From 4ae2bac4eeeda63df03dc002c8502956241fbfe7 Mon Sep 17 00:00:00 2001
From: Harald Welte <laforge@osmocom.org>
Date: Mon, 27 Dec 2021 12:53:11 +0100
Subject: OsmoDevCall on ETSI V5

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+Retronetworking: ETSI V5 interface in PSTN
+==========================================
+:author:	Harald Welte <laforge@osmocom.org>
+:copyright:	2021 by Harald Welte (License: CC-BY-SA)
+:backend:	slidy
+//:max-width:	45em
+
+== Overview
+
+What this talk is about
+
+* Retronetworking
+* digital telephony switching of the 1990ies
+* my research into ETSI V5
+* writing FOSS code for the LE side to talk to real-world AN
+
+== General Acronyms / Definitions
+
+[horizontal]
+TE:: Terminal Equipment (Phone, Modem, ...)
+NT:: [ISDN] Network Termination (e.g. NTBA in Germany)
+ISDN:: Integrated Services Digital Network
+PSTN:: Public Switched Telephony Network
+BRA:: Basic Rate (ISDN) Access (2x 64k B-Channels)
+PRA:: Primary Rate (ISDN) Access (30x 64k B-Channels)
+E1:: Primary Rate interface, 2048 kBps
+
+== History of telephone exchanges
+
+* 1878: manually switched
+* 1900: electromechanically switched
+* 1965: electronic switching, analog
+* 1976: digital switching
+
+== Trends in PSTN networks since ~ 1970
+
+* more and more telephone subscribers (and hence, lines)
+* capacity of switches increases as technology proceeds
+* operational cost of each exchange is substantial
+* trend towards centralization of exchanges
+** fewer exchanges (= switches)
+** more subscribers per exchange
+
+This creates the problem of managing a vast amount of subscriber line wiring
+
+Response: Modular architecture
+
+== Modular Digital Telephone Exchange
+
+* don't connect every subscriber local loop to a line card in the exchange
+* have remote _access multiplexers_ aggregating subscriber lines
+* reduces amount of cables terminating at a single geographical location
+* helps reducing the subscriber loop length
+* helps increasing capacity of the exchange by attaching more remote subscribers without the need of more
+  exchanges
+
+Vendors came up with their respective proprietary access multiplexers.
+
+ETSI V5 is the attempt to replace vendor proprietary access multiplexers with an interoperable,
+standards-based system.
+
+== The V5 AN / LE functional split
+
+V5 _disaggregates_ the telephone exchange into two parts:
+
+* *Access Network (AN)*
+* *Local Exchange (LE)*
+
+image::g964_figure14_pstn_user_port.png[width=1800,align="center"]
+
+The E1 based V5 interface can of course be carried over higher-order PDH/SDH
+
+== The V5.1 architecture
+
+image::g964_figure2_architecture.png[width=1400,align="center"]
+
+== V5 Acronyms / Definitions
+
+[horizontal]
+AN:: Access Network
+LE:: Local Exchange
+FE:: Functional Element
+LT:: Line Termination
+LC:: Line Circuit
+ET:: Exchange Termination
+
+
+== V5.related 1 specifications
+
+* V5.1 interface
+** ITU-T G.964
+** ETSI ETS 300 324-1
+** ETSI TR 150
+* Q3 interface (management)
+** ITU-T Q.512
+** ETS ETS 300-376-y, ETS 300 378-y (Q3AN)
+** ETS ETS 300-377-z, ETS 300 379-z (Q3LE)
+
+== V5.1 Protocol Stack
+
+== V5.1 Protocol Architecture
+
+image::g964_figure6_protocol_arch.png[width=1400,align="center"]
+
+== LAPV5: Data Link Layer
+
+image::g964_figure11_dl_mgmt.png[width=1300,align="center"]
+
+
+== Control Protocol
+
+* Common Control
+** Re-provisioning
+** Switch-over to new variant
+** Restart
+* Per-Port Control
+** Blocking
+** Unblocking
+** Activation / Deactivation (ISDN only)
+
+== Control Protocol (PSTN)
+
+* administrative blocking / unblocking
+** UNBLOCK + ACK
+** BLOCK + ACK
+** Functional Elements FE201-FE205 used
+
+== Control Protocol (ISDN)
+
+* administrative blocking / unblocking
