2.1.1. Key Words 
In order to prevent confusion, a number of key terms which are used
frequently within the text are defined here in more detail.
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Nodes:
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Designates a device with a port/connection
in a network.
This can be a router, a CGW module or any computer.
Also frequently referred to as “Host“.
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LAN segment:
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Part of a network in which all
nodes communicate with each other directly on Layer 2 (Ethernet MAC).
The nodes are thus switched on the same “shared“ medium and interconnected
via hubs or Layer 2 switches. In other words, they communicate without
routers (Layer 3). The communication with nodes beyond this segment
has to be realized via routers.
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IP address:
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A numerical Internet address comprising
4 sets of digits, e.g. 172.16.222.45. In this context, the term
always designates the individual, complete and unequivocal address of
a node.
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Network mask (Netmask):
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Internet addresses are broken
down into network-specific and node-specific sections. The size of these
sections differs, depending on the class of the address (determined by
the first digit of the address).
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Byte
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1
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2
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3
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4
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Class
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A
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Network [1 .. 126]
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Node
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Node
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Node
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B
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Network [128 .. 191]
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Network
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Node
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Node
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C
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Network [192 .. 223]
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Network
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Network
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Node
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The netmask allows subnets to
be generated within a network. Specific bits of the node section are
used for the purposes of addressing. The network mask specifies which
parts of the IP address are to be regarded as network/subnet sections
by means of the specified bits. The remaining digits (bits not specified
in the mask) designate the node section.
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Network address:
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In this document, the term network
address is used for the entire network and subnet part of the
IP address.
The network address is yielded by a bit-by-bit AND
operation of any IP address with the netmask.
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VLAN tagging
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According to IEEE 802.1 p/q, there
are two functions which are controlled using a common tag: the priority
and the VLAN ID. The term VLAN tagging is generally applied once
the tag is used - regardless of what it is being used for. The same
applies in the case of IPDA. When reference is made to deactivating
or activating VLAN tagging (AMOs SIPCO or CGWB:
VLAN),
it is the tag that is meant, not the VLAN function.According to
the standard there are three types of frames:
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Normal Ethernet frames without
tagging
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Ethernet frames with tagging
The
priority bits are used The VLAN ID is 0.
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Ethernet frames with tagging
The
priority bits are 0, The VLAN ID is > 0.
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Some IP equipment vendors only
allow priority bits to be used when VLAN ID > 0 is set.
When
tagging is being used, the IPDA components always use priority tagging,
but allow a setting of VLAN ID > 0
The priority bits are fixed
according to the traffic type.
The values are specified in Table
3, “TOS values”
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TOS byte
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The Type Of Service
byte is a component of the header for all IP packets in accordance with
RFC 791.
According to RFC 791 (Internet Protocol), the byte
is split up as follows (most significant -> least significant bit)
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3 bits for precedence
111
- Network Control
110 - Internetwork Control
101 - CRITIC/ECP
100
- Flash Override
011 - Flash
010 - Immediate
001 -
Priority
000 - Routine
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3 bits for priority
D-T-R
Slight
delay:
0 = Normal, 1 = Low
Throughput:
0
= Normal, 1 = High
Reliability:
0 = Normal, 1 = High
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2 bits reserved
for future
use
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According to RFC 2474 (Differentiated
Services), the six high-order bits are used as DiffServ Code Point
(DSCP), while the two least significant bits are reserved.
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Some of the values to be set are
specified as 6-bit values without the 2 reserved bits, and others as
8-bit values (with the 2 reserved bits = 0).
With IPDA, the entire
TOS byte is always specified. The two least significant bits are always
set to zero.
A pure DiffServ Code Point must therefore be moved
2 bits to the left or multiplied by 4 in order to obtain the TOS byte
setting for IPDA.
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Table 1. Example: Class B IP address, netmask and network address
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IP address
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172
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16
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222
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45
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1
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0
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1
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0
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1
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1
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0
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0
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0
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0
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0
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1
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0
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0
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0
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0
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1
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1
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0
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1
|
1
|
1
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1
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0
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0
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0
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1
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0
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1
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1
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0
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1
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Netmask
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255
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255
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240
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0
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||||||||||||||||||||||||||||
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1
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1
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1
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
1
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1
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0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
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0
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Subnet
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1
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1
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0
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1
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Network address
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172
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16
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208
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0
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||||||||||||||||||||||||||||
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1
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0
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1
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0
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1
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1
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0
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0
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0
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0
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0
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1
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0
|
0
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0
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0
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1
|
1
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0
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1
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0
|
0
|
0
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0
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0
|
0
|
0
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0
|
0
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0
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0
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0
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