IEEE 802.3ad Link Aggregation (LAG) What it is, and what it is not


1 1 Ottawa 17-April-2007 Robert Hays - Intel (LAG) IEEE 802.3 HSSG Geoff Thompson – Nortel Schelto Van Doorn – Intel Howard Frazier – Broadcom Paul Kolesar – CommScope Brad Turner – Juniper Networks Shimon Muller – Sun Microsystems what it is, and what it is not Bruce Tolley – Solarflare Communications IEEE 802.3ad Link Aggregation

2 2 IEEE 802.3 HSSG Outline • Overview of 802.3ad Link Aggregation • Current status and future plans • Improving Link Aggregation • Summary

3 3 IEEE 802.3 HSSG 802.3ad Link Aggregation – same data rate – point to point – full duplex transmitted on the same link to prevent mis-ordering • LAG assumes all links are: • LAG is performed above the MAC • Specified in Clause 43 • Provides graceful recovery from link failures • Traffic is distributed packet by packet • All packets associated with a given “conversation” are

4 4 IEEE 802.3 HSSG 802.3ad Link Aggregation

5 5 PHY MAC collector PHY MAC MAC Client PHY MAC distributor PHY MAC IEEE 802.3 HSSG PHY MAC collector PHY MAC MAC Client PHY MAC 802.3ad Link Aggregation distributor PHY MAC

6 6 IEEE 802.3 HSSG b) Duplication of frames. a) Mis-ordering of frames that are part of any given conversation, or 802.3ad Link Aggregation ... however, any distribution algorithm shall ensure that, when frames are received by a Frame Collector as specified in 43.2.3, the algorithm shall not cause 43.2.4 Frame Distributor This standard does not mandate any particular distribution algorithm(s); ... frames that compose a given conversation are transmitted on a single link in the order that they are generated by the MAC Client; hence, this requirement does not involve the addition (or modification) of any information to the MAC frame, nor any buffering or processing on the part of the corresponding Frame Collector in order to re-order frames. The above requirement to maintain frame ordering is met by ensuring that all

7 7 IEEE 802.3 HSSG 802.3ad Link Aggregation – No fragmentation or reassembly – No added headers or sequence numbers – Type/Length interpretation unchanged conversation simultaneous conversations • Does not require added buffers • Does not change packet format • Does not re-order or mis-order packets • Does not add significant latency • Does not increase the bandwidth for a single • Achieves high utilization only when carrying multiple • Is not transparent to some 802.1 sub-layers

8 8 IEEE 802.3 HSSG 802.3ad Link Aggregation because everything must be replicated N times the bandwidth – It does what it was intended to do – It is relatively easy to implement and use – N aggregated links cost N times as much as a single link, – N aggregated links usually do not provide individually managed of a single link • Incurs a linear multiple of the cost of a single link • Does not always provide a linear multiple of the data rate • Is a very good thing • Appears to the user as N individual links, which must be

9 9 IEEE 802.3 HSSG Current status enhancements or revisions • In the process of being “spun out” of 802.3 • 802.3ax project creating IEEE P802.1AX • No technical changes • After the transfer, 802.1 may undertake

10 10 IEEE 802.3 HSSG

11 11 or and IEEE 802.3 HSSG • Change the packet format Improving Link Aggregation – Inspect headers deep into packet – Add sequence number to packet – Add LARGE buffers to receiver • Can link aggregation be “fixed”?

12 12 IEEE 802.3 HSSG formats (layering violation) Adds LONG delay Requires a new 802.3 MAC client interface Requires a new 802.3 MAC definition Futile if packets are encrypted Layer 2 LAG would need to parse upper layer protocol header Improving Link Aggregation Fixing LAG is neither easy, or rewarding Why not change the packet format? Why not inspect headers deep into a packet? Why not add LARGE buffers to the receiver? – – – – – • • • •

13 13 IEEE 802.3 HSSG Summary LAG is good, but it’s not as good as a fatter pipe

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