Chapter 14 Connection-Oriented Chapter 14 Connection-Oriented Networking and ATMNetworking and ATM

ATMPVCSVCQOSAAL5

Connection-Oriented Connection-Oriented Packet Switching in ATMPacket Switching in ATM

Connection request by one computer Connection acceptance by other computer End-to-end connection established via a virtual

circuit– Connection identifiers assigned to both computers

Data exchange using VPI and VCI identifiers associated with VC

Connection teardown

Asynchronous Transfer Mode Asynchronous Transfer Mode (ATM) cell format(ATM) cell format

48 bytes of data5 bytes of header (figure 14.1)

– 4 bits flow control– 1 byte Virtual Path Identifier(VPI) – 2 bytes Virtual Channel Identifier (VCI)– 3 bits payload type– 1 bit priority– 1 byte CRC

Label Switching in ATMLabel Switching in ATM

Aka label rewriting VPI/VCI of cell changed by ATM switch during

forwarding using a forwarding table (figure 14.3) Incoming cell’s VPI/VCI used as index into table

containing output interface number and new VPI/VCI for outgoing cell header

Two computers using a given virtual circuit usually have different VPI/VCI values

Computer is aware of its own VPI/VCI, not that of the other computer

Permanent Virtual CircuitsPermanent Virtual Circuits(PVC)(PVC)

Created by network manager– forwarding tables on the ATM switches

manually configured (provisioning)

Survives power failureRequested by customer to ATM network

provider

Switched Virtual CircuitsSwitched Virtual Circuits(SVC)(SVC)

Virtual circuit created dynamically (on demand) Creation of SVC

– Computer sends a connection request to switch– As request propagates towards destination, each pair of

ATM switches chooses a VPI/VCI to use for the VC and initialize their forwarding tables.

– Once all switches along path and the destination computer agree to provide the SVC, a message is sent back to the originating computer to indicate connection request accepted.

– If any switch along the path does not agree to provide the VC, an error message is sent back with request denied.

Quality of Service (QOS)Quality of Service (QOS)

bandwidth(bps) and delay(ms) requirementsconstant bit rate (CBR) for uncompressed

audio and videovariable bit rate (VBR) for compressed

audio and videoAvailable bit rate (ABR) for bursty dataIf QOS requests cannot be satisfied,

connection request is denied.

ATM Adaptation Layer 5 ATM Adaptation Layer 5 (AAL5)(AAL5)

The only one of five adaptation protocols that is used to send data

Computer can send variable-size blocks (up to 64k bytes) to AAL5 on the switch

each block segmented into cells for transmission through ATM network.

AAL5 reassembles cells at destination

ATM vs. EthernetATM vs. Ethernet

Connection Unicast QOS WAN/LAN Fixed size cell Expensive Connection setup

latency 10% header overhead

Connectionless Broadcast RSVP LAN Variable sized frames No connection setup

latency 1% header overhead