Terminology.doc

Terminology

Application Server (AS) - A logical entity serving a specific Routing

Key An example of an Application Server is a virtual switch element handling all call processing for a unique range of PSTN trunks, identified by an SS7 SIO/DPC/OPC/CIC_range Another example is a virtual database element, handling all HLR transactions for a particular SS7 DPC/OPC/SCCP_SSN combination The AS contains a set of one or more unique Application Server Processes, of which one or more is normally actively processing traffic Note that there is a 1:1 relationship between an AS and a Routing Key.

Application Server Process (ASP) - A process instance of an

Application Server An Application Server Process serves as an active or backup process of an Application Server (e.g., part of a

distributed virtual switch or database) Examples of ASPs are

processes (or process instances) of MGCs, IP SCPs or IP HLRs An ASP contains an SCTP endpoint and may be configured to process signalling traffic within more than one Application Server.

Association - An association refers to an SCTP association The

association provides the transport for the delivery of MTP3-User protocol data units and M3UA adaptation layer peer messages.

IP Server Process (IPSP) - A process instance of an IP-based

application An IPSP is essentially the same as an ASP, except that it uses M3UA in a point-to-point fashion Conceptually, an IPSP does not use the services of a Signalling Gateway node.

Failover - The capability to reroute signalling traffic as required

to an alternate Application Server Process, or group of ASPs, within an Application Server in the event of failure or unavailability of a currently used Application Server Process Failover also applies upon the return to service of a previously unavailable Application Server Process.

Host - The computing platform that the process (SGP, ASP or IPSP) is

running on.

Layer Management - Layer Management is a nodal function that handles

the inputs and outputs between the M3UA layer and a local management entity.

Linkset - A number of signalling links that directly interconnect two

signalling points, which are used as a module.

MTP - The Message Transfer Part of the SS7 protocol.MTP3 - MTP Level 3, the signalling network layer of SS7

MTP3-User - Any protocol normally using the services of the SS7 MTP3

(e.g., ISUP, SCCP, TUP, etc.).

Network Appearance - The Network Appearance is a M3UA local reference

shared by SG and AS (typically an integer) that together with an Signaling Point Code uniquely identifies an SS7 node by indicating the specific SS7 network it belongs to It can be used to distinguish between signalling traffic associated with different networks being sent between the SG and the ASP over a common SCTP association An example scenario is where an SG appears as an element in multiple separate national SS7 networks and the same Signaling Point Code value may be reused in different networks.

Network Byte Order: Most significant byte first, a.k.a Big Endian.Routing Key: A Routing Key describes a set of SS7 parameters and

parameter values that uniquely define the range of signalling traffic to be handled by a particular Application Server Parameters within the Routing Key cannot extend across more than a single Signalling Point Management Cluster.

Routing Context - A value that uniquely identifies a Routing Key.

Routing Context values are either configured using a configuration management interface, or by using the routing key management

procedures defined in this document.

Signalling Gateway Process (SGP) - A process instance of a Signalling

Gateway It serves as an active, backup, load-sharing or broadcast

process of a Signalling Gateway.

Signalling Gateway - An SG is a signaling agent that receives/sends

SCN native signaling at the edge of the IP network [11] An SG appears to the SS7 network as an SS7 Signalling Point An SG

contains a set of one or more unique Signalling Gateway Processes, of which one or more is normally actively processing traffic Where an SG contains more than one SGP, the SG is a logical entity and the contained SGPs are assumed to be coordinated into a single management view to the SS7 network and to the supported Application Servers.

Signalling Process - A process instance that uses M3UA to communicate

with other signalling processes An ASP, an SGP and an IPSP are all signalling processes.

Signalling Point Management Cluster (SPMC) - The complete set of

Application Servers represented to the SS7 network under a single MTP entity (Signalling Point) in one specific Network Appearance SPMCs are used to aggregate the availability, congestion, and user part status of an MTP entity (Signalling Point) that is distributed in the IP domain, for the purpose of supporting MTP3 management procedures towards the SS7 network In some cases, the SG itself may also be a member of the SPMC In this case, the SG availability /congestion /User_Part status should also be taken into account when considering any supporting MTP3 management actions.

Stream - A stream refers to an SCTP stream; a unidirectional logical

channel established from one SCTP endpoint to another associated SCTP endpoint, within which all user messages are delivered in-sequence except for those submitted to the unordered delivery service.

Active destination transport address: A transport address on a

peer endpoint which a transmitting endpoint considers available for receiving user messages.

Bundling: An optional multiplexing operation, whereby more than

one user message may be carried in the same SCTP packet Each user message occupies its own DATA chunk.

Chunk: A unit of information within an SCTP packet, consisting of

a chunk header and chunk-specific content.

Congestion Window (cwnd): An SCTP variable that limits the data,

in number of bytes, a sender can send to a particular destination transport address before receiving an acknowledgement.

Cumulative TSN Ack Point: The TSN of the last DATA chunk

acknowledged via the Cumulative TSN Ack field of a SACK.

Idle destination address: An address that has not had user

messages sent to it within some length of time, normally the HEARTBEAT interval or greater.

Inactive destination transport address: An address which is

considered inactive due to errors and unavailable to transport user messages.

Message = user message: Data submitted to SCTP by the Upper Layer

Protocol (ULP).

Message Authentication Code (MAC): An integrity check mechanism

based on cryptographic hash functions using a secret key Typically, message authentication codes are used between two parties that share a secret key in order to validate information transmitted between these parties In SCTP it is used by an

endpoint to validate the State Cookie information that is returned from the peer in the COOKIE ECHO chunk The term "MAC" has

different meanings in different contexts SCTP uses this term with the same meaning as in [RFC2104].

Network Byte Order: Most significant byte first, a.k.a., Big

Ordered Message: A user message that is delivered in order with

respect to all previous user messages sent within the stream the message was sent on.

Outstanding TSN (at an SCTP endpoint): A TSN (and the associated

DATA chunk) that has been sent by the endpoint but for which it has not yet received an acknowledgement.

Path: The route taken by the SCTP packets sent by one SCTP

endpoint to a specific destination transport address of its peer SCTP endpoint Sending to different destination transport

addresses does not necessarily guarantee getting separate paths.

Primary Path: The primary path is the destination and source

address that will be put into a packet outbound to the peer endpoint by default The definition includes the source address since an implementation MAY wish to specify both destination and source address to better control the return path taken by reply chunks and on which interface the packet is transmitted when the data sender is multi-homed.

Receiver Window (rwnd): An SCTP variable a data sender uses to

store the most recently calculated receiver window of its peer, in number of bytes This gives the sender an indication of the space available in the receiver’s inbound buffer.

SCTP association: A protocol relationship between SCTP endpoints,

composed of the two SCTP endpoints and protocol state information including Verification Tags and the currently active set of

Transmission Sequence Numbers (TSNs), etc An association can be uniquely identified by the transport addresses used by the

endpoints in the association Two SCTP endpoints MUST NOT have more than one SCTP association between them at any given time.

SCTP endpoint: The logical sender/receiver of SCTP packets On a

multi-homed host, an SCTP endpoint is represented to its peers as a combination of a set of eligible destination transport addresses to which SCTP packets can be sent and a set of eligible source transport addresses from which SCTP packets can be received All transport addresses used by an SCTP endpoint must use the same port number, but can use multiple IP addresses A transport

address used by an SCTP endpoint must not be used by another SCTP endpoint In other words, a transport address is unique to an SCTP endpoint.

SCTP packet (or packet): The unit of data delivery across the

interface between SCTP and the connectionless packet network (e.g., IP) An SCTP packet includes the common SCTP header, possible SCTP control chunks, and user data encapsulated within SCTP DATA chunks.

SCTP user application (SCTP user): The logical higher-layer

application entity which uses the services of SCTP, also called the Upper-layer Protocol (ULP).

Slow Start Threshold (ssthresh): An SCTP variable This is the

threshold which the endpoint will use to determine whether to perform slow start or congestion avoidance on a particular destination transport address Ssthresh is in number of bytes.

Stream: A uni-directional logical channel established from one to

another associated SCTP endpoint, within which all user messages are delivered in sequence except for those submitted to the unordered delivery service.

Note: The relationship between stream numbers in opposite directions is strictly a matter of how the applications use them It is the responsibility of the SCTP user to create and manage these

correlations if they are so desired.

