Protocol stack diagrams

Layers all the way down

Published: Dec 20 2023

Updated: May 14 2026

A collection of ASCII-art protocol stack diagrams.

They can be used as a base for doing quick diagrams. Feel free to copy/reuse/adapt them for your own purpose.

These diagrams are released as CC0 (“No Rights Reserved”).

2025-07-27: added a few things (SOAP, Varlink, HL7).

2025-12-04: add PSP.

2026-01-05: add details about TURN.

2026-04-28: add details about DNS, DoH, DNSSEC.

2026-04-29: add WebTransport, fix MASQUE stacks.

2026-05-15: add DNS over CoAP (DoC) and EDHOC

Table of content

Notations

Layers:

[JSON \-/ CBOR]   Format conversion, eg. JSON/CBOR conversion
[HTTP \-/ CoAP]   Proxy/interworking, eg. HTTP/CoAP proxy/interworking
[(TLS) |(DTLS)]   Optional layers
[TCP   |   UDP]   TCP and UDP layers
[IPv4  /  IPv6]   Either IPv4 or IPv6
[Eth. \-/ Wifi]   Bridge, eg. Ethernet/Wifi bridge

[STUN¦app     ]   STUN and and some application protocol used together between the same peers

[HTTP + WebDAV]   Protocol with some extension, eg. HTTP with WebDAV
[TLS + PSK    ]   Protocol with some feature, eg. TLS with PSK key exchange

[ -           ]   Empty, not a protocol layer

[app.  ]          Some undefined application layer
[...   ]          Some protocol layer(s)
 Foo              Entity name

Communications:

 <----->          Bidirectional communications
 <----->o         Client/server relation, etc.
 ------>          One-way communications
 <=====>          Protected communications (usually both confidentiality and integrity)
 <=-=-=>          Integrity-protected communications (possibly with anti-replay protection)
    K             Interface name

Concepts

Layers, PDUs and SDUs:

                N+1 PDU
[N+1 Layer]<----------------->[N+1 Layer]
     ↑                             ↑
     |                             |  N SDU
     ↓                             ↓
     o           N PDU             o  N SAP
[N Layer  ]<----------------->[N Layer  ]
     ↑                             ↑
     |                             |  N-1 SDU
     ↓                             ↓
     o           N-1 PDU           o  N-1 SAP
[N-1 Layer]<----------------->[N-1 Layer]

Switches, bridges/hubs, routers, proxy:

[app.    ]<------------------------------------------------>[app. ]<-->[app. ]
[(TLS)   ]<================================================>[(TLS)]<-->[(TLS)]
[TCP     ]<------------------------------------------------>[TCP  ]<-->[TCP  ]
[IP      ]<------------------------------>[IP          ]<-->[IP   ]<-->[IP   ]
[Eth. MAC]<---------------->[Eth. MAC]<---[Eth. MAC|...]<-->[...  ]<-->[...  ]
[Eth. PHY]<-->[Eth. PHY]<-->[Eth. PHY]<-->[Eth. PHY|...]<-->[...  ]<-->[...  ]
(Client)           Hub       Switch/bridge   Router       (Reverse)   (Server)
                                                            Proxy

OSI

L7 [Application ]<-------------------------------->[Application ]
L6 [Presentation]<-------------------------------->[Presentation]
L5 [Session     ]<-------------------------------->[Session     ]
L4 [Transport   ]<-------------------------------->[Transport   ]
L3 [Network     ]<-->[Network  ]<-->[Network  ]<-->[Network     ]
L2 [Data link   ]<-->[Data link]<-->[Data link]<-->[Data link   ]
L1 [Physical    ]<-->[Physical ]<-->[Physical ]<-->[Physical    ]

IP

          [(DHCP)|DNS|app|DNS|app]                     [(DHCPv6)|DNS|app|DNS|app]
[ICMP|IGMP|UDP           |TCP    ]      [ICMPv6+NDP+MLD|UDP             |TCP    ]
[IPv4                            |ARP]  [IPv6                                   ]

IP model:

[app.]<---------------------------------->[app.]  (end to end)
[TCP ]<---------------------------------->[TCP ]  (end to end)
[IP  ]<--->[IP ]<--->[IP ]<--->[IP  ]<--->[IP  ]
[... ]<--->[...]<--->[...]<--->[... ]<--->[... ]  (local network layers)
           Router    Router    Router

IP transport protocols:

                                                              [app.]
                                       [app.]   [app.] [app.] [SCTP] [app.]
[app.] [app.] [app.    ] [app.] [app.] [SCTP]   [TLS ] [DTLS] [DTLS] [QUIC|TLS]
[TCP ] [UDP ] [UDP-lite] [DCCP] [SCTP] [UDP ]   [TCP ] [UDP ] [UDP ] [UDP     ]
[IP  ] [IP  ] [IP      ] [IP  ] [IP  ] [IP  ]   [IP  ] [IP  ] [IP  ] [IP      ]
TCP    UDP    UDP-lite   DCCP   SCTP   SCTP     TLS    DTLS   SCTP   QUIC
                                       /UDP     /TCP   /UDP   /DTLS

Application layers

DNS

                 [DNS    ]        [DNS       ]
       [DNS    ] [framing] [DNS ] [HTTP      ] [DNS ]
[DNS]  [framing] [TLS    ] [DTLS] [TLS / QUIC] [QUIC]
[UDP]  [TCP    ] [TCP    ] [UDP ] [TCP / UDP ] [UDP ]
[IP ]  [IP     ] [IP     ] [IP  ] [IP        ] [IP  ]
“Do53” “Do53”    “DoT”            “DoH”        “DoQ”
DNS    DNS       DNS       DNS    DNS          DNS
over   over      over      over   over         over
UDP    TCP       TLS       DTLS   HTTPS        QUIC

[DNS   ]    [DNS   ]
[CoAP  ]    [CoAP  ]
[(DTLS)]    [(TLS) ]
[UDP   ]    [TCP   ]
[IP    ]    [IP    ]
“DoC”       “DoC”
DNS         DNS
over CoAP   over CoAP      
(UDP)       over TCP

[DNS       ]
[Obliv. DNS]
[HTTP      ]    [CoAP  ]  [CoAP ]
[TLS / QUIC]    [(DTLS)]  [(TLS)]
[TCP / UDP ]    [UDP   ]  [TCP  ]
[IP        ]    [IP    ]  [IP   ]
“ODoH”          “DoC“     “DoC“
Oblivious DNS   DNS       DNS
over            over      over
HTTPS           CoAP      CoAP

Notes

DNS framing: When used on top of TCP or TLS, each DNS message is prefixed with a length field (2 bytes).

Classic DNS:

                            /Recurse\
             /(Cache)\      /(Cache)\      /Zone(s)\
[DNS  ]<--->o[DNS    ]<--->o[DNS    ]<--->o[DNS    ]
[UDP  ]<--->o[UDP|UDP]<--->o[UDP|UDP]<--->o[UDP    ]
[IP   ]<---->[IP |IP ]<---->[IP |IP ]<---->[IP     ]
Client       Stub           Recursive      Authoritative
             Resolver       Resolver       Server

Example of transport-level (hop-to-hop) protection for DNS (DNS over HTTPS, DoH):

                               /Recurse\
              /(Cache)\        /(Cache)\       /Zone(s)\
[DNS  ]<---->o[DNS     ]<---->o[DNS     ]<--->o[DNS    ]
                  [HTTP]<---->o[HTTP]
                  [TLS ]<====>o[TLS ]
[UDP  ]<---->o[UDP|TCP ]<---->o[TCP |UDP]<--->o[UDP    ]
[IP   ]<----->[IP |IP  ]<----->[IP  |IP ]<---->[IP     ]
Client        Stub             Recursive       Authoritative
              Resolver         Resolver        Server

Example with DNSSEC:

                              /Recurse  \
            /((Valid.))\      /(Valid.) \       /Zone(s)   \<---sign
            /(Cache   )\      /(Cache)  \
[DNS ]<--->o[DNS+DNSSEC]<-=->o[DNS+DNSSEC]<-=->o[DNS+DNSSEC]
[UDP ]<--->o[UDP   |UDP]<--->o[UDP  |UDP ]<--->o[UDP       ]
[IP  ]<---->[IP    |IP ]<---->[IP   |IP  ]<---->[IP        ]
Client      Stub              Recursive         Authoritative   Signing
            Resolver          Resolver          Server          Software

Oblivious DNS over HTTPS:

[DNS       ]<--------------------->o[DNS           ]<---->o[DNS]
[Obliv. DNS]<=====================>o[Obliv. DNS|-  ]
[HTTP      ]<--->o[HTTP      ]<--->o[HTTP      |-  ]
[TLS / QUIC]<===>o[TLS / QUIC]<===>o[TLS / QUIC|-  ]
[TCP / UDP ]<--->o[TCP / UDP ]<--->o[TCP / UDP |UDP]<----o>[UDP]
[IP        ]<---->[IP        ]<---->[IP        |IP ]<----->[IP ]
Oblivious         Oblivious          Oblivious
Client            Relay              Target

NTP

      ([NTP])
[NTP]  [TLS]
[UDP]  [TCP]
[IP ]  [IP ]
 NTP    NTS
        KE

Notes:

NTS-KE, Network Time Security Key Exchange

HTTP

                          [HTTP/1.x] [HTTP/2] [HTTP/3|TLS]
[HTTP/1.x] [HTTP/2]       [TLS     ] [TLS   ] [QUIC      ]
[TCP     ] [TCP   ]       [TCP     ] [TCP   ] [UDP       ]
[IP      ] [IP    ]       [IP      ] [IP    ] [IP        ]
HTTP/1.x   HTTP/2         HTTP/1.x   HTTP/2   HTTP/3
           w/o TLS        over TLS   over TLS (over QUIC)
           "h2c"                     "h2"     "h3"
(HTTP)     (HTTP)         (HTTPS)    (HTTPS)  (HTTPS)

WebSocket

[WebSocket]  [WebSocket]  [WebSocket]
[HTTP/1.x ]  [HTTP/2   ]  [HTTP/3   ]
[(TLS)    ]  [(TLS)    ]  [QUIC     ]
[TCP      ]  [TCP      ]  [UDP      ]
[IP       ]  [IP       ]  [IP       ]
WebSocket    Websocket    WebSocket
(HTTP/1.x)   (HTTP/2)     (HTTP/3)

Notes:

with HTTP/1, a HTTP upgrade (GET) is used to upgrade the HTTP connection into a WebSocket connection;
with HTTP/2, a HTTP/2 upgrade (extended CONNECT) is used to upgrade the HTTP/2 stream into a WebSocket stream;
with HTTP/3, a HTTP/3 upgrade (extended CONNECT) is used to upgrade the HTTP/3 stream into a WebSocket stream.

