Wide Area Ethernet Services Using GELS Architecture

1
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

2
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?

3
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!)

4
Tutorial Agenda

• PART-I
• Introduction to MPLS and MPLS Terminology
• Setting up a simulated MPLS network (Hands-on)
• PART-II
• Introduction to STP for Bridges
• PART-III
• GMPLS and the GELS Architecture
• Comparison of GELS with Rapid STP (Hands-on)
• PART-IV
• Restoration and Protection Routing with MPLS
• PART-V
• Comparison of GELS with RSTP (Hands-on)

5
PART-I

• Introduction to MPLS and MPLS Terminology
• Setting up a simulated MPLS Network

6
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

7
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

8
Forwarding and routing

• Forwarding
• Passing a packet to the next hop router
• Routing
• Computing the best path to the destination
• IP routing includes routing and forwarding
• 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

9
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)

10
How IP routing works
Searching Longest Prefix Match in FIB (Too Slow)
11
Problems with IP routing

• Too slow
• 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
• Too rigid no flexibility
• Routing decisions are destination-based
• Not scalable in some desirable applications
• When mapping IP traffic onto ATM

12
IP routing rigidity example
D
1
1
A
A
B
S
B
1
2
C

• 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
• Leads to IP hotspots!
• Solution?
• Try to divert the traffic onto alternate paths

13
IP routing rigidity example
D
1
4
A
A
B
S
B
1
2
C

• 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

14
Motivations behind MPLS

• Avoid slow IP lookup
• Led to the development of IP switching in 1996
• Provide some scalability for IP over ATM
• Evolve routing functionality
• Control was too closely tied to forwarding
• Evolution of routing functionality led to some
  other benefits
• Explicit path routing
• Provision of service differentiation (QoS)

15
IP routing versus MPLS routing
Traditional IP Routing
Multiprotocol Label Switching (MPLS)
2
1
S
D
3
5
4
MPLS allows overriding shortest paths!
16
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

17
MPLS label

• To avoid IP lookup MPLS packets carry extra
  information called Label
• Packet forwarding decision is made using
  label-based lookups
• Labels have local significance only!
• How routing along explicit path works?

IP Datagram
Label
18
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)

19
Label, LSP and LSR

• Label
• 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

20
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

21
Mpls Flow Progress
D
R1
R2
LSR4
LSR1
D
destination
LSR6
LSR3
LSR2
R1 and R2 are regular routers
LSR5
1 - R1 receives a packet for destination D
connected to R2
22
Mpls Flow Progress
D
R1
R2
LSR4
LSR1
D
destination
LSR6
LSR3
LSR2
LSR5
2 - R1 determines the next hop as LSR1 and
forwards the packet (Makes a routing as well as
a forwarding decision)
23
Mpls Flow Progress
R1
R2
LSR4
LSR1
D
31
D
destination
LSR6
LSR3
LSR2
LSR5
3 LSR1 establishes a path to LSR6 and PUSHES
a label (Makes a routing as well as a forwarding
decision)
24
Mpls Flow Progress
R1
R2
LSR4
LSR1
D
destination
LSR6
LSR3
D
17
LSR2
Labels have local signifacance!
LSR5
4 LSR3 just looks at the incoming label LSR3
SWAPS with another label before forwarding
25
MPLS Flow Progress
R1
R2
LSR4
LSR1
D
destination
LSR6
LSR3
D
17
LSR2
Path within MPLS cloud is pre-established LSP
(label-switched path)
LSR5
5 LSR6 looks at the incoming label LSR6 POPS
the label before forwarding to R2
26
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

27
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

28
More MPLS terminology
Upstream
Downstream
172.68.10/24
LSR1
LSR2
29
Label advertisement

• Always downstream to upstream label advertisement
  and distribution

Downstream
Upstream
171.68.32/24
LSR2
LSR1
30
Label advertisement

• Label advertisement can be downstream unsolicited
  or downstream on-demand

Downstream
Upstream
171.68.32/24
LSR2
LSR1
Downstream
Upstream
171.68.32/24
LSR1
LSR2
31
Setting up a simulated MPLS Network

• Need a simulator
• TOTEM with additional modules
• Need a network
• Use famous European and NA networks
• Need a traffic matrix
• Bandwidth for input-output pairs
• Place traffic matrix on the network using TOTEM
  simulator!