Stream Sequence Number: A 16-bit sequence number used internally

by SCTP to assure sequenced delivery of the user messages within a given stream One stream sequence number is attached to each user message.

Tie-Tags: Verification Tags from a previous association These

Tags are used within a State Cookie so that the newly restarting

association can be linked to the original association within the endpoint that did not restart.

Transmission Control Block (TCB): An internal data structure

created by an SCTP endpoint for each of its existing SCTP

associations to other SCTP endpoints TCB contains all the status and operational information for the endpoint to maintain and manage the corresponding association.

Transmission Sequence Number (TSN): A 32-bit sequence number used

internally by SCTP One TSN is attached to each chunk containing user data to permit the receiving SCTP endpoint to acknowledge its receipt and detect duplicate deliveries.

Transport address: A Transport Address is traditionally defined

by Network Layer address, Transport Layer protocol and Transport Layer port number In the case of SCTP running over IP, a

transport address is defined by the combination of an IP address and an SCTP port number (where SCTP is the Transport protocol).

Unacknowledged TSN (at an SCTP endpoint): A TSN (and the associated

DATA chunk) which has been received by the endpoint but for which an acknowledgement has not yet been sent Or in the opposite case, for a packet that has been sent but no acknowledgement has been received.

Unordered Message: Unordered messages are "unordered" with respect

to any other message, this includes both other unordered messages as well as other ordered messages Unordered message might be delivered prior to or later than ordered messages sent on the same stream.

User message: The unit of data delivery across the interface

between SCTP and its user.

Verification Tag: A 32 bit unsigned integer that is randomly

generated The Verification Tag provides a key that allows a receiver to verify that the SCTP packet belongs to the current association and is not an old or stale packet from a previous association.

Backhaul refers to the transport of signaling from the point of interface for the associated data stream (i.e., SG function in the MGU) back to the point of call processing (i.e., the MGCU), if this is not local.

Signaling Transport (SIG):

SIG refers to a protocol stack for transport of SCN signaling

protocols over an IP network It will support standard primitives to interface with an unmodified SCN signaling application being

transported, and supplements a standard IP transport protocol

underneath with functions designed to meet transport requirements for SCN signaling.

Switched Circuit Network (SCN):

The term SCN is used to refer to a network that carries traffic within channelized bearers of pre-defined sizes Examples include Public Switched Telephone Networks (PSTNs) and Public Land Mobile Networks (PLMNs) Examples of signaling protocols used in SCN include Q.931, SS7 MTP Level 3 and SS7 Application/User parts.

The following are terms for functional entities relating to signaling transport in a distributed gateway model.

Media Gateway (MG):

A MG terminates SCN media streams, packetizes the media data,, if it is not already packetized, and delivers packetized traffic to the packet network It performs these functions in reverse order for media streams flowing from the packet network to the SCN.

Media Gateway Controller (MGC):

An MGC handles the registration and management of resources at the MG The MGC may have the ability to authorize resource usage based on

local policy For signaling transport purposes, the MGC serves as a possible termination and origination point for SCN application protocols, such as SS7 ISDN User Part and Q.931/DSS1.

Signaling Gateway (SG):

An SG is a signaling agent that receives/sends SCN native signaling at the edge of the IP network The SG function may relay, translate or terminate SS7 signaling in an SS7-Internet Gateway The SG

function may also be co-resident with the MG function to process SCN signaling associated with line or trunk terminations controlled by the MG (e.g., signaling backhaul).

The following are terms for physical entities relating to signaling transport in a distributed gateway model:

Media Gateway Unit (MGU)

An MG-Unit is a physical entity that contains the MG function It may contain other functions, esp an SG function for handling facility-associated signaling.

Media Gateway Control Unit (MGCU)

An MGC-Unit is a physical entity containing the MGC function.

Signaling Gateway Unit (SGU)

An SG-Unit is a physical entity containing the SG function.

Signaling End Point (SEP):

This is a node in an SS7 network that originates or terminates signaling messages One example is a central office switch.

Signal Transfer Point (STP):

This is a node in an SS7 network that routes signaling messages based on their destination point code in the SS7 network.