Cisco 1700 Series Installation Guide download pdf (Page 28)

Configuring an ADSL WAN Interface Card on Cisco 1700 Series Routers

OL-3317-03

Configuring the SCC Clock Rate

Communciation between a DSL WIC and the host in a router takes place through a device called a serial

communications controller (SCC). Whenever the host wants to transmit data or send any control traffic

to the DSL WIC, it uses an SCC. Similarly, when a DSL WIC wants to forward incoming data from the

line to the host, it also uses an SCC. Each DSL WIC installed in a router uses two SCCs. One SCC,

SCC-A, is used for ATM adaptation layer 5 (AAL5) data traffic, while the other, SCC-B, is used for ATM

adaptation layer 2 (AAL2) data traffic and for control traffic. The speed at which an SCC transfers data

between the host and the WIC depends on the clock rate with which the SCC has been configured. This

clock rate is configured by the user, and it is always synchronous. The SCC clock rate is the same

whether the WIC is sending or receiving data through the SCC. For an asynchronous DSL (ADSL) WIC,

the SCC clock rate should be set slightly higher than the larger of the DSL line rates (upstream or

downstream). It is recommended that the SCC clock rate always be set higher than the DSL line rate to

accommodate any SCC overhead.

SCC Clock Rate Configuration

The following example is a configuration of SCC clock rates on an ATM interface. Clock rates are set

with the clock rate aal5 command and the clock rate aal2 command. On Cisco 1700 series routers, valid

clock rates are in the range from 4 Mbps to 8 Mbps. The clock rate values are entered as bits per second,

as shown in the example.

interface ATM0/0

no ip address

clock rate aal5 5300000

clock rate aal2 4000000

no atm ilmi-keepalive

bundle-enable

bundle ama-bundle12

dsl operating-mode auto

end

Note It is strongly recommended that on Cisco 1700 series routers, the SCC clock rate be set to the default

value of 8 Mbps (8000000 bps).

Note When an SCC clock rate is deconfigured on a Cisco 1700 series router by using the no form of the

command, it is reset to the default value of 8 Mbps.

SCC Clock Rate Verification

To verify the configuration of the SCC clock rate, use the show controller command. SCC-A represents

the clock rate for AAL5, while SCC-B represents the clock rate for AAL2.

Router#show controller atm0/0

Interface: ATM0/0, Hardware: DSLSAR (with Alcatel ADSL Module), State: up

IDB: 82115298 Instance: 82116A4C reg_dslsar:68030000 wic_regs: 68030080

PHY Inst:8213862C Ser0Inst: 8210F690 Ser1Inst: 8211281C us_bwidth:864

Slot: 0 Unit: 0 Subunit: 0 pkt Size: 4528

VCperVP: 256 max_vp: 256 max_vc: 65536 total vc: 1

rct_size:65536 vpivcibit:16 connTblVCI:8 vpi_bits: 8

vpvc_sel:3 enabled: 0 throttled: 0 cell drops: 0

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