RSVP Myungchul Kim firstname.lastname@example.org
From Ch 12 of book “IPng and the TCP/IP protocols” by Stephen A. Thomas, 1996, John Wiley & Sons. • Resource Reservation Protocol (RSVP) • RSVP operation • Flows • RSVP identifies a flows by its destination IP address and a source IP address. • RSVP does not understand the flowspec. • RSVP supports both unicast and multicast flows.
Reservation • receiver-initiated reservations. • easily support a dynamic environment: join, drop out. • how does a receiver know to make a reservation in the first place?
Path messages • make sure that resources are reserved along the correct path. • generated by a flow’s sender. • travel in the same direction as the flow itself. • at each hop, the router inserts its own IP address as the message’s last hop.
Reservation styles • shared explicit reservation: an application must explicitly identify every participating sender. • wildcard filter: an application shares a resource without identifying every sender.
RSVP and dynamic networks • a soft state because both its paths and its reservations are always considered tentative.
RSVP message formats • in the payload of IP datagrams • type: Table 12.2 • fragmentation: message ID, fragment offset and more fragments bits.
RSVP and INTSERV • RSVP: a signaling protocol, configure traffic handling mechanisms in network devices. • Integrated Services: a framework for providing end-to-end services in the context of RSVP • Integrated Services over Specific Link Layers (issll) : define the underlying traffic handling mechanisms that would offer QoS support on different media.
problems of RSVP and INTSERV • RSVP were available only on certain UNIX. • implemented on every network devices -> not scalable • no policy mechanisms in a secure manner. • not on the non-multimedia mission-critical applications. • valuable components because • RSVP in Windows 2000 • scalability <- disassociating RSVP from per-flow traffic handling • policy component • non-multimedia applications
VoIP (SIP, H.323) Myungchul Kim email@example.com
The Session Initiation Protocol: Internet-Centric Signaling • Henning Schulzrinne and Jonathan Rosenberg, The Session Initiation Protocols, IEEE Comm., pp. 134-141, Oct. 2000. • SIP • Signaling protocol: RFC 2543 (March 1999) • Initiates, modifies, and terminates network sessions • Services such as VoIP including instant messaging, event notification, distributed games • Does not reserve resources or establish circuits in the network • RTP, RTSP(streaming), Media Gateway Control Protocol, Megaco (H.248), Session Description Protocol, Session Announcement Protocol, Telephony Routing over IP (TRIP) • Anything addressable by a host name can participate in a SIP session • Discovery of a user: personal mobility • Could be though of as an application-layer anycast • Ability to have users and administrators program services • www.cs.columbia.edu/sip
Architecture: user agent, registrars, proxy, and redirect servers. • Signaling • URI • Figure (next slide) • The path of the signaling messages may be completely different from that of the media exchanged between caller and callee. • UDP • SDP: a description format (what media streams it wants to receive and its receive capabilities) • SIP message format: textual encoding • 838 –1240 bytes of SIP messages to set up a call (800 bytes for H.323) • Forking • A server can send out two or more requests to different destination • Call forwarding to voice mail, automatic call distribution, and user location
Reliability • UDP • Clients retransmit INVITE requests until a provisional response arrives, and servers retransmit responses until confirmed by an ACK request. • Security • SIP inherits the basic and digest authentication mechanisms from HTTP • Expressing Caller Preferences • Users register their terminal characteristics with the local proxy • Page 138, middle of the right column
Quality of Service • Using SIP to directly set up resource reservations is not appropriate • SIP can be used to negotiate the use of QoS mechanisms • COMET
Mobility • Precall terminal mobility • Mid-call mobility • SIP and MGCP/MEGACO
VoIP over IP Signaling: H.323 and Beyond • Hong Liu and Petros Mouchtaris, Voice over IP Signaling, pp. 142-148, Oct. 2000. • Introduction • Precommercial (1980-1995), PC-centric (1995-1998), and carrier grade (1998 on) • Previous limitation • A gateway handles signaling conversion, call control, and media transcoding • No provision for SS& connectivity • Call control: media gateway controller • Media transformation: media gateway • Media Gateway Control Protocol (MGCP) • H.248 or Megaco, in June 2000
H.323 Overview Architecture • Terminal • Gatekeeper: address translation, access control, bandwidth management, and locating GW • Gateway • Multipoint control unit: multipoint conference
Signaling and control • Registration Admission and Status (RAS) • Q.931 • H.245: for connection control to negotiate media processing control and used to exchange terminal capability • RTP
H.323 Interworking with the PSTN • H.323 TE to phone; phone to H.323 TE; and phone to phone via intermediate H.323 networks • GW • PSTN interface • VoIP interface • Signaling conversion • Media transformation • Connection management
Limitations of H.323 • Scalability: a few thousand • ISDN trunks instead of SS7 connectivity • Availability: no mechanism for failover • User friendliness: two-stage dialing • Separating the signaling and media transformation functions would allow for more scalable GWs. • Functional decomposition of H.323 GW
Improvement of H.323 • Scalability • SS7 connectivity • Availability • One-stage dialing • H.323 and SIP • SIP is much more light weight • Call agents or soft switches that support H.323, SIP and MGCP.