Evolution of Comm Networks For over 100 years

Evolution of Comm. Networks • For over 100 years, the POTS (Plain Old • Telephone System, a. k. a. PSTN) has been the • primary focus of conventional voice-band communications • POTS network is well designed and engineered • for the transmission and switching of 3 -Khz voice • – Real-time • – Low-latency • – High-reliability • – Moderate-fidelity

. Evolution of Comm. Networks (cont’d) • POTS network is not designed for other forms of communications (wide-band speech, audio, video, and data) • About 30 years ago, a second communications network was created with the goal of providing a better transport mechanism for data networking • The resulting network is called a packet network because data is transmitted and routed along the network in the form of units of information

. Evolution of Comm. Networks (cont’d) • Packet networks evolved independently of telephone networks for the purpose of moving bursty, non-realtime data among computers Packets consist of a header (info about source and destination addresses) and a payload (actual data being transmitted) Packet networks are especially well-suited for sending data of various types, including messages, facsimile, and still images. Packet networks are not well suited for sending • real-time communication signals such as speech, audio and video

. Congestion and Flow Control in Data networks • Congestion control • – Ensures that the subnet can carry the offered traffic • – Congestion happens when too many packets are present in (a part of) a subnet • Flow control: – Ensures that a fast sender does not continuously send data faster than the receiver can absorb it • Involves feedback from the receiver

. • • • Congestion and Flow Control (cont’d) Examples: – Fiber optic network at 1000 Gb/s on which a fast computer is trying to transfer a file to a PC at 1 Gb/s There is no congestion but flow control is required – Network with 1 Mb/s lines and 1000 computers, half of which are trying to transfer files at 100 Kb/s to the other half The total offered traffic exceeds what the network can handle (congestion)

Present Approaches in Data Broadcasting Over the Internet • IP Unicast - transmits data from a sender to a single receiver • IP Broadcast - transmits data from a sender to an entire subnetwork • IP Multicast - transmits data from a sender to a set of receivers that are members of a multicast group in various scattered subnetworks

Transmission Types • Unicast • Broadcast • Multicast

Unicast Transmissions Description One copy of each frame or packet is sent to each destination point Limitations Difficult to scale up multimedia applications for increased numbers of users If many users, traffic volume is high and requires high bandwidth

Unicast Transmissions

Broadcast Transmissions Description One copy of each frame or packet is sent to all points on a network, regardless of whether or not a node has requested it Limitations If not filtered by internetworking devices, multimedia broadcast traffic can produce even more load on a network than unicasts, because it potentially goes to more destinations

Broadcast Transmissions

Multicast Transmissions Description Server divides users who request certain applications into groups Each data stream of frames or packets is a one-time transmission that goes to multiple addresses Limitations More difficult to develop applications to use multicasting, but the payoff in improved network control and traffic patterns is well worth the effort

Multicast Transmissions

Protocols with Real-Time Streaming Multicasts • Real-Time Protocol (RTP) – Multicast protocol developed for real-time multimedia applications • Real-Time Transport Control Protocol (RTCP) – Works with RPT to provide specific controls over multicast transmissions – Provides management information

Applications and Internetworking Devices • Resources Reservation Protocol (RSVP) – Used on TCP/IP-based networks – Enables an application to reserve computer and network resources it needs (bandwidth, buffers, maximum burst, classes of service) – Dynamically allocates resources as demands increase or decrease – Also know as the Resource Reservation Setup Protocol

RSVP

Internet Protocol version 6 • New version of Internet Protocol • New features – Introduction of streams: Flow => Packet stream between sender and receiver – Larger address space: 128 bit – Improved multicast addressing – Priority – Security (authentication, integrity, and encryption) • Backward compatible to IPv 4 • Connectionless • No flow control • No error control

Multimedia Requirements • High bandwidth • Delay (critical for interactive applications) • Variation of delay (jitter) • Reliability • Commonly referred as quality-of-service (Qo. S) parameters • Low complexity codecs: Software only encoder/decoder • Multicasting: Bandwidth reduction • Support for heterogeneous system

Internet Protocol version 6 • Flow label: Multimedia flow can be identified • Special handling by the router • Soft state: Keep the state at the router until a time-out is reached

Migration to IPv 6 • Requires infrastructure changes • Internet providers work with small profit margins • IPv 4 is good enough • May take several years

User Datagram Protocol • Application interface to IP • Send datagrams without establishing connection • Eight byte header Source Port Destination Port UDP Length UDP Checksum

Real-Time Transport Protocol (RTP) • Transport protocol for multimedia streams over the Internet • Main functionality: Timing and synchronization • Used over UDP • Lightweight protocol – – No error correction No flow control No packet reordering No retransmission of lost packets • Does not support either resource reservation or Qo. S • Multicast capable • Associated control protocol: Real-Time Control Protocol (RTCP) – Measure connection parameters and send transmission records (participants can monitor the quality of the media flow) – Parameter negotiation

Real-Time Transport Protocol (RTP) • 12 byte header V P CC M Payload Type Sequence Number Timestamp Synchronization Source (SSRC) Identifier Contributing Source (CSRC) Identifier (Optional, up to 15 fields) V P CC M Version Number Padding On/Off CSRC Counter Mark

Real-Time Transport Protocol (RTP) • Timestamp: Intrastream and interstream synchronization • Synchronization Source (SSRC) Identifier: Random number generated by the source, unique identification of the stream • Contributing Source (CSRC) Identifier: If a router (mixer) combines media streams, the SSRC of contributing sources are recorded

Real-Time Transport Protocol (RTP) • Implemented as part of the application • Relatively new protocol • Used in vic and vat • Expected to be used in next generation WWW browsers

Resource Reservation Protocol • Earlier protocols – ST-II (Internet Stream Protocol): Parallel to IP – Tenet Protocol Suit (UC Berkeley) • Resource Reservation Protocol (RSVP) • To be used with IPv 6 (may also be used with IPv 4) • Reservations are made for flows (specified in IP header) • Based on the flow label, the router schedules transmission in accordance with the reservation setup • RSVP keeps soft states – Large amount of information – Must be refreshed within a given period

Resource Reservation Protocol • Receiver oriented: Each receiver may join or leave session • Each receiver decides based on its own characteristics and requirements => Heterogeneous reservation (multicast) • The path may change: Cannot provide hard Qo. S guarantees • Tunneling: Traffic may flow through routers that do not support RSVP => no guarantees can be given • Broken links are not handled

Now IP Qo. S Networking Integrated services • Defined by an IETF working group to be a keystone • IS was developed to optimize network and resource utilization which require Qo. S. • Divided traffic between into different Qo. S classes. • An internet router must be able to provide an appriopriate Qo. S for each flow. (according to a service model)