1COAP_RECOVERY(3) libcoap Manual COAP_RECOVERY(3)
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6 coap_recovery, coap_session_set_max_retransmit,
7 coap_session_set_ack_timeout, coap_session_set_ack_random_factor,
8 coap_session_get_max_transmit, coap_session_get_ack_timeout,
9 coap_session_get_ack_random_factor, coap_debug_set_packet_loss - Work
10 with CoAP packet transmissions
11
13 #include <coap2/coap.h>
14 void coap_session_set_max_retransmit(coap_session_t *session, unsigned
16 int value);
17 void coap_session_set_ack_timeout(coap_session_t *session,
19 coap_fixed_point_t value);
20 void coap_session_set_ack_random_factor(coap_session_t *session,
22 coap_fixed_point_t value);
23 unsigned int coap_session_get_max_transmit(coap_session_t *session);
25 coap_fixed_point_t coap_session_get_ack_timeout(coap_session_t
27 *session);
28 coap_fixed_point_t coap_session_get_ack_random_factor(coap_session_t
30 *session);
31 int coap_debug_set_packet_loss(const char *loss_level);
33 Link with -lcoap-2, -lcoap-2-gnutls, -lcoap-2-openssl or
35 -lcoap-2-tinydtls depending on your (D)TLS library type.
36
38 For CoAP Confirmable messages, it is possible to define the retry
39 counts, repeat rate etc. for error recovery. Further information can be
40 found in "RFC7272: 4.2. Messages Transmitted Reliably".
41 It is not recommended that the suggested default setting are changed,
43 but there may be some special requirements that need different values
44 and the consequences of changing these values is fully understood.
45 Changing the default values for multicast packets is not supported.
47 Some of the parameters or return values are in fixed point format as
49 defined by the coap_fixed_point_t structure as below
50 typedef struct coap_fixed_point_t {
52 uint16_t integer_part; /* Integer part of fixed point variable */
53 uint16_t fractional_part; /* Fractional part of fixed point variable
54 1/1000 (3 points) precision */
55 } coap_fixed_point_t;
56 The CoAP message retry rules are (with the default values to compute
58 the time)
59 1st retransmit after 1 * ack_timeout * ack_random factor (3 seconds)
61 2nd retransmit after 2 * ack_timeout * ack_random factor (6 seconds)
62 3rd retransmit after 3 * ack_timeout * ack_random factor (12 seconds)
63 4th retransmit after 4 * ack_timeout * ack_random factor (24 seconds)
64 5th retransmit after 5 * ack_timeout * ack_random factor (48 seconds)
65 As max_transmit (by default) is 4, then the 5th retransmit does not get sent,
67 but at that point COAP_NACK_TOO_MANY_RETRIES gets raised in the nack_handler
68 (if defined). Note that the sum of the seconds is 93 matching RFC7252.
69 It should be noted that these retries are separate from the DTLS or TLS
71 encrypted session setup retry timeouts. For DTLS, the initial
72 requesting packet will get sent max_retransmit times before reporting
73 failure. For TLS the initial TCP connection will timeout before
74 reporting failure.
75 It is also possible to set up packet losses, for both confirmable, and
77 non-confirmable messages. This can be used for stress testing packet
78 transmission recovery as well as application handling of lossy
79 networks.
80 The coap_session_set_max_retransmit() function updates the session
82 maximum retransmit count with the new value. The default value is 4.
83 The coap_session_set_ack_timeout() function updates the session initial
85 ack or response timeout with the new value. The default value is 2.0.
86 The coap_session_set_ack_random_factor() function updates the session
88 ack random wait factor, used to randomize re-transmissions, with the
89 new value. The default value is 1.5.
90 The coap_session_get_max_retransmit() function returns the current
92 session maximum retransmit count.
93 The coap_session_get_ack_timeout() function returns the current session
95 initial ack or response timeout.
96 The coap_session_get_ack_random_factor() function returns the current
98 session ack random wait factor.
99 The coap_debug_set_packet_loss() function is uses to set the packet
101 loss levels as defined in loss_level. loss_level can be set as a
102 percentage from "0%" to "100%". Alternatively, it is possible to
103 specify which packets of a packet sequence are dropped. A definition of
104 "1,5-9,11-20,101" means that packets 1, 5 through 9, 11 through 20 and
105 101 will get dropped. A maximum of 10 different packet sets is
106 supported. The packet count is reset to 0 when
107 coap_debug_set_packet_loss() is called. To remove any packet losses,
108 set the loss_level to "0%".
109
111 coap_session_get_max_retransmit(), coap_session_get_ack_timeout() and
112 coap_session_get_ack_random_factor() return their respective current
113 values.
114 coap_debug_set_packet_loss() returns 0 if loss_level does not parse
116 correctly, otherwise 1 if successful.
117
119 The libcoap recovery/re-transmit logic will only work for confirmable
120 requests.
121 To see what is happening (other than by sniffing the network traffic),
123 the logging level needs to be set to LOG_DEBUG in the client by using
124 coap_set_log_level(LOG_DEBUG) and coap_dtls_set_log_level(LOG_DEBUG).
125 The client needs to be sending confirmable requests during the test.
127 The server can either be stopped, or if packet loss levels are set to
129 100% by using coap_debug_set_packet_loss("100%") when receiving the
130 client requests.
131 NOTE: If the server end of the connection is returning ICMP unreachable
133 packets after being turned off, you will get a debug message of the
134 form "coap_network_read: unreachable", so libcoap will stop doing the
135 retries. If this is the case, then you need to make use of (on the
136 server) coap_debug_set_packet_loss("100%") or put in some packet
137 filtering to drop the packets.
138 The client should then restart transmitting the requests based on the
140 ack_timeout, ack_random_factor and max_retransmit values. The client’s
141 nack_handler will get called with COAP_NACK_TOO_MANY_RETRIES when the
142 confirmable request cannot be successfully transmitted.
143
145 See "RFC7252: The Constrained Application Protocol (CoAP)" for further
146 information.
147
149 Please report bugs on the mailing list for libcoap:
150 libcoap-developers@lists.sourceforge.net
151
153 The libcoap project <libcoap-developers@lists.sourceforge.net>
154coap_recovery 4.2.1 01/26/2021 COAP_RECOVERY(3)