Document chapter 01

* the routing structure
* the building blocks inside Element-Call

src/SUMMARY.md

@@ -7,8 +7,11 @@
 # Getting started
 
 - [Getting Started](ch01-00-getting-started.md)
-	- [The building blocks](ch01-01-building-blocks.md)
-	- [Hello Element-Call!](ch01-02-element-call-hello.md)
+	- [The routing structures](ch01-01-routing-structures.md)
+	- [The building blocks](ch01-02-building-blocks.md)
+<!--
+- [Hello Element-Call!](ch01-03-element-call-hello.md)
+-->
 
 - [Installation](ch02-00-installation.md)
 

src/ch01-00-getting-started.md

@@ -3,5 +3,5 @@
 Let’s start your Element-Call journey! There’s a lot to learn, but every journey starts
 somewhere. In this chapter, we’ll discuss:
 
+* WebRTC bases routing structures
 * The building blocks of Element-Call
-* Installing Element-Call

src/ch01-01-building-blocks.md

@@ -1,4 +0,0 @@
-## Building blocks
-
-[element_call_building_blocks]: https://gitea.networkx.de/rzerres/element-call/book/blob/main/src/img/element-call_building_blocks.png
-

src/ch01-01-routing-structures.md

@@ -0,0 +1,55 @@
+## WebRTC bases routing structures
+
+The following image visualize the concepts of actively used routing
+structures inside a RTC applications.
+
+![voip routing structures][voip_routing_structure]
+
+Historically `Elememnt-Call` did implement an infrastructure, where
+all participants were fully meshed. That means all participants had a
+direct peer to each other in a `Mesh`. This structure does work quite well with a
+low number of call partners (e.g 1:1 sessions). Clearly this structure
+is totally inefficient and collapsing, as soon as the number of
+participants rises: The needed number of streams that have to be
+synchronized are increasing exponentioally.
+
+Most `commercial solutions` overcome this bottleneck utilizing a
+Multipoint Connection Unit (`MCU`): Each participant of the call is
+directly connected to the controlling MCU. The MCU will consolidate
+all streams and has only one stream to each participant. It is able to linearly scale.
+
+MCU routing has disadvantages and shortcommings too. 
+
+* You can't assign different egress parameters from the MCU to
+  individual participant streams
+* A single MCU can't handle distributed structure
+
+Therefore `Element-Call` has choosen to implement the service on top of a
+Selective Forward Unit (`SFU`) capable backend:
+
+![Matrix structures][matrix_structure]
+
+Each participant will only send in one stream to the choosen
+`SFU`. The number of egress streams can scale linearly, comparable to
+the concept used with an MCU.  But in contrast to MCU based
+communication clients insede the MatrixRTC are able to dynamicaly
+advertise to their SFU what ingress streams they are interested in.
+Here are some commen szenarios:
+
+* I'm only interested to get participant A, B, C, E, G but not D and F
+* Please only send high resolutions for the speaker and reduce the
+  bitrate for all other participants
+* Change my own egress bitrate to a given value
+
+On top of this, the nature of a Matrix based communication makes use of a
+distributed infrastructure. Within MatrixRTC that allows communications 
+
+* between different involved SFU's
+* Require and handle E2EE meetings for all participants
+* Authenticate matrix accounts as well as guest accounts inside a call
+
+![Matrix SFU structures][matrix_sfu_structure]
+
+[matrix_structure]: ./img/matrix_structure.webp
+[matrix_sfu_structure]: ./img/matrix_sfu_structure.png
+[voip_routing_structure]: ./img/voip_routing_structures.png

src/ch01-02-building-blocks.md

@@ -0,0 +1,91 @@
+## Building blocks
+
+For good reasons `Element-Call` is subdevided into logical components that encapsulate given functionality
+
+* The Backend
+* The reverse Proxy
+* The Authentication service
+* The Frontend
+
+All this components have to be orchestrated to make up this realtime application. Let's have a look how they interact:
+
+![Element-call structure][element_call_structure]
+
+[element_call_structure]: ./img/element-call-structure.svg
+
+### Backend
+
+The MatrixRTC functionality is handled via [LiveKit][livekit_source].
+Livekit is very versatile and flexible. It offers a clean API which
+makes it an ideal fit to be used from the integration service.
+
+[livekit_source]: https://github.com/livekit
+
+### Reverse Proxy
+
+In computer networks, a reverse proxy or surrogate server is a proxy
+server that appears to any client to be an ordinary web server, but in
+reality merely acts as an intermediary that forwards the client's
+requests to one or more ordinary web servers. Reverse proxies
+help increase scalability, performance, resilience, and security.
+
+![Reverse-Proxy Service][reverse_proxy_service]
+
+For example, your server-domain is only accessible via one official ip
+address. But you like to offer multiple services that require secure
+web traffik (https). You have to assign officliy signed certificates to this web server, but also need a proxy that, that can distinguish
+which backend will handle the data exchange (rules, fqdn).
+
+Following list is an non-exauthive list of popular proxy
+implementation that may be run as reverse proxys:
+
+
+* [HAProxy][haproxy_source]
+* [NGINX][nginx_source]
+* [traefik][traefik_source]
+
+
+`Element-Call` will need to use such a reverse proxy, since it needs to re-route service traffik to other components that need to be exposed to the internet (explicitely: livekit, lifekit-jwt-service).
+
+[haproxy_source]: https://github.com/haproxy/haproxy
+[nginx_source]: https://github.com/nginx
+[reverse_proxy_service]: ./img/reverse_proxy_structure.png
+[traefik_source]: https://github.com/traefik/traefik
+
+### Frontend
+
+The `Element-Call` frontend handles the login of participants.  You
+can choose matrix account that is already registered on your
+homeserver, or connect as a guest user to an existing call.
+You may obtain the URL to the existing call from any room members.
+
+![Element-Call brower login][element_call_browser_login]
+
+The source code for the frontend is maintained at `github` in the
+[Element-Call][element_call_source] repository.
+
+[element_call_source]: https://github.com/element-hq/element-call
+[element_call_browser_login]: ./img/element-call-browser-login.png
+
+### Authentication service
+
+After a participant has registerd himself via the `element-call`
+frontend (as an existing matrix account or a guest user),
+[websockets][websockets_service] are used to forward and manage the
+required data via Json Web Tokens (`JWT`) to the livekit backend. This
+allows to keep any communication secure, which is an elementary
+request for E2EE calls.
+
+![websocket_connection`][websocket_connection]
+
+This job is handled from the
+[`livekit_jwt_service`][livekit_jwt_service], that will forward the
+correct tokens to the SFU endpoint inside the livekit instance the
+user is connected to.
+
+[livekit_jwt_service]: https://github.com/element-hq/lk-jwt-service
+[websocket_connection]: ./img/websocket_connection.png
+[websockets_service]: https://en.wikipedia.org/wiki/WebSocket
+
+
+

src/title-page.md

@@ -1,8 +1,8 @@
-# Element Call 
+# Element-Call 
 
 ![Element-Call][element_call]
 
-[element_call]: https://gitea.networkx.de/rzerres/element-call-book/book/blob/main/src/img/element-call.png
+[element_call]: https://gitea.networkx.de/rzerres/element-call-book/blob/main/src/img/element-call.png
 
 *annotated and documented by Ralf Zerres and all contributers*