📄 rfc905.txt
字号:
I Inactivity time
W Window time
TTR Time to try reassignment/resynchronization
TWR Time to wait for
reassignment/resynchronization
TS1 Supervisory timer 1
TS2 Supervisory time 2
MLR NSDU lifetime local-to-remote
MRL NSDU lifetime remote-to-local
ELR Expected maximum transit delay
local-to-remote
ERL Expected maximum transit delay
remote-to-local
R Persistence time
AL Local acknowledgement time
AR Remote acknowledgement time
4.5 Miscellaneous
TS-user Transport service user
TSAP Transport service access point
NS-provider Network service provider
NSAP Network service access point
QOS Quality of service
14
5 OVERVIEW OF THE TRANSPORT PROTOCOL
NOTE - This overview is not exhaustive and has been provided for
guidance to the reader of this International Standard.
5.1 Service provided by the transport layer
The protocol specified in this International Standard supports
the transport service defined in DP 8072.
Information is transferred to and from the TS-user in the
transport service primitives listed in table 1.
15
+-------------------------------------------------------------+
| Primitive | Parameter |
|--------------------------------|----------------------------|
|T-CONNECT request | Called Address, |
| indication | Calling Address, |
| | Expedited Data option, |
| | Quality of Service, |
| | TS User-Data. |
|--------------------------------|----------------------------|
|T-CONNECT response | Responding Address, |
| confirm | Quality of Service, |
| | Expedited Data option, |
| | TS User-Data. |
|--------------------------------|----------------------------|
|T-DATA request | TS User-Data. |
| indication | |
|--------------------------------|----------------------------|
|T-EXPEDITED DATA request | TS User-Data. |
| indication | |
|--------------------------------|----------------------------|
|T-DISCONNECT request | TS User-Data. |
|--------------------------------|----------------------------|
|T-DISCONNECT indication | Disconnect reason, |
| | TS User-Data. |
+--------------------------------|----------------------------+
Table 1. Transport service primitives
5.2 Service assumed from the network layer
The protocol specified in this International Standard assumes the
use of the network service defined in DP 8348.
Information is transferred to and from the NS-provider in the
network service primitives listed in table 2.
16
+---------------------------------------------------------------+
| Primitives |X/Y| Parameters |X/Y/Z|
|----------------------------|---|------------------------|-----|
|N-CONNECT request | X | Called Address, | X |
| indication | X | Calling Address, | X |
| response | X | NS User-Data, | Z |
| confirm | X | QOS parameter set, | X |
| | | Responding address, | Z |
| | | Receipt confirmation | Y |
| | | selection. | |
|----------------------------|---|------------------------|-----|
|N-DATA request | X | NS User-Data, | X |
| indication | X | Confirmation request | Y |
|----------------------------|---|------------------------|-----|
|N-DATA ACKNOWLEDGE | | | |
| request | Y | | |
| indication | Y | | |
|----------------------------|---|------------------------|-----|
|N-EXPEDITED DATA | | | |
| request | Y | NS User-Data. | Y |
| indication | Y | | |
|----------------------------|---|------------------------|-----|
|N-RESET request | X | Originator, | Z |
| indication | X | Reason. | Z |
| response | X | | |
| confirm | X | | |
|----------------------------|---|------------------------|-----|
|N-DISCONNECT request | X | NS User-Data. | Z |
| indication | X | Originator, | Z |
| | | Reason. | Z |
+---------------------------------------------------------------+
Table 2. Network service primitives
17
Key:
X - The Transport Protocol assumes that this facility is
provided in all networks.
Y - The Transport Protocol assumes that this facility is
provided in some networks and a mechanism is provided to
optionally use the facility.
Z - The Transport Protocol does not use this parameter.
NOTES:
1 - The parameters listed in this table are those in the
current network service (first DP 8348).
2 - The way the parameters are exchanged between the transport
entity and the NS-provider is a local matter.
5.3 Functions of the Transport Layer
5.3.1 Overview of functions
The functions in the Transport Layer are those necessary to
bridge the gap between the services available from the Network
Layer and those to be offered to the TS-users.
The functions in the Transport Layer are concerned with the
enhancement of quality of service, including aspects of cost
optimization.
These functions are grouped below into those used at all times
during a transport connection and those concerned with connection
establishment, data transfer and release.
NOTE - This International Standard does not include the following
functions which are under consideration for inclusion in future
editions of this standard:
a) encryption;
18
b) accounting mechanisms;
c) status exchanges and monitoring of QOS;
d) blocking;
e) temporary release of network connections;
f) alternative checksum algorithm.
5.3.1.1 Functions used at all times
The following functions, depending upon the selected class and
options, are used at all times during a transport connection:
a) transmission of TPDUs (see 6.2 and 6.9);
b) multiplexing and demultiplexing (see 6.15), a function
used to share a single network connection between two or
more transport connections;
c) error detection (see 6.10, 6.13 and 6.17), a function used
to detect the loss, corruption, duplication, misordering
or misdelivery of TPDUs;
d) error recovery (see 6.12, 6.14, 6.18, 6.19, 6.20, 6.21 and
6.22), a function used to recover from detected and
signalled errors.
5.3.1.2 Connection Establishment
The purpose of connection establishment is to establish a
transport connection between two TS-users. The following
functions of the transport layer during this phase must match the
TS-users' requested quality of service with the services offered
by the network layer:
19
a) select network service which best matches the requirement
of the TS-user taking into account charges for various
services (see 6.5);
b) decide whether to multiplex multiple transport connections
onto a single network connection (see 6.5);
c) establish the optimum TPDU size (see 6.5);
d) select the functions that will be operational upon
entering the data transfer phase (see 6.5);
e) map transport addresses onto network addresses;
f) provide a means to distinguish between two different
transport connections (see 6.5);
g) transport of TS-user data (see 6.5).
5.3.1.3 Data Transfer
The purpose of data transfer is to permit duplex transmission of
TSDUs between the two TS-users connected by the transport
connection. This purpose is achieved by means of two-way
simultaneous communication and by the following functions, some
of which are used or not used in accordance with the result of
the selection performed in connection establishment:
a) concatenation and separation (see 6.4), a function used to
collect several TPDUs into a single NSDU at the sending
transport entity and to separate the TPDUs at the
receiving transport entity;
b) segmenting and reassembling (see 6.3), a function used to
segment a single data TSDU into multiple TPDUs at the
sending transport entity and to reassemble them into their
original format at the receiving transport entity;
20
c) splitting and recombining (see 6.23), a function allowing
the simultaneous use of two or more network connections to
support the same transport connection;
d) flow control (see 6.16), a function used to regulate the
flow of TPDUs between two transport entities on one
transport connection;
e) transport connection identification, a means to uniquely
identify a transport connection between the pair of
transport entities supporting the connection during the
lifetime of the transport connection;
f) expedited data (see 6.11), a function used to bypass the
flow control of normal data TPDU. Expedited data TPDU
flow is controlled by separate flow control;
g) TSDU delimiting (see 6.3), a function used to determine
the beginning and ending of a TSDU.
5.3.1.4 Release
The purpose of release (see 6.7 and 6.8) is to provide
disconnection of the transport connection, regardless of the
current activity.
5.4 Classes and options
5.4.1 General
The functions of the Transport Layer have been organized into
classes and options.
A class defines a set of functions. Options define those
functions within a class which may or may not be used.
This International Standard defines five classes of protocol:
21
⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -