Internet Telephony: H.323 August 13, 2001 H.323 2 Overview H.323 - - PowerPoint PPT Presentation

▶
internet telephony h 323
SMART_READER_LITE
LIVE PREVIEW

Internet Telephony: H.323 August 13, 2001 H.323 2 Overview H.323 - - PowerPoint PPT Presentation

Sep 24, 2023 337 likes •667 views

H.323 1 Internet Telephony: H.323 August 13, 2001 H.323 2 Overview H.323 architecture elements: gatekeepers, terminals, ... H.323 call setup H.323 features comparison with SIP August 13, 2001 H.323 3 H.323 Components

slide-1
SLIDE 1

H.323 1

Internet Telephony: H.323

August 13, 2001

slide-2
SLIDE 2

H.323 2

Overview

  • H.323 architecture
  • elements: gatekeepers, terminals, ...
  • H.323 call setup
  • H.323 features
  • comparison with SIP

August 13, 2001

slide-3
SLIDE 3

H.323 3

H.323 Components

H.323: overall architecture = H.225.0: call control, RAS to gatekeeper: “may I?”, user location; RTP/RTCP H.235: security for H.323 terminals H.245: capabilities exchange, indications, notifications H.246: interoperability with PSTN H.332: large group conferences H.450: supplementary services H.246: interworking between H.323 and other H.xxx standards Q.931: call setup = ISDN, similar to Q.2931 (ATM) Q.932: supplementary services

August 13, 2001

slide-4
SLIDE 4

H.323 4

H.323

  • derived from H.320 (ISDN multimedia)
  • mostly ASN.1 (PER) based
  • signaling TCP-based, except for H.323v4

August 13, 2001

slide-5
SLIDE 5

H.323 5

H.323 Components

G.711: 64 kb/s µ/A-law audio G.723: 5.6 or 6.3 kb/s audio G.729: 8 kb/s audio H.261, H.263: conference video coding

  • ITU SG-16
  • version 2 in use (Feb. 1998), version 3 (Sep. 1999)

August 13, 2001

slide-6
SLIDE 6

H.323 6

H.323 Zones

R R Σ GK T3 T2 T1 MCU

zone

GW

August 13, 2001

slide-7
SLIDE 7

H.323 7

H.323 Elements

H.323 Terminal : PC with H.323 soft- ware MCU: multipoint control unit ➠ mixes audio and video MC: multipoint controller ➠ performs signaling for centralized confer- ences MP: multipoint process ➠ actual de- vice for mixing gatekeeper: session control: ad- dress translation, admission control, bandwidth control, zone management gateway: interface between H.323 systems and

  • ther

systems: PSTN, H.323 (PSTN mm), H.320 (ISDN), H.321 (ATM mm)

August 13, 2001

slide-8
SLIDE 8

H.323 8

H.323 gatekeeper

  • controls sessions
  • performs user location and registration
  • admission control
  • reroutes signaling
  • processes RAS (registration, admission, status) from H.323 terminals

August 13, 2001

slide-9
SLIDE 9

H.323 9

Gatekeeper Discovery

endpoint gatekeeper GCF GRJ GRQ

August 13, 2001

slide-10
SLIDE 10

H.323 10

Registration with Gatekeeper

RRQ UCF URJ URQ RCF RRJ URQ UCF

gatekeeper-initiated unregister request endpoint-initiated unregistration registration

August 13, 2001

slide-11
SLIDE 11

H.323 11

H.323 Phases

Initialization: register with GK GK admission: obtain permission; GK resolves address Call signaling: signaling connection to peer call initiation and completion/rejection Negotiation/configuration: negotiate roles during call capability exchange; determine mode of operation Media exchange: configure and open logical channels transmit and receive data streams Re-negotiation: change members, parameters, media, ... Shutdown: terminate the call/conference; deregister user on log-off

