A _very_ short and shallow overview of AVB, mostly with focus on what is required by the networking infrastructure.

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AVB-Audio/Video Bridging
Henrik Austad - haustad@cisco.com
Cisco Systems Norway

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AVB: What is it
Collection of (mostly) IEEE standards
● IEEE 1722 (Layer 2 transport protocol)
● IEEE 802.1Qat (Stream Reservation)
● IEEE 802.1AS & IEEE 1588 (PTP)
● IEEE 1722.1 (Device discovery)
● IEEE 802.1Qav (Queueing enhancements)
● IEEE 802.1BA (Network setup)
● IEC 61883 (audio/video over firewire)

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AVB is...
● “This standard specifies the protocol, data encapsulation, and
presentation time procedures used to ensure interoperability between
audio- and video-based end stations that use standard networking
services provided by all IEEE-802 networks meeting quality-of-service
requirements for time-sensitive applications by leveraging the concepts
of IEC 61883.”
IEEE 1722:2011
● “Use an existing network to connect media gear together and get decent
quality without buying more expensive stuff”
Henrik; 2014

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AVB
● Use existing network infrastructure
● Data streams from a Talker to a Listener
across a set of Bridges.
● PTP for synchronization of presentation (think
lipsync)
● Stream reservation to minimize jitter
● 2 types of devices, End-Stations (Talkers and
Listeners) and Bridges.

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802.1Qat – SRP: Stream Reservation Protocol
● SRP uses 3 signaling protocols
● Multiple MAC Registration Protocol
(optional, used for controlling the
propagation of Talker registration)
● Multiple VLAN Reg. Protocol
(declare membership for a VLAN,
required for MSRP)
● Multiple Stream Reg. Protocol
(reservation of network resources to
guarantee Rx/Tx of dataframes
across the network)
● Will not allow more than 75% of total
system BW to be reserved (this can
change, especially in a wireless
network)

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MSRP: Multiple Stream Reservation Protocol in a Bridged Network
●
Talkers define stream attributes via “Talker
Advertise”
●
Listeners request reception of streams via
“Listener Ready”
●
Bridges:
- process/adjust/modify attributes
- Talker advertise → Talker Failed
- Listener Ready→ Listener Ready Failed /
Listener Failed
- allocate stream resources
- Find/define domain boundaries
- Handle stream importance
●
Traffic over a shared medium (wireless, simplex
point-to-point) require DMN
●
Designated MSRP Node (DMN) has absolute
control over which node is allowed to transmit
at any given time.

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PTP: Precision Time Protocol
● Operation of Time-Aware Systems (TAS) on a bridged, packet-
switched LAN
● A TAS is a system that has its time adjusted by PTP.
● Time is of ns granularity since PTP epoch (Jan 01 1970
00:00:00 TAI)
● A set of TAS connected by PTP-capable LAN is a domain.
● Precise synchronization of clocks of all TAS in a domain
(typically <1us error).
● Master-slave hierarchy with “GrandMaster” (GM) at the top
● All nodes exchange timing information to determine delay and
domain boundaries.
● Best Clock Master Algorithm used to find the GM.
● Same time more important than right time (having the right
time is a close second).
● AVB uses “generalized PTP”, which is pretty close to standard
PTP.

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Why AVB is a good step forward
● Network is common infrastructure
● An open standard for Audio/Video over ethernet with QoS guarantees
(several proprietary solutions exists, many have failed).
● AVB-traffic can coexist with normal traffic, no dedicated network to AV
only. SRP will only allow up to 75% for AVB traffic
Excessive cabling is annoying/messy/<whateverfuelsyourgrudge>
● Interop between devices

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