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Content 1 LAN and VLAN: some considerations 3 1.1 Definitions 3
1.2 Domains in a traditional LAN 4 1.3 Domains in a VLAN 8 1.4
Traffic separation by VLAN 11 1.5 Tagging 12 1.6 VLAN Aware /
Unaware 19 1.7 Links Types 20 1.8 Q-in-Q 23 1.9 Spanning Tree
Protocol (802.1d) 27 1.10 Rapid Spanning Tree Protocol RSTP
(802.1w) 33 1.11 Multiple Spanning Tree Protocol MSTP (802.1s) 35 2
Carrier Ethernet: Some Concepts 41 2.1 What is Carrier Ethernet 41
2.2 MEF: Metro Ethernet Forum 42 2.3 Cooperation with Other
Standard Bodies 44 2.4 IEEE: Institute of Electrical and
Electronics Engineers 44 2.5 IETF: The Internet Engineering Task
Force 44 2.6 ITU: International Telecommunication Union
Telecommunication
Standardization Sector 45 2.7 Carrier Ethernet Terminology:
Basic Components 46 2.8 Carrier Ethernet Service Types 60 2.9
Circuit Emulation Services over Packet (CESoP) 61 2.10 FlexiPacket
EVC and Services 67 3 Quality of Service in the HUB 71 3.1 QoS
Mechanism 72 3.2 Classifier and Packet Marker 75 3.3 Policer 79 3.4
Buffer Manager: Congestion Avoidance 82
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1 LAN and VLAN: some considerations 1.1 Definitions A LAN or
Local Area Network is a computer network (or data communications
network) which is confined in a limited geographical location. A
Virtual (or logical) LAN is a local area network with a definition
that maps workstations/PCs on some other basis than geographic
location (for example, by department, type of user or primary
application)
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1.2 Domains in a traditional LAN In a traditional Ethernet LAN,
stations connected to the same media, share a domain. In this
domain, every station hears broadcast frames transmitted by every
other station. As the number of stations grows, contention and
broadcast traffic increase a lot. At some point, the Ethernet
becomes saturated. To operate efficiently, the LAN must be divided
into smaller pieces. In a traditional LAN, stations are connected
to each other by means of HUBS or REPEATERS.
HUB HUB
One collision Domain
One Broadcast Domain
Fig. 1 Domains in a traditional LAN (1)
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A BRIDGE (or a L2 SWITCH) is able to divide one collision domain
in different collision domains.
HUB HUB
Two collision Domains
One Broadcast Domain
BRIDGE
Fig. 2 Domains in a traditional LAN (2)
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A BRIDGE (or a L2 SWITCH) do not forward collisions, but allows
broadcast and multicast passing through. Broadcast domain refers to
a part of network where a single broadcast packet is transmitted to
all segments of the network (i.e. ARP request, NETBIOS name
request). This type of traffic, affects the whole network because
each device receiving a broadcast frame must analyze it. If
broadcast frames increases in frequency, available bandwidth
decrease up to be exhaust (BROADCAST STORM).
SWITCH = MULTIPORT BRIDGE
L2 SWITCH
Fig. 3 Domains in a traditional LAN (3)
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A ROUTER may be used to prevent Broadcast and Multicast from
traveling through the network because it is able to segment a LAN
in different Broadcast domains.
HUB HUB
Two collision Domains
Two Broadcast Domain
ROUTER
Fig. 4 Domains in a traditional LAN
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1.3 Domains in a VLAN VLANs allow a network manager to logically
segment a LAN into different broadcast domains without using
routers. Bridging software is used to define which workstations are
to be included in the broadcast domain.
VLAN 2 Broadcast Damain
VLAN 2 Broadcast Damain
VLAN 1 Broadcast Domain
VLAN 1 Broadcast Domain
L2 SWITCH L2 SWITCH
Fig. 5 Domains in a VLAN (1)
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ROUTERS are necessary only to make possible communication
between different VLANs. VLAN IS A LOGICALLY DEFINED BROADCAST
DOMAIN.
VLAN 2 Broadcast Damain
VLAN 2 Broadcast Damain
VLAN 1 Broadcast Domain
VLAN 1 Broadcast Domain
L2 SWITCH L2 SWITCH
ROUTER
Fig. 6 Domains in a VLAN (2)
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The advantages of VLANs as regards to traditional LANs are shown
in Fig. 7.
Periodically, sensitive data may be broadcast on a network.
Placing only those users who can have access to have access to that
data on a VLAN can reduce the chances of an outsider gaining access
to the data
SECURITY
Routers are only used to interconnect different broadcast
domains
REDUCED COSTS
Simply moves, adds and changesSIMPLIFIED ADMINISTRATION
Independent from the physical wiringVIRTUAL WORKGROUPS
Better control of broadcastPERFORMANCE
Fig. 7 Domains in a VLAN (3)
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1.4 Traffic separation by VLAN With VLANs it is possible to
separate different logical networks on one physical infrastructure
supporting the traffic separation. Figure Fig. 8 shows a Traffic
Separation Example by VLAN.
RNC
Ethernet Network
Flexi BTS Nr.1
Flexi BTS Nr.2
VLAN1 -> Voice from Flexi BTS Nr.1 to RNC
Traffic over same physical port separated by VLAN.
VLAN2 -> Data from Flexi BTS Nr.1 to RNC
VLAN4 -> Data from Flexi BTS Nr.1 to RNC
VLAN3 -> Voice from Flexi BTS Nr.2 to RNC
Fig. 8 Traffic separation by VLAN
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1.5 Tagging Tagging is a process used to identify the VLAN
originating. The VLAN tagging scheme in 802.1q results in four
bytes of information being added to the frame following the source
address and preceding the type/length field. This increases the
maximum frame size in Ethernet to 1522 bytes. Fig. 9 reports a IEEE
802.3 untagged frame Fig. 10and Fig. 11 explain the TAG fields.
