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Chapter 26

IPoverATM

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CONTENTSCONTENTS

• ATM WANS• CARRYING A DATAGRAM IN CELLS• ROUTING THE CELLS• ATMARP• LOGICAL IP SUBNET (LIS)

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ATM WANS

26.126.1

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Figure 26-1

An ATM WAN in the Internet

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Figure 26-2

ATM layers in routers and switches

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End devices such as routers use all End devices such as routers use all three layers, while switches use three layers, while switches use

only the bottom two layers. only the bottom two layers.

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Figure 26-3

AAL5

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The AAL layer used by the The AAL layer used by the IP protocol is AAL5. IP protocol is AAL5.

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Figure 26-4

ATM layer

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Figure 26-5 ATM headers

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CARRING ADATAGRAM

IN CELLS

26.226.2

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Figure 26-6

Fragmentation

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Only the last cell carries Only the last cell carries the 8-byte trailer the 8-byte trailer

added to the IP datagram. added to the IP datagram. Padding can be added only to Padding can be added only to

the last cell or the last two cells. the last cell or the last two cells.

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The value of the PT field The value of the PT field is 000 in all cells is 000 in all cells

carrying an IP datagram carrying an IP datagram fragment except for the last cell; fragment except for the last cell; the value is 001 in the last cell.the value is 001 in the last cell.

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Figure 26-7

ATM cells

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ROUTING THE

CELLS

26.326.3

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Figure 26-8

Entering-point and exiting-point routers

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ATMARP

26.426.4

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Figure 26-9ARP packet

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Figure 26-10

Binding with PVC

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The inverse request and The inverse request and inverse reply messages can bind inverse reply messages can bind

the physical address the physical address to an IP address in to an IP address in a PVC situation. a PVC situation.

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Figure 26-11

Binding with ATMARP

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The request and reply The request and reply message can be used message can be used

to bind a physical address to bind a physical address to an IP address to an IP address

in an SVC situation. in an SVC situation.

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Figure 26-12

Building a table

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The inverse request and inverse The inverse request and inverse reply can also be used to reply can also be used to

build the server’s mapping table.build the server’s mapping table.

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LOGICAL IP SUBNET

(LIS)

26.526.5

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Figure 26-13

LIS

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LIS allows an ATM network to LIS allows an ATM network to be divided into several logical subnets. be divided into several logical subnets.

To use ATMARP, To use ATMARP, we need a separate we need a separate

server for each subnet. server for each subnet.