Switch Implementation and Performance Simple switch - general - - PowerPoint PPT Presentation

switch implementation and performance
SMART_READER_LITE
LIVE PREVIEW

Switch Implementation and Performance Simple switch - general - - PowerPoint PPT Presentation

Switch Implementation and Performance Simple switch - general purpose workstation with multiple network adapters I/O Bus Network Interface 1 CPU Network Interface 2 Main Bus Network Interface 3 Main Memory Oct. 12. 2005 CS 440


slide-1
SLIDE 1
  • Oct. 12. 2005

CS 440 Lecture Notes 1

Switch Implementation and Performance

  • Simple switch - general purpose

workstation with multiple network adapters

Network Interface 1 Network Interface 2 Network Interface 3 CPU Main Memory Main Bus I/O Bus

slide-2
SLIDE 2
  • Oct. 12. 2005

CS 440 Lecture Notes 2

Simple Switch (cont.)

  • Advantages

– Simple – Inexpensive – Flexible

  • Disadvantages

– Limited performance due to single point of contention: I/O bus and main bus each traversed twice for each packet

slide-3
SLIDE 3
  • Oct. 12. 2005

CS 440 Lecture Notes 3

Simple Switch Performance

  • Upper bound on total throughput half

min(main memory bandwidth, I/O bus bandwidth)

– 66 MHz, 32 bit I/O bus allows 66 * 10^6 * 32 / 2 ≈ 1 Gbps – This is peak; practical limit is less – Could only support one Gigabit Ethernet adapter, or less than 10 Fast Ethernet adapters

slide-4
SLIDE 4
  • Oct. 12. 2005

CS 440 Lecture Notes 4

Simple Switch Performance (cont.)

  • For short packets, time to process packet

could also be limiting factor

– Max packets/sec (pps) * avg. packet length also limits max throughput

  • Solution to achieve higher performance –

custom hardware, able to switch packets between different ports in parallel

slide-5
SLIDE 5
  • Oct. 12. 2005

CS 440 Lecture Notes 5

Switch Construction

  • Switch block diagram
  • Ports include network interface, buffering,

possibly other logic

  • Fabric routes packets to correct output port

Control Processor Switch Fabric Input Ports Output Ports

slide-6
SLIDE 6
  • Oct. 12. 2005

CS 440 Lecture Notes 6

Switch Ports

  • Components of ports

– Virtual circuit tables – Bridge forwarding tables – Logic to analyze packet headers to decide how to route packets (input ports) – Buffers

  • Input ports are potential bottleneck – need

to inspect every received packet to determine where to forward

slide-7
SLIDE 7
  • Oct. 12. 2005

CS 440 Lecture Notes 7

Buffering Issues

  • Problem with buffering in the input ports:

head-of-line-blocking

– Packets destined for available output ports can be held up behind a packet destined for a busy output port

  • Buffering in output ports or possibly in

fabric (internal buffering) preferable

  • Buffer management might need to take

into account QoS guarantees

slide-8
SLIDE 8
  • Oct. 12. 2005

CS 440 Lecture Notes 8

Switching Fabric

  • Different types of fabrics

– Shared-bus: basic fabric as described for simple workstation-based switch – Shared-memory: input ports write to memory,

  • utput ports read from memory.
  • Wide, fast memory required
  • Multi-port memory can increase speed

– Crossbar: connect any input port to any

  • utput port
slide-9
SLIDE 9
  • Oct. 12. 2005

CS 440 Lecture Notes 9

Switching Fabric (cont.)

  • Fabric can either be controlled by input

port or control processor, or can access packet header to decide how to route (self- routing)

– Input port can add routing header to start of packet; this is removed when packet delivered to output port

slide-10
SLIDE 10
  • Oct. 12. 2005

CS 440 Lecture Notes 10

Self-Routing Fabrics

  • Self-routing fabric typically constructed of

layers of simple 2x2 switches

– Most scalable approach

slide-11
SLIDE 11
  • Oct. 12. 2005

CS 440 Lecture Notes 11

Banyan Networks

  • Need to ensure that packets on two inputs

to the same switch don’t need to go to the same output

– Banyan networks eliminate possibility of collisions – Each column of switches looks at next bit of routing header – route to top output if bit is 0, to bottom output if bit is 1

slide-12
SLIDE 12
  • Oct. 12. 2005

CS 440 Lecture Notes 12

Banyan Networks (cont.)

  • Switches wired in “perfect shuffle” pattern

so that if packets are presented on input ports in ascending order, they are delivered with no collisions

slide-13
SLIDE 13
  • Oct. 12. 2005

CS 440 Lecture Notes 13

Banyan Networks (cont.)

  • Can use a sorting network (like the

Batcher network) to order packets on input to Banyan network