MAC DA6 bytes
Payload46-1500 bytes
FCS4 bytes
Basic IEEE 802.3 Ethernet Frame: minimum length 64 bytes,
maximum length 1518 bytes
Destination & Source MAC Addresses:The Destination MAC
Address field identifies the station or stations that are to
receive the frame. The Source MAC Address identifies the station
that originated the frame. A Destination Address may be a unicast
destined for a single station, or a "multicast address" destined
for a group of stations. A Destination Address of all 1 bits refers
to all stations on the LAN and is called a "broadcast address".
Length/Type:If the value of this field is less than or equal to
1500, then the Length/Type field indicates the number of bytes in
the Payload field. If the value of this field is greater than or
equal to 1536, then the Length/Type field indicates protocol
type.
Payload (MAC Client Data):This field contains the data
transferred from the source station to the destination station or
stations.
Frame Check Sequence:This field contains a 4-byte cyclical
redundancy check (CRC) value used for error checking.
MAC SA6 bytes
Length/Type2 bytes
VLAN tags may be added here
Preamble+SD
8 bytes
InterframeGap
12 bytes
64-1518 bytes
Fig. 9 IEEE 802.3 Untagged Frame
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CFI
16 bits
TAG Protocol Identifier TPID 0x8100
1bit 12 bits3bits
Priority VLAN ID
TCI Tag Control Identifier
TPID TAG Protocol Identifier
2 bytes2 bytes
4 bytes
IEEE 802.3 Frame without VLAN Tag Header
IEEE 802.3 with 802.1Q 4-Byte VLAN Tag Header
User priority (Priority Code Point PCP) CFI (Canonical format
identifier)
VLAN ID
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1.5.1 Class of Service (CoS) IEEE 802.1p The IEEE 802.1p
provides a standard and interoperable way to set the priority bits
in a frames header and to map these settings to TRAFFIC CLASSES.
There are 8 TRAFFIC CLASSES (3 Bits) according to the table
reported in Fig. 12.
000BEBEST EFFORT
001BKBACKGROUND
010RRESERVRD FOR FUTURE USE
011EEEXCELLENT EFFORT TRAFFIC
100CLCONTROLLED LOAD TRAFFIC
101VIVIDEO TRAFFIC
110VOVOICE TRAFFIC
111NCNETWORK CONTROL TRAFFIC
Fig. 12 Quality Of Service IEEE 802.1p (1)
WARNING Of course, network operators may choose to implement
traffic differentiation on a per VLAN-ID basis rather than using
the three CoS bits.
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FlexiPacket First Mile 200, HUB 800 and FlexiPacket MultiRadio
have 8 queues and the association between PCP and Priority Queue is
reported in Fig. 15.
FPFM-200/HUB-800/FPMR PriorityQueue
PCP
Fig. 15 FPFM-200/HUB 800/FPMR PCP - Priority queues
association
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When 4 queues are available, like in the FlexiPacket ODU, the 8
PCPcodes could be associated to four priority values as reported in
Fig. 17 (FlexiPacket ODU default).
37
26
25
24
13
12
01
00
Queue PriorityValue
PCP
Fig. 17 FlexiPacket ODU Priority Code Point Configuration
When 5 queues are available, like in FlexiPacket HUB 2200/1200,
the 8 PCP codes could be associated to five priority values as
reported in Fig. 16 (HUB 1200/2200 configuration).
47
36
25
24
13
12
01
00
Queue PriorityValue
PCP
Fig. 18 FlexiPacket HUB (2200/1200) Priority Code Point
Configuration
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1.6 VLAN Aware / Unaware VLAN AWARE If the data is to go to a
device that knows about VLAN implementation (VLAN Aware), the VLAN
identifier is added to the data. VLAN UNAWARE If it is to go to a
device that has no knowledge of VLAN implementation (VLAN Unaware),
the BRIDGE sends the data without the VLAN identifier.
TAG added/removed
TAGTAG
FrameFrame
TAGTAG
FrameFrame
TAGTAG
FrameFrame
FrameFrameFrameFrame
FrameFrameFrameFrameFrameFrameFrameFrame
TAG added/removed
L2-Switch L2-Switch
VLAN awareBridge/L2-Switch
VLAN aware
VLAN unaware stations
Bridge/L2-Switch
Fig. 19 VLAN Aware/Unaware
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1.7 Links Types Devices on a VLAN can be connected in three ways
based on whether the connected devices are VLAN Aware or VLAN
Unaware as reported in Fig. 20, Fig. 21, Fig. 22. Recall that a
VLAN aware device is one which understands VLAN memberships (i.e.
which users belong to a VLAN) and VLAN formats.
This is a combination of the previous two links. This is a link
where both VLAN aware and VLAN Unaware devices are attached.A
hybrid link can have both tagged and untagged frames, but all the
frames for a specific VLAN must be either tagged or untagged.
Hybrid Link
An access link connects a VLAN Unaware device to the port of a
VLAN Aware Bridge.Access Link
All the devices connected to a trunk link, including
workstations, must be VLAN Aware.All frames on a trunk link must
have a special header attached. These special frames are called
TAGGED FRAMES.
