Logical Architecture

The SRE is composed of several instances grouped into 2 distinct instance types:

the Element Manager (EM): 2 instances
the Call Processing (CP): N instances (depending on the implementation)
the Media Processing (MP): N instances (optional, depending on the implementation)

A close up of a map Description automatically
generated

These instance types are interconnected.

The CP instances are interconnected with the Customer existing Call Control Server (SBC).

The MP instances are interconnected with the Customer existing Call Control Server (SBC) directly or via CP instances.

Element Manager Instances

The EM instances are responsible for handling the following functions:

hosting the local database (master-slave model with replication)
administration GUI
logs centralization
call tracing centralization
stats centralization
batch provisioning
control of the CP modules
CDR production and control

For redundancy purpose, two element managers are deployed, one as Master and the other one as Slave (hot standby).

One of the EM instances acts as master for the PostgreSQL database. The database is replicated to the second instance thanks to the streaming replication feature of PostgreSQL (RPM). This second node, which acts as a hot standby under normal operations, is ready to take over the master role. At that point, CP instances must in turn be updated to use this new master for their own replicated databases.

A screenshot of a cell phone Description automatically
generated

Call Processing Instances: Layered Architecture

Depending on the amount of traffic and for redundancy purposes, multiple CP instances can be deployed.

Several CP instances are responsible for handling the following functions:

acting as replicated database
processing INVITE/ENUM/HTTP requests from any network platform
processing OPTIONS polling to provide a correct health state indication and node isolation if needed collecting and sending logs, call tracing information and stats to the EM instances.

A screenshot of a cell phone Description automatically
generated

The layered architecture provides a modular, extensible, and future-proof model.

The first layer is the SIP engine element acting as the SIP interface towards the voice network and the business logic.

This business logic is composed of 2 modules:

the Service Orchestration (SO) module.
the Network Interaction (NI) module.

The CP instances are designed in a way to continue handling calls in case of connectivity loss with the EM layer. As such, they are self-contained call processing instances, able to work in an isolated mode until connectivity is restored.

Media Processing Instances

Depending on the amount of traffic and for redundancy purposes, multiple MP instances can be deployed.

Several MP instances are responsible for handling the following functions:

acting as replicated database
processing SIP requests from any network platform
processing RTP media streams
processing OPTIONS polling to provide a correct health state indication
collecting and sending logs, call tracing information and stats to the EM instances.

The first layer is the Asterisk engine acting as the SIP/RTP interface towards the voice network and the business logic.

The second layer functions as both a listener for events from the first layer and an actor towards the first layer.

The MP instances are designed in a way to continue handling calls in case of connectivity loss with the EM layer. As such, they are self-contained media processing instances, able to work in an isolated mode until connectivity is restored.

Infrastructure/Hardware Requirements

Operating System Requirements

SRE can be installed on the latest RedHat 8.x or 9.x release.

CPU and Memory Requirements

The minimum requirements for an SRE server are:

vCPU: 4
Memory Size: 8192 MB
Hard Disk Size: 200GB (SSD)

INFO

A more tailored dimensioning is needed on a project basis.

Networking Requirements

SRE should be equipped with a minimum of 1 Gigabit Ethernet link.

Element Managers can be configured with 1 or 2 NIC interfaces

1 for Management (GUI/SSH access)
1 for DB replication between all components (EM's and CP's) and for CP modules control

INFO

They can be combined in a single interface

Call Processors can be configured with multiple NIC Interfaces

1 for Management (SSH access)
1 for DB Replication and access to the element Managers
1 or more for the Call Processing in case SRE needs to communicate with multiple voice networks.

INFO

They can be combined in a single interface

Media Processors can be configured with multiple NIC Interfaces

1 for Management (SSH access)
1 for DB Replication and access to the element Managers
1 or more for the Media Processing in case SRE needs to communicate with multiple voice networks.

