PGM Reliability Settings
TTM supports the PGM Protocol, which ensures that TTM receives packets in the order in which they are sent across the network. If packets are dropped or received in the wrong order, TTM sends a negative acknowledgement (NAK) to the packet sender. When the sender receives the NAK, it resents the requested packets. This is referred to as a reliable multicast and is automatically enabled in all TTM daemons. Although reliable multicast is needed for most network transactions, it is not needed for price updates from PFX-enabled gateways, which are delivered as a full, contract-level update of the current market conditions. For these transactions, TTM automatically disables the PGM reliability, and eliminates unneeded NAKs and responses.
When a TTM daemon detects that a packet from a PFX-enabled gateway is out of sequence with a PGM header, it updates the number of Out-of-Sequence Data packets (OSD) and Unrecovered Dropped Data packets (UDD), but it no longer sends a NAK. Because the NAKs are not sent, the TTM daemon that sent the out-of-sequence data is not alerted to resend data.
Example Out-of-Sequence and Unrecovered Dropped Data Packets
TTM Receives Packets 0, 1, 4, 6, 7 (packets 2,3, and 5 are missing).
Before the timer for missing packets 2 and 3 expires (after 15 seconds), TTM receives packets 2 and 3, however the timer for packet 5 expires without TTM receiving it.
In this example, packets 2, 3, 4 and 6 are considered Out-of-Sequence Data. Packet 5 was not received in time, so it is not Out-of-Sequence Data, but instead is an Unrecovered Dropped Data packet. The OSD count would be 4 and the UDD count would be 1.
For more information about PFX, refer to the latest TT Gateways Architecture System Administration Manual.
To disable PGM Reliability, the TTM daemon running on the following components must use TTM 3.2 or later:
- Price Servers
- Client Applications
- WAN Routers (if applicable)
- X_TRADER Remote Host (if applicable)
Additionally, PFX must be enabled on the Gateways. For more information about PFX, refer to the latest TT Gateways Architecture System Administration Manual.
If a TTM 3.2 daemon receives a PGM NAK from a TTM 2.1/3.1 or earlier daemon, the TTM 3.2 daemon responds to the PGM NAK.
TTM 3.2 and later daemons automatically disable the unneeded reliability for packets from PFX-enabled gateways.
When a TTM daemon detects a packet that is out of sequence with a PGM header, it updates the number of Out-of-Sequence Data packets (OSD) and Unrecovered Dropped Data packets (UDD) on the PGM Service RX line in the once-a-minute section of the ttmd.log file.
Date Time PGM Service RX ODATA:X SPM:X NCF:X RDATA:X NAK:X RDP:X UNREC:X MPR:X[X] MBR:X[X] OSD:X UDD:X