Trunk Link
DESCRIPTIONLINK TYPE
Fig. 20 Link Types
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L2-SwitchL2-Switch
Trunk Link
Trunk Link
VLAN-aware Workstation
VLAN-aware Bridge/L2-Switch
VLAN-aware Bridge/L2-Switch
Fig. 21 Trunk Link
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L2-Switch
Access Link
VLAN-unaware Device
VLAN-aware Bridge/L2-Switch
Fig. 22 Access Link
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1.8 Q-in-Q In the VLAN tag field defined in IEEE 802.1Q, only 12
bits are used for VLAN IDs, so a device can support a maximum of
4,094 VLANs. In actual applications, however, a large number of
VLAN are required to isolate users, especially in metropolitan area
networks, and 4,094 VLANs are far from satisfying such
requirements. The so called Q-in-Q (IEEE 802.1ad) feature enables
the encapsulation of double VLAN tags within an Ethernet frame,
with the inner VLAN tag being the customer network VLAN tag while
the outer one being the VLAN tag assigned by the service provider
to the customer. In the backbone network of the service provider
(the public network), frames are forwarded based on the outer VLAN
tag only, while the customer network VLAN tag is shielded during
data transmission. The Q-in-Q feature enables a device to support
up to 4,094 x 4,094 VLANs.
DA SA
DA SA
DA SA
LEN/Etype Data FCS
TPID TAG LEN/Etype Data FCS
TPID TAG LEN/Etype Data FCSTPID TAG
Untagged Ethernet Frame
Service Provider Tagging
Customer Tagging
6 6 2 446 to 1500
2 2
2 2
Bytes
Single Tagged Ethernet Frame
Double Tagged Ethernet Frame
Fig. 23 Untagged, Single Tagged and Double Tagged Ethernet
Frames
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Double TAG VLAN Tag Control Identifier (TCI) is reported in Fig.
24
DA SA TPID TAG LEN/Etype Data FCSTPID TCI
2 2Double Tagged Ethernet Frame
User PriorityPriority Code Point D
EI S-VIDService V-LAN Identifier
3 bits 1 bit 12 bits
1 bit Drop Eligible Indicator drop first, if congestion
occurs
Fig. 24 Double TAG VLAN Tag Control Identifier
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Double Tag Example
S-VLAN 2
C-VLAN 2
A
D C
E
B
23
4
S-VLAN 2
C-VLAN 2
Swap outer with 4 and forward to D- port 2
221
Forwarding DecisionVLAN Outer Tag
VLAN Inner Tag
A-Port
S-VLAN 2
C-VLAN 2
x1S-VLAN 4
C-VLAN 2
1
2
S= Service ProviderC= Customer
Fig. 25 Double TAG Example
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1.8.1 Q in Q TPID The QinQ frame contains the modified tag
protocol identifier (TPID) value of VLAN Tags. By default, the VLAN
tag uses the TPID field to identify the protocol type of the tag.
The value of this field, as defined in IEEE 802.1Q, is 0x8100. The
device determines whether a received frame carries a service
provider VLAN tag or a customer VLAN tag by checking the
corresponding TPID value. After receiving a frame, the device
compares the configured TPID value with the value of the TPID field
in the frame. If the two match, the frame carries the corresponding
VLAN tag. For example, if a frame carries VLAN tags with the TPID
values of 0x88a8 and 0x8100, respectively, while the configured
TPID value of the service provider VLAN tag is 0x88a8 and that of
the VLAN tag for a customer network is 0x8200, the device considers
that the frame carries only the service provider VLAN tag but not
the customer VLAN tag. In addition, the systems of different
vendors might set the TPID of the outer VLAN tag of QinQ frames to
different values. For compatibility with these systems, you can
modify the TPID value so that the QinQ frames, when sent to the
public network, carry the TPID value identical to the value of a
particular vendor to allow interoperability with the devices of
that vendor. The TPID in an Ethernet frame has the same position
with the protocol type field in a frame without a VLAN tag.
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1.9 Spanning Tree Protocol (802.1d) In order to increase the
availability may be useful to introduce redundancy. In presence of
simultaneous alternative paths, copies of frames are created
producing the so called LOOPS. In order to avoid loops, a SPANNING
TREE algorithm must be implemented to disable some bridge
interfaces. Spanning Tree Protocol (STP) is a link manager protocol
that provides path redundancy while preventing loops in the
network. STP algorithm creates a tree topology, and loop free path
from the root to all of the nodes in the LAN.
1.9.1 Spanning Tree Root bridge selection The bridges exchange
Configuration Bridge Protocol Data Units (BPDUs) in order to learn
the topology of the network. A root bridge is selected according to
MAC or priority. A lowest cost path to the root is chosen, and
redundant links are blocked.
Root Bridge
= blocked links
Fig. 26
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In case of link failure, BPDUs are again exchanged in the
network to notify tree of the topology change. Redundant routes are
enabled.
Root Bridge
Fig. 27 Redundant root enabled
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1.9.2 Spanning Tree Port roles Spanning Tree port roles are:
Root port (R): pointing towards the root bridge. Designated port
(D): active ports that arent root ports. Non Designated Alternate
port (A): one side of a blocked link (the other side is
Designated port).
Root Bridge
R
RR
R DD
D
D
D
D
A
A
Fig. 28
TIP 1) The root sends hello BPDU (cost of 0) out all interfaces.
2) Neighboring bridges forward hellos out their non-root designated
ports, identifying root, with their cost added. 3) Each bridge in
the network repeats the previous step. 4) Root repeats step 1 every
{hello time}.
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1.9.3 Spanning Tree Port states Spanning Tree Port states
are:
Blocking Listening Learning Forwarding Disable
Root BridgePort role: RootPort state: Forwarding
Port role: RootPort state: Forwarding
Port role: Non DesignatedPort state: Blocking
Fig. 29 Spanning Tree Port States
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Port states diagram is reported in Fig. 30.
Listening
Forwarding
Blocking Learning
Forwarding
DelayM
ax Age
Forwarding
Delay
Fig. 30 Port States Diagram
Blocking - its the default state of an STP port when a bridge is
powered on, and when a port is shut down to eliminate a loop Ports
in a blocking state do not forward frames or learn MAC addresses.