HTTP Datagrams

[datagram ]  [datagram]  [datagram]
[Capsule  ]  [Capsule ]  [Capsule ]  [Capsule|datagram]
[HTTP/1.x ]  [HTTP/2  ]  [HTTP/3  ]  [HTTP/3 |H3 dgram]
[(TLS)    ]  [(TLS)   ]  [QUIC    ]  [QUIC    +dgram  ]
[TCP      ]  [TCP     ]  [UDP     ]  [UDP             ]
[IP       ]  [IP      ]  [IP      ]  [IP              ]
HTTP         HTTP        HTTP        HTTP
Datagrams    Datagrams   Datagrams   Datagrams
(HTTP/1.X)   (HTTP/2)    (HTTP/3)    (HTTP/3)
                         w/o HTTP/3  w/ HTTP/3
                         datagrams   datagrams

HTTP CONNECT proxy

Classic HTTP CONNECT:

[app. ]  [app.  ]
[HTTP ]  [HTTP/3]
[(TLS)]  [QUIC  ]
[TCP  ]  [UDP   ]
[IP.  ]  [IP.   ]

MASQUE (without HTTP/3 datagrams):

               [application]  [IP         ]          [application]       [Eth. MAC   ]
[application]  [UDP prox.  ]  [IP prox.   ]          [UDP-l prox.]       [Eth. prox. ]
[TCP prox.  ]  [HTTP dgram ]  [HTTP dgram |config.]  [HTTP dgram ]       [HTTP dgram ]
[Capsule    ]  [Capsule    ]  [Capsule            ]  [Capsule    ]       [Capsule    ]
[HTTP       ]  [HTTP       ]  [HTTP               ]  [HTTP       ]       [HTTP       ]
[(TLS)/ QUIC]  [(TLS)/ QUIC]  [(TLS) / QUIC       ]  [(TLS)/ QUIC]       [(TLS)/ QUIC]
[TCP  / UDP ]  [TCP  / UDP ]  [TCP   / UDP        ]  [TCP  / UDP ]       [TCP  / UDP ]
[IP.        ]  [IP         ]  [IP                 ]  [IP         ]       [IP         ]
TCP in HTTP    UDP in HTTP    IP in HTTP             UDP-listen in HTTP  Ethernet in HTTP

MASQUE with HTTP/3 datagrams:

                                                                                           
       [app.     ]  [config.|IP      ]         [application]         [Eth. MAC   ]
       [UDP prox.]  [Capsule|IP prox.]         [UDP-l prox.]         [Eth. prox. ]
[HTTP/3|H3 dgram ]  [HTTP/3 |H3 dgram]  [HTTP/3|H3. dgram  ]  [HTTP/3|H3 dgram   ]
[QUIC +dgram     ]  [QUIC +dgram     ]  [QUIC +dgram       ]  [QUIC +dgram       ]
[UDP             ]  [UDP             ]  [UDP               ]  [UDP               ]
[IP              ]  [IP              ]  [IP                ]  [IP                ]
UDP in HTTP/3       IP in HTTP/3        UDP-listen in HTTP/3  Ethernet in HTTP/3
datagrams           datagrams           datagrams             datagrams

WebTransport

[WT     |WT dgram]  [WT     |WT dgram]    [WT       ]            [WT ctrl]
[Capsule         ]  [Capsule         ]    [Capsule  |WT dgram ]  [Capsule]         [WT dgram ]
[HTTP/2          ]  [HTTP/3          ]    [HTTP/3   |H3. dgram]  [HTTP/3 |WT stream|H3. dgram]
[TLS             ]  [QUIC            ]    [QUIC      +dgram   ]  [QUIC             |+dgram   ]
[TCP             ]  [UDP             ]    [UDP                ]  [UDP                        ]
[IP              ]  [IP              ]    [IP                 ]  [IP                         ]
Capsule-based       Capsule-based         Capsule-based
WebTransport        WebTransport          WebTransport           WebTransport
(HTTP/2)            (HTTP/3)              (HTTP/3)               (HTTP/3)
                    w/o HTTP/3 datagram   w/ HTTP/3 datagram     w/ HTTP/3 datagram
("webtransport")    ("webtransport")      ("webtransport")       ("webtransport-h3")

File Transfer

[FTP  ] [SFTP] [HTTP+WebDAV ]       [SMB ]
[(TLS)] [SSH ] [(TLS) / QUIC] [SMB] [QUIC] [NFS]
[TCP  ] [TCP ] [TCP   / UDP ] [TCP] [UDP ] [TCP]
[IP   ] [IP  ] [IP          ] [IP ] [IP  ] [IP ]
FTP     SFTP   WebDAV         SMB   SMB    NFSv4
                                    /QUIC

Notes:

FTPS (FTP over TLS) ≠ SFTP (a different protocol, over SSH)!
SFTP uses SSH with the "sftp" as SSH subsystem.
SMB over QUIC uses "smb" as ALPN.

LDAP

[LDAP       ]
[(SASL sec.)]
[(TLS)      ]
[TCP        ]
[IP         ]
LDAP

UPnP

              [Device/service desc.]  [SOAP/1.1]  [UPnP event] [UPnP event]
              [XML                 ]  [XML     ]  [XML       ] [XML       ]
[HTTP+SSDP ]  [HTTP                ]  [HTTP    ]  [HTTP+GENA ] [HTTP+GENA ]
[UDP       ]  [TCP                 ]  [TCP     ]  [TCP       ] [UDP       ]
[IP (mcast)]  [IP                  ]  [IP      ]  [IP        ] [IP (mcast)]
Service       Service                 Control     Eventing     Eventing
Discovery     Description             (RPC)       (unicast)    (multicast)

CoAP

                   [CoAP     ]
                   [WebSocket]  [...        ]
[CoAP  ]  [CoAP ]  [HTTP     ]  [CoAP       ]  [EDHOC]
[(DTLS)]  [(TLS)]  [(TLS)    ]  [COSE       ]  [CBOR ]
[UDP   ]  [TCP  ]  [TCP      ]  [CoAP+OSCORE]  [CoAP ]
[IP    ]  [IP   ]  [IP       ]  [...        ]  [...  ]
CoAP      CoAP/TCP CoAP/WS(S)   OSCORE         EDHOC

RPC

SOAP:

             [SOAP+XOP ]
[SOAP     ]  [XML      |...]
[XML      ]  [multipart    ]
[HTTP     ]  [HTTP         ]  [SOAP     ]
(TLS      )  (TLS          )  [XML      ]
[TCP      ]  [TCP          ]  [email    ]
[IP       ]  [IP           ]  [...      ]
SOAP/HTTP    SOAP/HTTP        SOAP/email
             with MOTM

Varlink:

       [Varlink IDL]
[Varlink messages  ]
[JSON              ]
[NUL-framing       ]
[TCP|UDS           ]
[IP ]
Varlink

Query Languages

SPARQL:

[SPARQL   ] [RDF           ]
(multipart) [XML|Turtle|...] [SPARQL res.     ]
[HTTP     ] [HTTP          ] [XML|JSON|CSV|TSV]
(TLS      ) (TLS           ) [TLS             ]
[TCP      ] [TCP           ] [TCP             ]
[IP       ] [IP            ] [IP              ]
SPARQL      SPARQL RDF       SPARQL result
request     response         response
/HTTP       /HTTP            /HTTP

Multimedia

SIP, RTP, RTSP

Signaling:

                                                             [SDP      ]
                                                             [(S/MIME) ]
                              [SDP             ]  [SDP     ] [SIP      ]
[SDP  ]   [SDP             ]  [SIP             ]  [(S/MIME)] [WebSocket]
[RTSP ]   [(S/MIME)        ]  [S/MIME          ]  [SIP     ] [HTTP     ]
[(TLS)]   [SIP             ]  [SIP             ]  [TLS     ] [(TLS    )]
[TCP  ]   [UDP / TCP / SCTP]  [UDP / TCP / SCTP]  [TCP     ] [TCP      ]
[IP   ]   [IP              ]  [IP              ]  [IP      ] [IP       ]
RTSP      SIP                 Tunneling SIP       SIP-TLS    SIP/WebSocket

SIP call through proxy servers:

