Media Gateway Control and the Softswitch Architecture Chapter

Media Gateway Control and the Softswitch Architecture Chapter 6

Introduction n Voice over IP n n n Lower cost of network implementation Integration of voice and data applications New service features Reduced bandwidth Replacing all traditional circuit-switched networks is not feasible. Vo. IP and circuit-switching networks coexist n n Interoperation Seamless interworking Internet Telephony 2

Separation of Media and Call Control n Gateways n n n Signaling path and media path are different in Vo. IP systems. n n n Interworking To make the Vo. IP network appear to the circuit switched network as a native circuit-switched system and vice versa Media – directly (end-to-end) Signaling – through H. 323 gatekeepers (or SIP proxies) SS 7, Signaling System 7 n The logical separation of signaling and media Internet Telephony 3

Separation of Media and Call Control n A network gateway has two related but separate functions. n Signaling conversion n n Media conversion n n The call-control entities use signaling to communicate. A slave function (mastered by call-control entities) Figure 6 -1 illustrates the separation of call control and signaling from the media path. Internet Telephony 4

Separation of Media and Call Control n Advantages of Separation n n MGCP, Media Gateway Control Protocol n n Media conversion close to the traffic source and sink The call-handling functions is centralized. A call agent (media gateway controller - MGC) can control multiple gateways. New features can be added more quickly. IETF MEGACO/H. 248 n IETF and ITU-T Study Group 16 Internet Telephony 5

Softswitch Architecture [1/2] Internet Telephony 6

Softswitch Architecture [2/2] SS 7 Network SCP Signaling (SS 7) Gateway Internet SIGTRAN STP MGCP/ MEGACO CO Switch Trunking Gateway Call Agent RTP MGCP/ MEGACO Residential Gateway Internet Telephony 7

Softswitch n n The switching functions are handled by software International Softswitch Consortium (ISC) n n n www. softswitch. org To promote the softswitch concept and related technologies Why the softswitch approach is popular? n n A distributed architecture For network operators n n It is possible to use different network components from different vendors. For equipment vendors n It is possible to focus on one area. Internet Telephony 8

Softswitch/PSTN Interworking n SIP is often used as the signaling protocol between the MGCs. Internet Telephony 9

Requirements for Media Gateway Control [1/2] n RFC 2895 n n Media Gateway Control Protocol Architecture and Requirements Requirement n The creation, modification and deletion of media streams n n n Including the capability to negotiate the media formats The specification of the transformations applied to media streams Request the MG to report the occurrence of specified events within the media streams, and the corresponding actions Internet Telephony 10

Requirements for Media Gateway Control [2/2] n n Request the MG to apply tones or announcements The establishment of media streams according to certain Qo. S requirements Reporting Qo. S and billing/accounting statistics from an MG to an MGC The management of associations between an MG and an MGC n n n In the case of failure of a primary MGC A flexible and scalable architecture in which an MGC can control different MGs Facilitate the independent upgrade of MGs and MGCs Internet Telephony 11

Protocols for Media Gateway Control n The first protocol is MGCP n n RFC 2705, informational To be succeeded by MEGACO/H. 248 Has be included in several product developments MEGACO/H. 248 n n A standards-track protocol RFC 3015 is now the official version. Internet Telephony 12

Relation with H. 323 Standards SS 7/ISUP Signaling (SS 7) Gateway Internet SIGTRAN Gatekeeper H. 225/RAS H. 225/Q 931 H. 245 Call Agent CO Switch Terminal or Gateway MGCP Trunking Gateway RTP Internet Telephony 13

H 323, SIP & MGCP, MEGACO SS 7 PSTN CA SG MGCP GK GW TN PSTN CO TGW RGW H. 323 MCU GW GK TN MCU TN : Gateway : Gatekeeper : Terminal : Multipoint Control Unit RTP TN CA TGW RGW SG : Call Agent : Trunking Gateway : Residential Gateway : Singling Gateway Internet Telephony 14

H 323, SIP & MGCP/MEGACO n H. 323 , SIP n n n peer-to-peer internet oriented intelligent endpoint n n n n maintenance n n “dumb” terminal centralized Concept n cost & scalability of large systems signaling & media control are coupled interoperability with SS 7 client-server traditional telephony intelligent server n decentralized n MGCP/MEGACO optional GK Problems n n gateway decomposed n n n separate call control from media ports CA, MG, SG interoperability with PSTN Internet Telephony 15