They will still listen for BPDUs from other switches, to learn
about changes to the switching topology. Port remains in the state
of blocking as long as it continues to receive BPDUs containing
information better than those already held (i.e. it receives a BPDU
that indicates a better path to the root switch. When there is a
topology change, the port starts a Message_Age_Timer, which is
initialized to the value Max Age. When the timer expires, the port
goes into Listening state.
Listening- the port will listen for BPDUs to participate in the
election of a Root Bridge, Root Ports, and Designated Ports. Ports
in a listening state will not forward frames or learn MAC
addresses.
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Learning- After a brief period of time, called Forwarding Delay,
a port in a listening state will be elected either a Root Port or
Designated Port, and placed in a learning state. Ports in a
learning state listen for BPDUs, and also begin to learn MAC
addresses. However, ports in a learning state will still not
forward frames.(Note: If a port in a listening state is not kept as
a Root or a Designated Port, it will be placed into a blocking
state and not a learning state.)
Forwarding - After another Forward Delay, a port in learning
mode will be placed in forwarding mode. Ports in a forwarding state
can send and receive all data frames, and continue to build the MAC
address table.
Disabled - A port in disabled state has been administratively
shut down, and does not participate in STP or forward frames at
all.
Standard Parameters: Max Age = 20s Forwarding Delay = 15s
Spanning Tree Convergence(Time to change from Blocking to
Forwarding) Max Age + 2x Forwarding Delay = 50s
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1.10 Rapid Spanning Tree Protocol RSTP (802.1w) Regular STP
(802.1d) provides very slow failure recovery time: 30-60 sec. Thus
the STP mechanism was improved, and a new protocol was published:
RSTP (802.1w). RSTP offers ~1 sec failure recovery time. How RSTP
differs from STP In many aspects STP and RSTP work the same way.
They reduce the bridged network to a single spanning tree topology
in order to eliminate loops. Either algorithm reactivates redundant
connections in the event of a link or component failure. The main
difference is convergence time. While STP may take 30 to 50 seconds
to re-converge, RSTP does it in dramatically less time. In a
carefully designed network, RSTP re-converges in less than a
second. Although computation of the Spanning Tree is identical
between STP and RSTP, there are differences in the behavior of the
two algorithms. The main differences are reported in the following
figures
Nokia Siemens Networks
Fig. 31 STP/RSTP differences (1)
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Fig. 32 STP/RSTP differences (2)
Fig. 33 STP/RSTP differences (3)
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1.11 Multiple Spanning Tree Protocol MSTP (802.1s) The 802.1D
and 802.1w spanning tree protocols operate without regard to a
networks VLAN configuration, and maintain one common spanning tree
throughout a bridged network. These protocols map one loop-free,
logical topology on a given physical topology. In a VLAN
environment, the problem could be put in evidence considering the
Fig. 34. The figure shows a network of two switches with two
configured VLANs. If the switches are running STP or RSTP, all the
links for VLAN 2 would be blocked. This is because both STP and
RSTP support only a single spanning tree for the whole network and
block the redundant links. The above situation can be rectified by
using MSTP. The 802.1s Multiple Spanning Tree protocol (MSTP) uses
VLANs to create multiple spanning trees in a network, which
significantly improves network resource utilization while
maintaining a loop-free environment.
1 2 3 4 5 6 7 8
1 2 3 4 5 6 7 8
VLAN 1 VLAN 2
X X
Switch 1 (root Bridge)
Switch 2
Fig. 34 Example of two switches with two configured VLANs
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1.11.1 Multiple spanning tree concepts MST Instance (MSTI) MSTP
enables the grouping and mapping of VLANs to different spanning
tree instances each with a different root bridge. A MST Instance
(MSTI) is a particular set of VLANs that are all using the same
spanning tree.
Spanning tree of MSTI= 1 containingvlans 1, 2, 3, 4Spanning tree
of MSTI= 2 containingvlans 5, 6, 7, 8Spanning tree of MSTI= 3
containingvlans 9, 10, 11, 12
Same Physical connection
RootBridge
RootBridge
RootBridge
Fig. 35 Different spanning trees created by different MSTIs on
the same physical layout
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2.2 MEF: Metro Ethernet Forum The Metro Ethernet Forum (MEF) is
a global industry alliance comprising more than 145 organizations.
Nokia Siemens Network is part of the MEF The MEF develops technical
specifications and implementation agreements to promote
interoperability and deployment of Carrier Ethernet worldwide.
Fig. 41 MEF
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Fig. 42 Nokia Siemens Networks is part of the MEF
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2.7 Carrier Ethernet Terminology: Basic Components UNI, EVC and
NNI are the Fundamental Constructs of an Ethernet Service
2.7.1 The User Network Interface (UNI) The UNI is the physical
interface or port that is the demarcation between the customer and
the service provider. The UNI is always provided by the Service
Provider The UNI in a Carrier Ethernet Network is a physical
Ethernet Interface at operating speeds 10Mbs, 100Mbps, 1Gbps or
10Gbps.
CE: Customer Equipment, UNI: User Network Interface. MEF
certified Carrier Ethernetproducts
Carrier Ethernet Network
UNIUNICECE
Fig. 43 User Network Interface
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2.7.2 Network to Network Interface (NNI) NNI is the demarcation
between carrier Ethernet networks operated by one or more
carriers
UNI: User Network Interface, UNI-C: UNI-customer side, UNI-N
network sideNNI: Network to Network Interface, E-NNI: External NNI;
I-NNI Internal NNI
Service Provider 1 Carrier Ethernet Network
CECE
UNIUNI
Subscriber Site
ETHUNI-CETH
UNI-CETH
UNI-NETH
UNI-NETH
UNI-NETH
UNI-NETH
E-NNIETH
E-NNIETH
UNI-CETH
UNI-C
UNIUNI
CECE
I-NNII-NNI E-NNIE-NNI
Service Provider 2
I-NNII-NNI
ETHE-NNIETH
E-NNI
Subscriber Site
Fig. 44 UNI and NNI Interfaces
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2.7.3 FlexiPacket UNI / NNI ports In the FlexiPacket Indoor
Unit, each Ethernet port (both copper and fiber) can be configured
either as UNI (User to Network Interface) or NNI (Network to
Network Interface). As default, all ports are configured as NNI.
