Page 34 - ITUJournal Future and evolving technologies Volume 2 (2021), Issue 1

ITU Journal on Future and Evolving Technologies, Volume 2 (2021), Issue 1

Recon iguration calculus In addition to centrally man‑ Local Stream Switch ID Port ID
aging resources and providing admission control policies Registration Table
Queuing and Resource
to the network, the CNC can invoke the TAS recon igura‑ Forwarding Traffic Shapers Manager
tion strategy with the goal of borrowing BE time slots for TSN Switch
pending ST traf ic streams. This element consults the re‑ SW2
1) SC1 sends Stream Tx
source manager module on the bottleneck link and checks Request 3) Control Data Traffic is
whether the added stream will oversubscribe the link. propagated to next switch
on path
The TAS recon iguration incrementally (1% of total CT)
increases the traf ic class slot time and reserves it for the Source 1 - Talker 2) SW applies resource
reservation and admission
new stream. control on the egress port
4a) CDT message gets for the pending stream SW3
rejected due to no registration
resources available and TAS
Path computation For large scale and complex gating ratio for traffic class SW1
LAN/MAN topologies, it is often required to supple‑ is capped
4b) CDT message gets accepted at
ment streams with equal cost paths in the event of a each SW on path and a stream
path disruption (e.g., link failure, stream saturation, record is created at each hop SW4 Source 2 - Listener
and explicit congestion). The CNC’s path computation
element is tasked with inding such paths as a fail‑over Fig. 3 – A TSN fully distributed con iguration model example illustrat‑
approach to avoid any violations to any stream’s QoS. ing the general strategy and logic of each TSN switch with TAS support.
Presently, our model has a rudimentary application of In the absence of a CNC to centrally manage network parameters, each
path computation, i.e., it is de ined statically for all core switch performs admission control and resource reservation (accord‑
ing to the TAS time slot load) and propagates the information to the next
network components (shortest path), since our main hop on the stream path. A single rejection on one hop terminates the
emphasis in this study is on recon iguration based on forwarding of the CDT, and sends another CDT on the reverse path indi‑
stream characteristics as de ined by the source. cating the stream rejection outcome. If all switches on the path accept
the stream, then the source is noti ied of the stream acceptance outcome
and can begin forwarding in the next TAS cycle. In our model, CDT traf‑
3.1.3 Resource manager module ic has higher priority than non‑CDT traf ic (including ST). The formal
de inition of the CDT traf ic is left for future work.
The resource manager module centrally manages all net‑
work resources within the CNC’s domain. It includes the compose the forwarding and queuing operation with sev‑
network resource table that records all streams’ usage of eral traf ic shapers (802.1Qbv TAS in our network model).
resources, and the resource allocation scheme element to
whichwedelegatethetaskofcalculatingtherequirednet‑ Local stream registration table This data plane reg‑
work resources for a given stream according to an alloca‑ istry contains the subset of source streams that are estab‑
tion scheme. lished for the corresponding bridge gateway and attached
sources to each port. The CNC delegates some control to
Network resource table To remove certain overheads the bridge gateway to instruct and alert sources of any
on the con iguration module, the network resource table new network conditions and explicit changes.
operates in tandem with the global stream registration
table to accurately determine the required network re‑
sources (mainly bandwidth for our traf ic model). It clas‑ Traf ic shaper — Time‑Aware Shaper (TAS) The TAS
si ies streams based on periodic stream properties. Any is the main shaping and scheduling mechanism that con‑
stream that has been approved by the CNC has a record trols the gating schedules for all the traf ic classes within
attached to it in the network resource table. the TSN domain (which is considered to be equivalent
to the CNC domain). All bridges are synchronized to the
same gating schedule GCL Cycle Time (CT) given by the
Resource allocation scheme Several allocation CNC’s low schedule element (CT indicates the time pe‑
schemes can be implemented for all traf ic classes de‑ riod for the GCL to repeat).
ined in the network. For periodic streams, the time slot
given by the low scheduler (according to the TAS Cycle
Time and number of traf ic classes) and the data rate 4. DECENTRALIZED MODEL DESIGN AND
de ined by the source is used to calculate the required FRAMEWORK CONSIDERATIONS
bandwidth for each link on the path to the destination
(i.e., sink). This section presents our design methodology and frame‑
work for the TAS recon iguration in the decentralized
3.1.4 Data plane (fully distributed) model. Our current proposed architec‑
ture generally follows the steps enumerated below and il‑
The data plane contains all core switches. Any TSN switch lustrated in Fig. 3. Our description focuses on the addi‑
interfaced by the CNC is given a switch ID and has a local tions to the design of RAP over LRP, e.g., TAS slot compu‑
stream registration table. The remaining switch elements tation/reservations.

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