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8/8/2019 GMPLS Switching
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Grotto Networking 2004Page - 1
Fundamental Switching Types
Circuit Switching
Virtual Circuit Switching Datagram Switching
Implications for Signaling, Routing, PathComputation, and Restoration
MPLS and GMPLS control planes
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Differences in Switching Types
Is connection set up required?
Is statistical multiplexing possible? What are the QoS measures? How is
bandwidth allocated?
How much work is needed to provide QoS
guarantees?
How can reliability/protection/restoration be
provided and what are the trade offs?
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Forwarding at each switch
Datagram (e.g., IP)
Based on complete destination address within the packet.
Any valid destination must be forwarded correctly. Virtual Circuits (e.g., MPLS, ATM, Frame Relay)
Based only on a label with the packet header. Only
packets whose virtual circuit has been set up ahead oftime must be forwarded correctly.
Circuits (not packets)
Based implicitly on either time slot or wavelength. Noforwarding information needed in data. Only thosecircuits whose path has been set up ahead of time must be
forwarded correctly.
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Example Network
Datagram, Virtual Circuits, or Circuits
Switches 1-5, Hosts A-J
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Datagram Forwarding Example
Switch #1
Dest Port
A 1
B 2
C 3
D 3
E 4
F 4
G 4
H 4
I 3
J 3
Switch #2
Dest Port
A 2
B 2
C 1
D 3
E 2
F 2
G 4
H 4
I 4
J 4
Switch #3
Dest Port
A 1
B 1
C 1
D 1
E 2
F 4
G 3
H 3
I 3
J 3
Switch #4
Dest Port
A 1
B 1
C 3
D 3
E 1
F 1
G 2
H 4
I 3
J 3
Switch #5
Dest Port
A 1
B 1
C 1
D 1
E 2
F 2
G 2
H 2
I 3
J 4
Graph of our
example networ
with switch port
and hosts show
I
I I I I
I
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Virtual Circuit forwarding Example
Connections Host A to Host J, Host B to Host C, Host E to Host I,
Host D to Host H, and Host A to Host G
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Virtual Circuit Forwarding
Packets are forwarded based on a label in the header
Labels are not destination addresses, usually much
shorter Labels need to be unique on a link but not in a network,
i.e., we can reuse labels on each link.
Switch forwarding tables consist of a map between(input port, packet label) to (output port, new packet
label)
Table entry for each virtual circuit rather than for eachdestination (the datagram case)
Technologies: MPLS, Frame Relay, ATM, X.25
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VC Forwarding Table Example
Switch #2
In Port In Label Out Port Out Label
2 5 4 1
2 1 1 1
3 6 4 3
Switch #3
In Port In Label Out Port Out La
1 1 3 3
2 1 3 1
Switch #5
In Port In Label Out Port Out La
1 1 4 2
1 3 2 1
2 1 3 1
Switch #1
Port In Label Out Port Out Label
2 3 5
1 3 1
1 4 1
Switch #4
Port In Label Out Port Out Label
3 2 5
1 3 1
1 4 1 6
33
1
1
1
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Real Circuit Forwarding
No more packets
Bit streams are distinguished by port and
Time slots in the TDM case
Wavelength in the WDM case
Frequency in the FDM case Switching independent of bit stream contents
TDM example (same connections as VC case)
Host A to Host J, Host B to Host C, Host E to Host I,
Host D to Host H, and Host A to Host G
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Real Circuit Tables Example
Switch #2
In Port In Slot Out Port Out Slot
2 5 4 1
2 1 1 1
3 6 4 3
Switch #3
In Port In Slot Out Port Out Slo
1 1 3 3
2 1 3 1
Switch #5In Port In Slot Out Port Out Slo
1 1 4 2
1 3 2 1
2 1 3 1
Switch #1
Port In Slot Out Port Out Slot
2 3 5
1 3 1
1 4 1
Switch #4
Port In Slot Out Port Out Slot
3 2 5
1 3 1
1 4 1
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Time Division Multiplexing
Regenerator(3R) #1
Regenerator(3R) #2
TDM de-multiplexor
TDMMultiplexor
= Optical Fiber
= Regenerator section overhead
= Multiplex section (line) overhead
= User traffic (path layer)= Unused time slots
Path
MS
RS RS RS
Path
MS
RS
TDM Path
Multiplex Section
RegeneratorSection
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Real Circuits and Virtual Circuits
Virtual Circuits
Packet based, label (not destination address) in packet
header Doesnt always consume bandwidth, i.e., traffic can be
bursty
Real Circuits
No packets raw bit stream, implicit label with either
time slot or wavelength
Is always consuming a fixed bandwidth, easy to keep
track of bandwidth but not necessarily the most
efficient utilization of link capacity.
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QoS with Real Circuits
Bandwidth
Hard bandwidth guarantees are given by default
(even if you dont want them).
Delay
Very little delay variation. Most delay
attributable to propagation. Switching delays in
most circuit switches is minimal. Bit Error Rate
Is the primary signal quality measure
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QoS with Virtual Circuits
Bandwidth
Is by default shared with other users. Effort required to
make guarantees. Very good statistical multiplexinggain can be obtained.