+** UNBLOCK + ACK
+** BLOCK + ACK
+** Functional Elements FE101-FE106 and FE201-FE208 used
+** D-CHANNEL BLOCK/UNBLOCK
+* access activation
+** ACTIVATE ACCESS
+** DEACTIVATE ACCESS
+* miscellaneous
+** PERFORMANCE GRADING
+
+== PSTN subscriber
+
+* _Control Protocol_ handles low-level physical layer management
+* _PSTN Protocol_ handles analog siganling (on-hook/off-hook, pulse dialing)
+
+image::g964_figure14_pstn_user_port.png[width=1800,align="center"]
+
+== PSTN protocol
+
+* analogue line states
+* timing and duration of analogue signals
+* voltage/frequency of metering pulses
+* ringing current
+* FSMs for AN and LE side
+* Messages In PSTN protocol
+** ESTABLISH + ESTABLISH-ACK
+** SIGNAL + SIGNAL-ACK
+** DISCONNECT + DISCONNECT-COMPLETE
+** STATUS + STATUS-ENQUIRY
+** PROTOCOL-PARAMETER
+
+== PSTN protocol - Originating Call
+
+image::g964_figureB1_pstn_originating_call.png[width=1300,align="center"]
+
+== PSTN protocol - Terminating Call
+
+image::g964_figureB2_pstn_terminating_call.png[width=1300,align="center"]
+
+== PSTN protocol - Example IE
+
+image::g964_table24_pstn_steady_state.png[]
+
+== ISDN subscriber
+
+image::g964_figure31_isdn_model.png[width=1300,align="center"]
+
+== ISDN subscriber
+
+* _Control Protocol_ handles low-level physical layer management
+* _Frame Relay_ forwards Q.921 (LAPD) over V5
+** Actual ISDN L2 (Q.921) and L3 (Q.931) processing all in LE
+** not to be confused with the Packet WAN technology Frame Relay!
+
+As ISDN already has digital signaling (Q.921/Q.931), no need for any V5 specific ISDN protocol (like PSTN
+protocol).  Signaling from user is _relayed_ to LE via V5 (and vice-versa).
+
+== ISDN LAPD Frame Relay
+
+image::g964_figure13_frame_relay.png[width=1300,align="center"]
+
+== Control protocol - ISDN port activation
+
+[mscgen]
+----
+include::isdn-control.msc[]
+----
+
+
+
+== V5.2: Successor of V5.1
+
+V5.2 introduces the following major changes:
+
+* up to 16xE1 per V5.2 interface (V5.1: 1xE1)
+* support for ISDN PRA (Primary Rate Access) subscribers
+* concentration (overprovisioning of local loop vs V5 circuits)
+* fail-over between links
+
+The new features are added in a backwards compatible manner
+
+== The V5.2 architecture
+
+image::g965_figure2_architecture.png[width=1300,align="center"]
+
+
+== V5.2 specifications
+
+All of the V5.1 related specs plus the following new ones:
+
+* ITU-T G.965
+* ETSI ETS 300 347-1
+
+
+== V5.2 Protocol Stack
+
+* LAPV5 Data Link Layerlike in V5.1
+* L3 protocols like in V5.1 (PSTN, control)
+* additional, new L3 protocols on top of LAPV5
+** link control protocol
+** protection protocol
+** BCC (Bearer Channel Connection)
+
+
+
+== V5.2 Protocol Architecture
+
+image::g965_figure6_protocol_architecture.png[width=1400,align="center"]
+
+== V5.2 BCC
+
+* dynamically allocate B-channels on V5 to B-channels of subscribers
+* messages
+** ALLOCATION + COMPLETE / REJECT
+** DE-ALLOCATION + COMPLETE / REJECT
+** AUDIT + COMPLETE
+** AN FAULT + ACK
+** PROTOCOL ERROR
+
+== V5.2 link control protocol
+
+* identification of different links in V5.2 interface
+* blocking and coordinated unblocking of V5.2 links
+
+== V5.2 protection protocol
+
+* fail-over between different E1-links on V5.2 interface
+* monitoring of flag, data link layer establishment
+* mapping of logical / physical channels
+
+== Q3 interface (management)
+
+* Full Complex ISO/OSI protocol Stack
+
+image:q812_q3_upper_layer_stack.png[]
+
+== Nokia EKSOS
+
+* Nokia EKSOS N20: 512 bearer channels, 17-slot rack
+* important modules
+** Node Control Unit
+** PSTN unit (32xPSTN)
+** ISDN BRA U-interface unit (16xU)
+** TR2M4 unit (4xE1)
+* NodeManager software
+
+== Nokia EKSOS N20
+