[SDP]<------------------------>[SDP]
[SIP]<-->[SIP]<------>[SIP]<-->[SIP]
[TLS]<-->[TLS]<------>[TLS]<-->[TLS]
[TCP]<-->[TCP]<------>[TCP]<-->[TCP]
[IP ]<-->[IP ]<------>[IP ]<-->[IP ]
 UA      Proxy         Proxy   UA

RTP (media transport):

[A/V]      [A/V]             [A/V ]            [A/V ]      
[RTP|RTCP] [SRTP|SRTCP] [DTLS|SRTP|SRTCP] [ZRTP|SRTP|SRTCP]
[UDP     ] [UDP       ] [UDP            ] [UDP            ]
[IP      ] [IP        ] [IP             ] [IP             ]
RTP, RTCP  SRTP, SRTCP  DTLS-SRTP         ZRTP

Alternative transports for RTP:

              [A/V]      [A/V]
[A/V]         [RTP|RTCP  |RTP|RTCP  ]
[RTP|RTCP  ]  [RoQ stream|RoQ Datag.]
[framing   ]  [QUIC                 ]
[TCP       ]  [UDP                  ]
[IP        ]  [IP                   ]
RTP over TCP  RTP over QUIC (RoQ)

Notes:

RTCP usually used the next (odd) UDP port after the (even) one used by RTP. Nowadays, they tend to be multiplexed over the same port.
DTLS-SRT uses a DTLS handshake with mutual authentication and the use_srtp extension for key exchange and then switch to SRTP, SRCTP on the same port.
The SRTP keys are exported from DTLS (using the "EXTRACTOR-dtls_srtp" exporter label).
RTP-over-QUIC uses "rtp-mux-quic" for ALPN.

Message multiplexing:

A mix of (S)RTP, (S)RTCP, STUN, ZRTC and DTLS messages can be multiplexed over the same channel.
RTP and RTCP can be distinguished using the M and PT fields.
ZRTP messages can be can be distinguished from (S)RTP messages because the first two bits are zero.
ZRTP messages can be can be distinguished from STUN messages because they use different magic cookies.
See RFC 5764 section 5.1.2 for demultiplexing of DTLS, RTP/RTCP and STUN packets.

WebRTC

                                                     [DCEP|data. chan.]           
                 [DCEP|data. chan.]                  [SCTP            |A/V ]      
                 [SCTP            |A/V ]        [STUN|mDTLS           |SRTP|SRTCP]
            [STUN|mDTLS           |SRTP|SRTCP]  [framing                         ]
[SDP     ]  [UDP (+ ICE)                     ]  [TCP (+ ICE)                     ]
[anything]  [IP  (+ ICE)                     ]  [IP  (+ ICE)                     ]
WebRTC      WebRTC over UDP                     WebRTC over TCP                   
Signaling

Type of payloads:

                                                                               [DCEP|data chan.]
                              [DCEP|data chan.]            [A/V ]              [SCTP           ]
           [A/V ]             [SCTP           ] [STUN|mDTLS|SRTP|SRTCP]   [STUN|mDTLS          ]
[STUN|mDTLS|SRTP|SRTCP]  [STUN|mDTLS          ] [framing              ]   [framing             ]
[UDP (+ ICE)          ]  [UDP (+ICE)          ] [TCP (+ ICE)          ]   [TCP (+ICE)          ]
[IP  (+ ICE)          ]  [IP  (+ICE)          ] [IP  (+ ICE)          ]   [IP  (+ICE)          ]
WebRTC A/V streams       WebRTC Data Channel    WebRTC A/V streams        WebRTC Data Channel 
(DTLS-SRTP)              (SCTP/DTLS)            (DTLS-SRTP)               (SCTP/DTLS)

proto=UDP/TLS/RTP/SAVPF  proto=UDP/DTLS/SCTP    proto=TCP/TLS/RTP/SAVPF   proto=TCP/DTLS/SCTP

Example WebRTC stack with TURN tunneling:


     [DCEP|data. chan.]           
     [SCTP            |A/V ]      
[STUN|mDTLS           |SRTP|SRTCP]
[TURN                            ]
[(DTLS)                          ]
[UDP                             ]
[IP                              ]
WebRTC with TURN tunnel

Notes:

In WebRTC, the DTLS peers authenticate based on X.509 certificates exchanged through the signaling protocol (eg. in the identity SDP attribute).
The DCEP DATA_CHANNEL_OPEN message may specify a protocol identifier (from the WebSocket subprotocol registry) to be used on this channel.
See RFC 5764 section 5.1.2 for demultiplexing of DTLS, RTP/RTCP and STUN packets.
RTP/SAVPF combines RTP/SAVP (i.e., using SRTP) and RTP/AVPF (i.e., with RTCP-based Feedback).

Healthcare

HL7

                    
[HL7v2    ]        [HL7v3|CDA]     [FHIR    ]
[RE7  |XML]        [XML      ]     [XML|JSON]  [FHIR           ]
--------------------------------------------   [XML|JSON|Turtle]
                   [HTTP]  [SFTP]  [FTP]       [HTTP           ]
[MLLP ]            (TLS )  [SSH ]  (TLS)       (TLS            )
[TCP  ]  [MLLP  ]  [TCP ]  [TCP ]  [TCP]       [TCP            ]
[IP   ]  [serial]  [IP  ]  [IP  ]  [IP]        [IP             ]
MLLP      MLLP      HL7    HL7     HL7         FHIR API
/TCP      /serial   /HTTP  /SFTP   /FTP

LLMs and agents

MCP

MCP (Model Context Protocol):

              [MCP     ]
              [JSON-RPC]
              [JSON    ]
[MCP       ]  [(SSE)   ]
[JSON-RPC  ]  [HTTP    ]
[JSON      ]  [(TLS)   ]
[LF-framing]  [TCP     ]
[STDIO     ]  [IP      ]
 MCP           MCP
 /STDIO        /Streamable
               HTTP

A2A

A2A (Agent-to-agent) protocol:

[A2A      ]
[JSON-RPC ]  [A2A      ]
[JSON     ]  [Protobuf ]  [A2A      ]
[(SSE)    ]  [gRPC     ]  [JSON     ]
[HTTP     ]  [HTTP/2   ]  [HTTP     ]
[(TLS)    ]  [TLS      ]  [(TLS)    ]
[TCP      ]  [TCP      ]  [TCP      ]
[IP       ]  [IP       ]  [IP       ]
 A2A          A2A          A2A
 /JSON-RPC    /gRPC        /JSON REST

Security Layers

TLS

TLS sublayers:

[Handshake | ChangecipherSpec | Alert | Application]
[TLS Record Protocol: fragmentation                ] [Handshake | Alert | Application       ]
[TLS Record Protocol: compression                  ] [TLS Record Protocol: fragmentation    ]
[TLS Record Protocol: record protection            ] [TLS Record Protocol: record protection]
[Transport layer                                   ] [Transport layer                       ]
TLS v1.2                                             TLS v1.3

Some protocol stacks using TLS:

[... ] [...   ]     [email] [email]                 [mTLS   ]
[HTTP] [HTTP/3|TLS] [SMTP ] [IMAP ] [TLS|IP / Eth.] [EAP-TLS]    [mTLS   ]
[TLS ] [QUIC      ] [TLS  ] [TLS  ] [OpenVPN      ] [EAP    ]    [EAP-TLS]
[TCP ] [UDP       ] [TCP  ] [TCP  ] [TCP / UDP    ] [EAPOL  ]    [EAP    ]
[IP  ] [IP        ] [IP   ] [IP   ] [IP           ] [Wifi   ]    [PPP    ]
HTTPS  HTTPS        SMTPS   IMAPS   OpenVPN         WPA2-EAP     PPP
       (HTTP/3)                                     with EAP-TLS with EAP-TLS

DTLS

Transports:

[app.] [app.] [app.]
[DTLS] [DTLS] [DTLS]
[UDP ] [SCTP] [DCCP]
[IP  ] [IP  ] [IP  ]
DTLS   DTLS   DTLS
over   over   over
UDP    SCTP   DCCP

QUIC

[app.]      [app. streams|app. dgrams]
[QUIC|TLS]  [QUIC         +dgram.    |TLS]
[UDP     ]  [UDP                         ]
[IP      ]  [IP                          ]
QUIC        QUIC with QUIC datagrams

SSH

Applications:

       [SFTP]                [SSH]
[SSH ] [SSH ] [SOCKS|SSH]    [SSH]
[TCP ] [TCP ] [TCP      ]    [TCP]
[IP  ] [IP  ] [IP       ]    [IP ]
SSH    SFTP   OpenSSH        SSH
              dynamic proxy  ProxyJump

Alternative transports:

                    [SSH      ]
[SSH]    [SSH  ]    [VSOCK-MUX]
[UDS]    [VSOCK]    [UDS      ]
SSH/UDS  SSH/VSOCK  SSH-to-VSOCK
                    through VSOCK-MUX
                    (firecracker)

Internal protocol stack:

               [(GSS-API)|shell|command|forwarding]
[SSH Authentication Layer|SSH Connection Layer    ]
[SSH Transport Layer                              ]
[TCP                                              ]
[IP                                               ]

VPNs and tunnels

IPSec

SA (Security Associations) establishment:

        [...  ]
        [EAP  ]
[IKEv2] [IKEv2]
[UDP  ] [UDP  ]
[IP   ] [IP   ]
IKEv2   IKEv2
        w/ EAP

IPsec:

                                          [UDP|TCP|...] [IP ]
[UDP|TCP|...] [IP]   [UDP|TCP|...] [IP ]  [ESP        ] [ESP]
[AH         ] [AH]   [ESP        ] [ESP]  [UDP        ] [UDP]
[IP         ] [IP]   [IP         ] [IP ]  [IP         ] [IP ]
AH            AH     ESP           ESP    ESP/UDP       ESP/UDP
Transport     Tunnel Transport     Tunnel Transport     Transport

ESP transport mode:

[app.]<--------->[app.]
[TCP ]<--------->[TCP ]
[ESP ]<=========>[ESP ]
[IP  ]<--------->[IP  ]
correspondent    correspondent

ESP tunnel mode:

[app.]<------------------------------>[app.]
[TCP ]<------------------------------>[TCP ]
[IP  ]<-------->[IP ]<----->[IP ]<----[IP  ]
                [ESP]<=====>[ES ]
                [IP ]<----->[IP ]
correspondent   Gateway     Gateway   correspondent

AH transport mode:

[app.]<--------->[app.]
[TCP ]<--------->[TCP ]
[AH  ]<--------->[AH  ]
[IP  ]<=-=-=-=-=>[IP  ]
correspondent    correspondent

AH tunnel mode:

[app.]<---------------------------->[app.]
[TCP ]<---------------------------->[TCP ]
[IP  ]<-------->[IP]<----->[IP]<--->[IP  ]
                [AH]<----->[AH]
                [IP]<=-=-=>[IP]
correspondent   Gateway    Gateway  correspondent

PSP

[TCP] [UDP] [IPc4] [IPv6]
[PSP] [PSP] [PSP ] [PSP ]
[UDP] [UDP] [UDP ] [UDP ]
[IP ] [IP ] [IP  ] [IP  ]

VPNs

[IPv4|IPv6|(TLS)]   [Eth. MAC|(TLS)]  [IP       ]  [IP   ]  [Eth. MAC]
[OpenVPN        ]   [OpenVPN       ]  [WireGuard]  [SSH  ]  [SSH     ]
[TCP / UDP      ]   [TCP /  UDP    ]  [UDP      ]  [TCP  ]  [TCP     ]
[IP             ]   [IP            ]  [IP       ]  [IP   ]  [IP      ]
OpenVPN IP          OpenVPN Ethernet  WireGuard    OpenSSH  OpenSSH
(TUN mode)          (TAP mode)                     tunnel   tunnel
                                                   (IP)     (Ethernet)

                                [IP    ] 
[IP     ]  [IP               ]  [PPP   ]  [IP    ]
[Capsule]  [Capsule|-        ]  [SSTP  ]  [PPP   ]
[HTTP   ]  [HTTP3  |H3 dgram.]  [HTTP  ]  [HTTP  ]
[(TLS)  ]  [QUIC      +dgram.]  [TLS   ]  [TLS   ]
[TCP    ]  [UDP              ]  [TCP   ]  [TCP   ]
[IP     ]  [IP               ]  [IP    ]  [IP    ]
IP in HTTP IP in HTTP/3         MS-SSTP   FortiSSL

Notes:

OpenVPN does not work on top of TLS (TLS over TCP). TLS is encapsulated in the OpenVPN protocol and is used for the handshake. The inner frame/packets are not encapsulated by TLS (no IP-over-TLS or Ethernet-over-TLS).
MS-SSTP use a SSTP_DUPLEX_POST /sra_{BA195980-CD49-458b-9E23-C84EE0ADCD75}/ HTTPS request. The encapsulated protocol is chosen with the MS-SSTP Protocol ID field (0x0001 for PPP).

Simple Tunnels

          [IP        ]  [IP  ]
          [GRE       ]  [GRE ]
          [(UDP)     ]  [DTLS]        [Eth. MAC]
[IP]      [(AH / ESP)]  [UDP ]        [EtherIP ]
[IP]      [IP        ]  [IP  ]        [IP      ]
IP in IP  GRE           GRE-UDP-DTLS  EtherIP

L2TPv3

Pseudowires:

[PPP ] [Eth. MAC] [Frame Relay] [HDLC] [ATM ]
[L2TP] [L2TP    ] [L2TP       ] [L2TP] [L2TP]
[... ] [...     ] [...        ] [... ] [... ]

Transports:

                            [... ]
                            [L2TP]
[... ]                      [SNAP] [... ]
[L2TP] [... ] [...        ] [LLC ] [L2TP]
[UDP ] [L2TP] [L2TP       ] [AAL5] [AAL5]
[IP  ] [IP  ] [Frame Relay] [ATM ] [ATM ]
L2TP   L2TP   L2TP          L2TP   L2TP
/UDP   /IP    /Frame Relay  /ATM   /ATM
                            (LLC)  (VC mux)

Network virtualization

[Eth. MAC  ] [Eth. / IP / ...] [Eth. / IP / ...]
[VXLAN     ] [GENEVE         ] [GRE + Key ext. ]
[UDP       ] [UDP            ] [(UDP)          ]
[(AH / ESP)] [(AH / ESP)     ] [(AH / ESP)     ]
[IP        ] [IP             ] [IP             ]
VXLAN        GENEVE            NVGRE

Authentication, authorization

EAP

TLS-based EAP methods:

          [...     ]
          [EAP     ] [PAP     ] [CHAP    ] [... ] [... ]
          [AVP     ] [AVP     ] [AVP     ] [EAP ] [EAP ]
[mTLS   ] [TLS     ] [TLS     ] [TLS     ] [TLS ] [TLS ]
[EAP-TLS] [EAP-TTLS] [EAP-TTLS] [EAP-TTLS] [PEAP] [TEAP]
[EAP    ] [EAP     ] [EAP     ] [EAP     ] [EAP ] [EAP ]
[...    ] [...     ] [...     ] [...     ] [... ] [... ]
 EAP-TLS     EAP         PAP       CHAP    EAP    EAP
             over        over      over    over   over
           EAP-TTLS    EAP-TTLS  EAP-TTLS  PEAP   TEAP

EAP transports:

                          [... ] [...] [...      ] [...       ]
      [...     ] [...   ] [EAP ] [EAP] [EAP      ] [EAP       ]
[...] [EAP     ] [EAP   ] [PANA] [IKE] [RADIUS   ] [Diameter  ]
[EAP] [802.1X  ] [802.1X] [UDP ] [UDP] [UDP / TCP] [TCP / SCTP]
[PPP] [Ethernet] [Wifi  ] [IP  ] [IP ] [IP       ] [IP        ]
 EAP  802.1X     WPA-EAP  PANA   EAP   EAP over    EAP/Diameter
 for                             for   RADIUS
 PPP                             IKE

Example full protocol stacks:

           [EAP-MSCHAPV2]
           [EAP         ]
[mTLS   ]  [TLS         ]
[EAP-TLS]  [TEAP        ]
[EAP    ]  [EAP         ]
[802.1X ]  [802.1X      ]
[Wifi   ]  [Wifi        ]
WPA-EAP    WPA-EAP  
with       with     
EAP-TLS    EAP-EAP
           and MSCHAPv2

Kerberos

           [Kerberos]
           [MS-KKDCP]
           [HTTP    ]
[Kerberos] [TLS     ]
[UDP/TDP ] [TCP     ]
[IP      ] [IP      ]
Kerberos   MS-KKDCP

SASL

General SASL stack:

[mechanism]
[SASL     ]   [protocol   ]
[protocol ] → [(SASL sec.)]
[...      ]   [...        ]

Notes:

Protocol with support for SASL include LDAP, IMAP, POP, SMTP, XMPP, MQTT, etc.
SASL mechanisms include ANONYMOUS, PLAIN, EXTERNAL, etc.
Some SASL mechanisms may install a SASL security layer (providing features such as encryption and/or integrity protection to the protocol). Nowadays, this is seen as redundant with the usage of TLS which should be used instead.

GSSAPI

           [Kerberos] [MS-NLMP ]  [...    ]
[Kerberos] [SPNEGO  ] [SPNEGO  ]  [EAP    ]
[GSS-API ] [GSS-API ] [GSS-API ]  [GSS-API]
[SASL    ] [SASL    ] [SASL    ]  [SASL   ]
[...     ] [...     ] [...     ]  [...    ]
GSS-API    GSS-API    NTLM
with       with       with SNPEGO
Kerberos   SPNEGO     /SASL
/ SASL     /SASL

Notes:

GSS-API over SASL can use either the GSSAPI SASL mechanism or the newer GS2-* mechanisms (eg. GS2-KRB5, GS2-KRB5-PLUS).
The newer GS2-* mechanisms must not use mechanisms negotiation (such as SPNEGO).

