computer networks – Why processes on the internet are not required to use TCP or UDP?

Here is an excerpt from Andrew S. Tanenbaum, Computer Networks, 5th edition, Chapter 5 (The Network layer), Page 455:

(Fifth, processes on the Internet are not required to use TCP or UDP. If a user on machine A decides to use some new transport protocol to talk to a user on machine B (for example, for a multimedia application), introduction of a NAT box will cause the application to fail because the NAT box will not be able to locate the TCP Source port correctly.)

My question is in this context what does processes means? Is it a process of data exchange between routers? And why processes on the internet are not required to use TCP or UDP? Isn’t it apart of IP protocol and thus it will be used on the internet?

wireless – Network icon is not displayed in tray, and no WiFi networks displayed

I am running Ubuntu 18.04.4

XXXXXXXXXXXXXXXXXXXXX:~$ lsb_release -a
LSB Version:    core-9.20170808ubuntu1-noarch:printing-9.20170808ubuntu1-noarch:security-9.20170808ubuntu1-noarch
Distributor ID: Ubuntu
Description:    Ubuntu 18.04.4 LTS
Release:    18.04
Codename:   bionic

I read another question, “Ubuntu 18.04 WiFi Networks are not displaying even though there are 3 nearby”, on AskUbuntu and tried the solution there. It did not work. I still have no visible networks under WiFi settings. Additionally, I have no network icon on my tray. I am, however, connected to my 5GHz WiFi Network on channel 165.

These are the current responses to the commands asked in that post:

XXXXXXXXXXXXXXXXXXXXX:~$ lspci -nnk | grep 0280 -A3
04:00.0 Network controller (0280): Intel Corporation Wireless 7260 (8086:08b1) (rev 73)
    Subsystem: Intel Corporation Dual Band Wireless-AC 7260 (8086:4070)
    Kernel driver in use: iwlwifi
    Kernel modules: iwlwifi

And

XXXXXXXXXXXXXXXXXXXXX:~$ sudo iwlist chan
    eth0      no frequency information.

wlan0     32 channels in total; available frequencies :
          Channel 01 : 2.412 GHz
          Channel 02 : 2.417 GHz
          Channel 03 : 2.422 GHz
          Channel 04 : 2.427 GHz
          Channel 05 : 2.432 GHz
          Channel 06 : 2.437 GHz
          Channel 07 : 2.442 GHz
          Channel 08 : 2.447 GHz
          Channel 09 : 2.452 GHz
          Channel 10 : 2.457 GHz
          Channel 11 : 2.462 GHz
          Channel 36 : 5.18 GHz
          Channel 40 : 5.2 GHz
          Channel 44 : 5.22 GHz
          Channel 48 : 5.24 GHz
          Channel 52 : 5.26 GHz
          Channel 56 : 5.28 GHz
          Channel 60 : 5.3 GHz
          Channel 64 : 5.32 GHz
          Channel 100 : 5.5 GHz
          Channel 104 : 5.52 GHz
          Channel 108 : 5.54 GHz
          Channel 112 : 5.56 GHz
          Channel 116 : 5.58 GHz
          Channel 120 : 5.6 GHz
          Channel 124 : 5.62 GHz
          Channel 128 : 5.64 GHz
          Channel 132 : 5.66 GHz
          Channel 136 : 5.68 GHz
          Channel 140 : 5.7 GHz
          Channel 144 : 5.72 GHz
          Channel 149 : 5.745 GHz
          Current Frequency:5.825 GHz

lo        no frequency information.

And

XXXXXXXXXXXXXXXXXXXXX:~$ sudo iw reg get
global
country US: DFS-FCC
    (2402 - 2472 @ 40), (N/A, 30), (N/A)
    (5170 - 5250 @ 80), (N/A, 23), (N/A), AUTO-BW
    (5250 - 5330 @ 80), (N/A, 23), (0 ms), DFS, AUTO-BW
    (5490 - 5730 @ 160), (N/A, 23), (0 ms), DFS
    (5735 - 5835 @ 80), (N/A, 30), (N/A)
    (57240 - 63720 @ 2160), (N/A, 40), (N/A)

And

XXXXXXXXXXXXXXXXXXXXX:~$ nmcli dev wifi list
IN-USE  SSID  MODE  CHAN  RATE  SIGNAL  BARS  SECURITY

This is an annoyance, but not a major issue, unless I take the laptop somewhere else.

neural networks – Using the features embedding of the output from a transformers to represent probabilities of categorical data

I was considering using a transformer, on input data which can be represented as an embedding, so I can use the attention mechanism in the transformer architecture. As my data is of variable input and output length and the input is sequential. My question is that my output data is suppose to be either numerical or probabilities for each output variable. The output was originally supposed to 13 numerical outputs but I decided to use a probability score as way of normalizing the output. My question is can I use two output vectors with 7 features each instead of 13 numeric outputs. Each feature would map to one of the original output vectors and the the last feature would always be 0. As PyTorch expects your output to be the same number of features as your input. My input variables are embedded as 7 features. Should this approach work, as I am unsure of how the loss function works or is there a loss function that would allow for this.

