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Wide Area Ethernet Services Using GELS Architecture
Zartash Afzal UzmiDepartment of Computer Science
School of Science and EngineeringLahore University of Management Sciences
(LUMS)Lahore, Pakistan
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 2
What we are going to talk about?
Question– Is it feasible and/or better to use newly proposed GELS
architecture instead of traditional (STP) solution?
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 proposedGELS architecture
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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!)
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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)
PART-I
Introduction to MPLS and MPLS TerminologySetting up a simulated MPLS Network
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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)
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 10
How IP routing works
Searching Longest Prefix Match in FIB (Too Slow)
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 12
IP routing rigidity example
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
1 1
1 2
A B
C
A
B
S
D
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 13
IP routing rigidity example
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
1 4
1 2
A B
C
SA
B
D
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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)
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 15
IP routing versus MPLS routing
Traditional IP RoutingMultiprotocol Label Switching (MPLS)
S D
543
21
MPLS allows overriding shortest paths!
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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 DatagramLabel
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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)
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
Label = 20 bits Exp = Experimental, 3 bits S = Bottom of stack, 1bitTTL = Time to live, 8 bits
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
Label | Exp|S| TTL
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 21
Mpls Flow Progress
LSR1
LSR2
LSR3
LSR5
LSR6
R1 R2LSR4D
1 - R1 receives a packet for destination D connected to R2
R1 and R2 areregular routers
D
destination
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 22
Mpls Flow Progress
LSR1
LSR2
LSR3
LSR5
LSR6
R1 R2LSR4D
2 - R1 determines the next hop as LSR1 and forwards the packet(Makes a routing as well as a forwarding decision)
D
destination
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 23
Mpls Flow Progress
LSR1
LSR2
LSR3
LSR5
LSR6
R1 R2LSR4
D
3 – LSR1 establishes a path to LSR6 and “PUSHES” a label(Makes a routing as well as a forwarding decision)
D
destination
31
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 24
Mpls Flow Progress
LSR1
LSR2
LSR3
LSR5
LSR6
R1 R2LSR4
D
4 – LSR3 just looks at the incoming labelLSR3 “SWAPS” with another label before forwarding
D
destination
17
Labels have localsignifacance!
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 25
MPLS Flow Progress
LSR1
LSR2
LSR3
LSR5
LSR6
R1 R2LSR4
D
5 – LSR6 looks at the incoming labelLSR6 “POPS” the label before forwarding to R2
D
destination
17
Path within MPLS cloudis pre-established:LSP (label-switched path)
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 28
More MPLS terminology
172.68.10/24
LSR1 LSR2
Upstream Downstream
Data
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 29
Label advertisement
Always downstream to upstream label advertisement and distribution
171.68.32/24
LSR1LSR2
Use label 5 for destination 171.68.32/24
MPLS Data Packet
with label 5 travels
Upstream Downstream
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 30
Label advertisement
Label advertisement can be downstream unsolicited or downstream on-demand
171.68.32/24
LSR1 LSR2
Sends label Without any Request
Upstream Downstream
171.68.32/24
LSR1 LSR2
Sends label ONLY after receiving request
Request For label
Upstream Downstream
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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!
PART-II
Introduction to STP for Bridges
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 33
Transparent Bridging
…
Bridge
For stations, the two topologies are the same transparent bridging
stations
Ethernet LAN Segment
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
BPort 1
Port 2
Port 3
A Q
Z C
D M
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 36
Example 2: Two Bridges
B1Port 1 Port 2
B2Port 1 Port 2
A Q D M K T
What are the Station Caches after “complete” learning?
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 37
Topologies with Loops
Problems Frames proliferate Learning process unstable Multicast traffic loops forever
B1 B2 B3
LAN 1
LAN 2
A
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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…
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 40
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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
BPort Address
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 43
Example Topology
1
4 5 7
1068
11 2
0
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 44
After algorithm execution
1
4 5 7
1068
11 2
0
DP
RP
BP BP
RPRP
DP
RP
DP
RP
DP
DP
RP
BP
RP
DP
DP
RP
RP
DP
RP: Root PortDP: Designated PortBP: Blocked Port
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 45
The Spanning Tree
1
4 5 7
1068
11 2
0
DP
RP
BP BP
RPRP
DP
RP
DP
RP
DP
DP
RP
BP
RP
DP
DP
RP
RP
DP
RP: Root PortDP: Designated PortBP: Blocked Port
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 48
Applying STP on a wide area network
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 49
Applying STP on a wide area network
Things will work okay but we would like to do better!