RADIUS and DIAMETER

                  [RADIUS]                       [Diameter] [Diameter]
[RADIUS] [RADIUS] [TLS   ] [Diameter] [Diameter] [TLS     ] [DTLS    ]
[UDP   ] [TCP   ] [TCP   ] [TCP     ] [SCTP    ] [TCP     ] [SCTP    ]
[IP    ] [IP    ] [IP    ] [IP      ] [IP      ] [IP      ] [IP      ]
RADIUS   RADIUS   RADIUS   Diameter   Diameter   Diameter   Diameter
/UDP     /TCP     /TLS     /TCP       /SCTP      /TLS       /DTLS
                  (RadSec)

NAT traversal

STUN and TURN

                [App.        ] [App. ]
[STUN        ]  [TURN        ] [TURN ]
[(DTLS / TLS)]  [(DTLS / TLS)] [(TLS)]
[UDP   / TCP ]  [UDP   / TCP ] [TCP  ]
[IP          ]  [IP          ] [IP   ]
    STUN        TURN (UDP)     TURN-TCP

TURN:

      Client's       Client's               Peer's       Peer's
          Host       Reflexive           Reflexive       Host
     Transport       Transport           Transport       Transport
       Address       Address               Address       Address
             |       |                           |       |
             |       | TURN Server's   Relayed   |       |
             |       | Transport     Transport   |       |
             |       | Address         Address   |       |
             |       | |                   |     |       |
             |       | |                   |     |       |
 [App.      ]<------------------------------------------->[App.]
 [STUN      ]<--------->[STUN       ]
([TLS / DTLS]<=========>[TLS / DTLS ])
 [TCP / UDP ]<->[...]<->[TCP / UDP  | UDP ]<----->[UDP]<->[UDP]
 [IP        ]<->[IP ]<->[IP               ]<----->[IP ]<->[IP ]
 STUN client     NAT     STUN server              (NAT)   Peer

TURN-TCP:

      Client's       Client's              Peer's       Peer's
          Host       Reflexive          Reflexive       Host
     Transport       Transport          Transport       Transport
       Address       Address              Address       Address
             |       |                          |       |
             |       | TURN Server's  Relayed   |       |
             |       | Transport    Transport   |       |
             |       | Address        Address   |       |
             |       | |                  |     |       |
             |       | |                  |     |       |
 [App.      ]<------------------------------------------>[App.]
 [STUN      ]<--------->[STUN      ]
([TLS       ]<=========>[TLS       ])
 [TCP       ]<->[TCP]<->[TCP       | TCP ]<----->[TCP]<->[TCP]
 [IP        ]<->[IP ]<->[IP              ]<----->[IP ]<->[IP ]
 STUN client     NAT     STUN server             (NAT)   Peer

ICE

                                 [SDP ]
[STUN (+TURN)]   [SDP]           [HTTP]           [STUN|app.    ]
[(DTLS / TLS)]   [SIP]           [TLS ]           [(DTLS)/ (TLS)]
[UDP   / TCP ]   [TCP]           [TCP ]           [UDP   / TCP  ]
[IP          ]   [IP ]           [IP  ]           [IP           ]
STUN, TURN       ICE candidate   ICE candidates   ICE communications
(candidate       exchange        exchange         (direct)
 collection)     with SIP        with SDP/HTTPS

Example of ICE through TURN:

[STUN¦app ]<-------------------->[STUN¦app]
[TURN     ]<--->o[TURN]          [-       ]
[TLS      ]<===>o[TLS ]          [-       ]
[TCP      ]<--->o[TCP |UDP]<---->[UDP     ]
[IP       ]<---->[IP      ]<---->[IP      ]
Appl. Peer                       Appl. Peer
TURN client      TURN server

Link Layer

Ethernet (802.1)

       [...  ]  [IP|ARP|...  ]
       [EAP  ]  [SNAP        ]
[IP|ARP|EAPOL]  [LLC         ]
[(802.1Q    )]  [(802.1Q    )]
[(802.1ad   )]  [(802.1ad   )]
[Ethernet MAC]  [Ethernet MAC]
[Ethernet PHY]  [Ethernet PHY]
Ethernet II     802.1 with SNAP

Ethernet PHY sublayers (since Fast Ethernet):

[Ethernet PCS]  [Ethernet PCS]   (PHY)
[Ethernet PMA]  [Ethernet PMA]   (PHY)
[Ethernet PMD]  [Ethernet PMD]   (PHY)

Wifi (802.11)

[...      ]
[EAP      ]
[EAPOL    ]    [IP                   |ARP]
[SNAP     ]    [SNAP                     ]  (Link)
[LLC      ]    [LLC                      ]  (Link)
               [(WEP / TKIP / CCMP / GCM)]  (Link)
[Wifi MAC ]    [Wifi MAC                 ]  (Link)
[Wifi PLCP]    [Wifi PLCP                ]  (Phy.)
[Wifi PMD ]    [Wifi PMD                 ]  (Phy.)
WPA-Entreprise
Authentication
(WPA-EAP)

Access Point:

[app.    ]<--------------------------->[app.    ]
[TCP     ]<--------------------------->[TCP     ]
[IP      ]<--------------------------->[IP      ]
[SNAP    ]<--------------------------->[SNAP    ]
[LLC     ]<--------------------------->[LLC     ]
[sec. #1 ]<===>[sec. #1 | sec. #2]<===>[sec. #2 ]
[Wifi MAC]<--->[Wifi MAC         ]<--->[Wifi MAC]
[Wifi PHY]<--->[Wifi PHY         ]<--->[Wifi PHY]
Station 1         Access Point         Station 2

Ethernet/Wireless bridge:

[app.    ]<------------------------------->[app.    ]
[TCP     ]<------------------------------->[TCP     ]
[IP      ]<------------------------------->[IP      ]
[SNAP    ]<----[SNAP      ]
[LLC     ]<--->[LLC       ]
[security]<===>[security  ]
[Wifi MAC]<--->[Wifi MAC \-/ Eth. MAC]<--->[Eth. MAC]
[Wifi PHY]<--->[Wifi PHY  |  Eth. PHY]<--->[Eth. PHY]
Station 1      Ethernet/Wireless bridge     Station 2

ATM

        [...   /  ...]
        [NLPID / SNAP]
[... ]  [LLC         ]
[AAL5]  [AAL5        ]
[ATM ]  [ATM         ]
[phy. ] [phy.        ]
VC Mux  LLC Encap.

PPP

Configuration:

              [...        ]
[LCP] [CCP]   [compression]
[PPP] [PPP]   [PPP        ]
[...] [...] → [...        ]
LCP   CCP and compression

Authentication:

             [...]
[PAP] [CHAP] [EAP]
[PPP] [PPP ] [PPP]
[...] [... ] [...]
PAP   CHAP   EAP

Applications:

[IPCP|IPv4] [IPv6CP|IPv6]
[PPP      ] [PPP        ]
[...      ] [...        ]
IPv4/PPP    IPv6/PPP

Transports:

                               [...   ]       
                               [PPP   ]        [...]
[...   ]   [... ]   [...     ] [(SNAP)] [... ] [PPP]
[PPP   ]   [PPP ]   [PPP     ] [LLC   ] [PPP ] [SSH]
[HDLC  ]   [HDLC]   [PPPoE   ] [AAL5  ] [L2TP] [TCP]
[RS-232]   [V.92]   [Ethernet] [ATM   ] [... ] [IP ]
PPP/RS-232 PPP/PSTN PPPoE      PPPoA    L2TP   PPP
                                               /SSH

GPON (G.984)

Gigabit Passive Optical Network:

                                                 [PWE3          ]
                               [SIP |RTP      ]  [RTP           ]
                               [TCP |UDP      ]  [UDP           ]
                   [IP      ]  [IP            ]  [IP            ]  [MEF-8         ]
                   [VLAN    ]  [VLAN          ]  [VLAN          ]  [VLAN          ]
               [TDM|Eth. MAC]  [Eth. MAC      ]  [Eth. MAC      ]  [Eth. MAC      ]  [SDH           ]
[PLOAM|OMCI|ATM|GEM         ]  [GEM           ]  [GEM           ]  [GEM           ]  [GEM           ]
[GTC adaptation             ]  [GTC adaptation]  [GTC adaptation]  [GTC adaptation]  [GTC adaptation]
[GTC framing                ]  [GTC framing   ]  [GTC framing   ]  [GTC framing   ]  [GTC framing   ]
[GPM                        ]  [GPM           ]  [GPM           ]  [GPM           ]  [GPM           ]
General stack                  Voice (VoIP)      Voice with PWE3   Voice with MEF-8  Voice (TDM)

XG-PON (G.987)

                                                      [PWE3               ]
                               [SIP|RTP            ]  [RTP                ]
                               [TCP|UDP            ]  [UDP                ]
                  [IP  ]       [IP                 ]  [IP                 ]  [MEF-8              ]
           [802.1X|VLAN]       [VLAN               ]  [VLAN               ]  [VLAN               ]
           [Eth. MAC   |MPLS]  [Eth. MAC           ]  [Eth. MAC           ]  [Eth. MAC           ]
[PLOAM|OMCI|XGEM            ]  [XGEM               ]  [XGEM               ]  [XGEM               ]
[XGTC framing               ]  [XGTC framing       ]  [XGTC framing       ]  [XGTC framing       ]
[XGTC PHY adaptation        ]  [XGTC PHY adaptation]  [XGTC PHY adaptation]  [XGTC PHY adaptation]
[XGON PMD                   ]  [XGON PMD           ]  [XGON PMD           ]  [XGON PMD           ]
General stack                  Voice (voIP)           Voice with PWE3        Voice with MEF-8

Phone

SS7

                [... ]  [... ]       [...  ]       [...    ]  [... ]
           [ISUP|TCAP]  [TCAP]       [TCAP ]       [TCAP   ]  [TCAP]
[TUP / ISUP|SCCP     ]  [SUA |ISUP]  [SCCP ]       [SCCP   ]  [SCCP|ISUP]
[MTP-3               ]  [-        ]  [MTP-3|ISUP]  [MTP-3  ]  [M3UA     ]
[MTP-2               ]  [-        ]  [M2PA      ]  [M2UA   ]  [  -      ]
[MTP-1               ]  [(DTLS)   ]  [(DTLS)    ]  [(DTLS) ]  [(DTLS)   ]
                        [SCTP     ]  [SCTP      ]  [SCTP   ]  [SCTP     ]
                        [(IPSec)  ]  [(IPSec)   ]  [(IPSec)]  [(IPSec)  ]
                        [IP       ]  [IP        ]  [IP     ]  [IP       ]
SS7                     SUA          M2PA          M2UA       M3UA        ...