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postfix – iRedmail cannot send Email to outside networks “Connection timed out”

After a successful installation of the mail server with iRedmail installer, I cannot send Emails to the outside networks.

I can successfully receive mails, but I cannot create a new mail (to the outside networks) or reply from a received one.

Whenever I send an Email, this is what comes out on my mails log;

Jul  2 13:34:42 hostname postfix/smtp(113264): connect to gmail-smtp-in.l.google.com(2a00:1450:4010:c03::1a):25: Connection timed out
Jul  2 13:35:12 hostname postfix/smtp(113264): connect to alt1.gmail-smtp-in.l.google.com(2404:6800:4003:c06::1a):25: Connection timed out

and

         1   Jul  1 13:29:46 hostname postfix/smtp(54364): 49x3wF0hvGz2wtK: to=<myemail@live.com>, relay=none, delay=78302, delays=78241/0.04/60/0, dsn=4.4.1, status=deferred (connect to live-com.olc.protection.outlook.com(104.47.58.161):25: Connection timed out)

I have

iRedMail version: 1.3
Ubuntu: 20.04 LTS

I checked the server “mbuyufikra.org” is not blacklisted (yet)

Also the postfix main.cf file;

# --------------------
# INSTALL-TIME CONFIGURATION INFORMATION
#
# location of the Postfix queue. Default is /var/spool/postfix.
queue_directory = /var/spool/postfix

# location of all postXXX commands. Default is /usr/sbin.
command_directory = /usr/sbin

# location of all Postfix daemon programs (i.e. programs listed in the
# master.cf file). This directory must be owned by root.
# Default is /usr/libexec/postfix
daemon_directory = /usr/lib/postfix/sbin

# location of Postfix-writable data files (caches, random numbers).
# This directory must be owned by the mail_owner account (see below).
# Default is /var/lib/postfix.
data_directory = /var/lib/postfix

# owner of the Postfix queue and of most Postfix daemon processes.
# Specify the name of a user account THAT DOES NOT SHARE ITS USER OR GROUP ID
# WITH OTHER ACCOUNTS AND THAT OWNS NO OTHER FILES OR PROCESSES ON THE SYSTEM.
# In particular, don't specify nobody or daemon. PLEASE USE A DEDICATED USER.
# Default is postfix.
mail_owner = postfix

# The following parameters are used when installing a new Postfix version.
#
# sendmail_path: The full pathname of the Postfix sendmail command.
# This is the Sendmail-compatible mail posting interface.
#
sendmail_path = /usr/sbin/sendmail

# newaliases_path: The full pathname of the Postfix newaliases command.
# This is the Sendmail-compatible command to build alias databases.
#
newaliases_path = /usr/bin/newaliases

# full pathname of the Postfix mailq command.  This is the Sendmail-compatible
# mail queue listing command.
mailq_path = /usr/bin/mailq

# group for mail submission and queue management commands.
# This must be a group name with a numerical group ID that is not shared with
# other accounts, not even with the Postfix account.
setgid_group = postdrop

# external command that is executed when a Postfix daemon program is run with
# the -D option.
#
# Use "command .. & sleep 5" so that the debugger can attach before
# the process marches on. If you use an X-based debugger, be sure to
# set up your XAUTHORITY environment variable before starting Postfix.
#
debugger_command =
    PATH=/bin:/usr/bin:/usr/local/bin:/usr/X11R6/bin
    ddd $daemon_directory/$process_name $process_id & sleep 5

debug_peer_level = 2

# --------------------
# CUSTOM SETTINGS
#

# SMTP server response code when recipient or domain not found.
unknown_local_recipient_reject_code = 550

# Do not notify local user.
biff = no

# Disable the rewriting of "site!user" into "user@site".
swap_bangpath = no

# Disable the rewriting of the form "user%domain" to "user@domain".
allow_percent_hack = no

# Allow recipient address start with '-'.
allow_min_user = no

# Disable the SMTP VRFY command. This stops some techniques used to
# harvest email addresses.
disable_vrfy_command = yes

