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

2. 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

3. 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

4. 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

5. 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

6. 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.

7. 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.

8. 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

9. 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