Some application protocols:

                          [MAP  ]
                 [ISUP ]  [TCAP ]
[TUP  ] [ISUP ]  [SCCP ]  [SCCP ]
[MTP-3] [MTP-3]  [MTP-3]  [MTP-3]
[MTP-2] [MTP-2]  [MTP-2]  [MTP-2]
[MTP-1] [MTP-1]  [MTP-1]  [MTP-1]
TUP     ISUP     ISUP     MAP
                 /SCCP

Mobile

User Equipment (i.e., the phone) stacks:

                        PDP contexts        PDP contexts            EPS bearers          PDU sessions
                         |   |                 |   |                   |    |               |    |
           [SM      ]    ↓   ↓                 |   |                   |    |               ↓    ↓
           [GMM     ] [IP / PPP]  [CM|SM   ]   ↓   ↓      [LTE NAS ]   ↓    ↓    [5G NAS ] [IP|Eth.]
[CM     ]  [SNDCP   ] [SNDCP   ]  [MM|GMM  ] [IP / PPP ]  [LTE RRC ] [IP / PPP]  [5G RRC ] [SDAP   ]
[MM     ]  [GPRS LLC] [GPRS LLC]  [UMTS RRC] [UMTS PDCP]  [LTE PDCP] [LTE PDCP]  [5G PDCP] [5G PDCP]
[RRM    ]  [GPRS RLC] [GPRS RLC]  [UMTS RLC] [UMTS RLC ]  [LTE RLC ] [LTE RLC ]  [5G RLC ] [5G RLC ]
[LAPDm  ]  [GPRS MAC] [GPRS MAC]  [UMTS MAC] [UMTS MAC ]  [LTE MAC ] [LTE MAC ]  [5G MAC ] [5G MAC ]
[GSM PHY]  [GSM PHY ] [GSM PHY ]  [UMTS PHY] [UMTS PHY ]  [LTE PHY ] [LTE PHY ]  [5G PHY ] [5G PHY ]
   CP         CP         UP          CP          UP          CP         UP          CP        UP
--------   ---------------------  ----------------------  ---------------------  -----------------
GSM (2G)   GPRS (2.5G)            UMTS (3G)               LTE (aka EPS) (4G)     5G NR (5G)

Authentication stacks at the user equipment:

                                                  [...     ]
                                                  [AVP     ]
                                        [mTLS   ] [TLS     ]
                   [EAP-AKA] [EAP-AKA'] [EAP-TLS] [EAP-TTLS]
[EPS-AKA] [5G-AKA] [EAP    ] [EAP     ] [EAP    ] [EAP     ]
[NAS    ] [NAS   ] [NAS    ] [NAS     ] [NAS    ] [NAS     ]
EPS-AKA   5G-AKA   EAP-AKA   EAP-AKA'   EAP-TLS   EAP-TTLS
(4G)      (5G)     (5G)      (5G)       (5G)      (5G)

Notes:

5G primary authentication, access authentication;
5G secondary authentication, setting up user planes from other operators

Non-3GPP access

User equipment stacks for untrusted non-3GPP access (5G):

                                              PDU sessions
                                                 |   |
[EAP-AKA]                                        |   |
[EAP    / 5G-AKA]                                ↓   ↓
[NAS            ]  [NAS  ]                     [IP|Eth.]   ← Application IP (IMS, data)
[EAP-5G         ]  [TCP  ]                     [GRE    ]
[EAP            ]  [IP   ]                     [IP     ]   ← Inner IP (connect to the N3IWF)
[IKEv2          ]  [ESP  ]      [IKEv2]        [ESP    ]
[UDP            ]  [(UDP)]      [UDP  ]        [(UDP)  ]
[IP             ]  [IP   ]      [IP   ]        [IP     ]   ←  Non-3GPP Access Network
[L2             ]  [L2   ]      [L2   ]        [L2     ]
[L1             ]  [L1   ]      [L1   ]        [L1     ]
CP                 CP           UP             UP
(before SA)        (after SA)   establishment

Notes:

ESP/UDP may be used for NAT traversal.
Different IPSec SAs are established for:
- control plane (signaling) i.e., transporting NAS messages;
- user plane (one SA per PDU layer and QoS flow);
N3IWF (Non-3GPP Interworking Function) is responsible for the interworking of the non-3GPP access and the 5G core.

User equipment stacks for untrusted non-3GPP access with firewall traversal (5G):

                                             PDU sessions
                                                |   |
[EAP-AKA]                                       |   |
[EAP    / 5G-AKA]                               ↓   ↓
[NAS            ] [NAS]                       [IP|Eth.]   ← Application IP (IMS, data)
[EAP-5G         ] [TCP]                       [GRE    ]
[EAP            ] [IP ]                       [IP     ]   ← Inner IP (connect to the N3IWF)
[IKEv2          ] [ESP]       [IKEv2]         [ESP    ]
[TLS            ] [TLS]       [TLS  ]         [TLS    ]
[TCP            ] [TCP]       [TCP  ]         [TCP    ]
[IP             ] [IP ]       [IP   ]         [IP     ]   ←  Non-3GPP Access Network
[L2             ] [L2 ]       [L2   ]         [L2     ]
[L1             ] [L1 ]       [L1   ]         [L1     ]
CP                CP          UP              UP
(before SA)       (after SA)  establishment

IMS

IMS (IP Multimedia Subsystem) is an SIP/IP based-service to transporting voice, SMS, video over 4G (VoLTE), 5G (VoNR) or non-3GPP access (VoWLAN/WoWifi).

User equipment stacks for stacks for IMS:

[SMS]     [SDP|A/V ]
[SIP]     [SIP|RTP |RTCP]
[TCP]     [TCP|UDP / TCP]
[IP ]     [IP           ]
SMS       Audio/Video calls
over IMS      over IMs

Notes:

SMS may be transported over NAS as well.

SMS

User equipment stacks for SMS:

[SM-AL  ]           [SMS   ]
[SM-TL  ]           [SIP   ]
[SM-RP  ]  [SMS]    [TCP   ]
[SM-CP  ]  [NAS]    [IP    ]
[CM     ]  [RRC]    [(SDAP)]
[MM     ]  [RLC]    [PDCP  ]
[RR     ]  [RLC]    [RLC   ]
[LDAPDm ]  [MAC]    [MAC   ]
[GSM PHY]  [PHY]    [PHY   ]
SMS/GSM    SMS/NAS  SMS/IMS
(2G)       (4G/5G)  (4G/5G)

WAP

User equipment stacks for WAP (including MMS):

[WML | WMLScript | MMS]
[WSP                  ]  [XHTML MP|WAP CSS|MMS]
[(WTP )               ]  [(WP-)HTTP           ]
[(WTLS)               ]  [TLS                 ]
[WDP   / UDP          ]  [(WP-)TCP            ]
[SMS   / IP           ]  [IP                  ]
[...   / ...          ]  [...                 ]
WAP 1                    WAP 2.0

Devices

BlueTooth

                   ACL                           SCO
 /--------------------------------------------\ /---\

         [IP ]  [IP |... ]                                              [HID ]
         [PPP|AT|Eth. MAC]                                              [GATT| GAP]
    [SDP |RFCOMM|BNEP    |OBEX|HIDP|AVCTP|AVDTP]         [...      ]    [ATT | SM ]
    [L2CAP                                     |voice]   [L2CAP    ]    [L2CAP    ]   [GAP    ]   ↑ Host
------------------(HCI)-------------------------------   ---(HCI)---    ---(HCI)------------------
[LMP|-                                               ]   [Wifi PAL ]                              ↓Controler
[LCP                                                 ]   [Wifi MAC ]    [LE LL                   ]
[BR / EDR                                            ]   [Wifi PHY ]    [LE PHY (1M / 2M / Coded)]
Bluetooth Classic                                        Bluetooth HS   Bluetooth Low Energy (BLE)
                                                         (High Speed)

BLE:

[HID ]
[GATT| GAP]
[ATT | SM ]
[L2CAP    ]   [GAP    ]
[LE LL    ]   [LE LL  ]
[LE PHY   ]   [LE PHY ]
 BLE          BLE
 (connected)  (no
               connection)

Host/Controller interface (HCI) example (over USB):

[RFCOMM ]<-------------------------------------->[RFCOMM  ]
[L2CAP  ]<-------------------------------------->[L2CAP   ]
[HCI    ]<--->[HCI    |LMP     ]<--------------->[LMP     ]
[USB    ]<--->[USB    |LCP     ]<--------------->[LCP     ]
[USB PHY]     [USB PHY|BR / EDR]<--------------->[BR / EDR]
Host          Bluetooth Controler                Device

Radio link types:

ACL (Asynchronous Connection-Less), used for general data
SCO (Synchronous Connection-Oriented), reserved time slots (used for voice data)

USB

                                [Eth|...|MIDI1   |MIDI1|MIDI2]
[Std. Req.|HID|BOT|UAS|UASP|CCID|CDC    |USB-MIDI|USB-MIDI2  |IPP|...]
[USB Protocol layer                                                  ]
[USB PHysical                                                        ]

Appendix, details

Ethernet

Ethernet sublayers:

PMD (Physical Medium Dependent sublayer): eg. 100BASE-FX, 10GBASE-E, 10GBASE-L, 10GBASE-S, 10GBASE-LX4
PMA (Physical Medium Attachment sublayer): Framing, synchronization, etc.
PCS (Physical coding sublayer): Negotiation, coding (error detection)

Ethernet payloads:

