2-7 Synchronous Serial Interfaces | Cisco Field Manual[c] Router Configuration

Synchronous serial interfaces transport data and a clock signal across an end-to- end connection.
Serial interfaces include High-Speed Serial Interface (HSSI, 45 Mbps), Channelized T3, Channelized T1, G.702, and traditional router serial interfaces up to T1 (1.544 Mbps) and E1 (2.048 Mbps) speeds.
Synchronous serial connections can also include CSU/DSU devices at each end. These can be external, integrated, or integrated as service modules.
A channelized T3 interface supports up to 28 T1 channels as a single T3 group over a single DS3.
Each T1 channel can be configured for a fractional or full T1 bandwidth. If it's fractional , the remaining bandwidth is filled with idle data.

Configuration

Select and configure one of the serial interfaces described in the following sections (Channelized T3, Channelized T1 or E1 Interface, Synchronous Serial Interface).

Configuring Channelized T3 Serial Interfaces

Select the T3 controller:

 (global)  controller t3   slot/port-adapter/port

(Optional) Set the framing:
```
 (controller)  framing  {  c-bit   m23   auto-detect  } 
```
The T3 controller framing type can be set to C-bit, M23, or auto-detection ( auto-detect, the default).
(Optional) Set the cable length:
```
 (controller)  cablelength   feet  
```
The length of the cable from the router to the network equipment can be given in feet (0 to 450; the default is 224).
(Optional) Set the clock source:
```
 (controller)  clock source  {  internal   line  } 
```
The T3 clock can be taken from the network ( line ) or from an internal source ( internal, the default).
Configure each T1 channel.

After the T1 channels are configured, each can be configured further as a synchronous serial interface.
1. Set the T1 timeslot:
```
 (controller)  t1   channel   timeslot   range  [  speed  {  56   64  }] 
```
  The T1 timeslot with the T3 is given as channel (0 to 27 on most T3 interfaces; 1 to 28 on the CT3IP interface). The timeslot keyword identifies the timeslots within the T1 that will be used. The range uses numbers 1 to 24. It can be a list of timeslots separated by a comma. A low to high group of timeslots gives a range separated by a dash.
  
  The speed keyword can specify the data rate for the T1 channel as 56 kbps or 64 kbps (the default).
2. (Optional) Set the T1 framing:
```
 (controller)  t1   channel   framing  {  esf   sf  } 
```
  The framing for the T1 channel can be set to Extended Super Frame ( esf, the default) or Super Frame ( sf ).
3. (Optional) Set the T1 clock source:
```
 (controller)  t1   channel   clock source  {  internal   line  } 
```
  The T1 channel clock can be set to the network clock ( line ) or the internal clock ( internal, the default).
4. (Optional) Set the T1 line coding:
```
 (controller)  t1   channel   linecode  {  ami   b8zs  } 
```
  The T1 channel line coding can be set to AMI ( ami ) or B8ZS ( b8zs, the default).
5. (Optional) Set the T1 yellow alarm:
```
 (controller)  t1   channel   yellow  {  detection   generation  } 
```
  The T3 interface can be set to either detect yellow alarms ( detection ) or generate yellow alarms ( generation ) for the T1 channel. By default, yellow alarms are both detected and generated.

Configuring Channelized T1/E1 Serial Interfaces

Select the T1 or E1 controller:
```
 (global)  controller  {  t1   e1  }  number  
```
The controller at slot number is selected for configuration.
Define channel groups:
```
 (controller)  channel-group   channel   timeslots   range  [  speed  {  48   56   64  }] 
```
For a fractional T1 or E1, the channels can be grouped as one data stream. An arbitrary channel group numbered channel is selected, and the range of timeslots is defined. Timeslots can be given as a dash-separated range or a comma-separated list. The speed keyword specifies the speed of the timeslots in the range. It can be 48 kbps, 56 kbps (T1 default), or 64 kbps (E1 default).
(Optional) Define CAS signaling:
```
 (controller)  cas-group   channel   timeslots   range   type   signal   service data  
```
T1 channels can be configured for Channel Associated Signaling (CAS, also called robbed-bit signaling). The channel group channel defines a group or range of timeslots as a single group. Different types of robbed-bit signaling can be assigned to each group. The timeslot range can be a comma-separated list of numbers, including dash-separated ranges of numbers.

