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laforge gerrit-no-reply at lists.osmocom.orglaforge has uploaded this change for review. ( https://gerrit.osmocom.org/c/osmo-gsm-manuals/+/21267 ) Change subject: sigtran: Describe sctp/m3ua role, multi-homing, traffic-modes ...................................................................... sigtran: Describe sctp/m3ua role, multi-homing, traffic-modes Change-Id: I4c54dbde5a0b0f6ae38efdd047b17b4dbaae12c3 --- M common/chapters/sigtran.adoc 1 file changed, 62 insertions(+), 0 deletions(-) git pull ssh://gerrit.osmocom.org:29418/osmo-gsm-manuals refs/changes/67/21267/1 diff --git a/common/chapters/sigtran.adoc b/common/chapters/sigtran.adoc index 42135d5..cbf513e 100644 --- a/common/chapters/sigtran.adoc +++ b/common/chapters/sigtran.adoc @@ -333,3 +333,65 @@ stackings) operates on top of both IPv4 and IPv6. As the entire underlying IP transport is transparent to the SS7/SCCP applications, there is no restriction on whether to use SIGTRAN over IPv4 or IPv6. + +==== SCTP multi-homing in SIGTARN + +SCTP, unlike more traditional IP L4 protocols (TCP, UDP) doesn't work +based on a _connection_ between source IP:port and Destination IP:port. + +Instead, SCTP creates _associations_ between two endpoints, both of which +can have any number of IP addresses. This means that in case of +network outage, traffic can continue to flow through any of the IP +addresses of that association. + +The Linux kernel by default advertises all IP addresses of the local +system to the peer. This can be seen when inspecting the SCTP INIT +chunk e.g. in wireshark. While this may be a reasonable default in some +use cases, it is not always the best idea. Imagine addresses of +internal/private IP networks, for example local bridge devices between +lxc or docker containers, or local VMs. Such addresses have no +significance beyond the local machine. + +Subsequently, libosmo-sigtran allows the user to explicitly select which +local IP addresses shall be used in SCTP multi-homing for the SIGTRAN +associations it manages. The user can achieve this by specifying +multiple `local-ip` VTY commands within one `asp` (SCTP client role) or +within one `listen m3ua 2905` (SCTP server role). + +==== SCTP role + +The _SCTP role_ defines which of the two L4 protocol roles SCTP assumes: + +* The _SCTP server_ role binds to a local port and handles incoming + connections from clients +* The _SCTP client_ role connects to a remote SCTP sever. + +==== M3UA/SUA role + +The _M3UA role_ (or _SUA role_) determines which role a given peer of a +M3UA connection implements. 3GPP specifies the following role: + +* _SGP_ (Signaling Gateway): The entity connected to the larger SS7 + network +* _ASP_ (Application Server Process): A client application that connects + to the SGW to talk to the SS7 network +* _IPSP_ (IP Server Process): M3UA in point-to-point mode + +Osmocom (libosmo-sigtran) implements both the SGP and ASP roles, but not +the IPSP role. + +==== traffic modes in SIGTRAN + +Whenever an AS consists of multiple ASPs, the traffic mode expresses how +messages are distributed between those ASPs. + +* _Override_: There is always one active ASP and multiple hot standby + ASPs. If the active ASP fails, one of the remaining ASPs will become + the new active ASP. +* _Loadshare_: The messages will be distributed between the different + ASPs in a way to distribute the load among them. Details are + implementation specific. +* _Broadcast_: A copy of every incoming signaling message is sent to + _all_ the ASPs in broadcast traffic mode. + +Osmocom (libosmo-sigtran) implements all above-mentioned traffic modes. -- To view, visit https://gerrit.osmocom.org/c/osmo-gsm-manuals/+/21267 To unsubscribe, or for help writing mail filters, visit https://gerrit.osmocom.org/settings Gerrit-Project: osmo-gsm-manuals Gerrit-Branch: master Gerrit-Change-Id: I4c54dbde5a0b0f6ae38efdd047b17b4dbaae12c3 Gerrit-Change-Number: 21267 Gerrit-PatchSet: 1 Gerrit-Owner: laforge <laforge at osmocom.org> Gerrit-MessageType: newchange -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.osmocom.org/pipermail/gerrit-log/attachments/20201120/ac13ef1b/attachment.htm>