Protocol	EtherType	Description
ARP	0x0806	Address Resolution Protocol. Used for non-point-to-point networks.
801.1Q	0x8100	VLAN (Q-tag)
802.1ad (Q-in-Q)	0x88A8	VLAN in VLAN (outer 802.1ad tag is S-tag for service-tag; inner 802.1Q tag is c-tag for customer-tag)
802.1X (EAPOL)	0x888E	Port Authentication, used for WPA-Enterprise as well
IPv4	0x0800
IPv6	0x86DD
LLC	(length ≤ 1500)	Logical Link Control
SNAP	-	Subnetwork Access Protocol
PPPoE	0x8863 (discovery), 0x8864 (session)	PPP over Ethernet

IP protocols

Protocol	Protocol number	Description
ICMP	1
IGMP	2	Support for multicast
TCP	6	Connection oriented, stream-based, checksums, connection control.
UDP	17	Unreliable datagrams. Checksums (can be disabled in IPv4).
UDP-lite	136	Unreliable datagrams. Allows for partial checksums.
DCCP	33	Connection oriented, unreliable datagrams, with congestion control.
SCTP	132	Message-based (fragmentation, reliable, ordered), multiple-streams multiplexing over a single connection. Initially designed for PSTN signaling over IP.
ICMPv6	0x58
NDP	0x58	Part of ICMPv6. Replaces ARP in IPv6.
MLD	0x58	Part of ICMPv6. Replaces IGMP in IPv6.
AH	51	IPsec. Integrity, data origin authentication, anti-replay (including the outer IP packet).
ESP	50	IPsec. Integrity, data origin authentication, anti-replay, confidentiality (of the payload).
GRE	47	(next protocol defined as an EtherType; Optional 32 bit key (tunnel ID); optional 32 bit sequence number)
EtherIP	97
L2TP over IP	115

Ports

Protocol	Port(s)	ALPN	Description
DHCP (Dynamic Host Configuration Protocol)	UDP 67 (server) UDP 68 (client)
DHCPv6	UDP 546 (client), UDP 547 (server)		Usually NDP is used instead for address allocation, routes, DNS configuration, etc.
SCTP over UDP	-		Useful for NAT traversal and userspace implementations of SCTP.
SCTP over DTLS	-		Used by WebRTC for transporting data channels.
QUIC	-		Protected communications (relies on TLS for the handshake). Multiplexing of multiple streams per QUIC connection. Used by HTTP/3.
DNS over UDP (Do53)	UDP 53	-	General DNS traffic.
DNS over TCP (Do53)	TCP 53	-	Usually used when messages are too long for UDP.
DNS over TLS (DoT)	TCP 853	"dot"	DNS privacy.
DNS over DTLS	(UDP 853)	-	DNS privacy. Not used in practice, deprecated in favor of DoQ.
DNS over HTTPS (DoH)	TCP 443	"http/1.1", "h2", "h3", etc.	DNS privacy. One HTTP request per request/response pair.
DNS over QUIC (DoQ)	UDP 853	"doq"	DNS privacy. One QUIC stream per request/response pair.
Oblivious DNS over HTTPS (ODoH)	TCP/UDP 443	"http/1.1", "h2", "h3", etc.	More DNS privacy.
DNS over CoAP (DoC)	TCP/UDP 5684	"coap"/"co"
HTTP/1.x without TLS	TCP 80	-	-
HTTP/1.x over TLS (HTTPS)	TCP 443	"http/1.1", "http/1.0"
HTTP/2 without TLS	TCP 80	"h2c"	HTTP/2 without TLS is not widely supported and is deprecated.
HTTP/2 over TLS (HTTPS)	TCP 443	"h2"	-
HTTP/3 over QUIC (HTTPS)	UDP 443	"h3"	-
FTP (File Transfer Protocol)	TCP/21 (control) TCP/20 (data)
FTP over TLS	TCP/900 (control) TCP/989 (data)
WebDAV	TCP/80 (HTTP)		Extension of HTTP for remote resource (file) operation.
WebDAV Secure	TCP/443 UDP/443		WebDAV with HTTPS.
SFTP (SSH File Transfer Protocol)	TCP/22 (SSH)		File transfer over SSH. Not related to FTP! This is not FTP over TLS!
NFS v4 (Network File System)	TCP/2049
SMB over IP (modern)	TCP/445		Windows file sharing.
SMB over NetBIOS over TCP (SMB/NBT)	TCP/139		Windows file sharing over legacy Windows network protocols.
SMB over QUIC	UDP/443
RTSP (Real Time Streaming Protocol)	TCP 554		Control RTP streams (PLAY/PAUSE, etc.)
RTSPS (Secure RTSP)	TCP 322		RTSP over TLS
SIP (Session Initiation Protocol)	TCP 5060 UDP 5060 SCTP 5060
SIP over TLS	TCP 5061
SIP over WebSocket	TCP 80 TCP or UDP 443
IKEv2	UDP 500
ESP over UDP (and IKDEv2)	UDP 4500
OpenVPN	UDP 1194, TCP 1194
WireGuard	UDP 51820
GRE-in-UDP	UDP 4754 (dest.)
GRE-UDP-DTLS	UDP 4755 (dest.)
L2TP over UDP	UDP 1701 (control)
VXLAN	UDP 4789 (dest.)		(24 bit VNI (VXLAN Network Identifier), always encapsulates Ethernet)
GENEVE	UDP 6081 (dest.)		(24 bit VNI, can encapsulate different protocols (EtherType))
Kerberos	UDP or TCP 88
MS-KKDCP	TCP or UDP 443 (HTTPS)		Kerberos Key Distribution Center Proxy. Kerberos over HTTPS.

CoAP

Protocol	URI scheme	Port	ALPN	WebSocket protocol
CoAP over UDP	coap:	UDP 5683	-	-
CoAP over DTLS	coaps:	UDP 5684	coap	-
CoAP over TCP	coap+tcp:	TCP 5683	-	-
CoAP over TLS	coaps+tcp:	TCP 5684	coap	.
CoAP over WebSocket	coap+ws:	(80, HTTPS)	-	coap
	coaps+ws:	(443, HTTPS)	(http/1.x, …)	coap

HTTP Datagram

HTTP datagrams are unreliable datagrams, associated with a HTTP upgrade, transported over an HTTP connection. They can be sent after an upgrade to the Capsule protocol,

either as part of the HTTP stream in a DATAGRAM capsules,
or transported in QUIC datagrams (HTTP/3 Datagram), if supported by the peer.

HTTP datagrams are currently used for,

UDP in HTTP (RFC 9298);
IP in HTTP (RFC 9484);
Ethernet in HTTP (draft);
WebTransport datagrams.

HTTP Upgrade

Protocol	Upgrade token	Default URI template
Proxy TCP in HTTP (classic) (/1.x, /2, /3)	-	-
Proxy TCP in HTTP (template-based)	"connect-tcp"	/.well-known/masque/tcp/{target_host}/{tcp_port}/
Proxy UDP in HTTP	"connect-udp"	/.well-known/masque/udp/{target_host}/{target_port}/
Proxy UDP listen in HTTP	"connect-udp-listen"	/.well-known/masque/udp/{target_host}/{target_port}/
Proxy IP in HTTP	"connect-ip"	/.well-known/masque/ip/{target}/{ipproto}/
Proxy Ethernet in HTTP	"connect-ethernet"	(/.well-known/masque/ethernet/)

WebTransport

Features:

multiple (reliable) streams per WebTransport sessions;
datagrams can be exchanged over a WebTransport sessions;
multiple WebTransport session may be multiplexed over a single transport (eg. HTTP/2 or HTTP/3 connection).

Notes:

With HTTP/2, after an extended CONNECT, all streams and datagrams of a the WebTransport instance are transported over a single HTTP/2 stream.
With HTTP/3, after an extended CONNECT, each WebTranport stream is transported over a different QUIC stream and WebTransport datagrams are sent a HTTP/3 (QUIC) datagrams.
No specification for WebTransport over HTTP/1.

RTP

Protocol	Description
RTP	Transport A/V streams
RTCP	Flow/congestion control for RTP
SRTP and SRTCP
DTLS-SRTP	DTLS handshake (with mutual authentication) for keying SRTP (and SRTCP).
ZRTP	Diffie-Hellman key exchange on the same port as SRTP.
S/MIME	May be used in SIP to provide end-to-end protection of SDP content
Framing for RTP	When used over TCP, each RTP or RTCP packet is prefixed with a length field (2 bytes).
RTP-MIDI	Send MIDI 1 data over RTP
RTP-over-QUIC (RoQ)

WebRTC

WebRTC Payload type	SCTP PPID	Description
SRTP-DTLS	-
DCEP (Data Channel Establishment Protocol)	50	Used to create WebRTC data channels.
WebRTC String	51
WebRTC Binary	53
WebRTC Empty String	56
WebRTC Empty Binary	57

TLS

TLS Subprotocols	Description
Underlying transport layer	eg. TCP
TLS Record Protocol: Record Protection	Encryption and message authentication (Cipher+MAC or AEAD).
TLS Record Protocol: Compression	Message compression, if negotiated. Not available in TLS v1.3.
TLS Record Protocol: Fragmentataion	Subprotocols multiplexing and framing.
TLS Handshake Protocol	TLS handshake (version/ciphersuite negotiation, authentication, key exchange, etc.).
TLS ChangecipherSpec	Enables communication protection for this direction
TLS Alert	Errors.
Application Layer	eg. HTTP, SMTP, etc.