MGCP Connection Establishment Internet Telephony 16

MGCP n A master-slave protocol n Call agents (MGCs) control the operation of MGs n n n Do what the CA instructs A line or trunk on circuit-switched side to an RTP port on the IP side Types of Media Gateway n n Call-control intelligence Related call signaling Trunking Gateway to CO/Switches Residential Gateway to PSTN Phones Access Gateway Communication between call agents n Likely to be the SIP Internet Telephony 17

The MGCP Model n Endpoints n n n Sources or sinks of media Trunk interfaces POTS line interfaces Announcement endpoint Connections n n n Allocation of IP resources to an endpoint An ad hoc relationship is established from a circuited-switched line and an RTP port on the IP side. A single endpoint can have several connections Internet Telephony 18

MGCP Endpoints [1/3] n DS 0 channel n n A digital channel operates at 64 kbps. Multiplexed within a larger transmission facility such as DS 1 (1. 544 Mbps) or E 1 (2. 048 Mbps) G. 711 (u-law or A-law) Analog line n n n To a standard telephone line An analog voice stream Could also be audio-encoded data from a modem n The gateway shall be required to extract the data and forward it as IP packets. Internet Telephony 19

MGCP Endpoints [2/3] n Announcement server access point n n Provide access to a single announcement One-way n n Interactive voice response (IVR) access point n n Provide access to an IVR system Conference bridge access point n n No external circuit-switched channels Media streams from multiple callers can be mixed Packet relay n A firewall between an open and a protected networks Internet Telephony 20

MGCP Endpoints [3/3] n Wiretap access point n n n For listening to the media transmitted One way ATM trunk-side interface n n The termination of an ATM trunk May be an ATM virtual circuit Internet Telephony 21

Endpoint Identifier n n GW’s Domain Name + Local Name n n trunk 4/12/7@gateway. somenetwork. net n n A hierarchical form: X/Y/Z To identify DS 0 number 7 within DS 1 number 12 on DS 3 number 4 at gateway. somenetwork. net Wild-cards n n $, any; *, all e. g. , trunk 1/5/$@gateway. somenetwork. net n n CA wants to create a connection on an endpoint in a gateway and does not really care which endpoint is used. e. g. , trunk 1/5/*@gateway. somenetwork. net n CA requests statistical information related to all endpoints on a gateway. Internet Telephony 22

MGCP Calls and Connections n A connection n n A call n n Relationship established between a given endpoint and an RTP/IP session A group of connections The primary function of MGCP is to enable n n The connections to be created The session descriptions to be exchanged between the connections 23

MGCP Commands n 9 commands to handle Connection/Endpoints EPCF RQNT NTFY CRCX MDCX DLCX AUEP AUCX RSIP n n n n n Endpoint. Configuration (coding characteristics) Notification. Request (requested events) Notify (GW: detected events) Create. Connection Modify. Connection Delete. Connection Audit. Endpoint Audit. Connection Restart. In. Progress (GW : taken in/out of service) All commands are acknowledged. Internet Telephony 24

MGCP Command Format n A command line n n n A number of parameter lines An optional session description (SDP) n n Request verb (the name of the command) Transaction id Endpoint id (for which the command applies) Protocol version Separated by a single empty line Command Encapsulation n One command can be included within another Only one level of encapsulation E. g. , when instructing a gateway to create a connection, CA can simultaneously instruct the gateway to notify the CA of certain events. Internet Telephony 25

MGCP Parameters [1/6] n Bear. Information (B) n n n Call. Id (C) n n In response to an audit Connection. Id (I) n n Comprised of hexadecimal digits Capabilities (A) n n The line-side encoding B: e: mu Comprised of hexadecimal digits Connection. Mode (M) n Send only, receive only and send-receive Internet Telephony 26

MGCP Parameters [2/6] n Connection. Parameters (P) n n Detect. Events (T) n n n That an endpoint should detect during quarantine period E. g. , off-hook, on-hook, hook-flash, DTMF digits… Local. Connection. Descripter (LC) n n Connection-related statistical information Average latency, jitter, packets sent/received/lost GW -> CA An SDP session description Local. Connection. Options (L) n n Bandwidth, packetization period, silence suppression, gain control, echo cancellation… L: e: off, s: on n To turn echo cancellation off and to turn silence suppression on Internet Telephony 27

MGCP Parameters [3/6] n Event. States (ES) n n n Max. MGCPDatagram (MD) n n n An address for the CA Observed. Events (O) n n To indicate the maximum size MGCP packet supported by an MG Included in the response to an AUEP command Notified. Entity (N) n n In response to an audit command A list of events associated with the current state Detected by an endpoint Package. List (PL) n n Supported by an endpoint Events and signals are grouped into packages n Analog line endpoint Internet Telephony 28

