atm for iub

ATM Configuration for Nokia IUBATM Configuration for Nokia IUB

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ATM is a cell switching technology designed for the high-speed transfer of voice, video and data

AMT uses fixed sized cells. Fixed size cells allow for more efficient switching in hardware than can be achieved with variable sized cells

ATM is connection orientated, with ATM cells routed over Virtual Circuits

The asynchronous nature of the multiplexing allows for efficient interleaving of data of varying priority and size

The characteristics above make ATM well suited to support the QOS requirements which 3GPP has defined for UMTS, hence the reason ATM was chosen as the transport method for UMTS

Introduction to ATM

ATM BasicsATM Basics

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ATM BasicsATM Basics Each cell is fixed 53 bytes in length

The ATM switch does not need to detect the size of the cell which allows for fast switching

The small size means cells can be switched quickly with minimal delay, important for real-time services such as voice and video

Header

5 bytes

Payload

48 bytes

ATM uses Virtual Paths and Virtual Circuits A Virtual Path (VP) is a bundle of Virtual Circuits (VC) Virtual Paths are identified by the Virtual Path Identifier (VPI) Virtual Circuits are identified by the VPI and Virtual Circuit Identifier

(VCI)

Introduction to ATM

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ATM Adaptation LayersATM Adaptation Layers

ATM Adaptation Layers isolate higher layer protocols from the details of the ATM layer and ATM physical layer

The job of the AAL is to map the higher level data packets into ATM cells. It performs segmentation and reassembly of packets

For UMTS, the main ATM adaptation layers are: AAL5: used for control plane signalling AAL2: used for user data transfer

Introduction to ATM

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Virtual Circuits for IUBVirtual Circuits for IUB

Each IUB link is configured as a single Virtual Path (VP)

Within this VP there are a number of Virtual Circuits (VCs), which can be divided into 5 main types AAL2 User Plane – CBR, carries the actual user data AAL2 Signalling – CBR, carries control signalling related to setting

up AAL2 connections within the AAL2 User Plane VC DNBAP – CBR, Dedicated NodeB Application Part. This carries

messages related to the setting up and releasing of radio links CNBAP – CBR, Common NodeB Application Part. This carries

messages relating to setting up first radio links (SRBs) and RRI messages

O&M – UBR, Operations and Maintenance, alarms, software downloads

Nokia IUB

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Nokia IUBVirtual Circuits for IUBVirtual Circuits for IUB There is always only one CNBAP VC per site

There is always only one O&M VC per site

There is always 1 DNBAP VC per WAM card Recall: One WAM card supports up to 3 WSPC cards

The number of AAL2Sig VCs depends on whether AAL2 Multiplexing feature is used or not 1 AAL2Sig per WAM if AAL2 Multiplexing is not used 1 AAL2Sig VC per IUB if AAL2 Multiplexing is used

The number of AAL2 User Plane VCs depends on a number of factors Whether the AAL2 Multiplexing feature is used or not. If used there is an option to

configure a single AAL2 User Plane VC per WBTS Number of AAL2 connections for the traffic mix (see next slides)

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IUB VC capacities are usually quoted in units of ATM cells per second (cps) 1 cps = (53 x 8)/1000 kbps

IUB Capacity = User Plane + AAL2Sig + CNBAP + DNBAP + O&M

O&M is recommended to be 151 cps (~64kbps) per WBTS O&M is configured as Unspecified Bitrate (UBR) so that it can expand beyond

the 151cps if required – for example when performing software downloads

UBR does not offer any minimum cell rate guarantee, meaning the O&M link could be completely starved if the other links are full of traffic. This would be unacceptable for O&M since it needs to carry alarms

which can not be missed or delayed We can artificially create a minimum cell rate for O&M by making

sure the combined cell rates of the other links leave some headroom and do not completely fill the available bandwidth

In future, UBR+ will be available which allows a minimum cell rate to be defined for UBR links

Nokia IUBIUB CapacityIUB Capacity

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IUB DimensioningIUB Dimensioning

