate no traffic!
March 30, 2008
AICCSA 2008: Wide Area Ethernet Services Using GELS
118
Results: Using new solution (GELS)
There are no black links!
March 30, 2008
AICCSA 2008: Wide Area Ethernet Services Using GELS
119
Comparative Performance
Comparison Graph: Taken from IEEE Globecom 2007 paper
March 30, 2008
AICCSA 2008: Wide Area Ethernet Services Using GELS
120
Results: LSP placement percentage
GELS
with
protection
places fewer LSPs
GELS with restoration places
more
LSPs
than
than RSTP
RSTP
March 30, 2008
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121
Results: Bandwidth placement
GELS with restoration places more bandwidth
than RSTP
GELS with protection places less (primary) bandwidth
than RSTP
March 30, 2008
AICCSA 2008: Wide Area Ethernet Services Using GELS
122
Results: Average link utilization
GELS with protection quickly approaches almost full link
utilization
GELS approaches 92% average link
utilization
RSTP has
utilization
March 30, 2008
AICCSA 2008: Wide Area Ethernet Services Using GELS
lowest
average
link
123
Results: RSTP convergence time vs cost to root
RSTP convergence time is highest if the root
bridge fails
Convergence time decreases as cost to root
increases
March 30, 2008
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124
Results: Single link failure convergence
time
Single link failure average convergence time
Topology
RSTP
(ms)
Restoration
(ms)
tmin
tmax
PCE
(ms)
NMS
(ms)
Protection
(ms)
tmin
tmax
tmin
tmax
23.53
81.75
29.36
99.68
3.89
39.61 39.14
64.65
52.4
98.31
6.18
11 nodes
0.7
32.67 41.61
50 nodes
102.4
38.13
More links closer to root bridge in COST 266
More LSPs were restored in COST 239
March 30, 2008
AICCSA 2008: Wide Area Ethernet Services Using GELS
125
Results: Node failure convergence time
Small value
10
50+ ti
t1 - t10 are in milliseconds
i 1
11
Single link failure average convergence time
Topology
RSTP
(ms)
Restoration
(ms)
tmin
tmax
PCE
(ms)
tmin
tmax
NMS
(ms)
Tmin
tmax
Protection
(ms)
11 nodes
4850
30.07
39.34
22.21 62.34
29.81
95.25
2.56
50 nodes
3365
42.25
44.24
37.41 76.13
52.73
111.83
6.1
49
50+ ti
i 1
50
March 30, 2008
Small value
t1 – t49 are in milliseconds
AICCSA 2008: Wide Area Ethernet Services Using GELS
126
Summary

About 45% improvement with GELS over
native Ethernet in:
 LSP
acceptance
 Bandwidth placement

Failure recovery time orders of magnitude
less for GELS than for native Ethernet
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Conclusion
Ethernet is a flexible, cost effective and
efficient transport mechanism for
metro/core networks
 GMPLS promises to be a useful control
plane for Ethernet in metro/core
 Tremendous administrative benefits of
using a single control plane
 Vendors actively working on
standardization of GELS

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