August 13, 2001

slide-12
SLIDE 12

H.323 12

H.323 Channels

RAS: endpoint – gatekeeper: H.225.0 (UDP) Call signaling: call control & supplementary services; ≈ Q.931 (TCP; v3: also UDP) H.245 control: media control, capability exchange; open “logical channels” (TCP) Logical channel: carry audio, video, media (UDP)

August 13, 2001

slide-13
SLIDE 13

H.323 13

H.323v1 call setup (w/o fastStart)

RAS H.225 Connect Capabilities/Master-Slave Capabilities/MS-ack/cap-ack cap-ack/ms-ack/open-audio

  • pen ack/open audio
  • pen ack

audio H.245 SYN

caller gatekeeper callee

port 1720, 1300 H.225 Setup TCP SYN ACK ACK H.245 SYN ACK ACK H.225 TCP SYN dynamic port 2 dynamic ports

August 13, 2001

slide-14
SLIDE 14

H.323 14

Gatekeeper-routed Signaling

gatekeeper cloud endpoint 1

1 8 3 2

endpoint 2

4 5 6 7 ACF/ARJ ARQ ARQ ACF/ARJ setup connect connect setup

August 13, 2001

slide-15
SLIDE 15

H.323 15

Both Endpoints Registered – GK Routed

Setup ARQ ACF ARQ ARJ Setup Setup Setup ARQ ACF/ARJ

endpoint 1 gatekeeper 1 gatekeeper 2 endpoint 2

Connect Connect Connect Alerting Alerting Alerting Call Proceeding Call Proceeding Call Proceeding Call Proceeding Facility Release Complete

August 13, 2001

slide-16
SLIDE 16

H.323 16

H.323v3 call setup

caller callee port 1720, 1300 2 dynamic ports RAS gatekeeper audio

SETUP CALL PROCEEDING CONNECT ALERTING

August 13, 2001

slide-17
SLIDE 17

H.323 17

H.323 call holding: near & remote-end

near-end hold remote-end hold local MOH

served user A held user A FACILITY (holdNotific.inv) music on hold (MOH) FACILITY(remoteHold.inv) FACILITY(remoteHold.rr)

August 13, 2001

slide-18
SLIDE 18

H.323 18

H.323 call diversion

(caller) (final destination) Served B (original destination) Diverted-to C

ACF ARQ SETUP SETUP CALL PROCEEDING ALERTING CONNECT(...) ALERTING FACILITY(CallRerouting.invoke) RELEASE COMPLETE FACILITY(CallRerouting.ReturnResult) SETUP(diverting.LegInfo2.inv) (diverting.LegInfo2.inv) CONNECT(diverting.LegInfo3.inv) FACILITY

GK (rerouting) Originator A

August 13, 2001

slide-19
SLIDE 19

H.323 19

H.323 blind call transfer

RELEASE COMPLETE RELEASE COMPLETE.ctResult CALL PROCEEDING SETUP.ctTransfer=cid FACILITY.ctInvoke CONNECT SETUP ALERTING CONNECT transferring party transfer destination transferred party

August 13, 2001

slide-20
SLIDE 20

H.323 20

H.323 problems

  • very complex (200+ pages; 65 pages for call forwarding!)
  • no multicast signaling
  • limited multicast conferences (➠ MCUs)
  • call = TCP connection ↔ mobility, reliability
  • but: better capability negotiation (H.245)
  • no media servers
  • agile ports ➠ firewalls difficult

August 13, 2001

slide-21
SLIDE 21

H.323 21

H.323 delay

  • several TCP connections ➠ very long latency (6.5-8 RTTs)
  • 1 TCP SYN loss ➠ delay of 6 seconds
  • 2 TCP SYN losses ➠ delay of 24 seconds

➠ H.323v2 for fewer connections, UDP?

