T1 Framing
D4 Frame is 24 timeslots + framing bit.
100011011100
Ethernet II -- 14 octets.
MPLS -- 4 octets.
CESoPSN -- 4 octets.
TDM Payload -- 192 octets.
Each Ethernet II frame takes up 1712 bits on the wire.
T1 Channel Associated Signaling (CAS) [Used for voice]
Every 6th frame will have all the lowest order bits stolen on each channel for signaling information.
Super Framing does this 6 (A bit), 12 (B bit), 18 (A bit), 24 (B bit)
Extended Super Framing does this but makes four bits. A, B, C, D
Link Down
On RX
- 175 contigouse pulse positions with no positive or negative polarity.
On TX
- Sends
yellow alarmFar End Alarm - Next device downstream gets a
blue alarm
On this device marks the link as T1 LOS Loss of Signal.
T1 Clocking Types
| Command | Description |
|---|---|
clock source line | derive reference from external device. |
clock source internal | use local PLL for reference. |
network-clock-participate | join the TDM backplane of the router. |
network-clock-select | Tells the TDM backplane to use certain T1 as a reference clock, and share it. |
network-clock-select requires a T1 line to be in clock source line mode.
network-clock-participate is required for network-clock-select
Mainboard voice DSPs MUST use the backplane clock. They can't opt out.
All network-clock-participate devices share the same clocking-domain.
T1 Clocking Information
T1 reads from RX and TX buffers at the clock rate. Slips are reported when data is read at the wrong clock. Sometimes it might sample the same bit twice, sometimes it might miss bits completely.