Optical transport networks Introduction Dr. János Tapolcai tapolcai@tmit.bme.hu http://opti.tmit.bme.hu/~tapolcai/ 1
The final goal 2 • We prefer not to see:
Telecommunicaiton Networks 3 http://www.icn.co
Telecommunicaiton Networks Video Video PSTN PSTN Internet Internet Business Business Metro Metro Backbone High Speed Backbone Service providers Mobile access 4
Network faults 5 • We deal with two type of failures – Physical failts (has a specific location) Renesys analysis of the operating routers during Sandy hurricane – Logical faults (Murphy ’s law)
Traditional network architecture in backbone networks Routing, IP (Internet forwarding Protocol) Traffic engineering ATM (Asynchronous Transfer Mode) Transport and SDH protection (Synchronous Digital Hierarchy) High bandwidth WDM (Wavelength Division Multiplexing) 6
Evolution of network layers BGP-4: 15 – 30 minutes OSPF: 10 seconds to minutes SONET: 50 milliseconds Layer 3 Layer IP GMPLS 2 ATM 1 IP 2/3 MPLS SONET 0 Packet Packet Packet Thin SONET Inter- IP/Ethernet IP/Ethernet working Smart Smart 0/1 Optics Optics Optical Optical Optical 1999 2003 201x 7
IP - Internet Protocol • Packet switched – Statistical multiplexing – Packets are forwarded based on forwarding tables • Routing is performed via link-state protocols – OSPF (Open Shortest Path First), IS-IS (Intermediate System To Intermediate System) – Link states (delays) are spread into the network • Packets are forwarded on the shortest path tree • Widespread, its role is straightforward – From a technical point of view not very popular 8
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Overlapping prefixes 32 Longest matching prefix Default 128.9.176.0/24 24 Prefix Length router entry 128.9.172.0/21 128.9.16.0/21 142.12.0.0/19 128.9.0.0/16 65.0.0.0/8 8 0.0.0.0/ 0 0 128.9.16.14 2 32 -1 Forwarding decisions: find the longest prefix match for the destination address
IP/MPLS - Multiprotocol Label Switching • MPLS instead of ATM • Switching tables – Link state protocols • Distribute topology information • OSPF-TE, IS-IS-TE (Traffic Eng.) – Control plane and label distribution • LSPs (Label Switched Path) • LDP, RSVP-TE, CR-LDP ATM Switch IP Router MPLS Control: Control: Control: IP Router IP Router ATM Forum Software Software Software Forwarding: Forwarding: Forwarding: Longest-match Label Swapping Label Swapping Lookup 11
MPLS overview 4. egress LER 1a. Routing protocols (e.g. OSPF-TE, IS-IS-TE) removes the MPLS distribute topology information label from the packet 1b. Label Distribution Protocol (LDP) Configures the packet forwarding tables IP IP 2. Ingress LER (Label Edge Router) recieves a packet and 3. LSR (Label attach a label to it Switching Router) 12 forwarding and “label swapping”
Traffic Engineering • A survivable network provides – The user have to perceive sufficient service between the endpoints of the connection (e.g. congestion) – Efficient bandwidth usage (avoid heavily loaded links) – Even after a failure the network should operate in a reliable manner • Supervise and optimize routing decisions with applying traffic engineering (TE) . In TE, connection flows are routed on longer paths in order to optimize overall bandwidth usage along all links in the network. 13
What about Traffic Engineering at IP layer? • TE controls and (optimizes) the traffic in the network – The traffic is rerouted for better load balancing and utilization • The answer is yes in certain sense: – In case of conjectures TCP sends less packets – IP can deal with topology changes • There is still a lot of room to improve – Why using overloaded links if there are spare capacity along other routes? 14
TE - The classic example 6 6 7 8 9 9 Interference 1 1 2 3 4 5 5 15
Challenges of TE • Problems with long routes – Long routes need more network resources • Eventually every route may become longer than it should be. – We may limit the length of the routes • Shortest widest path – widest = with most free capacity along the path • Widest shortest path • Stalled routing information – Every route avoids the overloaded link – It may lead to oscillation of the traffic 16
SONET/SDH • Time-division multiplexing technology • Pros – Fast recovery with 50ms guaranteed recovery time – As a widely deployed and working technology it is cheap • Cons – Coarse granularity, provisioned (no control plane) – Framing overhead (an additional layer) – Good for voice traffic, but IP/MPLS/SDH for data … • New solutions in order to make it more flexible – Next generation SDH/SONET (ngSDH/SONET) • GFP: general framing procedure => enables statistical multiplexing • VCat: Virtual concatenation => allows finer granularity • LCAS: Link capacity adjustment scheme=> meet application bw need 17
