Atm technology

1 | P a g e

Ahmed Hussein Bebars Mob:01024614238

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)

2 | P a g e


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)

https://en.wikipedia.org/wiki/Segmentation_and_Reassembly

3 | P a g e


- 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.


- 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.


- File transfer (non-critical applications)

- E-mail

Below image show relation between four application with time

4 | P a g e


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

5 | P a g e


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

6 | P a g e


Two frame structure:

PT: One PTI bit is used in AAL 5 & User data / control data, Traffic management

7 | P a g e


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

8 | P a g e


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

9 | P a g e


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

10 | P a g e


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

11 | P a g e


VC36-37-38 for variable data:

Data type

Max and min BW for UBR data

12 | P a g e


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

13 | P a g e


VP parameter from two sides show VP support all traffic types & BW need for ATM

14 | P a g e


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

15 | P a g e


On Node B

Technology

Atm technology