atm technology
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ATM
Asynchronous Transfer Mode
ATM technology used to transfer data, Voice and video by use cell with fixed size 53 bytes (5
header+48 payload)
Why use ATM?
Circuit switched connections:
After initial setup no processing in network nodes
Fixed bit rates, fixed time delay
Packet switched connections:
Flexible bandwidth allocation due to statistical multiplexing, varying time delay
Complex processing in network nodes
ATM is based on virtual connections:
Minimal node processing (use VP/VC to reroute cell) , statistical multiplexing (dedicate
specific path for all packet through communication time & use fast switching VP/VC)
ATM is layer2 technology and divided into three layer inside layer2
Layer 2
ATM adaptation layer
(AAL) ATM layer
Physical layer (Cell)
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AAL definition:
It is designed to support different types of applications and different types of traffic, such as
voice, video, imagery, and data
Function:
Segmentation and reassembly
Handling of transmission errors
Handling of lost and misinserted cell conditions
Timing and flow control
ATM divided data through network to four categories and each category has QOS
1. Constant bit rate (CBR):
Specified for connections that require a certain amount of bandwidth, characterized by
a Peak Cell Rate (PCR) value that is continuously available during the entire connection
lifetime. The source may emit cells at or below the PCR at any time and for any
duration (or may be silent).
Typical applications:
- Voice (standard 64 kbit/s PCM)
- Circuit Emulation Services (CES)
This category is mainly intended for (but not restricted to) real-time (RT) services.
2. Variable bit rate (VBR)
RT-VBR: Specified by the ATM Forum for services with stringent timing
requirements (”real-time applications”), like CBR but for variable bit rate services, e.g.
compressed speech.
NRT-VBR: Specified by the ATM Forum for variable bit rate services without
stringent timing requirements (”non-real-time applications”). eg, compressed video or
voice applications
In both VBR service categories, we need to specify the following traffic parameters:
- Peak Cell Rate (PCR)
- Sustainable Cell Rate (SCR)
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- Maximum Burst Size (MBS)
3. Available bit rate
A relatively new concept. Based on flow control from the network (employing
Resource Management = RM cells). In ABR, we need to specify the following traffic
parameters:
- Peak Cell Rate (PCR)
- Minimum Cell Rate (MCR)
MCR is a bound (0 < MCR < PCR) on the cell rate that the network should support.
However, the cell rate of the source is allowed to vary between 0 … PCR.
Typical applications:
- LAN emulation / LAN interconnection
- File transfer (critical applications)
4. Unspecified Bit Rate (UBR)
No QoS requirements (i.e. ”best effort” service).
The only traffic parameter of interest is the PCR which the user is not allowed to exceed.
UBR supports a high degree of statistical multiplexing.
Typical applications:
- File transfer (non-critical applications)
Below image show relation between four application with time
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AAL Protocol Types:
1. AAL1 : Constant bit rate, small delay, small delay variation (Voice & Video
conference)
2. AAL2: Variable bit rate, small delay, small delay variation (compressed speech (VOIP)
& video transport as Video on demand)
3. AAL ¾: Supports variable bit rate data where there is no timing relationship between
source and destination, e.g., X.25, frame relay, and TCP/IP data
4. AAL5: Variable bit rate, not time sensitive, no retransmission mechanisms examples of
services that use AAL 5 are classic IP over ATM & 3G cabinet management
According to last classification for data at ATM network there are four types from QOS Class A
& Class B & Class C & Class D and below fig show relation between them & AAL protocols
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ATM Layer: at this layer we assign VP (Virtual Path) & VC (Virtual Circuit) that use to make
fast rerouting for cell between ATM switches & there are two types from ATM frame
UNI (User Network interface)
NNI (Network to Network Interface)
Below figure show usage for each frame type
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Two frame structure:
PT: One PTI bit is used in AAL 5 & User data / control data, Traffic management
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3G structure at real Mobile network
IMA (Inverse Multiplex ATM): this protocol use to convert between ATM frame to E1 frame
to transfer ATM over MW link that use E1 frame & when data reach to Node B IMA convert E1
to ATM frame
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At Ericsson RNC we configure VC 32 & 33 for management & Signaling, VC36-37-38 for data
and internet so we configure this VC under AAL 5 at Node B configuration
Use VC39-40-41-42 for calls & Video conference and VOIP according to service QOS class
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Node B Management IP through OSS & local management IP:
Node B OSS management scenario: we configure VC32 &33 terminated on tellabs 8630 it mean
this VC will stop on tellabs 8630 and we create static route from tellabs 8630 to reach
management router before OSS Server
Always VP at tellabs 8630 at HUB configure with VP=1 & VP at tellabs 8660 ATM Port that
connect with RNC use specific number for each site
At tellabs 8630 & tellabs 8660 we configure VC from 36 to 42 to transfer data and voice and
video & configure VC as switched it mean data inside VC frame will transfer till reach to RNC
For local Access
For OSS management
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Example from tellabs 8630 (HUB) configuration:
Assign IMA Number (random number) & VP & VC32-33 terminated and other VC switched
VC32-33 parameter
To allow IP over ATM service
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VC36-37-38 for variable data:
Data type
Max and min BW for UBR data
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Configuration from Tellabs 8660, there is ATM port so we not need IMA in this case
Each site under ATM port has VP ID in our case VP 16 and this number configured on RNC if it
wrong Node B will be down
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VP parameter from two sides show VP support all traffic types & BW need for ATM
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To configure Min E1 to allow Node B transfer data over IMA you should configure IMA on
tellabs 8630 & Node B in the same time