August 13, 2001

slide-22
SLIDE 22

H.323 22

SIP – H.323 comparison

H.323 SIP Architecture stack element Conference control yes no Protocol mostly TCP mostly UDP Encoding ASN.1, Q.931 HTTPish Emphasis telephony multimedia, multicast Address flat alias, E.164 SIP, E.164 URLs Both SIP and H.323 are evolving: SIP additions, H.323v2 implemented, v3 to be decided.

August 13, 2001

slide-23
SLIDE 23

H.323 23

SIP – H.323 comparison

  • I. Dalgic and H. Fang, “Comparison of H.323 and SIP for IP Telephony

Signaling”, Proc. of Photonics East, Boston, Massachusetts. Sept. 1999.

  • H. Schulzrinne and J. Rosenberg, “A Comparison of SIP and H.323 for

Internet Telephony”, NOSSDAV, Cambridge, England. July 1998.

August 13, 2001

slide-24
SLIDE 24

H.323 24

H.323 Resource Reservation

  • local admission decision
  • prior to call setup −

→ no information about bandwidth available

  • works only for “yellow cable Ethernet”
  • other applications have to notify GK
  • SIP: RSVP, YESSIR, DiffServ + call preconditions

August 13, 2001

slide-25
SLIDE 25

H.323 25

SIP vs. H.323 call setup

H.323v1: several TCP connections (H.245, Q.931) − → very long latency (6.5-8 RTTs), particularly with packet loss; currently in NetMeeting H.323v2: merge H.245 and Q.931 (“FastConnect”) H.323v3: allow UDP End systems need to support all versions.

August 13, 2001

slide-26
SLIDE 26

H.323 26

H.323 vs. SIP: basic call control

(modified from Dalgic and Fang, Comparison of H.323 and SIP) Service H.323v1 v2 v3 SIP Call holding no yes yes yes Call transfer no yes yes yes Call forwarding no yes yes yes Call waiting no yes yes yes

August 13, 2001

slide-27
SLIDE 27

H.323 27

H.323 vs. SIP: advanced features

Service H.323v1 v2 v3 SIP Third party control no no no yes Conference yes yes yes yes Click-to-dial ? ? ? PINT Capability exchange better better better yes HTML transport no no no yes

August 13, 2001

slide-28
SLIDE 28

H.323 28

H.323 vs. SIP: services

Service H.323 SIP Call transfer H.450.2 “30x” Call diversion H.450.3 “30x” Call hold H.450.4 SDP-based Call park H.450.5 REGISTER Call waiting H.450.6 INVITE Message waiting H.450.7 email, NOTIFY Call forward busy H.450.9 “30x”

August 13, 2001

slide-29
SLIDE 29

H.323 29

H.323 vs. SIP: quality of service

H.323v1 v2 v3 SIP Call setup delay 6-7 RTT 3-4 1.5-2.5 1.5 Loss recovery TCP TCP better better Fault detection yes yes yes yes Mid-call failure fail fail fail live Registrar failure fail fail backup multicast GK/Proxy redundancy no no backup SLP, DNS, DHCP Loop detection no no PathValue Via, hops, time

August 13, 2001

slide-30
SLIDE 30

H.323 30

H.323 vs. SIP: manageability

H.323v1 v2 v3 SIP Admission control yes yes yes no (RSVP) Policy control yes yes yes

  • b proxy

Resource reservation local local local no (RSVP)

August 13, 2001

slide-31
SLIDE 31

H.323 31

H.323 vs. SIP: scalability

H.323v1 v2 v3 SIP Complexity more more more+ less Server processing SF SF SF/SL, TSF SL, TSF/TSL Inter-server no no yes yes TS: transaction state; SF: call statefull; SL: call stateless

August 13, 2001

slide-32
SLIDE 32

H.323 32

H.323 vs. SIP: flexibility

H.323v1 v2 v3 SIP Transport protocols TCP TCP TCP/UDP any Extensibility unlabeled vendor extensions IANA, labeled Customization harder easier Version compatibility N/A yes yes N/A SCN interoperability good good good TBD protocol encoding binary (ASN.1, Q.931) text

August 13, 2001