Signaling link dimensioning is complicated and has many variables

CNBAP dimensioning is a function of the number of, and rate of, radio link setups and also the Radio Resource Indication period used for sending NodeB reports to the RNC

DNBAP dimensioning depends on many factors, including number of calls, call lengths, measurement reporting intervals. DNBAP dimension is particularly sensitive to the number of PS calls, as each

PS calls requires ~13 cps capacity on DNBAP

General guideline is to allocate ~6-8% of total IUB capacity to signalling links CNBAP, DNBAP, AAL2Sig Nokia recommendation is to dimension CNBAP:DNBAP:AAL2Sig in ratios of

1:2:1 respectively

Nokia IUB

Number of E1s O&M CNBAP DNBAP AAL2Sig Total

Signalling % of E1

1 151 80 159 80 319 7.292 151 158 315 158 631 7.213 151 233 466 233 932 7.104 151 312 624 312 1248 7.135 151 390 780 390 1560 7.136 151 469 938 468 1875 7.14

Nokia recommendations for Signalling link VC capacity as function of number of E1s

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Nokia IUB

Various NodeB architecture constraints, as well as ATM design constraints, influence the design decisions on the ATM layer of the IUB. This is especially the case with Ultrasite architecture.

WAMs and WSPC cards A single WAM can support up to 3 WSPC cards

There can be 6 WAMs in an Ultrasite WBTS => total of 18 WSPC cards

The IUB VC connections are routed to the WAM cards through the AXC. But the way this is done is dependent on whether AAL2 Multiplexing feature is enabled on the AXC No AAL2 Multiplexing

AXC is basically doing simple cross-connect. Each WAM needs it’s own DNBAP, AAL2Sig and AAL2UserPlane VC

AAL2 Multiplexing AXC is performing true VC level ATM switching. Each WAM still requires it’s own

DNBAP. However, with AAL2 multiplexing it is possible to configure only a single AAL2Sig and AAL2UserPlane VC per site (instead of per WAM)

Each WAM card can have up to 2 AAL2 User Plane VCs connected to it

Architecture ConstraintsArchitecture Constraints

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Nokia IUB

AAL2 Connection IDs Each Virtual Circuit can support a maximum of 248 AAL2 Connections

This is an ATM AAL2 specification limitation. The AAL2 CID address field in the AAL2 header is only 8 bits giving 256 possible addresses

CID 0 – 7 are reserved, giving 248 usable addresses

Common channels (CCCH) of each sector consume 4 AAL2 CIDs 3 sector site uses 12 CIDs for CCCH, 6 sector Moran site uses 24 CIDs for CCCH

Each DCH (AMR, Video or normal PS) uses 2 AAL2 CIDs 1 AAL2 CID for the DTCH logical channel 1 AAL2 CID for the DCCH logical channel

Voice only capacity of a single AAL2 User Plane VC 3 sector site: (248 – 3x4)/2 = 236/2 = 118 simultaneous AMR calls 6 sector site: (248 – 6x4)/2 = 224/2 = 112 simultaneous AMR calls

Example: Inner 3 sector site with 4 x WSPC cards, 3xE1s and a single AAL2UserPlane of 12,387cps. HSDPA enabled. Call mix is dominated by AMR calls, which is what we see at special events: WSPC Capacity is (4x64 – 16 – 32) = 208 CEs can support 208 AMR voice calls 3 E1s provides for approx 5.1Mbps bandwidth ~ 300 AMR calls But the single AAL2Userplane can only support 118 AMR voice calls before AAL2 CID limit. AAL2 CID limit is clearly the bottleneck despite WSPC and E1 capacity


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Nokia IUB

HSDPA Requirements The previous slide demonstrates how AAL2 CID limitations could

become the bottleneck when a single AAL2UserPlane VC is configured on the IUB Adding a second AAL2UserPlane VC, and splitting the total user plane

bandwidth between the two VCs would overcome this limitation by providing additional AAL2 CIDs on the second VC

However, a single users HSDPA connection must have a single AAL2 CID, and so can only flow within a single AAL2UserPlane VC With multiple AAL2UserPlane VCs, the maximum HSDPA throughput is

then limited to the size of the biggest VC only, not to the combined size

E.G. 3xE1 split evenly between 2 AAL2UserPlane VCs. Each VC is 12,387/2cps = ~ 6193cps = ~ 2.6Mbps. With ATM overheads, this would give maximum HSDPA speeds of approz 2Mbps.

