Chapter 14 Connection-Oriented Networking and ATM PVC SVC QOS AAL5

Connection-Oriented Packet 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 (ATM) cell format 48 bytes of data 5 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 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 Circuits (PVC) Created by network manager forwarding tables on the ATM switches manually configured (provisioning) Survives power failure Requested by customer to ATM network provider

Switched Virtual Circuits (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) bandwidth(bps) and delay(ms) requirements constant bit rate (CBR) for uncompressed audio and video variable bit rate (VBR) for compressed audio and video Available bit rate (ABR) for bursty data If QOS requests cannot be satisfied, connection request is denied.

ATM Adaptation Layer 5 (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. 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