Tag Archives: 1.1f

1.1.f Explain UDP operations

1.1.f [iii] RTP/RTCP concepts

Real-time Transport Control Protocol (RTCP) is a sister protocol of the Real -time Transport Protocol (RTP). RTCP provides out-of-band control information for an RTP flow. It partners RTP in the delivery and packaging of multimedia data, but does not transport any data itself. It is used periodically to transmit control packets to participants in a streaming multimedia session. The primary function of RTCP is to provide feedback on the quality of service being provided by RTP.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 1179-1180).  . Kindle Edition.

 

1.1.f Explain UDP operations

1.1.f [ii] Latency

UDP is faster (lower latency, better use of network pipe) than TCP (with the exception of applications that only confine to small writes). UDP is preferred if you’re transmitting some sort of real time data or just blasting packets over the network that don’t need reliable delivery.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 1174-1175).  . Kindle Edition.

 

1.1.f Explain UDP operations

1.1.f [i] Starvation

When TCP flows are combined with UDP flows within a single class and the class experiences congestion, TCP flows continually lower their transmission rates due to congestion control, potentially giving up their bandwidth to UDP flows that are oblivious to drops. This effect is called TCP starvation or UDP dominance.

Even if WRED is enabled on the class, the same behavior would be observed because WRED (for the most part) manages congestion only on TCP-based flows.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 1169-1172).  . Kindle Edition.

http://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND/QoS-SRND-Book/VPNQoS.html

 

1.1.f Explain UDP operations

1.1.f [ii] Latency

from rfc 1242 http://www.rfc-editor.org/rfc/rfc1242.txt
3.8   Latency

        Definition:
                For store and forward devices:
                The time interval starting when the last bit of the
                input frame reaches the input port and ending when
                the first bit of the output frame is seen on the
                output port.

                For bit forwarding devices:
                The time interval starting when the end of the first
                bit of the input frame reaches the input port and
                ending when the start of the first bit of the output
                frame is seen on the output port.

        Discussion:
                Variability of latency can be a problem.
                Some protocols are timing dependent (e.g., LAT and IPX).
                Future applications are likely to be sensitive to

Benchmarking Methodology Working Group                          [Page 5]

RFC 1242                Benchmarking Terminology               July 1991

                network latency.  Increased device delay can reduce
                the useful diameter of net.  It is desired to
                eliminate the effect of the data rate on the latency
                measurement.  This measurement should only reflect the
                actual within device latency.  Measurements should be
                taken for a spectrum of frame sizes without changing
                the device setup.

                Ideally, the measurements for all devices would be from
                the first actual bit of the frame after the preamble.
                Theoretically a vendor could design a device that
                normally would be considered a store and forward
                device, a bridge for example, that begins transmitting
                a frame before it is fully received.  This type of
                device is known as a "cut through" device.  The
                assumption is that the device would somehow invalidate
                the partially transmitted frame if in receiving the
                remainder of the input frame, something came up that
                the frame or this specific forwarding of it was in
                error.  For example, a bad checksum.  In this case,
                the device would still be considered a store and
                forward device and the latency would still be
                from last bit in to first bit out, even though the
                value would be negative.  The intent is to treat
                the device as a unit without regard to the internal
                structure.

1.1.f Explain UDP operations

1.1.f [iii] RTP/RTCP concepts

rfc 3550

http://www.ietf.org/rfc/rfc3550.txt

RTP provides end-to-end network transport functions suitable for
applications transmitting real-time data, such as audio, video or
simulation data, over multicast or unicast network services.  RTP
does not address resource reservation and does not guarantee
quality-of-service for real-time services.  The data transport is
augmented by a control protocol (RTCP) to allow monitoring of the
data delivery in a manner scalable to large multicast networks, and
to provide minimal control and identification functionality.  RTP and
RTCP are designed to be independent of the underlying transport and
network layers.  The protocol supports the use of RTP-level
translators and mixers.