Fig. 45 illustrates a generic network scenario in which UNI and NNI
interfaces are highlighted.
IDU -- 1 NNIUNI3rd
party IDU - N3rd
partyNNInetwork UNI
Access to Network Network to AccessNetwork to Network
End-to-end connection
Fig. 45 User to Network and Network to Network Interfaces
In order to provide end-to-end connections, mapping criteria are
required at each interface boundary:
Incoming packet arriving at the UNI port is mapped to a specific
connection, which is identified by VLAN.
The mapping operation is done once per packet in the
network.
After packet is mapped and tagged (VLAN), it already has its
association to the service, and on the next hopes (NNI port)
mapping is not needed.
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FlexiPacket Radio ODUs are connected to A2200/A1200/First
Mile/HUB 800 IDUs by either UNI or NNI ports, as illustrated in
Fig. 46, Fig. 47 and Fig. 48.
IDU
NNI
3rd
party
IDU
3rd
party
IDU
3rd
party
NNI NNI
-
NNI
network
NNI
UNI UNI UNI
Fig. 46 FlexiPacket ODU IDU connections by UNI/NNI ports (1)
3rdparty
FP-ODU
IDU
3rd
party
UNI
UNI NNI
FP-ODU FP-ODU
Fig. 47 FlexiPacket ODU IDU connections by UNI/NNI ports (2)
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network
IDU
NNIBTS
FP-ODU FP-ODU
UNI
Fig. 48 FlexiPacket ODU IDU connections by UNI/NNI ports (3)
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2.7.3.1 UNI Interface functions Here below are reported the UNI
functions
Mapping: performed on the incoming traffic in order to identify
the connection it is associated to. Mapping functionality allows
associating to all incoming traffic a specific VLAN ID identifying
the EVC. The mapping is based on configurable mapping rules,
different for each equipment and software releases.
WARNING Please refer yourself to the "HUB Structure chapter" for
further details about mapping
TIP Once the mapping has been performed, all the incoming
traffic has been associated to a specific EVC. This means that the
VLAN tag associated to the Carrier Ethernet service is appended to
each frame and it is used across the entire Carrier Ethernet
network for delivering the frame towards the destination. This tag
is called S-tag.
Manipulation: Manipulation is configurable per EVC. The
configuration foresees two options: VID preservation: transparent
transport of the incoming frames; no modifications are performed on
the incoming frame; in egress the S-VID is removed thus the frame
come out the original C-tag; VID translation: removal of the C-tag
of the incoming traffic (if present): in case of tagged frames the
tag of the incoming frames is overwritten by S-tag; this
functionality allows modifying the frame format from that one
received at the UNI to a new one suitable for the treatment inside
the network.
WARNING Please refer yourself to the HUB Structure chapter for
further details about Manipulation
Marking / Policing: the ingress traffic is marked by using 3
bits (Priority Code Point) for defining priority and color.
WARNING Please refer yourself to the HUB Structure chapter for
further details about Marking and Policing.
Congestion Management: mechanism used for congestion avoidance
by randomly dropping packets according to congestion level (queue
fill level), color and priority.
WARNING Please refer yourself to the QoS chapter for further
details about Congestion Management
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2.7.4 Ethernet Virtual Connection (EVC) The EVC is the Logical
representation of an Ethernet service as defined by the association
between 2 or more UNIs. It permits to transfer Ethernet Frames from
one site to another one. The EVC prevents data transfer between
sites that are not part of the same EVC They are typically
distinguished by VLAN tags or Q-in-Q. Three types of EVCs are
defined by MEF as reported in Fig. 49, Fig. 50 and Fig. 51:
Point-to-Point, Multipoint-to-Multipoint, Rooted Multipoint
(Point-to-Multipoint)
Point-to-Point EVC
Carrier Ethernet Network
CECE UNIUNI
CECEUNIUNI
CECE
UNIUNI
ISPPOP
UNIUNI
Storage Service Provider
Internet
Fig. 49 Point to Point EVC
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Multipoint-to-Multipoint EVC
Carrier Ethernet Network
CECE
UNIUNI
CECE
UNIUNI
Carrier Ethernet Network
Fig. 50 Multipoint to Multipoint
Service Multiplexed
Ethernet UNI
Point-to-Multipoint EVC
Carrier Ethernet Network
CECEUNIUNI
UNIUNI
UNIUNI
CECE
UNIUNI
CECE
Fig. 51 Point to Multipoint EVC
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2.7.5 EVC Basic Service Attributes Details regarding the EVC
include:
Bandwidth profiles Class of Service (CoS) Identification Service
Performance Frame Delay (Latency) Frame Delay Variation
(Jitter)
2.7.5.1 Definition Bandwidth Profiles parameters for policing 4
main parameters are defined to determine the Bandwidth Profiles:
two bandwidth limitsCIR and EIRand two burst sizes CBS and EBS. CIR
Committed Information Rate: the average rate up to which Service
Frames are delivered per the service performance parameters. The
CIR is an average rate because all Service Frames are always sent
at the UNI speed, e.g., 10Mbps, and not at the CIR, e.g., 2Mbps.