INFO

They can be combined in a single interface

Communication Matrix

Source	Destination	Interface	Protocol/DestinationPort	Description
terminal	EM	management	TCP/22	ssh/sftp
EM	CP/MP	internal	TCP/22	ssh
browser	EM	management	TCP/8080 (*)	http/https GUI access
external provisioners	EM	management	TCP/5000 () (*)	REST APIs
EM	DNS server	management	UDP/53 (**)	dns resolution
EM/CP	NTP server	management	UDP/123	time synchronization
EM	EM	internal	TCP/5432	DB traffic
CP/MP	EM	internal	TCP/5432	DB traffic
CP	CP	internal	TCP/5555 () (*)	kamailio-broker traffic for hitless update
CP/MP	EM	internal	TCP/5000 (*)	db updates from service logic
CP/MP	EM	internal	TCP/10000	SRE log and stats
CP/MP	EM	internal	TCP/10001	SRE internal requests
CP	EM	internal	TCP/10002	Accounting data
EM	EM	internal	TCP/10003	Accounting synchronization
EM	SNMP managers	management	UDP/162 () (*)	SNMP traps
EM	SMTP server	management	TCP/587 (**)	mail server
EM	syslog server	management	UDP/514 () (*)	syslog data
EM	LDAP server	management	TCP/389/636 () (*)	GUI authentication
SIP endpoint(s)	CP	SIP	UDP/TCP/5060 () (*)	SIP traffic interface
HTTP endpoints	CP	HTTP	TCP/6000 () (*)	http traffic interface
ENUM endpoints	CP	ENUM	UDP/TCP/53 () (*)	ENUM traffic interface
SIP endpoint(s)	MP	SIP	UDP/TCP/5060 () (*)	SIP traffic interface
SIP endpoint(s)	MP	RTP	UDP/10000-20000 () (*)	RTP traffic interface

(*) port can be customized (**) optional

Software Requirements

SRE 4.1 requires the following software:

postgres 14
influxdb 2.4 (only on EMs)
kamailio 5.7 (only on CPs)
asterisk 18 (only on MPs)
mongodb 5.0 (only if CAC or global caching is configured)

Operating System Configuration

Disk partitioning

Create the necessary partitions according to the table below.

The example below is sized for a total disk space of 250GB.

Partition	Size	Type	Description
/boot	1GB	Ext4 or XFS on LVM	boot partition
/boot/efi	200 MB	EFI s.p.	The EFI System Partition is required for UEFI-based platforms that no longer use the legacy Master Boot Record (MBR) partition table.
/opt	5 GB	Ext4 or XFS on LVM	SRE software
/var/log	10 GB	Ext4 or XFS on LVM	system and SRE logs
/var/lib/pgsql	65 GB	Ext4 or XFS on LVM	PostgreSQL database
/data/sre/db/backups	50 GB	Ext4 or XFS on LVM	workspace for backups
/data/sre/db/wals	20 GB	Ext4 or XFS on LVM	work-ahead logs
swap	8GB	Swap
/data/sre/provisioning	10 GB	Ext4 or XFS on LVM	provisioning data (EM only)
/	30 GB	Ext4 or XFS on LVM
/var/lib/mongo	10GB	Ext4 or XFS on LVM	Mongo database (only if CAC or global caching is configured)

INFO

Unused space is reserved for future expansion.

Networking

Normally, you should have configured the different network interfaces during the OS installation. If not (or if you want to modify or check the configuration) update the file ifcfg-eth0 in /etc/sysconfig/network-scripts/ with the IP interface information:

Parameter	Value	Example
BOOTPROTO	static	static
IPADDR	eth0 Interface IP address	10.0.11.30
NETMASK	eth0 Interface IP subnet mask	255.255.255.0
GATEWAY	default IP Gateway	10.0.11.1

Note that on your environment, and depending on the underlying hosting architecture, the interface might get a different name (e.g. ens192, ...)

Example:

  [root@localhost ~]# cat /etc/sysconfig/network-scripts/ifcfg-eth0
  TYPE="Ethernet"
  PROXY_METHOD="none"
  BROWSER_ONLY="no"
  BOOTPROTO="none"
  DEFROUTE="yes"
  IPV4_FAILURE_FATAL="no"
  IPV6INIT="no"
  IPV6_AUTOCONF="yes"
  IPV6_DEFROUTE="yes"
  IPV6_FAILURE_FATAL="no"
  IPV6_ADDR_GEN_MODE="stable-privacy"
  NAME="eth0"
  UUID="2910018a-36ec-4846-9f87-5d0278ec68ab"
  DEVICE="eth0"
  ONBOOT="yes"
  IPADDR="10.0.11.30"
  PREFIX="24"
  GATEWAY="10.0.11.1"
  DNS1="8.8.8.8"

Install a few additional packages

[root@localhost ~]# dnf update -y
[root@localhost ~]# dnf install -y tmux vim tcpdump wireshark libxslt libxml2 wget net-tools mlocate rsync lsof bind-utils chrony graphviz

Disable firewalld and selinux. Type commands:

[root@localhost ~]# systemctl stop firewalld
[root@localhost ~]# systemctl disable firewalld

Update the file selinux in /etc/sysconfig/ in order to prevent SELinux policy from being loaded. Set the parameter SELINUX to "disabled".