32
PART-II

• Introduction to STP for Bridges

33
Transparent Bridging
Ethernet LAN Segment

stations
Bridge
For stations, the two topologies are the same ?
transparent bridging
34
Transparent Bridge Functions

• Promiscuous Listening
• Every packet passed up to software
• Store and Forward
• Based on a forwarding database
• Filtering
• Also based on forwarding database

35
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
Port 3
B
Port 2
A
Q
D
M
Z
C
36
Example 2 Two Bridges
Port 1
Port 2
Port 1
Port 2
B1
B2
A
Q
D
M
K
T
What are the Station Caches after complete
learning?
37
Topologies with Loops

• Problems
• Frames proliferate
• Learning process unstable
• Multicast traffic loops forever

A
LAN 1
B1
B2
B3
LAN 2
38
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

39
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

40
Forwarding frames along the spanning treeForward
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

41
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
• Root Bridge is the one with lowest Bridge ID

B
Port Address
42
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

43
Example Topology
1
4
5
7
10
6
8
11
2
0
44
After algorithm execution
DP
1
RP
BP
BP
DP
4
5
7
RP
RP
RP
DP
DP
RP
10
6
8
RP
RP
DP
DP
BP
11
2
RP
RP
RP Root Port DP Designated Port BP Blocked Port
DP
0
DP
45
The Spanning Tree
DP
1
RP
BP
BP
DP
4
5
7
RP
RP
RP
DP
DP
RP
10
6
8
RP
RP
DP
DP
BP
11
2
RP
RP
RP Root Port DP Designated Port BP Blocked Port
DP
0
DP
46
Setting up a simulated STP Network

• Need a simulator
• TOTEM with additional modules
• Need a network
• Use famous European networks
• Need a traffic matrix
• Bandwidth for input-output pairs
• Compromised CSPF algorithm
• Paths over a shared medium network

47
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

48
Applying STP on a wide area network
49
Applying STP on a wide area network

• Things will work okay but we would like to do
  better!

50
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

51
Ethernet in the core - challenges

• Existing control plane (STP)
• Network link utilization Low
• Resilience mechanism Slow
• Rudimentary support for QoS and TE

Spanning tree computed
Spanning tree recomputed
Link failure
52
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

53
PART-III

• GMPLS and the GELS Architecture
• Comparison of GELS with Rapid STP (Hands-on)

54
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
• Solution
• Generalize MPLS to GMPLS (RFC 3945)

Incompatibility of MPLS with newer devices
GMPLS offers a control plane for devices with ANY
data plane
55
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

56
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

57
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

58
GMPLS Supported Interfaces

• Time Division Multiplex Capable (TDM) Interfaces
• Interfaces that switch data based on the datas
  time slot
• Examples SONET/SDH
• GMPLS labels are actual time slots

59
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
  Cross-Connect (OXC)
• GMPLS labels are either
• wavelength (value of lambda), or
• (waveband id lambda range)

60
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

61
GMPLS Enhancements to MPLS

• GMPLS incorporates enhancements to MPLS
  including
• Constraining Label Choices
• Out of Band Signaling
• Reducing Signaling Latency
• Link Management Protocol

62
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

63
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

64
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

65
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

66
Out of Band Signaling

• Reserve

• Data path

• Reserve

• Forward

• Control path

67
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

68
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

69
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

70
Suggested label Example

• Use label 11

• Use label 12

• Used labels
• 10
• 15
• 20

• Used labels
• 11
• 16
• 21

• 12

• 12

71
GMPLS/MPLS with Ethernet

• GMPLS support for Ethernet
• Ethernet control plane is replaced by GMPLS
  control plane
• Ethernet over MPLS
• 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

72
GELS

• Proposes to use GMPLS control plane for the
  Ethernet data plane!

Ethernet Bridge

• GELS is in draft stages in IETF
• No quantitative performance comparison available
  so far

GMPLS control plane
Ethernet control plane
Ethernet data plane
73
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.

74
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

75
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

76
E-LER and E-LSR functionality
Ethernet
Ethernet
E-LER
E-LER
E-LSR
77
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

78
ELS and E-LAN
Initial scope of GELS is limited to Point to
Point Ethernet LSPs
79
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
• IETFs role is restricted to GMPLS which mandates
  changes in control plane ONLY
• Any change in data plane is unlikely to be
  supported by IEEE.
• The label should allow large number of nodes to
  be addressed
• i.e., label space should be sufficient
• 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

80
Label Options VLAN ID

• VLAN ID can be used as a label with MAC learning
  switched off
• This ensures that switching is done on the basis
  of VLAN id
• Pros
• Doesnt require changes in Data Plane
• Cons
• VLAN id cannot be used within LANs --- their
  functionality would be lost
• Limited label space --- 12 bits

81
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 Ciscos Q in Q (used for metro Ethernet
  but doesnt use GMPLS control plane)
• Pros
• VLAN functionality is not lost
• Cons
• Requires modification in data plane since
  stacking of VLAN ids is not supported

82
Label Options MPLS shim label

• Already defined in MPLS to be used with Ethernet
  as layer 2 technology
• Pros
• Doesnt require changes in data plane
• Cons
• Doesnt 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?