# Enable both IPv4 and/or IPv6: ipv4, ipv6, all.
inet_protocols = all

# Enable all network interfaces.
inet_interfaces = all

#
# TLS settings.
#
# SSL key, certificate, CA
#
smtpd_tls_key_file = /etc/ssl/private/iRedMail.key
smtpd_tls_cert_file = /etc/ssl/certs/iRedMail.crt
smtpd_tls_CAfile = /etc/ssl/certs/iRedMail.crt
smtpd_tls_CApath = /etc/ssl/certs

#
# Disable SSLv2, SSLv3
#
smtpd_tls_protocols = !SSLv2 !SSLv3
smtpd_tls_mandatory_protocols = !SSLv2 !SSLv3
smtp_tls_protocols = !SSLv2 !SSLv3
smtp_tls_mandatory_protocols = !SSLv2 !SSLv3
lmtp_tls_protocols = !SSLv2 !SSLv3
lmtp_tls_mandatory_protocols = !SSLv2 !SSLv3

#
# Fix 'The Logjam Attack'.
#
smtpd_tls_exclude_ciphers = aNULL, eNULL, EXPORT, DES, RC4, MD5, PSK, aECDH, EDH-DSS-DES-CBC3-SHA, EDH-RSA-DES-CDC3-SHA, KRB5-DE5, CBC3-SHA
smtpd_tls_dh512_param_file = /etc/ssl/dh512_param.pem
smtpd_tls_dh1024_param_file = /etc/ssl/dh2048_param.pem

tls_random_source = dev:/dev/urandom

# Log only a summary message on TLS handshake completion — no logging of client
# certificate trust-chain verification errors if client certificate
# verification is not required. With Postfix 2.8 and earlier, log the summary
# message, peer certificate summary information and unconditionally log
# trust-chain verification errors.
smtp_tls_loglevel = 1
smtpd_tls_loglevel = 1

# Opportunistic TLS: announce STARTTLS support to remote SMTP clients, but do
# not require that clients use TLS encryption.
smtpd_tls_security_level = may

# Produce `Received:` message headers that include information about the
# protocol and cipher used, as well as the remote SMTP client CommonName and
# client certificate issuer CommonName.
# This is disabled by default, as the information may be modified in transit
# through other mail servers. Only information that was recorded by the final
# destination can be trusted.
#smtpd_tls_received_header = yes

# Opportunistic TLS, used when Postfix sends email to remote SMTP server.
# Use TLS if this is supported by the remote SMTP server, otherwise use
# plaintext.
# References:
#   - http://www.postfix.org/TLS_README.html#client_tls_may
#   - http://www.postfix.org/postconf.5.html#smtp_tls_security_level
smtp_tls_security_level = may

# Use the same CA file as smtpd.
smtp_tls_CApath = /etc/ssl/certs
smtp_tls_CAfile = $smtpd_tls_CAfile
smtp_tls_note_starttls_offer = yes

# Enable long, non-repeating, queue IDs (queue file names).
# The benefit of non-repeating names is simpler logfile analysis and easier
# queue migration (there is no need to run "postsuper" to change queue file
# names that don't match their message file inode number).
enable_long_queue_ids = yes

# Reject unlisted sender and recipient
smtpd_reject_unlisted_recipient = yes
smtpd_reject_unlisted_sender = yes

# Header and body checks with PCRE table
header_checks = pcre:/etc/postfix/header_checks
body_checks = pcre:/etc/postfix/body_checks.pcre

# A mechanism to transform commands from remote SMTP clients.
# This is a last-resort tool to work around client commands that break
# interoperability with the Postfix SMTP server. Other uses involve fault
# injection to test Postfix's handling of invalid commands.
# Requires Postfix-2.7+.
smtpd_command_filter = pcre:/etc/postfix/command_filter.pcre

# HELO restriction
smtpd_helo_required = yes
smtpd_helo_restrictions =
    permit_mynetworks
    permit_sasl_authenticated
    check_helo_access pcre:/etc/postfix/helo_access.pcre
    reject_non_fqdn_helo_hostname
    reject_unknown_helo_hostname

# Sender restrictions
smtpd_sender_restrictions =
    reject_non_fqdn_sender
    reject_unlisted_sender
    permit_mynetworks
    permit_sasl_authenticated
    check_sender_access pcre:/etc/postfix/sender_access.pcre
    reject_unknown_sender_domain