WDM • Frequency-division multiplexing technology (frequency = wavelength) • Without any changes in the optical fiber topology (digging is expensive) the transport capacity of the network is extended • Typical wavelengthe values are 8 (Coarse WDM) or 32 (Dense WDM), or even 155 • With the state-of-the-art modulation technologies each wavelength can carry 10-40Gbps data If a fiber is cut 155x40 Gbps = 6.2 Tb loss per second! 18
Evolution of transport technologies 1970 1995 Today 20xx 20xx Copper Fiber cable copper (Digital) (Analog) Point-point Transport technology Optical (circuit) switching Opticla packet switching (OPS) Transport SDH Optical Transport Network (OTN) ?? Centralized Network Management System Distributed Signalling System (CP) Signalling system 19
Increase in the transmission capacity 20
Basic IP-over WDM architecture • Permanent point-to-point connections, statically configured via the management system • Optical circuits are terminated at each node • O/E and E/O conversions at each node grooming/degrooming of all requests Francesco Musumeci, Massimo Tornatore, and Achille Pattavina, A Power Consumption Analysis for IP-Over-WDM Core Network Architectures , Journal of Optical Communication Networks, VOL. 4, NO. 2/FEBRUARY 2012 21
IP-over-SDH-over-WDM architecture • Digital Cross Connects (DXCs) are used • Low bit-rate requests can be grouped into the same Virtual Container, which is transmitted over a wavelength channel together with the other VCs. • At each node OE and EO conversions are performed in order to perform electronic switching of VCs (through the DXC). • VCs are terminated whenever a connection needs to be added (or dropped) to (from) them. Francesco Musumeci, Massimo Tornatore, and Achille Pattavina, A Power Consumption Analysis for IP-Over-WDM Core Network Architectures , Journal of Optical Communication Networks, VOL. 4, NO. 2/FEBRUARY 2012 22
All-Optical view • A lightpath is an optical path established between two nodes of the network, carrying only optical signals. Two lightpaths can use the same links if and only if they use different wavelengths. • Lightpaths are dynamically built and released connections using GMPLS via user initiated signals • Conversion to the electrical domain is needed only at the endpoints – Fast • no need to wait for O/E/O conversion at intermediate nodes – Wavelength converting transponders • 3R function Re-time, re-transmit, re-shape in the optical domain • But: topology mapping is a hard problem 23
Optical Cross-connects (OXC) • Generalized MPLS functions – Fiber-Switch Capable (FSC) – Lambda Switch Capable (LSC) • All Optical ADM or Optical Cross-connects (OXC) – Time Division Multiplexing Capable (TDMC) • SONET/SDH ADM/Digital Cross-connects – Packet Switch Capable (PSC) • Router/ATM Switch/Frame Relay Switch PSC TDMC LSC FSC TDMC LSC 24
Distributed signalling - Generalized MPLS Combining Low-Order LSP’s Splitting High-Order LSP’s PSC Cloud TDM Cloud LSC Cloud Packet LSP 1 TDM Slot 1 FSC Cloud Lambda 1 Fiber 1 Fiber Bundle Fiber N Lambda N Packet LSP N TDM Slot N Fiber LSP’s Lambda LSP’s 25 TDM LSP’s Packet LSP’s
Transparent IP-over-WDM architecture • Optical Cross Connects (OXCs), Reconfigurable Optical Add-Drop Multiplexers (ROADMs) • The requests are groomed and traffic flows bypass IP routers when neither signal regeneration nor traffic grooming/degrooming is needed. • In these cases, optical signals are converted into the electronic domain and electronically processed at the IP layer. Francesco Musumeci, Massimo Tornatore, and Achille Pattavina, A Power Consumption Analysis for IP-Over-WDM Core Network Architectures , Journal of Optical Communication Networks, VOL. 4, NO. 2/FEBRUARY 2012 26
Translucent IP-over-WDM architecture • The requests are groomed similarly to the TP-IPoWDM case, but when only signal regeneration is needed, 3R-regenerators are used; thus IP routers are bypassed. • Tunable Lambda converters and AWG based OXCs • All-optical wavelength conversion Francesco Musumeci, Massimo Tornatore, and Achille Pattavina, A Power Consumption Analysis for IP-Over-WDM Core Network Architectures , Journal of Optical Communication Networks, VOL. 4, NO. 2/FEBRUARY 2012 27
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