Walrand Lecture 11 TOC Switching Forwarding Why Switching Techniques Switch Characteristics Switch Examples Switch Architectures Summary Lecture 11 Switching Forwarding EECS 122 University of California Berkeley EECS 122 Switching Why Walrand Switching Techniques Direct vs Switched Networks Circuit Switching e g Telephone net Packet Switching n links Single link Switches Direct 2 Switched Datagram e g IP Ethernet Virtual Circuits e g MPLS ATM Source Routing Comparison Direct Network Limitations Distance coordination delay propagation limitation Number of hosts collisions shared bandwidth address tables Single link technology cannot mix optical wireless Internetworking Externality gain at low cost EECS 122 Walrand 3 Techniques Circuit Switching Circuit Switch Connection list Time scale connection EECS 122 Walrand 4 Whole link shared by all packets Mechanism e g TDM WDM Packet Switch Features Data 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 Packets not switched independently establish circuit before sending data Dedicated path and resources from source to destination Setup time low delays and guaranteed resources thereafter EECS 122 Walrand Techniques Packet Switching Link divided into fixed independent circuits Mechanism Features EECS 122 5 EECS 122 Walrand 6 Walrand Lecture 11 Techniques PS Datagram Datagram Layer 2 e g Ethernet 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 2 or Layer 3 Flat address space no structure Forwarding table Exact match of destination L2 address a b e b 1 4 a b c d e f 1 4 3 2 2 2 2 a b c d e f 1 1 1 1 2 3 4 2 4 3 c 3 d e f To From EECS 122 Walrand 7 Datagram Layer 3 e g IP E g 2 L3 network e g IP E g 1 E g 3 Topological structure match prefix Either fixed prefix length or longest match 10100111 11010001 11010000 B Fixed Longest D Other A 11010101 11001000 C 1100 11001101 C EECS 122 Walrand 9 11010101 11001101 11001000 C C C EECS 122 Walrand 11001001 10 01100101 matches 0 bit at A B 0 bit at B 0 at C 2 at D D LPM B 10100000 1101 11001001 01000000 11100000 A 11010101 11001101 E g 3 10100111 11010001 B 10100000 1100 11001000 C 1100 11011001 01000000 11100000 Datagram Layer 3 e g IP 10100111 A B 10100000 11010000 B Fixed Longest D Other A 11010101 11001101 E g 2 11010000 B Fixed Longest D Other A 10100111 A 11001001 E g 1 11011001 matches 4 bits at A 1 at B 3 at C A LPM 4 bits at A A EM 1101 01000000 11100000 11001001 matches 3 bits at A 1 at B 7 at C C LPM 1101 8 11010001 Datagram Layer 3 e g IP 11010001 Walrand Datagram Layer 3 e g IP B 10100000 1101 A EECS 122 11010000 B Fixed Longest D Other A 11001000 C 1100 C 01000000 11100000 01100101 EECS 122 EECS 122 Walrand 11001001 11 EECS 122 Walrand 11001001 12 Walrand Lecture 11 Techniques Source Routing Techniques PS Virtual Circuit Each packet specifies the sequence of routers or of output ports from source to destination Connection setup establishes a path through switches A virtual circuit ID VCI identifies path Uses packet switching with packets containing VCI VCIs are often indices into per switch connection tables change at each hop VC1 VC2 1 2 VC1 EECS 122 In VC Out VC 1 1 4 1 1 2 4 3 2 1 4 2 4 VC1 VC2 3 4 1 4 3 4 VC3 2 VC1 3 1 2 3 4 1 2 3 4 4 3 4 VC2 13 Techniques Comparison Forwarding cost Bandwidth utilization Resource reservations Robustness 1 2 3 4 VC1 Walrand Datagram source EECS 122 1 2 3 4 1 2 3 4 1 2 3 4 4 3 4 Walrand 14 Switching Characteristics Circuit switching high Virtual circuit switching low high flexible low none flexible yes high low low Ports Fast Ethernet OC 3 ATM Protocols none ST Link Agg VLAN OSPF RIP BGP VPN Load Balancing WRED WFQ Performance Throughput Reliability Power The idea is that in case of failure circuit and VC are lost datagram routing can adapt after routing update EECS 122 Walrand 15 Switching Examples EECS 122 Walrand 16 Examples Cisco GSR 12416 WAN Router Large throughput SONET links Up to 16 line cards at 10 Gbps each Crossbar Fabric Cisco GSR 12416 19 Line Cards 1 port OC 192c 4 port OC48c Many others ATM Ethernet Juniper M160 Cisco GSR Cisco 7600 Cisco catalyst 6500 Extreme Summit Foundry ServerIron 6ft 2ft EECS 122 EECS 122 Walrand 17 EECS 122 Walrand 18 Walrand Lecture 11 Examples Juniper M160 Examples Cisco 7600 WAN Router Large throughput SONET links Crossbar Fabric Line Cards 1 port OC 192c Juniper M160 4 port OC48c 19 Many others ATM Ethernet Capacity 3ft MAN WAN Router Up to 128 Gbps with Crossbar Fabric 10Mbps 10Gbps LAN Interfaces OC 3 to OC 48 SONET Interfaces MPLS WFQ LLQ WRED Traffic Shaping 80Gb s Power 2 6kW 2 5ft EECS 122 Walrand 19 Examples Cisco cat 6500 EECS 122 Walrand 20 Examples Extreme Summit 48 10 100 ports 2 GE SX LX or LX 70 17 5Gbps non blocking 10 1 Mpps Wire speed L2 Wire speed L3 static or RIP OSPF DVRMP PIM From LAN to Access 48 to 576 10 100 Ethernet Interfaces 10 GE OC 3 OC 12 OC 48 ATM QoS ACL Load Balancing VPN Up to 128Gbps with crossbar L4 7 Switching VLAN IP Telephony E1 T1 inline power Ethernet SNMP RMON EECS 122 Walrand 21 Examples Foundry ServerIron EECS 122 Walrand 22 Switching Architectures Generic Architecture First Generation Second Generation Third Generation Input Functions Output Functions Interconnection Designs Server Load Balancing Transparent Cache Switching Firewall Load Balancing Global Server Load Balancing Extended Layer 4 7 functionality including URL Cookie and SSL Session ID based switching Secure Network Address Translation NAT and Port address translation PAT OUT IN VOB Combined IN OUT EECS 122 EECS 122 Walrand 23 EECS 122 Walrand 24 Walrand Lecture 11 Architectures Generic Input and output interfaces are connected through an interconnect A interconnect can be implemented by Architectures First Generation Shared Backplane input interface CPU output interface CP I Line U nte rfa ce M em or y Interconnect Shared memory Line Interface Line Interface Line Interface MAC MAC MAC low capacity routers e g PC based routers Shared bus Medium capacity routers Buffer Memory Route Table Typically 0 5Gbps aggregate capacity Limited by rate of shared memory Point to point switched bus High capacity routers EECS 122 Slide by Nick McKeown Walrand 25
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