Re: Flow Control in Trunk

"Sailing" <sailing511@xxxxxxxxx> wrote:

well, what's the difference between "a trunk segment of a VLAN" and
link aggregation?
i don't think i have a clear idea referring to VLAN segment.
i looked up some documents and found the following definition:
a trunk link is a lan segment containing vlan-aware bridges and
vlan-aware end stations.
but can you explain it more explicately?

Link aggegation is a scheme whereby you tie together multiple Ethernet segments to behave as if it were only one, faster link. Typically, between two switches. This technique is sometimes referred to as "inverse multiplexing." This is described in 802.3-2005 Clause 43.

VLANs are described in 802.1Q. The idea is to have one physical Ethernet (or other link layer) behave as if you had multiple Ethernets. By adding overhead fields to the Ethernet frame, a VLAN trunk segment can carry frames which are meant to belong to different LANs. Typically, these trunk segments are only used between switches or routers, although in principle they could also be used between two hosts, between hosts and routers, between hosts and switches.

You're really doing two opposite things here. Either bundling multiple physical Ethernet segments to behave as if they were one, or adding overhead to Ethernet frames to allow a single segment to behave as if it were multiple physcal Ethernet segments.

So how does this relate to flow cntrol. Flow control operates on individual physical Ethernet segments, between switches, or between switches and hosts. So flow control would not work if you have multiple physical segments aggregated into a single trunk. There's no scheme (as of now) to guarantee that the flow control operation can be synchronized precisely among multiple Ethernet segments, which choreography would be needed if you expect to be able to aggregate multiple segments. But since flow control operates independently of the Ethernet data frames, it should work just fine in a VLAN trunk example. Flow control doesn't know or care whether that segment is pretending to be many different segments. It just applies backpressure as buffers reach a certain level.

Bert

.

Relevant Pages

  • Re: Find a period in multiple delayed time series
    ... > techniques there are for analysing multiple time-series with the same ... If you just have one set of low noise segments, ... and moving the individual segments around until they ...
    (sci.stat.math)
  • SUMMARY: Solaris 10, Oracle 10G, Shared Memory Segments
    ... It seems that Oracle, ... running on Solaris 10, has purposely broken up the SGA into multiple ... (10G SGA is split in multiple shared memory segments). ...
    (SunManagers)
  • Re: An RMS feature I wish for
    ... RMS development, ... Segmented keys allow one to use the same segments from a ... record in multiple combinations to create multiple 'overlapping' indexes,,, ... but each index structures is entirely independend. ...
    (comp.os.vms)
  • Re: Flow Control in Trunk
    ... i don't think i have a clear idea referring to VLAN segment. ... Link aggegation is a scheme whereby you tie together multiple Ethernet ... segments to behave as if it were only one, ...
    (comp.dcom.lans.ethernet)