+image:nokia_eksos_n20_photo.jpg[width=1300,align="center"]
+
+== Nokia EKSOS N20 Node Control Unit
+
+image:nokia_eksos_ncu.png[width=1000,align="center"]
+
+== Nokia EKSOS PSTN + ISDN Unit
+
+image:nokia_eksos_pstn_isdn.png[width=850,align="center"]
+
+
+
+== Fujitsu/DeTeWe ALIAN
+
+* Most common modules in FSX2000
+** MPU-H (Main Processor Unit)
+** HOS (Housekeeping, subscriber line test)
+** NMI (Network Management Interface)
+** TSA (Trunk to tributary cross-connect)
+** V5MC (V5.2 termination message control)
+** BRA12T (12x ISDN U)
+** SLM15G (15x POTS line)
+** E1B21 (21x E1 trunk or tributary)
+** E1BU4 (4x E1 trunk or tributary)
+* FLEXR management software
+
+== Fujitsu/DeTeWe ALIAN
+
+image:fujitsu_dtw_alian_photo.jpg[width=1300,align="center"]
+
+== Keymile MileGate
+
+Keymile MileGate is a combined POTS/ISDN/DSL subscriber access platform
+
+* Most common V5 related modules
+** PCOM1/2 (V5 AN)
+** TUXA1 (12x POTS)
+** SUIT1 (16x ISDN PRA U)
+** SUPx4 (48x POTS)
+
+== Siemens FastLink ONU
+
+* Most common V5 related modules 
+** IUL84 (8x ISDN BRA)
+** SUB102 (10x POTS)
+** SUB162 (16x POTS)
+** SUB322 (32x POTS)
+
+== The V5 master plan
+
+* collect decommissioned V5 access multiplexers
+* create some kind of working setup out of them
+** similar to the PBX-based _Osmocom retronetworking_ setup at last xxC3
+* deploy that at future hacker events
+** allow retronetworking interested people to get analog and Uk0 subscriber lines
+
+== Required for V5 master plan
+
+* V5 Access Multiplexers (almost done)
+* Equipment documentation (done)
+* Configuration/Mgmt Software (done)
+* E1 interface (done, icE1usb or DAHDI cards)
+* V5 protocol stack for LE side (in progress)
+** not supported in FreeSwitch, Asterisk or even yate
+** at least a wireshark disector exists (yay!)
+
+== Towards a FOSS implementation for V5 LE role
+
+* started an implementation of the LE side of V5
+* based around libosmocore and its TLV decoder + FSM
+* current status (WIP, about 3k lines of code)
+** core data structures
+** Control protocol encoding + decoding
+** Common Control FSM
+** Port control FSM
+** V5.2 Link Control Protocol FSM
+
+Waiting for actual V5 AN equipment to start testing it.
+
+== V5 LE PBX integration
+
+* how to integrate with PBX?
+** we definitely want to reuse Q.921 + Q.931 of these
+** B-channels could be accessed directly via DAHDI
+** D-channels would need to go through _Frame Relay_ de-concentration first
+
+[graphviz]
+----
+digraph G {
+  rankdir=LR;
+  subgraph cluster_AN {
+    subgraph cluster_subA {
+      label="Subscriber A";
+      TE_A;
+      NT_A;
+      TE_A -> NT_A [label="S0"];
+    }
+    subgraph cluster_subB {
+      label="Subscriber B";
+      TE_B;
+      NT_B;
+      TE_B -> NT_B [label="S0"];
+    }
+    subgraph cluster_subC {
+      label="Subscriber C";
+      TE_C;
+    }
+    subgraph cluster_subD {
+      label="Subscriber D";
+      TE_D;
+    }
+    AN;
+    NT_A -> AN [label="U"];
+    NT_B -> AN [label="U"];
+    TE_C -> AN [label="POTS"];
+    TE_D -> AN [label="POTS"];
+  }
+
+  subgraph cluster_LE {
+    label="LE";
+    DAHDI [shape="record",label="<DAHDI> DAHDI | <TS1> TS1 | <TS2> TS2 | <TS15> TS15 | <TSn> TSn"];
+    PBX [label="PBX\nQ.921\nQ.931"];
+    V5D [shape="diamond"];
+
+    DAHDI:TS15 -> V5D [label="V5"];
+    DAHDI:TS1 -> PBX [label="B-Channel"];
+    DAHDI:TS2 -> PBX [label="B-Channel"];
+    DAHDI:TSn -> PBX [label="B-Channel"];
+
+    V5D -> PBX [label="LAPDm Sub A"];
+    V5D -> PBX [label="LAPDm Sub B"];
+    V5D -> PBX [label="PSTN Ctrl Sub C"];
+    V5D -> PBX [label="PSTN Ctrl Sub D"];
+  }
+  AN -> DAHDI:DAHDI [label="E1"];
+}
+----
+
+
+== EOF
+
+End of File
-- 
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