EIR Excess Information Rate specifies the average rate up to which
Service Frames are admitted into the providers network. The EIR is
an average rate because all Service Frames are sent at the UNI
speed, e.g., 10Mbps, and not at the EIR, e.g. 8Mbps. PIR Peak
Information Rate: = CIR + EIR CBS Committed Burst Size: is the
maximum number of bytes (e.g. 2K bytes) allowed for incoming
packets to burst above the CIR, but still be marked green. EBS
Excess Burst Size: is the maximum number of bytes (e.g. 2K bytes)
allowed for incoming packets to burst above the EIR and are marked
yellow. When the burst size has been exceeded, packets above the
EIR are marked red.
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2.7.5.2 Color Marking A way to describe Service Frames when
their average rate is in profile or out of profile is using the
colors according to the Fig. 52
Green = conformant to CIR bandwidth profile
Yellow = conformant to EIR bandwidth profile. Yellow packets
have higher drop elegibility (will be dropped first in case of
congestion).
Performance requirements delay, jitter and loss are not applied
to yellow packets within transport network
Red = not conformant and discarded immediately.
CIR Conformant
Traffic CIREIR Conformant
Traffic CIRNo traffic
Traffic EIR
Fig. 52 Color Marking
TIP See more in MEF10.1, section 7.11
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EVC-1
CIR
EIREVC-2
CIR
EIR
EVC-3
CIREIR
Fig. 53
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2.7.5.3 Three Types of Bandwidth Profiles MEF defines three
Bandwidths profiles as reported in the example of Fig. 54
Fig. 54 Bandwidths Profiles
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2.8 Carrier Ethernet Service Types Using the EVCs it's possible
to support the Ethernet Services Three Ethernet Service types are
available as reported in Fig. 55:
E-Line Service Type E-LAN Service Type E-Tree Service Type
E-LINE
E-LAN
E-TREE
Fig. 55 Carrier Ethernet Service Types
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2.9 Circuit Emulation Services over Packet (CESoP) Circuit
Emulation Services Enables TDM Services to be transported across
Carrier Ethernet network, re-creating the TDM circuit at the far
end. They run on a standard Ethernet Line Service (E-Line).
TDM Circuits(e.g. T1/E1/STM Lines)
Carrier Ethernet NetworkTDM Circuits
(e.g. T1/E1/STM Lines)Circuit Emulated
TDM Traffic
Fig. 56 Circuit Emulation Services
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2.9.1 Standards Different standards are available to provide the
transport of a TDM service, typically an E1/T1, through a
bridged/routed packet network:
IETF RFC5086 (CESoPSN). IETF RFC5087 (TDMoIP), IETF RFC4553
(SAToP) MEF8 (CESoETH). The standard adopted by the 1st release of
the FlexiPacket Radio product family was the RFC5086. The A1200
Drop 3 is able to support the MEF8 standard. FM200 and HUB800
release 2 are able to support CESoPSN and SAToP
NSN FlexiPacket IDUs provide the Interworking Function (IWF) to
support the initiation and termination of a CESoPSN / SAToP
service. The ODU just provide prioritized transport of the packet
flows related to the CES service.
CESoPSN Internet Working Function (IWF)
Fig. 57 Internet Working Function
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2.9.2 Pseudowire Pseudowire is a mechanism that emulates the
attributes of a TDM service such as an E1, T1 or a fractional nx64
TDM service over a Packet switched network (PSN) TDM pseudowire has
to support:
Packetization and Encapsulation of TDM Traffic Packet Delay
Variation (PDV) attenuation Frame Loss and Out-of Sequence Packets
Clock recovery and Synchronization Packetization and Encapsulation
Packetization refers to the process of converting the PDH or
SONET/SDH bit stream into Ethernet frames. Specific packet
connectivity information is dependent on the type of PSN: Ethernet,
MPLS or IP. The encapsulation process places a pseudowire control
word in front of the TDM data in order to define the format
identifier, to support error flags, length and sequence number (see
"Frame Loss and Out-of Sequence Packets" point).
E1/T1Frame
E1/T1FrameEthernet Frames Ethernet Frames
PacketSwitchedNetwork
Header
Fig. 58 from TDM to Packets
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Packet delay variation (PDV) is mainly due to the variable load
conditions of network elements and interfaces, randomly occurring
in the network. Although priority-based schedulers are implemented
in each network element of the FlexiPacket products, still a delay
variation is present for high priority packets (such as CESoP
packets) passing through a network element. The packet delay
variation is compensated by the playout buffer located in the
receiving IWF. The basic criterion for dimensioning the playout
buffer is to estimate the overall packet delay variation of the
network between the initiating and the terminating CESoPSN IWF and
to assign the receiving IWF a buffer size more than twice the
estimated packet delay variation. Actually the packet delay
variation is defined as the difference between the maximum delay of
the CESoP packets to be supported without impairments (i.e. without
errors or out-of-service conditions on the E1 stream) and their
minimum delay. For what concerns the estimation of the total E1
end-to-end delay this will correspond to the network delay of CESoP
packets added to the delay provided by the playout buffer.
WARNING The "playout buffer" dimensioning is calculated by means
of a proper tool. Please refer yourself to the Annex for detailed
information about that.
Frame Loss and Out-of Sequence Packets Frames may occasionally
not arrive in the order in which they were sent out. In some cases,
the frames may arrive very late or not at all, resulting in frames
being discarded. TDM and SONET/SDH networks don't have the concepts
of resending frames hence such frames are considered lost if they
are not received within the window of the jitter buffer at the
destination. The destination must have the ability to re-sequence
the arriving frames. This is achieved through the use of sequence
numbers within the headers.
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Clock recovery and Synchronization In the PDH network, the
difference between in clock frequencies between TDM links is
compensated for using bit stuffing technologies. With a packet
network, that connection between the ingress and egress frequency
is broken, since the packets are discontinuous in time. The
consequence of a long-term mismatch in frequency is that the queue
at the egress of the packet network will either fill up or empty.
For this reason particular techniques such as "Differential Clock
Recovery" and "Adaptive Clock Recovery" must be implemented.