The type keyword defines the type of signaling for the channel group signal: e&m-fgb (ear and mouth with feature group B), e&m-fgd (ear and mouth with feature group D), e&m-immediate-start (ear and mouth with immediate start), fxs-ground-start (Foreign Exchange Station ground start), fxs-loop-start (Foreign Exchange Station loopstart signaling), sas-ground-start (Special Access Station with ground start), or sas-loop-start (Special Access Station with loopstart).
(Optional) Specify the clock source:
```
 (controller)  clock source  {  line  {  primary   secondary  }  internal  } 
```
The clock source can be set to the network ( line ) or to the free-running internal clock ( internal ). If the line clock is used, the T1 or E1 controller that it is applied to can be selected as the primary or secondary clock source. Choose the most reliable clock source as the primary.
(Optional) Select the framing type:
```
 (controller)  framing  {  sf   esf   crc4   no-crc4  } [  australia  ] 
```
For a T1, the framing can be set to Super Frame ( sf, the default) or Extended Super Frame ( esf ). For an E1, the framing can be CRC4 ( crc4, the default), non-CRC4 ( no-crc4 ), or Australian type ( australia ).
(Optional) Select the line coding:
```
 (controller)  linecode  {  ami   b8zs   hdb3  } 
```
The line coding can be set to Alternate Mark Inversion ( ami, T1 default), bipolar 8 zero sequence ( b8zs ), or high-density bipolar 3 ( hdb3, E1 default).
(Optional) Configure T1 cable length:
```
 (controller)  cablelength short  {  133   266   399   533   655  } (controller)  cablelength   long  {  gain26   gain36  } {  -22.5   -15   -7.5    } 
```
For cable lengths shorter than 655 feet, use the cablelength short command. Use the next -highest length (in feet) than the actual cable length. If the cable length is greater than 655 feet, use the cablelength long command. Choose the receiver gain that corresponds to the cable loss, as 26 dB ( gain26 ) or 36 dB ( gain36 ). Then choose the decrease in transmitter gain, as -22.5 dB ( -22.5 ), -15 dB ( -15 ), -7.5 dB ( -7.5 ), or 0 dB ( ).
(Optional) Configure the E1 line termination:
```
 (controller)  line termination  {  75-ohm   120-ohm  } 
```
The E1 line termination can be set to 75 ohms unbalanced or 120 ohms balanced.

Configuring Synchronous Serial Interfaces

NOTE

For channelized T3, E3, T1, or E1 interfaces, first configure the channelized interface and channel groups. Then you can treat the channel groups as a logical serial interface for the next configuration steps.

Choose an interface:
```
 (global)  interface serial   number  [:  channel-group  ] 
```
-OR-
```
 (global)  interface hssi   number  
```
The serial interface number (or slot/number ) is selected. If a channelized interface is being configured, add a colon and the channel group number channel-group. An HSSI can also be selected by using the hssi interface type.

NOTE

Some routers have interfaces that can operate in either asynchronous or synchronous mode. Before continuing with the synchronous serial commands, the interface should be set for synchronous mode with the (interface) physical-layer sync command.
(Optional) Choose an encapsulation:
```
 (interface)  encapsulation  {  hdlc   ppp  } 
```
The encapsulation can be set to HDLC (the default) or PPP. Other encapsulations can be chosen for ATM, SNA, Frame Relay, and SMDS. See the respective sections in this chapter for more information.
(Optional) Configure compression:
```
 (interface)  compress  {  stac   predictor  } 
```
HDLC frames can be compressed by a lossless Stacker ( stac ) LZS algorithm. PPP frames can be compressed by either a Stacker ( stac ) or a RAND ( predictor ) algorithm. Compression should be used only if the router CPU load is less than 40 to 65% and if the majority of traffic is not already compressed.
(Optional) Configure the serial data stream and handshaking.
1. Configure the CRC length:
```
 (interface)  crc   length  
```
  By default, the CRC length is 16 bits, but it can be set to length bits (16 or 32). The same CRC length must be used on both ends of a serial connection.
2. Set the line-coding format:
```
 (interface)  nrzi-encoding  [  mark  ] 
```
  By default, serial interfaces use NRZ encoding. NRZI encoding can be used instead if it is required. If the mark keyword is omitted, NRZI space encoding is used.
3. Invert the data stream:
```
 (interface)  invert data  
```
  The data stream can be inverted when a dedicated T1 line is used without B8ZS encoding. Don't invert the data at the router and at the CSU/DSU; invert at only one device.
4. Set a transmit delay:
```
 (interface)  transmitter-delay   delay  
```
  If packets are sent faster than a remote device can receive them, a delay can be inserted between serial packets. The FSIP, HSSI, and MIP interfaces require a delay value of the number of HDLC flags to send between packets. All other interfaces use a delay in microseconds (0 to 131071; the default is 0).
5. Enable DTR pulsing :
```
 (interface)  pulse-time   seconds  
```
  By default, DTR is held down during a line failure. If a remote serial device requires the toggling or pulsing of DTR to resynchronize after a line failure, DTR can be pulsed at an interval of seconds (the default is 0).
6. Monitor DSR instead of DTR:
```
 (interface)  ignore-dcd  
```
  By default, the DCD signal is monitored to determine whether the line is up or down. If this is not required, DCD can be ignored, and DSR will be monitored instead.
(Optional) Configure the serial clock.
1. Set the clock rate for DCE mode:
```
 (interface)  clock rate   bps  
```
  The serial interface is set to become a DCE device. It generates a clock signal at bps bits per second. On most routers, the rate must be set to a standard value of 1200, 2400, 4800, 9600, 19200, 38400, 56000, 64000, 72000, 125000, 148000, 250000, 500000, 800000, 1000000, 1300000, 2000000, 4000000, or 8000000. Some platforms will accept any value between 300 and 8000000 bps and will round a nonstandard value to the nearest supported rate.
  