# Recipient restrictions
smtpd_recipient_restrictions =
    reject_non_fqdn_recipient
    reject_unlisted_recipient
    check_policy_service inet:127.0.0.1:7777
    permit_mynetworks
    permit_sasl_authenticated
    reject_unauth_destination
    check_policy_service inet:127.0.0.1:12340

# END-OF-MESSAGE restrictions
smtpd_end_of_data_restrictions =
    check_policy_service inet:127.0.0.1:7777

# Data restrictions
smtpd_data_restrictions = reject_unauth_pipelining

# SRS (Sender Rewriting Scheme) support
#sender_canonical_maps = tcp:127.0.0.1:7778
#sender_canonical_classes = envelope_sender
#recipient_canonical_maps = tcp:127.0.0.1:7779
#recipient_canonical_classes= envelope_recipient,header_recipient

proxy_read_maps = $canonical_maps $lmtp_generic_maps $local_recipient_maps $mydestination $mynetworks $recipient_bcc_maps $recipient_canonical_maps $relay_domains $relay_recipient_maps $relocated_maps $sender_bcc_maps $sender_canonical_maps $smtp_generic_maps $smtpd_sender_login_maps $transport_maps $virtual_alias_domains $virtual_alias_maps $virtual_mailbox_domains $virtual_mailbox_maps $smtpd_sender_restrictions $sender_dependent_relayhost_maps

# Avoid duplicate recipient messages. Default is 'yes'.
enable_original_recipient = no

# Virtual support.
virtual_minimum_uid = 2000
virtual_uid_maps = static:2000
virtual_gid_maps = static:2000
virtual_mailbox_base = /var/vmail

# Do not set virtual_alias_domains.
virtual_alias_domains =

#
# Enable SASL authentication on port 25 and force TLS-encrypted SASL authentication.
# WARNING: NOT RECOMMENDED to enable smtp auth on port 25, all end users should
#          be forced to submit email through port 587 instead.
#
#smtpd_sasl_auth_enable = yes
#smtpd_sasl_security_options = noanonymous
#smtpd_tls_auth_only = yes

# hostname
myhostname = hostname.domain.org
myorigin = hostname.domain.org
mydomain = hostname.domain.org

# trusted SMTP clients which are allowed to relay mail through Postfix.
#
# Note: additional IP addresses/networks listed in mynetworks should be listed
#       in iRedAPD setting 'MYNETWORKS' (in `/opt/iredapd/settings.py`) too.
#       for example:
#
#       MYNETWORKS = ('xx.xx.xx.xx', 'xx.xx.xx.0/24', ...)
#
mynetworks = 127.0.0.1 (::1)

# Accepted local emails
mydestination = $myhostname, localhost, localhost.localdomain

alias_maps = hash:/etc/postfix/aliases
alias_database = hash:/etc/postfix/aliases

# Default message_size_limit.
message_size_limit = 15728640

# The set of characters that can separate a user name from its extension
# (example: user+foo), or a .forward file name from its extension (example:
# .forward+foo).
# Postfix 2.11 and later supports multiple characters.
recipient_delimiter = +

# The time after which the sender receives a copy of the message headers of
# mail that is still queued. Default setting is disabled (0h) by Postfix.
#delay_warning_time = 1h

# Do not display the name of the recipient table in the "User unknown" responses.
# The extra detail makes trouble shooting easier but also reveals information
# that is nobody elses business.
show_user_unknown_table_name = no
compatibility_level = 2
#
# Lookup virtual mail accounts
#
transport_maps =
    proxy:mysql:/etc/postfix/mysql/transport_maps_user.cf
    proxy:mysql:/etc/postfix/mysql/transport_maps_maillist.cf
    proxy:mysql:/etc/postfix/mysql/transport_maps_domain.cf

sender_dependent_relayhost_maps =
    proxy:mysql:/etc/postfix/mysql/sender_dependent_relayhost_maps.cf

