Ericsson HM200c/HM201c Instrukcja Użytkownika Pobierz pdf (Strona 7)

The time-division multiple access (TDMA)

transmissions from cable modems at various

distances from the head-end must be coor-

dinated so that all transmissions align with

the boundaries of the head-end minislots.

Discrepancies between individual modems

and the head-end are caused by propagation

delays in the CATV plant, the FEC inter-

leaving function (a variable-depth inter-

leaver supports latency-sensitive and

latency-insensitive data), and processing

time.

The CMTS informs the modem of the

propagation delay after it receives the rang-

ing request. Upstream frequency assign-

ments can change at any time. The head-end

ensures that the cable modem receives the

new frequency assignment before listening

for the modem’s transmission on the fre-

quency. After ranging is complete, the cable

modem must invoke dynamic host config-

uration protocol (DHCP) mechanisms to

obtain an IP address and continue the reg-

istration/configuration process (provision-

ing process).

The DHCP server responds with IP ad-

dresses, the name of the configuration file,

and server addresses. After establishing a se-

curity association, the cable modem must

download (via TFTP) a file with configura-

tion parameters from the configuration serv-

er. The CMTS then checks that the config-

uration was obtained from a legitimate con-

figuration server. Finally, the cable modem

registers (Figure 8) with the CMTS and be-

38

Ericsson Review No. 1, 2001

Downstream

sync

established

Baseline

privacy

initialized

Scan for

downstream

channel

Operational

Upstream

parameters

acquired

Register

with

CMTS

Obtain

upstream

parameters



Registration

complete

Ranging and

auto adjust.

complete

Transfer 

operational

parameters

Ranging and 

automatic

adjustments

Transfer

complete

IP

complete

Establish

IP

connectivity

Time of day

established

Establish

time of 

day



Figure 8

Initialization process.

Frame control (FC)

(1 byte)

FC TYPI

(2 bits)

FC PARI

(5 bits)

EDHR_ON

(1 bit)

MAC parameters

(MAC_PARAM:1 byte)

LED/(SID)

(1 byte)

Extended header

Header check sequence (H)

(2 bytes)

Figure 9

Generic frame format.

1 2 3 4 5 6 7 8 9 10 11 12

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