WARNING About Clock recovery and synchronization please, refer
to the chapter "Synchronization"
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Different pseudowires are available according to the different
standards: CESoPSN (Circuit Emulation over PSN) Pseudowire CESoPSN
Pseudowire is able to transmit emulated structured TDM signals.
That is it can identify and process the frame structure and
transmit signaling in TDM frames A benefit of CESoPSN is that
unused timeslots are not transported in the payload, thereby saving
on bandwidth. CESoPSN provides three encapsulation modes:
IP/UDP (IP over User Datagram Protocol : solution actually
adopted in FlexiPacket
MPLS (Multi-Protocol Label Switching) L2TPv3 (layer 2Tunneling
Protocol Version 3: alternative protocol to MPLS) TDMoIP Pseudowire
The main difference between TDMoIP and CESoPSN is that the first
packetizes TDM data in multiples of 48 bytes while the second uses
multiples of the TDM frame itself. TDMoIP provides the same
encapsulation modes as CESoPSN and the pure Ethernet encapsulation
SAToP (Structure Agnostic TDM over Packet) Pseudowire SAToP differs
from the previous Pseudowires technologies because it treats the
TDM traffic as a data stream and ignores the framing or the
timeslots. SATOP provides the same encapsulation modes as CESoPSN
CESoETH (CES over Ethernet) Pseudowire CESoETH define TDM Circuit
Emulation packets encapsulated by bare Ethernet. Emulated TDM CS
data is distinguished based on the Emulated Circuit Identifier
(ECID).
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2.10 FlexiPacket EVC and Services NSN FlexiPacket IDUs provide
Ethernet Virtual Connections (EVC), each one associated to a
service. Each service initiates at the ingress and terminates at
the egress of a network, running over both NNI and UNI ports.
WARNING Since the mapping of traffic into connections / services
is performed on UNI ports only, both the initiation and termination
of a service is possible on UNI ports only (see Fig. 59).
NNIUNI3rd
party3rd
partyNNInetwork UNI
Access to Network Network to Network
End-to-end connection
FlexiPacketIDU
FlexiPacketIDU
Access to Network
Fig. 59 User to Network and Network to Network Interfaces
Three types of Services are supported by FlexiPacket IDU:
CESoP (Circuit Emulation Service over Packet) SAToP (Structure
Agnostic TDM over Packet; it's implemented in FM200 R2.0 and
HUB800 R2.0)
CESoETH (CES over Ethernet) pseudowire; its implemented in A1200
release 5.0 Drop 3
E-line it is based on point-to-point EVC, running end-to-end
between UNI
ports. A unique VLAN ID is reserved in the network to identify
each E-line service.
E-LAN it is based on multipoint-to-multipoint EVC. In A1200 and
A2200
Release 4.5, only one management E-LAN can be defined and it
identifies the management domain between FPR and A2200/A1200
devices. A unique VLAN ID, VIDMGT, is reserved for the management
E-LAN service (default value = 127). Forwarding is based on bridge
functionality. Destination MAC address is used to reach the
target.
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WARNING In FPH-2200 Release 5.0 and FPH-1200 Release 5.0 Drop3
is possible to manage E-LAN services via CLI and Web UI.
WARNING In FPFM-200 and HUB 800, both E-Lines and E-LANs can be
configured; one E-LAN is reserved for the management/DCN service.
By default, this service is identified by (VLAN ID=127).
In Fig. 60, E-Lines and E-LAN (management) examples are shown.
At UNI:
Mapping of traffic to the Service Assignment to a Class of
Service Policing (CIR /EIR) according to SLA CE-VLAN manipulation
(transparent/translation) At NNI:
Traffic of a Service is identified by a VLAN ID
NNI
UNI
UNI
DCN
Untaggedframes
3rd
party
untagged framesUNI
3rdparty
E-line 1
UNI
3rd
party
NNI NNI
E-line 2
E-line 3
E-line 4
NNI
Packetnetwork
E-LAN
NMS
IDU IDU IDU
Fig. 60 FlexiPacket E-Lines and E-LAN Example
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8.3 Timing-over-Packet (ToP) IEEE1588 v2 (official Title:
Precision Time Protocol)
With this technique, Network clocks are organized in
Master-Slave hierarchy. A two way timing exchange will be
established where the Master sends messages to its slaves to
initiate synchronization. Each slave then responds to synchronize
itself to its Master. This sequence is repeated throughout the
specific network to achieve and maintain clock synchronization.
The ToP Master transmits timing packets over the asynchronous
data path The ToP Slave recovers timing from the timing packets
Timing packets are time stamped at the start of frame (SOF) of the
corresponding Ethernet packet. Timing packets can transparently
traverse both Layer 3 and Layer 2 networks. Using IEEE1588, it is
possible to synchronize, in the sub-microsecond range, the local
clocks using the same Ethernet network that also transports the
process data. No special requirements are placed on memory or CPU
performance, and only minimal network bandwidth is needed. The low
administration effort for this protocol is also significant. As
redundant masters are also supported, a PTP domain automatically
configures itself using the best master clock algorithm and is also
fault-tolerant. A Master-Slave connection is reported in Fig. 105
where the External Reference Synch could be a Signal coming from a
PRC or from a GPS system.
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1GbEPHY
1GbEPHY
Master ToPEngine
PLL
External Reference Clock
Slave ToPEngine
PLL
Data Packets Timing Packets
Master Slave
Fig. 105 IEEE1588 Master Slave Connection
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8.3.2 Precision Time Protocol (PTP) Clocks
Grandmaster Clock The ultimate source of time on the network is
called Grandmaster. Grandmasters are typically referenced to GPS or
PRC so that they are both very stable and very accurate. A
grandmaster time stamps PTP packets with very high time stamp
accuracy. A grandmaster has to be able to support hundreds or
thousands of PTP clients. This is usually made possible in part by
sending "PTP Synch" and "Follow Up Messages" periodically using
multicast addressing, and in part by being able to quickly and
accurately process PTP client initiated "Delay Request" and "Delay
Response messages".