  NOTE
  
  Be aware that higher speeds work properly only at shorter cable distances. Refer to Appendix B, "Cabling Quick Reference," for distance limitations.
2. Use the internal clock:
```
 (interface)  transmit-clock-internal  
```
  If a DTE device does not return a transmit clock, the internal clock can be used. Normally, the clock is derived from the line through the DCE device.
3. Invert the transmit clock:
```
 (interface)  invert txclock  
```
  With long cable distances and higher transmission speeds, a phase shift between the local transmit clock and the returned transmit clock can occur. If a large number of error packets are seen, you can try inverting the transmit clock to correct the phase-shift problem.
(Optional) Configure an integrated port adapter DSU.
1. Select the clock source:
```
 (interface)  clock source  {  line   internal  } 
```
  The clock source can be set to the network ( line, the default) or the internal clock.
2. Set the cable length (PA-T3 only):
```
 (interface)  cablelength   feet  
```
  The cable distance from the router to the network can be specified in feet (0 to 450; the default is 50).
3. Configure the CRC length (PA-T3 only):
```
 (interface)  crc  {  16   32  } 
```
  The CRC length can be set to either 16 (the default) or 32 bits.
4. Set the DSU bandwidth:
```
 (interface)  dsu bandwidth   kbps  
```
  The maximum bandwidth can be set as kbps (22 to 44736 kbps; the default is 34010 kbps for PA-E3 and 44736 kbps for PA-T3). Both ends of the serial connection must match, because the bandwidth is reduced to the maximum by padding frames.
5. Set the DSU mode:
```
 (interface)  dsu mode  {    1   2  } 
```
  The DSU interoperability mode can be set to support a Digital Link DL3100 DSU ( 0, the default; also used to connect two PA-T3s or two PA-E3s), a Kentrox DSU ( 1 ), or a Larscom DSU ( 2 ).
6. Select the framing type:
```
 (interface)  framing  {  bypass   g751   c-bit   m13  } 
```
  The framing mode can be set to bypass (frame data is not included in the frame; scrambling must be disabled, DSU mode must be 0, and DSU bandwidth must be set to 44736), g751 (G.751 E3 framing, the default for PA-E3), c-bit (C-bit framing, the default for PA-T3), or m13 (M13 framing).
7. Invert the data stream:
```
 (interface)  invert data  
```
  The data stream can be inverted if needed. For example, if a PA-T3 does not use B8ZS encoding, the data stream should be inverted to enable one's insertion.
8. Enable scrambling:
```
 (interface)  scramble  
```
  Payload scrambling can be enabled to prevent some bit patterns from being interpreted as alarms. If it is used, scrambling should be enabled on both ends.
9. Set the national and international bits (PA-E3 only):
```
 (interface)  national bit  {    1  } (interface)  international bit  {    1  } {    1  } 
```
  The national bit in the E3 G.751 frame can be set or reset (the default is 0). The first and second international bits can also be set or reset (the default is 0 0).
(Optional) Configure an integrated T1/FT1 service module:
1. Select the clock source:
```
 (interface)  service-module t1 clock source  {  internal   line  } 
```
  The clock source can be set to either the network ( line, the default) or the internal clock.
2. Select the framing type:
```
 (interface)  service-module t1 framing  {  sf   esf  } 
```
  The framing type can be set to D4 Super Frame ( sf ) or Extended Super Frame ( esf ).
3. Specify the fractional T1 timeslots:
```
 (interface)  service-module t1 timeslots  {  range   all  } [  speed  {  56   64  }] 
```
  The DS0 timeslots used in the T1 are given as range, a string of one or more ranges of dash-separated values, separated by commas. To use the entire T1, use the all keyword. The speed of each DS0 can be given as 56 kbps or 64 kbps (the default).
4. Enable data inversion:
```
 (interface)  service-module t1 data-coding  {  inverted   normal  } 
```
  The data stream can be inverted for alternate mark inverted (AMI) line coding ( inverted ). If the data stream is inverted, the CSU/DSUs on both ends must be inverted. By default, the data stream is not inverted ( normal ).
5. Select the line coding type:
```
 (interface)  service-module t1 linecode  {  ami   b8zs  } 
```
  The line coding can be set to either alternate mark inverted ( ami ) or bipolar 8 zero sequence ( b8zs, the default).
6. Set the line build-out:
```
 (interface)  service-module t1 lbo  {  -15db   -7.5db   none  } 
```
  The outgoing signal strength can be reduced by 15 dB ( -15db ), 7.5 dB ( -7.5db ), or 0 dB ( none, the default). Usually, this is needed only in back-to-back CSU/DSU scenarios.
7. Enable remote alarms:
```
 (interface)  service-module t1 remote-alarm-enable  
```
  The CSU/DSU can be configured to generate or detect remote alarms. This is disabled by default, and it should always be disabled if the line coding is set to D4 SF. Otherwise, some data bits in the SF stream will be falsely interpreted as alarms.
8. Enable remote loopback initiation:
```
 (interface)  service-module t1 remote-loopback  {  full   payload  } [  alternate   v54  ] 
```
  If the service module receives a loopback test request from the far end, it can be configured to go into loopback mode. The full keyword (the default) allows a response to all loopback requests . The payload keyword enables only payload-loopback commands. The alternate keyword configures an inverted loopback mode, with 4-in-5 loopup and 2-in-3 loopdown patterns. The v54 keyword (the default) configures the industry standard 1-in-5 loopup and 1-in-3 loopdown patterns.
(Optional) Configure an integrated two- or four-wire 56 or 64 kbps service module.
1. (Optional) Select the clock source:
```
 (interface)  service-module 56k clock source  {  line   internal  } 
```
  The clock reference can come from either the network ( line, the default) or the internal clock.
2. (Optional) Set the line speed:
```
 (interface)  service-module 56k clock rate   speed  
```
  The line speed can be configured to (in kbps) 2.4, 4.8, 9.6, 19.2, 38.4, 56 (the default), 64, or auto. The auto keyword is used to detect the line speed automatically from the sealing current on the network. auto should be used only with the line clock source and a dedicated leased line.
3. (Optional) Select the mode:
```
 (interface)  service-module 56k network-type  {  dds   switched  } 
```
  The mode can be set to dedicated leased line DDS mode ( dds, the default for four-wire circuits) or switched dialup mode ( switched, the default for two-wire circuits). For switched mode, the line clock source and a clock rate of 56 or auto must be used. Only in- band dialing is supported.
4. (Optional) Enable scrambled data for 64 kbps:
```
 (interface)  service-module 56k data-coding scrambled  
```
  On a four-wire 64 kbps DDS line, some data can be interpreted as loopback request codes. Data scrambling prevents this and should be enabled.
5. (Optional) Enable remote loopbacks:
```
 (interface)  service-module 56k remote-loopback  
```
  A service module can be configured to accept a remote loopback request. Even if remote-loopback is disabled, loopback requests can be sent to the far end.

Example

A channelized T3 interface is configured to have a T1 in channel 5, consisting of timeslots 1 through 12. The T1 framing is ESF, and the T3 cable length is about 300 feet. The line is the clock source. As soon as the controller is configured, a serial interface using T3 channel 5 can be given an IP address.

Also, a channelized T1 interface is configured. The controller is set to associate T1 timeslots 1 through 8 with a single channel group. The line clock is used for the T1, with a cable length of 300 (round up to the next choice of 399) feet. As soon as the controller is configured, a serial interface with the appropriate channel group can be configured with an IP address.

  controller t3 6/0/0   framing auto-detect   cablelength 300   clock source line   t1 5 timeslot 1-12 speed 64   t1 5 framing esf   interface serial 6/0/0:5   ip address 192.168.3.1 255.255.255.0   controller t1 7/0/1   channel-group 1 timeslots 1-8 speed 56   clock source line   cablelength short 399   interface serial 7/0/1:1   ip address 192.168.4.1 255.255.255.0