EAP

EAP Method	Method Type	Description
EAP-TLS	13	Mutual TLS authentication
EAP-TTLS	21	AVPs (attribute value pairs) in the Diameter format over TLS
PEAP	25	Protected EAP. Inner EAP exchange over a TLS tunnel
EAP-FAST	43
TEAP	55	Tunnel EAP. Inner EAP exchange over a TLS tunnel (standardized version of PEAP)
EAP-SIM	18	SIM-based authentication
EAP-AKA	23	SIM-based authentication
EAP-AKA'	50	SIM-based authentication
EAP-pwd	52	Authenticated key exchange based on a shared password
EAP-NOOB	56	Authentication for IoT devices based on an initial out-of-band channel

EAP Transport	Description
802.1X	Authentication of LAN/WLAN such as Ethernet and Wifi (WPA-EAP aka WPA-Entreprise)
PANA	Protocol for Carrying Authentication for Network Access.
RADIUS	EAP messages encapsulated in the EAP-Message attribute
Diameter	EAP messages encapsulated in EAP-Payload AVP

SASL

SASL Mechanism	Security Layer	Channel Binding	Description
GSSAPI	Optional (negotiated)	Yes	Kerberos 5 (not other mechanisms) with GSSAPI
GSS2-*	No	No	GSS-API mechanisms (without support for channel binding)
GSS2-*-PLUS	No	Yes	GSS-API mechanisms (with support for channel binding)
OAUTHBEARER	No	No	Oauth 2.0 Bearer token

RADIUS

Protocol	Port	SCTP PPID	Description
RADIUS (authentication and authorization)	UDP 1812, TCP 1812	-
RADIUS Accounting	UDP 1813, TCP 1813	-
RADIUS DynAuth	UDP 3799	-	Disconnect and Change-of-Authorization (CoA) messages
RADIUS over TLS (RadSec)	TCP 2083	-
Diameter	TCP 3868, SCTP 3868	46
Diameter over TLS/TCP	TCP 5658	-
Diameter over DTLS/SCTP	SCTP 5658	47

Wifi

Sublayers:

PMD (Physical Medium Dependent sublayer), (eg. 802.11 FHSS, 802.11 DSSS, 802.11a OFDM, 802.11b HR/DSSS, 802.11g ERP)
PLCP (Physical Layer Convergence Protocol sublayer)

Encryption:

WEP (Wired Equivalent Privacy), old encryption layer (based on RC4 and CRC-32)
TKIP (Temporal Key Integrity Protocol), encryption layer of WPA1 (RC4 stream cipher with “Michael” MIC)
CCMP, encryption layer of WPA2 (AES with CCM mode)
GCMP-256, encryption layer of WPA3 (56-bit Galois/Counter mode)

PPP

PPP protocols:

Protocol	PPP Protocol	Description
PPP (Point-to-Point Protocol)	-
LCP (Link Control Protocol)	0xc021
PAP (Password Authentication Protocol)	0xc023	Cleartext login/password
CHAP (Challenge-Handshake Authentication Protocol)	0xc223	Includes MC-CHAP and MS-CHAPv2 as well.
EAP (Extensible Authentication Protocol)	0xc227
IPCP (IP Configuration Protocol)	0x0021	Configuration of the IPv4 address
IPv4	0x0021
IPv6CP (IPv6 Configuration Protocol)	0x8057
IPv6	0x0057

PPP transports:

PPPoA, PPP-over-ATM (AAL5)
PPPoE, PPP-over-Ethernet
L2TP (Layer Two Tunneling Protocol)
HDLC-like framing (RFC 1662) for PPP
CCP (Compression Control Protocol)
PPP over SSH (it's not a standard thing but you can do it)

Optical

GPM (GPON Physical Media Dependent layer)
GTC framing
PLOAM (Physical Layer Operations, Administration and Maintenance)
OMCI (ONU Management and Control Interface)
GEM (G-PON Encapsulation Mode)
TDM (Time Division Multiple Access), emulation of any TDM-based circuit
PWE3 (pseudo Wire Emulation Edge-to-Edge) ,frame Relay/ATM/Ethernet/TDM/SONET/SDH over IP or MPLS
MEF-8, emulation of PDH over Ethernet

Phone

Protocol	SCTP PPID	Description
MTP-1 (Message Transfer Part layer 1)		Physical layer
MTP-2 (Message Transfer Part layer 2)		Link layer
MTP-3 (Message Transfer Part layer 3)		Nework layer
TUP (Telephone User Part)		Signaling for classic PSTN, mostly replaced by ISUP
ISUP (ISDN User Part)
SCCP (Signaling Connection Control Part)
TCAP (Transaction Capabilities Application Part)
CAP (CAMEL Application Part)
MAP (Mobile Application Part)		Transport layer on top of IP
SCTP (Stream Control Transmission Protocol)	-
SUA (SCCP User Adaptation)	4	Replaces SCCP when used over SCTP/IP
M2UA (MTP2 User Adaptation Layer)	2
M2PA (MTP2 User Peer-to-Peer Adaptation Layer)	5
M3UA (MTP3 User Adaptation Layer)	3

Mobile

Mobile network:

LAPDm (Link Access Procedures on the Dm channel), Link layer for GSM used between the mobile station (i.e., the phone) and the BSC
RR aka RMM (Radio Resource Management)
MM (Mobile Management)
CM (Connection Management)
RLC (Radio Link Control)
LLC (Logical Link Control)
- This is not the 802.2 LLC protocol used with Ethernet, Wifi, etc.
SNDCP (Subnetwork Dependent Convergence Protocol)
GMM (GPRS Mobility Management)
SM (Session Management)
PDCP (Packet Data Convergence Protocol)
RRC (Radio Resource Control)
NAS (Non-access stratum)
SDAP (Service Data Adaption Protocol)
SM (Session Management)
GMM (GPRS Mobile Management)

WAP:

Wireless Session Protocol (WSP), Similar to HTTP
Wireless Transaction Protocol (WTP), similar to TCP. Used for CO-WSP (Connection-oriented WSP), absent for CL-WSP (Connectionless WSP).
Wireless Transport Layer Security (WTLS), protection (similar to TLS)
Wireless Datagram Protocol (WDP), similar to UDP
WML (Wireless Markup Language), XML-based markup language, similar to HTML
WMLScript, Scripting language based on ECMAScript but compiled to a bytecode
XHTML MP (Mobile Profile)
WP-TCP, Profile of TCP
WP-HTTP, Profile of HTTP

Bluetooth

BR (Basic Rate)
EDR (Extended Data Rate)
LE (Low Energy) 1M
LE (Low Energy) 2M
LE (Low Energy) Coded
LCP
LMP (Link Manager Protocol)
LE LL (LE Link Layer)
L2CAP (Logical Link Control and Adaptation Protocol)
SDP (Service Discovering Protocol)
RFCOMM (Radio frequency communication), RS-232 port emulation
BNEP (Bluetooth Network Encapsulation Protocol),
- transports Ethernet traffic
- replaces the Ethernet header with its own header!
OBEX
HIDP (Bluetooth HID Protocol)
AVCTP (Audio/video control transport protocol)
AVDTP (Audio/video data transport protocol)
SM (Security Manager)
GAP
ATT
GATT
AT, Hayes Modem AT commands
HCI (Host Controller Interface), Communication between the host and the bluetooth controller

USB

Device Classes	Description
Standard Requests
HID (Human Interaction Device)	Keyboard, Mouse, Baseball and Golf clubs, etc.
MSB (Mass Storage Device)	USB stick, etc.
CDC (Communication Device Class)
IPP (Internet Printing Protocol)
MTP (Media Transfer Protocol)
CCID (Chip Card Interface Device)	Smartcard, Yubikeys, etc.
DFU (Device Firmware Upgrade)
BOT (Bulk Only Transfer)
UAS (USB Attached SCSI)
UASP (USB Attached SCSI Protocol)	Not the same as UAS!

References

General:

EventHelix, has a lot of nice sequence diagrams and other useful information
SampleCaptures from the WireShark website

Assignments:

DNS:

RFC 7858, DNS over TLS (DoT)
RFC 8094, DNS over DTLS
RFC 8686, DNS over HTTP (DoH)
RFC 9230, Oblivious DNS over HTTPS (ODoH)
RFC 9250, DNS over QUIC (DoQ)
RFC 9539, Unilateral Opportunistic Deployment of Encrypted Recursive‑to‑Authoritative DNS
RFC 9953, DNS over CoAP (DoC)

WebSocket:

WebSocket JS API (W3C)
WebSocket JS API (MDN)

WebTransport:

WebTransport JS API (W3C)
WebTransport JS API (MDN)

WebRTC:

WebRTC Protocol Layers
WebRTC For The Curious
RFC 8834, Media Transport and Use of RTP in WebRTC
RFC 8827, WebRTC Security Architecture
RFC 8835, Transports for WebRTC
Replacing WebRTC

QUIC:

QUIC, Why not use SCTP over DTLS?

Tunnels, VPNS:

RFC 4301, Security Architecture for the Internet Protocol
PSP Security Protocol

SSH:

References:

ATM:

Multiprotocol Encapsulation over AAL5, RFC 2684

Wireless:

RF Wireless World Tutorial

CoAP:

RFC7641, CoAP
RFC8223, CoAP over TCP, TLS, and WebSockets
RFC8613, OSCORE
RFC9529, EDHOC

USB:

Optical:

Phone:

SIGTRAN User Guide

Mobile:

Non-3GPP access:

IMS:

Rich Communication Suite 8.0 Advanced Communications Services and Client Specification version 9.0

WAP:

LLMs and agents: