Balaji Prabhakar

Spring 2011A history of big routers

(slides from Nick McKeown’s EE 384X presentation)

EE384MNetwork Algorithms

OutlineWhat is an Internet router?

– What limits performance: Memory access time

The early days: Modified computers– Programmable against uncertainty

The middle years: Specialized for performance– Needed new architectures, theory, and

practice– So how did we do?– Simple model breaking down

Definitions

12

34

56

78

…

……

N

R

N = number of linecards. Typically 8-32 per chassisR = line-rate. 1Gb/s, 2.5Gb/s, 10Gb/s, 40Gb/s, 100Gb/s

Capacity of router = N x R

What a Big Router Looks LikeCisco GSR 12816 Juniper T640

6ft

19”

2ft

Capacity: 640Gb/sPower: 5kW

3ft

2.5ft

19”

Capacity: 320Gb/sPower: 3kW

What Multirack Routers Looks Like

Cisco CRS-1 Juniper T1600 + TX Matrix

Lookup internet addressCheck and update age

Check and update checksum

Router Control and Management

Barebones Router

Barebones Router

Barebones Router

1 2

BottlenecksMemory, memory, …

OutlineWhat is an Internet router?

– What limits performance: Memory access time

The early days: Modified computers– Programmable against uncertainty

The middle years: Specialized for performance– Needed new architectures, theory, and

practice– So how did we do?– Simple model breaking down

Early days: Modified Computer

R

R

R

R

R

R

R

R

Must run at rate N x R

Bottlenecks

2nd Generation RouterR

R

R

R

Early days: Modified Computer

Function more important than speed

1993 (WWW) changed everything

We badly needed– Some new architecture– Some theory– Some higher performance

N x R

3rd Generation Router: Switch

1 x R

Arbiter

Arbiter Arbiter Arbiter Arbiter

Arbiter Arbiter Arbiter Arbiter

Arbiter

4th Generation RouterMultirack; optics inside

SwitchLinecards

Optical links

100sof metres

Alcatel 7670 RSP Juniper TX

TX

More 4th Generation Routers

Avici TSR Cisco CRS-1

Example of Theory

There’s something special about “2”

Case 1: Placing calls

A crosspoint switch supports all permutationsSo it is “non-blocking”But it needs N2 crosspoints

1

Permutation

1 0 0 0 0 0 0 00 0 0 0 0 0 00 0 0 0 1 0 0 00 0 0 1 0 0 0 00 0 1 0 0 0 0 00 0 0 0 0 1 0 00 0 0 0 0 0 0 10 0 0 0 0 0 1 0

1

11

1 11

1

11

Crosspoint switch1

11

11

1

1

Case 1: Placing CallsUncertainty costs

1 0 0 0 0 0 0 00 1 0 0 0 0 0 00 0 0 0 1 0 0 00 0 0 1 0 0 0 00 0 1 0 0 0 0 00 0 0 0 0 1 0 00 0 0 0 0 0 0 10 0 0 0 0 0 1 0

00000000

0 0 0 0 0 0 0 0 1

If I give you the permutation, you can route it. If I give you entries one at a time, you can’t.

1

1 1

1

Clos (1950s): But if you make it run 2 times faster

you can route calls one at a time.

Case 2: Mimicking

N x R

Case 2: Mimicking

1 x R

Are they equivalent?

NR

R

No.

Case 2: Mimicking

1 x R ? x R

Algorithm

Yes, if it runs 2 times faster.

Now are they equivalent?

R 2R

Algorithm

NR

Yes, if it runs 2 times faster.

Case 3: Are they equivalent?

1

Case 4: Routing packets with uncertainty

R

Algorithm

0.1 0.2 0.5 0.20.3 0.1 0.3 0.30.5 0.2 0.1 0.20.1 0.5 0.1 0.3

Rates

But we don’t know the rates (they are always changing)

If you know the rates, you can find a sequence of permutations:

0 0 1 00 1 0 00 0 0 11 0 0 0

0 0 1 01 0 0 00 0 0 10 1 0 0

1 0 0 00 0 1 00 0 0 10 1 0 0

=

Case 4: Routing packets with uncertainty

2If you choose the permutations one at a time, and you can spend as long as you want choosing, then you can support any pattern of rates.

3But if you have to make decisions one at a time, then the switch has to run 2 times faster.

Case 5: Load-balancing Load-balancing to support all rate matrices:– Requires the network to run 2 times faster– E.g. the VL2 (Valiant Load balancing)

architecture for Data Centers