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 50
EthernetEthernet
Dominant LAN transport technologySpeed and reach grew substantially in
the last 25 yearsVery flexible and cost-effective
transport
Ethernet is seeing increasing deployment in service provider networks
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 51
Ethernet in the core - Ethernet in the core - challengeschallenges
Existing control plane (STP)Network link utilization – LowResilience mechanism – SlowRudimentary support for QoS and TE
Spanning tree computed
Spanning tree recomputed
Link failure
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
PART-III
GMPLS and the GELS ArchitectureComparison of GELS with Rapid STP (Hands-
on)
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 54
MPLS challengesMPLS 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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 58
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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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)
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 61
GMPLS: Enhancements to MPLS
GMPLS incorporates enhancements to MPLS including: Constraining Label Choices Out of Band Signaling Reducing Signaling Latency Link Management Protocol
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 66
Out of Band Signaling
Control path
Data path
Forward
Reserve
Reserve
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 70
Suggested label: Example
Used labels101520
Used labels111621
Use label 11 Use label 12
12 12
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 72
GELS is in draft stages in IETF
No quantitative performance comparison available so far
Proposes to use GMPLS control plane for the Ethernet data plane!
GELSGELS
Ethernet Bridge
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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.
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 76
E-LER and E-LSR functionality
Ethernet Ethernet Ethernet Ethernet
E-LER E-LERE-LSR
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 78
ELS and E-LAN
Initial scope of GELS is limited to Point to Point Ethernet LSPs
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
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.
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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
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 AICCSA 2008: Wide Area Ethernet Services Using GELS 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: Cisco’s Q in Q (used for metro Ethernet but doesn’t use GMPLS control plane)
Pros VLAN functionality is not lost
Cons Requires modification in data plane since stacking
of VLAN ids is not supported
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 82
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 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 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
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 87
GELS EvaluationGELS Evaluation
Simulation based evaluation of GELSRapid STP (RSTP) versus GMPLS
How does old control plane compare with new control plane?
Considered:1.Normal network operation2.Single element failures
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MethodologyDevelop software tools for:(1) simulating GELS architecture(2) simulating traditional solution
Consider a well known network (e.g., European COST266)
Compare old and new solutions (STP vs. GELS)
Network behaves normally Portion of Network fails
Which solution places more traffic on the network?
Which solution recovers faster from the failure?
Compare resultsSTP vs. GELS
Approach for Evaluation of GELS
Approach for Evaluation of Approach for Evaluation of GELSGELS
PART-IV
Restoration and Protection with MPLS
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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)
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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
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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
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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
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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 LatencyLocal Protection Less Latency
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 95
Protection in MPLS
S 1 2 3 D
Primary PathBackup Path
Path Protection
This type of “path Protection” still takes 100s of ms.We may explore “Local Protection” to quickly switch onto backup paths!
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Local Protection: Fault Models
A B C DLink Protection
A B C D
A B C D
Node Protection
Element Protection
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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
PART-V
Comparison of GELS with RSTP(Hands-on)
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GELS EvaluationGELS Evaluation
Simulation based evaluation of GELSRapid STP (RSTP) versus GMPLS
How does old control plane compare with new control plane?
Considered:1.Normal network operation2.Single element failures
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Evaluation CriteriaEvaluation Criteria
Evaluation criteria
Normal network condition
Failed network condition
Total bandwidth
placed
Number of LSPs
placed
Average link
utilization
Single link failure
Single node
failure
RSTP convergenc
e time
GELS recovery
Restoration
Protection
GELS recovery schemes
How efficiently can we use the
network?
How quickly can we recover from
failure?
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GMPLS with Compromised CSPF
Evaluation challengesEvaluation challenges
How to compare contention-based Ethernet with reservation based GMPLS?Allow partial placement of LSPs in GMPLS
instead of YES/NO placement
Request: 25Placed: 0
GMPLS with CSPF
Placed: 15
LSP placedBandwidth placed: 60%
LSP not placedBandwidth placed: 0%
Capacity: 100
Available: 15
Available: 0
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Switch traffic onto new LSP
tsw: Switching delay
GELS: Convergence timeGELS: Convergence time
Link failure
Failure notification
sent to ingresstsig: Signaling
delay
Compute new LSP
tproc: Processing delay
Potential new path
Reserve new LSPtres: Reservation
delay
Ingress Egres
s
LSP
Restoration: trest = tsig + tproc + tres + tsw
Protection: tprot = tsig + tsw
Nearest upstream
node to the failure
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Timing parameter valuesTiming 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
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GELS restoration recovery timeGELS restoration recovery time