[root@localhost ~]# vi /etc/sysconfig/selinux

Example:

[root@localhost ~]# cat /etc/sysconfig/selinux
# This file controls the state of SELinux on the system.
# SELINUX= can take one of these three values:
# enforcing - SELinux security policy is enforced.
# permissive - SELinux prints warnings instead of enforcing.
# disabled - No SELinux policy is loaded.
SELINUX=disabled
...

Check NTP to ensure time synchronization, add ntp server configuration if needed.

[root@localhost ~]# chronyc sources
MS Name/IP address         Stratum Poll Reach LastRx Last sample
===============================================================================
^+ ntp1.unix-solutions.be        2  10   377   904  -1318us[-1307us] +/-   37ms
^- webserver.discosmash.com      3  10   373   713  +2133us[+2144us] +/-   74ms
^+ time.cloudflare.com           3  10   377   615    +36us[  +47us] +/-   14ms
^* time.cloudflare.com           3  10   377   487   +521us[ +532us] +/-   14ms

Reboot the server

[root@localhost ~]# reboot

SRE components Installation

Common components

The next chapters concern the installation and configuration steps for SRE which are commons to all SRE components (EM's and CP's)

PostgreSQL

Install the repository RPM:

[root@localhost ~]# dnf install -y https://download.postgresql.org/pub/repos/yum/reporpms/EL-8-x86_64/pgdg-redhat-repo-latest.noarch.rpm
[root@localhost ~]# dnf -qy module disable postgresql

Install PostgreSQL 14 and the replication manager repmgr_14:

[root@localhost ~]# dnf install -y postgresql14-server repmgr_14

Activate the service postgresql-14 such that it starts in the usual runlevels:

[root@localhost ~]# systemctl enable postgresql-14

Enable repmgrd for automatic db switchover

[root@localhost ~]# systemctl enable repmgr-14

Mongodb

INFO

Mongodb is needed only if CAC, the registrar functionality or global cache is used.

On all servers dedicated to Mongo DB (preferably 3 including the Arbiter), execute the following procedure. Create a /etc/yum.repos.d/mongodb-org-5.0.repo file so that you can install MongoDB directly, using dnf:

[root@localhost ~]# cat <<EOF | tee /etc/yum.repos.d/mongodb.repo
[mongodb-org-5.0]
name=MongoDB Repository
baseurl=https://repo.mongodb.org/yum/redhat/8/mongodb-org/5.0/x86_64/
gpgcheck=0
enabled=1
EOF

To install and enable the latest stable version of MongoDB, issue the following command:

[root@localhost ~]# dnf install -y mongodb-org-server mongodb-org-shell
[root@localhost ~]# systemctl start mongod
[root@localhost ~]# systemctl enable mongod

Ansible (optional)

If you plan to use the embedded ansible playbook to upgrade the system, ansible needs to be installed on the system. To do that:

[root@localhost ~]# dnf install -y ansible-core

Epel repository

Epel repository is needed to satisfy SRE dependencies, to add it run:

sudo subscription-manager repos --enable codeready-builder-for-rhel-8-x86_64-rpms
sudo dnf install https://dl.fedoraproject.org/pub/epel/epel-release-latest-8.noarch.rpm -y

InfluxDB and Telegraf repository

Run the following commands to add InfluxDB and Telegraf repository and install telegraf.

[root@localhost ~]# cat <<EOF | tee /etc/yum.repos.d/influxdb.repo
[influxdb]
name = InfluxDB Repository - RHEL \$releasever
baseurl = https://repos.influxdata.com/rhel/\$releasever/\$basearch/stable
enabled = 1
gpgcheck = 1
gpgkey = https://repos.influxdata.com/influxdata-archive_compat.key
EOF
[root@localhost ~]# dnf install -y telegraf
[root@localhost ~]# systemctl disable telegraf

EM component

Influx DB

Run the following commands to install InfluxDB.

