Panasonic UF-E1, Руководство по обслуживанию

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UF-E1
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3. PPP and Physical Conditions
PPP operates under the physical conditions shown in Table 6.5.2.1. The physical network used is a
general dedicated line of the full-duplex and point-to-point type or switchboard circuits. In concrete
terms, there are general telephone lines, dedicated circuits, X.25 packet exchange network, ISDN,
frame relay, Synchronous Optical Network (SONET), etc.
The transmission speed is dependent on the connection interface (Data Terminal Equipment (DTE),
Data Circuit-Terminating Equipment (DCE)) but it has been said that it can be as fast as 2488 Mbps
(OC-48) of SONET on theoretical terms. For transmission coding format, the non-return-to-zero (NRZ)
is recommended for transmission speed of 56 kbps to about 2Mbps and the non-return-to-zero-inverse
(NRZI) is possible at about 45Mbps. However, NRZI is to be used wtih CRC-32.
What is noteworthy is that PPP can be used with either synchronization methods of synchronous and
asynchronous formats. With synchronous format, bit and byte synchronization can be used but in
asynchronous format, 8-bit/no parity is used. (There is no format for 7-bit transmission.) The PPP-
physical layer interface is in byte format.
The idle sequences between frames (time fill) is set by flags but, in switchboard circuit that use bit-syn-
chronization and mark idle (continuation of 1 bit), 1 bit must be continued for 15 times. (1 bit from 7 to
14 bits are abort frame that nullify the frames). In that regard, the time fill between bites in asynchro-
nous format is in mark holding condition (bit is one).
Table 6.5.2.1 Physical conditions for PPP
NRZ : Non Return to Zero NRZI : Non Return to Zero Inverse
4. Data Link Layer (RFC 1662)
PPP has the frame with the same structure as the Un-numbered Information (UI) of HDLC and the
maximum length of the data section is 1500 bytes (default, adjustable).
a. Frame structure of PPP
The data link frame of the PPP has a structure similar to ISO 3309 (HDLC frame), as shown in Fig-
ure 6.5.2.2.
The flag has a value of 7Eh (7E of hexadecimal), an address of FFh (indicating all stations), and a
control field of un-numbered information (UI) of 03h. The poll/final (P/F) bit is not set (value is 0).
The default of FCS is CRC-2 of 16 bit (2 bytes). (32 bit is set by negotiation.)
The protocol field is a value for identifying the protocol of the data set at the data section (Table
6.5.2.2). This protocol value is a value set by RFC 1700 (Assigned Numbers) and they are catego-
rized in three major types.
Item Contents
Communication Line Dedicated/Switchboard lines
Communication Method Point-to-point
Transmission Mode Full duplex
Transmission Coding Format NRZ (Recommended default)/NARZI
(FCS must be used with CRC-32)
Connection Interface DTE/DCE (RS-232E/422, V.35, etc.)
Transmission Speed Depends on connection interface (network)
Control Signal None
Synchronization Method bit/byte synchronous, non-synchronous
(Start-stop synchronization: 8-bit/no parity)
Idle Sequence Flag
Data Link Interface byte format