Layer 1 & Layer 2 Protocols
• 7-6 •
The H.110 Basic Rate ISDN Board
most significant bit will be set to 1. For a TE port, this bit will be a 0. The
lower four bits represent the F or G state as defined in section 7.1. Thus,
state F7 will be represented by a 07h and state G3 will be represented as an
83h.
Each port also has eight bytes reserved for Layer 2 state information
beginning at an offset of 1C00h. The first seven bytes for a port represent
the Layer 2 states for each of the seven possible TEI’s. The last byte of
the eight is the Layer 2 state of the Packet Data Link. These states are:
1
TEI unassigned
2
Awaiting TEI assignment
3
Awaiting TEI establishment
4
TEI assigned, a TEI has been assigned, but multi-frame
operation has not been established
5
Awaiting multi-frame operation, an SABME frame has been
sent and awaiting a UA frame acknowledgment
6
Awaiting release form multi-frame state, a DISC frame has
been sent and awaiting a DM frame
7
Multi-frame operation, exchange of I frames is possible
8
Timer recovery, a timer has expired and recovery procedures
are in progress
7.4 TEI Management
While the board handles the basic procedures of TEI assignment, it is the
responsibility of the application to manage the process and keep track of
which TEI’s have been assigned for use in sending and receiving Layer 3
messages. A number of command and response messages have been
provided to facilitate this function.
TEI’s come in two types. One type, fixed TEI’s are in the range 0-63 and
are assigned by presubscription to a piece of terminal equipment. The
value of a fixed TEI is usually set in the terminal by some means such as
a set of switches or fixed in non-volatile memory. The second type of
TEI’s are assigned dynamically from the range 64-126. These TEI’s are