[root@localhost ~]# dnf install -y influxdb2 influxdb2-cli
[root@localhost ~]# systemctl start influxd
[root@localhost ~]# influx setup -u influxuser -p influxuser -t my-super-secret-token -o influxorg -b bucket -r 1h (it may ask for confirmation)
[root@localhost ~]# influx bucket delete -n bucket
[root@localhost ~]# influx bucket create -n telegraf -o influxorg -r 30d

Log aggregation (optional)

Log aggregation is implemented with Graylog. Graylog requires opensearch server. To install it:

[root@localhost ~]# rpm --import https://artifacts.opensearch.org/publickeys/opensearch.pgp
[root@localhost ~]# rpm -Uvh https://artifacts.opensearch.org/releases/bundle/opensearch/2.5.0/opensearch-2.5.0-linux-x64.rpm
[root@localhost ~]# systemctl daemon-reload
[root@localhost ~]# systemctl enable opensearch.service
[root@localhost ~]# mkdir -p /usr/share/opensearch/config/
[root@localhost ~]# cat > /usr/share/opensearch/config/opensearch.yml << EOF
cluster.name: graylog
path.data: /var/lib/opensearch
path.logs: /var/log/opensearch
action.auto_create_index: false
plugins.security.disabled: true
network.host: 0.0.0.0  
discovery.type: single-node
EOF
[root@localhost ~]# systemctl start opensearch

To install graylog server run:

[root@localhost ~]# rpm -Uvh https://packages.graylog2.org/repo/packages/graylog-5.0-repository_latest.rpm
[root@localhost ~]# dnf install -y graylog-server

CP component

Kamailio

You can install the Kamailio packages from the official repository, as shown in the following commands.

[root@localhost ~]# dnf -y install dnf-plugins-core
[root@localhost ~]# dnf config-manager --add-repo https://rpm.kamailio.org/centos/kamailio.repo
[root@localhost ~]# dnf install --disablerepo=kamailio --enablerepo=kamailio-5.8 kamailio kamailio-python

If you plan to use SRE as a SIP registrar you need also the kamailio-mongodb package.

Install it with:

[root@localhost ~]# dnf install --disablerepo=kamailio --enablerepo=kamailio-5.8 kamailio-mongodb

Download pyzmq-25.0.0-1.x86_64.rpm from the internal software repository and upload it to the call processor. Install the package with the command:

[root@localhost ~]# dnf install pyzmq-25.0.0-1.x86_64.rpm

MP component

Asterisk

Install it with:

[root@localhost ~]# dnf install asterisk asterisk-pjsip

Media files are needed for announcements download them from Asterisk Sound Repository

You need to download the right package for the language of the announcements. English for example is the following:

https://downloads.asterisk.org/pub/telephony/sounds/releases/asterisk-core-sounds-en-alaw-1.4.0.tar.gz

Copy the downloaded package to the target machine and run:

[root@localhost ~]# mkdir -p /usr/share/asterisk/sounds/en/
[root@localhost ~]# cd /usr/share/asterisk/sounds/en/
[root@localhost /]# tar xzvf <path of archive>

INFO

Additional languages can be installed by creating the appropriate directories and placing the corresponding media files within them. Custom WAV files can also be added to these directories. To use these files, simply reference the filename (excluding the extension) and the desired language in the Play Media node.

Logical Architecture ​

Element Manager Instances ​

Call Processing Instances: Layered Architecture ​

Media Processing Instances ​

Infrastructure/Hardware Requirements ​

Operating System Requirements ​

CPU and Memory Requirements ​

Networking Requirements ​

Communication Matrix ​

Software Requirements ​

Operating System Configuration ​

Disk partitioning ​

Networking ​

SRE components Installation ​

Common components ​

PostgreSQL ​

Mongodb ​

Ansible (optional) ​

Epel repository ​

InfluxDB and Telegraf repository ​

EM component ​

Influx DB ​

Log aggregation (optional) ​

CP component ​

Kamailio ​

MP component ​

Asterisk ​

Logical Architecture

Element Manager Instances

Call Processing Instances: Layered Architecture

Media Processing Instances

Infrastructure/Hardware Requirements

Operating System Requirements

CPU and Memory Requirements

Networking Requirements

Communication Matrix

Software Requirements

Operating System Configuration

Disk partitioning

Networking

SRE components Installation

Common components

PostgreSQL

Mongodb

Ansible (optional)

Epel repository

InfluxDB and Telegraf repository

EM component

Influx DB

Log aggregation (optional)

CP component

Kamailio

MP component

Asterisk