MGCP Packages n n n Group events and signals into packages Generic Media (G) Gateway Supported packages DTMF (D) Trunk GW (ISUP) G, D, T, R Trunk GW (MF) G, M, D, T, R MF (M) Network Access Server G, M, T, N Trunk (T) Combined NAS/VOIP GW G, M, D, T, N, R Access GW (VOIP) G, M, D, R Line (L) Access GW (VOIP + NAS) G, M, D, N, R Residential GW G, D, L, R Handset (H) Announcement GW A, R RTP (R) Network Access Server (N) Announcement Server (A) The experimental packages have names beginning with the two character “x-”. Internet Telephony 29

MGCP Parameters [4/6] n Quarantine. Handling (Q) n n n Reason. Code (E) n n When a GW deletes/restarts a connection Remote. Connection. Descripter (RC) n n Events that occur during the period in which the GW is waiting for a response to a Notify command Process the events or discard them An SDP session description Request. Events (R) n n n A list of events that an endpoint is to watch for Associated with each event, the endpoint can be instructed to perform actions E. g. , collect digits, or apply a signal Internet Telephony 30

MGCP Parameters [5/6] n Request. Info (F) n n n Request. Identifier (X) n n To correlate a given notification from a GW Restart. Delay (RD) n n In response to audit requests The current values of Request. Events, Digit. Map, Notified. Entity A number of seconds indicating when an endpoint will be brought back into service Restart. Method (RM) n Graceful or Forced Internet Telephony 31

MGCP Parameters [6/6] n Second. Connection. Id (I 2) n n Specific. Endpoint. ID (Z) n n A connection between two endpoints on the same GW Signal. Requests (S) n n A response to a command using a wild card Second. Endpoint. ID (Z 2) n n The connection on a second endpoint Signals to be applied by an endpoint Specific. Endpoint. ID (Z) n Used to indicate a single endpoint Internet Telephony 32

Digit Map n CA ask GW to collect user dialed digits n n Created by CA Usage n Gateways detect a set of digits. n n Inter-digit Timer e. g. , (11 x|080 xxxxxx|03 xxxxxxx|002 x. T) Match accumulated digits n n n under-qualified, do nothing further matched, send the collected digits to CA over-qualified, send the digits to CA Internet Telephony 33

MGCP Response n Header n n n A response line Return code + Trans. ID + Commentary A set of parameter lines (optional) n n E. g. , I: A 3 C 47 F 21456789 F 0 (Connection. Id) Session Description n n Session Description Protocol separated from header by an empty line Internet Telephony 34

Call Setup Using MGCP Internet Telephony 35

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Call Flow for RGW to TGW Internet Telephony 37

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Call Flow for RGW to TGW n RQNT(1) : Notification. Request n n n RQNT 1201 hrd 3/15@rgw. whatever. net MGCP 1. 0 N: CA@ca. whatever. net: 5678 N: Notify. Entity X: 0123456789 AC X: Request. Identifier R: hd(E(R(hu(N)), S(dl), D/(D))) R: Request. Events D: (11 x|080 xxxxxx|57 xxxxx|002 x. T) D: Digit. Map ACK to RQNT(1) n 200 1201 OK E: Embedded Request R: Notification Request N: Notify immediately S: Signal Request D: Digit Map Internet Telephony 40

Call Flow for RGW to TGW n NTFY(2) : Notify from RGW n n n NTFY 2002 hrd 3/15@rgw. whatever. net MGCP 1. 0 N: CA@ca. whatever. net: 5678 X: 0123456789 AC N: Notify. Entity O: 5721043 X: Request. Identifier ACK to NTFY(2) n O: Observed. Event 2002 OK Internet Telephony 41

Call Flow for RGW to TGW n CRCX(3) : Create. Connection n n n CRCX 1204 hrd 3/15@rgw. whatever. net MGCP 1. 0 C: A 3 C 47 F 21456789 F 0 L: p: 10, a: G. 711; G. 726 -32 M: recvonly C: Call. Id X: 0123456789 AD L: Local. CXOptions R: hu ACK to CRCX(3) n n n 200 1204 OK I: FDE 234 C 8 Session Description p: packetize period(ms) a: Compression Algo. M: Mode X: Request. Identifier R: Request. Events I: Connection. Id Internet Telephony 42

Call Flow for RGW to TGW n ACK to CRCX(3) Session Description n n v=0 c=IN IP 4 140. 96. 102. 166 m=audio 3456 RTP/AVP 0 96 a=rtpmap: 96 G 726 -32/8000 G 726~G 732 encoded audio sample at 8 k. HZ v: protocol version c: connection information m: media name and transport address a: more media attribute line Internet Telephony 43