TIP Nokia Siemens Networks has selected "Symmetricom", a leading
company in synchronization solutions, to become its first supplier
for IEEE 1588v2 masters.
Ordinary Clock Ordinary clock has a single PTP port in a domain
and maintains the time scale used in the domain.
TIP The PTP Domain is a logical grouping of PTP clocks that
synchronize to each other using the PTP protocol, but that are not
necessarily synchronized to PTP clocks in another domain.
It may provide time to an application or and device.
Boundary Clock Boundary clock (see Fig. 109) has multiple PTP
ports in a domain and maintains the timescale used in the domain.
It may serve as a source of time, i.e., be a master, or may
synchronize to another clock, i.e., be a slave. It may provide time
to an application. A boundary clock that is a slave has a single
slave port, and transfers timing from that port to the master
ports.
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Grandmaster
BoundaryClock
Ordinary Clock
M
S Ordinary ClockS
2MHz/2Mpbs
GPS
S
M M
Fig. 109 Boundary Clock
M M M
Switch with Grandmasterfunction
2MHz/2Mpbs
GPS
Switch with Boundaryfunction
Switch with Boundaryfunction
S
S
OrdinaryClock
OrdinaryClock
S S
M
OrdinaryClock
S
OrdinaryClock
S
OrdinaryClock
S
M
M M
Fig. 110 IEEE 1588 System Configuration
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10 Digital Radio Relay Signals
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10.1 Quadrant Amplitude Modulation (QAM) Fig. 119 represents a
generic Quadrant Amplitude Modulation (QAM). The bit rate defines
the rate at which information is passed. The Intermediate Frequency
(IF) is the Modulator Output Each symbol represents "N" bits, and
has "M" signal states, where "M = 2N". The symbol rate is the rate
at which the carrier moves from one point in the constellation to
the next point
QAM Modulator
Bit Rate
Intermediate frequency
Symbol Rate =Bit Rate
N
04 QAM N = 2 M = 4 16 QAM N = 4 M = 16 64 QAM N = 6 M = 64
128 QAM N = 7 M = 128 256 QAM N = 8 M = 256
Signal States in the Constellation = M
I
Q1
2
3
12
3
Time
QAM Constellation with M = 16
QAM Signal versus Time
Fig. 119 QAM (1)
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From Fig. 120 to Fig. 122, different QAM Modulations are shown.
As reported in Figures, the Phase and Amplitude can easily
represented in vector co-ordinates as a discrete point in the I-Q
Plane where I stands for in-phase (i.e. phase reference and Q
stands for Quadrature (i.e. 900 out of phase). Increasing the
modulation levels, more information is transmitted (bits associated
to the signal state) As the number of modulation stages increases,
the requirements concerning linearity and low AM/PM conversion of
all the stages used also rise sharply. This may lead to decrease
the Tx Output Power in order to increase the TX amplifier
linearity.
16QAM
I
Q
4QAM = 4PSK
Symbol Rate = Bit Rate/2
Symbol Rate = Bit Rate/4I
Q
Fig. 120 QAM (2)
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64QAM
Q
I Symbol Rate = Bit Rate/6
128QAMI
Q
Symbol Rate = Bit Rate/7
Fig. 121 QAM (3)
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256QAM
Q
I
Symbol Rate = Bit Rate/8
Fig. 122 QAM (4)
256QAM128QAM64QAM32QAM16QAM4QAM
FlexiPacket MultiRadio Supported Modulations
256QAM128QAM64QAM16QAM4QAM
FlexiPacket Radio Supported Modulations
Fig. 123 FlexiPacket Radio/MultiRadio supported Modulations
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10.3 Adaptive Modulation The concept of Dynamic Modulation rises
when thinking about the compromise between the planned Microwave
dimensioning (that has to take availability and performances into
consideration) and the need for more capacity. Usually Microwave
link is considered to work in normal conditions and to provide good
performances (according to Standards), and being unavailable or
giving poor performances for a certain percentage of time, due to
fading or bad propagation conditions (typically rain, affecting
propagation in frequency bands above 15 GHz). In planning phase,
the link is engineered (frequency, bandwidth/modulation, capacity,
antenna diameter) to meet the worst case, but this way the link
capacity is under utilized for most of the operating time. Thus,
basically Dynamic Modulation introduces a way to transmit more
capacity with higher modulation formats when the propagation
conditions are good, and switch to more robust modulation formats
in case of fading phenomena to preserve high priority traffic (i.e.
voice vs Data/Video). For basic and delay sensitive service
(voice), the basic capacity can be considered guaranteed, allowing
Data to exploit the rest of additional capacity provided, as shown
in Fig. 132.
Fig. 132 Dynamic Modulation
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10.3.1 FlexiPacket ODU Adaptive Modulation Five different
profiles (from 4QAM to 256QAM) are available inside the FlexiPacket
Radio and 6 profiles in the FlexiPacket MultiRadio 2.1. The
switching criteria to pass from a modulation to another one is
based on the Mean Square Error (MSE) estimation This parameters is
dependant from the received signal level and modulation type.
Capacity
16 QAM
4 QAM
64 QAM
128 QAM
FPR ACM Switching CriteriaThe switching criteria is based on the
Mean Square Error (MSE) estimationThis parameters is dependant from
the received signal level and modulation type
Rx Level
256 QAM
MostValuableTraffic
High Priority
Services
Max ThroughputAll services transported
Hitless Switchfor Speed of
Attenuation up to 50dB/s
Fig. 133 FlexiPacket Radio Adaptive Modulation (1)