SIP Explained Gary Audin Delphi, Inc. Sponsored by

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Speaker Background Communications and security consultant for 34 years Speaker at Enterprise Connect, ITExpo and 100s of user conferences Article and blog sites: o o o o o §3§3

Session Initiation Protocol A protocol is an information exchange procedure, a set of rules. SIP is a protocol to establish, manage, and terminate a connection (session) that is media independent. SIP is not specifically designed for digital voice. SIP operates over an IP network. §4§4

SIP Does This It locates the user and determines which end system will be used in the proposed session. It then learns the user's availability (is the user busy; can he/she be disturbed?). It determines the capabilities available at the user end system for the session such as what media is supported. It establishes the session. It manages the session, handling call termination, call transfer, changes to session parameters, and so forth. It is a peer-to-peer protocol running over UDP and TCP. §5§5

SIP Features User location can determine the end system to be used for communication User availability determines the willingness of the called endpoint to engage in communications User capabilities can determine the media and media parameters to be used Session setup endpoint ringing, establishment of session parameters at both called and calling endpoints Session management including session transfer and termination, changing session parameters, and invoking services §6§6

H.323 vs. SIP §7§7

What’s in a SIP Session “Session” = exchange of data between an association of participants Users can move among endpoints Users may have multiple names and addresses Users may communicate in different media SIP enables internet endpoints: o To discover each other o To characterize the session The location infrastructure supports name mapping and redirection services Endpoints can add/remove participants from session Endpoints can add/remove media from session §8§8

Not Part of SIP SIP is not a vertically integrated communications system. It is ONLY a component. SIP is independent of the services offered. o SIP provides mechanisms that can be used to implement different services. o SIP can locate a user and deliver content to the user’s current location. SIP does not offer conference control services nor prescribe how a conference is to be managed. §9§9

SIP Does Not SIP does not define the media carried (voice, video, IM, data, games, graphics, photos…) SIPPING 19 defines a minimum set of telephony features not SIP SIP trunks are not able to provide interoperability between different vendors’ IP PBXs § 10

SIP Components SIP is built upon a client/server architecture User Agents (SIP Phones, SIP PCs, other endpoints) Servers (Used to locate SIP users or to forward messages) SIP Gateways: To PSTN for telephony interworking To H.323 for IP Telephony interworking Client - originates message Server - responds to or forwards message § 11

Multimedia Protocol Stack § 12

SIP Applications SIP trunks SIP IP phones IP PBX-to-IP PBX trunks Computer Telephony Integration (CTI) connection; CSTA over SIP Alarms systems Pagers Doorphone Audio Alerter Callbox Multimedia Intercom Process control devices § 13

User Agent and Proxy Server Client/Server Interaction § 14

SIP Signaling Paths § 15

Browser A running HTML5 Browser M running HTML5 Peer-to-Peer (audio, video, data) Web Server Application SIP in WebRTC SIP Signaling SIP Signaling § 16

SIP User Agent, Server, and Location Service Interaction § 17

SIP Registration Example § 18

SIP Call Example, Proxy Server § 19

SIP Trunk Benefits Flexible provisioning Provider competition and enterprise leverage Eliminate VoIP gateways Reduced conferencing costs Low cost or free international calling On-Net free calling § 20

SIP Trunk Connections § 21 PSTN Legacy PBX VoIP Gateway SBC T1/E1/PRI Connections SIP Service Provider §IP PBX SBC

SIP Trunk Providers Can connect using vendor specific versions of SIP trunk software Standard SIP trunk connection is via SIPconnect (not a standard but an agreed upon recommendation from the SIP Forum SIPconnect version 1.1 is the latest one May limit the media carried: o Voice only o Video maybe o Secure connections maybe o Fax maybe o 911 and E911 information maybe § 22

Session Border Controllers A firewall rule set while also map layer 5 to layer 7 addresses Intrusion detection and prevention Denial-of-service (DoS) attack prevention VPN separation for shared resources SIP-Transport Layer Security (TLS) handshaking for authentication and encryption of SIP signaling Secure Real Time Protocol (RTP) support Support for IPsec tunnels Transcoding, or conversion between different VoIP codec technologies § 23

SIP Voice Bandwidth § 24 §Many providers recommend 20% extra for other overhead and control traffic

SIP Licenses for Trunking Needed for IP PBX and SBC Not required for provider trunks One license (session) can be one voice call or one video call Once purchased they are perpetual Cannot be reduced once purchased Some high end SBCs come with unlimited licenses Upper limit is usually hardware based Call establishment rate, calls/second usually not specified in licenses agreement § 25

Where Are the Problems? § 26 §“The SIP Survey 2012” by The SIP School, 2013 Survey Due In June

SIP Trunk Issues Firewall Problems: – Can block SIP packets – Cannot translate IP packet addresses TCP may be used instead of UDP One way audio Dropped connections Call transfer failure Registration failure § 27

State of SIP Relatively easy to implement Has gained considerable vendor and provider acceptance Allows flexible service creation Extensible and scalable Wide range of supporting products and services Does not make PSTN interworking easy Will not solve all IP Telephony issues such as QoS § 28

Resources Online education and certification IAUG Converge2013 sessions o “Sizing SIP Trunks” Tuesday, June 4,3:30 PM o “SIP Trunk Implementation Problems and Resolutions” Wednesday, June 5, 2 PM “Ten SIP Trunk Equipment License Issues That Can Ruin Your Day (or Month)” equipment-license-issues-that-can-ruin-your-day-or-month.htmlhttp:// equipment-license-issues-that-can-ruin-your-day-or-month.html “Avoiding SIP Trunking Equipment Problems” equipment-problems.html equipment-problems.html “How to avoid SIP Trunk Implementation Problems” implementation-problems-1.html implementation-problems-1.html “Easy SIP Trunking; No Yet”, § 29

FINI Gary Audin VN § 30