If the 3xE1 were configured as a single VC of 12,387cps we can achieve the full 3.2Mbps application throughput.


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IUB Configurations

A single WAM can support up to 3 WSPC cards

Without AAL2 Multiplexing, VCs are connected directly from the RNC interface card to the WAM cards in the WBTS The S-AXC and AXC simply cross-connect the VCs, no ATM switching is

performed

In this example there is only a single AAL2 User Plane connected to the WAM

O&M

NodeB

WA

M 2

WSPC

WSPC

192 HW

CH

WSPC

AX

UB

RNC S-AXC

IFU

IFUC

NIS

CNBAPDNBAP

AAL2SIGAAL2 User Plane

VC-33VC-34VC-35VC-36

Single WAM Configuration (1)Single WAM Configuration (1)No AAL2 MultiplexingNo AAL2 Multiplexing

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In this case the AAL2 User Plane has been split into two paths In the Optus network, this is the pre-HSDPA configuration when we have 3

WSPC cards and 3 E1s In RAN04 there was a limit that a single VC could not be more than 9,999

cps (3 E1s is 12,387cps) Typical Optus configuration would be 9,000cps for AAL2 User Plane 1 and

3,387cps for AAL2 User Plane 2

This limitation no longer applies from RAS05 onwards and so even this configuration could now be done with a single 12.387cps AAL2UserPlane VC as in the previous slide

O&M

NodeB

WA

M 2 WSPC

WSPC 192 HW

CH

WSPC

AX

UB

RNC S-AXC

IFU

IFUC

NIS

CNBAPDNBAP

AAL2SIGAAL2 User Plane 1


AAL2 User Plane 2 VC-37

Single WAM Configuration (2)Single WAM Configuration (2)No AAL2 MultiplexingNo AAL2 Multiplexing

IUB Configurations

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The second WAM is required because of the 4th WSPC card

The second WAM requires an additional DNBAP, AAL2Sig and AAL2 User Plane VC if AAL2 Multiplexing is not enabled

Ideally, the relative sizes of AAL2UserPlane 1 to AAL2UserPlane 2 should reflect the capacity of the WSPC cards behind each respective WAM In this case, AAL2 User Plane 1:AAL2 User Plane 2 would be in the ratio of ~

3:2

With limited total E1 bandwidth, this solution limits total HSDPA throughput since HSDPA can only flow within a single VC

O&M

NodeB

WA

M 2

WSPC

WSPC

WSPC

AX

UB

RNC S-AXC

IFU

IFUC

NIS

CNBAPDNBAP

AAL2SIGAAL2 User Plane 1


AAL2 User Plane 2

WA

M 4

WSPC

WSPC

VC-46AAL2SIG VC-45DNBAP VC-44

Multiple WAM ConfigurationMultiple WAM ConfigurationNo AAL2 MultiplexingNo AAL2 Multiplexing

IUB Configurations

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Nokia IUBNokia IUBTwo WAMs with AAL2 MultiplexingTwo WAMs with AAL2 Multiplexing

Still requires a second DNBAP VC

AAL2Sig and AAL2UserPlanes can now be configured as a single, larger pipe. The now switches the AAL2 Connections within the single VC towards the appropriate WAM card which is connected to the WSPC card hadling that traffic

O&M

NodeB

WA

M 2

WSPC

WSPC

WSPC

AX

UB

RNC S-AXC

IFU

IFUC

NIS

CNBAPDNBAP

AAL2SIG

AAL2 User Plane 1

VC-33VC-34

VC-35

VC-36

WA

M 4

WSPC

WSPC

AAL2SIG VC-45DNBAP VC-44

IUB Configurations

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