TOC: Switching & Forwarding

Transcription

1 Walrand Lecture TO: Switching & Forwarding Lecture Switching & Forwarding EES University of alifornia Berkeley Why? Switching Techniques Switch haracteristics Switch Examples Switch rchitectures Summary EES Walrand Switching: Why? irect vs. Switched Networks: irect Single link Switches n links Switched Switching: Techniques ircuit-switching (e.g., Telephone net.) Packet-Switching atagram (e.g., IP, Ethernet) Virtual ircuits (e.g., MPLS, TM) Source Routing omparison irect Network Limitations: istance (coordination delay; propagation limitation) Number of hosts (collisions; shared bandwidth; address tables) Single link technology (cannot mix optical, wireless, ) Internetworking: Externality gain at cost EES Walrand EES Walrand Techniques: ircuit-switching Techniques: Packet-Switching Mechanism: Link divided into fixed, independent circuits Mechanism: Whole link shared by all packets Features: ircuit Switch onnection list Time scale: connection (e.g., TM, WM) Packets not switched independently (establish circuit before sending data) edicated path and resources from source to destination Setup time; delays and guaranteed resources thereafter EES Walrand 5 Packet Switch Features: ata separated into packets Switching decision (output port) for each individual packet Statistical multiplexing: Sum of peak rates may exceed link bandwidth (as long as mean does not) EES Walrand 6 EES

2 Walrand Lecture Techniques: PS - atagram General idea: no connection establishment, but each packet contains enough info to specify destination Switches contain forwarding tables (but no per-connection state ) Forwarding tables contain info on which outgoing port to use for each destination Two types of addressing: Layer or Layer atagram: Layer (e.g., Ethernet) a b e b To From Flat address space (no structure) Forwarding table: Exact match of destination L address a b c d e f c a b c d e f f d e EES Walrand 7 EES Walrand 8 atagram: Layer (e.g., IP) L-network (e.g., IP) Topological structure match prefix Either fixed prefix length or longest match B E.g. E.g. E.g atagram: Layer (e.g., IP) E.g. 000 matches bits at, at B, at = LPM bits at = EM B EES Walrand EES Walrand atagram: Layer (e.g., IP) 0000 matches bits at, at B, 7 at = LPM E.g. atagram: Layer (e.g., IP) 0000 matches 0 bit at 0 bit at B, 0 at, at = LPM E.g B B EES Walrand EES Walrand 0000 EES

3 Walrand Lecture Techniques: PS Virtual ircuit onnection setup establishes a path through switches virtual circuit I (VI) identifies path Uses packet switching, with packets containing VI VIs are often indices into per-switch connection tables; change at each hop V V V V V V V V V In, V Out, V,,,,. EES,, Walrand Techniques: Source Routing Each packet specifies the sequence of routers (or of output ports) from source to destination source EES Walrand Techniques: omparison Forwarding cost Bandwidth utilization Resource reservations Robustness* atagram high high none high Virtual circuit switching flexible flexible ircuit switching none yes Switching: haracteristics Ports Fast Ethernet, O-, TM, Protocols ST, Link gg., VLN, OSPF, RIP, BGP, VPN, Load Balancing, WRE, WFQ Performance Throughput, Reliability, Power, *The idea is that in case of failure, circuit and V are lost; datagram routing can adapt after routing update. EES Walrand 5 EES Walrand 6 Switching: Examples Juniper M60 isco GSR isco 7600 isco catalyst 6500 Extreme Summit Foundry ServerIron Examples: isco GSR - 6 WN Router Large throughput; SONET links Up to 6 line cards at 0 Gbps each rossbar Fabric isco GSR 6 s: 9 -port O-9c -port O8c Many others (TM, Ethernet, ) 6ft ft EES Walrand 7 EES Walrand 8 EES