Call Flow for RGW to TGW n CRCX(4) : Create. Connection n CRCX 1205 card 6/5@tgw. whatever. net MGCP 1. 0 C: A 3 C 47 F 21456789 F 0 L: p: 10, a: G. 711; G. 726 -32 M: sendrecv n Session Description from ACK(3) n n ACK to CRCX(4) n 200 1205 OK I: 32 F 345 E 2 n Session Description n C: Call. Id M: Mode I: Connection. Id Internet Telephony 44

Call Flow for RGW to TGW n MDCX(5) : Modify. Connection n MDCX 1206 hrd 3/15@rgw. whatever. net MGCP 1. 0 C: A 3 C 47 F 21456789 F 0 C: Call. Id I: FDE 234 C 8 I: Connection. Id M: recvonly n Session Description from ACK(4) n n M: Mode ACK to MDCX(5) n 200 1206 OK Internet Telephony 45

Call Flow for RGW to TGW n RQNT(6) : Notification. Request n n n RQNT 1207 hrd 3/15@rgw. whatever. net MGCP 1. 0 N: CA@ca. whatever. net: 5678 X: 012345789 AE N: Notify. Entity R: hu X: Request. Identifier S: v (alerting) ACK to RQNT(6) n 200 1207 OK R: Request. Events S: Signal. Requests Internet Telephony 46

Call Flow for RGW to TGW n MDCX(7) : Modify. Connection n n n MDCX 1209 hrd 3/15@rgw. whatever. net MGCP 1. 0 C: A 3 C 47 F 21456789 F 0 C: Call. Id I: FDE 234 C 8 I: Connection. Id M: sendrecv M: Mode X: 012345789 AF R: hu ACK to MDCX(7) n 200 1209 OK Internet Telephony 47

Call Flow for RGW to TGW n DLCX(8) : Delete. Connection n n DLCX 1210 hrd 3/15@rgw. whatever. net MGCP 1. 0 C: A 3 C 47 F 21456789 F 0 C: Call. Id I: FDE 234 C 8 I: Connection. Id ACK to DLCX(8) n n 200 1210 OK P: PS=1245, OS=62345, PR=780, OR=45123, PL=10, JI=27, LA=48 PS: OS: PR: OR: PL: JI: LA: Packets sent Octets sent Packets received Octets received Packets lost Average Jitter (ms) Average Latency (ms) Internet Telephony 48

Usage of Commands n Notification. Request() n n n n n Request Notify Request Endpoint. Id, [Notified. Entity, ] Time [Requested. Events, ] Quarantine Period Q Request. Identifier, T Q: process/discard [Digit. Map, ] step/loop (notify) [Signal. Requests, ] T: events to detect [Quarantine. Handling, ] during quarantine [Detect. Events, ] [encapsulated Endpoint. Configuration] Internet Telephony 49

Usage of Commands n Create. Connection() n n n n Call. Id, Endpoint. Id, [Notified. Entity, ] [Local. Connection. Option, ] Hairpin Connection Mode, [{Remote. Connect. Descriptor|Second. Endpoint. Id}] [Encapsulated Notification. Request, ] [Encapsulated Endpoint. Configuration] Internet Telephony 50

Usage of Commands n Delete. Connection() n Delete one connection from Call Agent n n n Multiple connections from Call agent n n n Connection. Id in the parameter line GW responds with Connection parameters Only Endpont. Id (and Call. Id) in the parameter line GW does not respond with Connection parameters From gateway n Reason-Code & Connection-Parameters in Command Internet Telephony 51

Usage of Commands n Restart. In. Progress() n n n End. Point. Id Restart. Method [Restart. Delay] [Reason-code] Return. Code n [Notified. Entity] Restart. Method • Forced • Restart • Disconnected • Graceful Internet Telephony 52

Usage of Commands n Audit. End. Point() n n n Endpoint. Id [Requested. Info] Return. Code n End. Point. Id. List {Requested. Events Digit. Map Signal. Requests Request. Identifier, … } If Endpoint. Id is “wildcard”, End. Point. Id. List is returned Internet Telephony 53

Usage of Commands n Audit. Connection() n n n Connection. Id Requested. Info Return. Code n n n “Wildcard” shall not be used Call. Id Notified. Entity Local. Connection. Options … Internet Telephony 54

Interworking between MGCP and SIP Internet Telephony 55

Interworking between MGCP and SIP Internet Telephony 56