LSP 1LSP 2
Ingress has lost multiple LSPs
Nearest upstream
node for LSP 2
Nearest upstream
node for LSP 1
Failure signaled to
ingress
Link failure
1. Compute
2. Reserve3. Switch
SequentiallyOr
In parallel
Sequentially
Sequentially
Convergence time is tmin
Convergence time is tmax
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GELS Centralized restorationGELS 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)
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Path Computation Element (PCE)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 processPCE may or may not reside on the
same node as the PCC
PCE
PCC
Node A
PCC
Node B
PCE
Node C
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Path Computation Element (PCE)Path Computation Element (PCE)
PCC sends a targeted request to a PCEPCC may not broadcast a requestThe PCE may compute the end-to-end
path itselfA PCE may cooperate with other PCEs
to determine intermediate loose hops
PCC PCE PCE PCE
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Our PCE scenarioOur 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 LSPIngress switches traffic onto new LSP
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Switch traffic onto new LSP
tsw: Switching delay
GELS centralized restoration: PCEGELS centralized restoration: PCE
Link failure
Failure notification sent to PCE
tsig1: Signaling
delay
Potential new path
Reserve new LSPtres: Reservation
delay
Ingress Egres
s
LSP
Restoration: trest = tsig1 + tproc + tsig2 +
tres + tsw
Nearest upstream
node to the failure
PCE
Compute new LSP
tproc: Processing delay
Notify the ingress of the new path
tsig2: signaling delay
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GELS restoration: PCEGELS 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
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GELS restoration: NMSGELS 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 reservationOnce path has been reserved, the
ingress is notifiedIngress switches traffic onto new LSP
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Switch traffic onto new LSP
tsw: Switching delay
GELS centralized restoration: NMSGELS centralized restoration: NMS
Link failure
Failure notification sent to NMS
tsig1: Signaling
delay
Potential new path
Ingress Egres
s
LSP
Restoration: trest = tsig1 + tproc + tsig2 +
tres + tsw
Nearest upstream
node to the failure
NMS
Compute new LSP
tproc: Processing delay
Reserve resources along the new pathtsig2:
signaling delayNotify the ingress of the new LSP
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 113
Timing parameter valuesTiming 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
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Simulation setup - networksSimulation setup - networks
Milan (11)
Copenhagen (1)
London (2) Amsterdam (3) Berlin (4)
Brussels (5) Luxembourg (6) Prague (7)
Paris (8) Zurich (9) Vienna (10)
Oslo (2)Helsinki (1)
Stockholm (3)
Glasgow (4)
Copenhagen (6)
Dublin (7)
Birmingham (9)
London (10)
Amsterdam (11)Hamburg (12)Berlin (13) Warsaw (14)
Brussels (15)Dusseldorf (16)
Frankfurt (17)
Paris (19)Strasbourg (20)Munich (21)
Prague (22)
Krakow (23)
Zurich (26) Vienna (24)
Budapest (28)
Bordeaux (30) Lyon (31)Milan (32) Zagreb (33)
Belgrade (37)
Marseille (42)
Barcelona (41)Sofia (46)
Lisbon (43)Madrid (44)
Rome (45)
Seville (47)Palermo (49)
Athens (50)
Turin (35)Porto (39)Bukarest (38)
Neapel (48)
Belfast (5)
Graz (29)
Basel (25)
Toulouse (34)
Salzburg (27)
Liverpool (8)
Zaragoza (40)Bologna (36)
Leipzig (18)
COST 239: 11 nodesCOST 266: 50
nodes
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Traffic matricesTraffic matrices
LSP requests arrive one-by-oneRandomly chosen ingress and egress
nodesBandwidth request 1, 2 or 3 Gb/s
chosen with equal probability
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Simulation environmentSimulation environment
Based on:Bridgesim1 for native EthernetTOTEM2 for GMPLS-controlled Ethernet
Enhancements to simulators:Implementation of C-CSPFComputation of recovery time
1: http://www.cs.cmu.edu/~acm/bridgesim/index.html2: http://totem.info.ucl.ac.be/
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A famous European network (COST266)
How much traffic can be placed?
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Black links indicate no traffic!
Results: Using old solution (STP)
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There are no black links!
Results: Using new solution (GELS)
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Comparison Graph: Taken from IEEE Globecom 2007 paper
Comparative Performance
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Results: LSP placement percentageResults: LSP placement percentage
GELS with restoration places more LSPs than RSTP
GELS with protection places fewer LSPs than RSTP
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Results: Bandwidth placementResults: Bandwidth placement
GELS with protection places less (primary) bandwidth than RSTP
GELS with restoration places more bandwidth than RSTP
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Results: Average link utilizationResults: Average link utilization
RSTP has lowest average link utilization
GELS with protection quickly approaches almost full link utilization GELS approaches 92% average
link utilization
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Results: RSTP convergence time vs cost to rootResults: 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
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Single link failure average convergence time
Topology
RSTP (ms)
Restoration (ms)
PCE(ms)
NMS(ms)
Protection (ms)
tmin tmax tmin tmax tmin tmax
11 nodes
0.7 32.67
41.61
23.53 81.75 29.36 99.68 3.89
50 nodes
102.4 38.13
39.61
39.14 64.65 52.4 98.31 6.18
Results: Single link failure Results: Single link failure convergence timeconvergence time
More links closer to root bridge in COST 266More LSPs were restored in COST
239
March 30, 2008 AICCSA 2008: Wide Area Ethernet Services Using GELS 126
Single link failure average convergence time
Topology
RSTP (ms)
Restoration (ms)
PCE(ms)
NMS(ms)
Protection (ms)
tmin tmax tmin tmax Tmin tmax
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
Results: Node failure convergence Results: Node failure convergence timetime
t1 - t10 are in milliseconds
10
1iit
t1 – t49 are in milliseconds
50+
11
Small value
49
1iit50+
50
Small value
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SummarySummary
About 45% improvement with GELS over native Ethernet in: LSP acceptanceBandwidth placement
Failure recovery time orders of magnitude less for GELS than for native Ethernet
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ConclusionConclusion
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