4 Walrand Lecture Examples: Juniper M60 WN Router Large throughput; SONET links rossbar Fabric s: -port O-9c -port O8c Many others (TM, Ethernet, ) ft Juniper M60 9 apacity: 80Gb/s Power:.6kW Examples: isco 7600 MN-WN Router Up to 8 Gbps with rossbar Fabric 0Mbps 0Gbps LN s O- to O-8 SONET s MPLS, WFQ, LLQ, WRE, Traffic Shaping.5ft EES Walrand 9 EES Walrand 0 Examples: isco cat 6500 From LN to ccess 8 to 576 0/00 Ethernet s 0 GE, O-, O-, O-8, TM QoS, L Load Balancing; VPN Up to 8Gbps (with crossbar) L-7 Switching VLN IP Telephony (E, T, inline-power Ethernet) SNMP, RMON Examples: Extreme - Summit 8 0/00 ports GE (SX, LX, or LX-70) 7.5Gbps non-blocking 0. Mpps Wire speed L Wire speed L static or RIP OSPF, VRMP, PIM, EES Walrand EES Walrand Examples: Foundry - ServerIron Server Load Balancing Transparent ache Switching Firewall Load Balancing Global Server Load Balancing Extended Layer -7 functionality including URL-, ookie-, and SSL Session I-based switching Secure Network ddress Translation (NT) and Port address translation (PT) Switching: rchitectures Generic rchitecture First Generation Second Generation Third Generation Input Functions Output Functions Interconnection esigns OUT IN VOB ombined IN/OUT EES Walrand EES Walrand EES

5 Walrand Lecture rchitectures: Generic rchitectures: First Generation Input and output interfaces are connected through an interconnect interconnect can be implemented by Shared memory capacity routers (e.g., P-based routers) Shared bus Medium capacity routers Point-to-point (switched) bus High capacity routers input interface Interconnect output interface PU Shared Backplane PU Typically < 0.5Gbps aggregate capacity Limited by rate of shared memory Slide by Nick McKeown Route EES Walrand 5 EES Walrand 6 rchitectures: Second Generation rchitectures: Third Generation PU Route Switched Backplane Typically < 5Gb/s aggregate capacity Limited by shared bus ache ache ache PU Local PU Routing Local Typically < 50Gbps aggregate capacity Slide by Nick McKeown Slide by Nick McKeown EES Walrand 7 EES Walrand 8 rchitectures: Input Functions Packet forwarding: decide to which output interface to forward each packet based on the information in packet header examine packet header lookup in forwarding table update packet header rchitectures: Output Functions management: decide when and which packet to drop Scheduler: decide when and which packet to transmit Scheduler EES Walrand 9 EES Walrand 0 EES

6 Walrand Lecture rchitectures: Output Functions (ct) Packet classification: map each packet to a predefined f/connection (for datagram forwarding) use to implement more sophisticated services (e.g., QoS) F: a subset of packets between any two endpoints in the network EES Walrand lassifier f f f n management Scheduler rchitectures: Output Queued Only output interfaces store packets dvantage Easy to design algorithms: only one congestion point isadvantage Requires an output speedup Ro/ = N, where N is the number of interfaces not feasible for large N input interface Backplane output interface R O EES Walrand rchitectures: Input Queues Only input interfaces store packets dvantages Easy to build Simple algorithms isadvantages HOL Blocking In practice: Speedup of suffices input interface Backplane output interface R O Note: Head-of-line Blocking The cell at the head of an input queue cannot be transferred, thus blocking the foling cells Input Input Input annot be transferred because of HOL blocking Output Output Output annot be transferred because of output contention Being transferred EES Walrand EES Walrand rchitectures: Virtual Output s OUT buffers at each input port omplexity: Matching Problem Full throughput algorithm Good Heuristic VOB: Full Throughput Maximum Weighted Matching: = B = = 5 rossbar = 0 Note: Figure from Prof. Varaiya s notes for EE8b EES Walrand 5 B + > + => Serve (B, ) EES Walrand 6 EES

7 Walrand Lecture VOB: Good Heuristic i-slip Inputs request permission to send from outputs Outputs grant permissions to inputs (round-robin) Inputs accept permissions (round-robin) Request Grant ccept Iter rchitectures: ombined IN/OUT Both input and output interfaces store packets dvantages Easy to built Utilization can be input interface output interface achieved with limited Backplane input/output speedup (<= ) isadvantages Harder to design algorithms Two congestion points Need to design f control R O Last ccept Last Grant EES Walrand 7 EES Walrand 8 Switching: Summary Switching needed for big networks Internetworking externality ircuit Packet V: QoS possible Packet atagram L: Limited by flat address space L: Exact Match: Easy lookup less efficient Prefix Match Switch functions: control and data ifferent rchitectures: cost vs. performance EES Walrand 9 EES