83
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

84
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
• Acreo have built a tpid based solution for GELS
• Pros
• Large label space (2 bytes)
• Cons
• Require changes in data plane

85
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

86
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

87
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
• Single element failures

88
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
• simulating GELS architecture
• simulating traditional solution

Compare results STP vs. GELS
89
PART-IV

• Restoration and Protection with MPLS

90
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)

91
Protection and Restoration

• Restoration
• On-demand recovery no preset backup paths
• Example existing recovery in IP networks
• Protection
• Pre-determined recovery backup paths in
  advance
• Primary and backup are provisioned at the same
  time
• IP supports restoration
• Because it is datagram service
• MPLS supports restoration as well as protection
• Because it is virtual-circuit service

92
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

93
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
94
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
95
Protection in MPLS
Path Protection
S
1
2
3
D
This type of path Protection still takes 100s
of ms.
We may explore Local Protection to quickly
switch onto backup paths!
Primary Path
Backup Path
96
Local Protection Fault Models
Link Protection
Node Protection
A
B
C
D
Element Protection
A
B
C
D
97
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

98
PART-V

• Comparison of GELS with RSTP
• (Hands-on)

99
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
• Single element failures

100
Evaluation Criteria
How efficiently 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
GELS recovery schemes
Restoration
Failed network condition
Protection
How quickly can we recover from failure?
Single node failure
GELS recovery
101
Evaluation challenges

• How to compare contention-based Ethernet with
  reservation based GMPLS?
• Allow partial placement of LSPs in GMPLS instead
  of YES/NO placement

LSP placed Bandwidth placed 60
LSP not placed Bandwidth placed 0
Available 15
Available 0
GMPLS with Compromised CSPF
GMPLS with CSPF
Capacity 100
Request 25
Placed 0
Placed 15
102
GELS Convergence time
Restoration trest tsig tproc tres tsw
Switch traffic onto new LSP tsw Switching delay
Reserve new LSP tres Reservation delay
Protection tprot tsig tsw
Compute new LSP tproc Processing delay
Potential new path
Link failure
Failure notification sent to ingress tsig
Signaling delay
Nearest upstream node to the failure
103
Timing parameter values

• tsig(Signaling delay)
• Based on 1ms/200 km link propagation delay
• tproc(Processing delay)
• 5ms
• tres(Reservation delay)
• Based on 1ms/200 km link propagation delay
• tsw(Switching delay)
• 1ms

104
GELS restoration recovery time
LSP 1
LSP 2
Ingress has lost multiple LSPs
Nearest upstream node for LSP 1
Sequentially
Convergence time is tmax

• Compute
• Reserve
• Switch

Sequentially Or In parallel
Convergence time is tmin
Link failure
Nearest upstream node for LSP 2
Sequentially
Failure signaled to ingress
105
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)

106
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

107
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
PCE
PCE
PCE
108
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

109
GELS centralized restoration PCE
Notify the ingress of the new path tsig2
signaling delay
Restoration trest tsig1 tproc tsig2
tres tsw
PCE
Switch traffic onto new LSP tsw Switching delay
Reserve new LSP tres Reservation delay
Compute new LSP tproc Processing delay
Potential new path
Link failure
Failure notification sent to PCE tsig1 Signaling
delay
Nearest upstream node to the failure
110
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

111
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

112
GELS centralized restoration NMS
Reserve resources along the new path tsig2
signaling delay
Notify the ingress of the new LSP
Restoration trest tsig1 tproc tsig2
tres tsw
NMS
Switch traffic onto new LSP tsw Switching delay
Compute new LSP tproc Processing delay
Potential new path
Link failure
Failure notification sent to NMS tsig1 Signaling
delay
Nearest upstream node to the failure
113
Timing parameter values

• tsig(Signaling delay)
• Based on 1ms/200 km link propagation delay
• tproc(Processing delay)
• 1ms
• tres(Reservation delay)
• Based on 1ms/200 km link propagation delay
• tsw(Switching delay)
• 1ms

114
Simulation setup - networks
COST 239 11 nodes
COST 266 50 nodes
115
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

116
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.htm
l 2 http//totem.info.ucl.ac.be/
117
How much traffic can be placed?
A famous European network (COST266)
118
Results Using old solution (STP)
Black links indicate no traffic!
119
Results Using new solution (GELS)
There are no black links!
120
Comparative Performance
Comparison Graph Taken from IEEE Globecom 2007
paper
121
Results LSP placement percentage
GELS with protection places fewer LSPs than RSTP
GELS with restoration places more LSPs than RSTP
122
Results Bandwidth placement
GELS with restoration places more bandwidth than
RSTP
GELS with protection places less (primary)
bandwidth than RSTP
123
Results Average link utilization
GELS with protection quickly approaches almost
full link utilization
GELS approaches 92 average link utilization
RSTP has lowest average link utilization
124
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
125
Results Single link failure convergence time
More links closer to root bridge in COST 266
More LSPs were restored in COST 239
126
Results Node failure convergence time
Small value
t1 - t10 are in milliseconds
50
11
Small value
50
t1 t49 are in milliseconds
50
127
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

128
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