Delay
In addition to propagation and switch processing delaywe now have queueing induced delays
Queueing delays: can be quite large, can be quite
variable By default no guarantees made
Dropped/Errored Packets
Packets can be errored (bits errors), or dropped due tobuffer overflows.
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Protection/Restoration
Failure detection Most circuit technologies have very fast built-in failure
detection.
For packet technologies this hasnt been the case butnew work, e.g., BFD at IETF is underway.
Alternative Routes
Alternate routes for circuit consume bandwidth or mustbe set up on the fly costing time.
Alternate routes for virtual circuits do not consumebandwidth until they are used, hence can be set upahead of time.
Alternate routes can not be preconfigured for datagram
networks and all switches (routers) must recalculaterouting tables based on link failure info.
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Forwarding Tables
All switching types use them
Datagram Forwarding Tables
Need to account for all destinations no matter whos
communicating at any given time.
Circuit and Virtual Circuit Forwarding Tables Entry for each circuit or VC that traverses a particular
switch.
Note that if there areNhost and they all want to talkto each other at exactly the same time then the network
will need to supportN(N-1) circuits or VCs.
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Scaling Forwarding Tables
Modern networks like the Internet and Telephonenetworks consists of 100 of Millions or more hosts howcan we keep our routing tables under control?
Datagram Tables
We route based on networks and groups of networks.Addresses are given out accordingly. This allows theaggregation of destination addresses.
Circuit Tables
We multiplex circuits onto larger and larger trunks in ahierarchy. Switches generally only work at a couplelevels of the hierarchy. Example a switch working withSONET OC48 links (2.5Gbps) will switch with
50Mbps granularity but not 64kbps granularity!
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Setting up the Routing Tables
Finding Paths from Source to Destination
How do we choose our route?
Algorithms
Protocols
Datagram Routing Must make sure that the tables are consistent so
we dont get datagram loops.
Real Circuit Routing
Need to have enough bandwidth available on
the links to support the circuits.
Differences Between Optical Network
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Differences Between Optical NetworkRouting and IP Routing
IP routing
Per hop forwarding of datagrams based on destinationIP address
Every router must have exactly the same networktopology information (links, nodes, and link wts.)
Every router must run exactly the same pathcomputation algorithm
Failure to insure these last two requirements can resultin routing loops and black holes
Differences Between Optical Network
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Differences Between Optical NetworkRouting and IP Routing...
Optical routing
Circuits are source routed; no loops possible
No standardization of path computation required Okay for information to be slightly out of date, e.g.,
available capacity information; worst case crank-backof connection
Unless restoration action is taken based on link stateupdates, routing is not service impacting in transportdomain
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What is GMPLS?
GMPLS = Generalized MPLS
Refers to adaptation ofMPLS control plane for
the control of other technologies
Includes signaling and routing mechanisms
developed for MPLS traffic engineering GMPLS protocols developed under IETF
Previously called MP
S
Wh i MPLS?
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What is MPLS?
MPLS = Multi-Protocol Label Switching
A virtual circuit form of packet switching
such as frame relay or ATM but with a
more IP centric control plane and built in IP
adaptation.
MPLS and IP
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MPLS and IP
A combine IP router / MPLS switch assigns IP
packets to MPLS flows (virtual circuits)
This process is known as classification and can bevery simple or very complex depending upon the
context.
This box is known as a Label Edge Router (LER)
The IP packet header is not touched or looked at
while in the MPLS network The LSR (label switched routers) only switch based onMPLS labels.
An example
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An example
UnlabeledPacket arrives
IP
Egress routerremoves label
IP
IP20
Label switching &packet forwarding
Ingressrouter addslabel to packet
IP10
Autonomoussystem boundary
Label Switched Path (LSP)
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Label Switched Path (LSP)
A Label Switched Path is like a pipe or tunnel to IP packets.However its just another term for a virtual circuit. While travelingon a label switched path, forwarding is based on the label only,not on destination IP address in packet.
Label switched path
Controlling LSP Set-Up: Explicit
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10.1.1.2
10.1.1.6
10.1.1.3
10.1.1.710.1.1.4
10.1.1.5
10.1.1.1
12.0.0.1
Controlling LSP Set Up: ExplicitRouting
POP
Explicit route10.1.1.7 strict10.1.1.6 strict10.1.1.5 strict
10.1.1.2 strict
10.1.1.1 strict
Strict hop
LSP takes direct route to 10.1.1.7
10.1.1.2
10.1.1.6
10.1.1.7
10.1.1.5
Similar procedure can be used for optical connection set-up.
G li d MPLS
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Generalized MPLS
Virtual Circuits! Real Circuits
From real labels in MPLS to virtual labels in GMPLS
Labels in GMPLS TDM where time slots are the implicit labels (e.g.,
SONET)
FDM where frequencies (or s) are the implicit labels(e.g., WDM)
Space-division multiplexing where port numbers are
the implicit labels (e.g., OXCs) Generalized labels used in MPLS messaging =
Generalized MPLS