Internetworking - Computer Networks - Lecture Notes | CS 4590, Study notes of Computer Systems Networking and Telecommunications

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Internetworking

Outline

Best Effort Service ModelGlobal Addressing SchemeRouting

IP Internet

-^

Concatenation of Networks

-^

Protocol Stack

R

R

H

H

H

H

H1 Network 2 (Ethernet)

Network 1 (Ethernet)

H

Network 3 (FDDI)

Network 4(point-to-point) H

R

H

R

ETH

FDDI IP

TCP IP ETH

R

FDDI

PPP IP

R

PPP

ETH IP

H

TCP IP ETH

H

Example

Latency = 20m/(2.3x

8 m/s) + (1500bytes *

8bits/byte)/ 10Mbps Answer = 12ms

Example

Given a channel with a two way latency of 100ms

and a bandwidth of 45Mbps, how much data canbe “in flight?” Latency * bandwidth = volume

Service Model

-^

Connectionless (datagram-based)

-^

Best-effort delivery (unreliable service)–

packets are lost

-^

packets are delivered out of order

-^

duplicate copies of a packet are delivered

-^

packets can be delayed for a long time

-^

IP Packet format

Version

HLen

TOS

Length

Ident

Flags

Offset

TTL

Protocol

Checksum

SourceAddrDestinationAddr

Options (variable)

Pad(variable)

0

4

8

16

19

31

Data

Service Model

•^

Version

•^

Hlen

: length of header in 32 bit

words (20bytes w/o options

-^

TOS

: used when differentiated

services are provided

-^

Length

: size of data + header in

bytes. Max size 65,

-^

TTL

: time to live

•^

Protocol

: of upper layer

(UDP=6, TCP=

•^

Checksum

: adds up header in

16bit words using 1’scomplement then take 1’scomplement of result

-^

Source address

-^

Destination address

-^

Options

: not used

•^

Pad

: for even byte boundary

Version

HLen

TOS

Length

Ident

Flags

Offset

TTL

Protocol

Checksum

SourceAddrDestinationAddr

Options (variable)

Pad(variable)

0

4

8

16

19

31

Data

Example

H

R

R

R

H

ETH IP (1400)

FDDI IP (1400)

PPP IP (512)PPP IP (512)PPP IP (376)

ETH IP (512)ETH IP (512)ETH IP (376)

Ident= x

Offset= 0

Start of header

0

Rest of header1400 data bytes

Ident= x

Offset= 0

Start of header

1

Rest of header512 data bytes

Ident= x

Offset= 512

Start of header

1

Rest of header512 data bytes

Ident= x

Offset= 1024

Start of header

0

Rest of header376 data bytes

MTU ETH = 1500bytes

MTU FDDI=

MTU PPP=532bytes

1420 bytes total

R

Global Addresses

-^

Properties– globally unique– hierarchical: network + host

-^

Dot Notation– 10.3.2.4– 128.96.33.81– 192.12.69.

Network

Host

7

24

0

A:

Network

Host

14

16

1

0

B:

Network

Host

21

8

1

1

0

C:

Address Translation

-^

Map IP addresses into physical addresses– destination host– next hop router

-^

Techniques– encode physical address in host part of IP address

(won’t work for Ethernet addresses)

• table-based

Overview Routing

-^

Forwarding vs Routing– forwarding: to select an output port based on

destination address and routing table

• routing: process by which routing table is built

Forwarding Algorithm

D

destination

IP

address

for

each

entry

(SubnetNum,

SubnetMask,

NextHop)

D

SubnetMask

D

if

D

SubnetNum

if

NextHop

is

an

interface

deliver

datagram

directly

to

D

else

deliver

datagram

to

NextHop

-^

Use a default router if nothing matches

-^

Not necessary for all 1s in subnet mask to be contiguous

-^

Can put multiple subnets on one physical network

-^

Subnets not visible from the rest of the Internet

Overview Routing

-^

Network as a Graph

-^

Problem: Find lowest cost path between two nodes

-^

Factors– static: topology– dynamic: load

-^

Adaptive & Static algorithms for routing

4

3

6

2

1

9

1

1 D A

F

E

B

C

Example•

Initial Routing table for Node A

Destination

Cost

NextHop

A

A

B

B

C

C

D

X

E

E

F^

F

G

X

D

G

A F

E B

C

Example•

Finding a Routing table for Node A

Destination

Cost

NextHop

A

A

B

B

C

C

D

C

E

E

F^

F

G

F

D

G

A F

E B

C