Integrated Services; Introduction ATM

1. Integrated Services; Introduction ATM Dr. Farid Farahmand

2. Integrated Services Data Networks Initiated to combine all services Allowing access to and transporting information between private and public networks Transporting all information in digital format over a common communications systems Once the analog information is digitized, it is treated the same! Providing integrated services requires Facilities (transmission media) Protocols (organizing and regulating the flow of data) Examples X.25 User-to-Network Interface Integrated services digital Network (ISDN) Digital subscriber line (DSL) Asynchronous transfer mode (ATM) Frame relay (FR) Integrated Services Public Private Private

3. Integrated Services MAN LAN ISDN Interconnecting different networks through Public Telephone Network or Public Data Network managed by different carriers- all digitally WAN

4. ATM Basics • Defined in 1988 by ITU-T as a part of BISDN (Broadband ISDN) • Data can exist and enter BISDN asynchronously • Govern by ATM Forum • Supports video, sound, image, high-quality multimedia • Seamless and can be used on LAN and WAN • Intended to replace T1 yet not as successful as predicted • Unlike TDM, ATM does not assign any time slots to a given user • dynamically allocates ATM cells when user equipment wishes to transmit information High quality Broadband services TDM Circuit switching Statistical packet Switching

5. ATM Basics • Cell Based • The cell is comprised of 53 bytes (octet). • Five of the bytes make up the header field and the remaining – contains error checking • 48 bytes form the user information field – error checking is done in upper layers • Shorter assembly time – less delay • Easier buffer management and less processing/packet • supports both circuit switched and packet switched services • circuit mode services • packet mode services • Connection oriented service • Uses virtual paths • Supports different data rates from 16Kbps and up (OC-12)

6. ATM 5-Byte Header Structure • VCI—16 bits of virtual circuit identifier that is used, in conjunction with the VPI, to identify the destination of a cell - to identify the next destination of a cell as it passes through a series of switch routers on its way to its destination. • VPI—8 bits of virtual path identifier that is used, in conjunction with the VCI; A virtual path consists of multiple virtual channels to the same endpoint. • PT—3 bits of payload type. The first bit indicates whether the cell contains user data or control data. • CLP—1 bit of congestion loss priority that indicates whether the cell should be discarded if it encounters extreme congestion as it moves through the network. • HEC—8 bits of header error control that are a checksum calculated only on the header itself. • GFC—4 bits of generic flow control that are used to provide local functions, such as identifying multiple stations that share a single ATM interface. The GFC field is typically not used and is set to a default value.

7. Virtual Connections • VCI—16 bits of virtual circuit identifier that is used, in conjunction with the VPI, to identify the destination of a cell - to identify the next destination of a cell as it passes through a series of switch routers on its way to its destination. • VPI—8 bits of virtual path identifier that is used, in conjunction with the VCI; A virtual path consists of multiple virtual channels to the same endpoint. http://www.tekelec.com/ss7/protocols/atm10.asp

8. ATM Network Components • ATM End-point (end-systems) • Constitute source and destination • Can be a PC with ATM NIC or special devices • Supports multiple interfaces • ATM Switches (switch fabric) • Responsible for routing cells through public or private owned networks • ATM Switching Paths • ATM transmission media (twisted-pair, optical fiber link, etc.)

9. ATM Network Components Interfaces: UNI (user-to-network interface – within the same network NNI (network-to-network interface) From the ATM Switch ATM Endpoint Implementation

10. ATM Protocol Stack • Physical Layer • Transmission Convergence Sub-layer • Header error control • Cell rate control • Generating recovery cell • Physical Medium Dependent • Means of accessing to the transmission media • Specifying the actual bit rate • Cell Layer • Control flow • Produce/extract cell headers • Translating VPI and VCI • ATM Adaptation Layer • Convergence sub-layer • Placing bits into a common format • Cell sequencing • Identifies class of service • Segment and Assembly sub-later • Placing data format into ATM cells and de-segmenting data cells

11. ATM Protocol Stack

12. ATM Adaptation Layer (AAL) • The part of the ATM protocol that breaks up application packets into ATM cells • There are four types of AALs • AAL-1 Connection-oriented, Constant Bit Rate (CBR), such as DS1 and DS3. • AAL-2 Connection-oriented, Variable Bit Rate (VBR). • AAL-3/4 Connection-oriented and connectionless, Available Bit Rate (ABR). • AAL-5 Connection-oriented, Unspecified Bit Rate (UBR). Least amount of error checking and retransmission. • AAL-6 Connection-oriented, MPEG-2 video streams

13. ATM Traffic Types Low Latency Used for time sensitive data Bursty traffic No delivery guarantee Best effort based

14. Traffic in ATM Switches • Blocking • Switch Fabric • Head-of-line Blocking • Buffering • Input • Output • Traffic Engineering

15. Sources • Miller Text book • Tomasi Text Book

16. TCP/IP Stack Protocol

17. Extra Credit