1. George Swallow Martin Vigoureux Rahul Aggerwal July 30, 2008
Assignment of the Generic Associated Channel Header Label (GAL) draft-vigoureux-mpls-tp-gal-00
George Swallow
Martin Vigoureux
Rahul Aggerwal
July 30, 2008

2. Items to cover Segment OAM MEP to MEP MEP to MIP Stack operations
TTL of GAL
Applicability to MPLS

3. MPLS-TP Major Solution Constructs
MPLS-TP alert label (TAL) Allows OAM packets to be directed to an intermediated node on a LSP/PWE
Via label stacking or proper TTL setting
Define a new reserved label (13 is suggested):
Label 14 cannot be reused at this point
Generic Associated Channel (GE ACH)
supports full FCAPS functionality
Use of PWE-3 Associated Channel to carry OAM packets
GE ACH are codepoints from PWE ACH space but, not necessarily, for PWE purposes
GE ACH would be present for OAM of all LSPs .

4. LSP monitoring and alarming Generic Alert Label and Generic Associated Channel Proposal
MAC Header L1 L2
GAL/BoS
Generic ACH
Channel payload
0001 | Ver | Resv | Channel Type
Assign a Transport Alert Label as a Label For yoU (LFU) from reserved label space:
Label 13 has been proposed because,
Label 14 has been allocated to Y.1711
Y.1711 arch fits within “ACH” architecture
Bottom of Stack is always set on LFU in the transport profile
Define a Generic Associated Channel function
Similar to the PWE-3 Associated Channel
First nibble is 0001; Channel Type field the same (but more values)
Generic Associated Channel is always under a Generic Exception Label if endpoint (MEP)
Generalised Associated Channel defines what packet function using “channel type” field
Examples : What OAM function is carried, DCC, etc .

5. GAL Functions
Serves as a protcol/format identifier to identify the MPLS payload as containing an Generic Associated Channel header
The G-ACH in turn defines the specific contents
Note that this defines a means for having an Associated Channel for LSPs where the FEC does not define one, e.g. a VPN route
Serves to differentiate packets allowing them to be directed to the appropriate entity for processing
At MEP, GAL causes exception handling of OAM packet
At MIP, it is a combination of TTL of label above, plus GAL
(GAL does not require peeking down the label stack)

6. Placement in Label Stack
Always appears directly below the label for the LSP being monitored
For the MPLS-TP null labels are not permitted
This draft however, does not rule out use of the GAL in connection with a implicit or explicit null label
Clearly not all OAM functions will work identically in this case

7. Placement in Label Stack (2)
Note that more labels may be pushed onto the stack above the label of the LSP being monitored
However the GAL only has meaning when the label of the LSP being monitored is at the top-of-stack

8. Placement in Label Stack (3)
For the MPLS-TP the GAL always appears at EOS
In general, however, this need not be the case - particularly where the intervening labels may influence the choice of ECMP
Case in point - load balancing (aka entropy) labels

9. Canonical Format at a MIP or MEP
| LSP Label | CoS |S| TTL |
| GAL | CoS |S| TTL |
| Generic-ACH | |
MPLS-TP OAM packet |
Note: at MIP TTL of LSP Label is 1, at MEP any value

10. Nested T-MPLS Tunnels & OAM
Carrier 1
Region 1
Region 2 PE P PE PE P PE
INNI
Carrier 1 LSP OAM segment
MEP
MIP
MIP
MEP
MD Level 2
carrier 1 region 1
LSP OAM segment
carrier 1 region 2
LSP OAM segment
MEP
MIP
MEP
MEP
MIP
MEP
MD Level 1
Next Slide focus on MD Levels 1 & 2

11. Carrier 1 example MEPs/MIPs relationships
MEL x: Carrier 1
Carrier 1 LSP segment OAM Sk So
Pushing a new label at the MEP So starts a server layer trail that is terminated when the label is removed at the MEP Sk
MIP[1] verifies MEPx_So connectivity to MEPy_Sk
MIP[2] verifies MEPx_So connectivity to MEPz_So
MIP [1]
MIP [2]
MEL y: Carrier 1, Region 1
MEL z: Carrier 1,Region 2
region 1 OAM
region 2 OAM Sk So Sk So
MEP
MIP
Trail
A MIP must support monitoring on the ingress port (logically before the label swap)
An implementation may optionally support a second MIP to monitor the egress port
How will this MIP be addressed

12. Segment OAM Segment OAM is sent simply as GAL followed by the ACH
Note that if we wish to use GAL with implicit null label, care will need to be taken to clearly deliniate that case from any defined Segment OAM

13. TTL of GAL Label Stack Entry
This draft simply says TTL should be set to 1
When things are working properly (ignoring the cases of Segment OAM and Implicit Null) GAL TTL is never processed.
Further GAL is always directed to an OAM process (not switched out of a box)
Since GAL is a reserved label, a node that does not understand GAL will drop it

14. Forwarding and OAM: LSPs / PW OAM and Label Stacks

15. MEP to MIP OAM: TTL Processing for PWs and LSPs
In order to maintain individual levels of OAM and path detection
Use short pipe model per label level
TTL is not copied up the stack on a push
TTL is not copied down the stack on a pop
TTL is decremented on each swap and pop action
Traceroute for a level can be used to trap packets at each node that processes the label for that level in the label stack

16. Multi-Segment PW TTL Processing
LSP PW A B C D E
T-PE
T-PE
S-PE
LSP
LSP PW
Label stack TTLs used on the wire
TTL=k
TTL=k-1
TTL=n
TTL=n-1
TTL=j
TTL=j
TTL=j-1
TTL=j-1
A-B
B-C
C-D
D- …

17. Multi-Segment PW TTL Processing
LSP PW A B C D
LSP
LSP PW
Label stack TTLs used on the wire
TTL=k
TTL=n
TTL=n-1
TTL=j
TTL=j-1
TTL=j-2
TTL=j-2
A-B
B-C
C-D
D- …

18. Observation Indication of ACH can be done in FEC
GAL is absolutely needed for PHP
GAL is absolutely needed when FEC is already defined without GAL
Definition of an MPLS-TP FEC could be defined with an ACH

19. Next Steps Technical content (near) complete Some text clean up needed
Author believe far enough along to become a WG doc