# Lookup table with the SASL login names that own the sender (MAIL FROM) addresses.
smtpd_sender_login_maps =
    proxy:mysql:/etc/postfix/mysql/sender_login_maps.cf

virtual_mailbox_domains =
    proxy:mysql:/etc/postfix/mysql/virtual_mailbox_domains.cf

relay_domains =
    $mydestination
    proxy:mysql:/etc/postfix/mysql/relay_domains.cf

virtual_mailbox_maps =
    proxy:mysql:/etc/postfix/mysql/virtual_mailbox_maps.cf

virtual_alias_maps =
    proxy:mysql:/etc/postfix/mysql/virtual_alias_maps.cf
    proxy:mysql:/etc/postfix/mysql/domain_alias_maps.cf
    proxy:mysql:/etc/postfix/mysql/catchall_maps.cf
    proxy:mysql:/etc/postfix/mysql/domain_alias_catchall_maps.cf

sender_bcc_maps =
    proxy:mysql:/etc/postfix/mysql/sender_bcc_maps_user.cf
    proxy:mysql:/etc/postfix/mysql/sender_bcc_maps_domain.cf

recipient_bcc_maps =
    proxy:mysql:/etc/postfix/mysql/recipient_bcc_maps_user.cf
    proxy:mysql:/etc/postfix/mysql/recipient_bcc_maps_domain.cf

#
# Postscreen
#
postscreen_greet_action = drop
postscreen_blacklist_action = drop
postscreen_dnsbl_action = drop
postscreen_dnsbl_threshold = 2

# Attention:
#   - zen.spamhaus.org free tire has 3 limits
#     (https://www.spamhaus.org/organization/dnsblusage/):
#
#     1) Your use of the Spamhaus DNSBLs is non-commercial*, and
#     2) Your email traffic is less than 100,000 SMTP connections per day, and
#     3) Your DNSBL query volume is less than 300,000 queries per day.
#
#   - FAQ: "Your DNSBL blocks nothing at all!"
#     https://www.spamhaus.org/faq/section/DNSBL%20Usage#261
#
# It's strongly recommended to use a local DNS server for cache.
postscreen_dnsbl_sites =
    zen.spamhaus.org=127.0.0.(2..11)*3
    b.barracudacentral.org=127.0.0.2*2

postscreen_dnsbl_reply_map = texthash:/etc/postfix/postscreen_dnsbl_reply
postscreen_access_list = permit_mynetworks cidr:/etc/postfix/postscreen_access.cidr

# Require Postfix-2.11+
postscreen_dnsbl_whitelist_threshold = -2

#
# Dovecot SASL support.
#
smtpd_sasl_type = dovecot
smtpd_sasl_path = private/dovecot-auth
virtual_transport = dovecot
dovecot_destination_recipient_limit = 1

#
# mlmmj - mailing list manager
#
mlmmj_destination_recipient_limit = 1

#
# Amavisd + SpamAssassin + ClamAV
#
content_filter = smtp-amavis:(127.0.0.1):10024

# Concurrency per recipient limit.
smtp-amavis_destination_recipient_limit = 1

I have not touched this file a bit, it is just they way iRedmail configured it.

windows 10 – Linking two home wireless networks to access remote folders or use a printer

My wireless router is situated in a poor position in my house, and it can’t be moved. I got a wireless extender to extend the network. My printer is on the other side of the house from my desktop and so is on the extender’s network, as is my wife’s computer. I would like to be able to access shared folders on my wife’s computer, or at least be able to use the network printer (the second is highest priority). Is there a way to do this?

Currently, to use the printer I briefly connect to the extender’s network. Ideally I would want them to behave like they’re the same network.

random graphs – Efficient Algorithms for Complex Networks

Most standard works on random graphs focus on $G_{n,p}$ and random regular graphs. However, such models are far from a good abstraction to describe the types of networks that one typically encounters in the real world.

There are several simple models that mimic the behavior of real-world graphs, sometimes called Complex Networks.

https://en.wikipedia.org/wiki/Complex_network

There are many graph problems that become easier in the setting of $G_{n,p}$, such as finding a Hamiltonian path, finding a perfect matching, etc. I am sure that similar work has been done for random complex networks, but I haven’t been able to find a good book or survey paper on the subject. I must be using the wrong terminology.

I would be grateful if someone could point me towards something like that, or tell me what the subject of efficient algorithms for complex networks is called in the literature.

geolocation – Does android keeps a system log about location and networks?

By default Android does not save any local logs, even the logcat log is just a ring buffer that contains only the last log elements that fit into the log buffer (often this buffer has ~65KB).
Typically such abuffer is overwritten after a few hours, if the device use not used it may last up to one or two days but that is very device specific. Some devices log dozens of messages per minute even in Air-plane mode without any app active.

First you should check if the location services are activated at all. If they are not activated there is a high chance that they aware deactivated all the time and hence no app was able to access any location.

As far as I know Android itself does not record data on available or used mobile network bases or Wifi access points. Only if Google location services are activated such data is collected and uploaded to Google.

If you have support of the local authorities the easiest way would be to contact the mobile network provider the used SIM-card is from and use their log which antennas were used in the specified time span.